US3899710A

US3899710A - Color cathode ray tube with temperature-responsive color purity magnets

Info

Publication number: US3899710A
Application number: US329049A
Authority: US
Inventors: Hiromasa Machida; Noboru Yamaguchi
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1972-02-03
Filing date: 1973-02-02
Publication date: 1975-08-12
Anticipated expiration: 1992-08-12
Also published as: FR2170277B1; DE2305162A1; GB1415596A; JPS5150426Y2; NL175769C; JPS4890525U; CA960742A; NL175769B; FR2170277A1; NL7301612A; IT978773B; DE2305162B2

Abstract

A color cathode ray tube arrangement wherein a temperature responsive magnetic device which comprises a permanent magnet element and a magnetic element having temperature responsive variable permeability is provided on a color cathode ray tube to compensate for beam mislanding on the color phosphor screen of the color cathode ray tube caused by thermal expansion of a beam selecting mask in the tube thereby to maintain fine color purity.

Description

United States Patent Machida et al.

COLOR CATHODE RAY TUBE WITH TENIPERATURE-RESPONSIVE COLOR PURITY MAGNETS Inventors: Hiromasa Machida, Tokyo; Noboru Yamaguchi, Yokohama, both of Japan Assignee: Sony Corporation, Tokyo, Japan Filed: Feb. 2, 1973 Appl. No.: 329,049

Foreign Application Priority Data Feb. 3, 1972 Japan 47-14377 US. Cl. 313/412; 313/437; 335/212 Int. Cl. H01J 29/07; H01] 29/51 Field of Search... 313/75; 313/79; 313/70C; 313/84[USOnly1 313/84; 335/217 References Cited UNITED STATES PATENTS 2/1961 Clay 313/84 X 1 1 Aug. 12, 1975 3,296,570 1/1967 Uetake et a1. 313/84 x 3,512,035 5/1970 Egawa Cl 21]. 313/75 x 3,573,525 4/1971 Fuse 335/217 3,623,151 11/1971 [keuchi 335 217 FOREIGN PATENTS OR APPLICATIONS 1,199,891 9/1965 Germany 313/75 Primary Examiner-Robert Segal Attorney, Agent, or Firm-Lewis H. Eslinger; Alvin Sinderbrand l 5 7 ABSTRACT A color cathode ray tube arrangement wherein a temperature responsive magnetic device which comprises a permanent magnet element and a magnetic element having temperature responsive variable permeability is provided on a color cathode ray tube to compensate for beam mislanding on the color phosphor screen of the color cathode ray tube caused by thermal expansion of a beam selecting mask in the tube thereby to maintain fine color purity.

4 Claims, 11 Drawing Figures PATENTED AUG 7 2 I975 SHEET COLOR CATHODE RAY TUBE WITH TEMPERATURE-RESPONSIVE COLOR PURITY MAGNETS BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates generally to means for avoiding beam mislanding in a color cathode ray tube having a color phosphor screen, and more particularly to means of compensating for such mislanding caused by temperature variations in the color cathode ray tube.

2. Description of the Prior Art In a conventional color cathode ray tube there is a mask which has a number of slits or small apertures therethrough to allow the electron beams to reach, or land on, only the phosphor elements that emit light of selected colors. In such tubes, heat is generated by the impingement of the electron beams on the mask. This heat causes thermal expansion or distortion of the mask with the result that the positions of the slits or apertures are shifted relative to the phosphor elements of the screen. This causes the landing positions of the electron beam on the color phosphor screen to shift, and the mislanding of the electron beams, in turn. causes deteriorations in color purity. The mislanding of the electron beam is worse near the periphery of the screen than at the center and is particularly objectionable in the case of wide angle beam scanning tubes.

Several ways have been proposed to compensate for thermally-induced electron beam mislanding. One conventional system is to hold the mask by a bimetallic support to change the position of the mask in the tube relative to the screen in response to temperature change. Another compensating system uses an auxiliary beam deflection coil in addition to the main deflection coil. The current in the auxiliary beam deflection coil is changed in response to the mask temperature to change the electron beam path in order to avoid the mislanding of the electron beams.

However. the conventional systems mentioned above have several drawbacks. They are complicated in con struction, they require a number of parts, and they are expensive.

Accordingly, an object of this invention is to provide a color cathode ray tube arrangement which maintains excellent color purity with simple correcting means for compensating for temperature-caused deterioration's in color purity.

