Was formed from an Italian CRT Fabricant called ERGON which was sold to Thomson in 1971 and the technology further called PIL (Precision In Line) was produced by a collaboration with RCA. (ERGON S.P.A., ANAGNI, FROSINONE).
They have patented several technologyes like the LICHT-KOLLIMATOR
and various methods to improve the fabrication of shadowmasks in CRT
Tubes like the invention of a process of manufacturing a cathode-ray
tube (CRT)
having an anti-glare, anti-static, dark coating on an external surface
of a faceplate panel thereof, and more particularly, to the formulation
of such a coating. Further Inventions were related to inventions formulated for the control of electron beam for adjustment of, for example, static convergence and/or purity in a picture tube and others invention relates to a shadow mask or color selection electrode for a color television picture tube, as well as the support frame making it possible to stiffen or rigidify the mask.
Videocolor CRTs were widely used by many fabricants on European scale and even around the world.
Example of Videocolor CRTs were the P.I.L. (Precision In Line) the PIL S4 the PIL PLANAR the PIL MP the PIL FS10.......
In 2005 Videocolor was sold to Videocon An Indian monkeys dotheads imbeciles conglomerate of filth and dirt (WTF !) wich has converted it to Plasma Lcd (cheapshit Crap) manufacturing, resulting in a total FAIL !!
Now Videocolor has Stopped the production, it's gone (Forever-dead) !!
Here below the images of the rest of the completely abandoned Anagni VIDECOLOR Production Factory
VIDEOCOLOR
FS10 MP square screen black matrix improved electron gun focusing crt
tube, An improved color picture tube has an inline electron gun for
generating
and directing three electron beams, a center beam and two side beams,
along coplanar paths toward a screen of the tube. The gun includes a
main focus lens for focusing the electron beams. The main focus lens is
formed by two spaced electrode members, each having three separate
inline apertures therein, a center aperture and two side apertures. The
improvement comprises each of the apertures in each of the focus lens
electrodes having a shape that distorts a portion of the focus lens
thereat, to at least partially compensate for an astigmatic effect
within the tube that acts on an associated electron beam. The side
apertures in both of the electrodes are nonsymmetrical about axes that
pass through the respective side apertures and are perpendicular to the
initial coplanar paths of the electron beams. furthermore the gun
includes an additional accelerator electrode after G2 directly connected
to HV ultor voltage .The gun includes a plurality of electrodes which
form a beam-forming
region, a prefocusing lens, and a main focusing lens for the electron
beams. The prefocusing lens includes four active surfaces. At least one
of the active surfaces has asymmetric prefocusing recesses formed
therein.
1. In a color cathode-ray tube including an envelope having therein an inline electron gun for generating and directing three inline electron beams, including a center beam and two outer beams, along initially coplanar beam paths toward and screen on an interior portion of said envelope, said gun having six electrodes forming three electron lenses including a beam-forming lens, a prefocusing lens and a main focusing lens, the improvement wherein
said prefocusing lens includes four active surfaces, at least one of which has a recess formed therein, said active surfaces produce quadrupole fields which form an astigmatic prefocusing lens, said recess provides a preconverging action on said outer electron beams, three circular apertures being provided within said recess.
2. The tube as described in claim 1 wherein said recess is configured to minimize the sensitivity of said gun to variations in operating potentials.
3. In a color cathode-ray tube including an envelope having therein an inline electron gun for generating and directing three inline electron beams, including a center beam and two outer beams, along initially coplanar beam paths toward and screen on an interior portion of said envelope, said gun having six electrodes forming three electron lenses including a beam-forming lens, a prefocusing lens and a main focusing lens, the improvement wherein said prefocusing lens includes four active surfaces on three adjacent electrodes, at least two of said surfaces having substantial identical recesses formed therein, said active surfaces produce quadrupole fields which form an astigmatic prefocusing lens that provides a horizontally-elongated electron beam to said main focusing lens, said recesses provide a preconverging action on said outer electron beams, each of said adjacent electrodes having circular apertures therethrough said apertures being aligned along said beam paths.
4. The tube as described in claim 3 wherein said recesses are configured to minimize the sensitivity of said gun to variations in operating potentials.
5. In a color cathode-ray tube including an envelope having therein an inline electron gun for generating and directing three inline electron beams along initially coplanar beam paths toward a screen on an interior portion of said envelope, said gun including a plurality of longitudinally spaced electrodes which form a first lens, a prefocusing lens and a main focusing lens for said electron beams, said first lens comprising a beam-forming region including a first electrode, a second electrode and a first portion of a third electrode for providing substantially symmetrically-shaped beams to said prefocusing lens comprising a second portion of said third electrode, a fourth electrode an
d a first portion of a fifth electrode, said
prefocusing lens providing asymmetrically-shaped beams to said main
focusing lens comprising of a second portion of said fifth electrode and
a sixth electrode, said main focusing lens being a low aberration lens,
wherein the improvement comprises, said prefocusing lens including
four active surfaces with separate inline circular apertures
therethrough, said fourth electrode having substantially identical
asymmetric beam-focusing recesses formed in the oppositely disposed
active surfaces thereof, said apertures being disposed within said
recesses.6. The tube as described in claim 5 wherein a single recess is formed in each active surface of said fourth electrode.
7. The tube as described in claim 5 wherein three separate, substantially rectangular recesses comprising two outer recesses and a center recess are formed in each active surface of said fourth electrode.
8. The tube as described in claim 7 wherein each of said outer recesses having an outer aperture therethrough said outer recesses being displaced outwardly relative to said outer apertures.
9. The tube as described in claim 5, wherein each of said circular apertures of said first lens and said prefocusing lens being coaxially aligned along said beam paths.
10. In a color cathode-ray tube including an envelope having therein an inline electron gun for generating and directing three inline beams along initially coplanar beam paths toward a screen on an interior portion of said envelope, said gun including six longitudinally spaced electrodes each having three inline circular apertures therethrough, said electrodes forming a first lens, a prefocusing lens and a main focusing lens for said electron beams, said first lens comprising a beam-forming region including a first electrode, a second electrode and a first portion of a third electrode for providing substantially symmetrically-shaped beams to said prefocusing lens comprising a second portion of said third electrode, a fourth electrode and a first portion of a fifth electrode, said prefocusing lens providing asymmetrically-shaped beams to said main focusing lens consisting of a second portion of said fifth electrode and a sixth electrode, said main focusing lens being a low aberration lens, wherein the improvement comprises, said prefocusing lens including four active surfaces, said second portion of said third electrode and said first portion of said fifth electrode having substantially identical, asymmetric beam-focusing recesses formed in the active surfaces thereof, said circular apertures being formed within said recesses.
11. The tube as described in claim 10 wherein a single recess is formed in said second portion of said third electrode and said first portion of said fifth electrode.
12. The tube as described in claim 10 wherein three separate, substantially rectangular recesses comprising two outer recesses and a center recess are formed in said active surfaces of said second portion of said third electrode and of said first portion of said fifth electrode.
13. The tube as described in claim 12 wherein each of said outer recesses having one of said circular apertures therethrough, said recesses being displaced outwardly relative to said circular apertures.
14. The tube as described in claim 10 wherein each of said circular apertures in each of said electrodes of said first lens and said prefocusing lens being coaxially aligned along said beam paths.
Description:
The invention relates to a color picture tube having an
inline electron gun and, particularly to an electron gun having three
lenses including an asymmetric prefocusing lens. BACKGROUND OF THE INVENTION
An electron gun, such as a six electrode gun, designed for use in a large screen entertainment-type color picture tube must be capable of generating small-sized high-current electron b
eam spots over the entire
screen. A conventional television receiver utilizes a color picture tube
with an inline electron gun and a self-converging deflection yoke, for
providing a horizontal deflection field having a pincushion-shaped
distortion and a vertical deflection field having a barrel-shaped
distortion. The fringe fields of such a yoke introduce into the tube
strong astigmatism and deflection defocusing caused, primarily, by
vertical overfocusing and, secondarily, by horizontal underfocusing of
the deflected electron beams. Beam spots formed by the electron beams
passing through such distorted horizontal and vertical deflection fields
are asymmetrically-shaped when deflected to the periphery of the
screen. Additionally, many inline electron guns exhibit a misconvergence
of the outer electron beams due to a change in the strength of the
electron lens caused by changes in the focus voltage. Such a
misconvergence results in a variation in beam landing position with
changes in focus voltage. The present invention addresses these problems
in an expeditious and cost effective manner without sacrificing
performance. SUMMARY OF THE INVENTION
The present invention provides an improvement in a color picture tube. Such a tube includes an inline electron gun for generating and directing three inline electron beams along coplanar beam paths toward a screen. The gun includes a plurality of electrodes which form a beam-forming region, a prefocusing lens and a main focusing lens for the electron beams. The improvement resides within the prefocusing lens, which includes four active surfaces. At least one of the active surfaces has asymmetric prefocusing means formed therein.
In-line electron gun PRECISION IN LINE TECHNOLOGY p.i.l. VIDEOCOLOR (RCA TECHNOLOGY):The three co-planar beams of an in-line gun are converged near the screen of a cathode ray tube by means of two plate-like grids transverse to the beam paths and having corresponding apertures for the three beams. The three beam apertures of the first grid are aligned with the three beam paths. The two outer beam apertures of the second grid are offset outwardly relative to the beam paths to produce the desired convergence. The three sets of apertures also provide separate focusing fields for the three beams. The second plate-like grid is formed with a barrel shape, concave toward the first grid, to minimize elliptical distortion of beam spots on the screen due to crowding of the adjacent focusing fields. Each of the two outer beams is partially shielded from the magnetic flux of the deflecting yoke by means of a magnetic ring surrounding the beam path in the deflection zone, to equalize the size of the rasters scanned on the screen by the middle and outer beams. Other magnetic pieces are positioned on opposite sides of the path of the middle beam, to enhance one deflection field while reducing the transverse deflection field for that beam.
1.
In a color picture tube including an evacuated envelope comprising a
faceplate and a neck connected by a funnel, a mosaic color phosphor
screen on the inner surface of said faceplate, a multiapertured color
selection electrode spaced from said screen, an in-line electron gun
mounted in said neck for generating and directing three electron beams
along co-planar paths through said electrode to said screen, and a
deflection zone, located in the vicinity of the junction between said
neck and said funnel, wherein said beams are subjected to vertical and
horizontal magnetic deflection fields during operation of said tube for
scanning said beams horizontally and vertically over said screen; said
electron gun comprising: 2. The structure of claim 1, wherein said
electron gun further comprises a pair of magnetic elements positioned in
said deflection zone on opposite sides of the middle beam path and in a
plane transverse to the common plane of said paths for enhancing the
magnetic deflection field in said middle beam path transverse to said
common plane and for reducing the magnetic deflection field in said
middle beam path along said common plane, thereby increasing the
dimension of the raster scanned by the middle beam in said common plane
while reducing the dimension of said raster in said transverse plane.
3. In a color picture tube including an evacuated envelope comprising a
faceplate and a neck connected by a funnel, a mosaic color phosphor
screen on the inner surface of said faceplate, a multi-apertured color
selection electrode spaced from said screen, an in-line electron gun
mounted in said neck for generating and directing three electron beams
along co-planar paths through said electrode to said screen, and a
deflection zone, located in the vicinity of the junction between said
neck and said funnel, wherein said beams are subjected to vertical and
horizontal magnetic deflection fields during operation of said tube for
scanning said beams horizontally and vertically over said screen, and
wherein the eccentrity of the outer ones of said beams in the deflection
fields causes the sizes of the rasters scanned by the outer beams to
tend to be larger than the size of the raster scanned by a middle beam,
said electron gun comprising; 4. The tube as defined in claim 3,
including two small discs of magnetic material located at the fringe of
the deflection zone on opposite sides of the middle beam transverse to
the plane of the three beams, whereby the magnetic flux on the middle
beam transverse to the plane of the three beams is enhanced and the flux
in the plane of the three beams is decreased thereby increasing the
middle beam dimension in the plane of the three beams while reducing the
middle beam dimension in the plane of the three beams.
Description:
BACKGROUND OF THE INVENTION
The present invention relates to an improved in-line electron gun for a cathode ray tube, particularly a shadow mask type color picture tube. The new gun is primarily intended for use in a color tube having a line type color phosphor screen, with or without light absorbing guard bands between the color phosphor lines, and a mask having elongated apertures or slits. However, the gun could be used in the well known dot-type color tube having a screen of substantially circular color phosphor dots and a mask with substantially circular apertures.
An in-line electron gun is one designed to generate or initiate at least two, and preferably three, electron beams in a common plane, for example, by at least two cathodes, and direct those beams along convergent paths in that plane to a point or small area of convergence near the tube screen. Various ways have been proposed for causing the beams to converge near the screen. For example, the gun may be designed to initially aim the beams, from the cathodes, towards convergence at the screen, as shown in FIG. 4 of Moodey U.S. Pat. No. 2,957,106, wherein the beam apertures in the gun electrodes are aligned along convergent paths.
