US2227006A - Scanning device - Google Patents

Description

DBQ 1940- K. SCHLESINGER 2,227,006

SCANNING DEVICE Filed June 5, 1956 3 Sheets-Sheet l Dec. 1940- SCHLESINGYE-RY 2,227,006

SCANNING DEVICE Filed June 5, 1936 3 Sheets-Sheet 2 Dec. 31, 1940. scHLEslNGER 2,227,006

SCANNING DEVICE Filed June 5, 1936 s Sheets- Sheet 3 Jake/Mar:

Patented Dec. 31, 1940 PATENT OFFICE SCANNING DEVICE Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc, a corporation of New York Application June 5, 1936, Serial No. 83,705 In Germany June 11, 1935 1 Claim.

In the earlier application Ser. No. 22,115/35 the applicant has described a method which permits of the scanning of a continuously moved film according to the interlaced line-group method.

5 This method is based on the use of a multiplespiral disc, whereby the number of spirals have been made equal to the number of groups of lines of which an image is composed. In the case of a film moved at the rate of 25 images per sec- 0nd and adecomposition of each film image into two part-images there rotated, for example, a disc having two spirals, of which each spiral was half the height of the film image, at 50 revolutions per second, in such fashion that the appar- 1'15 ent radial movement of the image points is directed in opposition to the apparently radial movement of the projected film image.

In the present application there is retained the essence of the idea disclosed in the cited earlier application No. 22,115/35 of October, 1934. As in the latter there is employed in the present case a multiple-spiral disc, for example a disc having two connective image-point spirals, whereby the image points follow up radially in a direction opposite to the movement of the projected film image. The difference between the two methods resides in the production of the line displacement. If, in the manner described in the earlier application, there are employed an even numher of image points, for example 2 x 120 image points, on the spiral aperture disc, a line displace ment can only be obtained at the receiving station if upon the reception the relaxation oscillation commences and ends upon each second relaxation period to the extent of the width of one line higher or lower than the preceding period. The Vertical relaxation oscillation must perform in addition to the normal scanning movement a rocking movement of the height of a line width, i. e,. the so-called line jump. In order to produce this line jump at the receiving station it was necessary in accordance with the earlier method to transmit from the sending end imagechange impulses, of which each second one arrived to the extent of one-half of a line period too early or too late as compared with a sequence of exactly isochronous impulses. It was accordingly necessary to transmit the image-change signals in the form of a group each comprising two anisochronous part-impulses. This does not present any difiiculties in itself, and solutions in respect of transmitters and receivers are set forth in several earlier applications. On the other hand the anisochronous impulse method represents an increased load on the vertical relaxation apparatus of the receiver, as the same may no longer perform relaxation between two fixed limits, viz., the upper and lower edge of the image, but must perform the relaxation with good repetition rest in alteration altogether between four 5 limits. It is subject matter of the present invention to depart from the method employing the anisochronous image-change signals by the fact that there is introduced a well defined detuning of the line frequency as compared with the har- "10 monic vibration condition between the line and image-change periods. By reason of this detuning method it is possible to operate with purely isochronous image-change signals without the necessity for any line-jump movement in the case 15 of the receiver screen. The receiver screen in the case of the new method may perform relaxation between merely two fixed limits exactly as in the reception of simple television transmissions, and does not require to perform anything beyond that called for in the case of television with simple standard of scanning.

The fundamental idea consists in the fact that a line displacement occurs automatically when an odd number of lines are employed for continuously moved films as described in the following specification.

The novel features which I believe to be characteristic for my invention are set forth with particularity in the appended claims. My in- 3 vention, 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 in principlethe production of the line displacement with an odd number of scanning holes, whilst Fig. 2 shows a Scanning disc with a double spiral arrangement of the scanning holes.

Fig. 3 is intended to explain the manner in which the decomposition of the image is brought about.

Fig. 4 shows the principle of a multiple spiral 45 disc, particularly a disc having four complete spirals.

Fig. 5 serves to explain an operation of a multiple sipral disc, whilst Fig. 6 shows an arrangement of producing syn- 50 chronisation impulses, to which further reference is made in the following paragraphs.

In particular referring to Fig. 1 an image area I is scanned in three lines and two groups of lines, so that accordingly each group of lines com- .55

:of this character. --images produced one over the other, n the nummethod.

prises one and a half lines. The first group of lines comprises the lines a1 and (t2, the second group of lines the lines In and b2. It is to be recognized that the group of lines b is disposed in the intermediate spaces of the group of lines a without it being necessary for the vertical screen apparatus to depart from the two limiting pointsc, the upper edge of the image, and d, the lower edge of the image. An oscillation of this kind between two fixed lines of limitation can be produced and maintained in the usual fashion with isochronous synchronisation signals. The applicant formulates the condition under which a line displacement of thisnature occurs automatically between the groups of lines by the following formula:

In this 2 is the total number of lines in which the image appears in decomposed form. 2, therefore, is the actual screen quality and determines thefrequency band width of a transmitter b is the number of part- The number of lines is fractional in respect of each part-image.

