US3573525A

US3573525A - Color purity temperature compensation system for a color picture tube

Info

Publication number: US3573525A
Application number: US888340A
Authority: US
Inventors: Yuzo Fuse
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1967-11-21
Filing date: 1969-12-29
Publication date: 1971-04-06
Anticipated expiration: 1988-04-06
Also published as: FR2027278A1; GB1246199A; NL6919419A; DE1965291B2; NL169119C; FR1598193A; DE1965291A1; NL169119B; DE1965291C3; GB1246109A

Abstract

In a color picture tube having an apertured beam selecting grill or mask through which one or more electron beams are made to land on predetermined color phosphors applied to the face plate of the tube, thermal expansion of the grill or mask is compensated for, so as to avoid mislanding of the beam or beams, by providing an auxiliary magnetic deflection means in back of the main magnetic deflection or scanning means and operative in dependence on the operation of the main deflection means to produce magnetic flux in opposition thereto and including a core having a magnetic permeability that decreases with increasing temperature so as to similarly decrease the magnetic flux opposing that of the main deflection means, whereby the effective center of deflection of the beam or beams is shifted rearwardly in response to increasing temperature.

Description

United States Patent Inventor Yuzo Fuse Tokyo, Japan Appl. No. 888,340 Filed Dec. 29, 1969 Patented Apr. 6, 1971 Assignee Sony Corporation Tokyo, Japan Priority Dec. 28, 1968 Japan COLOR PURITY TEMPERATURE COMPENSATION SYSTEM FOR A COLOR PICTURE TUBE 6 Claims, 9 Drawing Figs.

US. Cl 313/75,

Int. Cl H01 j 29/70 Field of Search 313/75, 76,

[56] References Cited UNITED STATES PATENTS 3,408,520 10/1968 Lindeman 313/75 3,524,093 8/1970 Burdick et a1. 313/75 Primary Examiner-G. Harris Attorneys-Lewis I-I. Eslinger, Alvin Sinderbrand and Curtis,

Morris & Safford ABSTRACT: In a color picture tube having an apertured beam selecting grill or mask through which one or more electron beams are made to land on predetermined color phosphors-applied to the face plate of the tube, thermal expansion of the grill or mask is compensated for, so asto avoid mislanding of the beam or beams, by providing an auxiliary magnetic deflection means in back of the main magnetic deflection or scanning means and operative in dependence on the operation of the main deflection means to produce magnetic flux in opposition thereto and including a core having a magnetic permeability that decreases with increasing temperature so as to similarly decrease the magnetic flux opposing that of the main deflection means, whereby the effective center of deflection of the beam or beams is shifted rearwardly in response to increasing temperature.

Patented April 5, 1971 3,573,525

2 Sheets-Sheet 1 ATTORNEY 2 Sheets-Sheet 2 FIG. 4.

l w 1 F Patented April 6, 1971 FIG. 5.

FIG.

YUZO FUSE ATTORNEY COLOR PURITY TEMPERATURE COMPENSATION SYSTEM FOR A COLOR PICTURE TUBE This invention relates generally to color picture tubes, and more particularly is directed to compensating for the mislanding of the electron beam or beams that may result from temperature variations in the tube.

A color picture tube generally includes an electron beam selecting device, such as, apertured mask, grill or grid, disposed within the tube adjacent the screen of color phosphors applied to the face plate of the tube and by which each beam is made to land on a predetermined color phosphor in dependence on the angle of incidence of the beam with respect to the beam selecting device when passing through an aperture of the latter. During operation of the color picture tube, the impingement of the electron beam or beams on the beam selecting device increase the temperature of the latter and thereby effects thermal expansion of the latter. Such thermal expansion changes the positions or alignments of the apertures of the beam selecting device in relation to the respective sets or arrays of color phosphors of the screen, and the change in alignment increases progressively from the center of the beam selecting device toward the periphery of the latter. The change in positions or alignement of the apertures relative to the respective sets or arrays of color phosphors results in mislanding of the beams, that is, in the impingement of the beams on other than the respective color phosphors of the screen, and this causes deterioration of the color purity of the resultant picture on'the screen.

