US2376035A - Facsimile apparatus - Google Patents

Description

.May 15, 1945 F. c. coLLlNGs, JR

I FACSIMILE APPARATUS Filed Nov. so, 1942 Patented May 15, 1945 UNITED STATES PATENT OFFICE FACSIMILE APPARATUS Frederick C. Collinge, Jr., Riverton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application Noventa so. 1942, ser-m No. 401,424 s mima. (ci. 17a-sas) disclosed, it is apparent that by the use of the so-called black and white forms of recording, the signal energy which is to produce the recording e'ect changes from one value to another, that is. there may be a change in either amplitude frequency or phase, which, when translated into recordings, will produce the desired form of record.

In a companion case, Ser. No. 467,423, led concurrently herewith, entitled "Facsimile apparatus, there have been disclosed the related portions of the apparatus wherein the particular forms of transmitting and receiving equipment for producing the signal energy and for receiving the signal energy are set forth. In such forms of apparatus, it is known that the light values on a record are converted into variations in intensity of current output from a light translating element, such as a photo-electric tube or the like.

In the particular arrangement disclosed by the companion case above referred to, provision has been made for translating a record subject into a series of signalling impulses where the frequency of the produced impulses varies between two limiting values, so that by the use of appropriate forms of receiving instrumentalities the various produced signals may be caused to actuate a recorder which will either mark or space, depending upon the frequency of the energy received.

The present invention is more particularly concerned with the control of the complete instrumentality and the provision of a suitable means to control scanning and recording and, at the same time, provide for operating and controlling the equipment so as to maintain proper speed and the like.

Furthermore, the present invention is particularly `concerned with certain auxiliary apparatus for use with facsimile devices, and with suitable control provisions for actuating and starting the drivingl motor, depending upon the receipt of signals in the receiver dlscrlminator.

Among the objects and advantages of the invention are those of providing a system particularly adapted for facsimile uses and for the recording of signal energy as a permanent record of either the so-called tape or continuous or even interrupted type.

Other objects and advantages of the invention are those oi providing facsimile apparatus of a particular simplied and elciently operating form.

Still other objects and advantages are those of providing apparatus of a relatively simple and compact nature which overcomes the defects of the prior art through the omission of complex circuit arrangements and at the same time which provides a small and compact, and yet eiliciently operating unit particularly designed for the purposes herein set forth.

Another object oi' this invention is to provide for a high degree of regulation of the driving means used for driving the recording drum, and at the same time to increase substantially the range over which the control is made effective.

Other objects and advantages will become ap-V parent from considering the following speclca tion in conjunction with the accompanying drawing, wherein a portion of a complete facsimile recorder scanner unit has been shown.

In considering the drawing, the portions of the scanner and transmitter amplier and the recorder amplifier, which are not particularly applicable to the present invention, have not been shown in detail. However, reference is made to the companion application hereinabove named for illustration of one of several forms which such apparatus may assume.

Generally speaking, the scanner ampliner unit comprises a photo-electric tube which has been subjected to the light of an image to produce output currents varying in accordance with the intensity of light and shadow on the subject. The phototube then produces signal output energy which is duly amplified and caused to control, in a manner such `as that explained in the companion application, the modulating frequencies for a transmitter unit.

The form oi record scanned and the meansby which scanning is accomplished may, for example. be such as that conventionally represented in a publication by Shore and Whitaker, entitled Tape facsimile synchronizing systems published in a book entitled Radio Facsimile" in October. 1938, by RCA Institute, Technical Press, New

York, and particularly to the form of scanning system illustrated on page 271 of the said publication, wherein it can be seen that the tape mes- Sage is scanned preferably by means of a light sourceidirected byfway of a rotary prism to scan the message and by virtue of the reilectedlight to coniz'ol the output from a photo-electric tube.

Preferably, the transmitter unit comprises a fixed oscillator whose frequency is beaten against that of a variable oscillator adapted to generate two pre-selected frequencies, depending upon selected rate between the two limiting frequen-Y cies. After the oscillator frequency has been controlled, the outputs of the two oscillators are then fed through a detector and caused to control either a transmitter or to provide control signais for directly iniluencing a recorder amplifier.

