US2239748A - Television scanning apparatus - Google Patents

Description

April Z9, 1941. R. URTEL TELEVISION SGANNING APPARATUS Fi'led Nov. 5, 1936 Ih'y.

AMPl/F/ER H R om n TU N m WFQR .T VL .o M NO n W ,w .0 R/ M Y TOR Patented Apr. 29, 1941 TELEVISION SGANNING` APPARATUS Rudolf Urtel, Berlin, Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application November-5, 1936, Serial No. 109,206

` In Germany May 17, 1936 (o1. ris-7.1)

l Claims.

My invention relates broadly to scanning apparatus for television and more particul-arly to an apparatus of the Nipkow disc type wherein errors due to irregularities are compensated.

A Nipkow disc comprises a plane face Amember containing apertures each adapted to scan one line of the optical image, these apertures being spaced apart by a definite angular width from each other and a varying distance radially from the center of the disc.

Theoretically, the angular relationship of the spacing between any two of the scanning apertures should be constant. However, in actual practice it is not unusual to find that the angular relationship of two of these apertures may vary from that between two other apertures on the same disc, due to errors in construction. As avresult, if one scanning aperture is used to develop a synchronizing signal at the time immediately preceding that when another aperture is used to start its scanning function, there will be a definite relationship between the synchronizing signal so derived and the picture signal,

lf the apertures were all located yangularly with respect to each other at exactly the same distance, then each synchronizing signal would bear the same time relationship to the line picture signals developed. However, as set forth previously, these apertures do not all bearthe same relationship with respect `to each other and, as a result, unless some method is found for compensating this error, the time relationship between the occurrence of the synchronizing signal and the line picture signals will vary, a condition which will result in an unevenly edged and distorted picture at the receiver.

Accordingly, the broad idea of my invention is to develop the synchronizing signal with an aperture which very shortly thereafter develops a series of picture impulses corresponding to a line of the picture, and to delay the mixing of the synchronizing signal by a definite time intervalthereby making the time relationship between the occurrence of the line picture signals and the synchronizing signals a constant.

A solution to the aforementioned problem has been attempted by placing the photoelectric means which develop the line synchronizing impulse immediately adjacent the photoelectric means by means of which the picture signals are developed. For constructional reasons, this arrangement is decidedly faulty and, accordingly, it has been necessary to space the two photoelectric means from each other by a distance greater than the angular distance between two of the scanning apertures. It is, therefore, the object of my invention to eliminate the errors set forth previously herein, due to faulty pitch of the scanning apertures, when the photoelectric means are spaced apart from each other at least by a distance greater than the angular relationship of two of the apertures in the disc.

Time delay means have been used previously in the scanning art, as illustrated in British Patent No, 415,118. However, those means were not for the same purpose, nor to solve the same problem that is set forth herein.

The invention will best be understood by reference to the accompanying drawing in which:

Figure 1 is one embodiment of my invention.

Figure 2 is an illustration of receiver line alignment.

Figure 3 is an illustration of receiver line alignment of the prior art; and

Figure 4 is a schematic showing of my in- Vention.

Referring to Fig. 1,` a portion of a Nipkow disc Ill is shown, said disc containing scanning apertures of elemental area arranged in a spiral form around the center of the disc, said apertures being designated as a, b, c, d, e, f, and g. The correct angular relationship between any two of these apertures is illustrated by the radial lines separated by an angle 0. As shown by the drawing, the position of the scanning aperture does not always fall on the correct radial line of the disc, as illustrated by apertures e and which are incorrectly pitched due to errors which normally occur in the manufacture of these discs. The disc is so positioned that the scanning -apertures will each in turn develop a synchronizing impulse from photoelectric means Il located immediately adjacent said disc Ill. Photoelectric means Il is joined to a time delay circuit (not shown). Time delay circuits per se are well known and their specific embodiment does not form a part of this invention.

Located at a definite angular distance from the photoelectri'c means ll is another photoelectric means I2 by means of which the picture signals are developed. Located immediately in front of photoelectric means I2 is a picture window I3. Masking means I4 are located adjacent said window and are adapted to mask the photoelectric means during the rgeneration of a synchronizing signal. Such masking means per se are well known in the art and, for purposes of simplicity, are not illustrated here.

Referring to Fig. 2, there is illustrated a view of a vertical portion of elemental width of the recreated picture which would occur at the receiver if the spacing of the scanning apertures were entirely accurate. Due to the correct time relationship between the line synchronizing signals and the line picture signals, the beginning of each line would occur immediately under the beginning of the previous line in such ya fashion as to make a perfectly even and undistorted recreation. Unfortunately, this does not occur in actual practice.