In order to avoid the described mislanding of the beams resulting from thermal expansion of the beam selecting device, it has been proposed to reduce the distance from the beam selecting device to the screen as the temperature of the beam selecting device increases. However, mounting the beam selecting device for temperature responsive movement relative to the screen requires the use of complicated structures for supporting the beam selecting device and such struc tures have reduced resistance to shocks or impacts.

Another previously proposed arrangement for avoiding the described mislanding of the beams resulting from variations in the temperature within the tube, includes an auxiliary deflection coil mounted on the neck of the tube, for example, adjacent the main deflection yoke by which the beam or beams are horizontally and vertically deflected so as to scan the screen, and a circuit by which a deflection current is made to flow through the auxiliary deflection coil and is varied in response to changes in the temperature of the beam selecting device. Such variation of the deflection current is selected so that the magnetic field produced by the auxiliary deflection coil serves to shift the effective center of beam deflection in response to temperature changes and thereby maintains proper landing of the beams on the respective .color phosphors. However, such proposed arrangement does not provide sufficient compensation for fully and reliably avoiding the described mislanding, and the circuit required for varying deflection current in response to changes of temperature is complex and costly. Further, the proposed compensating arrangement adversely affects the linearity characteristic of the beam deflection die to the additional circuit elements required to provide the variable deflection current.

Accordingly, it is an object of this invention to provide a relatively simple and reliable arrangement by which the effective center of beam deflection in a color picture tube is shifted in response to temperature variations in the tube so as to effectively compensate for the mislanding of the beam or beams that would otherwise result from the thermal expansion or distortion of the beam selecting device.

Another object is to provide a compensating arrangement, as aforesaid, which is operable by the current supplied to the main deflection yoke of the tube for effecting the horizontal, or the horizontal and vertical deflections of the beam or beams, without adversely affecting the linearity characteristic of such deflections.

In accordance with an aspect of this invention, a color picture tube is provided with an auxiliary magnetic deflections means disposed in back of the main deflection yoke and being operative in dependence on the operation of the main deflection yoke to produce magnetic flux in opposition to the magnetic flux provided by the latter, with such auxiliary magnetic deflection means including a core having a permeability that decreases with increasing temperature so as to similarly decrease the magnetic flux acting in opposition to the magnetic flux produced by the main deflection yoke, whereby the effective center of deflection of the beam or beams by the combined effects of the main deflection yoke and the auxiliary deflection means is shifted rearwardly in accordance with increasing temperature to compensate for thermal expansion of the beam selecting device.

More particularly, in a compensating arrangement according to this invention, the auxiliary magnetic deflection means includes a coil or coils wound on the core of varying permeability and connected with the corresponding coil or coils of the main deflection yoke so as to receive deflecting currents flowing through the latter and thereby produce the magnetic flux in opposition to that of the main deflection yoke.

The above, and other objects, features and advantages of this invention, will be apparent in the following detailed description of illustrative embodiments thereof which is to be read in connection with the accompanying drawings, wherein:

FIG. 1A is a schematic, axial sectional view of a color picture tube to which reference will be made in explaining the mislanding of an electron beam that may result from thermal changes within the tube;

FIG. 1B is an enlarged detail view of a portion of the structure shown in FIG. 1A, and to which particular reference will be made in explaining the compensation effected according to this invention;

FIG. 2 is a schematic elevational view of a color picture tube embodying this invention and as viewed from the top thereof;

FIG. 3 is a front elevational view of an auxiliary deflection device provided on the tube of FIG. 2 in accordance with this invention;

FIG. 4 is a graph showing the variation of permeability with temperature of a core included in the auxiliary deflection device of FIG. 3;

FIG. 5 is a schematic wiring diagram illustrating the manner in which the coil of the auxiliary deflection device of FIG. 3 is connected with a coil of the main deflection yoke of the color picture tube;

Fig. 6 is a schematic view illustrating the magnetic flux produced by the auxiliary deflection device of FIG. 3 at an elevated temperature;

FIG. 7 is a view similar to that of FIG. 6, but showing the flux distribution at a low temperature; and

FIG. 8 is a view similar to that of FIG. 3, but illustrating another embodiment of this invention.