The recorder amplifier preferably comprises the usual type oi' input transformer with suitable limiting devices, such as those disposed in the companion application, after which the output energy isfapplied through a discriminator network into a final driver and power ampliner combination to actuate a recording instrumentality.

Under such circumstances, the signal energy fed to the recorder amplifier through the threshold limiter may be either the output from the scanner amplifier, where monitoring of the transmitted signals is desired, or the energy may be that received from remote'sourcea for the purpose of directly controlling the recorder in accordance with remotely received signals.

In the recording, the tape record strip upon which the recordings are to be reproduced is preferably passed over a roller of appropriate form, and by virtue of the helical ridge on the miler being caused to bear against a suitable presser bar under signal marking conditions, the e is reproduced In many instances the message becomes a double record where the spiral extends for a plurality of hirns on the rotary element, such as has been illustrated, forinstance, by the British Patent 427,257, which shows one convenient form of recording member for use in the system herein disclosed.

Examples of the form of tape record resulting under such circumstances may be found in the publication IRadio Facsimile" hereinabove identifled, and particularly in the article therein entitled Practical application of tape facsimile system 4written by J. N. Whitaker and this applicant, which commenced on page 284 of the text.

Referring now to the drawing, and with the foregoing brief description of the-general nature of the recorder amplifier having been set forth, it is apparent that the received signals may be applied to an input discriminator transformer I5 by way of the input terminals. and I3, so that the-output energy from the discriminator transformer I5 may be fed to each of a pair of transformer secondaries i1 and Il vwhich are suitably tuned-by the parallel capacity elements 2| and 23 respectively, and which may, where desired, be shuntedby suitable damping resistor elements 22 and 24.

It may be assumed, for instance, that the acceptor circuit comprising the parallel combination of the secondary winding I1, the capacitor 2| and the resistor 22, all connected in parallel, is tuned to one frequency, say of the order of 1800 cycles, to represent one extreme frequency value, such for instance as white in the picture, and the other acceptor combination, comprising the inductance, in the form of the transformer secondary i9, the capacitor 23 and the resistor 24,v al1 tuned in parallel, is tuned to another extreme frequency value, say ofv the order of 1000 cycles, to represent black. The tuned circuit combination comprising the inductance I1 and the capacitor 2| then has its energy supplied to the cathode 25 of a discriminator tube 21, while the energy output from the circuit comprising the transformer secondary i9, the capacitor 23 and the resistor 24 is fed by way of the conductor 28 to the second cathode 30 ofthe tube 21.

'I'he tube '21 is preferably one of the double diode ytype consisting of two independent cathodes and anodes contained within a single envelope and, accordingly, may be a tube of the type known as the 12H6, for instance, although various other types of tubes may be substituted Where desired, and the two sections even may be in separate envelopes.

'I'he opposite ends of the tuned receiving circuits are then connected by way of a conductor which is joined into a. second conductor 31 which preferably connects at a, junction point 42 to the midpoint of two relay resistor elements 39 and 4|, of which the resistor element 39 is connected to the plate or anode element 32 of the second half of the discriminator tube, and the combination forms a load circuit for the tube. The other anode or plate element 5| of the tube 21 preferably connects to ground 40 by way of the conductor 43 and across the series resistor combination 39 and 4| there is also connected a pair of series connected capacity elements 45 and 41 which also connect to ground as indicated.

At a point intermediate the connection of the two series connected capacity elements 45 and 41 a connection is made to the junction point 42 for the resistors 39 and 4I. The outer terminal of the capacity element 45 is connected at its upper end to both the resistor 39 and the anode 32, so that at the junction point 49 a connection may be made through a resistor element 5| and conductor 52 tothe printer amplifier unit (not shown), but shown in the companion application hereinabove referred to.

From the same junction point 49 a connection is made by way of the conductor 53, the resistor 55 and the condenser 51 to ground at 40, and at a point intermediate the connection of the series combination of the resistor 55 and the capacitor 51 a connection is made by Way of a capacitor 59 to the anode 55 of what will be termed an lautomatic start-stop tube 53, and also the grid 13 of the second section of this tube. The anode element of the first half of the tube is connected by way of a conductor 1I to provide a direct current connection to the control electrode 13 of the second half of tube Il. 'I'he anode 65 derives its voltage through resistors 19 and 11 from the source 86 connected to conductor I5.

