US3694686A

US3694686A - Unidirectional double deflection type cathode ray tube

Info

Publication number: US3694686A
Application number: US105279A
Authority: US
Inventors: Norio Harao; Motohiro Yano
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1970-01-09
Filing date: 1971-01-11
Publication date: 1972-09-26
Anticipated expiration: 1989-09-26

Abstract

A unidirectional double deflection type cathode ray tube comprises an evacuated envelope, a target at one end of the envelope, an electron gun at the other end of the envelope for emitting an electron beam, main deflection means positioned between the electron gun and the target for deflecting the electron beam in one direction, an arcuate lens electrode device curved about the deflection center of the electron beam caused by the main deflection means, the lens aperture electrode device being provided with a plurality of lens apertures equally spaced apart in the direction of the scanning of the electron beam. Further provided is an auxiliary deflection means co-operating with and synchronized with the main deflection means for further deflecting the beam by a length equal to the pitch of the projection of the lens apertures the electron beam being thereby deflected to the positions of respective lens apertures.

Description

United States Patent Harao et al.

[54] UNIDIRECTIONAL DOUBLE DEF LECTION TYPE CATHODE RAY TUBE [72] Inventors: Norio Harao; Motohiro Yano, both of Yokohama, Japan [73] Assignee: Tokyo Shibaura Electric Co. Ltd.,

Kawasaki-shi, Japan [22] Filed: Jan. 11, 1971 [21] Appl. No.: 105,279

[30] Foreign Application Priority Data Jan. 9, 1970 Japan ..45/2517 Jan. 9, 1970 Japan ..45/2518 [52] US. Cl. ..313/75, 313/79, 313/76, 313/89 [51] Int. Cl. ..H01j 29/06, 1-10lj 29/76 [58] Field of Search ..313/75, 76, 79, 77, 89

[56] References Cited UNITED STATES PATENTS 2,741,720 4/1956 Laflerty ..313/79 X 2,617,060 11/1952 De Gier ..313/75 X 2,185,138 12/1939 Hanns-Hwolff ..313/79 X [451 Sept. 26, 1972 2,454,345 1 H1948 Rudenberg ..313/79 2,081,344 5/1937 Von Ardenne ..313/79 2,824,250 2/1958 McNaney et al ..313/79 X Primary ExaminerHerman Karl Saalbach Assistant Examiner-Saxfield Chatmon, Jr. At!0rney-Flynn & Frishauf [5 7 ABSTRACT A unidirectional double deflection type cathode ray tube comprises an evacuated envelope, a target at one end of the envelope, an electron gun at the other end of the envelope for emitting an electron beam, main deflection means positioned between the electron gun and the target for deflecting the electron beam in one direction, an arcuate lens electrode device curved about the deflection center of the electron beam caused by the main deflection means, the lens aperture electrode device being provided with a plurality of lens apertures equally spaced apart in the direction of the scanning of the electron beam. Further provided is an auxiliary deflection means co-operating with and synchronized with the main deflection means for further deflecting the beam by a length equal to the pitch of the projection of the lens apertures the electron beam being thereby deflected to the positions of respective lens apertures.

16 Claims, 21 Drawing Figures 5 9 w 2. 1 3 1 Q2 Q 7 ll n 20 I A) 1: 2

Ml 1o 1 5 i 19 114a- "a L a 1" PATENTEU SEPZS I972 SHEET 1 BF 6 FIG.

FIG?) on O PATENTEDsEP2s I972 SHEET 2 BF 6 TIME O hZn-EKDQ FIG.4

TIME

O P2m130 ll 5 TIME O Do 6 TIME PATENTEDsarzs I972 SHEET 3 BF 6 FIG. 8

UNIDIRECTIONAL DOUBLE DEFLECTION TYPE CATHODE RAY TUBE BACKGROUND OF THE INVENTION:

This invention relates to a unidirectionally scanning type cathode ray tube, and more particularly to a unidirectional double deflection type cathode ray tube.

