US2006063A - Cathode ray apparatus - Google Patents

Description

June 25, 1935. A, w. VANCE CATHODE RAY APPARATUS Filed Oct. 15, 1952 luv/ me: ArZhm'I IZ Ham's.

mw tg HIS A TT'OIEWEK Patented June 1935 UNITED STATES CATHODE RAY APPARATUS Arthur W. Vance, Camden, N.. 1., minor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application October 15, 1932, Serial No. 637,885

3- Claims.

' tube at the transmitting station, and in which the tube comprises a photosensitive mosaic screen on which an image of an object is projected, and

which is scanned by a cathode ray, it has been found to be advantageous to project the image on the same side of the screen which is scanned by the ray. When this is done, the axis of the optical system for projecting the image is preferably perpendicular to the screen, but the axis of the so-called gun for developing and directing the ray of electrons is, of necessity, disposed at an acute angle to the screen. On account of this arrangement, the outline of the area scanned by the ray has a keystone shape rather than the desired rectangular shape. This distortion of the scanned pattern is manifested by a substantial and. corresponding distortion of the reproduced image at the receiving station, the reproduced image being also the shape of a keystone, with the vertical lines inclined to each other.

With the foregoing in mind, it is one of the objects of my invention to provide an improved television system of the character referred to wherein the keystone distortion is corrected.

Other objects and advantages will hereinafter appear.

In accordance with my invention, in a cathode ray tube of the character referred to, the ray is deflected in part by an electromagnetic field wherein the flux is disposed in planes substantially perpendicular to the axis of the electron gun, and wherein the distribution of the flux density on one side of the axis of the gun is dif-- ferent than such distribution on the other side of the axis. In this manner, the ray is caused to scan a keystone area in an intermediate plane perpendicular to the axis of the electron gun, whereby the ray is caused to scan the surface of the inclined screen structure over a substantially rectangular area.

. ratus of the character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawing, wherein Figure 1 is a perspective'view, partly diagrammatic, of a television transmitting app ratus embodying my invention;

Fig. 2 is a simplified, sectional view, the section being taken on the 'line 2-2 in Fig. l; and 5 Fig. 3 is a diagrammatic view illustrative of the principle of operation.

With reference to Fig. l, the reference numeral i0 designates a cathode ray tube provided with some suitable form of mosaic, photosensitive screen structure 82 upon which an image of the object is projected. The screen structure 62 comprises, generally, a supporting plate provided on the front surface thereof with a great number of minute metallic elements insulated from each other and from the plate, and each provided with a coating of photosensitive material.

An image of the object, shown as being in the form of a moving picture film i i, is projected upon the photosensitive surface by a suitable optical system it, the axis it of which is perpendicular to the screen structure i2.

An electron gun 20, of any suitable construction, operates to develop a my 22 of electrons, and to direct the ray at the photosensitive surface of the screen i2, the axis 24 of the tube being inclined at an acute angle of about 60 to the plane of the screen I 2.

For the purpose of causing the ray 22 to scan the photosensitive surface of the screen i2, sawtooth current waves at different frequencies are caused to flow through the coils 26, 28, 30 and 32. The coils 26 and 30 operate to deflect the ray vertically, while the coils 28 and 32 operate to deflect the ray horizontally.

In the constructions proposed heretofore, the ray 22 scanned the screen i2 over a keystone area ABCD as shown in Fig. 3, and as further illustrated in Fig. 1. This is accounted for by the fact that the screen i 2, in these constructions, was disposed at an acute angle to the axis 24 of the electron gun.

For the purpose of correcting for this action, I propose to make the coil 32 of a substantially greater number of turns than the coil 28, so that the deflecting field below the center line 34 of the tube will be substantially stronger than the field above this line. 'By this arrangement, the tendency is for the ray 22 to scan a keystone area EFGH in a planeperpendicular to the axis 24 of the gun. Therefore, when the ray strikes the screen l2; it will scan the surface thereof over a substantially rectangular area JKLM.

In cathode ray tubes of this type constructed so 6 hen. That is, there isuneven spacing betw the horizontal lines, the spaces between adjacent lines increasing from the lower edge of the scanned area to the top edge thereof. In my improved apparatus, 1 correct for this distortion by causing the vertical deflecting field to inc es the seem is deflected vertically, toward the portion of the screen where the lines are crowded and this is done by supporting the vertical defleeting cells 26 and 39 with the center line 3% oi the poles thereof ofiset or spaced downwardly from the center line 36 oi the tube 98.

It be understood that various m tions within the conception of those skilled in the art are possible without departing from the spirit of my invention or the scope of the c.

I claim as my invention:

1. Cathode ray epperatus comprising screen structure, means for developing a ray oi electrons and directing the ray at one side oi said structure, and means for deflecting said my to cause the same to scan seid structure, said deflecting means compriidng coils csed tively on opposite sides of the axis oi sold roydeveloping means, the turns of one coil bemg substantially greater in number than the t of the other cell.

2. Cathode my cpperretue comp screen structure, menus for developing o my of electrons end ectine the my act one-side oi emd structure, the axis of said ray-developing means being inclined at an acute angle to said structure, and means for deflecting the my to cause the some to scan it keystone area, in a. plane perpendicular to said axis whereby the ray is caused to the surface of said structure over a. substontieily rectangular area, said ray-deflecting meens comprising coils disposed respectively on opposite sides of the axis of said ray-developing meter, the. of one coil being substantially greeter in number then the turns of the other coil.

3. Cethode rey apparatus comprising screen structure, means ior developing a. ray of electrons and directing the ray at one side of said structure,- the axis of said ray-developing means being inclined at an acute angle to said structhe same to seen the surface of said structure; sold deflecting means comprising a. first set of complementary deflecting devices disposed respectively on opposite sides of said axis, the

center line of sold devices being substantially the second set being substantially greater in number then the turns of the other coil of the second set. I

An W. VANCE.

,ture, and means for deflecting the my to cause

Images