Also at a point intermediate the resistor 55 and the capacitor 51, corresponding to the junction of the condenser 59 to these elements, there is connected a second conductor 60 providing a direct connection to the control electrode 6| of the iirst half c! the automatic start-stop tube t8. .i

It will be assumed that for a white portion oi.' the picture record to be reproduced by the printer ampliiler unit. there is voltage appearing at the point l which is negative in sign, so that the control electrode 'Il is carried negative for a white portion c: the picture. whereas lor a black portion of the picture, the polarity at the point l0 will be positive relative to ground 40, so that the control `electrode 0l likewise tends to be carried positive but this potential is not suinciently positive for the tube section including control element 0| to draw current. The rst half of the tube 03 is, however, caused to draw current if the black signal is o! a duration long enough to charge condenser l1 positive with regard to the control electrode or grid element Under normal conditions, the black signal is ci relatively short duration, for it is the inarltn ing signal, and usually the messages transmitted are letters, so that except for peculiar types of letters the marking ig not oi' lengthy duration. This type or signal then is such that the control electrode 8i oi' the ilrst half oi the tube 83 is not permitted to go sumciently positive during the black signal to cause the mst half oi' the tube to draw current, as above mentioned. The result is that the second bali oi the tube 0l will draw current for the white signal because control electrode 13 is connected with the anode or plate 05 ci the ilrst hali of the tube, and when no current is drawn by that section, the anode I6 (and consequently control electrode 13) is atits maximum positive potential since no anode current is flowing through resistors 11 and 18 to produce a voltage drop therein. The result is that the relay 02 will operate by reason of the current flowing in the secondv half of the tube 03.

The current ilow through the second half ot the tube 03 is controlled by the control electrode 13 which, in the absence of current ilowing through the rst hall' of the tube, will tend to assume its maximum positive potential, as above noted, so as to cause current to now.

The combination of the resistor 55, the capacitor I0 and the capacitor 5T has a relatively long time constant in order to hold the effects of the white signal in a negative sense for an appreciable time on the tlxst half of the tube 63 so as to permit the second half of the tube 83 to remain in a conducting state in the manner last herein explained.

It can be seen that the second half of the tube 03 has its cathode 10 biased by means of the bleeder resistor combination 18 and 19. The anode 1i connects by way of the conductor Il to one terminal of the winding 03 of the relay I2, and thence, b y way of the conductor 05 to the source of positive potential or anode voltage connected to the terminal 06. I'he result of the combination of the long time constant circuit, consisting of the resistor 50 and the condensers or capacitors I1 and 00 is that the whole arrangement has substantially the eilect of a continuouswhite signal, generally speaking for most types of message transmission, as far as the operation of the second hal! ot the tube 03 is concerned, so that the relay 02 is maintained in an energized state due to the current ilowing through the second haii' of the tube 83 which will, in turn, maintain contact between the armature I1 and the contactor Il.

The cathode circuits o! the tube 0I, like those oi the tube 2l, have not been completed. lo lar as the heater circuits are concerned, merely for the sake offsimplicity. However, the cathode It oi' the first half c! the tube 03 connects by waiy oi' the switching element 01 through the conductor BI to one terminal point or contact element |00 of the switch unit |09, as will later be explained,

The tube V08 serving, as will hereinafter be appreciated, as an automatic start-stop tube, is preferably one oi the type known as the |2SN1GT. and is essentially a double triode. However, various other forms oi' tubes may be substituted, and it is contemplated withinv the scope of this invention to use also tubes contained in completely separate tube envelopes.

Under the circumstances hereinabove exiplained, it is apparent that ii a signal potential 20 is developed at the junction point 09 from the discriminator tube 21 which is of negative volt age herein assumed to be white in the pictural the current ilowwill be interrupted through the first half of tube 8i, but will iiow through the second half ci the tube and. the coil 8l to energize the relay til. Energization oi the relay 0E will then close the armature Il against the conv tact 0@ and supply energy to a driving motor Ill and .to the vibrator coil |09, in, a manner o later herein to be explained.

