CRT TUBE SONY TRINITRON A34JBU10X VIEW.
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Trinitron is Sony's brand name for its line of aperture grille based CRTs used in televisions and computer monitors. One of the first truly new television systems to enter the market since the 1950s, the Trinitron was announced in 1966 to wide acclaim for its bright images, about 25% brighter than common shadow mask televisions of the same era. Constant improvement in the basic technology and attention to overall quality allowed Sony to charge a premium for Trinitron devices into the 1990s.
Patent protection on the basic Trinitron design ran out in 1996, and it quickly faced a number of competitors at much lower price points. Sony responded by introducing their flat-screen FD Trinitron designs (WEGA), which maintained their premier position in the market into the early 2000s. However, these designs were surpassed relatively quickly by plasma and LCD designs. Sony removed the last Trinitron televisions from their product catalogs in 2006, and ceased production in early 2008. Video monitors are the only remaining Trinitron products being produced by Sony, at a low production rate, although the basic technology can still be found in downmarket televisions from 3rd parties.
The name Trinitron was derived from trinity, meaning the union of three, and tron from electron tube, after the way that the Trinitron combined the three separate electron guns of other CRT designs into one.
Trinitron
In the autumn of 1966 Ibuka finally gave in, and announced he would personally lead a search for a replacement for Chromatron. Susumu Yoshida was sent to the U.S. to look for potential licenses, and was impressed with the improvements that RCA had made in overall brightness by introducing new rare earth phosphors on the screen. He also saw General Electric's "Porta-color" design, using three guns in a row instead of a triangle, which allowed a greater portion of the screen to be lit. His report was cause for concern in Japan, where it seemed Sony was falling ever-farther behind the U.S. designs. They might be forced to license the shadow mask system if they wanted to remain competitive.[10]Ibuka was not willing to give up entirely, and had his 30 engineers explore a wide variety of approaches to see if they could come up with their own design. At one point Yoshida asked Senri Miyaoka if the in-line gun arrangement used by GE could be replaced by a single tube with three cathodes; this would be more difficult to build, but be lower cost in the long run. Miyaoka built a prototype and was astonished how well it worked, although it had focussing problems.[10] Later that week, on Saturday, Miyaoka was summoned to Ibuka's office while he was attempting to leave work to attend his weekly cello practice. Yoshida had just informed Ibuka about his success, and the two asked Miyaoka if they could really develop the gun into a workable product. Miyaoka, anxious to leave, answered yes, excused himself, and left. That Monday Ibuka announced that Sony would be developing a new color television design, based on Miyaoka's prototype.[11] By February 1967 the focusing problems had been solved, and because there was a single gun, the focusing was achieved with permanent magnets instead of a coil, and required no after manufacturing manual adjustments.
During development, Sony engineer Akio Ohgoshi introduced another modification. GE's system improved on the RCA shadow mask by replacing the small round holes with slightly larger rectangles. Since the guns were in-line, they would shine onto the back of the tube onto three rectangular patches instead of three smaller spots, about doubling the lit area. Ohgoshi proposed removing the mask entirely and replacing it with a series of vertical slots instead, lighting the entire screen. Although this would require the guns to be very carefully aligned with the phosphors on the tube in order to ensure they hit the right colors, with Miyaoka's new tube this appeared possible.[11] In practice this proved easy to build but difficult to place in the tube – the fine wires were mechanically weak and tended to move when the tubes were bumped, resulting in shifting colors on the screen. This problem was solved by running fine tungsten wires across the grille horizontally to keep them in place.
The combination of three-in-one electron gun and the replacement of the shadow mask with the aperture grille resulted in a unique and easily patentable product. Officially introduced by Ikuba in April 1968, the original 12 inch Trinitron had a display quality that easily surpassed any commercial set in terms of brightness, color fidelity, and simplicity of operation. The tube was also flat vertically, a side-effect of the vertical wires in the aperture grille, which gave it a unique and appealing look. It was also all solid state, with the exception of the picture tube itself, which allowed it to be much more compact and cool running than designs like GE's Porta-color.
Ikuba ended the press conference by claiming that 10,000 sets would be available by October, well beyond what engineering had told him was possible. Ikuba cajoled Yoshida to take over the effort of bringing the sets into production, and although Yoshida was furious at being put in charge of a task he felt was impossible, he finally accepted the assignment and successfully met the production goal.[12] The KV-1310 was introduced in limited numbers in Japan in October as promised, and in the U.S. as the KV-1310U the following year.
In spite of Trinitron and Chromatron having no technology in common, the shared single electron gun has led to many erroneous claims that the two are similar, or the same.[13]
Despite the statement above claiming that there were no valves inside Trinitron TV sets, for a brief period in the United Kingdom between 1969 and 1971/72, the KV-1320UB was fitted with 3AT2 valves for the extra high tension. Later on, the KV-1320UB was redesigned internally and externally to become all solid-state. Despite containing vacuum tubes, the first version of the KV-1320UB was promoted as being all solid-state. The later version of this model is identified as having no wooden outer-shell. These early color sets intended for the UK market had a PAL decoder that was different from those invented and licensed by Telefunken of Germany, who invented this color system. The decoder inside the UK-sold Sony color Trinitron sets, from the KV-1300UB to the KV-1330UB had an NTSC decoder adapted for PAL. The decoder used a 64 microsecond delay line to store every other line, but instead of using the delay line to average out the phase of the current line and the "remembered" line (as with "Deluxe PAL"), it simply repeats the same line twice. Any phase errors can then be compensated for by using a Tint control on the front of the set.
The Trinitron design incorporates two unique features: the single-gun three-cathode picture tube, and the vertically aligned aperture grille.
The single-gun consists of a long-necked tube with a single electrode at its base, flaring out into a horizontally-aligned rectangular shape with three vertically-aligned rectangular cathodes inside. Each cathode is fed the amplified signal from one of the decoded RGB signals.
The electrons from the cathodes are all aimed toward a single point at the back of the screen where they hit the aperture grille, a steel sheet with vertical slots cut in it. Due to the slight separation of the cathodes at the back of the tube, the three beams approach the grille at slightly different angles. When they pass through the grille they retain this angle, hitting their individual colored phosphors that are painted in vertical stripes on the inside of the tube. The main purpose of the grille is to ensure the beams are properly registered with the phosphors.
