US2008272A - Scanning system for television apparatus - Google Patents

Description

July 16, 1935. J. A. BRIGGS SCANNING SYSTEM FOR TELEVISION .APPARATUS Filed Jan. 16, 1932 2 Sheets-Sheet l AMPLIFIER :MODULATOR C RADlO TRANsmmPV AMFUHER AMPUHER ATTORN EY R 0 T N E V m J.A. amass BY July 16, 1935. J. A. BRIGGS SCANNING SYSTEM FOR TELEVISION .APPARATUS 2 Sheets-Sheet 2 Filed Jan. 16, 1932 JMPZ/HER INVENTOR J. A. BR! 5 BY Mir-M ATTORNEY Patented July 16, 1935 PATENT OFFICE SCANNING SYSTEM FOR TELEVISION Y APPARATUS Joseph A. Briggs, Erlton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 16, 1932, Serial No. 587,006

3 Claims.

The present invention relates to television system and is directed principally to the transmitting end of the system, that is, to the means by which the subject, of which an image is to be 5 transmitted, is scanned at the point of transmission, and ,the manner in which impulses, used at the points of reception of the" transmitted image signals, may be generated to insure synchronous operation of the various receivers with the transmitter.

Various ways and means have already been suggested in the artfor transmitting television images and motion picture film, but, for the most part, these systems, so far as I am aware, have not made provision for scanning the subject in a sufiiciently large number of lines to insure sufficient detail in the transmission unlesscumbersome and excessively large scanning'elements are used to achieve the desired result.

When it is desired to transmit television images from motion picture film, it is preferable to use transmitter scanning systems of a type such that the film is advanced at a uniform and continuous as is used in most motion'picture projectors, thefull utilization of the transmission time for sending intelligence is not attainable because it is necessary to interrupt the transmission following the scanning of each individual picture frame of the film during the time period when the film is intermittently advanced to present a new film 40 frame before the scanning device. This time period of interruption in the intermittent film advance usually requires from fifteen to twenty-five percent of the total time available, so that to transmit any predetermined amount of detail in the picture the intermittent operation would require a frequency band of a width greater than that for the same amount of'intelligence' using constant feed film proportionate to the ratio of the transmission time periods available for each system. I It has already been suggested in connection with" scanning objects or subjects of whichcan image is to be transmitted that the size of the scanning element, assuming this to be a. rotary disk or drum or theequivalent, might be reduced by providing this scanning element with a plurality of continuous spiral tracks and then screening by means of a rotary shutter element all but one of these tracks at any instant, as has been disclosedby Ramsey Patent #1,602,121 of October 5, 1926. An arrangement of this general type is, of course, necessary where the scanning element itself must provide for the scanning in two directions, i. e., transverse to the subject and, at the same time, vertical of the subject. When motion picture film which is being advanced continuously and uniformly is to be scanned, it is well known from the prior art that it is unnecessary to arrange the scanning elements along a spiral path but, on the other hand, they must be arranged along a path upon the scanning element so that all scanning apertures or lenses or the equivalent are placed upon equal radii. Therefore, for continuously moving film, if it is desired to divide each motion picture film frame into one hundred and twenty elemental strips transverse to the film, for example, to correspond to one hundred and twenty lines of scanning per frame, it would be possible to have a scanning device with the scanning apertures or lenses arranged thereon on equal radii while at the same time providing only a relatively small number of apertures upon the scanning element. Thus, for

example, the scanning element might be provided with thirty, forty, sixty or more or less apertures, assuming that the number of revolutions of the scanning element during the period when the film was uniformly and continuously advanced one picture frame corresponded to four, three and two revolutions, or a number of revolutions per film frame proportionate to the number of scamiing apertures, and still the same result would be obtained as if a scanning element provided with one hundred and twenty apertures all arranged on equal radii were rotated relative to the film in such manner that the scanning element made one complete revolution during the time period within which the film was advanced one picture film frame.