The unidirectionally scanning type cathode ray tube (CRT) is utilized mainly as a printing tube in the fields of facsimile and electronic printing arts and utilized subsidiarily as a flying spot scanning tube in the field of optical character reading arts. There are two types of the printing tube. According to one type an information pattern to be recorded is converted into variations in the intensity of the electron beam of the cathode ray tube and the information contained in the electron beam is converted into light or an electrostatic charge at a target for printing the information on a printing medium. According to the other type, the electron beam is caused to impinge directly upon the printing medium through the target thus printing the information. An example of the former type is the so-called fiber optics CRT in which the intensity of the electron beam is converted into the variation in the light by means of the target and the light is led out of the cathode ray tube through optical glass fibers for printing the information on a photosensitive printing paper.

The printing tube is generally required to have a high degree of resolution and the degree of resolution is determined dependent upon the diameter of a spot formed by the electron beam impinging upon the target. More particularly, the more smaller is the spot diameter, the higher is the degree of resolution. The electron beam from the electron gun of a conventional printing tubes crosses over between the first and second grid electrodes, focused by a focusing coil and is then caused to impinge upon the target through deflection means. The spot diameter of the electron beam of a cathode ray tube having the construction described above, is generally proportional to the beam diameter at the point of crossover and to the ratio between the distance between the air gap center of the focusing coil and the target and the distance between the air gap center of the focusing coil and the crossover point. For this reason, in order to decrease the diameter of the beam spot on the target, it is necessary to reduce as far as possible the beam diameter at the crossover point and to increase the distance between the air gap center of the focusing coil and the crossover point. The former measure is not practical because it is not permissible to reduce the beam diameter beyond a certain limit in view of the characteristics of the tube so that the latter measure is generally employed. However, this approach increases the length of the neck of the tube, and hence the overall length thereof thus increasing the physical dimension of the apparatus utilizing the tube.

Accordingly, the principal object of this invention is to provide an improved unidirectional double deflection type cathode ray tube of reduced length, yet preserving the high degree of resolution.

Another object of this invention is to provide an improved unidirectional double deflection type cathode ray tube including a novel lens aperture electrode device of the construction not causing aberration of the electron beam.

SUMMARY OF THE INVENTION According to this invention, there is provided a unidirectional double deflection type cathode ray tube comprising an evacuated envelope, a target on one end of the envelope, an electron gun provided on the other end of the envelope for emitting an electron beam toward the target, main deflection means positioned between the electron gun and the target for successively deflecting the electron beam in one direction with a predetermined interval, an arcuate lens aperture electrode device curved about the deflection center of the electron beam caused by the main deflection means, said lens aperture electrode device being provided with a plurality of lens apertures therein equally spaced apart in the direction of the scanning of the electron beam, and auxiliary deflection means co-operating with and synchronized with the main deflection means for further deflecting the electron beam by a length equal to the pitch of the projection of the lens apertures when the electron beam being thereby deflected to the positions of respective lens apertures.

BRIEF EXPLANATION OF THE DRAWINGS This invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic longitudinal section of one example of a fiber optics CRT embodying the invention;

FIG. 2 is an enlarged sectional view of a portion of the target of the tube shown in FIG. 1;

FIG. 3 shows a front elevation of the lens aperture electrode device shown in FIG. 1;

FIGS. 4 to 7 inclusive show waveforms of signals useful to explain the operation of the tube shown in FIG. 1;

FIGS. 8 and 9 are diagrams to explain the manner of deflecting the electron beam in the tube shown in FIG. 1; wherein FIG. 8 shows the deflection of the electron beam at the air gap center of the target and FIG. 9 that at the periphery of the target;

FIG. 10 is a plan view of a modified lens aperture electrode device;

FIG. 11 shows the scanning locus of the electron beam on the lens aperture electrode device where the electron beam of the tube shown in FIG. 1 is wobbled;

FIG. 12 is a view showing a portion of the target of an electrostatic charge printing tube embodying this invention;

FIG. 13 shows a front view of yet another modification of the lens aperture electrode device of the tube embodying this invention;

FIG. 14 shows a schematic longitudinal section of a modified tube;

FIGS. 15 and 16 show potential distributions along the tube shown in FIG. 14;

