US1788476A - Electrical picture transmission - Google Patents

Description

Jan. 13, 1931. v E: WATSON 1,788,476

ELECTRICAL PICTURE TRANSMISSION Filed Feb. 12. 1927 2 Sheets-Sheet 1' Arromvn Patented Jan. 13,1931

UNITED STATES PATENT OFFICE EDWARD F. WATSON, OF LARCHMONT, NEW YORK, ASSIGNOR- TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK ELEGTRICAL PICTURE TRANSMTSSION Application fllcdlebruary 12, 1927. Serial No. 167,784.

Tiii's invention relates to electro-optical transmission and more particularly to a p cture'transmission system in which the pleture characteristics are transmitted by current impulses of varying duration.

It is an object of the present inventlon to provide simple means to convert the light effects of elemental areas of an object into electrical code impulses.

In the attainment of this object,'a. relay is preferably employed to control the duration and character of the impulses impressed upon a transmission circuit. This relay is energize-(l by cyclicly varying current of constant amplitude which causes periodic impulses to be transmitted. This current preferably varies linearly, that is, it is of saw-toothed wave Form. The bias of the relay is controlled in accordance with the tone values of the elemental areas of the picture or object at the transmitter, thus causing corresponding variations in the'durationsof the impulses transmitted.

The invention contemplates obtammg the cyclicly varying current by alternately charging a condenser through a resistance by currents of opposite polarities and operating the relay as a leak on the condenser, the current through the relay being proportional to the voltage across the condenser.

The invention also contemplatesobtaining the cyclicly varying waves by alternately applying voltages of opposite polarities to a series circuit containing inductance and re- 1 sistance and operating the relay by the current through the inductance.

The arrangements for obtaining alternat ing current of saw-toothed wave form are adapted to be used in other fields than that of electrical picture transmission. The appended claims are drafted in contemplation of such use.

A more detailed description of the invention follows and is illustrated in the accompanying drawing.

Fig. 1 is a schematic diagram of an electrical picture transmission system wherein the signal forming relay is operated as a leak on the condenser of the source of cyclic current;

Fig. 2 is a modified arrangement wherein voltages of opposite polarities are impressed through a resistance upon an inductance to v The operation of relay 5 which is a polar relay of well known type, is controlled by three kinds of energizing current. A steady bias of the relay is obtained by current from battery 9 through winding 10. The amplitude of this biasing current is controlled by resistance 36. A cyclically varying energization is obtained by current through winding 11. y A

variable bias is produced by picture current of varying amplitude flowing through windmg 12. The combined action of these three currents causes the armature of role. 5 to vibrate from its spacing (S) to marking (M) contacts and vice versa at a rate determined by the frequency of the cyclically varying current'while the periods of closure of the spacing and marking contacts are determined by the steady bias in cooperation with the varying bias.

The source of cyclically varying current in Flg. 1 consists of acondenser 13 and a resistance 14 connected in series with grounded batteries 15 and 16 of opposite polarities through the vibrating armature 17 of relay 18. The voltage across the condenser 13 is impressed upon the winding 11 of relay 5 through the resistance 19. By properly choosing the rate of vibration of the armature 17, the voltage of batteries 15 and 16 and the constants of condenser 13 and resistances 19 and 14, the current impressed upon winding 11 of relay 5 may be given a saw-toothed wave form'like that shown by graph P in Fig. 5.

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Vibrating relay 18 is a simplified form of the Gulstad vibrating relay. The simplification consists in the omission of theline winding so that the Operation of the relay is con trolled entirely by the constants of the condenser 20, resistances 21 and 22 and the inductances of the accelerating winding 23 and the opposing'winding 24. 'For a more de tailed description of the operation of this relay reference may be made to pages 287 to 29.0 of a book by H. H. Harrison Printing Telegraph Systems and Mechanisms published by Longmans, Green and Company, New York, 1923.

1f the relay were energized solely by cyclically. varying current of wave form P shown in Fig. 5, its armature would vibrate from spacing to marking and viceversa at the same rate that the armature l? of relay 18 vibrates. The durations of the spacing and marking intervals would therefore be the spacing position may be completely neu-,

tralized or so nearly so that the spacing interval is of very short duration.

The picture current flowing through winding 12 then opposes the steady bias so that the actual bias may vary from minus 100% to plus 100% In this specification and the accompanying drawings the convention followed with regardto the efiect of current in the windings of relays 5 and 40 is that when the voltage applied to the upper terminals is positive, the tendency is to move the armature to the marking. contact, and-when the voltage is negative the tendency is to move the armature to the spacing contact.