Consequently, the present invention, as applied to motion picture film transmission, is directed to a scanning element-having a lesser number of scanning apertures or lens elements than the number of'lines or elemental strips into which the film picture frame is to be divided for the purpose of scanning. To illustrate a concrete example, it is assumed that the scanning element shown in the present invention shall include sixty scanning elements and that the film picture frames are to be divided into one hundred and .twenty elemental strips, so that the scanning element will make two complete revolutions during the time period required for the film to be advanced for one complete film picture frame, although these values are merely illustrative and the invention should not be regarded as limited to the number of scanning lines or to the number of separate scanning elements to produce the chosen number of scanning lines suggested.

In connection with the television transmission of film or 'other subjects, it is desirable that the transmitter send out signals which are to be received at all receiving points for indicating the instantaneous position of the transmitter relative to the subject, so that all receiving points may be synchronized properly with the transmitter. It has been proposed to provide for this transmission of the synchronizing pulsations of current by omitting, for example, two or three elemental areas of each line or elemental strip, into which the subject or film picture record is assumed to be divided, at one side of the picture record, and then, for example, to omit two or three complete lines of scanning from the bottom of the picture record. This being done, it is, of course, obvious that as the subject for transmission is scanned there will occur a transmission of signals representative of the light and shadow on elemental sections or areas of each elemental strip followed by a signal indication of position or synchronism, and then after a complete series of these signals has been transmitted, which would, according to the example above suggested, be signals corresponding to one hundred and twenty elemental strips, a second signalindicating the completion of the period of scanning a complete subject might be transmitted. This latter time period, it will be recognized, is really a slight loss in the utilization of the full transmission time available but is justifiable because the synchronizing signals are thus definitely separated from the image signals and because of the improvement resulting in the image reception due to positively synchronizing the receiv'ed'record with that transmitted.

In film transmission this period during which synchronizing signals are transmitted would usually be lost whether or not a synchronizing impulse is transmitted at the end of scanning a complete film picture frame or not. This loss would be because of the fact that the frame line separating successive picture portions of successive motion picture frames does not contain intelligence and yet the film at the frame line portion requires a certain time interval to pass before the scanning apparatus. Therefore,-it is most convenient to use this otherwise unusable time period, which is effectively blank on the pic'- ture record, to provide for transmitting a synchrom'zing pulse.

As has been suggested in the copending application filed by Ray D. Kell as Serial No. 565,953 on September 30, 1931, a distinction is made between the type of signal transmitted at the end of each line of scanning and the signal transmitted at the end of scanning of each complete picture frame. The two types of signals may be identical inamplitude but different in time duration and in the steepness of the wave front, or maybe of equal duration and different amplitude, so that by suitably arranging the receiving devices selection between the two types of signals may be provided. In order to provide for this same type of synchronizingsighal separation and selection when using a multi-spiral scanning elethe element used to generate the indication of vertical synchronism every second revolution of the scanning device an indication of vertical synchronism will interfere with the transmission of the picture record. To overcome this difiiculty, a masking or shutter device has been used to screen in suitable manner the element used to generate the vertical synchronizing signal and to permit it to function only every second revolution of the scanning device. Thus, the element used to generate the vertical synchronizing signal will be screened after the scanning element has made one complete rotation but will be uncovered after two complete rotati0ns,then again screened as the scanning element makes its third complete rotation but uncovered after four complete rotations, and so on until a complete transmission of the motion picture film or of a complete scene of action has been transmitted. 7

With the foregoing in mind, it is an object of the present invention to provide a scanning system for motion picture film adapted at the same timeto function as an element for the production of indications of synchronism to accompany the picture record.

A still further object of the invention is to provide an' arrangement wherein a reduced size scanning element may function both as a means for scanning or analyzing successive elemental picture areas of the subject 'or film record for transmission and, at the same time, serve as a means to control the production of signal indications of horizontal and vertical synchronism.

A further object of the invention is to provide a novel means for preventing indications of vertical framing or synchronism from occurring at points other than at the end of the transmission of a suflicient number of image signals to represent in the pre-established detail a complete representation of the subject or of each complete picture filmframe.

Other objects of the invention are to provide a scanning device and a device for use in the production of synchronizing signals to accompany the picture signals which is relatively simple in its construction and arrangement of parts, a system which occupies a minimum amount of space, a system wherein the scanning and synchronizing signal producing means are coordinated and related in operation so as to maintain always the desired relative position of occurrence of each and to provide a system which is simple and easy to operate.