Advantages
In comparison to early shadow mask designs, the Trinitron grille cuts off much less of the signal coming from the electron guns. RCA sets built in the 1950s cut off about 85% of the incoming signal, while the grille cuts off about 25%. Improvements to the shadow mask designs continually narrowed this difference in the two designs, and by the late 1980s the difference in performance, at least theoretically, was eliminated.Another advantage of the aperture grille was that the distance between the wires remained constant vertically across the screen. In the shadow mask design the size of the holes in the mask is defined by the required resolution of the phosphor dots on the screen, which was constant. However, the distance from the guns to the holes changed; for dots near the center of the screen the distance was its shortest, at points in the corners it was at its maximum. To ensure that the guns were focused on the holes, a system known as dynamic convergence had to constantly adjust the focus point as the beam moved across the screen. In the Trinitron design the problem was greatly simplified, requiring changes only for large screen sizes, and only on a line-by-line basis.
For this reason, Trinitron systems are easier to focus than shadow masks, and generally had a sharper image. This was a major selling point of the Trinitron design for much of its history. In the 1990s new computer controlled real-time feedback focusing systems eliminated this advantage, as well as leading to the introduction of "true flat" designs.
Visible Support Wires
Even small changes in the alignment of the grille over the phosphors can cause the coloring to shift. Since the wires are thin, small bumps can cause the wires to shift alignment if they are not held in place. Monitors using this technology have one or more thin tungsten wires running horizontally across the grille to prevent this. Screens 15" and below have one wire located about two thirds of the way down the screen, while monitors greater than 15" have 2 wires at the one-third and two-thirds positions. These wires are less apparent or completely obscured on standard definition sets due to larger scan lines of the video being displayed. On computer monitors, where the lines are much closer together, the wires are often visible. This is a minor drawback of the Trinitron standard which is not shared by shadow mask CRTs.GRID STRUCTURE FOR SONY TRINTRON COLOR PICTURE TUBES:
A support for the grid structure of a cathode-ray tube in which the support is stressed to compensate for any expansion of the grid wires due to heating, the support having a pair of opposed parallel arms with the grid wires attached to and extending transversely between the arms, and a pair of braces supporting the arms at the Bessel points, the braces being stressed in a direction substantially parallel to the direction of the grid wires so that as the grid wires expand due to heat the braces will expand a
corresponding amount to maintain a substantially constant tension of the grid wires.
1. A support for the grid elements of a cathode ray tube comprising a pair of opposed parallel arms, a plurality of said grid elements affixed to said arms and extending transversely therebetween, a pair of generally C-shaped braces supporting said arms and attached thereto substantially at the Bessel points and formed to lie in surfaces substantially parallel to the surface defined by said grid elements, said braces being stressed a sufficient amount in a direction substantially parallel to the direction of said grid elements whereby as said grid elements expand said braces expand a corresponding amount to maintain the tension on all of said grid elements substantially uniform.
2. A support for a grid structure of a cathode ray tube comprising a pair of opposed parallel arms, a plurality of flexible grid wires affixed to said arms and extending therebetween, a pair of mechanically resilient braces supporting said arms and attached thereto at locations inwardly spaced from the ends of said arms substantially at the Bessel points, and said braces being stressed in a direction substantially parallel to the direction of said flexible grid wires to apply tension stress to said grid wires whereby as said flexible grid wires expand due to heat generated during the operation of the tube, said braces expand due to their resiliency and their being stressed a corresponding amount to maintain the tension on all of said flexible grid wires substantially uniform.
3. A support in accordance with claim 2 wherein said braces are substantially C-shaped.
4. A support in accordance with claim 2 wherein a damping rod extends over said flexible members to substantially eliminate mechanical vibration of said flexible members.
5. A support in accordance with claim 4 wherein said damping rod is stretched between said braces.
6. A support in accordance with claim 5 wherein said damping rod is flexible and is attached substantially to the center of said braces.
7. A support according to claim 6 wherein the damping rod is inclined relative to flexible grid wires.
8. A support in accordance with claim 6 wherein said damping rod resiliently presses against said flexible members.
9. A support according to claim 8 wherein said damping rod has a diameter of between 30 and 50 microns.
Description:
This invention relates to a novel grid structure for color picture tubes, and more particularly to a grid structure which is of particular utility when employed in color picture tubes.
As is well known in the prior art, color cathode ray tubes employ, for electron beam postdeflection and focusing, a grid structure such that a plurality of parallel grid wires are stretched across a parallelogramic frame between a pair of opposed sides. Such a grid structure is produced in the following manner. A plurality of parallel grid wires are stretched on a master frame under predetermined taut conditions and a grid frame is put on the grid wires from inside of the master frame.
The grid wires are then fixed to a pair of opposed supports of the grid frame and are thereafter severed along the margins of the grid frame. In this case, the grid frame is prestressed inwardly by a turnbuckle to apply a maximum tension to the grid wires secured to the central portion of the opposed supports of the grid frame and a smaller tension to those fixed to end portions of the supports, ensuring that all the grid wires are subjected to substantially uniform tension by the restoring force of the prestressed grid frame after disassembling it from the master frame.
Such a grid structure may be regarded as one where a plurality of grid wires are stretched at substantially uniform tension on a parallelogramic frame prestressed in a manner to be displaced the most at the center of the frame. When a predetermined positive potential is applied to such a grid structure and electron beams are emitted from the electron gun of a cathode ray tube toward the fluorescent screen thereof, electron beams of several to 10-odd percent strike against the grid wires and are discharged therethrough to thereby heat the grid wires. As a result of this, the temperature of the grid wires is raised several-10 degrees and the wires expand. An examination of the expanded grid wires shows that since the displacement of the frame is greatest at the center thereof, elongation of the grid wires of that portion due to thermal expansion is cancelled by the restoring force of the prestressed frame as if the grid wires had not been elongated. Accordingly, the grid wires are still subjected to substantially the same original tension, and hence do not sag. The elongation of the grid wires lying on both sides of the central grid wires cannot be absorbed with the displacement of the frame at those particular portions, since the displacement is basically small. Consequently, when the elongation of the grid wires exceeds the displacement of the frame, the grid wires are likely to sag. Even if the grid wires do not sag, they are not pulled at a predetermined tension and are readily vibrated at great amplitude to lower the picture quality of the reproduced picture when subjected to accidental small shocks.
The above can easily be understood from the fact that when all the grid wires have substantially the same length 1, their elongation resulting from thermal expansion is 1 and the amount of restoration of the distorted frame is 1 at the center thereof, the amount of restoration of the frame on both sides of the center thereof is smaller than that at the central portion.
This defect is remarkable especially in the grid structure of a color cathode ray tube of the type where a plurality of ribbonlike grid elements are stretched in parallel with phosphor strips and function as a kind of shadow mask. In this type of structure three electron beams are impinged upon three different color emissive phosphor strips through slits defined between adjacent grid elements.