The picture current is produced in wellknown manner and is a uni-directional current varying in amplitude corresponding to the tone values of successive elemental areas of an object or picture to be transmitted. As shown in Fig. 1 a transparency. 25 of the picture to be transmitted is mounted on a lation in the direction of the axis.

drum 26 which is adapted to be given a motion of rotation around its axis and of transtation of shaft 27 by a suitable source of power causes the rotation of the drum 26 through gears 28 and 29 and the longitudinal movement of the drum 26 by the movement of carriage 30 along the support 31 by means of screw threads on the shaft'27 engaging a nut on the carriage 30. Light from a source 32 is focused by means of lens 33 on the surface of the transparency 25. The light passing through the transparency The ro-v enters photoelectric cell 34 and the amount of this li ht is determined by the tone value of the e emental area through which the light is passing. The current flowing through the photoelectric cell is amplified preferably in an electron discharge amplifier 35 the output current of-which flows through the winding 12 of relay 5. For a more detailed description of this arrangement for producing picture currents reference may be had to Patent No. 1,654,374, Dec. 27, 1927, of J. WfHorton.

The effect of varying the bias of relay 5 is shown in; Figs. 4 'and5. To explain this effect let it first be assumed that relay 5 is being energized solely by current of sawtoothed wave form P'fiowing-in winding 11. The positive half waves above the zero line 0 will then (by convention) cause closure of the marking contact and the negative half waves below line 0 Will cause closure of the spacing contact. Since the positive and negative halfzwaves are substantially equal the marking and. spacing contacts will be closed for substantially equal intervals.

Next assume that the steady biasing current I becomes effective through winding 10. The positive voltage from battery 9 being connected to the upper terminal of winding 10, the effect of the biasing current is to tend to cause closure of the marking contact. This may be represented in Fig. 5 by moving the reference line 0 to the position 0. lVith respect. to the new reference line 0' the graph P represents the combined energization ofirelay 5 due to the current of sawtoothedwave form P and the steady biasing current I When this graph extends above line 0, which for the assumed value of L is all'the time, the marking contact of relay 5 is closed. This represents the condition of plus 100% bias.

If new the picture current becomes effective in winding 12 and since the upper terminal of winding 12 has a negative voltage impressed thereon, the effect of this current is to oppose the effect of the steady biasing current. The effect of this current is represented in Fig- 5 for one condition by I and the effect on relay 5 may be represented in Fig. 5

by moving the reference line from the position 0 to the position 0 The armature of relay 5 willtherefore be moved to close the marking contact for a period t during each cycle while the graph P is above the reference line 0 and to the spacing contact for a period t while thegra'ph is below the ref erence line 0 Similarly for other values of picture currents represented by 1 ,1 I and L; the reference lines in Fig. 5 become O 0 0 and O When the picture current has a value I thev armature of-relay 5 will be moved to a position to closethe marking contact for a'period tand thespacing contact for a is 2T.

5. It may be noted that for a value of picture current represented by L; the new reference line 0 coincides with the base reference line 0 for zero bias and the marking and spacin intervals are of substantially equal duration.

The current impulses transmitted to the line 6 for the several conditions of Fig. 5 are shown in Fig. 4. The period of the cyclically varying current is represented by 2T, therefore the interval between the midpoints of successive marking and spacing impulses is T and between the mid-points of successive marking or spacing, impulses In the actual transmission of a picture the picture current will vary from portron to portion between its maximum and minimum values and the type of impulses which Wlll be impressed upon line 6 is represented by the current graph of Fig. 6.

From Fig. 6 it is evident that while the time interval between the mid-point of any marking or spacing interval to the mid-point of the succeeding marking or spacing interval respectively is constant and may be represented by 2T, the length of time between the beginning of a'marking or a spacing interval to the beginning of the succeeding marking or spacing interval respectively is continuously changing as the tone values of elemental areas of the picture change as shown by the distances f, g, h, a and k.

In the foregoing description of Fig. 1 it is assumed that anincrease of current in the photoelectric cell 34 causes an increase of current in the output circuit of the amplifier 35. Thus for a dark spot on the picture a small amount of light passes to the photoelectric cell 34 and a small value of picture current flows in the winding 12 of relay 5. This corresponds, for example, to a value of current I in Fig. 5 and would result in a large ratio of marking to spacing on the reproduced record as represented by graph A in Fig. 5, and where the ratio of marking to spacing is large a dark condition is represented. Obviously then for a light spot the picture current will be large, for example, of the value represented by I in Fig. 5,the ratio of marking to spacing will be small, and the corresponding portion of the reproduced picture will be light. Obviously by reversing the connections to the relay contacts or reversing the action of amplifier 35 the ratio of marking to spacing can be made large for a light spot in the film and small for a dark spot.

