CATHODE RAY TUBE AND DEFLECTION UNIT FOR A CATHODE RAY TUBE

Abstract: A cathode ray tube comprising an electron gun for generating at least one electron beam and a deflection unit for deflecting the electron beam(s) across a display screen. The deflection unit comprises a first system inside the coil holder (42) and a second system (43) of saddle-shaped deflection coils. Said deflection-coil systems are interconnected via connecting pieces (41, 51, 63, 64) which are flexibly arranged with respect to each other, so that differences in thermal expansion between the deflection-coil systems have a reduced influence on the deflection of the electron beam(s).

Description: Cathode ray tube and deflection unit for a cathode ray tube. The invention relates to a cathode ray tube comprising, in an evacuated envelope, a means for generating at least one electron beam and a display screen, said cathode ray tube being provided with a deflection unit for deflecting the electron beam(s) across the display screen, and said deflection unit comprising at least one system of saddle- shaped deflection coils. The invention also relates to a deflection unit for a cathode ray tube. Such cathode ray tubes are used, inter alia, for television receivers, computers etc. Cathode ray tubes of the type mentioned in the opening paragraph are well-known. During operation of said cathode ray tubes, the electron beams are deflected across the display screen by the deflection unit. During operation of the cathode ray tube, its temperature and that of the deflection unit increase, inter alia, as a result of the fact that heat is generated in the deflection coils. This causes the position of the coils to change with respect to each other and/or with respect to the rest of the cathode ray tube. This change in position has an influence on the deflection of the electron beams. It is an object of the invention to provide a cathode ray tube of the type mentioned in the opening paragraph and a deflection unit for a cathode ray tube, which ensure that the influence of a rise in temperature of the cathode ray tube on the deflection of the electron beams is reduced. This object is achieved in accordance with a first aspect of the invention by a cathode ray tube of the type mentioned in the opening paragraph, which comprises a first and a second system of saddle-shaped deflection coils, and which is characterized in accordance with the invention in that the deflection coil systems are interconnected via connecting pieces which are flexibly arranged with respect to each other. In accordance with a second aspect of the invention, a cathode ray tube of the type mentioned in the opening paragraph, which comprises a system of saddle-shaped deflection coils and a deflection-coil holder is characterized according to the invention in that the deflection coil system and the deflection-coil holder are interconnected via connecting pieces which are flexibly arranged with respect to each other. In well-known deflection units, the saddle-shaped coils are mounted on a rigid coil holder. Said coil holder is composed of a rigid, more or less funnel-shaped, synthetic resin body. The coil holder forms the support of the deflection unit on which the deflection coils and any further components are provided. The deflection coils often are secured to the inside and the outside of the funnel-shaped coil holder. A rise in temperature causes the deflection coils and the holder to expand. This may result in a change of place of the deflection coils with respect to each other. This has a negative effect on the deflection of the electron beams. A cathode ray tube in accordance with the invention, or a deflection unit for a cathode ray tube in accordance with the invention, comprises saddle-shaped deflection coil systems which are interconnected via connecting pieces which are flexibly arranged with respect to each other, or, if there is only one system of saddle-shaped deflection coils, said system and the coil holder are interconnected by connecting pieces which are flexibly arranged with respect to each other. By virtue of said flexible arrangement of the connecting pieces, differences between the coefficients of thermal expansion of the coil systems and the coil holder are compensated for during use of the cathode ray tube. As a result, the coil systems remain aligned with respect to each other. The advantage over the well-known construction is caused by the fact that in said well-known construction there is a fairly large difference in thermal expansion between the coils (which are predominantly composed of metal, mostly copper) and the coil holder, which is generally made of a synthetic resin, whereas in the cathode ray tube in accordance with the invention, this difference in thermal expansion hardly plays a role, or perhaps none at all, owing to the flexible arrangement of the connecting pieces relative to each other. Both coil systems are interconnected in such a manner that they expand