A grid structure such as described above has been proposed in an attempt to increase the electron beam transmission factor of the so-called shadow mask in which a plate having bored therethrough a plurality of apertures is used as a mask for the electron beam. In such a grid structure, however, the grid elements are secured only at both ends to the frame, so that the grid elements heated by electron beams striking thereon radiate heat mainly through the ends fixed to the frame. Further, the transmission factor of the electron beam through such a grid is 10-odd to 20-odd percent and the temperature of the grid elements rises up to 100° to 130° C. Consequently this type of grid structure encounters the same problems as in the Chromatron (Registered Trademark) type color cathode ray tube.
In addition to the sag of the grid elements, nonuniformity in the tension applied to the grid elements raises another problem in such a grid structure as mentioned above. Even slight nonuniformity in the tension causes the grid elements to twist and the space between adjacent grid elements becomes wider in a direction normal to the incident direction of the electron beam, although the pitch of the grid elements remains unchanged. As a result of this, there is the possibility that the electron beam strikes on a phosphor strip other than a predetermined one, especially a phosphor strip adjacent the predetermined one to cause unnecessary color emission. Therefore, the nonuniformity in the tension applied to the grid elements should be avoided.
Accordingly, one object of this invention is to provide a grid structure which is adapted such that the grid elements are always subjected to a predetermined tension and do not sag during operation, though heated by electron beams.
Another object of this invention is to provide a grid structure for shadow-mask type color cathode ray tubes in which the grid elements heated by electron beams do no sag during operation to thereby ensure uniformity in the spacing between adjacent grid elements and hence prevent unnecessary bombardment of the phosphor strips by the electron beam.
Still another object of this invention is to provide a grid structure which is constructed such that the grid elements are protected from shocks applied from the outside and caused by electron beam bombardment.
Other objects, features and advantages of this invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIGS. 1 and 2 are schematic diagrams for explaining the present invention;
FIG. 3 is a plan view showing one example of a grid structure for color cathode ray tubes produced according to this invention;
FIG. 4 is a side view of the grid structure illustrated in FIG. 3;
FIG. 5 is a plan view illustrating another example of the grid structure of this invention;
FIG. 6 is a schematic diagram showing the manner in which the grid elements are mounted on a grid frame;
FIG. 7 is a plan view showing another modified form of the present invention;
FIG. 8 is a cross-sectional view taken along the line A--A in FIG. 7;
FIG. 9 illustrates in perspective the plate supports employed in the example of FIG. 7;
FIG. 10 similarly shows in perspective a resilient support;
FIG. 11 is a plan view showing still another modification of the present invention;
FIG. 12 is a side view of the grid structure depicted in FIG. 11; and
FIG. 13 is a perspective view of the grid structure shown in FIG. 11.
FIG. 1 is a schematic diagram showing displacement (indicated by broken lines) of a bar 1 of a length L having two fulcra 2A and 2B when subjected to a uniformly distributed load 3 acting substantially perpendicular to the bar. In order to minimize the displacement of the bar 1, the fulcra 2A and 2B are located at such positions that the displacement δ 1 of both end portions of the bar 1 is equal to the displacement δ 2 of the central portion. Such positions of the fulcra are referred to as the Bessel points, and when the distance from the end of the bar 1 to the fulcrum 2A or 2B is taken as b, b/L=0.223. The length L of the bar does not indicate the actual length but a range over which the load 3 is applied.
If a pair of such bars are arranged in parallel relation as a pair of opposed frame members of a grid frame, a plurality of grid wires or elements stretched between the frame members at substantially uniform tension are subjected to the aforementioned uniformly distributed load 3. In other words, where a pair of bars 1 and 1' (not shown) of a length L constituting two frame members are arranged in parallel relation and a plurality of parallel grid wires or elements are stretched between the bars substantially at right angles thereto under approximately uniformly tensioned conditions and fulcra 2A, 2B and 2A', 2B' (not shown) respectively supporting the bars are located at positions satisfying the aforementioned requirement b/L=0.223, the bars are deformed to be bent at both ends and between the fulcra by the load caused by the tension of the grid wires or elements in a direction of the tension but the displacement ratio, that is, the displacement per unit load is at minimum. Consequently, the displacement ratio of the frame of this invention (indicated by the broken line B in FIG. 2) is far smaller than that of the conventional grid frame (indicated by the full line A in FIG. 2) of the type where the fulcra are located at both ends of two bars constituting the frame members, and accordingly the grid frame of this invention virtually deformed as compared with the deformation of the conventional grid frame. If the rigidity of the bar 1 is increased up to maximum, the deformation of the frame can be neglected.
The tension of the grid wires or elements stretched between the two bars 1 and 1' (not shown) corresponding to the load 3 shown in FIG. 1 is produced by pressing the two bars with a resilient support (not shown) in a direction opposite to the load 3 in a manner to force away the two fulcra 2A and 2A' (2A' not shown) and 2B and (2B' not shown) from each other.
Referring now to FIGS. 3 to 10, the construction of the grid structure of this invention will be described in detail by way of example.
As clearly shown in the figures, the grid structure of this invention comprises a frame of a predetermined configuration which consists of bar supports 4 and 4' corresponding to the aforementioned bars 1 and 1' and a pair of substantially C-shaped resilient supports 5 and 5' supporting the bar supports 4 and 4' at or in the vicinity of the Bessel points B A , B B and B A ', B B ' thereof, and a plurality of ribbon-shaped grid elements of, for example, stainless steel are stretched between the bar supports 4 and 4' at a predetermined pitch under predetermined distribution of tension. Reference numeral 7 indicates generally the grid structure.
The bar supports 4 and 4' may be formed of a metal such as iron, stainless steel or the like and in the illustrated example the bar supports 4 and 4' are square in cross section and are bent to conform to the panel to which the grid structure will be attached. The resilient supports 5 and 5' may be formed of a metal such as iron, stainless steel or the like and are substantially C-shaped so as not to disturb the irradiation of the phosphor screen by the electron beam emitted from the electron gun of a cathode ray tube. It is a matter of course that the supports 5 and 5' may be configured at will so long as they do not disturb the electron beam directed to the fluorescent screen of the cathode ray tube. The grid elements 6 may also be formed of a metal such as iron, stainless steel or the like.
With such an arrangement, since the pair of bar supports 4 and 4' constituting one portion of the frame are jointed to the resilient supports 5 and 5' as a unitary structure at or in the vicinity of the Bessel joints B A , B B and B A ', and B B ', the bar supports 4 and 4' may be regarded as a rigid body with respect to the load caused by the tension of the grid elements. Accordingly, when the grid elements 6 that are stretched between the bar supports 4 and 4' uniformly at a predetermined tension expand by heat resulting from the electron beam bombardment thereon, the bar supports 4 and 4' are pulled outwards by the resilient supports 5 and 5' in a parallel relationship by a distance corresponding to the length of the grid elements which have been extended by the thermal expansion. Consequently, although the absolute value of the tension is different from the initial one, the initial distribution of the tension over the entire grid elements remains unchanged.
