WO2003054905A1

WO2003054905A1 - Device for suspending a frame/mask assembly for cathode-ray tubes

Info

Publication number: WO2003054905A1
Application number: PCT/EP2002/014097
Authority: WO
Inventors: Enzo Arata; Paolo Basilischi; Paolo Fava; Paolo Ginesti
Original assignee: Thomson Licensing S.A.
Priority date: 2001-12-20
Filing date: 2002-12-11
Publication date: 2003-07-03
Also published as: TWI223304B; TW200411702A; ITMI20012713A1; AU2002361054A1

Abstract

Colour cathode-ray tube comprising a glass faceplate, on which a screen of phosphors is deposited and a frame/colour selection mask assembly, the mask being held by welding to the frame, the frame/mask assembly being suspended inside the tube using support means, at least one of the support means integrates a metal part (19) forming a spring and comprises an opening (26) in which a metal lug inserted in the glass faceplate of the tube is engaged, the size (24) of the said opening in the direction parallel to the surface of the screen is greater than the size (25) of the said opening in the direction perpendicular to the screen. The shape of the opening makes it possible to prevent variations in positioning of the mask with respect to the surface of the phosphor screen.

Description

DEVICE FOR SUSPENDING A FRAME/MASK ASSEMBLY FOR CATHODE-RAY TUBES

The invention relates to a colour cathode-ray tube and more specifically to the system for suspending the frame/mask device for selecting colours placed inside the glass envelope of the tube. The invention is applicable to any type of tube comprising a colour selection mask and is also well suited to tubes where the mask is held under tension by the frame to which it is secured such as tubes where the mask is formed by pressing a metal foil.

Cathode-ray tubes comprise a colour selection mask located at a specific distance from the inside of the glass faceplate of the tube, a faceplate on which arrays of red, green and blue phosphors are deposited.

Under the effect of three electron beams, each corresponding to a given primary colour, the phosphor arrays allow the reproduction of images on the screen, the mask allowing each given beam to illuminate only the phosphor of the corresponding colour.

The colour selection mask must be placed and held during manufacture of the tube, then during its operation, in a specific position inside the said tube.

The holding functions are carried out using a rectangular metal frame, which is generally very rigid, to which the mask is conventionally welded. The frame/mask assembly is mounted in the faceplate of the tube using suspension means comprising at least three metal parts welded to the frame, each of said parts comprising an end forming a spring and perforated with an opening in which one of the metal lugs, incorporated in the glass faceplate, is engaged. The springs must be rigid enough to support the weight of the frame/mask assembly, which may reach several kilos for large tubes. Two arrangements of the suspension means are conventionally used: either at the middle of the sides of the frame, or at the corners of the latter. Large screen tubes have suspensions which are preferably placed in the corners, this arrangement having the advantage of offering improved mechanical rigidness, guaranteeing that the initial adjustment of the mask/screen distance will not be altered during the steps of manufacturing the tube and that the finished tube will offer a better guarantee against implosions.

The frame/mask assembly must be able to be dismantled and accurately remounted several times during the various steps of the tube manufacturing process by compressing suspension springs to release them from the metal lugs incorporated in the glass of the faceplate, and without it being necessary to readjust the distance from the mask to the screen on each remounting.

Large frames comprise four suspension springs placed either on the sides of the frame, or in the corners thereof. The springs are welded to the frame with a certain tolerance, then the frame/mask assembly is fitted in the faceplate of the tube. For the openings of each spring to be able to engage in each metal lug incorporated in the skirt of the faceplate of the tube, it is necessary that the openings of the springs coincide with the said lugs. In order to solve the problems of positioning arising from the tolerances allowed in the position of the lugs and of the spring openings, it is common to use three identical springs having an opening of a given diameter, suitable for being positioned accurately on the frustoconical-shaped lug, and one spring having an opening of greater diameter than the previous one. The frame is then fitted into the faceplate without mechanical stress, the larger opening absorbing the various tolerances. In order to prevent any mechanical clearance of the frame with respect to the lugs, a disc of a diameter equal to the diameter of the openings of the three identical springs is then inserted onto the lug and welded over the fourth spring.

However, it has been noted that this manufacturing process had too great a variation in the positioning of the mask with respect to the screen, a variation due to the phase of welding the disc to the spring, in which unwanted movements of the parts with respect to each other may mean that the final position of the disc is not the nominal position. As a result, an entire region of the mask surface is no longer in the optimum position of the initial adjustment, which may lead to expensive recycling of the frame/mask assembly.

The system for suspending a frame/mask assembly according to the invention makes it possible to position this assembly in the faceplate of the cathode- ray tube without having the drawbacks of the prior art.