Referring to the drawings in detail and initially to FIG. 1A thereof, it will be seen that a color picture tube 1, as there illustrated, has a phosphor screen 2 formed on the inner surface of its face plate and an apertured beam selecting device 3, for example, in the form of a shadow mask or aperture grill or grid suitably supported within the the tube and spaced rearwardly from the phosphor screen 2. As is well known and particularly shown on FIG. 1B, the phosphor screen 2 is made up of sets or arrays of primary color phosphors, as indicated at R, G and B, and the purpose of the beam selecting device 3 is to determine which of the color phosphors a particular electron beam lands upon in dependence on the angle of incidence of the beam with respect to device 3 at an aperture 4 of the latter through which the beam passes prior to impinging against the corresponding set or array of color phosphors. It will be understood that the beam selecting device 3 is heated by the impingement of the electron beam or beams thereon during scanning of the screen, and such heating of the beam selecting device causes its thermal expansion, for example, from the conditions shown in full lines of FIGS. 1A and 18 to the condition shown in broken lines at 3, where the beam selecting device is spaced rearwardly from its normal or actual position merely for convenience of illustration. It will be seen that the thermal expansion of the device 3 to the condition indicated at 3' results in the displacement of the apertures 4 away from the central axis x-x of the tube, and that the extent of such displacement of the apertures increases progressively towards the periphery of the screen 2 and the beam selecting device. Thus, for example, with respect to the aperture 4 a, the heating of the beam selecting device 3 will effect the displacement of such aperture away from the tube axis to the position indicated at 4'11.

Assuming that an electron beam B is deflected about the effective center 0, as by the usual main deflection yoke 6 provided on the color picture tube 1, so as to follow the path 5 through the aperture 40 of beam selecting device 3 and to land on the corresponding color phosphor G, of the array or set A when the beam selecting device 3 is at a relatively low temperature, it will be apparent that, in response to heating and the resulting thermal expansion of the beam selecting device, the electron beam B will be in the position 5 when it passes through the displaced aperture 4'a and thus will no longer land on the corresponding color phosphor G, but rather will misland on the color phosphor R with resulting deterioration of the color purity of the picture.

However, if the effective center of deflection of the beam B is shifted from the position on FIG. 1A in the rearward direction, that is, away from the screen 2 or beam selecting device 3, for example, to the position 0', the beam, when deflected to the position will pass through aperture 4'1 of the thermally expanded beam selecting device 3' and again land on the corresponding color phosphor G,, of the respective phosphor set A, whereby to compensate for the thermal expansion of the beam expansion of the beam selecting device and to avoid deterioration of the color purity of the picture. Thus, mislanding of the electron beam or beams can be avoided by suitably shifting the effective center of deflection of each electron beam in response to temperature changes within the tube.

In accordance with the present invention, particularly as illustrated on FIG. 2, a color picture tube 1 having an electron gun 7 directing three beams B B and B toward color screen 2 and causing such beams to converge at a common aperture of the beam selecting device 3 is provided with an auxiliary magnetic deflection device 8 in addition to the usual main deflection yoke 6 by which the three beams are deflected horizontally and vertically so as to scan the screen. When the color phosphors of screen 2 are applied in the form of vertical stripes and beam selecting device 3 is constituted by an aperture grill having vertical slits therein corresponding to the respective sets or arrays of color phosphor stripes, then the auxiliary deflection device 8 according to this invention need provide mislanding compensation only with respect to the horizontal deflections of the beams.

As shown on FIG. 2, the auxiliary deflection device 8 is mounted on the neck of tube I at the side of main deflection yoke 6 remote from screen 2, that is, in back of yoke 6, and comprises an annular magnetic core 10 and a coil 11 made up of two coil portions Ila and 11b (FIG. 3) which are electrically connected, for example, in series, and wound on opposed side portions of core 10 so that, in response to a current flow through coil 11, there is produced a magnetic flux, as indicated at F on FIG. 6, to effect horizontal deflection of the beams B B and B,,. As indicated on FIG. 5, the coil 11 of device 8 is connected, for example, in series, with the horizontal deflection coil 6H of the main deflection yoke 6 so that, when a horizontal deflection current is supplied to coil 6H by way of terminals 9a and 9b to effect horizontal scanning deflection of the beams, such current will also flow in coil II to produce the magnetic flux F in opposition to the magnetic flux produced by the current flowing in the coil 6H.

