US3706909A

US3706909A - Cathode ray tube with mutually intersecting focusing coils

Info

Publication number: US3706909A
Application number: US83507A
Authority: US
Inventors: Asahide Tsuneta; Norio Harao
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1969-10-28
Filing date: 1970-10-23
Publication date: 1972-12-19
Anticipated expiration: 1989-12-19
Also published as: DE2052958C3; DE2052958A1; JPS50180B1; DE2052958B2

Abstract

A cathode ray tube comprising an envelope, a target disposed at the front of the envelope, an electron gun emitting electron beams toward the target, a deflecting coil and a focusing device comprised of a pair of mutually intersecting focusing coils positioned between the target and deflecting coil, the focusing device providing an electromagnetic field acting in the same direction as that in which the electron beams are deflected so as to focus them.

Description

ilnited States Patent 'isuneta ct a1.

[ 1 Dec. 19, 1972 CATHODE RAY TUBE WITH MUTUALLY INTERSECTING FOCUSING COILS Inventors: Asahide Tsuneta, Kawasaki; Norio Han-a0, Yokohama, both of Japan Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi, Japan Filed: on. 23, 1970 Appl. No: 83,507

Assignee:

Foreign Application Priority Data Oct. 28, 1969 Japan ..44/85716 [1.8. Ci. ..315/27 G11), 313/84, 313/92 LF, 315/31 R Int. Cl ..H0lj 29/66 Field of Search ..315/31 R, 27, 31 TV, 22; 313/84, 92 LF [56] References Cited UNITED STATES PATENTS 3,084,276 4/1963 Severin ..315/27 R 3,449,621 6/1969 Himmelbauer et al ..315/27 R X 3,585,432 6/1971 Oberg ..313/92 LF 2,898,509 8/1959 Clay et al 315/27 R X 3,316,433 4/1967 Reiches et al ..315/27 XY Primary Examiner-Carl D. Quarforth Assistant Examiner-E. E. Lehmann Attorney-Flynn & Frishauf [57 ABSTRACT A cathode ray tube comprising an envelope, a target disposed at the front of the envelope, an electron gun emitting electron beams toward the target, a deflecting coil and a focusing device comprised of a pair of mutually intersecting focusing coils positioned between the target and deflecting coil, the focusing device providing an electromagnetic field acting in the same direction as that in which the electron beams are deflected so as to focus them.

5 Claims, 5 Drawing Figures PATENTED use 19 I972 SHEET 1 [1F 2 FIG.

PRIOR ART PATENTED DEC 1 9 i972 SHEET 2 UF 2 FIG. 3

FIG. 4

TiME

FlG. 5

EATIIODE RAY TUBE WITH MUTUALLY TNTERSECTING FOCUSING COILS BACKGROUND OF THE INVENTION The present invention relates to a cathode ray tube. In the conventional optical fiber type cathode ray tube, for example, the envelope 11 assumes a funnel shape having a conical portion 12 and a neck portion 13. At the end of the conical portion 12 of the envelope 11 is positioned a target 16 having a fluorescent layer formed on one side of its fiber plate 14 with said fluorescent layer turned inside. In the neck portion is received an electron gun 17 which consists of a cathode electrode 18, first and

second grid electrodes

19 and 20 coaxially arranged in turn therefrom toward the target 16 and an anode electrode 21. Electron beams 22 emitted from the cathode electrode 18 of the electron gun 17 pass through the opening of the first grid electrode 19, are focused at a crossover point 23 by an electron lens system disposed between the first and

second grid electrodes

19 and 20 and then scattered toward the target 16. The scattered electron beams 22 are again focused on the fluorescent surface 15 by a focusing coil 24 placed on the outer periphery of the neck portion ahead of the electron gun 17. Before reaching the fluorescent surface 15, the electron beams 22 are deflected by a deflecting coil 25 so as to scan the fluorescent surface 15 in one dimension.

With a cathode ray tube of such construction, the diameter S of the spot of electron beams 22 on the fluorescent surface 15 may be expressed by the following equation:

(Ql I o where:

P distance from the crossover point of electron beams to the air gap center of the focusing coil 24 Q distance from the air gap center of the focusing coil to the fluorescent layer 15 of the target 16 S diameter of the electron beam spot at the crossover point 23. Generally, the cathode ray tube is demanded to have a high degree of resolution. To this end, the spot should have as small a diameter S as possible. Though it is only required to reduce S in order to decrease S, the reduction of S is subject to limitation from the standpoint of preserving the properties of the cathode ray tube. A]- ternatively, therefore, there is adopted the process of limiting S to a certain value and instead increase P However, this generally results in an extremely elongated cathode ray tube.

