EP1647042B1 - Frame/mask assembly for a cathode-ray tube - Google Patents

Description

The present invention relates to a color cathode ray tube having a substantially planar screen, and more specifically to a set frame / color selection mask equipping such a tube.

The invention finds its application in any type of tube comprising a color selection mask, and is more particularly adapted to the tubes whose mask is made by stamping and is held in place inside the tube by a rigid frame on which he is solidarized.

A conventional color cathode ray tube is composed of a vacuum glass envelope. The tube comprises inside the envelope, a color selection mask located at a precise distance from the glass front face of the tube, the front face on which are deposited red, green and blue phosphor arrays to form a screen. An electron gun is disposed inside the tube, in its rear part, in the direction of the longitudinal axis of the tube, said axis passing through the center of the front face, said barrel generating three electron beams towards said front face. An electromagnetic deflection device, generally disposed outside the tube and close to the electron gun has the function of deflecting the electron beams to scan the surface of the panel on which the phosphor arrays are arranged. Under the influence of three electron beams each corresponding to a predetermined primary color, phosphor arrays allow the reproduction of color images on the screen, the mask allowing each determined beam to illuminate only the luminophore of the color. corresponding.

The color selection mask must be arranged and maintained during operation of the tube in a precise position within the tube. The functions of maintaining the mask are achieved through a generally very rigid rectangular metal frame on which the mask is conventionally welded.

The frame / mask assembly is mounted in the front face of the tube by means of suspension welded to the frame and cooperating with pins inserted in the glass constituting the front face of the tube.

The color selection mask is made from a metal sheet of very small thickness and comprises a so-called effective surface area, pierced with openings, said openings being made by chemical etching and generally arranged in vertical columns; the effective surface is surrounded by a non-perforated peripheral edge; a skirt generally made by stamping, borders the assembly extending in a direction substantially perpendicular to the effective surface. The mask is secured to the frame by spot welding at the skirt.

The generally rectangular frame has a pair of long sides and a pair of short sides, the section of which is generally L-shaped. The frame must have excellent rigidity, allowing the frame / mask assembly to be able to withstand shape modification the many manipulations that occur during the steps of the method of manufacturing a cathode ray tube, as explained in US4639230.

• le poids final du tube rendu important par le poids du cadre qui atteint généralement au moins trois fois le poids du masque.
• le coût final du tube du fait de l'important coût matière du cadre

To reach this level of rigidity the frames of the state of the art are of thick section and heavy weight which has two disadvantages:

• the final weight of the tube made important by the weight of the frame which usually reaches at least three times the weight of the mask.
• the final cost of the tube due to the material cost of the frame

Moreover, it has been noticed that a mask formed by stamping has a very important sensitivity to heating caused by the fact that about 70% of the electrons emitted by the gun are intercepted by the mask. The cause of this sensitivity lies in the significant difference in mass between the frame and the mask, making the thermal behavior of two parts are, for the sets according to the state of technology, very different.

The frame according to the invention makes it possible, among other advantages, to reduce the weight of materials used for the manufacture of the frame / mask assembly, while improving the thermal behavior of said assembly.

For this, the tube according to the invention comprises a tube according to claim 1.

• La figure 1 est une vue en coupe d'un tube à rayons cathodiques en couleurs selon l'état de la technique
• La figure 2 est une vue ne perspective, partiellement en éclaté d'un ensemble cadre/masque pour tubes à rayons cathodiques selon l'état de la technique
• Les figures 3A, 3B, 3C représentent des vues de face et de coté d'un ensemble cadre/masque selon l'invention
• Les figures 4A et 4B comparent l'état de la technique et l'invention dans des vues en coupe de l'ensemble cadre/masque

The invention and its various advantages will be better understood with the aid of the description below and the drawings among which:

• FIG. 1 is a sectional view of a color cathode ray tube according to the state of the art
• FIG. 2 is a perspective, partially exploded view of a frame / mask assembly for cathode ray tubes according to the state of the art.
• FIGS. 3A, 3B, 3C show front and side views of a frame / mask assembly according to the invention
• FIGS. 4A and 4B compare the state of the art and the invention in sectional views of the frame / mask assembly

Figure 1 shows a sectional view of the structure of a cathode ray tube in color. In such a tube 10, there is a frame / mask assembly 20 comprising a shadow mask 21 whose curved surface is made by stamping a sheet of steel or invar, which surface is disposed at a precise distance from a phosphor screen 11 disposed on the glass front face 1 of the tube; the mask is held in place by a rigid frame 22 to which it is secured by welding at its peripheral skirt 23 which is folded so as to extend inside the frame in a direction substantially parallel to the longitudinal axis Z The frame itself is rectangular in shape with at least partly L-shaped section sides, with a flank extending in a direction parallel to the longitudinal axis and a flange substantially perpendicular to this flank; the flange 25 and the flank 24 are connected to each other at the inner edge 26 of the flank farthest from the screen.