In Fig. 2 there is shown a scanning disc suitable for the transmission of 2 x 120 lines. The

sectional area on to which the film image is projected is designated 2. The same is formed by two radii 3 and 4, which are taken through the points I and 239, the two extreme image points of a double spiral. The double spiral itself is an Archimedian spiral running continuously from number I to number 239 without interruption and without irregularities. A double spiral of this kind has a central point, in the present case the point I20. This central image point is situated exactly at the centre of the sectional area of the disc. or, the angle between each two radii of a disc of this kind, is represented in the case of n points'by This angle amounts for example in the case of a disc having 239 points to 3 45"; in the case of a disc having 2 x 89.5 lines, i. e., n=179 image points, the angle is, for example, 4 1' '30". A transmission with a disc of this kind will be performed with advantage in conjunction'with the so-called self-synchronising image point If the disc, viewed from the projection light, rotates clockwise, as shown in Fig. 2, each image element must traverse a starting line 5 at the edge of the image on the left hand side. This is accentuated in relation to the image by particularly bright lighting and provides the line synchronisation signal with excess of amplitude. For sorting out the two image-point spirals there is combined with the disc according to Fig. 2 a spiral diaphragm, which is designated 6 in Fig. 2- and rotates in the same direction at half the circumferential velocity. In-practice I the circumferential velocity of the disc is, for example, 6000 R. P. M. and that of the diaphragm B 3000 R. P. M. The diaphragm may rotate in the plane of an optical intermediate image, in which manner diaphragm screening may be obtained without loss of light or lack of sharpness of the diaphragm shadow.

In addition to the line synchronisation, which is effected by the starting line, there is also required an image-change synchronisation. This is obtained by a single synchronisation slot I.

This synchronisation slot, cuts a projection 5' of the starting line 5, Which may be regulated by means of a shiftable gap, so that the height of the light signal of the slot 1 is just as great as the height of the line impulse over the starting line 5. The image-change slot 1, on each occasion when it passes through the starting line 5, is freed up to the photo-cell. For this purpose the shading diaphragm 6 is furnished with two recesses 8 and 9 which are generously dimensioned in the peripheral direction. The length of the slot I determines the duration of darkening of the vertical return line. It has been found'that in the television art a duration of the return amounting to 1% :is fully adequate. 'I may accordingly have the length of 1--3 line periods.

To explain the manner in which the decomposition of the image i brought about there'is also provided Fig. 3. In Fig. 3 there isto 'be seen in what manner the reproduction of the original film passes over the decomposing'points of the disc and both sections move one against the other. The movement of the film image III is divided into 7 phases. The image moves evenly from the bottom towards the top and the image points of the disc move at the same rate but in opposition from 'thetop towards the bottom. The disc contains seven points and decomposes the film into 2 x 3.5 lines. In phase a there operates the point 4. Up to the phase b it has scanned the topmost line I ofthe reproduction of the film.- At 27 phase therecommences the point 5, and up to phase c-it has scanned the line 3. In phase 0 there commences the point 6 which up to phase d'hasscanned the line 5. In phase 11 the lowermostpoint I. 'scansline I of the original. It does not complete this, however, but moves away from the original image at the lower edge after completion ofa half-line. At this moment theimage change impulse commences. The commencement of the image change signal is entered as I. By reason of the jump in the disc section from the point I to the following point I there is-initiated the scanning of the second group of-lines. A'condition for this is, in accordance with theinvention:

The height of the projected film image amounts to somany line widthsas there are-image points on the disc.

The point I passesdiiring'e over the line 2, which was free. The point 2 passes during over the line 4, whichwas previously-free,- and in similar fashion the point" 3 scans 'the line 6 during g. Point 4 is unable to' reacHtheoriginal' image, which has now been completely scanned twice, and already commences the scanning of 'the'next image. Phaseh'accordingly follows on phase a. At thismonient, in accordance with the invention, there must 'co'mmence/the second image-change-s'ignals I. "The position of both {image-"change signals -is 'ex- 'actly isochronous. The spacing of the't'wo si nals amounts to half the total of all line periods. This condition is satisfied by provision of the synchronisation slot shown in Fig. 2. The end of this slot 1 requires to pass exactly over the projection 5 of the starting line 5 when the radius of the middle point passes through the central image point and the middle of the image area.

It is possible in accordance with the above statements to design other transmission discs for a different number of lines and for a difierent number of part-image transmissions. In this connection the number of complete spiral turns is always equal to the number of part-image transmissions if the disc rotates as many times per part-image as image repetitions are desired. The total height of jump of all spirals is equal to the height of reproduction of the film image.

It is, however, also possible to make the arrangement in accordance with the diagram in Fig. 3 in those cases in which the disc performs twice the number of revolutions.