III

In accordance with this invention, the core 10 of auxiliary deflection device 8 is formed of a magnetic material having a permeability that varies in response to temperature changes, and more particularly having a permeability that decreased with increasing temperature. Such magnetic material having a permeability varying in accordance with temperature may be an alloy composed of 70 percent iron and 30 percent nickel having the temperature-permeability characteristic illustrated on FIG. 4. Thus, when core 10 is substantially at room temperature, it has a relatively high permeability 11., and, as the core 10 is progressively heated, its permeability is progressively reduced until it is lowered to the value t, at the critical temperature T which value of permeability corresponds to that of a vacuum.

Although the auxiliary deflection device 8 is mounted on the neck of tube 1, for example, adjacent to the main deflection yoke 6, as shown, it has been found that, during operation of the color picture tube, the rise in temperature of the core 10 will be a function of, or correspond to the rise of temperature of the beam selecting device 3.

When the operation of tube I is initiated, that is, when core 10 is relatively cool and has a high permeability, the magnetic flux F produced by coil 11 in response to the horizontal deflection current flowing therethrough will be substantially concentrated within the neck of tube 1 (FIG. 7) to oppose the magnetic flux resulting from the flow of the same current through main coil 6H. Since device 8 is disposed in back of yoke 6, that is, at the side of yoke 6 remote from screen 2, the magnetic flux F of coil 11 will more or less counteract the magnetic flux of coil 6H at the back end portion of yoke 6 in that the effective center of deflection of the beams will be at a relatively forward position, for example, at the position 0 on FIG. 1A, whereby proper landing of the beams on the respective color phosphors will be obtained with the beam selecting device at a relatively low temperature. As the operation of the color picture tube continues with consequent heating and thermal expansion of beam selecting device 3 and corresponding heating of core 10, the permeability of the core is reduced to diminish the concentration of the magnetic flux F which acts within the tube neck on the beams B B and B (FIG. 6). Thus, as the permeability of core 10 is progressively decreased, the efi'ect of magnetic flux F in opposition to the magnetic flux produced by coil 6H at the back end portion of yoke 6 is also progressively decreased so that the effective center of deflection of the beams is moved rearwardly, for example, to the position 0 on FIG. 1A. Finally, at the temperature T,,, the core 10 has its permeability reduced to the value t, so that the core is then without any magnetic effect and the flux of coil 11 is diffused.

It will be understood that the number of windings or turns in the coil 11 is relatively small as compared with that of coil 6H, and is selected so as to be sufficient only to provide, in association with the core 10, the displacement of the center of deflection of the beams for achieving the described compensation. Although the inductance of the auxiliary deflection device 8 may vary with changes in temperature, the number of windings of coil 11 is sufficiently small, as compared with the number of windings in coil 6H, so that the effect of the varied inductance on the horizontal deflection current can be neglected. Thus, in accordance with the present invention it is not intended to seek to compensate for mislanding by varying the deflection current itself, for example, by varying the inductance of the circuit for the deflection current in response to temperature changes.

When the color picture tube has a shadow mask as its beam selecting device and the color phosphors are applied in sets or arrays of dots, then it is necessary to compensate for temperature induced mislanding in the vertical as well as the horizontal directions. As shown on FIG. 8, when the beam selecting device 3 is a shadow mask and the screen 2 has its color phosphors in the form of dots, the auxiliary deflection device IOHHK mu e...

111;, a second coil 12 wound in portions 12a and 12b on the top and bottom portions of core 10.