The foregoing description has been made in connection with a grid structure in which the grid elements are of substantially the same length at the both end portions and central portion of the bar supports and hence they are expanded substantially equally due to thermal expansion. According to our experiments on a grid structure in which the bar supports of square cross section were made of stainless steel and had a size of about 10 mm. × 10 mm. × 240 mm. and 400 grid elements 0.5 mm. wide, 0.1 mm. thick and about 180 mm. long (the length of the grid elements on the end portions of the bar supports were 175 mm. and that of the elements of the central portion: 185 mm.) were stretched between the bar supports at a tension of about 350 g. for each grid element, it has been ascertained that although the grid elements were heated by electron beams and extended due to thermal expansion during operation, accidents such as vibration of the grid elements due to nonuniformity of the tension or color contamination due to irregularity of the space between adjacent grid elements were not caused. Further, it has been found that the deviation from the initial distribution of the tension of the grid elements caused by the thermal expansion thereof resulting from the collision of the electron beam therewith were compensated for by the stretch or shrinkage of the grid elements or slight restoring force of the bar supports.
In addition, it has also been found that if the deviation of the length of the grid elements is in a range of ±20 percent relative to its mean value, the length of the grid elements extended by the thermal expansion is extremely short and the initial distribution of the tension of the grid elements is maintained during operation by the stretch and shrinkage of the grid elements or by compensation due to the restoring force of the bar supports.
In the prior art a very complicated device is required for stretching grid elements on a grid frame, but this can be readily achieved by the following method. As shown in FIG. 5, for example, a thin stainless steel plate 8 of a predetermined size is first prepared and is subjected to etching to remove selected areas, thus providing metal strips 8a arranged at a predetermined pitch. At the same time, slits 8b are formed for a predetermined number of metal strips 8a (every three metal strips in the figure) in the plate 8 at both marginal portions thereof. In a similar manner, slits 8c are formed in the plate 8 on both sides of the metal strips 8a. Portions 8d separated by the slits 8b are then respectively held by chucks 9A and 9B as shown in FIG. 6. In this case, the number of the chucks 9A and 9B corresponds to that of the portions 8d. The chucks 9B are supplied with a moderate tension in accordance with the thickness and the quality of material of the portions 8d, but such tension may be applied to both of the chucks 9A and 9B. Substantially the same tension is applied to the metal strips by means of, for example, a coiled spring 10 as shown in the figure. Under such taut conditions, a pair of bar supports 11 and 11' are disposed under the plate 8 at predetermined positions and the plate 8 is welded to the bar supports. In this case, the bar supports 11 and 11' are supported by a pair of resilient supports at or in the vicinity of their Bessel points, though not shown, and the resilient supports are slightly bent inwardly so as to apply a predetermined tension to the metal strips when the portions 8d are released from the chucks 9A and 9B. It is preferred that the force for bending the two resilient supports be equal to the tension (the total tension of all the metal strips) applied to the metal strips 8a by the spring 10. In such a case when the chucks 9A and 9B are removed, the tension of the metal strips 8a due to the spring 10 is applied to the strips 8a by the resilient supports, so that the tension of the metal strips 8a remains unchanged before and after the removal of the chucks.
Subsequent to the welding of the plate 8, the portions 8d projecting outside of the bar supports 11 and 11' are cut off and both end portions of the slits 8c are also cut off. The slits 8c are provided for facilitating the cutting of the plate 8, and hence they are not always necessary. In the manner described above, the metal strips 8a can readily be stretched between the bar supports 11 and 11' with predetermined distribution of the tension. In this case, the metal strips 8a are coupled together at both ends. It is possible, of course, that the end portions of the metal strips 8a are welded to the bar supports 11 and 11'. The slits 8b are provided for preventing the plate 8 from becoming creased when applying a tension to the edges of the plate 8 and for ensuring uniformity of the tension applied to each metal strip 8a. In the absence of the slits 8b, it is extremely difficult to apply the tension to the metal strips 8a with the predetermined distribution.
While the metal strips 8a are subjected to substantially equal tension by the chucks 9A and 9B in the above example, the distribution of the tension may be changed as desired in accordance with the shapes of the bar supports and the resilient supports and the condition of the resilient supports welded to the bar supports in the vicinity of the Bessel points thereof to ensure uniformity of the tension applied to the metal strips by the resilient supports.
The electron beam transmission factor depends upon the width of the metal strips or the diameter and the pitch of the metal wires, which are usually selected to render the electron beam transmission factor approximately 20 percent in view of the relationship to the width of each phosphor strip of the fluorescent screen of cathode ray tubes.
I
n FIGS. 7 and 8 there is illustrated another example of this invention, in which reference numeral 15 designates generally a grid structure. A pair of plate supports 12 and 12' are supported by a framelike resilient support 13 at or in the vicinity of their Bessel points to provide a frame of a predetermined configuration, and grid elements 14 in the form of, for example, metal strips are stretched between the pair of platelike supports 12 and 12'.
The plate supports 12 and 12' may be formed of a metal such as iron, stainless steel or the like and, as shown in FIG. 9, one marginal edge of each plate support is curved so as to conform to the surface of the panel of a cathode ray tube with which the finished grid structure will be assembled. The resilient support 13 may also be formed of a metal such as iron, stainless steel or the like and this support 13 has projections 13a at places substantially corresponding to the Bessel points of the plate supports 12 and 12' as illustrated in FIG. 10. Further, the support 13 has L-shaped plate support-retaining members 13b formed integrally at places corresponding to the projections 13a.
The pair of plate supports 12 and 12' are mounted on the retaining members 13b of the resilient support 13 in such a manner that the projections 13a of the support 13 engage the plate supports 12 and 12' at or in the vicinity of their Bessel points, and the plate supports and the resilient supports are held together by predetermined jigs in a manner to produce a predetermined pressure at or in the vicinity of the Bessel points of the plate supports 12 and 12' by the projections 13a of the resilient support 13. Then, the grid elements 14 are stretched between the pair of plate supports 12 and 12' at a predetermined distribution of tension.