SUMMARY OF THE INVENTION The object of the present invention is to provide a cathode ray tube which is decreased in its entire length without lowering its resolution. According to one aspect of the invention, there is provided a cathode ray tube wherein there is disposed between the target and deflecting coil a dynamic focusing device comprising a pair of mutually intersecting focusing coils and there is introduced through said focusing device current of saw tooth wave having the'same frequency as that of the current supplied to the deflecting coil to generate an electromagnetic field acting in the same direction as that in which there are deflected electron beams, thereby reducing the spot of electron beams.

BRIEF EXPLANATION OF THE DRAWINGS FIG. 1 is a sectional view of the conventional cathode ray tube;

FIG. 2 is a perspective view of a cathode ray tube according to an embodiment of the present invention;

FIG. 3 is a sectional view of FIG. 2;

FIG. 4 illustrates the wave form of current flowing through the dynamic focusing coil included in FIG. 2; and

FIG. 5 is a vectorial chart showing the direction of an electromagnetic field generated in the dynamic focusing device.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 2 and 3, the envelope 30 assumes a funnel shape and consists of a conical or front portion 31 and neck or rear portion 32. At the front part of the conical portion 31 of the envelope 30 is disposed a target 33, which is formed of a fiber plate 34 prepared from a large number of optical fibers arranged in the same direction and a fluorescent layer 35 formed on the inside of said plate 34. Said fluorescent layer 35 has a metal backing 35a mounted on the inside. In the neck portion 32 is received an electron gun 36, which comprises a cathode electrode 38 for emitting electron beams 37 toward the target 16 and first, second grid and

anode electrodes

39, 40 and 41 arranged in turn toward the target 16 coaxially with the cathode electrode 38. On the inner wall of the conical portion 31 is deposited a metal coating 31a as a final anode. On the outer periphery of the cathode ray tube near the boundary between the conical portion 31 and neck portion 32 is provided a deflecting coil 42 for deflecting electron beams 37 through an angle 0. At that part of the outer periphery of the conical portion 31 which is defined between the deflecting coil 42 and target 33 is set a dynamic focusing device 43, which consists of a pair of focusing

coils

44 and 45 intersecting each other at the same angle 6 as that through which there are deflected electron beams 37. The axis L-L of the focusing coil 44 intersects at right angles the electron beams 370 which are deflected toward the left side of the fluorescent layer 35 to generate an electromagnetic field acting in the same direction as that in which the electron beams 37a travel. 0n the other hand, the axis R-R of the focusing coil 45 intersects at right angles the electron beams 37b deflected to the right side of the fluorescent layer 35 to generate an electromagnetic field which acts in the same direction as that in which the electron beams 37b are conducted (FIG. 3). Through the focusing

coils

44 and 45 of the dynamic focusing device 42 is introduced current of saw tooth wave having the same frequency as that of the current flowing through the deflecting coil 42. Through the focusing coil 44 runs current 46 of saw tooth wave shown in solid line in FIG. 4, and through the focusing coil 45 flows current 47 having the same polarity as the current 46 and a saw tooth wave symmetrical with that of the current 46 as indicated in broken line in FIG. 4, these two currents being introduced synchronizingly with the electron beam deflecting current. When electron beams 37 are deflected to the left side of the fluorescent layer 35, that is, assume the position of 37a, the focusing coil 44 is supplied with maximum saw tooth current 46 indicated at point tl in FIG. 4. In the focusing coil 45, the saw tooth current 47 has zero value, that is, no current flows therethrough. Under such condition, there is only generated an electromagnetic field in the focusing coil 44. Said electromagnetic field is produced, as indicated by the arrow 48 of FIG. A, in the same direction as that in which the electron beams 37a are deflected. When the electron beams are brought to the center of the deflection range, the

focus ing coils

44 and 45 receive current of an equal magnitude shown in FIG. 4, thereby creating electromagnetic fields acting in the directions denoted by the

arrows

49 and 50 of FIG. 58 respectively. The resulting composite electromagnetic field is generated, as indicated by the arrow 51, in the same direction as that in which the electron beams 37 are deflected toward the center of the deflection range. Conversely where the electron beams 37 are deflected to the right side of the fluorescent layer 35, that is, assume the position of 37b, there flows no current through the focusing coil 44 as indicated at point tr in FIG. 4, whereas the focusing coil 45 is supplied with maximum saw tooth current 47. In the focusing coil 45 alone, therefore, is produced an electromagnetic field acting in the same direction indicated by the arrow 52 of FIG. 5C as that in which the electron beams 37b are deflected.

