CATHODE RAY TUBE

Abstract: The invention relates to a cathode ray tube in which a shadow mask 10 is suspended via pins 19. Each pin 19 comprises a base 23 in the form of a truncated cone and a gradually widening free part 25. A contact spring 15 is connected to a pin in a clamping manner, at least a portion 24 of the contact spring 15 engaging the gradually widening free end 25. The contact spring 15 produces a simple and reliable electric connection between the shadow mask 10 and the electrically conductive layer 20 against which the contact spring 15 bears under a pre-stress.

Description: The invention relates to a cathode ray tube comprising an envelope having an electrode system for generating three electron beams, a substantially rectangular display window having an upright edge and comprising a display screen with phosphor elements luminescing in different colours, the display screen being coated with an electrically conductive layer, a substantially rectangular shadow mask comprising a large number of apertures which allot each electron beam to luminescent phosphor elements of one colour, a substantially rectangular supporting frame to which the shadow mask is connected, and pins which are connected to the upright edge of the display window and each of which has at least partly the shape of a truncated cone for suspending the supporting frame in the display window from suspension means, the said shadow mask being electrically connected to the conductive layer by at least one contact spring, a part of which engages one of the pins and another part of which engages the layer. Such a cathode ray tube is known from German Offenlegungsschrift 2622695. The electric connection between the shadow mask and the electrically conductive layer in this case is produced by at least one contact spring which is interposed between a suspension means and a pin having the shape of a truncated cone and which is fixed on the pin by the suspension means. The pressure which the contact spring exerts on the electrically conductive layer depends upon the distance between the place where the contact spring engages the suspension means of the shadow mask and the electrically conductive layer. If a good electric connection is to be produced for various types of cathode ray tubes or with the occurring tolerances in the dimensions of the shadow mask and/or the display window, different contact springs are necessary per type or with deviating tolerances. Since the contact spring engages the suspension means in a resilient manner the contact spring and the display window can perform different movements with respect to each other in the case of vibrations, for example, those which are present in the shadow mask and are transmitted to the suspension means. As a result of this the contact spring at the area where it engages the electrically conductive layer under pressure rubs over the layer so that the electric connection is detrimentally influenced. It is the object of the invention to provide a cathode ray tube having a simple electric connection of the shadow mask with the electrically conductive layer and in which the above-mentioned detrimental influences do not occur. For this purpose, the cathode ray tube according to the invention is characterized in that the pin comprises a gradually widening free end and the at least one contact spring is connected to the pin in a clamping manner, at least a part of the contact spring engaging the gradually widening free end. As a result of this, the contact spring is fixed by the pin and a good electric connection is obtained between the shadow mask and the electrically conductive layer which is no longer detrimentally influenced by vibrations. Furthermore the contact spring may be chosen independently of the differences in size of the shadow mask and/or display window. The gradually widening free end may have different shapes, for example, in the form of a cone or a ball. The use of pins having a gradually widening free end in the form of a ball for suspending the supporting frame and the shadow mask is known per se , for example, from EP-A-156362. The invention is based on the recognition of the fact that a pressure can be built up by connecting a contact spring in a clamping manner on a pin having a gradually widening free end with at least a part of the contact spring engaging the gradually widening free end, so that the contact spring engages the electrically conductive layer under a pre-stress. The advantage is that the contact spring and the display window perform the same movement with respect to each other in the case of vibrations since the contact spring is connected to the pin in a clamping manner and the pin is rigidly connected to the display window. As a result of this rubbing of the conductive layer by the contact spring at the area where it engages the conductive layer under pressure during vibrations, and consequent wearing of the layer, is prevented. As a result of this the good electric connection is maintained. An additional advantage is that contact springs may be used which engage the electrically conductive layer under a great pre-stress, which is desirable for a good electric connection between the shadow mask and the electrically conductive layer. When a contact spring is fixed with a great pre-stress by a suspension means of the shadow mask, as described in German Offenlegungsschrift 2622695, the allotment of the electron beam to the luminescent phosphor elements through the apertures in the shadow mask may be detrimentally influenced by the great pre-stress. In a cathode ray tube according to the invention the contact spring and the suspension means are provided on the pin while separated from each other so that the contact spring does not adversely influence the suspension means of the shadow mask even in the case of a great pre-stress. A preferred form of a cathode ray tube in accordance with the