Referring now to Fig. 2 a modified arrangement is employed. Relay 40 is quite similar to relay 5 of Fig. 1 having the three energizing windings 41, .42, 43. Winding 43 is the steady biasing windingwhich is energized by current from battery 44 throu h resistance 45. finding 42 is energized 3" picture "current from the source 46 WhlC'l may be identical with that shown in Fig. 1. The energizing current in winding 41 is also of saw-toothed wave form but this wave form is obtained in a difierent manner, i. 0., by means of a variable resistance in series with the inductance of the relay winding.

The source of cyclically varying current in Fig. 2 consists of the winding 41 of relay4O in series with resistance 47 upon which are impressed positive and negative potentials from batteries 48 and 49 respectively through the commutator 50 which is driven by amotor 51.

The action of the relay in impressing marking and spacing current on the line 6 is the same as in Fig. 1 which is indicated by the use of the same reference characters.

The commutator arrangement of Fig. 2 for producing potentials of opposite polarities in the source of cyclically varying current may be used in place of the vibrating relay of Fig. 1 and likewise the vibrating rc- 'lay of Fig. 1 may be used in place of the com mutator of Fig. 2. a

In Fig. 3 an arrangement quite similar to that of Fig. 1 is shown except that winding 11 is energized by current of sine waveform obtained fromu enerator 55. In this arrangement the length of the marking and spacing impulses are not directly proportional to the amplitude of the picture current and therefore distortion would be introduced into the reproduced picture. Under some circumstances this may not be objectionable and animproved result may actually be obtained in improving the contrast in the reproduced picture or other desired character istics.

A suitable type of reprodueer may be used which is operable by current impulses. The reproducers disclosed in Patent No. 1,613,970, Jan. 11, 1927, of D. C. Tanner, are mentioned by way of example. Synchronism must, of course, be maintained between the transmitting and reproducing drums. Arrangements for accomplishing this result are well known in the art. I

In the arrangements selected for illustration of the inventon the spacing and marking impulses are of opposite polarity. Obviously impulses of a single polarity may be I used for marking-and no current for spac-' ing or vice versa. The type of impulses to be used is dependent upon the nature of the transmitting channel to be employed which may bear-wire line, like line 6 of the drawings, either long or short, a wire carrier'channel or a radio channel.

In order to assist in understanding the theory of the invention'and to aid in the design of actual circuits, a mathematical explanation will now be given.

Referring to Fig. 3 the polar relay 5 is operated from a sine wave (L sin w), the contacts of this 'rela forming the telegraph Sig-- nals shown in Figs. 4 to 6. The reproduced picture shade can be defined as which will vary from 0 to 1 as the bias varies from -100% to +100%.- The relation be tween 1 and sending picture shade S is It is seen that S and S are related by a sine function which is approximately linear over the central range, but will be distorted in the light and dark shades.

T his difiiculty of distortion will be over- ,g sign- (a) This will be approximately linear for a short time and it is assumed that the charging pe tential reverses before departing materially from linearity. The approximate equation of the straight line representing the charging 5 current for the first small interval of timeis obtained by taking the first derivative and evaluating when t=0. That is A saw-toothed wave willbe obtainedmhich has a slope 5? from 0 to 1r/2,'E from 1r /2 to? etc.

Let I represent the current when the reversal takes place, i. e. the peak value of the sawtoothed wave. Then the reproduced shade and the original shade are related as follows varies from 1 to l the reproduced sh'acl'e'will vary lln'early'fPGXfiO to 1 'Eqlltfl tion (5)- neglects the-effect of'the shunt-on the condenser and the inductance of the m lay and assumes infinite sensitivity; conse* quentlyit only approximately represents actual condition.

The voltage across the condenser will riseapproxnnately l nearly-with the time until which-forms a basis for the design of the circuit constants. Assume that the-reversal: frequencyis 10, that is a lO-dot per second signal is to be biased from -10!) per; cent. to

+ per cent. Then v l 1 v t 0R (7) if C IOMF R- X 10 10,000. ohms.

from (4) E- 100 1 e6 oza' wl aitm That is the condenser voltage rises to 1/2" of its final steady state value (with no rel eisal) in E I the saw-toothed wave will be- 1/2 of this or 25 volts. I

Inthe circuit-ofrFig. '2, which accomplishes seconds. J The peakvalue of the same thing but whichdifiers inthatthe;

current through an inductance instead of voltage across acondenser 15' being; considered. The currentwave is-given by the following.-

Proceedingas before the equation of the ap-- proximate straight line is The relation between reproduced and original shade is the same as Equation (5) namely A comparison of Equations (10) and (3) shows :the wave shapeto be identical when I L'=0R (12)" Thatis when B= 10* and L=10 10- 10 =1000 henries (13),

which is probably impractical.