With such an arrangement, the pair of plate supports 12 and 12' are supported by the projections 13a of the resilient support 13 at or in the vicinity of their Bessel points, so that the equilibrium of the tension is very stable after the grid elements 14 have once been stretched at the predetermined distribution of the tension. Accordingly, the equilibrium of the tension is not lost by a slight variation in the tension after stretching the grid elements 14 and the grid frame is not deformed. Further, the equilibrium of the tension is difficult to loose by thermal expansion of the frame or the grid elements 14 due to a temperature rise during operation, and even if the equilibrium of the tension is lost, the tension promptly balances, so that deformation of the frame is very slight. Consequently, the position of the grid elements 14 is not shifted and the electron beam always impinges upon the fluorescent screen accurately at a predetermined location, so that phenomenon such as color contamination is not caused thereby ensuring reproduction of a clear picture. In addition, since the grid structure described above is simple in construction, its fabrication is easy and the yield is greatly increased. Even if the grid elements 14 are stretched between the plate supports 12 and 12' at substantially uniform tension, the deformation of the frame is very slight as indicated by the dotted line B in FIG. 2. Accordingly, there is no possibility that the position of the grid elements 14 is shifted by a slight deformation of the frame and by thermal expansion of the grid elements or the frame due to a temperature rise. That is, even if the grid elements 14 are stretched at uniform tension, the aforementioned many advantages can still be obtained.
The assembling of the grid structure with the panel of a cathode ray tube can readily be achieved by the same means as mentioned previously or by other known means, and accordingly no description will be given. Further, it is needless to say that the aforementioned method can be used for stretching the grid elements, and the metal wires may be stretched as the grid elements 14 at a predetermined pitch in place of the metal strips.
The foregoing description has been made in connection with only several examples of this invention, and the material, shape and the like of the bar supports, plate supports, grid elements, resilient supports and so on can be suitably selected at will, if necessary. However, the bar supports and the plate supports are desired to be formed of a conductive material so as to establish electric fields between the supports and the grid elements. Further, these supports are not restricted to the bar and plate supports.
When the grid structure is used in color picture tubes the grid elements are caused to vibrate by mechanical vibration due to external shocks or electron beam bombardment. In FIGS. 11 to 13 there is shown still another example of this invention in which the grid structure is designed to prevent such unwanted vibration of the grid elements.
In the figures reference numerals 21A and 21B indicate a pair of bar supports, and 22A and 22B represent substantially C-shaped resilient supports supporting the bar supports 21A and 21B at or in the vicinity of their Bessel points to constitute a grid frame generally designated by 23. Reference numeral 24 identifies grid elements such as ribbonlike metal strips which are stretched between the pair of bar supports 21A and 21B at a predetermined tension distribution and pitch. These members are identical with those described in the foregoing examples.
In the present example, a damping rod formed of, for example, a metal wire is provided in contact with the grid elements 24.
For example, resilient pieces 26A and 26B are planted on the outside of the resilient supports 22A and 22B substantially at the center thereof, and the damping rod 25 is stretched between the resilient pieces 26A and 26B. In this case the damping rod 25 is stretched in a direction of the lines of the raster (in the electron beam-scanning direction) and it is preferred that the damping rod 25 be stretched obliquely in a range of 30° to 45° relative to the electron beam scanning direction.
With such an arrangement, the grid elements 24 are resiliently pressed by the damping rod 25, and hence are not likely to be caused to vibrate by mechanical shocks from the outside and electron beam bombardment. Even if vibration occurs, it is immediately suppressed by the damping rod 25, thus preventing a bad influence by the vibration of the grid elements. The provision of the damping rod 25 avoids not only the vibration of the grid elements but also irregularity in the spacing thereof which results from twisting of the grid elements. Namely, when the grid elements 24 are heated by collision of the electron beam therewith and are to be twisted due to thermal expansion, the damping rod 25 presses the grid elements 24 to prevent twisting of the grid elements to hold the space between adjacent grid elements as predetermined, ensuring that the electron beam impinges only on a predetermined phosphor strip. Further, the provision of the damping rod 25 is only to stretch it in contact with the surfaces of the grid elements and hence can be achieved with great ease. The damping rod 25 may be a mechanically strong metal wire of, for example, tungsten, stainless steel, inconel or the like. The use of such a mechanically strong wire avoids breakage of the damping rod or insufficient pressing of the grid elements as with conventional damping rods of glass fiber in grid structures for the Chromatron (Registered Trademark) type picture tubes.
The damping rod 25 formed of the above-mentioned metals or other ones is preferred in terms of mechanical strength and is free from secondary electron beam emission by the electron beam. It is preferred that the diameter of the damping rod 25 to 30 to 50 microns. With a diameter of, for example, 100 microns, the mechanical strength of the damping rod increases but the reproduced picture is adversely affected by the damping rod. With a diameter of less than 30 microns, the mechanical strength of the rod 25 decreases and its pressing effect of the grid elements becomes weak. With a smaller diameter damping rod, the bad influence on the reproduced picture is decreased correspondingly, but the influence of a damping rod 50 microns in diameter on the reproduced picture is hardly noticeable. According to our experiments, a tungsten wire of a diameter from 30 to 50 microns yields good results. In the foregoing example, the damping rod 25 is stretched between the two resilient pieces 26A and 26B but either or both of them may be dispensed with. The shape and position of the resilient pieces are not limited to those in the above example. For example, it is possible that resilient wires are stretched on the frame on both sides of the grid elements instead of the resilient pieces and the damping rod is stretched between the resilient wires. Further, the damping rod 25 may be attached to the grid elements 25.
It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of this invention.
As is well known in the prior art, color cathode ray tubes employ, for electron beam postdeflection and focusing, a grid structure such that a plurality of parallel grid wires are stretched across a parallelogramic frame between a pair of opposed sides. Such a grid structure is produced in the following manner. A plurality of parallel grid wires are stretched on a master frame under predetermined taut conditions and a grid frame is put on the grid wires from inside of the master frame.
The grid wires are then fixed to a pair of opposed supports of the grid frame and are thereafter severed along the margins of the grid frame. In this case, the grid frame is prestressed inwardly by a turnbuckle to apply a maximum tension to the grid wires secured to the central portion of the opposed supports of the grid frame and a smaller tension to those fixed to end portions of the supports, ensuring that all the grid wires are subjected to substantially uniform tension by the restoring force of the prestressed grid frame after disassembling it from the master frame.