FIG. 17 shows a schematic longitudinal section of another modification of the cathode ray tube constructed according to the principle of this invention;

FIG. 18 shows the potential distribution of the electron lens of the lens aperture electrode device of the tube shown in FIG. 17;

FIG. 19 shows the potential distribution of a modified electron lens of the lens aperture electrode device;

FIG. 20 is a front view of a portion of a modified lens aperture electrode device; and

FIG. 21 shows a sectional view taken along a line XXI XXI in FIG. 20.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to FIGS. 1 to 3 of the accompanying drawings, a printing tube 1 shown therein comprises an evacuated envelope 2 having a flat funnel shaped cone section 3 and a cylindrical neck 4 connected to the reduced diameter end of the cone 3. At the large diameter end of the cone 3 is provided an elongated target 9 comprising a fiber plate 5 including a plurality of optical fibers with one end thereof contacted against a printing paper 6, a fluorescent screen 7 on the inner surface of fiber plate 5 and a metal back electrode 8 of aluminum, as shown in FIG. 2. A main deflection device 10 and an auxiliary deflection device 11 operating in synchronism with the main deflection device for generating magnetic fields in the same direction, as will be described later in more detail, are disposed to surround the joint between cone 3 and neck 4. Neck 4 contains an electron gun 16 comprising spaced apart cathode electrode 12, a first grid electrode 13, a second grid electrode 14 and a cylindrical anode 15 which are disposed coaxially. On the outside of the electron gun 16 is disposed a focusing coil 17. Since the purpose of the focusing coil 17 is to focus the electron beam 18 emitted from the electron gun 16 at a point near the deflection center 19 of the deflection device, such focusing coil may be omitted in an electron gun which can focus the electron beam without the focusing coil, such as a unipotential type electrostatic focusing electron gun. A perforated electrode or lens aperture electrode 20 is disposed in the envelope between the main deflection device 10 and the target 9. The perforated electrode 20 takes the form of a circular are having an air gap center at the deflection center 19 of the deflection device 10. The electrode 20 is provided with a plurality of circular perforations disposed at a uniform spacing along a line parallel to the longitudinal axis of the target 9. Generally, since the intensity of the magnetic field of the auxiliary deflection device 11 is smaller than that of the main deflection device, the deflection center 19 generally coincides with the deflection center of the main deflection device 10. However, in the case when the field of the auxiliary deflection device 1 l affects the field of the main deflection device, the deflection center 19 will be a resultant or apparent deflection center formed by both the main and

auxiliary deflection devices

10 and 11.

In this tube, the electron beam 18 emitted from cathode electrode 12 is squeezed or focused at the crossover point 23 between the first and

second grid electrodes

13 and 14 and then the diverged beam is again focused at a point near the deflection center 19 by the action of focusing coil 17. Thereafter, the beam is deflected to reach perforated electrode 20 by

deflection devices

10 and 11. As above described, since the perforated electrode 20 is a circular arc having its air gap center at the deflection center 19, the electron beam 19 is caused to impinge at right angles to any perforation 22 of the electrode 20. Accordingly, when supplied with a suitable voltage, the perforated electrode 20 creates a focusing field so as to focus the electron beam 18 on the target without the problem of any aberration.

If the printing tube was provided with a conventional deflection system, the electron beam 18 would be intercepted by the solid portions between perforations of the electrode 20 so that the electron beam scans the target intermittently. To provide the continuous scanning of the target 9, according to this invention, the main and auxiliary deflection devices 10 and'l l are provided and a saw tooth auxiliary deflection current 24 as shown in FIG. 4 is applied to the auxiliary deflection device 11 whereas a stepped wave saw tooth main deflection current 25 as shown in FIG. 5 is applied to the main deflection device 10. In both FIGS. 4 and 5 the ordinate represents current and the abscissa represents the time.