In order to avoid wide spacings between the cathodes, which are undesirable in a small neck tube designed for high deflection angles, it is preferable to initiate the beams along substantially parallel (or even divergent) paths and provide some means, either internally or externally of the tube, for converging the beams near the screen. Magnet poles and/or electrostatic deflecting plates for converging in-line beams are disclosed in Francken U.S. Pat. No. 2,849,647, Gundert et al. U.S. Pat. No. 2,859,378 and Benway U.S. Pat No. 2,887,598.
The Moodey patent referred to above also includes an embodiment, shown in FIG. 2 and described in lines 4 to 23 of column 5, wherein an in-line gun for two co-planar beams comprises two spaced cathodes, a control grid plate and an accelerating grid plate each having two apertures aligned respectively with the two cathodes (as in FIG. 2) to initiate two parallel co-planar beam paths, and two spaced-apart beam focusing and accelerating electrodes of cylindrical form. The focusing electrode nearest to the first accelerating grid plate is described as having two beam apertures that are offset toward the axis of the gun from the corresponding apertures of the adjacent accelerating grid plate, to provide an asymmetric electrostatic field in the path of each beam for deflecting the beam from its initial path into a second beam path directed toward the tube axis.
Netherlands U.S. Pat. application No. 6902025, published Aug. 11, 1970 teaches that astigmatic aberration resulting in elliptical distortion of the focused screen spots of the two off-axis beams from an in-line gun, caused by the eccentricity of the in-line beams in a common focusing field between two hollow cylindrical focusing electrodes, can be partially corrected by forming the adjacent edges of the cylindrical electrodes with a sinusoidal contour including four sine waves. A similar problem is solved in a different manner in applicant's in-line gun.
Another
problem that exists in a cathode ray tube having an in-line gun is a
coma distortion wherein the sizes of the rasters scanned on the screen
by a conventional external magnetic deflection yoke are different,
because of the eccentricity of the two outer beams with respect to the
center of the yoke. Messineo et al. U.S. Pat. No. 3,164,737 teaches that
a similar coma distortion caused by using different beam velocities
can be corrected by use of a magnetic shield around the path of one or
more beams in a delta type gun. Barkow U.S. Pat. No. 3,196,305 teaches
the use of magnetic enhancers adjacent to the path of one or more beams
in a delta gun, for the same purpose. Krackhardt et al. U.S. Pat. No.
3,534,208 teaches the use of a magnetic shield around the middle one of
three in-line beams for coma correction.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, at least two electron beams are generated along co-planar paths toward the screen of a cathode ray tube, e.g., a shadow mask type color picture tube, and the beams are converged near the screen by asymmetric electric fields established in the paths of two beams by two plate-like grids positioned between the beam generating means and the screen and having corresponding apertures suitably related to the beam paths. The apertures in the first grid (nearest the cathodes) are aligned with the beam paths. Two apertures in the second grid (nearest the screen) are offset outwardly with respect to the beam paths to produce the desired asymmetric fields. In the case of three in-line beams, the two outer apertures are offset, and the middle apertures of the two grids are aligned with each other. The pairs of corresponding apertures also provide separate focusing fields for the beams. In order to minimize elliptical distortion of one or more of the focused beam spots on the screen due to crowding of adjacent beam focusing fields, at least a portion of the second grid may be substantially cylindrically curved in a direction transverse to the common plane of the beams, and concave to the first grid. Each of the two outer beam paths of a three beam gun may be partially shielded from the magnetic flux of the deflection yoke by means of a magnetic ring surrounding each beam in the deflection zone of the tube, to minimize differences in the size of the rasters scanned on the screen by the middle and outer beams. Further correction for coma distortion may be made by positioning magnetic pieces on opposite sides of the middle beam path for enhancing one field and reducing the field transverse thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view, partly in axial section, of a shadow mask color picture tube in which the present invention is incorporated;
FIG. 2 is a front end view of the tube of FIG. 1 showing the rectangular shape;
FIG. 3 is an axial section view of the electron gun shown in dotted lines in FIG. 1, taken along the line 3--3 of that figure;
FIG. 4 is an axial section view of the electron gun taken along the line 4--4 of FIG. 3;
FIG. 5 is a rear end view of the electron gun of FIG. 4, taken in the direction of the arrows 5--5 thereof;
FIG. 6 is a transverse view, partly in section, taken along the line 6--6 of FIG. 4;
FIG. 7 is a front end view of the electron gun of FIGS. 1 and 4;
FIG. 8 is a similar end view with the final element (shield cup) removed; and
FIGS. 9 and 10 are schematic views showing the focusing and converging electric fields associated with two pairs of beam apertures in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a plan view of a 17V-90° rectangular color picture tube, for example, having a glass envelope 1 made up of a rectangular (FIG. 2) faceplate panel or cap 3 and a tubular neck 5 connected by a rectangular funnel 7. The panel 3 comprises a viewing faceplate 9 and a peripheral flange or side wall 11 which is sealed to the funnel 7. A mosaic three-color phosphor screen 13 is carried by the inner surface of the faceplate 9. The screen is preferably a line screen with the phosphor lines extending substantially parallel to the minor axis Y-Y of the tube (normal to the plane of FIG. 1). A multi-apertured color selection electrode or shadow mask 15 is removably mounted, by conventional means, in predetermined spaced relation to the screen 13. An improved in-line electron gun 19, shown schematically by dotted lines in FIG. 1, is centrally mounted within the neck 5 to generate and direct three electron beams 20 along co-planar convergent paths through the mask 15 to the screen 13.
The
tube of FIG. 1 is designed to be used with an external magnetic
deflection yoke, such as the yoke 21 schematically shown, surrounding
the neck 5 and funnel 7, in the neighborhood of their junction, for
subjecting the three beams 20 to vertical and horizontal magnetic flux,
to scan the beams horizontally and vertically in a rectangular raster
over the screen 13. The initial plane of deflection (at zero deflection)
is shown by the line P--P in FIG. 1 at about the middle of the yoke
21. Because of fringe fields, the zone of deflection of the tube
extends axially, from the yoke 21, into the region of the gun 19. For
simplicity, the actual curvature of the deflected beam paths 20 in the
deflection zone is not shown in FIG. 1.
The in-line gun 19 of the present invention is designed to generate and direct three equally-spaced co-planar beams along initially-parallel paths to a convergence plane C--C, and then along convergent paths through the deflection plane to the screen 13. In order to use the tube with a line-focus yoke 21 specially designed to maintain the three in-line beams substantially converged at the screen without the application of the usual dynamic convergence forces, which causes degrouping misregister of the beam spots with the phosphor elements of the screen, the gun is preferably designed with samll spacings between the beam paths at the convergence plane C--C to produce a still smaller spacing, usually called the S value, between the outer beam paths and the central axis A--A of the tube, in the deflection plane P--P. The convergence angle of the outer beams with the central axis is arc tan e/c+d, where c is the axial distance between the convergence plane C--C and the deflection plane P--P, d is the distance between the deflection plane and the screen 13, and e is the spacing between the outer beam paths and the central axis A--A in the convergence plane C--C. The approximate dimensions in FIG. 1 are c = 2.7 inches, d = 9.8 inches, e = 0.200 inch (200 mils), and hence, the convergence angle is 55 minutes and s = 157 mils.
The
details of the improved gun 19 are shown in FIGS. 3 through 8. The gun
comprises two glass support rods 23 on which the various electrodes
are mounted. These electrodes include three equally-spaced co-planar
cathodes 25, one for each beam, a control grid electrode 27, a screen
grid electrode 29, a first accelerating and focusing electrode 31, a
second accelerating and focusing electrode 33, and a shield cup 35,
spaced along the glass rods 23 in the order named.
Each cathode 25 comprises a cathode sleeve 37, closed at the forward end by a cap 39 having an end coating 41 of electron emissive material and a cathode support tube 43. The tubes 43 are supported on the rods 23 by four straps 45 and 47 (FIG. 6). Each cathode 25 is indirectly heated by a heater coil 49 positioned within the sleeve 37 and having legs 51 welded to heater straps 53 and 55 mounted by studs 57 on the rods 23 (FIG. 5). The control and screen grid electrodes 27 and 29 are two closely-spaced (about 9 mils) flat plates having three pairs of small (about 25 mils) aligned apertures 59 centered with the cathode coatings 41 to initiate three equally-spaced coplanar beam paths 20 extending toward the screen 13. Preferably, the initial paths 20a and 20b are substantially parallel and about 200 mils apart, with the middle path 20a coincident with the central axis A--A.
Electrode
31 comprises first and second cup-shaped members 61 and 63,
respectively, joined together at their open ends. The first cup-shaped
member 61 has three medium-sized (about 60 mils) apertures 75 close to
grid electrode 29 and aligned respectively with the three beam paths 20,
as shown in FIG. 4. The second cup-shaped member 63 has three large
(about 160 mils) apertures 65 also aligned with the three beam paths.
Electrode 33 is also cup-shaped and comprises a base plate portion 60
positioned close (about 60 mils) to electrode 31 and a side wall or
flange 71 extending forward toward the tube screen. The base portion 69
is formed with three apertures 73, which are preferably slightly larger
(about 172 mils) than the adjacent apertures 67 of electrode 31. The
middle aperture 73a is aligned with the adjacent middle aperture 67a
(and middle beam path 20a) to provide a substantially symmetrical beam
focusing electric field between apertures 67a and 73a when electrodes 31
and 33 are energized at different voltages. The two outer apertures
73b are slightly offset outwardly with respect to the corresponding
outer apertures 67b, to provide an asymmetrical electric field between
each pair of outer apertures when electrodes 31 and 33 are energized,
to individually focus each outer beam 20b near the screen, and also to
deflect each beam, toward the middle beam, to a common point of
convergence with the middle beam near the screen. In the example shown,
the offset of each beam aperture 73b may be about 6 mils.
The
approximate configuration of the electric fields associated with the
middle and outer apertures are shown in FIGS. 9 and 10, respectively,
which show the equipotential lines 74 rather than the lines of force.
Assuming an accelerating field, as shown by the + signs, the left half
75 (on the left side of the central mid-plane) of each field is
converging and the right half 77 is diverging. Since the electrons are
being accelerated, they spend more time in the converging field than in
the diverging field, and hence, the beam experiences a net converging
or focusing force in each of FIGS. 9 and 10. Since the middle beam 20a
passes centrally through a symmetrical field in FIG. 9, it continues in
the same direction without deflection. In FIG. 10, the outer beam 20b
traverses the left half 75 of the field centrally, but enters the right
half 77 off-axis. Since this is the diverging part of the field, and
the electrons are subjected to field forces perpendicular to the
equipotential lines or surfaces 74, the beam 20b is deflected toward the
central axis (downward in FIG. 10) as it traverses the right half 77,
in addition to being focused. The angle of deflection, or convergence,
of the beam 20b can be determined by the choice of the offset of the
apertures 73 b and the voltages applied to the two electrodes 31 and 33.
For the example given, with an offset of 6 mils, electrode 33 would be
connected to the ultor or screen voltage, about 25 K.V., and electrode
31 would be operated at about 17 to 20 percent of the ultor voltage,
adjusted for best focus. The object distance of each focus lens, that
is, the distance between the first cross-over of the beams near the
screen grid 29 and the lens, is about 0.500 inch; and the image distance
from the lens to the screen is about 12.5. inches.
The above-described outward offset of the beam apertures to produce beam convergence is contrary to the teaching of FIG. 3 of the Moodey patent described above, and hence, is not suggested by the Moodey patent.
The focusing apertures 67 and 73 are made as large as possible, to minimize spherical aberration, and as close together as possible, to obtain a desirable small spacing between beam paths. As a result, the fringe portions of adjacent fields interact to produce some astigmatic distortion of the focusing fields, which produces some ellipticity of the normally-circular focused beam spots on the screen. In a three-beam in-line gun, this distortion is greater for the middle beam than for the two outer beams, because both sides of the middle beam field are affected. In order to compensate for this effect, and minimize the elliptical distortion of the beam spots, the wall 69, or at least the surface thereof facing the electrode 31, is curved substantially cylindrically, concave to electrode 31, in the direction normal or transverse to the plane of the three beams, as shown at 79 in FIG. 3. Preferably, this curvature is greater for the middle beam path than for the outer beam paths, hence, the wall 69 may be made barrel-shaped. In the example given, the barrel shape may have a stave radius of 8 inches (FIG. 4) and a hoop radius of 2.28 inches (FIG. 3), with the curvature 79 terminating at the outer edges of the outer apertures 73b.
The
shield cup 35 comprises a base portion 81, attached to the open end of
the flange 71 of electrode 33, and a tubular wall 83 surrounding the
three beam paths 20. The base portion 81 is formed with a large middle
beam aperture 85 (about 172 mils) and two smaller outer beam apertures
87 (about 100 mils) aligned, respectively, with the three initial beam
paths 20a and 20b.