Such a grid structure may be regarded as one where a plurality of grid wires are stretched at substantially uniform tension on a parallelogramic frame prestressed in a manner to be displaced the most at the center of the frame. When a predetermined positive potential is applied to such a grid structure and electron beams are emitted from the electron gun of a cathode ray tube toward the fluorescent screen thereof, electron beams of several to 10-odd percent strike against the grid wires and are discharged therethrough to thereby heat the grid wires. As a result of this, the temperature of the grid wires is raised several-10 degrees and the wires expand. An examination of the expanded grid wires shows that since the displacement of the frame is greatest at the center thereof, elongation of the grid wires of that portion due to thermal expansion is cancelled by the restoring force of the prestressed frame as if the grid wires had not been elongated. Accordingly, the grid wires are still subjected to substantially the same original tension, and hence do not sag. The elongation of the grid wires lying on both sides of the central grid wires cannot be absorbed with the displacement of the frame at those particular portions, since the displacement is basically small. Consequently, when the elongation of the grid wires exceeds the displacement of the frame, the grid wires are likely to sag. Even if the grid wires do not sag, they are not pulled at a predetermined tension and are readily vibrated at great amplitude to lower the picture quality of the reproduced picture when subjected to accidental small shocks.
The above can easily be understood from the fact that when all the grid wires have substantially the same length 1, their elongation resulting from thermal expansion is 1 and the amount of restoration of the distorted frame is 1 at the center thereof, the amount of restoration of the frame on both sides of the center thereof is smaller than that at the central portion.
This defect is remarkable especially in the grid structure of a color cathode ray tube of the type where a plurality of ribbonlike grid elements are stretched in parallel with phosphor strips and function as a kind of shadow mask. In this type of structure three electron beams are impinged upon three different color emissive phosphor strips through slits defined between adjacent grid elements.
A grid structure such as described above has been proposed in an attempt to increase the electron beam transmission factor of the so-called shadow mask in which a plate having bored therethrough a plurality of apertures is used as a mask for the electron beam. In such a grid structure, however, the grid elements are secured only at both ends to the frame, so that the grid elements heated by electron beams striking thereon radiate heat mainly through the ends fixed to the frame. Further, the transmission factor of the electron beam through such a grid is 10-odd to 20-odd percent and the temperature of the grid elements rises up to 100° to 130° C. Consequently this type of grid structure encounters the same problems as in the Chromatron (Registered Trademark) type color cathode ray tube.
In addition to the sag of the grid elements, nonuniformity in the tension applied to the grid elements raises another problem in such a grid structure as mentioned above. Even slight nonuniformity in the tension causes the grid elements to twist and the space between adjacent grid elements becomes wider in a direction normal to the incident direction of the electron beam, although the pitch of the grid elements remains unchanged. As a result of this, there is the possibility that the electron beam strikes on a phosphor strip other than a predetermined one, especially a phosphor strip adjacent the predetermined one to cause unnecessary color emission. Therefore, the nonuniformity in the tension applied to the grid elements should be avoided.
Accordingly, one object of this invention is to provide a grid structure which is adapted such that the grid elements are always subjected to a predetermined tension and do not sag during operation, though heated by electron beams.
Another object of this invention is to provide a grid structure for shadow-mask type color cathode ray tubes in which the grid elements heated by electron beams do no sag during operation to thereby ensure uniformity in the spacing between adjacent grid elements and hence prevent unnecessary bombardment of the phosphor strips by the electron beam.
Still another object of this invention is to provide a grid structure which is constructed such that the grid elements are protected from shocks applied from the outside and caused by electron beam bombardment.
Other objects, features and advantages of this invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIGS. 1 and 2 are schematic diagrams for explaining the present invention;
FIG. 3 is a plan view showing one example of a grid structure for color cathode ray tubes produced according to this invention;
FIG. 4 is a side view of the grid structure illustrated in FIG. 3;
FIG. 5 is a plan view illustrating another example of the grid structure of this invention;
FIG. 6 is a schematic diagram showing the manner in which the grid elements are mounted on a grid frame;
FIG. 7 is a plan view showing another modified form of the present invention;
FIG. 8 is a cross-sectional view taken along the line A--A in FIG. 7;
FIG. 9 illustrates in perspective the plate supports employed in the example of FIG. 7;
FIG. 10 similarly shows in perspective a resilient support;
FIG. 11 is a plan view showing still another modification of the present invention;
FIG. 12 is a side view of the grid structure depicted in FIG. 11; and
FIG. 13 is a perspective view of the grid structure shown in FIG. 11.
FIG. 1 is a schematic diagram showing displacement (indicated by broken lines) of a bar 1 of a length L having two fulcra 2A and 2B when subjected to a uniformly distributed load 3 acting substantially perpendicular to the bar. In order to minimize the displacement of the bar 1, the fulcra 2A and 2B are located at such positions that the displacement δ 1 of both end portions of the bar 1 is equal to the displacement δ 2 of the central portion. Such positions of the fulcra are referred to as the Bessel points, and when the distance from the end of the bar 1 to the fulcrum 2A or 2B is taken as b, b/L=0.223. The length L of the bar does not indicate the actual length but a range over which the load 3 is applied.
If a pair of such bars are arranged in parallel relation as a pair of opposed frame members of a grid frame, a plurality of grid wires or elements stretched between the frame members at substantially uniform tension are subjected to the aforementioned uniformly distributed load 3. In other words, where a pair of bars 1 and 1' (not shown) of a length L constituting two frame members are arranged in parallel relation and a plurality of parallel grid wires or elements are stretched between the bars substantially at right angles thereto under approximately uniformly tensioned conditions and fulcra 2A, 2B and 2A', 2B' (not shown) respectively supporting the bars are located at positions satisfying the aforementioned requirement b/L=0.223, the bars are deformed to be bent at both ends and between the fulcra by the load caused by the tension of the grid wires or elements in a direction of the tension but the displacement ratio, that is, the displacement per unit load is at minimum. Consequently, the displacement ratio of the frame of this invention (indicated by the broken line B in FIG. 2) is far smaller than that of the conventional grid frame (indicated by the full line A in FIG. 2) of the type where the fulcra are located at both ends of two bars constituting the frame members, and accordingly the grid frame of this invention virtually deformed as compared with the deformation of the conventional grid frame. If the rigidity of the bar 1 is increased up to maximum, the deformation of the frame can be neglected.
The tension of the grid wires or elements stretched between the two bars 1 and 1' (not shown) corresponding to the load 3 shown in FIG. 1 is produced by pressing the two bars with a resilient support (not shown) in a direction opposite to the load 3 in a manner to force away the two fulcra 2A and 2A' (2A' not shown) and 2B and (2B' not shown) from each other.
Referring now to FIGS. 3 to 10, the construction of the grid structure of this invention will be described in detail by way of example.
As clearly shown in the figures, the grid structure of this invention comprises a frame of a predetermined configuration which consists of bar supports 4 and 4' corresponding to the aforementioned bars 1 and 1' and a pair of substantially C-shaped resilient supports 5 and 5' supporting the bar supports 4 and 4' at or in the vicinity of the Bessel points B A , B B and B A ', B B ' thereof, and a plurality of ribbon-shaped grid elements of, for example, stainless steel are stretched between the bar supports 4 and 4' at a predetermined pitch under predetermined distribution of tension. Reference numeral 7 indicates generally the grid structure.