The coil portions 120 and 12b are connected to each other, as shown, and also connected with the vertical deflection coil (not shown) of yoke 6 so that, when the vertical deflection current flows in the vertical deflection coil of yoke 6, such current also flows through coil 12 to cause the latter to produce a magnetic flux which is more or less concentrated to act on the beams in dependence or the permeability of core 10. Such flux produced by coil 12 acts similarly to the described action of the flux of coil 11 to achieve the desired compensation with respect to the vertical deflection of the beams.

Although illustrative embodiments of the invention have been described in detail herein with reference to the drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein without departing from the scope or spirit of the invention.

lclaim:

1. In a color picture tube including an envelope having a faceplate, a screen of phosphors coated on said faceplate for emitting light of respective predetermined colors, an electron gun device for generating at least one electron beam directed toward said faceplate, apertured beam selecting means disposed adjacent said faceplate to land said beam on selected phosphors of said screen in accordance with the angle of incidence of said beam to said beam selecting means at the apertures of the latter, and main magnetic deflection means for deflecting said beam so as to cause scanning of said screen; the improvement comprising auxiliary magnetic deflection means disposed at the side of said main deflection means remote from said screen and being operative in dependence on the operation of said main magnetic deflection means to produce magnetic flux in opposition thereto, said auxiliary magnetic deflection means including a core having a permeability that decreases with increasing temperature so as to similarly decrease said magnetic flux in opposition to the magnetic flux produced by said main magnetic deflection means, whereby the effective center of deflection of said beam by the combined effects of said main and auxiliary magnetic deflection means is shifted in the direction away from said screen in accordance with increasing temperature to compensate for thermal expansion of said beam selecting means.

2. A color picture tube according to claim 1, in which said main deflection means include coil mans to produce magnetic flux for deflecting said beam upon a current flow therethrough, and said auxiliary deflection means includes additional coil means wound on said core and electrically connected with said coil means of the main deflection means to produce said magnetic flux in opposition to the flux of said main deflection means in response to said current flow.

3. A color picture tube according to claim 2, in which said auxiliary deflection means is disposed adjacent to said main deflection means.

4. A color picture tube according to claim 2, in which said coil means of the main deflection means includes horizontal and vertical deflection coils to produce magnetic flux for deflecting said beam horizontally and vertically, respectively, said additional coil means is connected electrically with said horizontal deflection coil and is arranged to deflect said beam horizontally in opposition to the horizontal deflection of said beam resulting from said current flow through said horizontal coil, said phosphors are in the form of vertical stripes on said faceplate, and said apertures of the beam selecting means are in the fonn of vertical slits.

5. A color picture tube according to claim 2, in which said coil means of the main deflection means includes main horizontal and vertical deflection coils to produce magnetic flux for deflecting said beam horizontally and vertically, respectively, and said additional coil means includes auxiliary horizontal and vertical deflection coils electrically connected with said main horizontal and vertical deflection coils, res ectrvely, and being arranged to deflect sard beam horizon ally and vertically in opposition to the horizontal and vertical deflections of the beam resulting from current flows through said main horizontal and vertical deflection coils, respectively. 6. A color picture tube according to claim 2, in which said core is in the form of a ring disposed on the neck of said tube.

Claims

4. A color picture tube according to claim 2, in which said coil means of the main deflection means includes horizontal and vertical deflection coils to produce magnetic flux for deflecting said beam horizontally and vertically, respectively, said additional coil means is connected electrically with said horizontal deflection coil and is arranged to deflect said beam horizontally in opposition to the horizontal deflection of said beam resulting from said current flow through said horizontal coil, said phosphors are in the form of vertical stripes on said faceplate, and said apertures of the beam selecting means are in the form of vertical slits.

5. A color picture tube according to claim 2, in which said coil means of the main deflection means includes main horizontal and vertical deflection coils to produce magnetic flux for deflecting said beam horizontally and vertically, respectively, and said additional coil means includes auxiliary horizontal and vertical deflection coils electrically connected with said main horizontal and vertical deflection coils, respectively, and being arranged to deflect said beam horizontally and vertically in opposition to the horizontal and vertical deflections of the beam resulting from current flows through said main horizontal and vertical deflection coils, respectively.

6. A color picture tube according to claim 2, in which said core is in the form of a ring disposed on the neck of said tube.