Inclined portions

26 and 27 of

deflection currents

24 and 25 are well synchronized and correspond to respective perforations 22 of the perforated electrode 20. More particularly, by denoting the periods of the

inclined portions

26 and 27 of the auxiliary and

main deflection currents

24 and 25 by t and the number of perforations 22 of the perforated electrode 20 by N, the time interval T required for the main deflection current 25 to vary from a minimum to a maximum is expressed by an equation T M. As shown, the inclined portions 26 of the auxiliary deflection current 24 vary in the positive and negative directions about a line through zero points 28. When the current is zero, electron beam 18 is not deflected but as the current varies in the positive or negative direction, the beam is deflected about the zero line alternately in the positive and negative directions. The main deflection current 25 comprises a superposition of a stepped currentcomponent 29 shown in FIG. 6 and acts to select the perforations 22 and a saw tooth current component 30 shown in FIG. 7 acts to adjust the incident angle of the electron beam 18 so that it passes into perforations 22. The electron beam 18 is deflected according to respective inclined portions 27 of the main deflection current 25, and the beam scans target 9 once while current 25 varies from its minimum to the maximum. For this reason, by passing repeatedly the stepped wave saw tooth main deflection current which varies from the minimum to the maximum in synchronism with the auxiliary deflection current 24, the electron beam 18 is caused to repeatedly scan the target. It is to be noted that the directions of deflection action of the main and

auxiliary deflection devices

10 and 11 are the same.

Considering now the case wherein the electron beam 18 is caused to scan the central portion of the target by the main and

auxiliary deflection currents

25 and 24, when a current +is flows through the auxiliary deflection device 11 and a current im, flows through the main deflection device 10, as shown in FIG. 8, the electron beam 18 is deflected by an angle +0 by the auxiliary deflection device 11 and by an angle I by the main deflectiondevice 10 to enter a corresponding perforation 22a of the perforated electrode 20 thus forming a focused bright spot 31 on target 9. On the other hand, when there is no current flowing through the main and

auxiliary deflection devices

10 and 11, the electron beam is not deflected and passes straight through

respective deflection devices

10 and 11 and through perforation 22a to form a focused bright spot 32 on the target 9. Where a current -is flows through the auxiliary deflection device 11 and a current +im, flows through the main deflection device 10, the electron beam 18 is deflected by an angle 0 by the auxiliary deflection device 11 and by an angle +4) by the main deflection device to pass through perforation 22a whereby a focused bright spot 33 is formed on the target. In other words, during the interval T in which the current through the auxiliary deflection device 11 varies from +11: to is along the inclined portion 26, when the current through the main deflection device 10 varies from -im, to +im, along the inclined portion 27 the electron beam 18 continuously scans the surface of the target 9 from bright spot 31 to bright spot 33. In the same manner during the interval T in which the current through the auxiliary deflection device 11 varies from +is to is along inclined portion 26 when the current flowing through the main deflection device 10 varies from im to +im along the inclined portion 27, the electron beam 18 passes through another perforation 22b next to the perforation 2211 thus continuously scanning the target 9 from

bright spot

33 or 34 to bright spot 35. The main and

auxiliary deflection currents

25 and 24 are set so that

bright spots

33 and 34 are closely adjacent along the direction of scanning thus continuously scanning the entire surface of the target 9 by the electron beam 18. Even when the electron beam passes obliquely through perforation 22 as in the case of

bright spots

31 and 33, since the angle of inclination of the beam with respect to the perforation is small, there is not any appreciable aberration.

However, since the target 9 is flat whereas the perforated electrode is arcuate, the distance between these members increases from the air gap center toward periphery, with the result that as shown by

bright spots

36 and 37 in FIG. 9 the scanning range of the electron beam 18 passing through perforation 22c and that of the electron beam passing through next perforation 22d partially overlap each other. Such overlapping can be avoided by varying the angle of inclination of the

inclined portions

26 and 27 of the auxiliary and

main deflection currents

24 and 25, as shown by

inclined portions

38 and 39 shown in FIGS. 4 and 5, respectively. More particularly, the current through the auxiliary deflection device 11 is increased from is to i's and the current through the main deflection device 10 is decreased from +im, to +im,,. Then the electron beam 18 will be deflected 0' (0' 0) by the auxiliary deflection device 11 and by an angle corresponding to current +i'm, by the main deflection device 10 so that the bright spot is formed at 40 which is located closer to the air gap center of the target than bright spot 36. On the contrary, when the current through the auxilia ry deflection device 11 is decreased from +is to +is and the current through the main deflection device 10 is increased from im(n+1) to im(n+l the beam will be deflected outwardly by an angle corresponding to +i'm(n+l) to form a bright spot 41 on the outside of bright spot 37. In this manner, while scanning the outer end portions of the target by varying the inclination angles of the

