US2114572A - Cathode ray ture system - Google Patents

Description

April 19, 1938. H. c. RESSLER 2,114,572

CATHODE RAY TUBE SYSTEM Filed June 1, 1936 Patented Apr. 19,1938

, UNITED. FSfl'ATES.

. w anws ca'rnona any man mm I nun c. me, new York. N. 1., assignor to Radio Inventions, Ina, New York, N. Y.,' a corporation of New York Application June 1, ast, w No. 82,693 -11Claims. (01.25040 This invention relates to cathode ray tubes. More particularly it relates to such tubes 01! the types commonly employed in the cathode ray cscillograph. v

1 My invention deals particularly with means and methods for focusing a stream of electrons upon the screen of a cathode ray tube, and for deflecting the so-focused stream in order to trace some particular pattern upon the screen such as l the reproduction of an image transmitted by television, or the reproduction of geometric figures for purposes of electrical analysis.

Cathode ray tubes, as hitherto constructed; have been unable to secure at the same time a l5. high degree of sensitivity and a high velocity of the electron stream impinging upon thescreen. By the term sensitivity, I refer to the displacement or deflection of the electron stream to a comparatively great extent, by the use of a rela- 20 tively low deflecting voltage applied to electrostatic plates. The high velocityof the electron stream when it impinges upon the screen is desirable in order that a high degree of luminosity may be produced by such impingement.

Furthermore, cathode ray tubes have encountered great difllculty because of certain irregular deflection effects-giving rise to an irregular or distorted curve or other figure upon the screen.

, Such irregularities in reproduction have been w especially harmful when it has been desired to reproduce a television image. In the type of cathode ray tube employed with electrostatic deflection to produce a two dimensional image upon the screen, the distortion e1- facts which have been found especially troublesome have been the effects which gave rise to an image of these-called keystone type. By this type of distortion, is meant the lengthening of such an image either in its vertical or its horim zontal dimension, at one side only. That is to i say, a figure which should be truly rectangular,

has one side lengthened with respect to the corresponding opposite side, so that obtuse angles appear on one side of the figure and acute angles 5 on the corresponding opposite side of the flgure. The reasons iorthe distortion eflects above described have been obscure and not well-known 4 in the art, but I have discovered the underlying reasons for certain of these distortion eflects and go have devised an apparatus and a method oi operating the same which will to a very great degree,

or even completely, overcome these" distortion eilects.

One purpose of my invention is to produce a a cathoderay tube whereby theelectron stream 7 may be deflected while of low velocity and may be accelerated after such deflection, in order to secure a brilliant screen spot.

Yet another purpose of this invention is to accelerate an electron stream whose direction of motion is subject to deflection, and yet have such acceleration act upon the electron stream so that .its initial direction of motion alter deflection will not be altered by the accelerating forces afterward applied to the stream.

A still further object of my invention is to provide electrostatic field producing, or screening means located between deflecting systems, so that the deflecting action of the second system will be substantially independent of the deflecting action of the preceding system.

Another purpose of this invention is to provid means for securing in a cathode ray tube, electrostatic fields of radial nature, whereby electrons having diflerent radial paths from a common center will encounter an accelerating field oi uniform or varying intensity but invariably directed substantially along said radial paths, and thus will be accelerated without change of direction.

Still another object of my invention is toprovide a plurality of deflecting systems acting upon a single electron stream, where the second and subsequent deflecting systems are so constructed that the electron stream passing through the complex deflecting system will be subject to deflecting and/or accelerating fields of such character that the angular deflection caused by the flrst elements of the deflecting system will remain unchanged despite the transverse or other deflection caused by later deflecting elements.

Another object of this invention is to combine in a single cathode ray tube the qualities of high deflectionsensitivity and high luminosity.

A still further purpose of this invention is to provide a cathode ray tube whose screen displays a two-dimensional image, wherein the displayed -image'will be substantially free from distortion due to the keystone eflfect.

I have illustrated the principles involved in my invention and certain embodiments thereof in the accompanying drawing where Fig. 1 represents schematically a portion of the interior of a cathode ray tube.

- 2 shows in detail a pair of accelerating anodes as used in the system of Fig'. 1.

Fig. 3 illustrates a conventional tube system shown in order to illustrate the keystone eflect.

Fig.1 illustrates diagrammatically the appearance of images upon the screen of a cathode ray tube, illustrating the production of the keystone eii'ect.

Fig. 5 represents schematically a simplified form of my invention as applied to a cathode ray oscillograph tube. I

Fig. 6 illustrates diagrammatically the electrostatic fields of the system of Fig. 5.