The foregoing description relates to the cases where the electron beams 37 are deflected to the left, right and center of the fluorescent layer 35. Even where the electron beams 37 are deflected in other directions, the aforementioned dynamic focusing device 43 always generates a composite electromagnetic field acting in the same direction as that in which said electron beams 37 are deflected.

Thus the electron beams 37 emitted from the cathode electrode 38 pass through the opening of the first grid electrode 39, are temporarily focused at crossover point 53, scattered, deflected by the deflecting coil 42, again focused by the dynamic focusing device 43 and finally impinge on the fluorescent layer 35. Thus the electron beams 37 linearly scan the fluorescent layer 35 in one dimension. The distance Q between the target 33 and the intersection of the paired focusing

coils

44 and 45 of the dynamic focusing device 43 is far shorter than the distance Q between the target to of the conventional cathode ray tube and focusing coil 23. The shortened Q realizes a prominent elevation of resolution. Further based on the same degree of resolution as in the prior art, the distance P between the crossover point 53 and the intersection of the paired focusing

coils

44 and 45 of the dynamic focusing device 43 is also shortened in proportion to Q to reduce the entire length of a cathode ray tube.

In the aforementioned embodiments, the intersecting angle of the paired focusing

coils

44 and 45 is chosen to be equal to the deflection angle 0 of electron beams. However, this is not always necessary. The point is that current be introduced in such a manner that a composite of the electromagnetic fields generated by the focusing

coils

44 and 45 acts in the same direction as that in which the electron beams 37 are deflected. Further, the saw tooth current supplied to the focusing

coils

44 and 45 may have a wave form variable with the construction of a cathode ray tube used.

In the above-mentioned embodiments there was described a cathode ray tube including an optical fiber plate for scanning the target 33 in one dimension. However, the present invention is applicable to any other types of cathode ray tubes for one-or two-dimensional scanning. Further, the invention may be used not only in an electromagnetic deflection cathode ray tube, but also in a static deflection type.

What we claim is:

l. A cathode ray tube comprising:

an envelope including a front portion and a neck portion;

a target disposed in the forward end of the front portion;

an electron gun positioned in the neck portion so as to emit electron beams toward the target;

electron beam deflecting means placed on the envelope; and

a dynamic focusing device comprising a pair of mutually intersecting focusing coils, said focusing device being interposed between the target and deflecting means so as to generate an electromagnetic field acting in substantially the same direction as that in which the electron beams are deflected, thereby focusing said electron beams.

2. The cathode ray tube according to claim 1 wherein the pairedfocusing coils intersect each other at the same angle as the maximum deflection angle of electron beams.

3. The cathode ray tube according to claim 2 wherein the paired focusing coils are supplied with saw tooth currents respectively which have the same polarity and mutually symmetrical wave forms.

4. The cathode ray tube according to claim 3 wherein the target includes a fiber plate prepared from a large number of optical fibers arranged in the same direction and a fluorescent layer mounted on one side of said plate.

5. The cathode ray tube according to claim 4 wherein the fluorescent layer is provided with a metal backing.

l060l l 0624

Claims

1. A cathode ray tube comprising: an envelope including a front portion and a neck portion; a target disposed in the forward end of the front portion; an electron gun positioned in the neck portion so as to emit electron beams toward the target; electron beam deflecting means placed on the envelope; and a dynamic focusing device comprising a pair of mutually intersecting focusIng coils, said focusing device being interposed between the target and deflecting means so as to generate an electromagnetic field acting in substantially the same direction as that in which the electron beams are deflected, thereby focusing said electron beams.

2. The cathode ray tube according to claim 1 wherein the paired focusing coils intersect each other at the same angle as the maximum deflection angle of electron beams.

4. The cathode ray tube according to claim 1 wherein the target includes a fiber plate prepared from a large number of optical fibers arranged in the same direction and a fluorescent layer mounted on one side of said plate.