. Still other and further objects of'the invention will become apparent-and at once suggest themselves to those skilled in the art to which this in- Fig. 1 is a diagrammatic illustration of one suit-- able form which the invention may assume when applied to film transmission;

Fig. 2 is a sectional view of the motion picture film scanning element and shutter element for cooperating therewith shown by Fig. 1;

Fig. 3 is a diagrammatic representation of the principles of the invention applied to the scanning of subjects other than film; and,

Fig. 4 represents the invention as applied to the ian iult-spiral Nipkow-type scanning element of To refer now to the drawings, and first to Figs. 1 and 2 thereof, the film subject I of which an electro-optical image is to be reproduced at the various points of reception is advanced uniformly and continuously by means of the sprocket wheels 3 and 5 which may be driven through suitable gearing, as disclosed in mycopending application relating to television apparatus which was filed concurrently herewith as Serial No. 587,005, and is arranged to move immediately in front of a scanning element 1. The scanning element 1 is provided with aplurality of scanning apertures 9 extending completely around the circumference thereof and all arranged on equal radii, so that as the scanning element 1 is rotated in the direction shown by the arrow about the supporting shaft or spindle ll, these apertures will, when directing light from a light source l3 which is focused by means of an optical system l5 upon the, apertures 9, trace by means of a focusing lens system I! light spots I9 across elemental strips of the film record l.

The light which passes beyond the film and which varies in intensity in accordance with the varying intensities of light and shadow on successive elemental areas of these elemental strips as explored by the passage of the light spot transversely to the film may then be focused by means of a lens element or optical system 2| upon the light sensitive .electrode 23 of a photo tube 25. It is preferable to focus the light which passes beyond and through the film upon a particular point of the light sensitive element so that no unfaithful or .exact responses will be produced from the photo tube due to possible variations or unevenness in the distribution of the photosensitive material upon the light sensitive electrode.

The minute photoelectric currents produced within the phototube 25 by the varying intensities of illumination thereon may then be amplified in any suitable type of amplifying medium 21, and the resulting amplified currents are then supplied to a connecting line 29 from which these currents are fed to the line amplifier 3| which may also be of any suitable form and design.

The scanning element 1. is also provided with a plurality of apertures 39, each of equal size, which are also arranged circularly thereof and upon equal radii, The function-of these apertures, as was disclosed in the aforementioned application of'Ray D. Kell, is to produce at the end v of the scanning period for each elemental strip frame and the resulting signal which is produced at this time may then be utilized at the various points of reception to frame properly the picture or electro-optical image produced.

As, washereinabove suggested, it is desirable to have the number of scanning apertures on the scanning element of a number less than the number which would correspond to the lines or paths into which each film frame is assumed to be divided and, therefore,to scan each complete film frame more than one rotation of the scanning element is necessary. In order to prevent the aperture 4| used to indicate verticalframing from functioning at times other than a time when a complete motion picture film frame has been scanned, a shutter element 43 has been provided immediately adjacent the scanning element This shutter disk or element is provided with a slot 45 which is arranged to uncover at suitable time intervals a synchronizing aperture 4| while at other times block or mask the aperture 45. As can be seen from the drawings, and especially Fig. 2 thereof, the aperture M which is used to produce the indication of vertical framing or synchronism is arranged a slight distance inwardly of the scanning element from the apertures 39 used to indicate horizontal synchronism, so that all that will be necessary in order to mask or screen the aperture fil without masking the apertures 39 is a disk or screen element 43 which extends outwardly of the scanning element from a distance only as far as the outer edge of the aperture or 7 slot 46 I e If it is assumed now that each film frame is divided into one hundred and twenty elemental strips and assumed that the scanning element 1 is provided with only sixty scann'ng apertures 9, then it is clear that the scanning element must rotate twice during the timethat a single picture frame of the film I passes in front of the point I9 where the light from the source is passing through the scanning apertures 9 is focused. Consequently, since it is desirable to transmit only a single indication of vertical framing or synchronism during the time that one hundred and twenty elemental strips ofthe picture film have been scanned, it will be necessary to rotate the screen disk 43 only half as fast as the scan-,.

ing element. To accomplish this result a suitable gearing arrangement, such as has been herein indicated conventionally, has been provided so that the small gear wheel 41 secured rig'dly to the shaft driving the disk is arranged to rota-te a larger gear wheel 49 which "is secured rigidly to the shaft or spindle 5| upon which the masking or screening disk 43 is-supported.