Another object of this invention is to provide a color cathode ray tube arrangement wherein mislanding of electron beams on the screen of the color cathode ray tube caused by temperature variations in the mask and screen is compensated for by simple correcting means that may be located on the funnel portion of the tubev Still another object of this invention is to provide a color cathode ray tube arrangement in which temperature-induced mislanding of the electron beams is prevented by a temperature-responsive permanent magnetic device of simple construction.

A further object of this invention is to provide a simple color-purity correcting means comprising a temperature-responsive permanent magnetic device.

SUMMARY OF THE INVENTION According to this invention, a color cathode ray tube arrangement for compensating for electron beam mislanding comprises a temperature-responsive magnetic device. the magnetic flux density of which changes in response to temperature variation. The magnetic compensating means is located at a predetermined position between the beam deflection center of the tube and the screen in order to modify by the magnetic flux originated from the magnetic device the paths of the beams.

Various devices may be used as the temperatureresponsive magnetic device. An example of such a temperature-responsive magnetic device is a permanent magnet which will change magnetic flux originated therefrom in response to temperature changes. A preferable example is a combination of a normal permanent magnet and a temperature-responsive magnetic material whose permeability changes in response to temperature changes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of one example of a temperature-responsive magnetic device employed in a color cathode ray tube temperature compensating arrangement according to the invention.

FIG. 2 is a cross-sectional view of the device shown in FIG. 1.

FIG. 3 is a graph that shows the temperatureresponsive characteristic of the device shown in FIGS. 1 and 2.

FIGS. 4 and 5 are perspective views illustrating the color cathode ray tube temperature compensating arrangements according to the invention.

FIG. 6 is a cross'sectional view of a fragment of the color cathode ray tube arrangements depicted in FIGS. 4 and 5.

FIGS. 7 to 10, inclusive, are diagrams for explaining compensation for mislanding of electron beams by means of the invention.

FIG. 11 is a perspective view of another example of the color cathode ray tube arrangement according to the invention with a section of the tube broken away to show the interior construction thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show an embodiment of a temperature-responsive magnetic device 1 used in accordance with this invention. The device I designates generally a temperature-responsive magnetic device which consists of a permanent magnet 2 and a temperatureresponsive magnetic material 3. The permanent magnet 2 is made of, for example, Ba-ferrite containing BaCO and Fe O in the ratio of 15:85 by mol.% and may be formed as a disc magnetized along its diameter. The temperature-responsive magnetic material 3 may be made of Mn Zn-ferrite and formed as a disc having a recess bounded by an annular projection at the periphery of one surface. The disc 3 has a magnetic permeability that decreases as the temperature increases. An example of a suitable material for the disc 3 is a MnZn-ferrite composed of Fe O MnCO and ZnO combined in the ratio of 50:27:23 by mol.%. In this case, when the permanent magnet 2 is fitted to the recess in the temperature-responsive magnetic material 3, one side of the permanent magnet 2 and its periphery are covered with the magnetic material 3.

With such an arrangement, since the permeability of the magnetic material 3 is high when temperature is low, the magnetic flux that originates in the permanent magnet 2 is almost completely shunted by the magnetic material 3 with the result that the magnetic flux density of the external magnetic field produced by the magnetic device I is low. On the other hand, when the temperature becomes high, the permeability of the magnetic material 3 is reduced, with the result that the magnetic flux density of the external magnetic field of the magnetic device 1 becomes high due to the fact that the magnetic flux from the magnet 2 is less shunted by the magnetic material 3. Accordingly, it will be understood that the relationship between the temperature and the flux density of the external magnetic field from the magnetic device 1 can be made such as shown in the graph of FIG. 3 in which the ordinate represents the magnetic flux density in Gauss and the abscissa temperature in C.

It is not necessary that the permanent magnet 2 and the temperature-responsive magnetic material 3 used in the device 1 be limited to the configurations mentioned above. They can be formed, for example, with rectangular perimeters with one side of the permanent magnet and its rectangular perimeter covered by the magnetic material. Other polygonal forms may also be used.