In order to compensate for the coma distortion wherein the sizes of the rasters scanned on the screen by the external magnetic deflection yoke are different for the middle and outer beams of the three-beam gun, due to the eccentricity of the outer beams in the yoke field, the electron gun is provided with two shield rings 89 of high magnetic permeability, e.g., an alloy of 52 percent nickel and 48 percent iron, known as 52 metal, are attached to the base 81, with each ring concentrically surrounding one of the outer apertures 87, as shown in FIGS. 4 and 7. These magnetic shields 89 by-pass a small portion of the fringe deflection fields in the path of the outer beams, thereby making a slight reduction in the rasters scanned by the outer beams on the screen. The shield rings 89 may have an outer diameter of 150 mils, an inner diameter of 100 mils, and a thickness of 10 mils.
A further correction for this coma distortion is made by mounting two small discs 91 of magnetic material, e.g., that referred to above, on each side of the middle beam path 20a. These discs 91 enhance the magnetic flux on the middle beam transverse to the plane of the three beams and decrease the flux in that plane, in the manner described in the Barkow patent referred to above. The discs 91 may be rings having an outer diameter of 80 mils, an inner diameter of 30 mils, and a thickness of 10 mils.
Each of the electrodes 27, 29, 31 and 33 are mounted on the two glass rods 23 by edge portions embedded in the glass. The two rods 23 extend forwardly beyond the mounting portion of electrode 33, as shown in FIG. 3. In order to shield the exposed ends 93 of the glass rods 23 from the electron beams, the shield cup 35 is formed with inwardly-extending recess portions 95 into which the rod ends 93 extend. The electron gun 19 is mounted in the neck 5 at one end by the leads (not shown) from the various electrodes to the stem terminals 97, and at the other end by conventional metal bulb spacers (not shown) which also connect the final electrode 33 to the usual conducting coating on the inner wall of the funnel 7.
The present invention relates to an improved in-line electron gun for a cathode ray tube, particularly a shadow mask type color picture tube. The new gun is primarily intended for use in a color tube having a line type color phosphor screen, with or without light absorbing guard bands between the color phosphor lines, and a mask having elongated apertures or slits. However, the gun could be used in the well known dot-type color tube having a screen of substantially circular color phosphor dots and a mask with substantially circular apertures.
An in-line electron gun is one designed to generate or initiate at least two, and preferably three, electron beams in a common plane, for example, by at least two cathodes, and direct those beams along convergent paths in that plane to a point or small area of convergence near the tube screen. Various ways have been proposed for causing the beams to converge near the screen. For example, the gun may be designed to initially aim the beams, from the cathodes, towards convergence at the screen, as shown in FIG. 4 of Moodey U.S. Pat. No. 2,957,106, wherein the beam apertures in the gun electrodes are aligned along convergent paths.
In order to avoid wide spacings between the cathodes, which are undesirable in a small neck tube designed for high deflection angles, it is preferable to initiate the beams along substantially parallel (or even divergent) paths and provide some means, either internally or externally of the tube, for converging the beams near the screen. Magnet poles and/or electrostatic deflecting plates for converging in-line beams are disclosed in Francken U.S. Pat. No. 2,849,647, Gundert et al. U.S. Pat. No. 2,859,378 and Benway U.S. Pat No. 2,887,598.
The Moodey patent referred to above also includes an embodiment, shown in FIG. 2 and described in lines 4 to 23 of column 5, wherein an in-line gun for two co-planar beams comprises two spaced cathodes, a control grid plate and an accelerating grid plate each having two apertures aligned respectively with the two cathodes (as in FIG. 2) to initiate two parallel co-planar beam paths, and two spaced-apart beam focusing and accelerating electrodes of cylindrical form. The focusing electrode nearest to the first accelerating grid plate is described as having two beam apertures that are offset toward the axis of the gun from the corresponding apertures of the adjacent accelerating grid plate, to provide an asymmetric electrostatic field in the path of each beam for deflecting the beam from its initial path into a second beam path directed toward the tube axis.
Netherlands U.S. Pat. application No. 6902025, published Aug. 11, 1970 teaches that astigmatic aberration resulting in elliptical distortion of the focused screen spots of the two off-axis beams from an in-line gun, caused by the eccentricity of the in-line beams in a common focusing field between two hollow cylindrical focusing electrodes, can be partially corrected by forming the adjacent edges of the cylindrical electrodes with a sinusoidal contour including four sine waves. A similar problem is solved in a different manner in applicant's in-line gun.
Another
problem that exists in a cathode ray tube having an in-line gun is a
coma distortion wherein the sizes of the rasters scanned on the screen
by a conventional external magnetic deflection yoke are different,
because of the eccentricity of the two outer beams with respect to the
center of the yoke. Messineo et al. U.S. Pat. No. 3,164,737 teaches that
a similar coma distortion caused by using different beam velocities
can be corrected by use of a magnetic shield around the path of one or
more beams in a delta type gun. Barkow U.S. Pat. No. 3,196,305 teaches
the use of magnetic enhancers adjacent to the path of one or more beams
in a delta gun, for the same purpose. Krackhardt et al. U.S. Pat. No.
3,534,208 teaches the use of a magnetic shield around the middle one of
three in-line beams for coma correction.SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, at least two electron beams are generated along co-planar paths toward the screen of a cathode ray tube, e.g., a shadow mask type color picture tube, and the beams are converged near the screen by asymmetric electric fields established in the paths of two beams by two plate-like grids positioned between the beam generating means and the screen and having corresponding apertures suitably related to the beam paths. The apertures in the first grid (nearest the cathodes) are aligned with the beam paths. Two apertures in the second grid (nearest the screen) are offset outwardly with respect to the beam paths to produce the desired asymmetric fields. In the case of three in-line beams, the two outer apertures are offset, and the middle apertures of the two grids are aligned with each other. The pairs of corresponding apertures also provide separate focusing fields for the beams. In order to minimize elliptical distortion of one or more of the focused beam spots on the screen due to crowding of adjacent beam focusing fields, at least a portion of the second grid may be substantially cylindrically curved in a direction transverse to the common plane of the beams, and concave to the first grid. Each of the two outer beam paths of a three beam gun may be partially shielded from the magnetic flux of the deflection yoke by means of a magnetic ring surrounding each beam in the deflection zone of the tube, to minimize differences in the size of the rasters scanned on the screen by the middle and outer beams. Further correction for coma distortion may be made by positioning magnetic pieces on opposite sides of the middle beam path for enhancing one field and reducing the field transverse thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view, partly in axial section, of a shadow mask color picture tube in which the present invention is incorporated;
FIG. 2 is a front end view of the tube of FIG. 1 showing the rectangular shape;
FIG. 3 is an axial section view of the electron gun shown in dotted lines in FIG. 1, taken along the line 3--3 of that figure;
FIG. 4 is an axial section view of the electron gun taken along the line 4--4 of FIG. 3;
FIG. 5 is a rear end view of the electron gun of FIG. 4, taken in the direction of the arrows 5--5 thereof;
FIG. 6 is a transverse view, partly in section, taken along the line 6--6 of FIG. 4;
FIG. 7 is a front end view of the electron gun of FIGS. 1 and 4;
FIG. 8 is a similar end view with the final element (shield cup) removed; and
FIGS. 9 and 10 are schematic views showing the focusing and converging electric fields associated with two pairs of beam apertures in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a plan view of a 17V-90° rectangular color picture tube, for example, having a glass envelope 1 made up of a rectangular (FIG. 2) faceplate panel or cap 3 and a tubular neck 5 connected by a rectangular funnel 7. The panel 3 comprises a viewing faceplate 9 and a peripheral flange or side wall 11 which is sealed to the funnel 7. A mosaic three-color phosphor screen 13 is carried by the inner surface of the faceplate 9. The screen is preferably a line screen with the phosphor lines extending substantially parallel to the minor axis Y-Y of the tube (normal to the plane of FIG. 1). A multi-apertured color selection electrode or shadow mask 15 is removably mounted, by conventional means, in predetermined spaced relation to the screen 13. An improved in-line electron gun 19, shown schematically by dotted lines in FIG. 1, is centrally mounted within the neck 5 to generate and direct three electron beams 20 along co-planar convergent paths through the mask 15 to the screen 13.
The
tube of FIG. 1 is designed to be used with an external magnetic
deflection yoke, such as the yoke 21 schematically shown, surrounding
the neck 5 and funnel 7, in the neighborhood of their junction, for
subjecting the three beams 20 to vertical and horizontal magnetic flux,
to scan the beams horizontally and vertically in a rectangular raster
over the screen 13. The initial plane of deflection (at zero deflection)
is shown by the line P--P in FIG. 1 at about the middle of the yoke
21. Because of fringe fields, the zone of deflection of the tube
extends axially, from the yoke 21, into the region of the gun 19. For
simplicity, the actual curvature of the deflected beam paths 20 in the
deflection zone is not shown in FIG. 1.
The in-line gun 19 of the present invention is designed to generate and direct three equally-spaced co-planar beams along initially-parallel paths to a convergence plane C--C, and then along convergent paths through the deflection plane to the screen 13. In order to use the tube with a line-focus yoke 21 specially designed to maintain the three in-line beams substantially converged at the screen without the application of the usual dynamic convergence forces, which causes degrouping misregister of the beam spots with the phosphor elements of the screen, the gun is preferably designed with samll spacings between the beam paths at the convergence plane C--C to produce a still smaller spacing, usually called the S value, between the outer beam paths and the central axis A--A of the tube, in the deflection plane P--P. The convergence angle of the outer beams with the central axis is arc tan e/c+d, where c is the axial distance between the convergence plane C--C and the deflection plane P--P, d is the distance between the deflection plane and the screen 13, and e is the spacing between the outer beam paths and the central axis A--A in the convergence plane C--C. The approximate dimensions in FIG. 1 are c = 2.7 inches, d = 9.8 inches, e = 0.200 inch (200 mils), and hence, the convergence angle is 55 minutes and s = 157 mils.
The
details of the improved gun 19 are shown in FIGS. 3 through 8. The gun
comprises two glass support rods 23 on which the various electrodes
are mounted. These electrodes include three equally-spaced co-planar
cathodes 25, one for each beam, a control grid electrode 27, a screen
grid electrode 29, a first accelerating and focusing electrode 31, a
second accelerating and focusing electrode 33, and a shield cup 35,
spaced along the glass rods 23 in the order named.
Each cathode 25 comprises a cathode sleeve 37, closed at the forward end by a cap 39 having an end coating 41 of electron emissive material and a cathode support tube 43. The tubes 43 are supported on the rods 23 by four straps 45 and 47 (FIG. 6). Each cathode 25 is indirectly heated by a heater coil 49 positioned within the sleeve 37 and having legs 51 welded to heater straps 53 and 55 mounted by studs 57 on the rods 23 (FIG. 5). The control and screen grid electrodes 27 and 29 are two closely-spaced (about 9 mils) flat plates having three pairs of small (about 25 mils) aligned apertures 59 centered with the cathode coatings 41 to initiate three equally-spaced coplanar beam paths 20 extending toward the screen 13. Preferably, the initial paths 20a and 20b are substantially parallel and about 200 mils apart, with the middle path 20a coincident with the central axis A--A.
Electrode
31 comprises first and second cup-shaped members 61 and 63,
respectively, joined together at their open ends. The first cup-shaped
member 61 has three medium-sized (about 60 mils) apertures 75 close to
grid electrode 29 and aligned respectively with the three beam paths 20,
as shown in FIG. 4. The second cup-shaped member 63 has three large
(about 160 mils) apertures 65 also aligned with the three beam paths.
Electrode 33 is also cup-shaped and comprises a base plate portion 60
positioned close (about 60 mils) to electrode 31 and a side wall or
flange 71 extending forward toward the tube screen. The base portion 69
is formed with three apertures 73, which are preferably slightly larger
(about 172 mils) than the adjacent apertures 67 of electrode 31. The
middle aperture 73a is aligned with the adjacent middle aperture 67a
(and middle beam path 20a) to provide a substantially symmetrical beam
focusing electric field between apertures 67a and 73a when electrodes 31
and 33 are energized at different voltages. The two outer apertures
73b are slightly offset outwardly with respect to the corresponding
outer apertures 67b, to provide an asymmetrical electric field between
each pair of outer apertures when electrodes 31 and 33 are energized,
to individually focus each outer beam 20b near the screen, and also to
deflect each beam, toward the middle beam, to a common point of
convergence with the middle beam near the screen. In the example shown,
the offset of each beam aperture 73b may be about 6 mils.
The
approximate configuration of the electric fields associated with the
middle and outer apertures are shown in FIGS. 9 and 10, respectively,
which show the equipotential lines 74 rather than the lines of force.
Assuming an accelerating field, as shown by the + signs, the left half
75 (on the left side of the central mid-plane) of each field is
converging and the right half 77 is diverging. Since the electrons are
being accelerated, they spend more time in the converging field than in
the diverging field, and hence, the beam experiences a net converging
or focusing force in each of FIGS. 9 and 10. Since the middle beam 20a
passes centrally through a symmetrical field in FIG. 9, it continues in
the same direction without deflection. In FIG. 10, the outer beam 20b
traverses the left half 75 of the field centrally, but enters the right
half 77 off-axis. Since this is the diverging part of the field, and
the electrons are subjected to field forces perpendicular to the
equipotential lines or surfaces 74, the beam 20b is deflected toward the
central axis (downward in FIG. 10) as it traverses the right half 77,
in addition to being focused. The angle of deflection, or convergence,
of the beam 20b can be determined by the choice of the offset of the
apertures 73 b and the voltages applied to the two electrodes 31 and 33.