Thus, if the gear ratio is designed for a two to one reduction in speed, the shutter or screen disk 43 will rotate only half as fast as the scan: ning disk or element 1.

To generate the horizontal and vertical indi-- cationpf synchronism, light from any suitable source is projected through an optical system? 51 and screened by a diaphragm 59 so as to be projected along a path which will include only the width. between the outside of the apertures 39 and theinside of the aperture 4|, and the light which passes through these apertures may then be focused by means 'of a lens element Si or the equivalent upon the light sensitive electrode 63 of the photo tube 65 in the manner and width, the time period during which the light from the source 55 may activate the photo tube 65 is limited to the time period required for the slot 4| or the apertures 39 to pass before a light beam of a width equal to the width of one of the synchronizing apertures 39, and, further, it is apparent that-due to the slot 4I being elongated light will pass through the slotat every second revolution 'of the scanning element for a time period corresponding, as shown by the drawings, to a time required to scan three picture lines, but after one complete rotation of the scanning element the slot or aperture 4| will not be uncovered because the slot 45 of the shutter or screening disk 43 is now at the top position or advanced through an angle of one hundred and eighty degrees and thus it requires two complete rotations of the disk or element I to uncover the slot 4|, whereas the apertures 39 are uncovered and pass light to the photo tube 65 after each elemental strip of the picture film I] is explored or analyzed.

As was suggested in copending application Serial No. 544,959, filed June 17, 1931, by A. W; Vance, it is desirable to have the indications of synchronism one hundred and eighty degrees out-of-phase with the picture signal indications, so that if the receiving systems used to-recons-truct the electro-optical image of the picture film are cathode ray tubes the effect of the synchronizing pulse on the tube will-be to cause extinction of the light spot on the fluorescent screen of the tube, and thus prevent any observable efiects during the reversal of the cathode ray stream necessary for unilateral or one-way scanning. Therefore, the photo tube amplifier 67 which is used to amplify the currents produced within the photo tube 65 is provided with one less or one more stage of amplification than the photo tube amplifier 21 which produces a phase shift in the signals from both photo amplifiers of one hundred and eighty electrical degrees, so that when the output energy from the photo tube amplifier 61 is.connected with the supply conductor 29 to the line amplifier 3| there will be produced therein sgnal indications -corresponding both to white and to black where it is assumed, for example, that the picture signals produce white indications and the synchronizing signals produce black indications. The output energy of the amplifier 3| may then besupplied to the modulator 69 and then to a radio transmltter II and from the transmitter II signals are distributed to various points of reception by transmission from theantenna I3. Of course,

it is within'the scope of the present invention.

to utilize, where desired, wire line or. network transmission .of the resulting picture and synchronizing signals, and while a radio system of transmission has been suggested, it is obvious that any other desired form might be substituted.

Furthermore, it is, of,course, to be recognized that it is, as above suggested, within the scope of the present invention to provide a system. wherein the number of complete revolutions ,of

that recourse may be had to my aforesaid copending application, wherein was disclosed a method of adjusting an impedance roller used to advance the film so as to position the film in any desired frame relationship relative to the film gate (not shown herein) through which the film is passing during the periods of exploration.

By the form in which the invention is shown in Figs. 3 and 4, provision has been made for scanning a subject of which an electro-optical image is to be produced at the various points of reception by a scanning element which provides, itself, for two directions of scanning, that is, both horizontally and vertically of the subject.

To refer now to Figs. 3 and 4, the subject for transmission IUI is illuminated by the source of light I3 projected through an optical system I03 which spreads the beam of light to a width corresponding to the height of the scanning apertures or lenses,or the equivalent, arranged on the scanning element I05. These scanning apertures or the like III! are arranged along spiral paths, accordingto the teachings-of Nipkow, but extend about the disk or drum for a plurality of turns. In the example shown, these apertures extend fortwo complete turns and thus, of course, it is possible to increase the height of the scanning area materially without increasing the diameter of the scanning element.