For comparatively large numbers of lines it is advisable to employ scanning discs operating at high speeds. A further feature of the invention is a disc of this kind which effects scanning according to the interlaced line-group method, whereby the image appars in decomposition into an odd number of lines. In contradistinction to the scanning disc described in connection with Fig. 2 which rotates twice for a single image transmission and contains two spiral turns, there is shown in Fig. 4, for example, as representative of the high speed discs according to the invention a disc having four spirals which rotates four times for each image transmission. In the case of 25 images per second this disc requires to perform 6,000 revolutions per minute. The disc carries an odd number of image points corresponding with the. total number of lines transmitted per image, for example 179 or 239 image points. Each image point encloses with the succeeding one a central angle a, which is represented by the formula film reproduction on the disc.

3. Total height of the disc section is equal to the total height of the film reproduction, i. e., :2 line widths of 2 image points are present.

4. The middle image point with the number 2+1/2 bisects the angle formed between the points 1 and 2.

If the first and last points of the disc, number I and number 5 or, generally speaking, a, are connected by a secant, this secant must meet the middle point 3 or, generally speaking,

This middle point bisects the angle a. formed between I and z. The points of intersection 3 and 4 of the secant with the spirals likewise meet image points with the disc, which rotates clockwise, there runs in the ratio of 1. e., in the present case at 1,500 revs., a shading diaphragm 6. This shading diaphragm may be reproduced either immediately in front of the disc, i. e., so that it throws a comparatively sharp shadow on to the disc, or it may also be reproduced in accordance with the invention in the intermediate image of the disc. To explain the intermediate-image method the plane of the disc is designated 23 in Fig. 5. The film 25 is reproduced sharply on this disc by means;

number of apertures is elfected by means of a,

synchronisation slot 1. The slot '1 must commence with the same central angle either with the point I or with the middle point The slot is uncovered as many times as partimages are to be disposed one over the other. In the present case the slot is uncovered twice upon four revolutions of the main disc. By reason of the bisecting of the angle a by the middle section point in accordance with the invention it is accomplished that each part-image is scanned to the extent of one-half of a line period too late as compared with the preceding one and in this way the line-group displacement is brought about automatically with the use of a harmonic sequence of image-change signals 1.

The method as set forth is contemplated primarily in conjunction with synchronisation by means of a starting line. More concise statement in this connection is included in connection with 2 and the starting line has been designated 5 and 5 respectively in Figs. 1 and 4. It is also possible to employ a light screen, which contains a special row of slots M. In order to obtain the characteristic line synchronisation frequency a slot l4 must be provided in accordance with the invention for every radius taken from any image point to the central point, and in addition there must be employed a frequency reduction in the ratio of 1km. This frequency reduction may be produced in simple fashion electrically, preferably by the use of a relaxation connection.

In Fig. 6 there is shown an arrangement of this kind. The disc having 4 or 2 spirals and rotating with 6,000 or 3,000 revolutions generates with its apertures in conjunction with a lighting means l5 and a photo-cell l6 behind a slot tone amplifier I! a control frequency. This is not capable of being employed in direct fashion for synchronisation of the received image. In accordance with the invention it is passed to frequency reducer It. This frequency reducer l8 may consist of a flash connection, in which a condenser I9 is charged by a resistance 20 with a frequency of A,. or of the aforesaid slot frequency. In the manner well known per se there is then employed merely every second or every fourth oncoming change for the synchronisation of an ignition in the thyratrcn 2!. All 7 remaining changes pass through unutilised. "At a transformer 22 an impulse series may accordingly be tapped as subharmonic. This may be employed, possibly after filtering, in immediate fashion for synchronisation of the receiver in the case of operations of this kind with interlaced groups of lines. An advantage of this method of frequency reduction With synchronously rotating sirenesin" accordance with the invention" is to be regardedin the fact that no conjointly rotating screening diaphragms are required, and that a singlesynchronously rotatingshaft is sufiicientfor solving the problem.

I claim:

In a television systemfor interlaced scanning, a disc element having arranged thereon an odd number of scanning elements positioned along a spiral path of 11; complete turns, a shutter disc having arranged thereon asingle complete spiral slot of a pitch'corresponding to n times the pitch of eachspiral turn of the scanning elements on the first disc element; means to rotate the shutter disc and the scanning disc'so that the shutter disc revolves at a speed of as compared to the of a length such that-there will be complete a 1 registry of a slot'of the shutter disc and the syn- 360 measured by masking means having a radial slot extending for a length at least equal to the height of the plurality of spiral turns of scanning elements of the scanning disc and for an additional length therebeyond to a point corresponding at leastto the radial distance of the synchronizing slot of the scanning disc, means to illuminate the slot of the masking'means so that each scanning element when traversing the slot causes a line synchronizing impulse to be developed immediately prior to the production of image signal impulses and a field synchronizing impulse to be developed at periods when the synchronizing slot of the scanning disc and one of the slots of the shutter disc are in reigster with the radial slot of the masking means whereby a field synchronizing impulse is initiated for each rotation of the scanning disc at a time period when the scanning elements thereof have traced scanning paths corresponding to a predetermined number of complete scanning lines plus a fractional part of a scanning line corresponding to KURT SCI-ILESINGER.

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