The bar supports 4 and 4' may be formed of a metal such as iron, stainless steel or the like and in the illustrated example the bar supports 4 and 4' are square in cross section and are bent to conform to the panel to which the grid structure will be attached. The resilient supports 5 and 5' may be formed of a metal such as iron, stainless steel or the like and are substantially C-shaped so as not to disturb the irradiation of the phosphor screen by the electron beam emitted from the electron gun of a cathode ray tube. It is a matter of course that the supports 5 and 5' may be configured at will so long as they do not disturb the electron beam directed to the fluorescent screen of the cathode ray tube. The grid elements 6 may also be formed of a metal such as iron, stainless steel or the like.
With such an arrangement, since the pair of bar supports 4 and 4' constituting one portion of the frame are jointed to the resilient supports 5 and 5' as a unitary structure at or in the vicinity of the Bessel joints B A , B B and B A ', and B B ', the bar supports 4 and 4' may be regarded as a rigid body with respect to the load caused by the tension of the grid elements. Accordingly, when the grid elements 6 that are stretched between the bar supports 4 and 4' uniformly at a predetermined tension expand by heat resulting from the electron beam bombardment thereon, the bar supports 4 and 4' are pulled outwards by the resilient supports 5 and 5' in a parallel relationship by a distance corresponding to the length of the grid elements which have been extended by the thermal expansion. Consequently, although the absolute value of the tension is different from the initial one, the initial distribution of the tension over the entire grid elements remains unchanged.
The foregoing description has been made in connection with a grid structure in which the grid elements are of substantially the same length at the both end portions and central portion of the bar supports and hence they are expanded substantially equally due to thermal expansion. According to our experiments on a grid structure in which the bar supports of square cross section were made of stainless steel and had a size of about 10 mm. × 10 mm. × 240 mm. and 400 grid elements 0.5 mm. wide, 0.1 mm. thick and about 180 mm. long (the length of the grid elements on the end portions of the bar supports were 175 mm. and that of the elements of the central portion: 185 mm.) were stretched between the bar supports at a tension of about 350 g. for each grid element, it has been ascertained that although the grid elements were heated by electron beams and extended due to thermal expansion during operation, accidents such as vibration of the grid elements due to nonuniformity of the tension or color contamination due to irregularity of the space between adjacent grid elements were not caused. Further, it has been found that the deviation from the initial distribution of the tension of the grid elements caused by the thermal expansion thereof resulting from the collision of the electron beam therewith were compensated for by the stretch or shrinkage of the grid elements or slight restoring force of the bar supports.
In addition, it has also been found that if the deviation of the length of the grid elements is in a range of ±20 percent relative to its mean value, the length of the grid elements extended by the thermal expansion is extremely short and the initial distribution of the tension of the grid elements is maintained during operation by the stretch and shrinkage of the grid elements or by compensation due to the restoring force of the bar supports.
In the prior art a very complicated device is required for stretching grid elements on a grid frame, but this can be readily achieved by the following method. As shown in FIG. 5, for example, a thin stainless steel plate 8 of a predetermined size is first prepared and is subjected to etching to remove selected areas, thus providing metal strips 8a arranged at a predetermined pitch. At the same time, slits 8b are formed for a predetermined number of metal strips 8a (every three metal strips in the figure) in the plate 8 at both marginal portions thereof. In a similar manner, slits 8c are formed in the plate 8 on both sides of the metal strips 8a. Portions 8d separated by the slits 8b are then respectively held by chucks 9A and 9B as shown in FIG. 6. In this case, the number of the chucks 9A and 9B corresponds to that of the portions 8d. The chucks 9B are supplied with a moderate tension in accordance with the thickness and the quality of material of the portions 8d, but such tension may be applied to both of the chucks 9A and 9B. Substantially the same tension is applied to the metal strips by means of, for example, a coiled spring 10 as shown in the figure. Under such taut conditions, a pair of bar supports 11 and 11' are disposed under the plate 8 at predetermined positions and the plate 8 is welded to the bar supports. In this case, the bar supports 11 and 11' are supported by a pair of resilient supports at or in the vicinity of their Bessel points, though not shown, and the resilient supports are slightly bent inwardly so as to apply a predetermined tension to the metal strips when the portions 8d are released from the chucks 9A and 9B. It is preferred that the force for bending the two resilient supports be equal to the tension (the total tension of all the metal strips) applied to the metal strips 8a by the spring 10. In such a case when the chucks 9A and 9B are removed, the tension of the metal strips 8a due to the spring 10 is applied to the strips 8a by the resilient supports, so that the tension of the metal strips 8a remains unchanged before and after the removal of the chucks.
Subsequent to the welding of the plate 8, the portions 8d projecting outside of the bar supports 11 and 11' are cut off and both end portions of the slits 8c are also cut off. The slits 8c are provided for facilitating the cutting of the plate 8, and hence they are not always necessary. In the manner described above, the metal strips 8a can readily be stretched between the bar supports 11 and 11' with predetermined distribution of the tension. In this case, the metal strips 8a are coupled together at both ends. It is possible, of course, that the end portions of the metal strips 8a are welded to the bar supports 11 and 11'. The slits 8b are provided for preventing the plate 8 from becoming creased when applying a tension to the edges of the plate 8 and for ensuring uniformity of the tension applied to each metal strip 8a. In the absence of the slits 8b, it is extremely difficult to apply the tension to the metal strips 8a with the predetermined distribution.
While the metal strips 8a are subjected to substantially equal tension by the chucks 9A and 9B in the above example, the distribution of the tension may be changed as desired in accordance with the shapes of the bar supports and the resilient supports and the condition of the resilient supports welded to the bar supports in the vicinity of the Bessel points thereof to ensure uniformity of the tension applied to the metal strips by the resilient supports.
The electron beam transmission factor depends upon the width of the metal strips or the diameter and the pitch of the metal wires, which are usually selected to render the electron beam transmission factor approximately 20 percent in view of the relationship to the width of each phosphor strip of the fluorescent screen of cathode ray tubes.
I
n FIGS. 7 and 8 there is illustrated another example of this invention, in which reference numeral 15 designates generally a grid structure. A pair of plate supports 12 and 12' are supported by a framelike resilient support 13 at or in the vicinity of their Bessel points to provide a frame of a predetermined configuration, and grid elements 14 in the form of, for example, metal strips are stretched between the pair of platelike supports 12 and 12'.