inclined portions

26 and 27 of the auxiliary and main deflection currents 24 and as shown by

inclined portions

38 and 39 it is possible to contiguously form

bright spots

40 and 41, that is without overlapping or interruption whereby the scanning range of the electron beam passing through perforation 22c and that of the electron beam passing through the next perforation 22d become contiguous. Thus, by gradually varying the inclination angles of the

inclined portions

26 and 27 of the auxiliary and

main deflection currents

24 and 25 while the beam is deflected to scan the outer end portions of the target, it becomes possible to scan the target continuously.

Moreover, when the distance between the target and the perforated electrode increases, from the air gap center toward the outer ends, it often becomes difflcult to obtain uniform focusing over the entire surface of the target. This difficulty can be avoided by the socalled dynamic focusing, that is by varying the potential impressed upon the perforated electrode 20 in synchronism with the

currents

24 and 25 passing through

deflection devices

10 and 11.

In the illustrated printing tube the diameter d of the bright spot formed by the electron beam on target 9 is expressed by the following equation where:

P the distance between perforated electrode 20 and deflection center 19,

Q: the distance between perforated electrode 20 and target 9,

P the distance between the air gap center of focusing coil 17 and crossover point 23,

Q: the distance between the air gap center of focusing coil 17 and deflection center 19 and d the diameter of the electron beam at the crossover point.

In the above equation, if

then the resolution of the disclosed printing tube becomes substantially the same as that of the prior art printing tube, where Q and P, represent the distances between the air gap center of the focusing coil and the target and the crossover point respectively. In the novel printing tube, since the focusing device or coil 17 is disposed on the outside of electron gun 16 it is quite easy to make Q IP, to be less than or equal to unity. Moreover, since it is possible to locate the perforated electrode 20 at any desired position and to select any desired diameter and spacing of the perforations 22, it is easy to satisfy the condition thus providing the desired degree of resolution. Especially, a printing tube satisfying the latter condition manifests high degree of resolution. In any case, the

length of the neck 4 is determined primarily by the dimensions of the electron gun 16, so that the length of the neck 4, hence the overall length of the tube can be greatly reduced.

The electron beam 18 emanatedfrom the electron gun 16 is deflected along a circular locus in the magnetic field produced by the main deflection device 10. Accordingly, the deflection center 19 is shifted toward the target 9 as the deflection angle increases. For this reason, when the perforated electrode 20 is an arcuate segment having a single center, the beam crosses the perforated electrode at larger angles as the beam is deflected at larger angles for scanning the end portions of the target. This causes increase in the aberration and decrease in the resolution. Decrease in the resolution does not cause by serious trouble in a printing tube of small deflection angle, but is not permissible in a printing tube. of wide deflection angle. For this reason, a perforated electrode comprised by arcuate segments of different radii is desirable in which the electron beam penetrates every perforations substantially at right angles.

FIG. 10 shows one example of such a modified perforated electrode 200, comprising a central arcuate segment having a radius R about a deflection center 19a and two adjacent arcuate segments having a radius R, about another deflection center 19b. With this composite perforated electrode, it is possible to make equal the resolution at the outer end portions of the target and that at the central segment.

Even when a series of perforations 22e to 22h are not aligned on a straight line X X that is the direction of scanning of the electron beam, as shown in FIG. 11, it is possible to cause the electron beam to pass through these perforations always at right angles by designing the auxiliary deflection device 11 so as to wobble or oscillate the beam over a width W at a high frequency about the axis X X While in the foregoing description, both the main and

auxiliary deflection devices

10 and 11 were shown as of the electromagnetic type, one or both may be of the electrostatic type.