However; it 'is not -necessa'ry to have R as high as 10,000 ohms. for this circuit is The design equation for a ll) cycle signal, we get ries and in Fig. 2 it would be a resistance and condenser in series. The theoretical equation governing their design would be the same n each case, namely and if R was made=R the circuit would act like a pure resistance. Practical considerations might probably prevent making R =R \Vhat is claimed is:

1. In a signaling system, a movable circuitcontrolling element, means for applying a linearly varying periodic force to said element to actuate it, and means 'for applying a biasing force to said element which varies in accordance with signals.

2. In a signaling system, a relay, means for biasing the armature of said relay, means for impressing upon said relay a linearly varying periodic current of constant amplitude, and means for varying the amount of bias of said armature in accordance with sig nals. i

3. In a picture transmission system, a relay. a source of "direct potential, a transmission circuit, the armature of said relay controlling the association of said source with said transmission circuit, a source of linearly varying periodic current of constant amplitude for actuatin said relay, and means for varying the bias or the armature of said relay in accordance with the tone values of the elemental areas of the picture or object to be transmitted whereby the length of time during which said source of direct potential is associated with said transmitting circuit corresponds to said tone values.

current so as to tend to actuate it in the opposite direction. y

N5. In a picture transmission system, a source -of periodically varying "current, a source of varying current modulated in accordance'with the tone values of the elemental areas of the picture to. be transmitted, at transmitting circuit, a source of signaling voltage, and switching means for associating said source of signs. ing voltage with said transmitting circuit, said switching means being actuated by said periodically varying current to tend to move said switching means in one direction and by said second source of varying current to tend to movesaid switching means in the dpposite direction.

6. In a picture transmission system, a source of alternating current, a source of pulsating current of amplitude corresponding to the tone values of elemental areas of a picture to be transmitted, a source of steady biasing current, means for producing ma netic effects by currents from said sources, the

effects produced by the two last mentioned sources being in opposition, and switching means actuated by said magnetieeflt'ects' to produce code impulses. I

7. In a picture transmission system, a source of alternating current Waves, having a form which rises and falls substantially linearly with time, a relay energized by current from said source, an armature for said relay which vibrates under the influence of said alternating current( energization, means to produce a steady bias in said relay, a second source of pulsating current of amplitude corresponding to the tone values of elemental areas of a picture to be transmitted, and means to oppose the steady'bias by current from said second source for controlling the duration of the intervals between movements of the armature.

"a 8. In a picture transmission system, a current operated switching device, means for impressing current upon said device for caus ing a switching operation during successive equal time intervals, means for determining the time of initiation of a switching operation in accordance with the tone values of elemental areas of a picture to be transmitted, and means for producing impulses of current controlled by said switching device.

9. In a picture transmission system, a series circuit comprising a resistance, a condenser and a source of current, a vibrating relay having contacts in said series circuit adapted to change the polarity of said source at uniform intervals, at multi-winding polarized relay, an energizing circuit for one winding of said relay connected in shunt of said condenser, a resistance connected in series in said energizing circuit, a source of signaling current connected to a second winding, a contact closing armature controlled jointly by said two windings, and a signaling circuit,

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t Qmrenti which-is controlled hysaidm mature.

.10. In a picture transmission system a series (cir u t comp i ng a resistance, arendenser and a source of current, a v brating relay having contacts in said series circuit ,cadapted to change the polarity of said source at uniform intervals, a multi-winding polarie'ed relay, anenergiaing circuit for one 0- winding of said relay connected in sh nt to -said.-condenser, a resistance connected in seniesin said energizing circuit, a source of pic- ;ture current connected :tO a second winding, said :source comprising a photoelectric cell, 515 .an amplifier and means to illuminate .the photoelectric cell in accordance with the tone values of a-picture, -a.-contact closing armattur-econtrolled jointly by said :two windings {a transmission circuit the current in 120 i w ich is controlled by said armature.

1-1. In a picture transmission system, means :for preducing electrical current'jim- -;p ulses of the same polari y d ing successive equal time interyfilaand means for deterininingathe time of initiation of said impulses gin accordance with the tone .values of elemental areas of; a picture to be trans- .mitted. I

12. {In a picturetransmission system, means forproducingelectrical current impulses of the samepolari-ty duringsucoessiveequal time intervals, and means-fordetermining both the time of'initiationand of the termination of said impulses in accordance with the tone 5 values of elemental areas of ,a :picture-to be transmitted.