The plate supports 12 and 12' may be formed of a metal such as iron, stainless steel or the like and, as shown in FIG. 9, one marginal edge of each plate support is curved so as to conform to the surface of the panel of a cathode ray tube with which the finished grid structure will be assembled. The resilient support 13 may also be formed of a metal such as iron, stainless steel or the like and this support 13 has projections 13a at places substantially corresponding to the Bessel points of the plate supports 12 and 12' as illustrated in FIG. 10. Further, the support 13 has L-shaped plate support-retaining members 13b formed integrally at places corresponding to the projections 13a.
The pair of plate supports 12 and 12' are mounted on the retaining members 13b of the resilient support 13 in such a manner that the projections 13a of the support 13 engage the plate supports 12 and 12' at or in the vicinity of their Bessel points, and the plate supports and the resilient supports are held together by predetermined jigs in a manner to produce a predetermined pressure at or in the vicinity of the Bessel points of the plate supports 12 and 12' by the projections 13a of the resilient support 13. Then, the grid elements 14 are stretched between the pair of plate supports 12 and 12' at a predetermined distribution of tension.
With such an arrangement, the pair of plate supports 12 and 12' are supported by the projections 13a of the resilient support 13 at or in the vicinity of their Bessel points, so that the equilibrium of the tension is very stable after the grid elements 14 have once been stretched at the predetermined distribution of the tension. Accordingly, the equilibrium of the tension is not lost by a slight variation in the tension after stretching the grid elements 14 and the grid frame is not deformed. Further, the equilibrium of the tension is difficult to loose by thermal expansion of the frame or the grid elements 14 due to a temperature rise during operation, and even if the equilibrium of the tension is lost, the tension promptly balances, so that deformation of the frame is very slight. Consequently, the position of the grid elements 14 is not shifted and the electron beam always impinges upon the fluorescent screen accurately at a predetermined location, so that phenomenon such as color contamination is not caused thereby ensuring reproduction of a clear picture. In addition, since the grid structure described above is simple in construction, its fabrication is easy and the yield is greatly increased. Even if the grid elements 14 are stretched between the plate supports 12 and 12' at substantially uniform tension, the deformation of the frame is very slight as indicated by the dotted line B in FIG. 2. Accordingly, there is no possibility that the position of the grid elements 14 is shifted by a slight deformation of the frame and by thermal expansion of the grid elements or the frame due to a temperature rise. That is, even if the grid elements 14 are stretched at uniform tension, the aforementioned many advantages can still be obtained.
The assembling of the grid structure with the panel of a cathode ray tube can readily be achieved by the same means as mentioned previously or by other known means, and accordingly no description will be given. Further, it is needless to say that the aforementioned method can be used for stretching the grid elements, and the metal wires may be stretched as the grid elements 14 at a predetermined pitch in place of the metal strips.
The foregoing description has been made in connection with only several examples of this invention, and the material, shape and the like of the bar supports, plate supports, grid elements, resilient supports and so on can be suitably selected at will, if necessary. However, the bar supports and the plate supports are desired to be formed of a conductive material so as to establish electric fields between the supports and the grid elements. Further, these supports are not restricted to the bar and plate supports.
When the grid structure is used in color picture tubes the grid elements are caused to vibrate by mechanical vibration due to external shocks or electron beam bombardment. In FIGS. 11 to 13 there is shown still another example of this invention in which the grid structure is designed to prevent such unwanted vibration of the grid elements.
In the figures reference numerals 21A and 21B indicate a pair of bar supports, and 22A and 22B represent substantially C-shaped resilient supports supporting the bar supports 21A and 21B at or in the vicinity of their Bessel points to constitute a grid frame generally designated by 23. Reference numeral 24 identifies grid elements such as ribbonlike metal strips which are stretched between the pair of bar supports 21A and 21B at a predetermined tension distribution and pitch. These members are identical with those described in the foregoing examples.
In the present example, a damping rod formed of, for example, a metal wire is provided in contact with the grid elements 24.
For example, resilient pieces 26A and 26B are planted on the outside of the resilient supports 22A and 22B substantially at the center thereof, and the damping rod 25 is stretched between the resilient pieces 26A and 26B. In this case the damping rod 25 is stretched in a direction of the lines of the raster (in the electron beam-scanning direction) and it is preferred that the damping rod 25 be stretched obliquely in a range of 30° to 45° relative to the electron beam scanning direction.
With such an arrangement, the grid elements 24 are resiliently pressed by the damping rod 25, and hence are not likely to be caused to vibrate by mechanical shocks from the outside and electron beam bombardment. Even if vibration occurs, it is immediately suppressed by the damping rod 25, thus preventing a bad influence by the vibration of the grid elements. The provision of the damping rod 25 avoids not only the vibration of the grid elements but also irregularity in the spacing thereof which results from twisting of the grid elements. Namely, when the grid elements 24 are heated by collision of the electron beam therewith and are to be twisted due to thermal expansion, the damping rod 25 presses the grid elements 24 to prevent twisting of the grid elements to hold the space between adjacent grid elements as predetermined, ensuring that the electron beam impinges only on a predetermined phosphor strip. Further, the provision of the damping rod 25 is only to stretch it in contact with the surfaces of the grid elements and hence can be achieved with great ease. The damping rod 25 may be a mechanically strong metal wire of, for example, tungsten, stainless steel, inconel or the like. The use of such a mechanically strong wire avoids breakage of the damping rod or insufficient pressing of the grid elements as with conventional damping rods of glass fiber in grid structures for the Chromatron (Registered Trademark) type picture tubes.
The damping rod 25 formed of the above-mentioned metals or other ones is preferred in terms of mechanical strength and is free from secondary electron beam emission by the electron beam. It is preferred that the diameter of the damping rod 25 to 30 to 50 microns. With a diameter of, for example, 100 microns, the mechanical strength of the damping rod increases but the reproduced picture is adversely affected by the damping rod. With a diameter of less than 30 microns, the mechanical strength of the rod 25 decreases and its pressing effect of the grid elements becomes weak. With a smaller diameter damping rod, the bad influence on the reproduced picture is decreased correspondingly, but the influence of a damping rod 50 microns in diameter on the reproduced picture is hardly noticeable. According to our experiments, a tungsten wire of a diameter from 30 to 50 microns yields good results. In the foregoing example, the damping rod 25 is stretched between the two resilient pieces 26A and 26B but either or both of them may be dispensed with. The shape and position of the resilient pieces are not limited to those in the above example. For example, it is possible that resilient wires are stretched on the frame on both sides of the grid elements instead of the resilient pieces and the damping rod is stretched between the resilient wires. Further, the damping rod 25 may be attached to the grid elements 25.
It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of this invention.
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