jointly and constitute an integral part as regards thermal expansion. In the well-known deflection units, the coil systems are separated by a coil holder and there is no connection between the thermal expansion values of the coils. The deflection unit preferably comprises a coil holder which is provided on the inside and on the outside with, respectively, the first and the second system of deflection coils, and the connecting pieces are connected to the coil holder via flexible connections. Said flexible connections compensate for differences in expansion between the holder and the coil assembly. In an embodiment, the connecting pieces comprise a first and a second set of connecting pieces which are arranged along the z-axis at some distance from each other, the connection between the first and the second set being formed by the coils only. In this embodiment, the coils are interconnected by said connecting pieces, said coils forming a self- supporting integral part and hence constituting the supporting part of the deflection unit. In these embodiments, the main function of the coil holder is taken over by the assembly of both coil systems. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the drawings: Fig. 1 is a sectional view of a cathode ray tube; Fig. 2 is a schematic, sectional view of a well-known construction of a cathode ray tube comprising a deflection unit; Fig. 3 is a perspective, much simplified, view of a well-known coil holder; Figs. 4A and 4B show a detail of a deflection unit in accordance with the invention; Figs. 5A, 5B and 6A, 6B show a detail of further embodiments of a deflection unit in accordance with the invention. The Figures are not drawn to scale. In the Figures, like reference numerals generally refer to like parts. A colour cathode ray tube 1 has an evacuated envelope 2 comprising a display window 3, a cone portion 4 and a neck 5. In said neck 5, there is provided an electron gun 6 for generating three electron beams 7, 8 and 9. A display screen 10 is situated on the inside of the display window. Said display screen 10 comprises a phosphor pattern of phosphor elements luminescing in red, green and blue. On their way to the display screen, the electron beams 7, 8 and 9 are deflected across the display screen 10 by means of a deflection unit 11 and pass through a colour selection electrode 12 which is arranged in front of the display window 3 and which comprises a thin plate having apertures 13. The colour selection electrode is suspended in the display window by means of suspension means 14. Said three electron beams pass through the apertures of the shadow mask and each electron beam impinges on phosphor elements of only one colour. Fig. 2 is a schematic, sectional view of a well-known construction of a cathode ray tube comprising a deflection unit 11. Said deflection unit comprises a coil holder 18 of an electrically insulating material (often synthetic resin) having a front end portion 19 and a rear end portion 20. Between said end portions, on the inside of the coil holder, there is a line deflection coil system 21 for generating a (line) deflection field for deflecting electron beams generated by the electron gun 6 in the horizontal (line) direction, and a field deflection coil system 22 for generating a (field) deflection field in the vertical direction is situated on the outside of the coil holder. Each coil system generally comprises two sub- coils. Both coil systems are attached to the coil holder. During operation of the cathode ray tube, its temperature and, in particular, that of the deflection unit increase. The coil systems are attached (for example by means of an adhesive or by means of hooks) to the coil holder. Differences in thermal expansion between the coil holder and the coils cause the positions of the line and field deflection coil systems 21, 22 to change relative to each other and bring about thermal stresses between the coil systems 21, 22 and the coil holder 18. These effects have a negative influence on the quality of the deflection field. Fig. 3 is a perspective, much simplified, view of a well-known coil holder 31 having a sub-coil 32. In this case, said sub-coil is attached to the coil holder by means of hooks 33. Fig. 4A is a perspective view of a coil holder for a deflection unit in accordance with the invention. Connecting pieces 41 are flexibly attached to the coil holder 42 by means of strips. In Fig. 4B, the coil holder shown in Fig. 4A is provided with coils 43. Two coils 43 form a coil system which is attached via connecting pieces 41 to the outside of the coil holder 42. The coil holder is also provided on the inside with two coils (not shown), which are attached to the connecting pieces 41 . The coil systems are attached to the connecting pieces, for example, by means of an adhesive. If the temperature increases, the coil systems can expand simultaneously relative to each other and relative to the coil holder. Consequently, the positions of the coil systems