invention is characterized in that the part of the contact spring which engages the gradually widening free end of the pin comprises a recess and two projections situated on each side of the recess, said recess fitting in a clamping manner around the transition from the part in the form of a truncated cone of the pin to the gradually widening free end of the pin. As a result of this the contact spring is readily fixed by the gradually widening free end and the parts of the pin in the form of a truncated cone and consequently is difficult to move. A further preferred form of a cathode ray tube in accordance with the invention is characterized in that the contact spring is a flat metal element having a flat portion comprising the recess, and the two projections are at such an angle with the flat portion that the two projections engage a part of the cone. Optimal fixing is obtained in that the two projections situated on each side of the recess engage a part of the cone, the flat portion of the flat metal element in which the recess is provided engaging the gradually widening free end. Even in the case of a blow or shock, for example when the cathode ray tube is dropped, the contact spring will remain firmly connected to the pin and ensures a good electric connection. Moreover, as a result of this the contact spring may be given a greater pre-stress. An alternative preferred form of a cathode ray tube in accordance with the invention is characterized in that the contact spring is a metal wire the ends of which engage the conductive layer, the wire comprising an arcuate portion which surrounds the recess and comprises the two projections engaging a part of the cone. The contact spring can be provided on the pin in a very simple manner. A few embodiments of the invention will now be described in greater detail with reference to the drawing in which Figure 1 is a sectional view of a cathode ray tube according to the invention, Figure 2 is a sectional view on an enlarged scale of a part of the cathode ray tube according to the invention, and Figures 3 a and 3 b and Figures 4 a and 4 b show two preferred embodiments of the invention. In the horizontal sectional view of Figure 1 the cathode ray tube comprises an envelope consisting of a display window 1, a cone 2 and a neck 3. An electrode system 4 having three electron guns for generating three electron beams 5, 6 and 7 is provided in the neck 3. The electron beams are generated in one plane (in this case the plane of the drawing) and are directed to a display screen 8 which is provided internally on the display window and comprises a great number of phosphor elements luminescing in green, red and blue and coated with an aluminium layer 20. The phosphor elements may be, for example in the form of dots or strips. The invention will hereinafter be described, by way of example, with reference to elements in the form of strips, the longitudinal direction of which is perpendicular to the plane through the electron guns (in this case perpendicular to the plane of the drawing). On their way to the display screen 8 the electron beams 5, 6 and 7 are deflected over the display screen 8 by means of a number of deflection coils 9 placed coaxially around the tube axis and pass through a shadow mask 10 which consists of a metal plate having apertures 11 the longitudinal direction of which is parallel to the phosphor elements of the display screen 8. The three electron beams 5, 6 and 7 pass through the apertures 11 at a small angle with each other and consequently each impinge only on phosphor elements of one colour. The cathode ray tube further comprises an internal resistance layer 12 and a readily conducting layer 13 provided externally on the cone 2. The resistance layer 12 is connected to a high voltage contact 14 provided in the wall of the tube. The shadow mask 10 is connected to the supporting frame 18 which is suspended in the cathode ray tube, by means of suspension means 40, to metal pins 19 which are provided in the upright edge 36 of the display window 1. Contact springs 15 are connected to said pins 19 in a clamping manner. Since the shadow mask 10 is suspended on the metal pins 19, the shadow mask 10 is electrically connected to the aluminium layer 20 of the display screen 8 via the pins 19 by means of the contact springs 15. A metal screening cone 16 is connected at one end to the shadow mask 10 and at the other end to the resistance layer 12 by means of contact springs 17. During operation of the tube the layers 12 and 20 are at an operative potential of approximately 25 kVolt and the layer 13 is at earth potential because it is connected to the chassis of the picture display apparatus of which the cathode ray tube forms part. Figure 2 shows a part of the cathode ray tube according to the invention on an enlarged scale. Each pin 19 comprises a base 23 in the form of a truncated cone and a gradually widening free end 25 in the form of a ball. The supporting frame 18 supporting the shadow mask 10 is carried on the ball-shaped end 25 of the pin by way of a suspension means 40. The base 23 of the pin 19 is connected to the upright edge 36 of the display window 1, for example by melting the base 23 partly into the upright edge 36. However, the pin 19 may also be connected to the upright edge differently, for example by thermocompression. The contact spring 15 is connected to the pin 19 in a clamping manner, at least a portion 24 of the contact spring 15 engaging the ball-shaped end 25. Moreover, the contact spring 15 engages the electrically conductive layer 20 under pressure. Since the contact spring 15 is connected in a clamping manner on the pin 19 which in turn is fixed in the upright edge 36, the contact spring 15 and the electrically conductive layer 20 on the display window 1 perform the same movement with respect to each other in the event of vibrations so that relative movement between the contact spring