For the example given, with an offset of 6 mils, electrode 33 would be
connected to the ultor or screen voltage, about 25 K.V., and electrode
31 would be operated at about 17 to 20 percent of the ultor voltage,
adjusted for best focus. The object distance of each focus lens, that
is, the distance between the first cross-over of the beams near the
screen grid 29 and the lens, is about 0.500 inch; and the image distance
from the lens to the screen is about 12.5. inches.
The above-described outward offset of the beam apertures to produce beam convergence is contrary to the teaching of FIG. 3 of the Moodey patent described above, and hence, is not suggested by the Moodey patent.
The focusing apertures 67 and 73 are made as large as possible, to minimize spherical aberration, and as close together as possible, to obtain a desirable small spacing between beam paths. As a result, the fringe portions of adjacent fields interact to produce some astigmatic distortion of the focusing fields, which produces some ellipticity of the normally-circular focused beam spots on the screen. In a three-beam in-line gun, this distortion is greater for the middle beam than for the two outer beams, because both sides of the middle beam field are affected. In order to compensate for this effect, and minimize the elliptical distortion of the beam spots, the wall 69, or at least the surface thereof facing the electrode 31, is curved substantially cylindrically, concave to electrode 31, in the direction normal or transverse to the plane of the three beams, as shown at 79 in FIG. 3. Preferably, this curvature is greater for the middle beam path than for the outer beam paths, hence, the wall 69 may be made barrel-shaped. In the example given, the barrel shape may have a stave radius of 8 inches (FIG. 4) and a hoop radius of 2.28 inches (FIG. 3), with the curvature 79 terminating at the outer edges of the outer apertures 73b.
The
shield cup 35 comprises a base portion 81, attached to the open end of
the flange 71 of electrode 33, and a tubular wall 83 surrounding the
three beam paths 20. The base portion 81 is formed with a large middle
beam aperture 85 (about 172 mils) and two smaller outer beam apertures
87 (about 100 mils) aligned, respectively, with the three initial beam
paths 20a and 20b.In order to compensate for the coma distortion wherein the sizes of the rasters scanned on the screen by the external magnetic deflection yoke are different for the middle and outer beams of the three-beam gun, due to the eccentricity of the outer beams in the yoke field, the electron gun is provided with two shield rings 89 of high magnetic permeability, e.g., an alloy of 52 percent nickel and 48 percent iron, known as 52 metal, are attached to the base 81, with each ring concentrically surrounding one of the outer apertures 87, as shown in FIGS. 4 and 7. These magnetic shields 89 by-pass a small portion of the fringe deflection fields in the path of the outer beams, thereby making a slight reduction in the rasters scanned by the outer beams on the screen. The shield rings 89 may have an outer diameter of 150 mils, an inner diameter of 100 mils, and a thickness of 10 mils.
A further correction for this coma distortion is made by mounting two small discs 91 of magnetic material, e.g., that referred to above, on each side of the middle beam path 20a. These discs 91 enhance the magnetic flux on the middle beam transverse to the plane of the three beams and decrease the flux in that plane, in the manner described in the Barkow patent referred to above. The discs 91 may be rings having an outer diameter of 80 mils, an inner diameter of 30 mils, and a thickness of 10 mils.
Each of the electrodes 27, 29, 31 and 33 are mounted on the two glass rods 23 by edge portions embedded in the glass. The two rods 23 extend forwardly beyond the mounting portion of electrode 33, as shown in FIG. 3. In order to shield the exposed ends 93 of the glass rods 23 from the electron beams, the shield cup 35 is formed with inwardly-extending recess portions 95 into which the rod ends 93 extend. The electron gun 19 is mounted in the neck 5 at one end by the leads (not shown) from the various electrodes to the stem terminals 97, and at the other end by conventional metal bulb spacers (not shown) which also connect the final electrode 33 to the usual conducting coating on the inner wall of the funnel 7.
VIDEOCOLOR (FS10) (MP) Color picture tube having an inline electron gun with an astigmatic prefocusing lens:
A color picture tube includes an inline electron gun for generating and
directing three inline electron beams along coplanar beam paths toward a
screen. The gun includes a plurality of electrodes which form a
beam-forming region, a prefocusing lens, and a main focusing lens for
the electron beams. The prefocusing lens includes four active surfaces.
At least one of the active surfaces has asymmetric prefocusing recesses
formed therein.1. In a color cathode-ray tube including an envelope having therein an inline electron gun for generating and directing three inline electron beams, including a center beam and two outer beams, along initially coplanar beam paths toward and screen on an interior portion of said envelope, said gun having six electrodes forming three electron lenses including a beam-forming lens, a prefocusing lens and a main focusing lens, the improvement wherein
said prefocusing lens includes four active surfaces, at least one of which has a recess formed therein, said active surfaces produce quadrupole fields which form an astigmatic prefocusing lens, said recess provides a preconverging action on said outer electron beams, three circular apertures being provided within said recess.
2. The tube as described in claim 1 wherein said recess is configured to minimize the sensitivity of said gun to variations in operating potentials.
3. In a color cathode-ray tube including an envelope having therein an inline electron gun for generating and directing three inline electron beams, including a center beam and two outer beams, along initially coplanar beam paths toward and screen on an interior portion of said envelope, said gun having six electrodes forming three electron lenses including a beam-forming lens, a prefocusing lens and a main focusing lens, the improvement wherein said prefocusing lens includes four active surfaces on three adjacent electrodes, at least two of said surfaces having substantial identical recesses formed therein, said active surfaces produce quadrupole fields which form an astigmatic prefocusing lens that provides a horizontally-elongated electron beam to said main focusing lens, said recesses provide a preconverging action on said outer electron beams, each of said adjacent electrodes having circular apertures therethrough said apertures being aligned along said beam paths.
4. The tube as described in claim 3 wherein said recesses are configured to minimize the sensitivity of said gun to variations in operating potentials.
5. In a color cathode-ray tube including an envelope having therein an inline electron gun for generating and directing three inline electron beams along initially coplanar beam paths toward a screen on an interior portion of said envelope, said gun including a plurality of longitudinally spaced electrodes which form a first lens, a prefocusing lens and a main focusing lens for said electron beams, said first lens comprising a beam-forming region includi
ng a first
electrode, a second electrode and a first portion of a third electrode
for providing substantially symmetrically-shaped beams to said
prefocusing lens comprising a second portion of said third electrode, a
fourth electrode and a first portion of a fifth electrode, said
prefocusing lens providing asymmetrically-shaped beams to said main
focusing lens comprising of a second portion of said fifth electrode and
a sixth electrode, said main focusing lens being a low aberration lens,
wherein the improvement comprises,
said prefocusing lens including
four active surfaces with separate inline circular apertures
therethrough, said fourth electrode having substantially identical
asymmetric beam-focusing recesses formed in the oppositely disposed
active surfaces thereof, said apertures being disposed within said
recesses.6. The tube as described in claim 5 wherein a single recess is formed in each active surface of said fourth electrode.
7. The tube as described in claim 5 wherein three separate, substantially rectangular recesses comprising two outer recesses and a center recess are formed in each active surface of said fourth electrode.
8. The tube as described in claim 7 wherein each of said outer recesses having an outer aperture therethrough said outer recesses being displaced outwardly relative to said outer apertures.
9. The tube as described in claim 5, wherein each of said circular apertures of said first lens and said prefocusing lens being coaxially aligned along said beam paths.
10. In a color cathode-ray tube including an envelope having therein an inline electron gun for generating and directing three inline beams along initially coplanar beam paths toward a screen on an interior portion of said envelope, said gun including six longitudinally spaced electrodes each having three inline circular apertures therethrough, said electrodes forming a first lens, a prefocusing lens and a main focusing lens for said electron beams, said first lens comprising a beam-forming region including a first electrode, a second electrode and a first portion of a third electrode for providing substantially symmetrically-shaped beams to said prefocusing lens comprising a second portion of said third electrode, a fourth electrode and a first portion of a fifth electrode, said prefocusing lens providing asymmetrically-shaped beams to said main focusing lens consisting of a second portion of said fifth electrode and a sixth electrode, said main focusing lens being a low aberration lens, wherein the improvement comprises, said prefocusing lens including four active surfaces, said second portion of said third electrode and said first portion of said fifth electrode having substantially identical, asymmetric beam-focusing recesses formed in the active surfaces thereof, said circular apertures being formed within said recesses.
11. The tube as described in claim 10 wherein a single recess is formed in said second portion of said third electrode and said first portion of said fifth electrode.
12. The tube as described in claim 10 wherein three separate, substantially rectangular recesses comprising two outer recesses and a center recess are formed in said active surfaces of said second portion of said third electrode and of said first portion of said fifth electrode.
13. The tube as described in claim 12 wherein each of said outer recesses having one of said circular apertures therethrough, said recesses being displaced outwardly relative to said circular apertures.
14. The tube as described in claim 10 wherein each of said circular apertures in each of said electrodes of said first lens and said prefocusing lens being coaxially aligned along said beam paths.
Description:
The invention relates to a color picture tube having an
inline electron gun and, particularly to an electron gun having three
lenses including an asymmetric prefocusing lens.
BACKGROUND OF THE INVENTION
An electron gun, such as a six electrode gun, designed for use in a large screen entertainment-type color picture tube must be capable of generating small-sized high-current electron beam spots over the entire screen. A conventional television receiver utilizes a color picture tube with an inline electron gun and a self-converging deflection yoke, for providing a horizontal deflection field having a pincushion-shaped distortion and a vertical deflection field having a barrel-shaped distortion. The fringe fields of such a yoke introduce into the tube strong astigmatism and deflection defocusing caused, primarily, by vertical overfocusing and, secondarily, by horizontal underfocusing of the deflected electron beams. Beam spots formed by the electron beams passing through such distorted horizontal and vertical deflection fields are asymmetrically-shaped when deflected to the periphery of the screen. Additionally, many inline electron guns exhibit a misconvergence of the outer electron beams due to a change in the strength of the electron lens caused by changes in the focus voltage. Such a misconvergence results in a variation in beam landing position with changes in focus voltage. The present invention addresses these problems in an expeditious and cost effective manner without sacrificing performance.
SUMMARY OF THE INVENTION
The present invention provides an improvement in a color picture tube. Such a tube includes an inline electron gun for generating and directing three inline electron beams along coplanar beam paths toward a screen. The gun includes a plurality of electrodes which form a beam-forming region, a prefocusing lens and a main focusing lens for the electron beams. The improvement resides within the prefocusing lens, which includes four active surfaces. At least one of the active surfaces has asymmetric prefocusing means formed therein.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view, partially in axial section, of a shadow mask color picture tube embodying the invention.
FIGS. 2 and 3 are schematic axial section side views of electron guns in which the invention may be employed.
FIG. 4 is an axial section top view of electron gun according to the present invention.
FIG. 5 is a partial section top view of a first embodiment of the prefocusing lens of the present invention.
FIG. 6 is a section view of an electrode of the prefocusing lens of FIG. 5, taken along line 6--6.
FIG. 7 is a graph of the beam current density contour at the center of the screen for an electron gun utilizing the prefocusing lens electrode of FIG. 5.
FIGS. 8 and 9 are section views of the electron gun shown in FIG. 4, taken along lines 8--8 and 9--9.
FIG. 10 is a partial section top view of a second embodiment of the prefocusing lens of the present invention.
FIG. 11 is a section view of an electrode of the prefocusing lens of FIG. 10, taken along line 11--11.
FIG. 12 is a graph of the beam current density contour at the center of the screen for an electron gun utilizing the prefocusing lens of FIG. 10.
FIG. 13 is a partial section top view of a third embodiment of the prefocusing lens of the present invention.
FIG. 14 is a graph of the beam current density contour at the center of the screen for an electron gun utilizing the prefocusing lens of FIG. 13.
FIG. 15 is a partial section top view of a fourth embodiment of the prefocusing lens of the present invention.
FIG. 16 is a graph of the beam current density contour at the center of the screen for an electron gun utilizing the prefocusing lens of FIG. 15.
FIG. 17 is a section view of a prior embodiment of an electrode of the prefocusing lens.
FIG. 18 is a graph of the beam current density contour at the center of the screen for an electron gun using the prior prefocusing lens electrode of FIG. 17.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a rectangular color picture tube 10 having a glass envelope 11 comprising a rectangular faceplate panel 12 and a tubular neck 14 connected by a rectangular funnel 16. The panel 12 comprises a viewing faceplate 18 and a peripheral flange or sidewall 20 which is sealed to the funnel 16 with a frit seal 21. A mosaic three-color phosphor screen 22 is located on the inner surface of the faceplate 18. The screen, preferably, is a line screen with the phosphor lines extending substantially perpendicular to the high frequency raster line scan of the tube (normal to the plane of FIG. 1). Alternatively, the screen could be a dot screen. A multiapertured color selection electrode or shadow mask 24 is removably mounted, by conventional means, in predetermined, spaced relation to the screen 22. An improved inline electron gun 26, shown schematically by dashed lines in FIG. 1, is centrally mounted within the neck 14 to generate and direct three electron beams 28, along coplanar convergent beam paths, through the mask 24 to the screen 22.