' shown enclosed in a shielding element II, with which it cooperates to form the socalled electron gun. Elements l2 and iii are metal plates pro vided with slots l4 and i5 respectively, through which the electron stream passes in order to secure a proper definition thereof, and for other purposes as set forth in copending application Serial Number 738,220 filed August 3rd, 1934.

In this application the production of an electron stream of a desired cross section, direction of motion, and whose component electrons have a substantially uniform velocity is disclosed, but it is to be understood that this present invention may be used in connection with any other method of securing an electron stream having approximately these characteristics. While it is desirable that electron stream have the qualities just described yet this present invention will function, even if to a less perfect degree, upon electron streams which do not possess precisely the qualities Just enumerated.

The electron stream emerging from the apertures ll and I5 is denoted by reference numeral l6 and this stream then passes through an aperture il in an anode structure i8, which may be iii the form of a metal plate, disc or other suitable shape.

-At l9 and 20 I have shown two deflecting plates of the electrostatic type, producing a substantially uniform electrostatic field therebetween. Located beyond deflecting plates l9 and 20, lies another anode 2| in the form of a cylindrical metal plate (see Fig. 2).

Beyond plate 2| lies still another anode 22. also in the form of a cylindrical plate. Plates 2| and 22 are provided respe tivel with elongated slots 23 and 24 extending in a ection at right angle-s10 slots [4 and |5,'through which the electron stream can readily pass after being deflected substantially only in one direction. The electron stream it, after passage through deflection system I9, has its direction of motion altered according to the relative electrostatic charges upon the respective plates of this system, and I have illustrated by means of a series of lines 25, they varied direction of motion which this stream may assume. It is to be understood that at any one instant, the electron stream can only occupy the position shown by a single one of these lines.

While I have shown plates 19 and 20 as being parallel it is to be understood that they may be obliquely disposed, relatively to each other, as well known in the art. I

The anode 2l is electrically connected with the anode I8, so'that the electron stream is not sub- I stontioily accelerated in its passage-through deflection system i9, 20. Anode 22 has applied to it an accelerating potential, with respect to anode 2|, so that the electron stream which has passed through slot 23 will be accelerated during its passage between this slot and slot 24 in anode 22. its well known in the art that by the proper design of plates l9 and 20, the electron stream which has been acted upon by these plates so as sequentially to occupy the various lines of direction, as indicated at 25, may be considered always 10 emanate from a fixed point 25, located in the space between these deflecting plates. In

other words, point 26 may be looked upon as the virtual common center of origin of the variously deflected electron streams coming from deflection system I9, 20. Since plates 2| and 22 produ'ce therebetwcen a radial field centered at the point 26, it will be seen that electrons entering slot 23, provided that they always come from a single central source 26, will encounter between plates 2| and 22 a uniform radial fleld of traverse, so that the acceleration of these electrons will be accomplished without any change in their direction of motion due to the fact that such motion and such accelerating field are both identical in direction.

It can be seen that the particular system Just illustrated and described is suited for acting upon an electron stream which has motion in one dimension only.

However, unless the accelerating field between anodes 2| and 22 is made of too high a value, the rays passing through slot 24 may then be further deflected in a dimension at right angles to the dimension in which deflecting system I8, 20 has already caused them to be. deflected. Thus. by dividing the accelerating action into two stages,

y it is possible to construct a cathode ray tube according to this invention, which shall be operative to give two dimensional scanning.

It is to be understood that the principles of this, invention are equally operative with deflecting elements which produce a substantially uniform and concentrated magnetic field and since the equivalency of these two types of deflecting structures is well known in the art, it is thought unnecessary to explain the operation of my invention in detail, when a magnetic deflecting hold is employed.

My system provides a short path of traverse for the electron stream, permitting the use of low velocity and yet aflording a comparatively high sensitivity of deflection. At the same time it minimizes the shielding and shadowing dlfflcflll. fies which present themselves when a low velocity electron stream has a long traverse path, or when the path between the deflecting system and the screen is not free of obstructions.

Referring now to Fig. 3 I have here shown A deflecting system of the conventional type employed in two-dimensional cathode ray tubes. A pair of deflecting plates 29 and 30 deflect the stream in one dimension and as previously explained this stream will seem to originate from a virtual central point 3| located between these plates. After leaving these plates, the electron stream then passes through another pair of plates 32 and 33 which are perpendicular to the first set and which deflect the beam in the other dimension'. If both these sets of plates are independent from one another and if the relative potential of each plate of a given set is simultaneously equal in degree, but of opposite sign with'respect to the anode of the electron system, then the two sets of plates will theoretically function independently of one another.