It is also to be understood that the invention is applicable to the electrostatic charge printing tube in addition to the fiber optics CRT described hereinabove. FIG. 2 illustrates the construction of the target 9 of such a modified printing tube, which comprises a glass substrate 50, 1 'mm thick, for example, and a plurality of insulated fine parallel metal wires 51. These metal wires have a width of 35 microns, a height of 10 microns and a spacing of 75 microns. The metal wires may be arranged in one row or a plurality of rows in the direction of travel of the electron beam 18. As these metal wires 51 extend throguh the glass substrate 50 they are charged negatively when scanned by the electron beam, whereby an electrostatic latent image can be formed on a printing paper 6 mounted on the outer side of the glass substrate 50.

I-Iowever, it is extremely difficult to arrange neatly a plurality of fine metal wires on the glass substrate at right angles, rendering it difficult to correctly scan target 9 with the electron beam. One approach for this problem involves the wobbling to the beam as has been described in connection with FIG. 11 and another approach involves the use of rectangular perforations.

FIG. 13 illustrates such modification. The perforated electrode 55 shown therein is provided with a plurality of equally spaced apart perforations in the form of narrow rectangular slits 56 disposed at right angles with reference to the direction of scanning of the electron beam. With this construction, since the beam is strongly focused in the direction of the width of the slit, that is the direction of the rows of the fine metal wires 51 of the target 9 shown in FIG. 12 whereas weakly in the direction of the length of the slits the beam takes the form of an elongated slit perpendicular to the rows of fine metal wires 51 as it impinges upon the target. Consequently, even when the fine metal wires 51 are not neatly aligned on a straight line, the beam would not miss the fine metal wires thus assuring correct scanning of the target.

As above described, in the target illustrated in FIG. 1, the distance between the target 9 and the perforated electrode 20 is different at the central portion and at the peripheral or end portions of the target. The target is generally impressed with a potential, say about 15 RV with respect to the zero cathode potential so that the electric field created by the target will not be applied uniformly upon the perforated electrode but disturbed at the end portions thus causing a spherical aberration to the electron beam.

The embodiment shown in FIG. 14 obviates this problem. In this embodiment, a pair of

mesh electrodes

60 and 61 are disposed on the opposite sides of the perforated electrode 20 concentrically therewith but spaced apart therefrom. Although not shown in the drawing it is to be understood that

mesh electrodes

60 and 61 are applied with an equal potential as the anode electrode 15 whereas the perforated electrode 20 is supplied with a somewhat lower potential. Other elements are identical to those shown in FIG. 1.

To have better understanding of the operation of the tube shown in FIG. 14, reference is made to FIG. 15 in which the internal construction of a tube not using the

mesh electrodes

60 and 61 and the potential distribution along the tube axis are shown diagrammatically. FIG. 16 shows the internal construction of a tube provided with the mesh electrodes and the potential distribution along the tube axis.

As shown in FIG. 15, in a tube having only the perforated electrode 20, the secondary differential of the potential distribution curve A along the tube axis varies from a negative to a positive and then to a negative. Thus, the function of the perforated electrode 20 as an aperture lens for the electron beam varies in the order of diversion, focusing and diversion, but manifesting focusing as a whole. I

On the other hand, with the tube shown in FIG. 1 the potential distribution along the tube axis is represented by a curve B, in which the secondary differ'ential thereof is a positive between

mesh electrodes

60 and 61 whereas zero at other positions, which means that there is no diversion manifested by curve A in FIG. 15. Actually, however, slight diversion occurs near the mesh electrodes, but the effect of this is negligibly small so that very strong focusing action is possible, thus greatly shortening the focal length.

The mesh electrode 20 also acts to absorb the secondary electrons which are formed by the collision of the electron beam against the perforated electrode.

FIG. 17 shows still further modification of the invention wherein the perforated electrode 20 is of the bipotential type electron lens system comprised by two arcuate

perforated electrode plates

201 and 202 concentric with respect to deflection center of the electron beam 18.

Electrode plates

201 and 202 are provided with the same number of

perforations

221 and 222 which are aligned in the radial direction of the electrode plates.