As was shown by the Ramsey Patent, '#l,602,12l, above. mentioned, the scanning element I55 may be rotated about a shaft I09, and then rotating upon a shaft or spindle coaxially therewith is a shutter or screen disk, or the equivalent, III. The shutter or screening disk II! is provided with a single spiral path II3 which assumes the form of a wide slot of a width at least as great or greater than the height of two adjacent scanning apertures. If now the scanning-element I05 is rotated at a speed 11, so

as to permit light from the source I3 as directed I through the optical system I03 to pass through element only if the shutter or screeningelement I I I is rotating in the same direction as the scanning element but at a speed equal to With this type of scanning system, the light I directed by means of an optical system I I5 to- I ward a spot II'I-on the subject IlII of which the electro-optical image is to be transmitted.

In accordance with'the varying intensities of light and shadow on successive elemental areas I! of the subject IOI varying amounts of light are reflected from the subject IIII and these varying amounts of-reflected' lightmay then be directed upon the photoelectric light translating elements I I9 by means of the collecting reflecting devices IZI which are preferably in the nature of parabolic reflectors having their focus point on the light sensitive element of the photoelectric devices H9! r f In accordance'w ith the illumination upon the photoelectric light translating elements 8, which have their outputs connected in parallel,

varying currents flow in the output circuits.-

I'hese currents may be amplified in any suitable aphragm 59.

manner by, the amplifying system 21 and then directed to a transmitter in the manner disclosed by Fig. 1.

In a manner similar to that disclosed by the film transmitting scanner of Fig. 1, the scanning element I05, corresponding to the scanning element 1 of Fig. l, is provided with apertures or slots 39' about the periphery thereof which serve to generate signal indications representative of the time when each transverse elemental strip of the subject II I has been scanned. Similarly, the scanning clement I is provided with a slotlike aperture 4| similar to the aperture M of Fig. 2, which is for the purpose of producing a vertical framing signal to indicate the completion of each time period of scanning the subject.

Since it is necessary to transmit this signal only upon the completion of two rotations of the scanning element I05, assuming that there are two spiral turns on the scanning element, a screening disk 43 has also been provided. This disk, as was shown by Fig. 1, rotates at a speed equal to jected through the apertures 39 and H of the scanning element I05 each time these scanning elements pass within the field of illumination of the light source 55 as limited by the di- In accordance with the time period when light from the source 55 is projected through the apertures of the scanning element are this light is then directed by means of the optical system Bl to fall upon the light sensitive signals amplified by the amplifier 21.

electrode 63 of the photoelectric translating element 65. As was shown and explained in connection with Fig. 1, these currents generated in 'the photoelectric element 65 are then amplified single spiral turn,'having a spiral width equalv to the combined width of both spirals of the scanning element, it is nevertheless to be understood that a small eccentrically mounted screening element may be substituted without involving any change in the spirit or scope of this application. Such a screening element might be in the nature ofa small shutter or screening disk of about the size shown by the disk 43 but provided with several spiral slots which extend inwardly from the periphery thereor and serve, "when'the screen disk is rotated at a suitable speed, to permit the light from the source I3 to pass at any instant through a single aperture of the scanning element only., Such a screening disk would, oi course, be rotated at reduced speed from that of the scanning element in a manner well known in the art.

Also, it is apparent that in cases where it is not desirable to transmit the indication of vertical synchronism or framing at the time of completion of each scanning of the subject but to transmit this signal only after several complete scannings the shutter or screen disk of each type of apparatus herein shown may be operated at still further reduced speed from that of the scanning element. That is, for example, if the vertical synchronizing or framing indication is desired only after three complete picture scannings, the shutter or screen disk 43, when operating in conjunction with the scanning devices I or I05 might turn one-sixth as fast as the scanning element or at a speed .Of course, other speeds to coordinate the time period of the production of this signal indication with the time of completion of still difierent numbers of pictures would be used where desired. i

Also it is to be understood that a pair of photo electric tubes parallelly connected may be used to produce the signal indications used to synchronize the receiving apparatus reproducing electro -optical images. of the subject scanned.