13. in a signaling system, aseries circuit comprising a resistance, a condenser, and a sourceof current, meansto change the polarity of said source at uniform intervals, a translating device having an energizing ci r.

cuit connected inshunt to said condenser only,

whereby said translating device :is energized by alternating en rgy having .a -Wave form which rises and ialls substantially linearly with time and means associated with said itranslatingdenice for propagatingsignals.

' 1d. a p'icture transmission system, a

value .of the resistance and. inductance being so proportioned that the time constant of the series circuit is appreciably greater than the interval of time-betweenchanges of polarity of said sdurce, to produce an alternating current in said inductance having a wave form which rises and falls substantially linearly with time, a movable circuit controlling ele-' ment, means for-applying to said element to actuate it, a linearly-Marrying periodic force produced by said alternating current, and means for applying a biasing force to said elelment which varies in accordance with signa- 5.

16. In a picture transmission system a series circuit comprising a resiscancejan inductance, and a source of current, means to change the polarity of said sourceat uniform intervals. the value of the resistance and inductance being so proportioned that the time constant of the series circuit is appreciably greater than the interval of time between changes of polarity of said source, to produce an alternating current in said inductance having a wave form which rises and falls subso stantially linearly with time, a relay ener- I gized by said alternating current, an armature for said relay which vibrates underthe luence of said alternating current waves, means !to produce-a steady bias in said relay, a second source of pulsatingcurrent ofarnplitude corresponding to the tone .values of elemental areas ofa picture to be transmitted, and means to oppose the steady'bias by current irom said source .for controlling .the 1 duration of the intervals between movements of the armature. I

In vtestimony evhereof, I have signed my name t this specification this 9th day of February, 19.27..

. EDWARD F. 'WATSON.

source of alternating icurrent waves of subso .stantic ly si usoidal were fio m, areley e eraired by current romsaidsourc'e, an arma ture for said relay which vibrates under the nfluence of said al ernating current energ cation, to produce a steadyihias in said no lian e s condsource of pulsating current hf an'amplitud corresponding to the one alues of elemental areas at a picture to be transknitted, an means to-opposethe ste y bias Jay cur e dram said second source 2fer (coneo itrolling'thed n ticn-of the n e nalsbetwee merements .of the armature.

15.. 'In a signaling system, a series circuit comprising a resistance, an inductance, and

a-source of current, means t ohange the -po-.

5 iea'iayn fseidsaurceiatiunifiormyinterralsahe 1 DI'SQLMME 1,788,476.Edward F. Watson, Larchmont, N. Y. Ennc'rmcan Pic'runn Tnims- MISSION. Patent dated 'January13, 1931. Disclaimer filed August 16, 1935,

by the assignee, American Telephone and Telegraph Company.

. Hereby enters this disclaimer to the subject-matterof the said claims of said Letters Patent which are in the following words, to wit: 4 a 1 4. In a signaling-system, a source of periodically varying current, a source of current varying 1n accordance with signals, a transmitting circuit, a source of signaling transmitting circuit, said switching means beingacted upo said source 'of perivoltage, switching'means for associating said source of wag voltage with said odically varyin current-so as to tend to actuate it in one 'rection and by said second source 0 varying current so as to tend .to actuate it inthe opposite direction. 5*. In a picture transmission system, a sourceof periodically 'varymg current, a source of varying current modulated in accordance with the tone values of the elemental areas of the picture to be transmitted, a transmitting circuit, a source of si aling voltage, and switching means for associating said source of signaling voltage with said transmitting circuit, said switchingvmeans being actuated by saicl'periodically varying current to tend to move said switching means in one direction and by said second source of varying current to tend to move saidswitching means in the opposite direction. I

8. In a picture transmission system, 'a current operated switching device, means for impressing current upon said device for causing a switching operation during successive equal time intervals, means for determining the time of initiation of a switching operation in accordance with the tone values of elemental areas of t a picture to be transmitted, and means for producing impulses of. current controlled by said switchiri'gdevice. I

11. In a picture transmission system, means for producing electrical current i impulses of the ,same polarity during successive equal time intervals,- and means for determining th 'time of initiation of said impulses 1n accordance with the tone values of elemental areas of a picture to be transmitted.

12'. Ina picture transmission system, means for producing electrical current impulses of the same polarlty during successive equal time intervals, and means for determining both the -tiine of initiation and of the termination of said impulses 1n accordance with the tone values of elemental areas of a picture to be transmitted.-

[Qjfic'ial Gazette September 10, 1935.]

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