The tube of FIG. 1 is designed to be
used with an external magnetic deflection yoke, such as the yoke 30,
located in the neighborhood of the funnel-to-neck junction. When
activated, the yoke 30 subjects the three beams 28 to magnetic fields
which cause the beams to scan horizontally and vertically, in a
rectangular raster, over the screen 22. The initial plane of deflection
(at zero deflection) is shown by the line P--P in FIG. 1, at about the
middle of the yoke 30. Because of fringe fields, the zone of deflection
of the tube extends axially from the yoke 30 into the region of the gun
26. For simplicity, the actual curvature of the deflection beam paths in
the deflection zone is not shown in FIG. 1.
The inline electron gun 26 includes six electrodes, G1 through G6, in addition to the cathodes, K. The gun may be of a first type 26', shown in FIG. 2, in which the G2 and G4 electrodes are interconnected and operated at a first potential, and the G3 and G5 electrodes are interconnected and operated at a second potential, or the gun may be of a second type 26", shown in FIG. 3, in which the G3 and G5 electrodes are interconnected and operated at a third potential, and the G4 and G6 electrodes are interconnected and operated at a fourth potential. In each of the electron guns 26' and 26", three electron lenses, L1, L2, and L3, are formed by the aforementioned electrodes. The present invention relates primarily to the second or prefocusing lens, L2.
The
details of a first embodiment of the novel electron gun 26' are shown
in FIGS. 4 through 9. With reference to FIG. 4, the gun 26' comprises
three equally spaced coplanar cathodes 42 (one for each beam), a control
grid 44 (G1), a screen grid 46 (G2), a third electrode 48 (G3), a
fourth electrode 50 (G4), a fifth electrode 52 (G5), the G5 electrode
includes a portion G5' identified as element 54, for a purpose to be
described hereinafter, and a sixth electrode 56 (G6). The electrodes are
spaced, in the order named, from the cathodes and are attached to a
pair of support rods (not shown).
The G1 electrode 44, the G2 electrode 46 and a first portion 72 of the G3 electrode 48, facing the G2 electrode 46, comprise a beam-forming region of the electron gun 26' and form the first electron lens, L1. Another portion 74 of the G3 electrode 48, the G4 electrode 50 and the G5 electrode 52 comprise an asymmetric prefocusing or second electron lens, L2, one embodiment of which is shown in FIG. 5. The portion 54 of the G5' electrode and the G6 electrode 56 comprise a third or main focusing lens L3.
Each cathode 42 comprises a cathode sleeve 58 closed at its forward end by a cap 60 having an end coating 62 of an electron emissive material thereon, as is known in the art. Each cathode 42 is indirectly heated by a heater coil (not shown) positioned within the sleeve 58.
The G1 and G2 electrodes, 44 and 46, are two closely spaced, substantially flat, plates each having three inline apertures, 64 and 66, respectively, therethrough. The apertures 64 and 66 are centered with the cathode coating 62 to initiate three equally-spaced coplanar electron beams 28 (shown in FIG. 1), which are directed towards the screen 22. Preferably, the initial electron beam paths are substantially parallel, with the middle path with the central axis, A--A, of the electron gun.
The G3 electrode 48 includes a substantially flat outer plate portion 68 having three inline apertures 70 therethrough, which are aligned with the apertures 66 and 64 in the G2 and G1 electrodes, 46 and 44, respectively. The G3 electrode 48 also includes a pair of cup-shaped first and second portions, 72 and 74, respectively, which are joined together at their open ends. The first portion 72 has three inline apertures 76, formed through the bottom of the cup, which are aligned with the aperture 70 in the plate 68. The second portion 74 of the G3 electrode has three apertures 78 formed through its bottom, which are aligned with the apertures 76 in the first portion 72. Extrusions 79 surround the apertures 78. Alternatively, the plate portion 68, with its inline apertures 70, may be formed as an internal part of the first portion 72.
As shown in FIG. 5, the G4 electrode 50 comprises a plate having identically-shaped recesses 51a and 51b formed in the opposed major surfaces thereof. Three inline
apertures 80 are formed through the body of the electrode 50, within
recesses 51a and 51b, and aligned with the apertures 78 in the G3
electrode 48.
Again with respect to FIG. 4, the G5 electrode 52 is a deep-drawn, cup-shaped member having three apertures 82, surrounded by extrusions 83, formed in the bottom end thereof. A substantially flat plate member 84, having three apertures 86, aligned with the apertures 82, is attached to and closes the open end of the G5 electrode 52. A first plate portion 88, having a plurality of openings 90 therein, is attached to the opposite surface of the plate member 84.
The G5' electrode portion 54 comprises a deep-drawn, cup-shaped member having a recess 92 formed in the bottom end thereof, with three inline apertures 94 extending therethrough. Extrusions 95 surround the apertures 94. The opposite open end of the G5' electrode portion 54 is closed by a second plate portion 96 having three openings 98 formed therethrough. The openings 98 are aligned and cooperate with the openings 90, in the first plate portion 88, in a manner described below.
The G6 electrode 56 is a cup-shaped, deep-drawn member having a large opening 100 at one end through which all three electron beams pass, and an open end which is attached to and closed by a plate member 102 that has three apertures 104 therethrough which are aligned with the apertures 94 in the G5' electrode portion 54. Extrusions 105 surround the apertures 104.
The shape of the recess 51b, formed in the G4
electrode 50, is shown in FIG. 6. The recesses 51a and 51b have a
uniform vertical height at each of the apertures 80 and have rounded
ends. Such a shape has been referred to as the "race-track" shape. The
recess 92, formed in the bottom end of the G5' electrode portion 54, is
also "race-track-shaped" but differs in dimension from the recesses 51a
and 51b in the G4 electrode 50 as described below.
The shape of the large aperture 100 in the G6 electrode 54 is shown in FIG. 8. The opening 100 is vertically higher at the outside apertures 104 than it is at the center aperture. Such a shape has been referred to as the "dog-bone" or "barbell" shape.
With respect to FIG. 4, the first plate portion 88 of the G5 electrode 52 faces the second plate portion 96 of the G5' electrode portion 54. The apertures 90 in the first plate portion 88 have extrusions extending from the plate portion that have been divided into two segments, 106 and 108, for each aperture. The apertures 98 in the second plate portion 96 of the G5' electrode portion 54 also have extrusions extending from the plate portion 96 that have been divided into two segments, 110 and 112, for each aperture. As shown in FIG. 9, the segments 106 and 108 are interleaved with the segments 110 and 112. These segments are used to create quadrupole lenses in the paths of each electron beam when different potentials are applied to the G5 and G5' electrode and electrode portion, 52 and 54, respectively. By proper application of a dynamic voltage differential to either the G5 electrode 52 or the G5' electrode portion 54, it is possible to use the quadrupole lenses established by the segments 106, 108, 110 and 112 to provide an astigmatic correction to the electron beams, which compensates for astigmatism occurring in either the electron gun or the deflection yoke. Such a quadrupole lens structure is described in U.S. Pat. No. 4,731,563, to Bloom et al. on Mar. 15, 1988, which is incorporated by reference herein for the purpose of disclosure.
The novel second lens, L2, of the present invention does not require the use of a quadrupole lens formed by the above-described G5 and G5' electrode and electrode portion, 52 and 54, respectively. A unitized G5 electrode, fabricated by eliminating the first and second plate portions 88 and 96 and attaching together the open ends of elements 52 and 54, may be used; however, such a gun structure would not provide an optimized deflected electron beam shape, although it might be useful where a tradeoff between performance and cost is permissible.
GENERAL CONSIDERATIONS
Specific dimensions of a computer modeled electron gun for the first preferred embodiment are presented in TABLE I.
In the embodiment presented in TABLE I, the electron gun is electrically connected as shown in FIG. 2. Typically, the cathode operates at about 150V, the G1 electrode at ground potential, the G2 and G4 electrodes are electrically interconnected and operate within the range of about 300V to 1000V, the G3 and G5 electrodes also are electrically interconnected and operate at about 7650V and the G6 electrode operates at an anode potential of about 25 kV.
In the present electron gun 26', the first lens, L1 (FIG. 2), provides a symmetrically-shaped, high quality
electron beam into the second lens, L2. The first lens, L1, comprises
the beam forming region of the gun and includes the G1 electrode 44, the
G2 electrode 46, and the first portion of the G3 electrode 48 adjacent
the G2 electrode.
The second lens, L2, is the novel asymmetric prefocusing lens which comprises the G4 electrode 50 and the adjacent portions of the G3 electrode 48 and the G5 electrode 52. In the first embodiment, the identical pair of recesses, 51a and 51b, are formed in the opposed, major, active surfaces of the G4 electrode 50 (see, e.g., FIGS. 5 and 6). While the recesses are, preferably, race-track-shaped, other shapes, e.g., rectangular, which produce the effect described below, are within the scope of the present invention. The active, facing surfaces of the G3 and G5 electrodes, 48 and 52, respectively, are substantially flat. The combination of the above-described active elements produce quadrupole fields which form the asymmetric or astigmatic prefocusing lens which provides a horizontally-elongated electron beam (not shown) into the third or main focusing lens, L3. By providing the astigmatic focusing correction in the prefocusing lens, L2, beyond the electron beam cross-over point which occurs within the first lens, L1, the effectiveness of each quadrupole field is substantially independent of changes in the beam current. Additionally, the race-track-shaped recesses, 51a and 51b, provide a preconverging action which eliminates misconvergence of the outer beams at the screen, due to changes in the focus voltage, by providing a compensating change in the strength of the prefocusing lens, L2.
While the invention is described in terms of two recesses, it is possible to achieve the same results by forming only one recess in either surface of the G4 electrode 50. The single recess would have a greater depth than either of the recesses 51a or 51b, and the lateral dimension, i.e., vertical height and horizontal width, would be less than those of either of the recesses to provide equivalent asymmetric and convergence corrections to the beams. The dimensions of the single recess would depend upon the extent of beam corrections required.
The main focusing lens, L3,
formed between the G5' electrode portion 54 and the G6 electrode 56,
also is an asymmetric lens, having low aberration, which provides a
vertically elongated, or asymmetrically-shaped, electron beam spot at
the center of the screen. The spacing between adjacent apertures 94 in
the G5' electrode portion 54 and the apertures 104 in the G6 electrode
56 is 6.22 mm, rather than the 6.60 mm aperture-to-aperture spacing that
exists from the cathodes to the apertures 82 in the bottom G5 electrode
52. This reduced main lens aperture-to-aperture spacing ensures that
the preconverged outer beams pass through low-aberration regions of the
main lens, L3, to minimize coma distortions. A graph of a computer
simulation of the electron beam spot at the center of the screen of a 27
V110° tube, operated at a cathode drive voltage of 103.2 V, a G3/G5
focus voltage of 7650 V, and an ultor voltage of 25 kV and 4 mA beam
current, is shown in FIG. 7. The beam spot is elliptically-shaped along
the vertical axis to reduce the overfocusing action of the yoke when the
beam is deflected. The undeflected, center beam spot includes a
substantially rectangularly-shaped 90% peak beam current density portion
which is circumscribed by larger elliptically-shaped 50% and 5% peak
beam current density portions. The size of the 5% peak beam current
density spot is about 2.5 mm×4.2 mm (H×V). With the width of the G4
recesses 51a and 51b as specified in TABLE I, and the overall length of
the gun from the G3 bottom to the top of the G5' electrode portion
adjusted to 35.05 mm, the focus voltage is kept below 7700 V, and the
misconvergence of the outer beam is reduced to substantially zero.
By utilizing the multipole lens described with respect to FIG. 4, and applying to the G5' electrode portion 54 a dynamic differential focus voltage that ranges from the potential on the G5 electrode 52, with no deflection, to about 1000 volts more positive at maximum deflection, the beam current density spot size can be optimized when the beams are deflected to the periphery of the screen. This mode of operation is discussed in U.S. Pat. No. 4,764,704, issued to New et al. on Aug. 16, 1988, which is incorporated by reference herein for the purpose of disclosure.
A second embodiment of the present invention is
obtained by increasing the length of the G3 electrode 148 to 5.84 mm,
from the value of 5.08 mm shown in TABLE I, and modifying the asymmetric
prefocusing lens, L2, as shown in FIG. 10. In the second embodiment of
the lens L2, the G4 electrode 150 comprises a substantially flat plate
having a thickness of about 0.025 inch (0.64 mm) with circular apertures
180 formed through the oppositely disposed, active, major surfaces
thereof. The active surfaces of the facing G3 and G5 electrodes, 148 and
152, respectively, have rectangular slots enclosing the electron beam
apertures. As shown in FIG. 11, each of the slots 149, in the G3
electrode 148, has a slot width, W, of 5.82 mm, and a slot height, H, of
10.16 mm. Each of the slots 149 has a depth, d, of 0.76 mm, shown in
FIG. 10. The slot-to-slot spacing, S, shown in FIG. 11, is 7.11 mm.