Under such conditions one photoelectric tube will be" adapted to produce the horizontal synchronizing current impulse and the other parallelly connected photoelectric tube will be adapted to produce the vertical synchronizing or framing current impulse. So arranged, the use of the shutter element or screen 43 might be avoided by a switch arranged to connect the photoelectric tube, used to reproduce the vertical synchronizing or framing signals, with the amplifier Ii'l only at such times as the scanning element I or I05 had turned'through an angle (720 degrees as shown) sufiicient to scan a complete subject. It is, of course, clear that when using this sug* gested form of the system, it would be possible to rotate the scanning element through any suitable angle and then produce the synchronizing impulse, so that the angular rotation suggested is intended tobe regarded as illustrative only and in no sense limited to any particular angular movement.

It is to be understood that while the present disclosure does not suggest any arrangement by which the sound accompaniment on the usual motion picture film may bev transmitted, it is nevertheless understood that this sound record may be translated from the picture film and transmitted to the various points of reception in any manner known in the art without departing from the spirit and scope of the present invention;

Also, it is equally within the scope of the present invention to provide for tha simultaneous sound accompaniment in the studio type of scanning arrangement shown by Figs. 3 and 4.

The invention has herein been shown in only which it may assume, and it will, of course, be obvious to those skilled in the art'to which the invention relates that many modifications and changes may be made without departing from the spirit and scope of this disclosure.

I, therefore, believe that I am entitled to make and use any and all of these modifications protwo of a great number of forms and embodiments of the hereinafter appended claims.

Having now descr. bed my invention, what is claimed and desired to protect by Letters Patent is the following:-

1. In television apparatus a rotary scanning element having a plurality of scanning apertures arranged about the periphery thereof at equal distances from thecenter of rotation and a plurality of apertures used for-synchronizing also arranged about the periphery thereof and positioned on equal radii, and an elongated apertureadjacent said synchronizing apertures and extending over an arc of the element at least the arcuate distance of a pair of adjacent synchronizing apertures, means for directing light beams through said scanning and synchronizing apertures at substantially diametrically opposite points thereon, means for causing the scanning element to rotate so as to trace through each scanning aperture predetermined paths of light across a subject of which an electro-optical image is to be reproduced, means for causing light of unvaried intensity to produce a signal indication of the time of complet'on of each individual scanning path and normally to produce a signal indication of the time of completion of each rotation of the scanning element, and independent means for limiting the production of said last named signal indications to predetermined time periods.

2. A scanning system for television apparatus or the like comprising a rotary element provided with a plurality of apertures arranged upon a plurality of continuous spiral paths, means for producing the light of constant intensity and directing said light through successive apertures of said spiral paths so that after a predetermined plurality of rotations of said scanning element the complete area of a subject, of which an image'i s to be reproduced, is scanned, means for limiting the effect of illumination-oi said subject to a sinvided they fall fairly within the spirit and scope gle aperture of said scanning element only at any instant, a plurality of synchronizing apertures also arranged about the periphery of said scanning element and positioned on equal radii and a slot for producing an indication of vertical synchronism also positioned on said scanning element, means for'projecting light of constant intensity through said synchronizing apertures and said synchronizing slot to produce signal indications of predetermined strength to designate the instantaneous positions of said scanning element,-

and means for limiting the production of synchronizing indications of vertical synchronism to a single occurrence during the number of revolutions required for each complete scanning of the.

element, means for producing the light'of constant intensity and directing said light through success've apertures of said path so that after-.a

predetermined plurality of rotations of said scanning element a complete area of the subject, of which an image is to be reproduced, isscanned, said scanning element also having a synchroniz ing slot arranged as a part thereof, means for projecting light of constant intensity through said synchronzing slot to produce a signal indication of predetermined strength to designate upon the passage of light through said slot the comple-w tion of each rotation of said scanning element, and means for limiting the production of said signal indication to a single occurrence during the number of revolutions of said scanning element required for each complete scanning of the subject.

JOSEPH A. BRIGGS.

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