However, in actual practice, not only is it extremely difllcult to keep each set of plates symmetrically charged with respect to the anode potential at a given instant, but also for reasons of practical construction and for minimizing the number of external connections necessary in a tube employing'such a system, it is frequently desirable-to connect one deflecting plate of each pair directly to the anode. Under such conditions, I have discovered that the second deflecting system not only will act to displace the elecstream, due to the fact that the mean instantaneous potential or the deflecting plates will be finite and either positive or negative with respect to the potential of the anode proper, and not zero as desired.

In Fig. 3 I have illustrated by the line 0Q the path of a ray leaving deflecting system 29, 30, when the mean potential of the deflecting plates 32 and 33 is the potential of the anode proper, i. e., when no electrical signals are being applied to these last mentioned plates. If we now consider that plate 33, the insulated oneo! the pair of plates 32, 33, has applied to it a voltage positive with respect to the anode voltage of the system, th s positive voltage will cause the electron stream to assume the position denoted by the line OR, since the field thus establishedbetween plates 29, 30, and 32, 33, gives the beam a net acceleration in the forward direction, whereas the beam has a component of motion in two directions, due to its radial nature, as previously described.

It is' to be understood that the motion of the stream within the rear plates is really a parabola, although it appears a straight line, due to its relatively slight curvature, and that the curvature between the rear and forward plates has been exaggerated, in order to more clearly display the principles of my invention.

This change of direction of the beam takes place principally between the forward edges of plates 29, 30 and the rear edges of plates 32, 33, so that during this portion of its path of traverse, the ray is curved concavely downward.

A similar analysis will show that a negative potential applied to insulated plate of the pair 32, 33 will decelerate the electron stream with respect to its forward motion, so that the line OP will represent the line of direction of the stream.

under such conditions.

Considering now additionally Fig. 4, the point 40 represents the center of the pattern which the electron stream can place upon the screen. The lines XX and YY represent the conventional axes of a Cartesian system of coordinates. The lines 4i, 42 and 43, 44 represent two lines parallel to the X axis of this system, and manifestly in reconstructing a television image for example, it is desirable that all the horizontal elements of the picture take up positions which will correspond to such lines, with respect to their being parallel to the X axis. However, in the case of the system shown in Fig. 4, it will be evident that the line 43, 44 which should be parallel to the X axis,

will actually take up a position corresponding to the line 45, 46. The reason for this displacement,

will be apparent when it is considered that the,

electron stream at the instant itis at the left hand end of line 45, 46, will be subjected to a decelerating action of deflecting plates 32, 33, as

just described in the discussion of Fig. 3, causing an increase in the vertical displacement of the -At the right hand end of line 45, 46, the electron stream will be accelerated by the system 32, 33, thus causing a decrease in the net vertical displacement of the spot. This species of distortion just described is the so-calied keystone eii'ect.

Referring now to Fig. 5 I have there shown a radially shaped shield provided with a longi: tudinal slot 5| and located between the first deflecting system 29, 30 and the- second deflecting system 32, 33. This plate 50 is connected to the anode of the system.

The shield 50 isa segment of a cylindrical sur face, whose center is the point 3| located in deflecting system 29, 30. Since the deflected rays leaving the plates 29, 30 are radial about point 3 i, and since the field shown by the dotted lines of Fig. 6 is also radial, these rays will suffer no displacement of direction for the reasons previously pointed out in connection with Figs. 1 and 2.

Referring now additionally to Fig. 6, I have here illustrated by dotted lines the electrostatic equipotential lines existing in the plane 01 the drawing and between the adjacent edges of the plates of the respective deflecting systems. It will be noted that the interpositioning of plate 50 has caused the electrostatic field between tne two sets of plates to assume a substantially radial shield 50 as centered about point 3|, yet in practice- I' have found that it often is desirable to give this element a greater degree of curvature. to

compensate for any departure from the assiuned radial path, such as may occur when the accelerat-ing field is produced by a plane electrode.

The mode of construction shown in Fig. 5 thus practically or completely eliminates the species of distortion giving rise to the keystone eflect, since the direction of the ray is not altered when it passes from one set of deflecting plates to another.

While I have shown the pairs of deflecting plates of dissimilar sizes, it is to be understood that they may be of the same size.