Four temperature-responsive magnetic devices 1, each of which is constructed as mentioned above, are mounted on a color cathode ray tube 4 at the corners of its funnel portion 4F, as shown in FIG. 4. In the case of a color cathode ray tube provided with a beam selecting mask having a number of vertical slits and a phosphor screen in which respective sets of color phosphor strips extended in the vertical direction are arranged successively along the horizontal beam scanning direction, a shift of the landing position of the electron beams in the horizontal scanning direction, namely in the left and right direction, becomes a problem that must be corrected. Accordingly, it may be possible in such a case that further temperature-responsive magnetic devices similar to the device 1 in FIG. 1 be mounted on the tube at the mid-portion of the right and left peripheral sides of the funnel portion 4F, respectively, in addition to those mounted at the corners thereof, as shown in FIG. 5. Further, it may be possible in a color cathode ray tube with a shadow mask that additional temperature-responsive magnetic devices similar to the devices I be mounted on the tube at the midportion of the upper and lower peripheral portions of the funnel portion 4F thereof at the positions 1 as indicated in FIG. 5 in broken lines.

It is preferred that the respective temperatureresponsive magnetic devices 1 be mounted on the tube 4 in such a manner that the side surface of each permanent magnet 2 which is not covered with the temperature-responsive magnetic material 3 faces away from the tube, as shown in FIG. 6.

FIGS. 7 and 8 illustrate how mislanding of electron beams may be prevented by mounting the temperature responsive magnetic device I in the manner described above. In the case where the magnetic device 1 has the characteristic such as is shown in FIG. 3 and is mounted on the funnel portion 4F of the tube 4 in a manner to make the magnetized direction of the permanent magnet 2 perpendicular to the plane of the sheet of FIG. 7, the magnetic field H+ produced by the permanent magnet 2 will be directed into the plane of the drawing in the tube 4, as indicated by the X within the circle. With such an arrangement, if there is no magnetic flux, an electron beam 5 deflected by a deflection coil (not shown) follows the path shown by the solid line in FIG. 7, while if there is a magnetic field H+ produced by the device I, the electron beam 5 is subjected to a force designated by an arrow F+ and is deflected to the path shown by the broken line.

It is assumed that a typical vertical slit or aperture 6a of the beam selecting mask is positioned as shown in FIG. 8 at room temperature. An electron beam having passed through a virtual deflection center 7 on the tube axis 8 follows along a path shown by the solid line 50 through the aperture 6a. When the temperature increases, the position of the aperture is shifted to the position 6b. In order to pass through the aperture in this new location, the electron beam follows a path shown by the solid line 5b in FIG. 8. When the magnetic device is mounted on the tube 4, the electron beam is deflected a little as shown by the broken line 5A at room temperature because the magnetic field I-I+ produced by the magnetic device 1 is weak at room temperature as described above. On the other hand, the magnetic field I-I-lincreases as the temperature increases, so that the electron beam is deflected more, as shown by the broken line 58. As a result, the electron beam lands at substantially the same position on the phosphor screen 9 irrespective of temperature changes that cause thermal expansion or distortion of the beam selecting mask. It will be easily realized that the electron beams directed along other paths will also land on respective constant positions on the screen.

It is also possible to use a temperature-responsive magnetic material having a different characteristic such that, as the temperature increases, the permeability also increases. If the material having such a characteristic is employed as the magnetic material 3, the temperature-responsive magnetic device 1 has a relationship between the magnetic flux density and temperature that is the reverse of that shown in FIG. 3. That is to say, as the temperature goes down, the magnetic flux density of the external magnetic field from the magnetic device 1 increases, while as the temperature rises, the magnetic flux density decreases. Mislanding of electron beams can also be prevented by the use of such a temperature-responsive magnetic device I. With reference to FIGS. 9 and 10, such a case will now be described.

In FIG. 9 the temperature-responsive magnetic device 1 is mounted on the tube 4 in such a manner that the magnetic field I-I- from the magnetic device I passes through the tube 4 in the direction into the plane of the drawing. This is opposite to the direction of the flux H+ in FIG. 7. With such an arrangement the electron beam 5 is subjected to the force shown by an arrow F- by the magnetic field H- and hence is deflected as shown by the broken line in FIG. 9. Accordingly, as shown in FIG. 10, the electron beam having passed through the virtual deflection center 7 on the tube axis 8, is deflected more at room temperature, as shown by the broken line 5A, since the magnetic field H- is greatest when the tube structure is at room temperature. On the other hand, since the magnetic field H- decreases as the temperature increases, the electron beam is deflected less as shown by the broken line 5B in FIG. 10. Accordingly, it will be understood that in this case the landing position of the electron beam 5 on the phosphor screen 9 of the tube 4 is kept constant irrespective of thermal expansion or distortion of the beam selecting mask due to temperature variations.