For this, the colour cathode-ray tube according to the invention comprises a glass faceplate on which a screen of phosphors is deposited, a colour selection mask placed close to the screen, a frame to which the mask is secured, the said frame being of substantially rectangular shape, the frame/mask assembly being held inside the faceplate by support means, cooperating with lugs of substantially frustoconical shape fixed in the thickness of the faceplate, at least one of the support means integrating a metal part forming a spring and comprising an opening in which one of the metal lugs is engaged, characterized in that the size of the opening in the direction parallel to the surface of the screen is greater than the size of the said opening in the direction perpendicular to the screen. The invention and its advantages will be better understood using the description below and the drawings, among which:

Figure 1 represents a cathode-ray tube according to the invention, seen partially exploded,

Figure 2 represents suspension means according to the prior art,

Figure 3 illustrates one embodiment of a suspension means according to the invention, - Figure 4a shows, in section, a frame/mask support according to a second embodiment of the invention,

Figure 4b shows, in top view, the embodiment of Figure 4a.

A colour cathode-ray tube (1), such as illustrated by Figures 1 and 2, comprises a glass envelope in three distinct parts, the faceplate 2 inside of which a screen 3 made of phosphors is deposited, the funnel- shaped rear at 4 and the substantially cylindrical neck 5 surrounding the electron gun 6 generating three electron beams in the direction of the screen.

A colour selection mask 11, perforated with openings or slots 12, is placed in the tube over the paths of the electron beams, between the screen 3 and the gun 6. The mask 11 is welded to a rigid frame 10 held in position in the faceplate of the tube using suspension means comprising metal lugs 8 set in the glass skirt 7 of the faceplate and springs 9 welded to the frame and having openings 13 intended to cooperate with the said lugs, the ends of which are generally of frustoconical shape.

The mask must be placed at a very specific distance from the screen in order to allow the correct operation of the finished tube, that is to say mainly that each of the beams will illuminate the phosphors of the primary colour corresponding thereto. This measured distance in the direction of the main Z axis of the tube is known by the name of "Q distance". As illustrated in the diagram of Figure 1, adjustment of the Q distance is carried out by accurately positioning, by welding to the frame, the springs 9 and therefore their openings 13, by considering the distance of the metal lugs 8 from the screen. The lugs are embedded in the glass of the faceplate during manufacture of the said plate by the glass manufacturer, and must all be positioned in the same plane parallel to the surface of the screen.

To date, variations in the positioning of the metal lugs, which could be located in different planes, mean having to use at least one spring with an opening of a diameter greater than the diameters of the openings of the other springs in order to compensate for these variations. A disc was placed beforehand on the lug before the insertion of the spring then the spring/disc assembly was welded together in order to immobilize the frame thereby preventing any mechanical play. However, it was realized that the positioning of the mask in the direction of the main axis Z could be subject to very large variations due mainly to two factors, at the time of welding, the positioning of the disc may not be optimal, it being possible for the disc to be in an oblique position on the lug, the welding machine may possibly alter the position in Z of the spring at the time of welding, thus locally altering the distance Q.

The invention originates in the fact that the manufacturers of the front glass panel are able to control, more accurately than in the past, at least one parameter for positioning the lug 8, and for example that of the position in the direction of the Z axis. Modelling and experiments have shown that the frame/mask system could allow a tolerance in the Q value of about 0.25 mm, a tolerance which could be controlled during the manufacture of the faceplate for the positioning of the lugs.

As a result, the shape of the suspension springs may be altered with respect to the prior art. Figure 3 illustrates one embodiment of a spring 19 according to the invention, intended to support the frame/mask using suspensions placed in the corners of the front panel. The spring generally consists of a metal plate comprising, by folding, a first end 20 intended to be secured, for example, by welding, to a plate connected to the frame 10, a second end 22 intended to lie in a direction substantially parallel to the main Z axis of the tube and a connection portion 21 between the two ends. The end 22 comprises an opening 26 which, for at least one of the springs, is of elongate shape, lying over a length 25 along a first axis of symmetry Δ substantially parallel to the Z axis of the tube and over a length 24 along a second axis of symmetry Δ' substantially parallel to the screen of the tube. The size 25 of the opening 26 along the direction parallel to the Z axis, and therefore perpendicular to the screen 3 of the tube, is substantially identical to the openings of the other springs intended to be engaged and positioned on the frustoconical surface of the lugs 8. Thus the frame may comprise three standard suspension springs 9, each one with a substantially circular opening 13, and a fourth spring 19 with an elongate opening 26. Since the lugs are in the same plane, to within the tolerances allowable by the system, the mask is at the predetermined distance Q provided that the frame is not twisted when it is inserted into the faceplate to make the openings of the springs coincide with the lugs of the faceplate; this is because it is necessary to leave the suspension system, consisting of the springs and the lugs, a degree of freedom to absorb the tolerances which have to be allowed for the position of the lugs in the plane parallel to the screen 3. This degree of freedom is given by the elongate opening 26 in a direction perpendicular to the direction of the screen 3. According to the manufacturing tolerances, it could be desirable to make the suspension of the frame/mask by using one or more springs according to Figure 3, with other suspension springs, the ends of which are provided with a round orifice 13. The final immobilization of the support, incorporating a spring 19 according to the invention, is achieved by welding a disc of a diameter substantially equal to the diameter of the other round orifices 13 of the standard springs