An electroconductive film 65 is formed on the inner surface of the portions of the envelope 2 between one of the perforated electrodes, 201, and the target 9 to electrically interconnect the electrode and target to maintain them at the same potential. The other perforated electrode plate 202 and the electron gun 16 are also interconnected by similar electroconductive film 66 applied on the inner surface of the envelope. These

electroconductive films

65 and 66 are connected to

terminals

67 and 68, respectively, extending through the envelope to apply necessary voltages to the target and perforated electrode plates.

Thus, for example, a voltage of KV is impressed upon perforated electrode platel through terminal 67 whereas a voltage amounting to about 10 to 40 percent of said voltage, that is a voltage of about 1,500 to 6,000 volts is impressed upon perforated electrode plate 202, whereby

electrode plates

201 and 202 cooperate to comprise a bipotential type electron lens system to form a potential distribution pattern in terms of equipotential lines 70 between confronting pairs of

perforations

221 and 222, as shown in FIG. 18.

Instead of forming the electron lens system with two sheets of the perforated electrode plates 20] and 202, as shown in FIGS. 17 and 18, such a lens system can also be comprised by a combination of three sheets of arcuate

perforated electrode plates

203, 204 and 205,

as shown in FIG. 19. Perforated electrode plates 203,

204 and 205 are concentrically disposed about the deflection center (not shown) of the electron beam in the same manner as in FIG. 17 with a suitable spacing therebetween. Each pair of

perforations

223, 224 and 225 of these electrode plates are aligned in the radial direction.

Electrode plates

203 and 205 are maintained as the same potential as the target and the anode (not shown) by the

identical electroconductive films

65 and 66 shown in FIG. 17. The remaining perforated electrode plate 204 is connected to a terminal, not shown, but similar to those shown in FIG. 17 to receive a voltage considerably lower than the anode voltage.

When applied with voltages as above described

electrode plates

203, 204 and 205 operate to form a unipotential type electron lens having a potential distribution pattern as shown by equipotential lines 71 shown in FIG. 19.

FIGS. 20 and 21 show another example of the perforated electrode constructed in accordance with this invention and provided with an arcuate plate 76 having a plurality of radial cylinders 75, the plate having an air gap center of curvature at the deflection center of the electron beam. The axes of the cylinders are in the radial directions with respect to the deflection center so as to deflect the electron beam along the axis of the cylinders toward the target, not shown.

What we claim is:

l. A unidirectional double deflection type cathode ray tube comprising:

an evacuated envelope,

a target at one end of said envelope,

an electron gun provided at the other end of said envelope for emitting an electron beam toward said target, first main deflection means positioned between said electron gun and said target for successively deflecting said electron beam in one direction with a predetermined interval between successive deflections, an arcuate lens aperture electrode device curved about the deflection center of said electron beam which is deflected by said first deflection means, said lens aperture electrode device having a plurality of lens apertures therein equally spaced apart in the direction of scanning of said electron beam, said target being maintained at an electric potential about the same as, or higher than, that of said arcuate lens aperture electrode device, and

second auxiliary deflection means synchronized with said first main deflection means for further deflecting said electron beam by an amount equal to the pitch of the projection of the lens apertures of said arcuate lens aperture electrode device, said elec tron beam being deflected to the positions of respective lens apertures by said first and second deflection means.

2. The cathode ray tube according to claim 1 wherein each of said lens apertures of said lens aperture electrode device is circular.

3. The cathode ray tube according to claim 1 wherein each of said apertures of said lens aperture electrode device is in the form of a slit perpendicular to the direction of deflection of said electron beam.

4. The cathode ray tube according to claim 2 wherein said lens electrode device comprises a lens aperture electrode and at least one mesh electrode substantially of the same configuration and disposed on the side thereof facing said target.

5. The cathode ray tube according to claim 3 wherein said lens aperture electrode device comprises a lens aperture electrode and at least one mesh electrode substantially of the same configuration and disposed on the side thereof facing said target.