relative to each other do not change. In this embodiment, use is still made of the coil holder. In this embodiment, two coil systems are attached to the coil holder. In an alternative embodiment, one of the coil systems can be attached to the coil holder, for example the coil system formed by coils 43 as shown in Fig. 4B, while the other coil system is a so-called toroidal coil system, i.e. two coils are wound around a magnetic core, so that the magnetic core comprising coils is arranged around the coils 43 like a ring. The advantage of such an embodiment is that the coils 43 are flexibly arranged relative to the coil holder, so that thermal stresses between the coil holder and the coils 43 are precluded. Figs. 5A and 5B show a further embodiment of a coil holder for a deflection unit in accordance with the invention. This example represents more or less a skeleton structure of the coil holder. In this example, the connecting pieces 51 are interconnected by synthetic resin strips 52 in which expansion bends 53 are formed which ensure that the connecting pieces can move relative to each other. Fig. 5A shows the holder without coils, Fig. 5B shows the holder with coils 55. Figs. 6A and 6B show another embodiment of a deflection unit in accordance with the invention. In this embodiment, the coil holder is replaced by a front portion 61 and a rear portion 62. Said front portion comprises connecting pieces 63; the rear portion comprises connecting pieces 64. Said connecting pieces are resiliently attached to the front and rear portions. Fig. 6A shows the various components of the coil holder without the connecting coils; Fig. 6B shows the coil holder with the coils 65. In the embodiment shown in Figs. 6A and 6B, the connecting pieces comprise two sets of connecting pieces (63 and 64) which are arranged along the z-axis at some distance from each other, the connection between the first and the second set being formed only by the coils 65. Said coils 65 are naturally somewhat flexible. The invention is also based on the following insight: In the manufacture of deflection units and in positioning a deflection unit on a cathode ray tube, forces are exerted on said deflection unit. Also during transport and use of the cathode ray tube, the deflection unit is subject to forces. So far it has been assumed that, in order to withstand such forces, deflection coils must be attached to a rigid coil holder. However, the inventors have come to recognize that by securing both coil systems to each other via connecting pieces, the technique of manufacturing coils is improved to such an extent that the assembly of coils and connecting pieces can be rendered self- supporting. It will be obvious that within the scope of the invention many variations are possible.

Claims: CLAIMS; 1. A cathode ray tube comprising, in an evacuated envelope, a means for generating at least one electron beam and a display screen, said cathode ray tube being provided with a deflection unit for deflecting the electron beam(s) across the display screen, and said deflection unit comprising at least one system of saddle-shaped deflection coils, characterized in that the deflection unit comprises a first and a second system of saddle- shaped deflection coils which are interconnected via connecting pieces which are flexibly arranged with respect to each other. 2. A cathode ray tube as claimed in Claim 1, characterized in that the deflection unit comprises a coil holder, the first and the second system of deflection coils being situated on the inside and on the outside, respectively, of the coil holder, and the connecting pieces being connected to the coil holder via flexible connections. 3. A cathode ray tube as claimed in Claim 1, characterized in that the connecting pieces comprise a first and a second set of connecting pieces which are arranged along the z-axis at some distance from each other, the connection between the first and the second set being formed by the coils only. 4. A cathode ray tube comprising, in an evacuated envelope, a means for generating at least one electron beam and a display screen, said cathode ray tube being provided with a deflection unit for deflecting the electron beam(s) across the display screen, and said deflection unit comprising at least one system of saddle-shaped deflection coils, characterized in that the deflection unit comprises a deflection-coil holder and a system of saddle-shaped deflection coils which are interconnected via connecting pieces which are flexibly arranged with respect to each other. 5. A deflection unit which can suitably be used in a cathode ray tube as claimed in any one of the preceding Claims.

Inventors: GRUBBEN ANTONIUS PIERRE MARIE, MAESEN EDWARD PETER VINCENT, SIEBEN JOHANNES HENRICUS FRANC, GRUBBEN, ANTONIUS, PIERRE, MARIE, MAESEN, EDWARD, PETER, VINCENT, SIEBEN, JOHANNES, HENRICUS, FRANCISCUS, CORNELIUS
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1996
Main classification: H01J29
IPC codes: H01J29