The tube comprises a funnel-shaped rear portion 30 terminating in a cylindrical neck 31 inside which there is an electron gun 40 generating three electron beams 41 in the direction of the color selection mask 21. The beams electronics sweep the surface of the screen 11 under the influence of the magnetic deflection device 50.

FIG. 2 illustrates an example of a frame / mask assembly according to the state of the art, as described for example in patent US6064146. The frame, massive, has a substantially rectangular connecting edge 26 and a flange 25 having a smaller width in the corners of the frame to reduce the weight of said frame without changing its rigidity. However, with this type of structure, there is a significant difference between the masses of the frame and the mask whose ratio is generally greater than or equal to three.

When the tube operates, about 20 to 30% of the electrons emitted by the barrel 40 can pass through the mask through the orifices disposed on its surface facing the screen. Electrons are therefore largely intercepted by the color selection mask 21 and they also hit its support frame 22. As a result, the frame and the mask will undergo thermal expansion, and when the frame and the mask are made of the same material, for example in steel, the expansion of the mask will be faster than that of the frame because of the important difference between the masses of the two elements. The mask, held on its periphery by the frame, will then bend (phenomenon called "doming") and the distance from its surface to the phosphor screen will change until the set reaches a thermal equilibrium. The changes in the mask distance 21 / screen 11 will cause discoloration of the image on said screen electron beams no longer properly illuminate phosphors corresponding to them.

• le rapport de masse entre le cadre et l'écran qui doit être inférieur à 2 de manière à minimiser le temps nécessaire à ce que l'ensemble cadre/masque atteigne son équilibre thermique, temps qui est normalement de l'ordre d'une heure et demie
• le gradient de température sur la surface du masque, gradient de température qui dans l'état de la technique, fait que la température au centre de l'écran est maximum et est minimum sur les bords. Plus le gradient de température est faible et plus les phénomènes de « doming » sont peu apparents.

He discovered that two factors came to influence the appearance of this transient phenomenon:

• the mass ratio between the frame and the screen must be less than 2 so as to minimize the time required for the frame / mask assembly to reach its thermal equilibrium, which time is normally of the order of one hour and a half
• the temperature gradient on the surface of the mask, temperature gradient which in the state of the art, makes the temperature in the center of the screen is maximum and is minimum on the edges. The lower the temperature gradient, the less obvious are the doming phenomena.

The temperature at the periphery of the mask is governed by boundary conditions: contacts with the frame, thermal inertia of the frame, shapes of the frame edges allowing the electron beams to strike the folded peripheral skirt 23 of the mask.

FIGS. 3A, 3B, 3C show an embodiment of a frame / mask assembly according to the invention in different views.

Figure 3A shows a frame 122 according to the invention in a rear view. The frame of substantially rectangular shape has two long sides 121 and two short sides 120. The sides of the frame have a section L-shaped with flanges substantially perpendicular to the longitudinal axis Z, respectively 125 for short sides and 125 'for long sides. The flanges are delimited by internal edges, 130 for short sides, 127 for long sides, and outer edges, 131 for short sides and 126 for long sides. The sides of the frame also have a flank 124 for the short sides and a flank 124 'for the long sides, substantially flat flank and parallel to the longitudinal axis Z.

The short sides have a flange whose width varies from the center to the ends in such a way that the width 150 of said flange at its center is smaller than the width 151 at its ends. In this way the inner edges 130 of the short sides present a concavity turned inward to allow the electron beams to intercept to a greater part of the surface of the skirt of the mask which is welded to the frame. FIGS. 4A and 4B show in cross-section respectively close to the middle of a short side and near its end, the lower limits of the skirt that the electron beams can reach for a frame according to the state of the art (in dotted line) and according to the invention (in solid lines).

