US2248554A - Production of an interlaced line screen with mechanical scanning means - Google Patents

Description

y 1941- K. SCHLESINGER 2 248,554-

PRODUGTION OF AN INTERLA CED LINE SCREEN WITH MECHANICAL SCANNING MEANS Filed Feb. 19, 1938 .7nvenf0r:

Patentecl July 8, 1 941 its T PRODUCTION OF AN INTERLACED LINE SCREEN WITH MECHANICAL SCANNING MEAN S Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, 1110., a corporationof New York Application February 19, 1932, Serial No. 191,449

In Germany February 22, 1937 g 1 Claim; (01. 178-7.6)

be understood as consisting of two field scanning operations with each part tracing n-l-M; lines of the complete picture frame where the complete scanning operation is assumed to include 2n+1 scanning lines, where n is a whole integer so that an odd number of scanning linesresults in the complete scanned frame. It is, however, geometrically impossible without optical compensating means, that is, merely by simple projection of a spiral aperture disc on the object, to obtain the desired n+ scanning lines per picture frame twice in succession without a jump being produced in the line period.

A further dilficulty, even if the first one did not exist, would consist in the fact that it would be impossible in practice to shade off by an interceptor one and the other of two spirals having a radial distance of only one image point diameter.

The present invention has as its primary object that of overcoming both of the above named difficulties, that is, the geometric as well as the shading condition. These results are accomplished by the two spiral discs operating as described in the following specification, and illustrated by the accompanying drawing; wherein- Fig. la. shows the image scanning disc; Fig. 1b shows the obtinator or masking disc for use with the disc of Fig. 1a; and, Fig. 2 schematically illustrates the manner of operating the discs and a suitable form of optical system.

According to the invention a scanning disc for the direct interlaced line scanning of stationary objects is arranged to rotate U+ /2 times for each part or field scanning, where U is an integer number, at least 1, and to rotate 2U+1 times for the complete or for each frame scanning so that the disc always completes an odd number of revolutions during a complete scanning operation.

The main scanning disc 4 is provided with two spirals a and b of apertures with each spiral having U+ turns and each of the spirals is displaced against the other by an angle of 180. An interceptor disc 3 is arranged to rotate once per image so as to uncover alternately the apertures of the one or the other of the spiral turns a and b of the scanning disc l.

As shown particularly by Fig. 1a, the image scanning disc t contains two separate partspirals a and h, each vof'which has 1 /2 turns, in this example U being 1. The spirals a and b are exactly congruent and aredisplaced against each other by For the'sake'of. better comprehension the part-spiral a is shown iniull lines and the part-spiral bin dotted lines. Scanning apertures, or the equivalent lens elements, are arranged along each spiral path a and b with the angular spacing between the scanning apertures being determined, generally speaking, by the Width of the pattern traced and the viewing Width desired for the scanned and reproduced images. The main scanning disc 4 performs three revolutions for a complete frame scanning. As will be seen, the image points never approach each other more closely than one-third of the height of the image, so that it is easy to shade oif the two part-spirals alternately by an interceptor which has its slotted portions a1 and 121 formed to reveal in sequence the apertures of spirals a and b of the disc 4 as these apertures pass before a viewing window. Each single part-spiral has such a pitch as to scan the complete height of the image and the spacing of successive apertures is such as to substantially equal the width of the image. If the scanning commences at the point A with the time mark 0 and the image change always takes place isochronously, i. e. always at the moment when the point A traverses the 0 line, the last image point of the a-spiral, A, has scanned exactly one-half of a line when the image change passes over from the first to the second part-scanning at B, as indicated by the arrow. At this moment the interceptor disc 3, illustrated in Fig. 1b, rotating at one-third the angular speed of disc 4 uncovers the second partspiral b for scanning.

The interceptor disc 3 performs exactly one revolution for a complete scanning, that is, for three turns of disc 4. The interceptor disc comprises two congruent half-spiral slots a1 and 171, each of which possesses a pitch equal to the height H of the image. The spiral slot (11 reveals the apertures arranged along the scanning spiral path a of disc 4 and the spiral slot b1 reveals the several scanning apertures arranged along the scanning spiral path b of the disc l. The cooperation of the interceptor disc 3 and scanner disc 4 may be perfected in different ways.

According to Fig. 2 the interceptor and scanning discs 3 and i are arranged in close proximity and the light of the source I, concentrated by a. reflector 8 and parallelized by a condenser I, traverses both the discs and is then projected by the lenses 2 and 9 upon the object plane l0. Nu-

merals 6 and represent conventionally the synchronous motors driving the discs 3 respectively 4.

In the case of a high number of lines as employed or proposed at the present time, namely, more than 400, a triple spiral is not sufficient to place so many apertures. In this case the value of U may be assumed as equal to 2 and then a 441 line picture there may be provided two spirals of scanning apertures on disc 4 with each spiral being approximately 2 turns and the angle of division between adjacent apertures being approximately 4 per scanning line. Under such circumstances circumferential velocity of the scanning disc with 5/2 turns per field scanning and 50 field scannings per second will be found to be of the order of 7,500 turns per minute. This circumferential velocity is naturally only possible in the case of discs running in a vacuum.

The 125-period current for the motor 5 is produced from the Ell-period current by a synchronous converter consisting of a four-pole driving motor and a -pole generator, while the motor 5 is bipolar. The interceptor 4 rotates once for each complete scanning and runs, therefore, with 500 revolutions per minute. It is driven from the power supply through the medium of a four-pole synchronous motor 6.

The design of the scanning device does not fundamentally vary in the case of other frequencies of the power supply so long as the image change coincides with the power supply frequency, which is usual in all interlaced line systems in order to prevent interferences in the synchronization by humming of the power supply. The method, therefore, is also capable of being employed without variation for example for -cycle power supply lines, with the exception that all stated circumferential velocities are to be understood as being 20% higher.

I claim:

In a television transmitter, a rotary scanning device for interlaced scanning of a stationary object, said disc having two substantially congruent spirals of apertures displaced one from the other by an angle of and each spiral forming U+ turns where U is a small integer number at least as great as unity, a rotary interceptor disc provided with two congruent spiral slots each extending for an angle of 180, and means to rotate said interceptor disc once per transmitted image and said scanning disc at a rate of 2U+1 times faster so that said interceptor slots uncover alternately the apertures of one of said spirals after those of the other spiral.

KURT SCHLESINGER.

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