6. The cathode ray tube according to claim 1 wherein said lens aperture electrode device comprises two spaced apart lens aperture electrodes of substantially the same configuration, said lens aperture electrodes being provided with a plurality of spaced pairs of aligned lens apertures and wherein there are provided a first electroconductive film provided on the inner surface of the portions of said envelope near said target for electrically interconnecting said target and one of said lens aperture electrodes, a second electroconductive film on the inner surface of said envelope for interconnecting the other of said lens aperture electrode and the anode electrode of said electron gun and means for applying predetermined potentials to said first and second electroconductive films.

7. The cathode ray tube according to claim 1 wherein said lens aperture electrode device comprises three parallel spaced apart lens apertureelectrodes of substantially the same configuration, said lens aperture electrodes being provided with a plurality of spaced pairs of aligned lens apertures and wherein there are provided a first and second electroconductive films on the inner surface of said envelope for electrically interconnecting said target, first and third lens aperture electrodes and the anode electrode of said electron gun, and means for applying predetermined potentials to said first and second electroconductive films and the second aperture electrode.

8. The cathode ray tube according to claim 1 wherein said lens aperture electrode device comprises an arcuate electrode plate and a plurality of cylinders extending through said electrode plate toward said electron gun.

9. The cathode ray tube according to claim 1 wherein said target comprises a fiber plate, and a fluorescent and a metal back electrode laminated on one side of said fiber plate.

10. The cathode ray tube according to claim 1 wherein said target comprises a glass substrate, and a plurality of fine metal wires secured to one side of said glass substrate.

11. The cathode ray tube according to claim 1 wherein said second auxiliary deflection means includes means for wobbling said electron beam at a high frequency and over a predetermined amplitude in a direction perpendicular to the direction of scanning of said beam.

12. The cathode ray tube according to claim 1 wherein the electron beam, as deflected by said first and second deflection means, passes through successive ones of said respective lens apertures to impinge on said target.

13. A cathode ray tube according to claim 1 wherein the deflection current applied to said second auxiliary deflection means is a saw-tooth current symmetrically centered about a predetermined current level.

14. A cathode ray tube according to claim I wherein said first main deflection means is supplied with a sawtooth main deflection current wherein a predetermined number of saw-tooth portions thereof are successively increased in current level.

15. A cathode ray tube according to claim 13 wherein said first main deflection means is supplied with a saw-tooth main deflection current wherein a predetermined number of saw-tooth portions thereof are successively increased in current level.

16. A cathode ray tube according to claim 15 wherein the ramp portions of said main and auxiliary deflection currents vary in opposite directions and are synchronized with each other, so that the effective deflection current becomes the equivalent of a step wave form.

* =r a: a

Claims

1. A unidirectional double deflection type cathode ray tube comprising: an evacuated envelope, a target at one end of said envelope, an electron gun provided at the other end of said envelope for emitting an electron beam toward said target, first main deflection means positioned between said electron gun and said target for successively deflecting said electron beam in one direction with a predetermined interval between successive deflections, an arcuate lens aperture electrode device curved about the deflection center of said electron beam which is deflected by said first deflection means, said lens aperture eleCtrode device having a plurality of lens apertures therein equally spaced apart in the direction of scanning of said electron beam, said target being maintained at an electric potential about the same as, or higher than, that of said arcuate lens aperture electrode device, and second auxiliary deflection means synchronized with said first main deflection means for further deflecting said electron beam by an amount equal to the pitch of the projection of the lens apertures of said arcuate lens aperture electrode device, said electron beam being deflected to the positions of respective lens apertures by said first and second deflection means.

7. The cathode ray tube according to claim 1 wherein said lens aperture electrode device comprises three parallel spaced apart lens aperture electrodes of substantially the same configuration, said lens aperture electrodes being provided with a plurality of spaced pairs of aligned lens apertures and wherein there are provided a first and second electroconductive films on the inner surface of said envelope for electrically interconnecting said target, first and third lens aperture electrodes and the anode electrode of said electron gun, and means for applying predetermined potentials to said first and second electroconductive films and the second aperture electrode.

14. A cathode ray tube according to claim 1 wherein said first main deflection means is supplied with a saw-tooth main deflection current wherein a predetermined number of saw-tooth portions thereof are successively increased in current level.