The electron beams reach the midpoints of the short sides at higher angles of incidence in the middle of the frame sides than at their ends. Thus when the flange is of constant width (dashed lines) the skirt of the mask is less sprinkled by the electron beams in the middle than at its ends, whereas if its width decreases from its ends towards its center (solid lines) the beams electrons can reach a substantially constant width of the skirt all along the portion thereof welded to the short side of the frame. This results in a better distributed heating of the mask with a low temperature gradient between the different parts of the mask. The inner edge 130 of the flange thus has an inwardly oriented concavity, with a mean radius of curvature less than the mean radius of curvature of its outer edge 131. In an exemplary embodiment according to the invention for a diagonal tube of screen of the order of 60cm, illustrated by FIGS. 3A, 3B, 3C, the frame of format 16/9 has an inner edge 130 of radius of average curvature of about 1.1 meters and an outer edge 131 of radius of curvature of the order of 2.2 meters.

The curved shape of the flange provides a high mechanical rigidity of the frame to obtain a lightening of the amount of metal used to make said frame. The rigidity of the frame / mask assembly can be improved by coupling the curved shape of the flanges of the short sides with flanges of long sides having instead a width 160 in the middle greater than its width 161 at its ends. In the exemplary embodiment according to FIGS. 3A, 3B, 3C, the inner edge 127 of the flange has a concavity turned towards the outside of the frame and the outer edge 126 has a concavity turned towards the inside. The radii of curvature of the outer and inner edges are respectively of the order of 7m and 7.3m.

Although the type of frame structure according to the invention can be adapted to all types of suspension means in the tube of the frame / mask assembly, the rigidity of said assembly, once inserted into the tube is improved by means suspensions arranged in the corners. Thus suspension springs may be arranged in the corners 140 of the frame to cooperate with pins 2 inserted into the glass skirt of the front portion 1 of the tube. In this way it is both possible to reduce the amount of material used to make the frame and use a set frame / mask steel, less expensive material than the Invar.

In the embodiment according to FIG. 3A to 3C, it was noted that the thermal behavior of the mask frame assembly was improved as soon as the ratio between the weight of the mask and that of the frame was greater than 0.5 and tended to tend towards 1. Thus for a screen diagonal tube of 60cm, format 16/9, the selected mask is 0.25mm thick steel, while the frame, in the same material has a thickness of 0.5mm; the result is a mask weighing about 340 gr and a frame about 450 gr which brings a mass ratio equal to about 0.75.

Claims (5)

1. Cathode ray tube comprising:

   - a front face (1) on which a luminophore screen (11) is arranged on its internal part,

   - a rear part in the form of a funnel (30) terminating in a cylindrical part (31) in which an electron gun (40) extends in the direction of the longitudinal axis Z of the tube, axis passing through the centre of the front face,

   - a colour selection mask (21) formed by stamping and presenting a peripheral flange folded in a direction noticeably parallel to the longitudinal axis

   - a frame (122) designed to hold the mask at a distance from the screen, the said frame of a noticeably rectangular form has at least one pair of parallel short sides (120) of a noticeably L-shaped cross-section with a lateral flank extending in a direction parallel to the longitudinal axis connected to a flange (125) noticeably perpendicular to the said longitudinal axis, the width of the said flange being smaller at the middle of the side than at its extremities so that the inner edge (130) of the flange defines a curve whose concavity is oriented toward the longitudinal axis of the tube,

   the said frame being characterized in that the said long sides of the frame also comprise a L-shaped cross-section and in that the width of the flange (125') of each long side is greater at the middle of the said side than at its extremities so that the inner edge (127) of the said flange of each long side defines a curve whose concavity is oriented toward the longitudinal axis of the tube.
2. Cathode ray tube according to the claim 1 characterized in that the mask is made of steel.
3. Cathode ray tube according to claim 2 characterized in that the weight of the frame is less than two times the weight of the mask.
4. Cathode ray tube according to claim 1 characterized in that the connecting edge (131) of the flange (125) of each long side to the lateral flank defines a curve whose concavity is oriented toward the longitudinal axis of the tube.
5. Cathode ray tube according to claim 1 characterized in that the frame/mask assembly is held inside the tube by a support means at the corners (140) of the frame.

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