Since the aperture-to-aperture spacing, s, within the prefocusing lens,
L2, is 6.60 mm, and the slot-to-slot spacing, S, is 7.11 mm, it can be
seen, in FIG. 11, that the two outer slots 149 in the G3 electrode 148
are displaced outwardly relative to the outer apertures 178 formed
therein. This displacement of the slots 149 in the G3 electrode, and a
similar displacement of the identically dimensional slots 153 in the G5
electrode 152, cooperate to form an asymmetric prefocusing lens, L2,
which provides a horizontally-elongated electron beam (not shown) into
the third lens, L3. The novel slot configuration in the G3 and G5
electrodes 148 and 152, respectively, also provides a preconverging
action to eliminate misconvergence of the outer beams at the screen, in a
manner similar to that described for the first embodiment. A computer
simulation of the resultant vertically-elongated beam spot at the center
of the screen is graphically shown in FIG. 12. When operated at an
ultor voltage of 25 kV and 4 mA beam current in a 27 V110° tube, the
beam sizes at 90% and 50% peak current density are comparable to those
of the first embodiment, shown in FIG. 7, and the beam size at 5% peak
current density is about 2.26 mm×3.68 mm (H×V), at a cathode drive
voltage of 103.2 V and a G3/G5 focus voltage of 7650 V. All other gun
parameters are as listed in TABLE I.
Equivalent performance can be achieved by forming the slots in only one of the active surfaces, i.e., in either the G3 electrode 148 or the G5 electrode 152. Slots formed in only one active surface must be deeper than the slots described above, and the small dimension of each slot must be reduced while the amount of outer slot offset must be increased.
A third
embodiment of the present invention is achieved by modifying the
electron gun to provide the electrical configuration shown in FIG. 3.
The asymmetric prefocusing lens, L2, of the gun 26" is shown in FIG. 13.
The length of the G3 electrode 248 is maintained at 5.84 mm, the same
dimension utilized in the second embodiment, and a race-track shaped
recess 249 is formed in the active, major surface of the G3 electrode
facing the G4 electrode 250. The recess 249 has a horizontal width of
19.43 mm, a vertical height of 5.84 mm and a depth of 0.76 mm. An
identically-shaped and dimensioned race track recess 253 is formed in
the active surface of the G5 electrode 252, facing the substantially
flat G4 electrode 250. While the race-track shape is preferred, other
geometric shapes which provide an asymmetric lens with a preconvergence
correction may be used. In the third embodiment, the G4 electrode 250
has a thickness of about 0.64 mm, with circular apertures 280 formed
therethrough. The asymmetric prefocusing lens, L2, of the third
embodiment provides the preconverging action, and forms
horizontally-elongated electron beams (not shown), as previously
described, into the third lens, L3. A computer simulation of the
resultant vertically-elongated beam spot at the center of the screen is
graphically shown in FIG. 14. When operated at an ultor/G4 voltage of 25
kV and 4 mA beam current in a 27 V110° tube, the beam size and shape at
90% peak beam current density is larger and more elliptical than in the
first and second embodiments, while at 50% peak beam current density
the elliptically-shaped spot is more vertically elongated than in the
first two embodiments. At 5% peak beam current density, the beam spot
size is about 1.94 mm×3.44 mm (H×V). The cathode drive voltage in this
embodiment is 103.2 V, the G3/G5 focus voltage is 7650 V and the G2
voltage is typically about 400 V. All other gun parameters are as listed
in TABLE I.
As described above, a single recess can be formed in either the active surface of the G3 or G5 electrodes, 248 or 252, respectively, if the depth is increased and the lateral dimensions are suitably reduced to provide equivalent performance.
A fourth
embodiment of the asymmetric prefocusing lens, L2, is shown in FIG. 15.
The length of the G3 electrode 348 is 5.08 mm, and the active surface
facing the G4 electrode 350 is substantially flat, with three circular
apertures 378 formed therethrough. The apertures 378 have a diameter of
4.01 mm. The G4 electrode 350 has rectangular slots 350a and 350b formed
in the opposed major active surfaces thereof, with the slots 350a
facing the G3 electrode 348 and the slots 350b facing the G5 electrode
352. Each of the slots 350a and 350b has a width of 5.79 mm, a height of
10.16 mm and a depth of 0.76 mm. The slot-to-slot spacing is 7.01 mm.
The circular apertures 380, formed through the G4 electrode 350, have a
diameter of 4.01 mm and are enclosed within the rectangular slots 350a
and 350b, in the same manner as discussed with respect to the slots
shown in FIG. 11. The active major surface of the G5 electrode 352
facing the G4 electrode 350 also is substantially flat, with three
circular apertures 382 formed therethrough. The apertures 382 also have a
80 diameter of 4.01 mm.
Since the aperture-to-aperture spacing
within the prefocusing lens, L2, is 6.60 mm and the slot-to-slot spacing
of the slots 350a and 350b of the G4 electrode 350 is 7.01 mm, the two
outer slots are displaced outwardly relative to the outer apertures 380
formed within the slots. The configuration and displacement of the G4
slots form an asymmetric lens which provides the preconverging action
and horizontally-elongated electron beams (not shown), as previously
described, into the third lens, L3. A computer simulation of the
resultant vertically-elongated beam spot at the center of the screen is
graphically shown in FIG. 16. The beam spot shape is similar to that
shown in FIG. 14. When operated at an ultor/G4 voltage of 25 kV and 4 mA
beam current in a 27 V110° tube, the beam size at 5% peak beam current
density is about 1.96 mm×3.49 mm (H×V), at a cathode drive voltage of
103.2 V and a G3/G5 focus voltage of 7700 V. The G2 voltage in this
embodiment is typically about 400 V. All other gun parameters are as
listed in TABLE I.
Alternatively, slots can be formed in only one of the active surfaces of the G4 electrode 350. The depth of the slots must be increased, and the small dimension of each slot must be decreased, from the respective dimensions described immediately above. Additionally, the amount of offset of the outer slots must be increased to obtain performance equivalent to that of the fourth embodiment.
GENERAL CONSIDERATIONS
The novel electron gun of the present invention is to be contrasted to an electron gun of the type described in U.S. Pat. No. 4,764,704, referenced above. In that patent, a G4 electrode, similar to the G4
electrode 450 of the prefocusing, or second, lens shown in FIG. 17, has
rectangularly-shaped apertures 480 therethrough. Specific dimensions of a
computer model of an embodiment of that prior electron gun are
presented in TABLE II. That embodiment has the electrical configuration
shown in FIG. 2 herein, and is similar in construction to the electron
gun shown in FIG. 4 herein, with similar gun elements being identified
with corresponding numbers, prefixed by the number "4".
*unitized electrode, no multipole lens **the apertureto-aperture
spacing of th
e G3 bottom apertures 470 is increased to 0.2635 inch (6.69
mm) to eliminate any displacement of the outer electron beams with
changes in the focus voltage.
In the prior electron gun described in TABLE II, the cathode operates at a drive voltage of about 103.2 V, the G1 electrode is at ground potential, the G2 and G4 are electrically interconnected and operate within the range of 300 V to 1000 V, the G3 and G5 electrodes also are interconnected and operate at about 6600 V, and the G6 electrode operates at an anode potential of about 25 kV. The prefocusing lens, L2, of the prior electron gun, with the rectangular apertures 480 formed through the substantially flat G4 electrode 450, provides a horizontally-elongated electron beam (not shown) into the main focusing lens, L3. A computer simulation of the resultant vertically-elongated beam spot at the center of the screen is graphically shown in FIG. 18. The beam size at 5% peak current density is about 2.30 mm×3.49 mm (H×V) at the previously described operating parameters.
CONCLUSION
The performance of the present prefocusing lens, L2, of embodiments 1 through 4, as measured by the resultant electron beam spot size on the screen, is comparable to that of the prior electron gun described in U.S. Pat. No. 4,764,704, which utilizes a prefocusing lens having rectangularly-shaped apertures in the G4 electrode thereof. A comparison of results is contained in TABLE III.
The
four embodiments of the present electron gun structure provide ease of
manufacturing, because the use of circular apertures throughout the
electron gun reduces the misalignment problems posed by the
rectangularly-shaped G4 apertures of the prior gun. Additionally, the
prior gun requires a slight increase in the G3 aperture-to-aperture
spacing (from 6.60 mm to 6.69 mm) to eliminate the misconvergence of the
outer electron beams with changes in focus voltage. The present
invention achieves comparable performance by controlling either the
horizontal width of the race-track-shaped recesses within the
prefocusing lens, L2, in embodiments 1 and 3, or the slot-to-slot
spacing of the rectangular slots formed within prefocusing lens, L2, in
embodiments 2 and 4. In each of the four embodiments, the
aperture-to-aperture spacing from the cathode 42 to the bottom of the G5
electrode 52 is maintained at a constant value of 6.60 mm, thereby
simplifying the assembly and alignment of the gun components.
BACKGROUND OF THE INVENTION
An electron gun, such as a six electrode gun, designed for use in a large screen entertainment-type color picture tube must be capable of generating small-sized high-current electron beam spots over the entire screen. A conventional television receiver utilizes a color picture tube with an inline electron gun and a self-converging deflection yoke, for providing a horizontal deflection field having a pincushion-shaped distortion and a vertical deflection field having a barrel-shaped distortion. The fringe fields of such a yoke introduce into the tube strong astigmatism and deflection defocusing caused, primarily, by vertical overfocusing and, secondarily, by horizontal underfocusing of the deflected electron beams. Beam spots formed by the electron beams passing through such distorted horizontal and vertical deflection fields are asymmetrically-shaped when deflected to the periphery of the screen. Additionally, many inline electron guns exhibit a misconvergence of the outer electron beams due to a change in the strength of the electron lens caused by changes in the focus voltage. Such a misconvergence results in a variation in beam landing position with changes in focus voltage. The present invention addresses these problems in an expeditious and cost effective manner without sacrificing performance.
SUMMARY OF THE INVENTION
The present invention provides an improvement in a color picture tube. Such a tube includes an inline electron gun for generating and directing three inline electron beams along coplanar beam paths toward a screen. The gun includes a plurality of electrodes which form a beam-forming region, a prefocusing lens and a main focusing lens for the electron beams. The improvement resides within the prefocusing lens, which includes four active surfaces. At least one of the active surfaces has asymmetric prefocusing means formed therein.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view, partially in axial section, of a shadow mask color picture tube embodying the invention.
FIGS. 2 and 3 are schematic axial section side views of electron guns in which the invention may be employed.
FIG. 4 is an axial section top view of electron gun according to the present invention.
FIG. 5 is a partial section top view of a first embodiment of the prefocusing lens of the present invention.
FIG. 6 is a section view of an electrode of the prefocusing lens of FIG. 5, taken along line 6--6.
FIG. 7 is a graph of the beam current density contour at the center of the screen for an electron gun utilizing the prefocusing lens electrode of FIG. 5.
FIGS. 8 and 9 are section views of the electron gun shown in FIG. 4, taken along lines 8--8 and 9--9.
FIG. 10 is a partial section top view of a second embodiment of the prefocusing lens of the present invention.
FIG. 11 is a section view of an electrode of the prefocusing lens of FIG. 10, taken along line 11--11.
FIG. 12 is a graph of the beam current density contour at the center of the screen for an electron gun utilizing the prefocusing lens of FIG. 10.
FIG. 13 is a partial section top view of a third embodiment of the prefocusing lens of the present invention.
FIG. 14 is a graph of the beam current density contour at the center of the screen for an electron gun utilizing the prefocusing lens of FIG. 13.
FIG. 15 is a partial section top view of a fourth embodiment of the prefocusing lens of the present invention.
FIG. 16 is a graph of the beam current density contour at the center of the screen for an electron gun utilizing the prefocusing lens of FIG. 15.
FIG. 17 is a section view of a prior embodiment of an electrode of the prefocusing lens.
FIG. 18 is a graph of the beam current density contour at the center of the screen for an electron gun using the prior prefocusing lens electrode of FIG. 17.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a rectangular color picture tube 10 having a glass envelope 11 comprising a rectangular faceplate panel 12 and a tubular neck 14 connected by a rectangular funnel 16. The panel 12 comprises a viewing faceplate 18 and a peripheral flange or sidewall 20 which is sealed to the funnel 16 with a frit seal 21. A mosaic three-color phosphor screen 22 is located on the inner surface of the faceplate 18. The screen, preferably, is a line screen with the phosphor lines extending substantially perpendicular to the high frequency raster line scan of the tube (normal to the plane of FIG. 1). Alternatively, the screen could be a dot screen. A multiapertured color selection electrode or shadow mask 24 is removably mounted, by conventional means, in predetermined, spaced relation to the screen 22. An improved inline electron gun 26, shown schematically by dashed lines in FIG. 1, is centrally mounted within the neck 14 to generate and direct three electron beams 28, along coplanar convergent beam paths, through the mask 24 to the screen 22.