InFig. 7 I have shown an alternative method of producing such a radial field between deflecting plates 23, 30 and a second set of deflecting plates 53, and 54. In this case each plate, 53 and 54. has both of its curved edges in the shape of arcs approximately concentric with point of ray origin 3|. Such a shape of plate will establish a substantially radial electrostatic field between the two sets of plates.

I have found, however, that a still better result is had by making-the curved edge nearest the point of ray origin at 3! a true circular arc centering on 3 I, and by making the curved edge more distant from the origin according to a curve having a smaller average curvature. The optimum form for this more remote edge, when the plates 53 and 54 are used in conjunction with a substantially planar accelerating electrode, is determined by the polar equation:

D R=R+ cos 0 where R is the distance from the point 3| to the more remote edge of the plate. R0 is the uniform distance from the point 3| to the nearer edge of the plate. D is the distance between the nearer I and more remote edges 01' the plate in the direc- "where, R is the distance origin to said arc, Ro is the uniiorm distance bodiments of my invention, yet it is to be understood that this invention is not limited to the speciflc forms herein shown, but merely to the extent of the claims hereunto appended. Furthermore it is to be understood that many variatlons oi the forms here shown are possible without departing from thespirit'oi this invention.

- ,Iclaim:

1. In a cathode ray tube, the method of securing distortionless projection of an electron stream which includes generating said stream,

deflecting said stream, and passing the-deflected stream through an electrical fleid whose accelerating action upon said deflected stream is always coincident in direction with the motion of said stream after deflection.

2. A cathode ray deflection and acceleration system including in the orderspecified, means for producing an electron stream, means ior'de fleeting said stream, and means for accelerating the deflected stream, said last means producing a substantially radial electrostatic fleld about thevirtual point of origin of said stream, located within said deflecting means.

3. A cathode ray tube system including a tubehaving an anode. two sets oi deflecting plates at right angles to one another and a slitted electro-. static shield located between said two sets of plates and having a radius of curvature substantially about the virtual center oi ray origin located within said flrst set of deflecting plates, saidshield being connected to said anode and also including means for applying electrical energy to said deflecting plates.

4. In a cathode ray system, a tube having an anode and means for producing, an electron stream, means for deflecting said stream in one direction about a virtual focal point or origin,

slitted shielding means substantially concentric means for producing and'proiecting a cathode' ray beam along said system of elements. 6. In a cathoderay tube system, a deflecting system comprising two conducting plates closely adjacent to one another and-.between'which the cathode ray stream passes, said plates taking the form substantially oi outer portions of segments oi a circle whose center is substantially at the point oi virtual origin of said cathode ray. stream, the arc oi said segment more remote from the centre being deiined by the polar equation:

'irom said point of ray origin to the arc of the segment nearer the centre, D is the minimum distance between the nearer and the more remote arcs, and is the angle measured from the iongitudinal axis of said deflecting system, and means for causing said cathode ray stream to pass between said-plates, including connections to sources oi electrical energy.

7. A cathode ray deflection and acceleration system including means ior, generating cathode rays, means for deflecting said rays so that they will have substantially a unique virtual point of origin, and means for accelerating the deflected rays, said last accelerating means comprising two spaced-apart cylindrical conducting sheets having slits therein and being curved about a center substantially coincident with unique point oi ray origin.

8. A cathode ray tube system including cathode ray accelerating apparatus for operation upon cathode rays having a common point of virtual origin, comprising two spaced-apart cylindrical conducting .sheets curved about said common point of origin of said rays and also including means i'or generating said cathode rays and bringing them to said common point 0! virtual origin..

9. 'A cathode ray deflecting system including means for producing an electron stream; means for deflecting said stream in one plane so that said stream shall at all times have substantially a single virtual point of origin, means for. de-

fleeting said stream in another plane and corrective means positioned between said two deflecting means and comprising a slitted cylindrically-shaped conducting sheet whose radius of curvature is flnite and greater than the radius oi curvature centered about said virtual point oi oncin.

10. A cathode ray system including means for generating an electron stream, means receiving said stream and deflecting it substantially in one direction only, and means for accelerating said stream alter it has been deflected, said last means comprising means ior producing about the point of virtual origin of said stream, located within said deflecting means, an electrostatic fleld substantially radial in character whose accelerating action upon said deflected stream is substantially coincident in direction with the direction or motion. or said stream after deflection, said accelerating means exerting substan- .tially no deflecting action upon said stream.

1 entering and passing through the fleld remains substantially the same and the projection of I 1 I; l, the stream-is substantially undistorted. from the point, of ray I noon 0. RESSLER.

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