US2227010A - Television scanning means - Google Patents

Description

Dec. 31, 1940. K. SCHLESINGER TELEVISION SCANNING MEANS Fild Aug. 4, 1936 2 Sheets-Sheet 1 Fig. 2.

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Dec. 31, 1940. K. SCHLESINGER 2,227,010

I TELEVISION SCANNING MEANS Filed Aug. 4, 1936 2 Sheets-Sheet 2 Patented Dec. 31, 1940 UNITED STATES JPATJENT QFFlCE Kurt Schlesinger, Berlin, Germany, assignor, by mesne assignments, to Loewe Radio, Inc-ya corporation of New York Application August 4, 1936, Serial No. 94,129

In Germany August 6, 1935 1 Claim. (Cl. 178' 7.1)

As well known, a transmission with interlaced groups of lines is brought about in the case of a televisiontransmitter with Nipkow disc (see application Ser. No. 36,008, filed August 13, 1935) bythe use of a perforated disc having a plurality of spirals and having its direction of rotationso arranged that the radial movement of the image pointsoccurs in opposition to the movement of the film image projected on to the disc. In the above-mentioned application it has then also been proved in what manner in the case of a relative movement of this nature between image point and image the correct scanning with interlaced lines takes :place. t It has already been pointed out in the applicationTSer. No. 60,295, filed January 22, 1936, that a considerable difficultyresults in this method due to the fact that the length of the arc in respect of theinner image points is smaller than that in respect of the outer image points of the spiral. Thesectional area of a spiral aperture disc is not a rectangle, but a trapezium, whilst the light image projected on to the disc is, generally speaking, a rectangular image. Since these figures are not adapted to each other, the two part-images in the method do not exactly register. As a remedy there was set forth the production of a trapezium in optical fashion by inclination of the plane of the film and the lens.

It is not a simple matter to adjust this trapezium so accurately that the desired coincidence is brought about. As a remedy and for the purpose of facilitating the adjustment there may be employed with large measure of success the following method in accordance with the invention which consists in thatthe time spacing between each two successive line changing impulses is varying in such a manner that an inaccurately projected image may still be reproduced in exact rectangular fashion at the receiving screen.

The novel features which I believe to be characteristic for my invention are set forth with particularity in the appended claim. My invention, however, both as to its organization and method of operation together with further objects and advantages thereof may be best understood by reference to the following description taken in connection with the accompanying drawings, in which Fig. 1 shows an example of a distorted image projection.

Fig. 2 the bad result in the received picture which is due to this distortion in the projection to the Nipkow disc, While Figs. 3 and 4 show exemplary embodiments in schematic form with which remedy may be obtained.

Referring now in particular to the figures in Fig. 1 the trapezoidal sectional area of the scanning spiral 5 is represented by the. four corners l 2, 3, 4. This spiral is shown as a double spiral; the idea, however, may also be extended to discs having a greater number of spirals. It is assumed that the light image projected on to the disc, due to a slight error in the optical adjustment, is not exactly congruent with the sectional trapezium, but differs from the same as shown by the lines I, 2', 3', 4. This light image is indicated by shading. If an image of this nature is transmitted by the disc 5 and is composed at the receiver in such fashion that the sectional area A is disposed over the sectional area B, there is obtained a received image according to Fig. 2 The rectangular frame of the received image a, b, c, d is filled out in'such fashion by the partscreen A that the upper edge a, b of the frame properly coincides with the length of the image line to be transmitted. Of the lowermost image line of the part-screen A, however, there are reproduced in the received image merely the points 4 and 3. The image contents of 4' to 4 and of 3 to 3 fall outside of the received image. All vertical lines in this image incline towards the inside, i. e., to all the greater extent the more they are situated towards theedge of the image-in the case of the area B the position is the reverse to that shown in Fig. 2. In this case the image angles a, I, 4 and b, 2', 3 are not recorded.

The fundamental idea of the invention consists in chronologically correcting in such fashion by the transmitter the initiation of the impulses which determine the commencement of a new line at the receiver that the images A and B coincide. This may be performed in its most simple form by proceeding according to the method making use of self-synchronising image points.

In this method the image points traverse either a particularly bright or a particularly dark edge of the image. If it is desired to correct the periods of initiation in the case of the sectional areas A and B independently of each other, there is employed for this purpose in accordance with the invention a divided marginal line. Two steel knife edges according to Fig. 3, which are freelymovable in relation to one another and of which each is half the height of the image, are applied by optical reproduction at the transmission end to the edge of the image. The meeting point between the two knife edges passes through the centre of the image. The middle line passes through the point 8 and agrees in length with the section are of the disc. An image point which moves over the surface from the left to the right supplies a synchronising signal after leaving the edge 6 or 1 of the upper or lower knife edge. These signals occur in advanced or retarded fashion dependent on the position of the edges 6 and 1. It is possible by movement of these two edges to cause the coincidence error in Fig. 2 at the right hand edge of the image to disappear entirely. Theoretically it again occurs in part at the left hand edge of the image; it has been found in practice, however, that this error in the screen may be made so small by correct adjustment of the two starting edges 6 and 1 that it is less than one image element. A condition for this is that the preliminary adjustment of the trapezium is made to be correct so far as possible.

Figure 4 shows still further the manner in.

which the invention may be practiced when the line synchronizing impulses are generated by means of a light margin projected upon one radial edge of the scanning disc 5.

. In order to obtain the synchronizing impulses at exactly equal intervals it is necessary toadjust this diaphragm ring exactly as shown schematically by the arrows in Fig. 4, a condition not easily accomplished in the case of double spiral scanning systems having large radial dimensions. Referring now more particularly to Fig. 4 of the drawings, 5 represents, as in Fig. l, the Nipkow disc having a spiral of two turns of apertures I and 2., The arrow indicates the direction of rotation of the disc and accordingly the projection of the image moves upward. The part image areas belonging to the two separate spiral turns are designated B and A as in Fig. 1 and such image areas may be rectangular or trapezoidal. The designation ll represents, as also does the legend, the radial light margin causing the synchronization signals. According to the invention the left edge margin of the field is defined by two diaphragm elements 6 and I which may be adjusted separately and tangentially to the spiral turns. Thus it is possible to adjust the outer edge of the synchronizing margin strip separately for the two areas B and A so that the synchronizing 5 impulses are generated at exactly equal intervals. The position of the two diaphragms 6 and I is drawn for rectangular image areas. In the case of trapezoidal areas the inner edges of the diaphragm should be positioned radially. 10

I claim:

In television apparatus for interlaced scanning, a scanning disc having positioned thereon a plurality of elemental scanning openings arranged about the outer area of the disc in spiral forma- 15 tion to form two complete spiral turns, each of said spiral turns having a pitch substantially equal to the height of an image area to be scanned and the separation of the individual elemental scanning openings on each spiral having 20 substantially an equal angular spacing one from the other and a linear spacing along the spiral path varying in accordance with the radial spacing from the disc center, so that an image pattern of predetermined configuration is scanned, said disc being adapted to be illuminated with a band of light of substantially fixed intensity along a strip adjacent a radial edge of the said image pattern area, the combination of two light masking elements each having one edge coincide with a radial edge of the pattern scanned by the disc and located in the path of the fixed intensity light, and each masking element being associated with one of the spiral paths only and adapted to be moved tangentially relatively to its associated spiral path to vary thereby the radial position at which the fixed intensity light is revealed to the disc so that substantially identical areas are scanned by each spiral turn .of the scanning element.

KURT SCHLESINGER.

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