The tube of FIG. 1 is designed to be
used with an external magnetic deflection yoke, such as the yoke 30,
located in the neighborhood of the funnel-to-neck junction. When
activated, the yoke 30 subjects the three beams 28 to magnetic fields
which cause the beams to scan horizontally and vertically, in a
rectangular raster, over the screen 22. The initial plane of deflection
(at zero deflection) is shown by the line P--P in FIG. 1, at about the
middle of the yoke 30. Because of fringe fields, the zone of deflection
of the tube extends axially from the yoke 30 into the region of the gun
26. For simplicity, the actual curvature of the deflection beam paths in
the deflection zone is not shown in FIG. 1. The inline electron gun 26 includes six electrodes, G1 through G6, in addition to the cathodes, K. The gun may be of a first type 26', shown in FIG. 2, in which the G2 and G4 electrodes are interconnected and operated at a first potential, and the G3 and G5 electrodes are interconnected and operated at a second potential, or the gun may be of a second type 26", shown in FIG. 3, in which the G3 and G5 electrodes are interconnected and operated at a third potential, and the G4 and G6 electrodes are interconnected and operated at a fourth potential. In each of the electron guns 26' and 26", three electron lenses, L1, L2, and L3, are formed by the aforementioned electrodes. The present invention relates primarily to the second or prefocusing lens, L2.
The
details of a first embodiment of the novel electron gun 26' are shown
in FIGS. 4 through 9. With reference to FIG. 4, the gun 26' comprises
three equally spaced coplanar cathodes 42 (one for each beam), a control
grid 44 (G1), a screen grid 46 (G2), a third electrode 48 (G3), a
fourth electrode 50 (G4), a fifth electrode 52 (G5), the G5 electrode
includes a portion G5' identified as element 54, for a purpose to be
described hereinafter, and a sixth electrode 56 (G6). The electrodes are
spaced, in the order named, from the cathodes and are attached to a
pair of support rods (not shown). The G1 electrode 44, the G2 electrode 46 and a first portion 72 of the G3 electrode 48, facing the G2 electrode 46, comprise a beam-forming region of the electron gun 26' and form the first electron lens, L1. Another portion 74 of the G3 electrode 48, the G4 electrode 50 and the G5 electrode 52 comprise an asymmetric prefocusing or second electron lens, L2, one embodiment of which is shown in FIG. 5. The portion 54 of the G5' electrode and the G6 electrode 56 comprise a third or main focusing lens L3.
Each cathode 42 comprises a cathode sleeve 58 closed at its forward end by a cap 60 having an end coating 62 of an electron emissive material thereon, as is known in the art. Each cathode 42 is indirectly heated by a heater coil (not shown) positioned within the sleeve 58.
The G1 and G2 electrodes, 44 and 46, are two closely spaced, substantially flat, plates each having three inline apertures, 64 and 66, respectively, therethrough. The apertures 64 and 66 are centered with the cathode coating 62 to initiate three equally-spaced coplanar electron beams 28 (shown in FIG. 1), which are directed towards the screen 22. Preferably, the initial electron beam paths are substantially parallel, with the middle path with the central axis, A--A, of the electron gun.
The G3 electrode 48 includes a substantially flat outer plate portion 68 having three inline apertures 70 therethrough, which are aligned with the apertures 66 and 64 in the G2 and G1 electrodes, 46 and 44, respectively. The G3 electrode 48 also includes a pair of cup-shaped first and second portions, 72 and 74, respectively, which are joined together at their open ends. The first portion 72 has three inline apertures 76, formed through the bottom of the cup, which are aligned with the aperture 70 in the plate 68. The second portion 74 of the G3 electrode has three apertures 78 formed through its bottom, which are aligned with the apertures 76 in the first portion 72. Extrusions 79 surround the apertures 78. Alternatively, the plate portion 68, with its inline apertures 70, may be formed as an internal part of the first portion 72.
As shown in FIG. 5, the G4 electrode 50 comprises a plate having identically-shaped recesses 51a and 51b formed in the opposed major surfaces t
hereof. Three inline
apertures 80 are formed through the body of the electrode 50, within
recesses 51a and 51b, and aligned with the apertures 78 in the G3
electrode 48. Again with respect to FIG. 4, the G5 electrode 52 is a deep-drawn, cup-shaped member having three apertures 82, surrounded by extrusions 83, formed in the bottom end thereof. A substantially flat plate member 84, having three apertures 86, aligned with the apertures 82, is attached to and closes the open end of the G5 electrode 52. A first plate portion 88, having a plurality of openings 90 therein, is attached to the opposite surface of the plate member 84.
The G5' electrode portion 54 comprises a deep-drawn, cup-shaped member having a recess 92 formed in the bottom end thereof, with three inline apertures 94 extending therethrough. Extrusions 95 surround the apertures 94. The opposite open end of the G5' electrode portion 54 is closed by a second plate portion 96 having three openings 98 formed therethrough. The openings 98 are aligned and cooperate with the openings 90, in the first plate portion 88, in a manner described below.
The G6 electrode 56 is a cup-shaped, deep-drawn member having a large opening 100 at one end through which all three electron beams pass, and an open end which is attached to and closed by a plate member 102 that has three apertures 104 therethrough which are aligned with the apertures 94 in the G5' electrode portion 54. Extrusions 105 surround the apertures 104.
The shape of the recess 51b, formed in the G4
electrode 50, is shown in FIG. 6. The recesses 51a and 51b have a
uniform vertical height at each of the apertures 80 and have rounded
ends. Such a shape has been referred to as the "race-track" shape. The
recess 92, formed in the bottom end of the G5' electrode portion 54, is
also "race-track-shaped" but differs in dimension from the recesses 51a
and 51b in the G4 electrode 50 as described below. The shape of the large aperture 100 in the G6 electrode 54 is shown in FIG. 8. The opening 100 is vertically higher at the outside apertures 104 than it is at the center aperture. Such a shape has been referred to as the "dog-bone" or "barbell" shape.
With respect to FIG. 4, the first plate portion 88 of the G5 electrode 52 faces the second plate portion 96 of the G5' electrode portion 54. The apertures 90 in the first plate portion 88 have extrusions extending from the plate portion that have been divided into two segments, 106 and 108, for each aperture. The apertures 98 in the second plate portion 96 of the G5' electrode portion 54 also have extrusions extending from the plate portion 96 that have been divided into two segments, 110 and 112, for each aperture. As shown in FIG. 9, the segments 106 and 108 are interleaved with the segments 110 and 112. These segments are used to create quadrupole lenses in the paths of each electron beam when different potentials are applied to the G5 and G5' electrode and electrode portion, 52 and 54, respectively. By proper application of a dynamic voltage differential to either the G5 electrode 52 or the G5' electrode portion 54, it is possible to use the quadrupole lenses established by the segments 106, 108, 110 and 112 to provide an astigmatic correction to the electron beams, which compensates for astigmatism occurring in either the electron gun or the deflection yoke. Such a quadrupole lens structure is described in U.S. Pat. No. 4,731,563, to Bloom et al. on Mar. 15, 1988, which is incorporated by reference herein for the purpose of disclosure.
The novel second lens, L2, of the present invention does not require the use of a quadrupole lens formed by the above-described G5 and G5' electrode and electrode portion, 52 and 54, respectively. A unitized G5 electrode, fabricated by eliminating the first and second plate portions 88 and 96 and attaching together the open ends of elements 52 and 54, may be used; however, such a gun structure would not provide an optimized deflected electron beam shape, although it might be useful where a tradeoff between performance and cost is permissible.
GENERAL CONSIDERATIONS
Specific dimensions of a computer modeled electron gun for the first preferred embodiment are presented in TABLE I.
| TABLE I |
| ______________________________________ |
| inches mm |
| ______________________________________ |
K-G1 spacing 0.003 0.08 Thickness of G1 electrode 44 0.004 0.10 Thickness of G2 electrode 46 0.028 0.71 G1 and G2 aperture diameter 0.025 0.64 G1 to G1 spacing 0.008 0.20 G2 to G3 spacing 0.030 0.76 Thickness of G3 plate portion 68 0.010 0.25 Diameter of G3 apertures 70 0.045 1.14 Diameter of G3 apertures 78 0.148 3.76 Length of G3 electrode 48 0.200 5.08 G3 to G4 spacing 0.050 1.27 Thickness of active area of G4 electrode 50 0.025 0.64 Diameter of G4 aperture 80 0.158 4.01 Horizontal width of recesses 51a and 51b 0.785 19.94 Vertical height of recesses 51a and 51b 0.239 6.07 Depth of recesses 51a and 51b 0.030 0.76 G4 to G5 spacing 0.050 1.27 Overall length of G5 electrode 0.970 24.64 52 and G5' electrode portion 54 Spacing between plate portions 88 and 96 0.040 1.02 Horizontal width of recess 92 0.755 19.18 Vertical height of recess 92 0.326 8.28 Depth of recess 92 0.115 2.92 Diameter of apertures 82, 90, 98 0.158 4.01 Aperture-to-aperture spacing K to G5 bottom 0.260 6.60 Diameter of G5' aperture 94 (center) 0.160 4.06 Diameter of G5' apertures 94 (outer) 0.180 4.57 G5' to G6 spacing 0.050 1.27 Length of G6 electrode 56 0.150 3.81 Horizontal width of opening 100 0.742 18.85 Maximum height of opening 100 0.295 7.49 Minimum height of opening 100 0.289 7.34 Depth of opening 100 0.135 3.43 Diameter of G6 aperture 105 (center) 0.160 4.06 Diameter of G6 apertures 105 (outer) 0.180 4.57 Aperture-to-aperture spacing G5'top/G6 0.245 6.22 Length of G3 extrusions 79 0.045 1.14 Length of G5 extrusions 83 0.045 1.14 Length of G5' extrusions 95 0.034 0.86 Length of G6 extrusions 105 0.045 1.14 |
| ______________________________________ |
In the embodiment presented in TABLE I, the electron gun is electrically connected as shown in FIG. 2. Typically, the cathode operates at about 150V, the G1 electrode at ground potential, the G2 and G4 electrodes are electrically interconnected and operate within the range of about 300V to 1000V, the G3 and G5 electrodes also are electrically interconnected and operate at about 7650V and the G6 electrode operates at an anode potential of about 25 kV.
In the present electron gun 26', the first
lens, L1 (FIG. 2), provides a symmetrically-shaped, high quality
electron beam into the second lens, L2. The first lens, L1, comprises
the beam forming region of the gun and includes the G1 electrode 44, the
G2 electrode 46, and the first portion of the G3 electrode 48 adjacent
the G2 electrode. 
The second lens, L2, is the novel asymmetric prefocusing lens which comprises the G4 electrode 50 and the adjacent portions of the G3 electrode 48 and the G5 electrode 52. In the first embodiment, the identical pair of recesses, 51a and 51b, are formed in the opposed, major, active surfaces of the G4 electrode 50 (see, e.g., FIGS. 5 and 6). While the recesses are, preferably, race-track-shaped, other shapes, e.g., rectangular, which produce the effect described below, are within the scope of the present invention. The active, facing surfaces of the G3 and G5 electrodes, 48 and 52, respectively, are substantially flat. The combination of the above-described active elements produce quadrupole fields which form the asymmetric or astigmatic prefocusing lens which provides a horizontally-elongated electron beam (not shown) into the third or main focusing lens, L3. By providing the astigmatic focusing correction in the prefocusing lens, L2, beyond the electron beam cross-over point which occurs within the first lens, L1, the effectiveness of each quadrupole field is substantially independent of changes in the beam current. Additionally, the race-track-shaped recesses, 51a and 51b, provide a preconverging action which eliminates misconvergence of the outer beams at the screen, due to changes in the focus voltage, by providing a compensating change in the strength of the prefocusing lens, L2.
While the invention is described in terms of two recesses, it is possible to achieve the same results by forming only one recess in either surface of the G4 electrode 50. The single recess would have a greater depth than either of the recesses 51a or 51b, and the lateral dimension, i.e., vertical height and horizontal width, would be less than those of either of the recesses to provide equivalent asymmetric and convergence corrections to the beams. The dimensions of the single recess would depend upon the extent of beam corrections required.
The main focusing lens, L3,
formed between the G5' electrode portion 54 and the G6 electrode 56,
also is an asymmetric lens, having low aberration, which provides a
vertically elongated, or asymmetrically-shaped, electron beam spot at
the center of the screen. The spacing between adjacent apertures 94 in
the G5' electrode portion 54 and the apertures 104 in the G6 electrode
56 is 6.22 mm, rather than the 6.60 mm aperture-to-aperture spacing that
exists from the cathodes to the apertures 82 in the bottom G5 electrode
52. This reduced main lens aperture-to-aperture spacing ensures that
the preconverged outer beams pass through low-aberration regions of the
main lens, L3, to minimize coma distortions. A graph of a computer
simulation of the electron beam spot at the center of the screen of a 27
V110° tube, operated at a cathode drive voltage of 103.2 V, a G3/G5
focus voltage of 7650 V, and an ultor voltage of 25 kV and 4 mA beam
current, is shown in FIG. 7. The beam spot is elliptically-shaped along
the vertical axis to reduce the overfocusing action of the yoke when the
beam is deflected. The undeflected, center beam spot includes a
substantially rectangularly-shaped 90% peak beam current density portion
which is circumscribed by larger elliptically-shaped 50% and 5% peak
beam current density portions. The size of the 5% peak beam current
density spot is about 2.5 mm×4.2 mm (H×V). With the width of the G4
recesses 51a and 51b as specified in TABLE I, and the overall length of
the gun from the G3 bottom to the top of the G5' electrode portion
adjusted to 35.05 mm, the focus voltage is kept below 7700 V, and the
misconvergence of the outer beam is reduced to substantially zero. By utilizing the multipole lens described with respect to FIG. 4, and applying to the G5' electrode portion 54 a dynamic differential focus voltage that ranges from the potential on the G5 electrode 52, with no deflection, to about 1000 volts more positive at maximum deflection, the beam current density spot size can be optimized when the beams are deflected to the periphery of the screen. This mode of operation is discussed in U.S. Pat. No. 4,764,704, issued to New et al. on Aug. 16, 1988, which is incorporated by reference herein for the purpose of disclosure.