It will be also realized that the electron beams travelling along the other paths land on the phosphor screen at respective constant positions as in the above case without illustrating them.

The temperature responsive magnetic device 1 is not restricted to being mounted on the funnel portion 4F of the tube 4, but it may be mounted on a holder of the deflection coil or a frame for the beam selecting mask 6 inside the tube 4 with the same effect mentioned above. In the case of mounting the device 1 on the frame 10, variation in temperature of the beam selecting mask 6 can be directly detected by the magnetic device I.

With the color cathode ray tube arrangement of this invention described as above, mislanding of electron beams caused by thermal expansion of distortion of the beam selecting mask can be avoided to maintain excellent color purity.

We claim as our invention:

1. A color cathode ray tube arrangement comprising:

A. a color cathode ray tube comprising:

l. a color phosphor screen comprising areas arranged in a predetermined pattern to emit light of different colors when struck by electrons,

2. electron beam generating means to direct electron beams at said screen, and

3. a beam selecting element disposed near said screen comprising electron passages positioned relative to said areas to allow said electron beams to land on predetermined areas of said screen according to the directions along which said beams pass through said passages; and

B. temperature responsive magnetic means provided on said tube for compensating for mislanding of said electron beams on incorrect ones of said areas of said screen due to thermal expansion of said beam selecting element resulting in displacement of at least some of said passages relative to their respective areas of said screen, said temperature responsive magnetic means comprising:

1. a permanent magnet, and

2. a magnetic shunt element having temperature responsive variable permeability, said magnetic shunt element forming a path for at least a part of the magnetic flux originating in said permanent magnet and being located on said tube to be heated by heat from said beam selecting element to change the intensity of magnetic flux from said magnetic means with temperature variations in said tube to cause the path of said electron beams landing on the screen to change in response to said thermal expansion of the beam selecting element thereby to maintain excellent color purity of light emitted by said screen, said magnetic element being formed into a block-like shape having a recess on one surface, and said permanent magnet being placed in said recess.

2. A color cathode ray tube arrangement according to claim 1, wherein said magnetic element is formed into a disc shape having a pair of opposite flat surfaces one of which is provided with said recess therein and said permanent magnet is also formed into a disc shape having a pair of opposite flat surfaces and placed in said recess with one of said flat surfaces of said magnet exposed to the outside.

3. A color cathode ray tube arrangement according to claim 1, wherein said tube comprises a funnel portion and said temperature responsive magnetic means is attached to the outer surface of said funnel portion.

4. A color cathode ray tube arrangement according to claim 1, wherein said temperature responsive magnetic means is attached to said beam selecting element in said tube.

Claims

1. A color cathode ray tube arrangement comprising: A. a color cathode ray tube comprising: 1. a color phosphor screen comprising areas arranged in a predetermined pattern to emit light of different colors when struck by electrons, 2. electron beam generating means to direct electron beams at said screen, and 3. a beam selecting element disposed near said screen comprising electron passages positioned relative to said areas to allow said eLectron beams to land on predetermined areas of said screen according to the directions along which said beams pass through said passages; and B. temperature responsive magnetic means provided on said tube for compensating for mislanding of said electron beams on incorrect ones of said areas of said screen due to thermal expansion of said beam selecting element resulting in displacement of at least some of said passages relative to their respective areas of said screen, said temperature responsive magnetic means comprising: 1. a permanent magnet, and 2. a magnetic shunt element having temperature responsive variable permeability, said magnetic shunt element forming a path for at least a part of the magnetic flux originating in said permanent magnet and being located on said tube to be heated by heat from said beam selecting element to change the intensity of magnetic flux from said magnetic means with temperature variations in said tube to cause the path of said electron beams landing on the screen to change in response to said thermal expansion of the beam selecting element thereby to maintain excellent color purity of light emitted by said screen, said magnetic element being formed into a block-like shape having a recess on one surface, and said permanent magnet being placed in said recess.

2. electron beam generating means to direct electron beams at said screen, and

3. a beam selecting element disposed near said screen comprising electron passages positioned relative to said areas to allow said eLectron beams to land on predetermined areas of said screen according to the directions along which said beams pass through said passages; and B. temperature responsive magnetic means provided on said tube for compensating for mislanding of said electron beams on incorrect ones of said areas of said screen due to thermal expansion of said beam selecting element resulting in displacement of at least some of said passages relative to their respective areas of said screen, said temperature responsive magnetic means comprising: