US2122456A - Television system and method - Google Patents

Description

July 5, 193s; L, DE FOREST 2,122,456

TELEVISION SYSTEM AND METHOD' Filed lom. s, 193sv 4 sheets-sheet 1 INVENTOR. Lee de Fares ATTORNEYS July 5, 1938. DE FOREST TELEVISION SYSTEM AND METHOD Filed oct. 5, 193e 4 sheets-sheet 2 1NVENTOR.

Lee de Fores ATTORNEYS July 5, 1938. L. DE FOREST TELEVISION SYSTEM AND METHOD Filed Oct. 3, 1936 4 Sheets-Sheet 3 INVENTOR.` l. ee de Fores ATTORNEYS July5,193s. L DE FOREST 2,122,456

TELEVISION SYSTEM AND METHOD Filed Oct. 5, 1936 4 Sheets-Sheet 4 INVENTOR. L e de Fares af ATTORNEYS Patented July 5, 1938 UNITED STATES PATENT OFFICE TELEVISION SYSTEM ANDl METHOD Application October 3,

11 Claims.

An object of the invention is to provide apparatus for radial scanning in a television system. Another object of the invention is to provide a radial scanning system for television in which .51 there are no vibrating parts.

Another object of the invention is to provide a novel television scanner consisting of a disc or drum having a zig-zag linear aperture, and apparatus for and method of operating the same.

Another object of the invention is to provide a radial scanning system in which the picture may be of any desired shape without the necessity of using biasing voltages in order to produce this result.

Another object of the invention is to provide a scanning system having an intricate interweaved scanning pattern.

Another object of the invention is to provi-de a radial scanning system which avoids irregularities in the degree of illumination at the center or at the borders of the picture.

Another object of the invention is to provide an apparatus and method for linear scanning with a scanning disc or drum having a zig-zag linear aperture.

Other objects of the invention will be apparent from the drawings and the following description of the features of the invention and in the provision of apparatus and methods of operation for accomplishing the foregoing objects.

In the drawings,

Fig. 1 is an elevation partly in section of a portion of one species of my invention in which my novel scanning disc is used;

Fig. 2 is a section along the lines of 2-2 of Fig. 1;

Fig. 3 is an enlarged schematic View illustrating the cooperation between a plate having a linear aperture which I use in connection with my scanner, and the zig-zag linear aperture of the scanner itself;

Fig. 4 is an elevation of another form of my invention in which a scanning drum is used;

Fig. 5 is a section along the lines 5--5 of Fig. 4;

Fig. 6 is a schematic showing oi another species of my invention in which my novel scanning disc is used;

Fig. 7 is a, front elevation of my viewing screen 50 with a portion of radial scanning lines outlined thereon;

Fig. 8 is an enlarged schematic showing illustrating the operation of my Zig-Zag linear aperture in the scanning disc and drum, and further illustrating the arrangement of this aperture to 1936, Serial No. 103,844

secure a picture that may be square or of any other -desired shape;

Fig. 9 is a view illustrating the nature of the scanning pattern produced with my novel scanning arrangement;

Fig. 10 is a view of a modification of an aperture in an opaque plate in order to produce a desired amount of illumination;

Fig. 11 is a side elevation partly in section, illustrating how my novel scanning means may be used to produce parallel line scanning;

Fig. 12 is a schematic view illustrating a portion of the apparatus shown in Fig. 11;

Fig. 13 is a diagrammatic view illustrating the parallel line scanning obtained with the Figs. of 11 and l2, or Fig. 14; and

Fig. 14 is a partial elevation of a modification of the apparatus shown in Figs. 11 an-d 12 in which parallel line scanning is obtained with my novel scanning disc.

In my application Serial No. 70,061, iiled March 21, 1936, for Radial scanning television system I have disclosed a television scanning system in which a vibrating mirror is mounted upon a resonant torsional'member and located in line with axis of a small motor, and is caused to rotate by said motor at the same time that it is vibrating or twisting through a plane at right angles to the axis of the motor. By this arrangement a beam of light reflected from the vibrating and rotating mirror is caused to trace a multiplicity of approximately radial lines of light upon a screen, the center of which is located in line with the axis of the motor.

The invention herein described attains the same general object of radial scanning without any vibrating mechanism, and may also be used to obtain rectangular, linear scanning. By means of the present invention I am enabled not only to avoid any complications which might occur due to changes in the mechanical vibrating system, etc., but I am enabled to use much larger mirror surfaces with resulting enhanced intensity of light upon the viewing screen. I am also able to throw upon the screen a picture of any desired shape such as square, oblong, oval, etc., without the necessity of using biasing voltages as disclosed in my copending application above referred to.

Similar reference numerals refer to similar parts throughout the specification.

In Figs. 1 and 2 a circular opaque disc l is mounted with its center in line with the shaft of a synchronous motor 1. The disc l has arranged near its periphery a series of transparent zigzag lines 3 of equal spacing and length arranged in circular formation. These transparent lines may be made by sawing or cutting zig-Zag lines in a metallic disc, or the disc may be a glass photographic plate and an enlarged black and white drawing of the desired dimensions may be photographed thereon, preferably with photographic `reduction of dimensions in order to reduce any 'errors or irregularities which may exist in the original drawings. In one form of the invention which I have constructed, this circular photographic plate I is 6 inches in diameter and` carries a central, circular orice 2, one-half inch in diameter. The length of the individual lines of the circular zig-Zag pattern is one-half inch. This opaque plate is preferably mounted in a vertical plane with its center a short distance from the end of the projecting shaft 6 of the motor ll. It may be mounted in a pheripheral rim 5E:- of metal or plastic in order to support it. The shaft 6 of the motor 1 carries a radial arm I 5 attached tothe outer end of which is a thin, opaque plate 4 which carries a radial slit 5 so arranged that the plate 4 travels in a circular path close to, and parallel with the opaque disc I. The radial arm I5 also carries an incandescent lamp 8 having a filament so arranged that it represents a continuation of the radial line of the arm I5, and is therefore parallel to the slit 5 in the plate or the new high pressure capillary quartz mercury vapor lamp may be used. A small semi-cylindrical condensing lens 9 may be placed between the light source 8 andthe plate 4, so arranged so that the light of the filament is concentrated upon the slit 5, and a cylindrical reflector I0 may be mounted behind the lamp to increase the brilliancy of the light. One lead from the lamp 8 may be connected through a conductor IE to a connector ring I2 mounted upon the shaft the motor. Bearing on this connector ring is a brush I3 which is connected to a suitable source of potential I4 to light the filament of the lamp. The return lighting circuit is completed to the arm I5 and the frame of the motor T. The motor should preferably be a single phase synchronous motor of i800 or 3600 revolutions per minute.

By the above described arrangement I obtain through the disc I, a small point of light 3i, Fig. 3, through the small diamond shape aperture formed where the radial slit intersects or crosses one of the Zig-Zag transparent lines in the opaque disc I. The point of light thus obtained moves in and out along the radial line towards and from the center of the circular disc I as the lamp 8 and the plate 4 carries in a circular motion around and close to the transparent zig-Zag track the opaque disc I.

In connection with the apparatus shown in Figs. 1 and 2 I employ additional apparatus as shown in Fig. 6 and described in connection therewith. I also may employ a system of gears and connections BU, 6I, 62, 53, 64to move the disc I in order to vary the scanning pattern. This will be described later. For the purpose of the description up to this point the disc I may be considered as stationary.

Instead of the opaque discy carrying the Zigzag transparent line as described above in connection with Figs. 1 and 2, I may employ for my scanner an opaque cylindrical strip I1 as illustrated in Fig. 4 through the surface of which a transparent Zigzag line I8 has been cut, or if the strip' be of glass has been photographed as above described. In Fig. 4 the synchronous motor 'I constitutes the driving means as before and has fixed to an armI 5 a reflector III, linear light source 8, lens 9, and opaque plate 4' having a linear slit 5. The opaque cylindrical band I'I is stationary and its center lies in the axis of the shaft of the motor 1. The intersection or crossing of the slit 5 with the zig-Zag slit I8 in the periphery of the cylindrical band Il results in a diamond shaped point 3|, Figure 3, as before, through which a small pencil of light is projected radially toward the axis of the motor. As the motor drives the lamp 8 and plate 4 around the periphery of the band I'I and in close proximity thereto, this point of light travels back and forth to and from a plane perpendicular to the axis of the motor and. in the directions always parallel to said axis. Also secured to the shaft ll of the motor 'I and rotated thereby is a funnel shaped holder 35, within which, and rotated therewith, are mounted a mirror 34 at an angle of 45 degrees with the plane of the cylindrical band I1, a Kerr cell having a circular polarizing plate 52, a circular analyzing polaroid plate 5i, and a condenser system 53, 54. A cross section of the Kerr cell taken along the line 5=5 of Figure 4 is shown in Figure 5 with the same reference numerals.

A brush 51 bearing upon the periphery 55 of an 'i insulated collector ring mounted on the holder 35 is electrically connected to one output terminal of the modulating amplier which suppliesk the television signals, while the other terminal of said modulator is connected to the framework of the apparatus.

Also mounted within the holder 35 and rotating therewith is a lens 31 which may be a spherical lens, or a cylindrical lens with its axis set at right angles to the axis of the cylindrical lensr 9 in order to focus the beam of light after is reiected from the mirror 34 so that at the screen 38 it becomes a small point of light. If the mirror 34 were a plane mirror, as indicated in broken lines, the beam of light from the aperture which is shifting in planes radial to the shaft of the motor and towards or from a plane perpendicular to the axis of the motor, would be caused to lill a cylinder of light as the motor and light system rotate. Such cylinder of light is indicated by the broken lines 32 in Fig. 4. If, however, in place of the iiat mirror I employ a convex cylindrical mirror 34, the shifting beam of reflected light is caused to spread out radially so that the limits of its trajectory represent a conical instead of a cylindrical envelope, as indicated by the full lines from the mirror 34'v to the points nearer the upper and lower edges of the viewing screen 38. The angle of this cone may be made anything desired within reasonable limits simply by increasing the angle of curvature of the convex mirror 34. A slit 35 in the side of the holder 35 admits light from the lamp 'Sto the mirror 34.

The area of the beam of light upon the viewing screen depends upon the size of the picture area but ordinarily I prefer to restrict it'to an area equivalent to that of a circle -fg to 1A; inch diameter, when the screen is of Ithe order of '34 inches in diameter, if a circle, o1' 24 inches on each side if a square. The screen 38 is preferably located 4 or 5 feet from the mirror 34 and may of course be of translucent material and viewed from behind.

In Fig. 6 I have illustrated diagrammatically an arrangement whereby the light source instead of being attached to the motor shaft and made to travel in a circular path may be stationary. In this figure I have again shown a reflector IIJ and a linear light source 8, and a condensing lens 55.- I have shown the-Kerr'cell 5 I-54;which kning lines A--A outlined thereon.

laisance receives .themodulated signal wave, in line with the beam of light from the lamp 8. A synchronous motor 'l is again used. In this case it is provided with a hollow shaft, which is preferably blackened, and the light system is mounted axially with respect thereto so as to direct the beam through the shaft. Mounted on an arm secured to the motor shaft is a 45 degree mirror or prism 22, a second45 degree mirror 23, a lens 9, and a plate 4 with a slit 5. Mounted on another arm securedto the motor shaft is another 45 degree mirror 24 and another 45 degree convex mirror 25. The stationary scanning disc l, which is again an opaque disc with zig-zag transparent circular lines as already described in Figs. 1 and 2, is placed between the two mirrors 23 and 24. The light from the lamp 8 after being modulated in the `Kerr cell is reflected from the mirror 22 tothe mirror 23 where it is condensed into a narrow vbeam of light by the lens 9 and projected through the slit and the zig-zag aperture 3. Itis then reflected by the mirrors 24 and 25 and from there, due to the rotation of the light vand mirror system, projects as a cone of light through the mask 40 and lens 26 onto the screen 38. A slit in vthe hollow shaft 6 of `the motor 'l permitsV the narrow beam of light to be reected from the mirror 22 to the mirror 23. The axially shifting pencil of light which is reflected from the mirror` 24 upon the mirror 25 is there reflected so that it describes approximately radial lines upon the` screen 38, completely covering the same in the form of a circular area of illumination as in the case of the apparatus shown in Fig. 4. The mirrors 24 and 25 which are carried on an arm rotated by the motor shaft, and the lens 26 and mask 40 may also be used in connection with the apparatus shown in Figs. 1 and 2 to` complete the system there described. It will thus be seen that in the case of the apparatus .caused toscan the entire surface of the viewing' screen so that the signals will be reproduced.

Ihe lens 26v of Fig. 6l may be made spherical and remain stationary instead of being cylindrical and rotating with the motor shaft, as in the case of the lens 31 of Fig. 4. A similar sta- .tionary lens could, of course, also be used with Fig. 4.

I In Fig. 7 I have shown the viewing screen in front elevation with a portion of the radial scan- If it is desired to show only a square frame picture, such as outlined in broken lines D, E, F, G, I may employ a mask of non-reiiecting material, such as blackl velvet, to mask the viewing screen, or I mayv employ a square metal mask, such as 4U in Fig. 6, located between the revolving convex mirror 25 and the stationary lens 26; or if the lens 26 is attached to the frame 35 as the lens 3l in Fig. 4, and made to rotate with the mirror 34, this stationary frame should be placed between `the-lens 3T and the screen 38. The area of illumination will then be cut down to the shape of a square, as indicated by the broken lines D, E, F,- G, and the scanning lines B-B, Fig. 7.

Inasrnuch as all of the radial paths traversed by the light beam must pass through the center of thel screen as at C, Fig. 7, this portion of the screen becomes more luminous than the outlying sections, notwithstanding the fact that the light beam traverses the centersection with the maximum velocity of transit. Similarly, around the peripheral section of the circular screen illumina.-

tion where the radial movement of the light beam is slowed up and reversed in direction, there exists a brighter ring of illumination. If the mask D, E, F, G, is not used and the picture therefore vis circular in outline, this latter ring affords an artistic circular frame bordering the projected television picture. If the square masking frame D, E, F, G is employed, this bright peripheral ring is masked from View except for a small portion in each of the four corners of the picture.

It is usually desirable that the central area of the screen be no more brightly illuminated than the remaining portions. To accomplish this, I simply darken a small circular area of the screen as shown at C', Fig. 7, preferably by lightly spraying it with some opaque, or poorly translucent, or poorly reflecting material.

When the above described square mask is employed, the four arcual sections of the illuminated circle are lost to View, the sweeps of the point of light which extend beyond this square frame being quite useless. However, by altering the lengths of successive lines of the zig-zag aperture in my scanner it is possible to limit the excursions of the beam so that the envelope of the reversal points will become a square in outline. Such an arrangement is illustrated in the circular drum scanner of Fig. 4 and in enlarged detail in Fig. 8.

Referring to Fig. 8, I have there shown an enlarged plan view of the circular drum l1 with the zig-zag aperture IB so arranged that the two symmetrical envelopes upon which the successive apices of the zig-zag lines around the cylindrical drum terminate, instead of being parallel lines, follow a secantial form. In this iigure the divisions along the horizontal or abscissal axis represent equal angular deflections of the radial beam about the central axis of the motor shaft. 'I'he ordinates of the two symmetrical curves are proportional to the successive secants of these angles from zero to 45 degrees, from which limiting angle the course of the envelope or secantial curve is reversed, inasmuch as the radial deection at the 45 degree angle of the horizontal line is the maximum actually obtained. If, therefore, the lengths of the zig-Zag transparent lines photographed upon or cut through the circular band Il of Figs. 4

and 8 are limited in accordance with this secantial quadrant curve, four times repeated about the circumference, I obtain corresponding increases and decreases of the radial excursions of the beam of light reflected from the convex mirror 34 as the optical system is rotated, and thereby obtain a square picture. Similarly, where I employ a circular opaque disc I as in Figs. 1, 2 and 6, I may also limit the radial sweeps of the beam of light so that its limiting envelope upon the viewing screen becomes a square instead of a circle.

The envelope limiting the zig-zag transparent lines as these extend around the band Il or the disc I may be arranged in any desired arbitrary manner so that I may throw upon the viewing screen a picture of any desired shape or form, for example, rectangular, oval, elliptical, etc.

In Fig. 8 the opaque shield 4 is indicatedin broken lines with the light slit 5 therein. The transparent lines in the opaque drum or disc instead of being straight may be made slightly curved if desired in such a manner as to equal ze to some extent the speed of transit of the light spot over the surface of the viewing screen. Also the bright spot at each terminus of the radial excursion of the beam over the surface ofthe screen may be obliterated by simply separating the ends of each pair of converging zigzag lines at their terminae upon an opaque disc or drum so that when the straight line slit in the moving member 4 passes across the apex of two approaching zig-Zag lines nolight is transmitted therethrough.

Similarly, instead of rendering more opaque or less reflective a small central area of the viewing screen, I can make the central region of the Zig-zag lines narrower than the outer portions thereof so that'less light is transmitted at the point where the slit crosses the central portion of each zig-zag line, thereby automatically reducing the brilliance of the central region of the viewing screen. Or, as illustrated in Fig. 10, I may make the slit 5 narrower at its central region than it is at its extremities in order to accomplish this same result.

I have pointed out that the speed of transit of the light spot as it crosses the central area of the viewing screen is at a maximum and also that all diametric excursions of the light are concentrated in this central area. This constitutes one of the especial advantages of my radial type of scanning as the central portions of any picture are usually the most important portions and demand the greatest amount of illumination and the maximum neness of detail. These qualities are automatically afforded by the increased speed of the spot over the central section of the picture and by the fact that the spot of light traverses these central sections twice for every diametric excursion of the spot regardless of the peripheral separations of the radial excursions. v

`In Fig. 9 I have outlined the approximate paths which the radially moving spot of light actually traverses over the surface of the screen. Therein the line 0 1 represents the first radius over which the beam of light would be deflected outwardly from the center of the screen if said deflection were at infinite speed. As'the speed is not infinite the spot instead follows the narrow elliptical or approximately elliptical path as there shown between the radiallines 1 and 2. Thus the return of the spot of light approaches the straight radial line 2 as the spot approaches the center of the circle and its speed of travel is correspondingly increased. When the spot passes the center and goes into the lower section of the circle its trajectory instead of lighting the ,screen between the extensions of radii 1 and 2 will light it between the extensions of radii 2 and 3 and upon the re-entry of the spot into the upper sector of the circle it will traverse the space between radii. 3 and 4, and so on around the circle until one-half of a revolution of the motor shaft has been completed. Thus if there are 64 diametric excursions of the spot `of light during one revolution of the motor, the last excursion of the spot of light before a half In order to obtain a more intricate interweaving of scanning lines across the face of the picture than the simple alternate weaving above described, I may slowly rotate (or oscillate through a small angle) the fixed opaque disc l of Figs. 1, 2 and 6, or the drum I'l of Fig. 4, in a direction preferably opposite to the direction of travel of the radial arm I5. This slow motion of the disc or drum may be Very simply effected by means illustrated in connection with the disc in Figures 1 and 2 in which I show a worm 60 on the motor shaft meshed with a gear 6| on a flexible shaft 62 which terminates in a spur gear 63 meshing with gear teeth 64 in the periphery of the frame which supports the disc l. In such an arrangement I may choose a speed reduction ratio between the number of revolutions of the motor shaft and that of the opaque disc or drum which is incommensurable. When such a gear ratio or uneven speed ratio is chosen the motor must theoretically make a very great number or even an infinite number of revolutions before any given path of the scanning spot across the screen exactly repeats itself. I thereby obtain the effect of an extremely complicated system of line interweaving which has never been remotely approached by any other known method of scanning, either mechanical or with the cathode beam. It is thereby impossible for the human eye to detect a marked linear action or linear quality of the projected television picture. This adds greatly to the sense of continuity of the picture thus projected as well as affording a finen'ess of detail which is quite impossible to obtain by any ordinary method of interweaved scanning.

In Figs. 11, 12 and 14 I have shown an arrangement whereby the essential elements of Figs. l, 2, 4 and 6 are used but in which by maintaining the source of light, the rectilinear slitvand the convex mirror stationary while the opaque disc or drum is rotated at high speed, I can obtain a parallel line scanning of the screen or object such as is had with the more conventional devices for scanning known in the art to-day.

In Fig. 11v I have illustrated apparatus for accomplishing this result with the opaque drum I1. In this case all of the transparent zig-zag lines I 8 are of the same length. I mount the drum upon the shaft of the synchronous motor 1 and centrally locate it with respect lthereto and attach to the frame of the motor by an arm 'IT the linear source of light 8, reflector IIJ, lens 9, and plate 4 with slit 5, with the linear light source and aperture placed parallel to the axis of the motor shaft and so located that the cylindrical surface of the drum I1 passes under and close to the plate 4. Between the drum l1 and the motor shaft I mount the convex 45 degree mirror 34 in fixed position upon an arm T8 so that its chordal plane is at right angles to a vertical plane passing through the axis of the motor shaft. The mirror 34 need not be located in line with the axis of the motor shaft but is preferably quite close to the inner surface of the drum I1. This arrangement gives me a sweep up and down ina vertical plane of the beam or pencil of light which passes through the crossed apertured line of the drum and fixed plate as the drum revolves. 'Ihe angle of deflection of this beam in the vertical plane may be made as large as desired with.

in reasonable limits by altering the convexity of the mirror 34. In order to scan completely a viewing screen or object by means of this rapidly moving pencil of light, it is now necessary merely to cause the vertical plane of its sweep to move horizontally and to repeat this horizontal movement periodically. This is simply accomplished by the use of a plane mirror or mirrors 80 rotating about a vertical axis which maybe driven by a gear 6| on the motor shaft which meshes with a gear 82 on which the mirror is mounted in order to move the mirror in synchronism with the scanning drum Il. A four sided or polygonal drum mirror 8i) may of course be used instead of a simple planedouble mirror and by properly arranging the mirrors 34 and 8U relatively to each other in a manner wellrknown in the art it is possible to obtain essentially continual illumination of the screen.

In Figure 12 I have shown a diagrammatic plan view of the apparatus of Figure 10 in which the opaque plate 4, slit 5, mirror 80, and screen 38 are shown.

I have also illustrated in Figure 13 the scanning pattern from which it will be seen that the object or viewing screen is scanned in parallel vertical lines.

With an arrangement for rectangular parallel line scanning such as I have described, I prefer to employ motor and mirror speeds for a given number of zig-zag lines about the apertured drum to give 200 to 300 vertical sweeps of light per sweep of the horizontal deflecting mirror and 24 or 30 such horizontal sweeps per second. The former defines the line frequency and the latter the so-called picture frequency of scanning.

In Figure 14 I have disclosed an alternative arrangement for parallel line scanning in which a zig-zag apertured disc l similar to that shown in Figures 1, 2 and 6 is used. In this case, however, the reflector I0, linear light source 8, opaque plate ll with its light slit 5, and convex mirror 34 are stationary, while the disc I is being rotated by the motor l. I also rotate a mirror or mirror system 8U by means of gears 6| and 82 similarly to Figure 11. In this case the beam of light is reflected back and forth in a horizontal path across the screen 38 and its vertical movement is controlled by mirrors 80. To obtain vertical line scanning which gives better picture effects than does horizontal, it is necessary only to mount the apparatus so that the motor shaft is vertical rather than horizontal.

I have also shown in Figure 14 a Kerr cell 5l, 52 for producing a modulated beam in accordance with signal modulations, between the light source 8 and the opaque plate 4. The Kerr cell may be used in a similar location in the showing of Figure 11 or it may bev located as shown in Figure 4.

Regardless of how complicated the scanning pattern of the television receiver may be, as for example with the apparatus illustrated in Figure l, it is only necessary that an identical scanning pattern be followed at the transmitter and that perfect synchronism between transmission and receiver motors be maintained in order to receive successfully the picture which is being transmitted. Therefore the descriptions of various types of mechanism above in connection with a television receiver will apply equally for pickup scanning devices, with the substitution, of course, of a `fixed brilliant spot light source at the transmitter pickup in place of the modulating light which I have described in conenction with the receiver scanning apparatus. Thus, for example, if I am illuminating the object at the transmitter by means of the so-called flying spot, the arrangement of Figures 1, 2 and 11 is applicable, or the arrangement shown in Figures 4, 6 and 14 may be directly substituted as the flying spot pick-up simply by omitting the light modulating arrangement there shown. In other Words, the source of light for the iiying spot pickup may be either stationary as shown in Figures 6, 11 and 14 or may be mounted on a radial arm driven by the synchronous motor as shown in Figures 1, 2 and 4.

It is of course necessary that the synchronous motors at the transmitter and receiver stations be kept in exact synchronism. I have found that when single phase synchronous motors of suiiicient power are employed perfectly satisfactory synchronism may be obtained by simply connecting them to the same power network, even though there may be from time to time slight variations in the exact cycle speed of the powerhouse generators supplying the mains. As both synchronous motorsare identical any slight alteration in driving speed from the powerhouse will affect all such motors alike.

If, however, it is desired to synchronize a transmitter station with a receiver lying outside of the same lighting supply district, the receiving motor may always be kept in perfect synchronism by means well known in the art, such as by transmitting a synchronizing signal intermingled with the television carrying signal, filtering the synchronizing signal out from the picture signal at the receiving station, amplifying this synchronizl ing signal, and causing it to control b y means of a small so-called sonic motor a larger motor of adequate power, which motor may be supplied from any suitable source of current.

The exact shape of the spot of light which I obtain from instant to instant as the straight line slit 4 passes the zig-zag slit, while in general of diamond shape as illustrated at 3|, Figure 3, may slightly alter its shape while passing through the scanning cycle. This change of shape of the spot is unimportant so long as the area of the spot is maintained sufficiently small for satisfactory fneness of picture detail and so long as the spot upon the receiving screen is identical in shape and location with the corresponding flying spot produced by the transmitter pickup.

While I have mentioned a flying spot pickup at the transmitter, it is equally possible by means of my apparatus described above to scan a small photograph, as when transmitting motion pictures from a positive film. In this case the lm is held stationary in front of the flying spot signal and sufficiently close thereto so that a frame of the motion picture film lies entirely within the circular area scanned by the flying spot or within the rectangular area scanned if the zig-zag line in the opaque section is of the type illustrated in Figures 4 and 8. For iilrn scanning purposes the whole scanning device is made sufliciently small and the projected spot sufficiently fine that the necessary detail of the small picture is obtained. Additional lenses may of course be employed, if necessary, in a manner well known in the art. The iiying spot or pencil of light passes through the transparent film and falls upon the cathode of a photoelectric cell having a sensitive surface of area equal to or larger than the projected motion picture frame.

By my system of scanning, it is obvious that the motion picture frame being scanned should be held stationary for a period at least equal to that of a complete scanning cycle, that is of one revolution of the motor. Inasmuch as the standard speed of motion picture projection is 24 picture frames per second, it is desirable that my motor shall turnv at a speed of 24 or more revolutions per second. .11 For directpickup, as' of outdoor scenes or from a brilliantly illuminated stage, I prefer to use a large lensfas in a portrait camera and project the' picture of the outside scene or stage scene upon the ground glass of such a camera, behind which I locate my pickup scanning mechanism. This screen is preferably of lsmall dimensions to give maximum light intensity toii'the projected scene. I then use a photoelectric cell in place of the ylamp 8, the leads from which are carried tothe rst stagelof the photoelectric amplifier, using acollector Vring and brush as in Figure l for one lead and Ythe motor frame for the other the photoelectric cell is mounted for revjplution as in Figures 1, Zand 4. Then in addition to or substitution for the cylindrical lens 37, Figure 4, I prefer to employ a narrow viewing slit-placed in front of said lens and parallel to its axis. 'I'he thicknessof the opaque biock through which this slit is cut is made sufficiently great so that the light which falls through this deep slit upon the convex mirror 3i is limited to a singlepicture elementorv line of the ground glass screen of the eamera upon which the scene to be transmitted is projected. Although the lightY thus picked up Vby the photoelectricl cell from la singleY picture element is extremely small, it is possible by use of the now Well known-.electron multiplier tube to obtain adequate signal impulses With this form of direct pickup. Obviously, the intensity of the light isrenhanced byusing a very fast lens o VYshort focal length and locating the pickup mechassiVY nism close to the small but brilliant picture which is projected upon the ground glass screen of the viewing camera.V Y

In place of the 45 cenvex mirror 25, Yor 34, of

nthe attached figures I may employ a simple flat mirror and a double concave, or'a plano-concave, lens suitably, located-in front of this flat mirror, with the lens axis inline with the axis of the motorshaft. The action of Such lens will be to deflect the beam of light from the 45 flat mirror,

and thereby-greatly accentuate the angle of deture of linea-r outline, a' second opaque member having a-linjear transparentn aperture, a light source, a system ofmirrors for reflecting the lightf from said source which projects through said apertures, and rneans for moving said parts so that the mirrors cause the light beam toi dene radial scanning paths. i

3. In a television system a stationary opaque member having a Zig-zag linear transparent aperture therein, anopaque plate having a linear 'transparentj aperture therein, a light source,

means for moving said plate and light source relatively toY said stationary opaque memberg-and means for reflecting the beam froinsaid iight source to cause itto traverse radialpaths within a prescribed envelope. Y

4. A television scanning system comprising a stationary opaquef: member having a zig-zag linear transparent aperture therein, a source of light, an opaqueplate having alinear transparent aperture therein, means for projecting a light beam through said transparent apertures to cause la moving pencil of light to be projectedfgthrough said opaque member, and means for reflecting said pencil of light to cause it outline a radial Yscanning pattern. 1;

5. A Ytelevisionk system comprising an opaque member having a Zig-zag linear transparent aperture therein, an opaque plate having a' linear transparent aperture therein, a source of light, a rst-,mirror arranged at a 45 degree angle to g the direction of travel of said light beam, a second 1 mirror arranged at a 45 degree angle in the Y directicn of travel of said light beam after itis Y reflected fromsaid first mirror, and means for Y rotating said source or light, Yopaque plate and mirrors about said opaque member.

6. A television system comprising an opaque member having a zig-zag linear transparent aperture therein, an opaque plate having a linear transparent aperture therein, a source Eof light, a rst mirror arranged at a 45 degree angle to the direction of travel of said light beamafter it is projected through said apertures, a second mirror arranged at a 45 degree angle to the direction of light reflected from said rst mirror, means for rotating ,said source of light, opaque plate and mirrors about said opaque member,` and means for moving said opaque member to vary the scanning pattern. "Y

7. A television system comprisinggan opaque member having a zig-Zag linear transp-arent aperture therein, an opaque plate having a linear transparent aperture thereina source of light, a rst mirror arranged at a 45 degree angle to the direction of :travel of said light beam afterit is projected through sai-d apertures, a second mirror arranged at a 45 degree angle to the direction of said light beam after it is reflected from said :iirst mirror, means for rotating said source of light, opaque plate and mirrors about said opaque memberyand means for modulating said light beam in accordance Withreceivedtelevision signals.

8.V A television system comprising an'opaque drum having a Zig-zag linear transparent aperture therein, a light source, an opaque plate having a linear aperture therein, means for rotating said light source and opaque plate about'said drum, a mirror at the center of said drum, andv means for rotating said mirror about the axis of said drum.

9'. A television system cemprising an opaque drum having a Zigi-Zag linear transparent aperture therein, a light source, an opaque plate having a linear aperture therein, means for rotating said light source and opaque platefabout said drum, a mirror at the center of said 'drum, means for rotating said mirror abeutthe axis of said drum, and means for modulating said light beam in accordance with received television sigin, said plate and member being arranged to pass-*75' a pencil of light reiiected from said second mirror, a third mirror rotated by said motor shaft arranged at a 45 degree angle with respect to light reflected from said second mirror and projected through said plate and member, and a fourth mirror rotated by said motor shaft and arranged at a 45 degree angle with respect to light projected from said third mirror.

11. A television system comprising an opaque member having a zig-zag linear transparent aperture therein, an opaque plate having a linear transparent aperture therein, an optical system for projecting a beam of light through said apertures and reiiecting the same to dene a linear path, a mirror, and means for periodically shifting said mirror to shift said beam over a restricted area at right angles to its path.

LEE DE FOREST.

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