A second embodiment of the present invention is
obtained by increasing the length of the G3 electrode 148 to 5.84 mm,
from the value of 5.08 mm shown in TABLE I, and modifying the asymmetric
prefocusing lens, L2, as shown in FIG. 10. In the second embodiment of
the lens L2, the G4 electrode 150 comprises a substantially flat plate
having a thickness of about 0.025 inch (0.64 mm) with circular apertures
180 formed through the oppositely disposed, active, major surfaces
thereof. The active surfaces of the facing G3 and G5 electrodes, 148 and
152, respectively, have rectangular slots enclosing the electron beam
apertures. As shown in FIG. 11, each of the slots 149, in the G3
electrode 148, has a slot width, W, of 5.82 mm, and a slot height, H, of
10.16 mm. Each of the slots 149 has a depth, d, of 0.76 mm, shown in
FIG. 10. The slot-to-slot spacing, S, shown in FIG. 11, is 7.11 mm.
Since the aperture-to-aperture spacing, s, within the prefocusing lens,
L2, is 6.60 mm, and the slot-to-slot spacing, S, is 7.11 mm, it can be
seen, in FIG. 11, that the two outer slots 149 in the G3 electrode 148
are displaced outwardly relative to the outer apertures 178 formed
therein. This displacement of the slots 149 in the G3 electrode, and a
similar displacement of the identically dimensional slots 153 in the G5
electrode 152, cooperate to form an asymmetric prefocusing lens, L2,
which provides a horizontally-elongated electron beam (not shown) into
the third lens, L3. The novel slot configuration in the G3 and G5
electrodes 148 and 152, respectively, also provides a preconverging
action to eliminate misconvergence of the outer beams at the screen, in a
manner similar to that described for the first embodiment. A computer
simulation of the resultant vertically-elongated beam spot at the center
of the screen is graphically shown in FIG. 12. When operated at an
ultor voltage of 25 kV and 4 mA beam current in a 27 V110° tube, the
beam sizes at 90% and 50% peak current density are comparable to those
of the first embodiment, shown in FIG. 7, and the beam size at 5% peak
current density is about 2.26 mm×3.68 mm (H×V), at a cathode drive
voltage of 103.2 V and a G3/G5 focus voltage of 7650 V. All other gun
parameters are as listed in TABLE I. Equivalent performance can be achieved by forming the slots in only one of the active surfaces, i.e., in either the G3 electrode 148 or the G5 electrode 152. Slots formed in only one active surface must be deeper than the slots described above, and the small dimension of each slot must be reduced while the amount of outer slot offset must be increased.
A third
embodiment of the present invention is achieved by modifying the
electron gun to provide the electrical configuration shown in FIG. 3.
The asymmetric prefocusing lens, L2, of the gun 26" is shown in FIG. 13.
The length of the G3 electrode 248 is maintained at 5.84 mm, the same
dimension utilized in the second embodiment, and a race-track shaped
recess 249 is formed in the active, major surface of the G3 electrode
facing the G4 electrode 250. The recess 249 has a horizontal width of
19.43 mm, a vertical height of 5.84 mm and a depth of 0.76 mm. An
identically-shaped and dimensioned race track recess 253 is formed in
the active surface of the G5 electrode 252, facing the substantially
flat G4 electrode 250. While the race-track shape is preferred, other
geometric shapes which provide an asymmetric lens with a preconvergence
correction may be used. In the third embodiment, the G4 electrode 250
has a thickness of about 0.64 mm, with circular apertures 280 formed
therethrough. The asymmetric prefocusing lens, L2, of the third
embodiment provides the preconverging action, and forms
horizontally-elongated electron beams (not shown), as previously
described, into the third lens, L3. A computer simulation of the
resultant vertically-elongated beam spot at the center of the screen is
graphically shown in FIG. 14. When operated at an ultor/G4 voltage of 25
kV and 4 mA beam current in a 27 V110° tube, the beam size and shape at
90% peak beam current density is larger and more elliptical than in the
first and second embodiments, while at 50% peak beam current density
the elliptically-shaped spot is more vertically elongated than in the
first two embodiments. At 5% peak beam current density, the beam spot
size is about 1.94 mm×3.44 mm (H×V). The cathode drive voltage in this
embodiment is 103.2 V, the G3/G5 focus voltage is 7650 V and the G2
voltage is typically about 400 V. All other gun parameters are as listed
in TABLE I. As described above, a single recess can be formed in either the active surface of the G3 or G5 electrodes, 248 or 252, respectively, if the depth is increased and the lateral dimensions are suitably reduced to provide equivalent performance.
A fourth
embodiment of the asymmetric prefocusing lens, L2, is shown in FIG. 15.
The length of the G3 electrode 348 is 5.08 mm, and the active surface
facing the G4 electrode 350 is substantially flat, with three circular
apertures 378 formed therethrough. The apertures 378 have a diameter of
4.01 mm. The G4 electrode 350 has rectangular slots 350a and 350b formed
in the opposed major active surfaces thereof, with the slots 350a
facing the G3 electrode 348 and the slots 350b facing the G5 electrode
352. Each of the slots 350a and 350b has a width of 5.79 mm, a height of
10.16 mm and a depth of 0.76 mm. The slot-to-slot spacing is 7.01 mm.
The circular apertures 380, formed through the G4 electrode 350, have a
diameter of 4.01 mm and are enclosed within the rectangular slots 350a
and 350b, in the same manner as discussed with respect to the slots
shown in FIG. 11. The active major surface of the G5 electrode 352
facing the G4 electrode 350 also is substantially flat, with three
circular apertures 382 formed therethrough. The apertures 382 also have a
80 diameter of 4.01 mm. 
Since the aperture-to-aperture spacing
within the prefocusing lens, L2, is 6.60 mm and the slot-to-slot spacing
of the slots 350a and 350b of the G4 electrode 350 is 7.01 mm, the two
outer slots are displaced outwardly relative to the outer apertures 380
formed within the slots. The configuration and displacement of the G4
slots form an asymmetric lens which provides the preconverging action
and horizontally-elongated electron beams (not shown), as previously
described, into the third lens, L3. A computer simulation of the
resultant vertically-elongated beam spot at the center of the screen is
graphically shown in FIG. 16. The beam spot shape is similar to that
shown in FIG. 14. When operated at an ultor/G4 voltage of 25 kV and 4 mA
beam current in a 27 V110° tube, the beam size at 5% peak beam current
density is about 1.96 mm×3.49 mm (H×V), at a cathode drive voltage of
103.2 V and a G3/G5 focus voltage of 7700 V. The G2 voltage in this
embodiment is typically about 400 V. All other gun parameters are as
listed in TABLE I. Alternatively, slots can be formed in only one of the active surfaces of the G4 electrode 350. The depth of the slots must be increased, and the small dimension of each slot must be decreased, from the respective dimensions described immediately above. Additionally, the amount of offset of the outer slots must be increased to obtain performance equivalent to that of the fourth embodiment.
GENERAL CONSIDERATIONS
The novel electron gun of the present invention is to be contrasted to an electron gun of the type described in U.S. Pat. No. 4,764,704, referenced above
. In that patent, a G4 electrode, similar to the G4
electrode 450 of the prefocusing, or second, lens shown in FIG. 17, has
rectangularly-shaped apertures 480 therethrough. Specific dimensions of a
computer model of an embodiment of that prior electron gun are
presented in TABLE II. That embodiment has the electrical configuration
shown in FIG. 2 herein, and is similar in construction to the electron
gun shown in FIG. 4 herein, with similar gun elements being identified
with corresponding numbers, prefixed by the number "4". | TABLE II |
| ______________________________________ |
| inches mm |
| ______________________________________ |
K-G1 spacing 0.003 0.08 Thickness of G1 electrode 444 0.004 0.10 Thickness of G2 electrode 446 0.028 0.71 G1 and G1 aperture diameters 0.025 0.64 G1 to G2 spacing 0.008 0.20 G2 to G3 spacing 0.030 0.76 Thickness of G3 bottom plate 468 0.010 0.25 Diameter of G3 aperture 470, center 0.045 1.14 Diameter of G3 apertures 470, outer 0.052 1.32 Diameter of G3 apertures 478 0.148 3.76 Length of G3 electrode 448 0.200 5.08 G3 to G4 spacing 0.500 1.27 Thickness of G4 electrode 450 0.025 0.64 Dimensions of G4 electrode apertures 480 0.158 V 4.01 V × × 0.172 H 4.37 H G4 to G5 spacing 0.050 1.27 Length of G5 electrode* 452-454 0.830 21.08 Diameter of apertures 482 0.158 4.01 Diameter of aperture 494 (center) 0.160 4.06 Diameter of apertures 494 (outer) 0.180 4.57 Horizontal width of recess 492 0.755 19.18 Vertical height of recess 492 0.326 8.28 Depth of recess 492 0.115 2.29 Aperture-to-aperture spacing K to G5 0.260 6.60 bottom** G5 to G6 spacing 0.050 1.27 Length of G6 electrode 0.150 3.81 Horizontal width of opening 400 0.742 18.85 Maximum height of opening 400 0.295 7.49 Minimum height of opening 400 0.289 7.34 Depth of opening 400 0.135 3.43 Diameter of aperture 404 (center) 0.160 4.06 Diameter of apertures 404 (outer) 0.180 4.57 Aperture-to-aperture spacing G5 top/G6 0.245 6.22 Length of G3 extrusions 479 0.045 1.14 Length of G5 extrusions 483 0.045 1.14 Length of G5 extrusions 495 0.034 0.86 Length of G6 extrusions 405 0.045 1.14 |
| ______________________________________ |
e G3 bottom apertures 470 is increased to 0.2635 inch (6.69
mm) to eliminate any displacement of the outer electron beams with
changes in the focus voltage. In the prior electron gun described in TABLE II, the cathode operates at a drive voltage of about 103.2 V, the G1 electrode is at ground potential, the G2 and G4 are electrically interconnected and operate within the range of 300 V to 1000 V, the G3 and G5 electrodes also are interconnected and operate at about 6600 V, and the G6 electrode operates at an anode potential of about 25 kV. The prefocusing lens, L2, of the prior electron gun, with the rectangular apertures 480 formed through the substantially flat G4 electrode 450, provides a horizontally-elongated electron beam (not shown) into the main focusing lens, L3. A computer simulation of the resultant vertically-elongated beam spot at the center of the screen is graphically shown in FIG. 18. The beam size at 5% peak current density is about 2.30 mm×3.49 mm (H×V) at the previously described operating parameters.
CONCLUSION
The performance of the present prefocusing lens, L2, of embodiments 1 through 4, as measured by the resultant electron beam spot size on the screen, is comparable to that of the prior electron gun described in U.S. Pat. No. 4,764,704, which utilizes a prefocusing lens having rectangularly-shaped apertures in the G4 electrode thereof. A comparison of results is contained in TABLE III.
| TABLE III |
| ______________________________________ |
| Beam Spot Size on Screen EMBODIMENT Horizontal (mm) Vertical (mm) |
| ______________________________________ |
1 2.50 4.20 2 2.26 3.68 3 1.94 3.44 4 1.96 3.49 Prior 2.30 3.49 |
| ______________________________________ |
The
four embodiments of the present electron gun structure provide ease of
manufacturing, because the use of circular apertures throughout the
electron gun reduces the misalignment problems posed by the
rectangularly-shaped G4 apertures of the prior gun. Additionally, the
prior gun requires a slight increase in the G3 aperture-to-aperture
spacing (from 6.60 mm to 6.69 mm) to eliminate the misconvergence of the
outer electron beams with changes in focus voltage. The present
invention achieves comparable performance by controlling either the
horizontal width of the race-track-shaped recesses within the
prefocusing lens, L2, in embodiments 1 and 3, or the slot-to-slot
spacing of the rectangular slots formed within prefocusing lens, L2, in
embodiments 2 and 4. In each of the four embodiments, the
aperture-to-aperture spacing from the cathode 42 to the bottom of the G5
electrode 52 is maintained at a constant value of 6.60 mm, thereby
simplifying the assembly and alignment of the gun components.
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