In order to minimize the number of metal parts used in the manufacture of the cathode-ray tubes, the lugs 8, springs 9, 19, and discs are identical for all types and sizes of tube. However, depending on the tube types and sizes, various tolerances may or must be allowed either since the manufacturer of the glass parts cannot go below a certain tolerance or because then the glass part would become too expensive to manufacture. Thus, in order to cover all tube sizes ranging from a diagonal of 36 cm to a diagonal of 82 cm, it is preferable to have an opening 26 where the ratio of its largest dimension 24 to its smallest dimension 25 is between 1.5 and 2.5.

The embodiment of Figures 4a and 4b advantageously makes it possible to decrease, if necessary, the variation in the values of Q obtained by using a spring according to the invention. It has been noticed that if the diameter D of the opening 30 of the disc 29 has the same value as the dimension 25 of the opening of the spring 19, the spring 19 is raised on the lug with respect to the position of the disc and because of the frustoconical shape of the said lug, it would then be free to move in the Z direction before welding to the disc, thus causing a positioning error in Z with a value equal to: d = ±e.tan(Θ) where Θ is the angle at the apex of the frustoconical end of the lug, and e the thickness of the disc. In order to prevent this problem, the size 25 of the opening of the spring is chosen to have a value which is smaller than the diameter D of the opening 30 of the disc; thus, in a chosen embodiment implementing the invention, the angle Θ is 12°, the disc, with a thickness of 0.4 mm, has an opening 30 with a diameter equal to 5.61 mm and the size of the opening 26 of the spring 19, of thickness 0.635 mm, in the direction of the Z axis, is 5.51 mm. Moreover, the other suspension means comprise springs 9 with a circular-opening diameter 13 equal to 5.61 mm so as to have an identical reference position on each lug.

Experience shows that the difference between the sizes of the opening 30 of the disc 29 and of the opening of the spring in the Z direction must be chosen preferably between d and 2d since beyond 2d, the spring no longer comes in contact with the disc and below d, too great a variation is again noted in the position of the mask along Z, with respect to the screen.

The embodiments described in the examples are not limiting and the invention may equally well be implemented for frame/mask suspensions placed in the middle of the sides of the frame.

Claims

1. Colour cathode-ray tube (1) comprising a glass faceplate (2) on which a screen of phosphors (3) is deposited, a colour selection mask (11) placed close to the screen, a frame (10) to which the mask is secured, the said frame being of substantially rectangular shape, the frame/mask assembly being held inside the faceplate by support means (9, 19, 29), cooperating with lugs (8) of substantially frustoconical shape fixed in the thickness of the faceplate, at least one of the support means integrating a metal part forming a spring (19) and comprising an opening (26) in which one of the metal lugs is engaged, wherein that the size (24) of the opening (26) in the direction parallel to the surface of the screen is greater than the size (25) of the said opening in the direction perpendicular to the screen.

2. Cathode-ray tube according to the preceding claim, wherein it furthermore comprises three other identical support means, each of these three means integrating a metal part forming a spring (9) and comprising an opening (13) whose periphery, intended to bear against the surface of the lug, is substantially circular.

3. Cathode-ray tube according to the preceding claim, wherein the diameter of the opening of the three identical means has substantially the same value as the size of the opening of the fourth means in the direction perpendicular to the screen.

4. Cathode-ray tube according to Claim 1, wherein the ratio between the size of the opening in the direction parallel to the screen and the size of the opening in the direction perpendicular to the said screen is preferably chosen between 1.5 and 2.5.

5. Cathode-ray tube according to Claim 1, wherein the support means integrating a metal part forming a spring and comprising an opening whose size in the direction parallel to the surface of the screen is greater than the size in the direction perpendicular to the screen, furthermore comprises a disc (29) fixed, for example, by welding, to the part forming a spring, and the opening (30) of which coincides with the opening (26) of the spring.

6. Cathode-ray tube according to the preceding claim, wherein the disc is welded to the face of the spring opposite the frame and in that the diameter D of the opening (30) of the disc is greater than the size of the opening of the spring in the direction perpendicular to the screen.

7. Cathode-ray tube according to the preceding claim, wherein it furthermore comprises suspension means forming a spring (9) comprising a circular opening (13), the diameter of which is substantially equal to the diameter D of the disc.