Referring to Figure 3, there is illustrated a vertical line of elemental width of a recreated picture at a receiver when the scanning -apertures of the Nipkow disc are subject to pitch errors. As shown, the beginning of a line due to scanning apertures b, c and d would fall in the correct position due to the correct location of these apertures on the disc. However, due to the difference in time relationship between a synchronizing signal developed by scanning aperture e, for instance, and the line picture signal, the beginning of the line scanned would fall considerably to the right of the line scanned by the aperture d, for instance. Immediately thereunder would be the line developed in accordance with the location or" scanning aperture f and this would begin considerably to the left of the vertical section provided by scanning apertures bl, c and d. The result is a distorted image.

The operation of the device is as follows, it

being borne in mind that the line synchronizing signal immediately preceding a line to be recreated is developed by the same scanning aperture that develops the line itself. For purposes of illustration, using scanning aperture e which is shown subject to the pitch error, the aperture e will pass before the photoelectric means ll which will develop a synchronizing impulse. This impulse is fed to a time delay circuit which delays the mixing of the picture signal and the synchronizing signal by a constant definite amount. Accordingly, when the aperture e moves to a position in which it is ready to scan a line of the picture, the relationship between the time of occurrence of the synchronizing pulse and the beginning of the scanning, will have to be constant since no matter what the pitch of the scanning aperture may be, assuming a constant rotation of the disc, it will always take any scanning aperture the same time to go from the position in which it develops a synchronizing pulse to the position in which it begins to scan a line of the picture. Hence, any pitch errors are obviated. This apparatus is particularly adaptable for use in conjunction with receivers of the cathode ray tube type.

Referring to Figure 4, there is shown schematically my invention. In this ligure the object 20 is optically passed through well known lens means 2|, and one line thereof passes through the aperture 2| in the scanning disc I0 and thence through the lens member 22 to imping-e onto the photocell l2. The signal from the photocell is amplied by means of an ampli- Iier, and the amplified signal is passed to a modulator. The masking means Hi is positione-d between the disc and the photocell I2. In this gure the photocell for developing the synchronizing signal has been positioned near the bottom of the disc since the amount of time that the synchronizing signal must be delayed is a function of its inception relative to the development of a video signal by the same aperture producing` the synchronizing signal.

What I claim is:

1. Television scanning apparatus comprising a Nipkow disc having spaced scanning apertures of elemental size, an optical window, photoelectric means located adjacent said optical window and adapted to be responsive to light values passing through the picture aperture Within said picture frame space, photoelectric means for developing synchronizing impulses, said latter means being spaced apart from said picture signal developing photoelectric means by a predetermined angular spacing, and a time delay means responsive to signals developed in said synchronizing photoelectric means for delaying the mixing of the picture and synchronizing signals developed by each scanning aperture for a deiinite interval.

2. Television scanning apparatus comprising a Nipkow disc having a plurality of scanning apertures therein and adapted to scan an optical image in strips of elemental width, means for developing electrical impulses representative of the light values of the adjacent elemental areas of said elemental strips, means for developing a line synchronizing impulse by each scanning aperture, means for masking the picture signal developing means during the period of development of said synchronizing pulse, and means for maintaining a constant relationship between the time of occurrence of a synchronizing pulse developed by a scanning aperture and the picture signals developed by the same aperture.

3. In scanning apparatus of the Niplrow disc type, the method or maintaining a constant relationship between the `time of occurrence of picture line signals and the synchronizing signals which comprises the steps of masking the picture and simultaneously developing a synchronizing pulse, delaying the joining of the pulse with picture signals for a denite period of time,

. sequentially developing picture signals representative of the optical values of strips of the picture of elemental width, and joining the synchronizing pulses with the picture line signal pulses developed by a single developing element while maintaining a constant time relationship between said synchronizing pulses and picture line signals.

fl. Television scanning apparatus comprisinga Nipkow disc having a plurality of scanning apertures therein and adapted to scan an optical imagein strips of elemental Width, means for developing a line synchronizing impulse by each of said scanning apertures, means for developing electrical impulses representative of the light values of the adjacent elemental areas of an elemental strip of said optical image by each scanning aperture at a time interval differing from that in which said synchronizing impulse is developed by said aperture, and means for maintaining a constant time relationship between the time occurrence of a synchronizing pulse developed by a scanning aperture and the picture signals developed by the same aperture,

RUDOLF URTEL.

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