and the electrically conductive layer, and consequently wearing of this layer, does not occur. The electric connection between the shadow mask 10 and the electrically conductive layer 20 is thus maintained. Moreover, the contact spring 15 is not adversely influenced by vibrations which are present in the shadow mask 10, even though the contact spring 15 and the shadow mask 10 are provided on the pin 19, since they are separated from each other. Figure 3 a is a perspective view of a preferred form of a part of a cathode ray tube according to the invention, in which the contact spring is shown disconnected from the pin for clarity. Figure 3b shows the contact spring connected to the pin. The contact spring 15 is manufactured from a flat metal element having a flat portion 24 comprising a recess 21. The contact spring 15 is provided on the pin 19 by moving the flat portion 24 of the contact spring 15 from the side of the display window 1 such that of the recess 21 clips around the transition of the conical base 23 to the ball-shaped end 25 of the pin 19. The contact spring 15 fits around the pin 19 in a clamping manner when, for example, the cross-section of the recess 21 in the initial position is slightly smaller than the cross-section of the transition from the conical base 23 to the ball-shaped end 25 of the pin 19. As a result of this, sliding of the contact spring 15 off the pin 19 in the event of vibrations of the cathode ray tube is prevented. A better connection of the contact spring 15 on the pin 19 which is even insensitive to blows or shocks, for example when the cathode ray tube is dropped, is obtained when the two projections 22 present on each side of the recess 21 are at such an angle with the flat portion 24 that, when the contact spring 15 is provided on the pin 19, the two projections 22 engage a portion of the conical base 23. Since the flat portion 24 of the contact spring 15 engages the ball-shaped end 25 of the pin 19 and the two projections 22 engage the conical base 23, a pressure is built up so that the contact spring 15 engages the electrically conductive layer 20 under a prestress. Although the contact spring 15 produces a good electric connection between the shadow mask and the layer, providing the contact spring on the pin from the side of the display window may be impeded just due to the restricted space between the pin and the display window. Figure 4 a is a perspective view of a second preferred embodiment of a part of a cathode ray tube according to the invention in which, again for clarity, the contact spring is shown disconnected from the pin and the contact spring can simply be connected to the pin. Figure 4b shows the contact spring connected to the pin. The contact spring 15 is manufactured from a metal wire 30 the ends 35 of which engage the conductive layer 20 as is shown in Figure 4 b . The wire 30 comprises an arcuate portion 34 defining a recess 31. The contact spring 15 is moved over the pin 19 so that the arcuate portion 34 of the wire 30 fits in a clamping manner around the transition from the conical base 23 to the ball-shaped end 25. The arcuate portion 34 further comprises two projections 32 which, when the wire 30 is connected on the pin 19, engage the conical base 23. The wire 30 can be mounted on the pin 19 without any difficulty and engages the conductive layer 20 with its ends 35 under a pre-stress so that a good electric connection is produced.

Claims: 1. A cathode ray tube comprising an envelope having an electrode system (4) for generating three electron beams (5, 6, 7), a substantially rectangular display window (1) having an upright edge (36) which display window comprises a display screen (8) having phosphor elements luminescing in different colours, the display screen being coated with an electrically conductive layer (20), a substantially rectangular shadow mask (10) comprising a large number of apertures (11) which allot each electron beam to luminescent phosphor elements of one colour, a substantially rectangular supporting frame (18) to which the shadow mask is connected, and pins (19) which are connected to the upright edge of the display window and each of which has at least partly the form of a truncated cone (23) for suspending the supporting frame in the display window by suspension means (40), the said shadow mask being connected electrically to the conductive layer by at least one contact spring (15) a part of which engages one of the pins and another part of which engages the layer, characterized in that the pin comprises a gradually widening free end (25) and the at least one contact spring is connected to the pin in a clamping manner, at least a part of the contact spring engaging the gradually widening free end. 2. A cathode ray tube as claimed in Claim 1, characterized in that the part of the contact spring which engages the gradually widening free end of the pin comprises a recess (21) and two projections (22) situated on each side of the recess, said recess fitting in a clamping manner around the transition from the part in the form of a truncated cone (23) of the pin to the gradually widening free end (25) of the pin. 3. A cathode ray tube as claimed in Claim 2, characterized in that the contact spring is a flat metal element having a flat portion (24) which comprises the recess (21), and the two projections (22) are at such an angle with the flat portion that the two projections engage a part of the cone. 4. A cathode ray tube as claimed in Claim 2, characterized in that the contact spring is a metal wire (30) the ends of which engage the conductive layer, the wire comprising an arcuate portion (34) which surrounds the recess (31) and comprises the two projections (32) which engage a part of the cone.

Inventors: SERIO, GIOVANNI, VERHOEVEN, MARTINUS CORNELIS MARIA
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1988
Main classification: H01J29
IPC codes: H01J29, H01J31