To provide for this operation, a power switch 00 connects through a voltage source 00 (such as that to drive the dynamotor 2lb and motor ||1 later to be explained) to ground l0. When closed, this switch is adapted to close a circuit, so that energy from the source flows through the conductors 02 and 94 through the relay amature 81 and the contact 89 (it being assumed that the second half of tube 63 draws current to close the relay 02) to the conductor 9|,- and thence through the conductor ill into the motor coil H5 and to the motor H1, and thence to ground 40 by way of the conductor is and one of the paths embodying resistor |23, the governor` I2 i, or one of the conductors |00 or |05. At the same time that energy is supplied from this source 90 to the contactor 09, a parallel cur rent path to ground 00 is provided through a current regulator tube and the conductor ||0 to the vibrator coil |09, and thence through the contactor |38 and the vibrating tongue |31, with the capacitor I4 connected between one end terminal of the vibrator coil |09 and ground 40.

In order to provide the correct voltage for the vibrator coil |09, as will herein later be more particularly explained, suitable variable resistor elements 98 and 99 respectively are connected by way of the conductor 91A to one terminal of the current regulator tube 05 and to the conductor ||0 which feeds energy from the source 90 to the coil |09. Depending upon the position ci the switch element |00 relative to the contactors |0| and |03 respectively, will determine which of the resistor elements 98 and 90 is effective to provide the voltage correction, and. after the correction is made, it is apparent that the resistor elements 0B and 89 may be varied to provide the desired voltage.

The motor ||1, which is driven, as above explained, from the energy source conventionally represented by the energy source 90 through the power switch 08 being closed, and by virtue of the closure on the contactor 09 oi the armature I1 by operation of the relay 82, is adapted to drive the recording drum and helix combination (not shown) but which is preferably of the general type disclosed for instance by Reissue Patent No. 20,152,`dated October 27, 1938, granted to Charles J. Young, and also Patent No. 2,215,806 granted September 24, 1940, to Charles J. Young, or, for instance, by British Patent No. 427,257.

It will be understood that where the system herein disclosed is particularly adapted for use in so-called tape facsimile type of arrangement where a tape of a width just slightly in excess of one letter height or two letter heights is being recorded, then the length of the drum and the contacting drum helix, which is made to contact a suitable presser bar auch as disclosed in the aforesaid patents, will be materially shorter than intimated for the page width recording, but, in principle, will operate in a similar manner.

Also. it is to be understood that the present invention, while disclosing, like the companion case Serial No. 487,423, filed concurrently herewith hereinabove referred to, the use of printer coils such as the coils |33 and |32 later to be referred to, to drive the presser bar, may be replaced by the contact bar itself where electrolytic recording is relied upon, as disclosed, for instance, in the mentioned Young Patent No. 2,215,806.

Referring now more particularly to the motor ||1 which is to drive the said recording drum or the scanning prism (or its equivalent), depending upon whether the ysystem is being used for the purpose of reception or monitoring, r for the purpose of transmission, the motor is essentially intended to be rotated at a predetermined optimum speed to maintain it substantially in synchronism with a suitable control frequency, say of the order of 60 cycles. To this end, a governor |2| is driven from the motor shaft ||9 and, at the same time, a movable armature member |3| is likewise moved between the contact points |33 and |34 by reason of a cam contact (not shown) carried on the end of the motor shaft which permits contact momentarily to be established between the armature |3| and either the contact |33 or |34 during each rotation of the motor shaft. Suitable gear reduction is provided from the motor to the cam contacter so that the contact between the armature |3| and the points |33 or |34 will be broken at the frequency of the vibrator |31 when the motor ||1 is operating at its desired and rated speed. In such operation the break period is but a minor fraction ofthe total time of each motor shaft rotation, so that the effective control period is relatively long.

The governor |2`I, it will be seen from the conventional showing, consists of a rotating element having two contact points |31 and |88 which, when rotating, and at times when the motor is not rotating as fast as the desired speed, are in contact with each other so that the motor connection or terminal remote fromvthe coil IIS is maintained at ground potential, which tends to speed up the motor to a speed which, for instance, might even be too fast for that desired. However, When'the motor is lup to the desired speed by reason of rotation of the governor |2| due to its connection to the motor shaft H3, the contacts |31 and Ill separate so that there is no longer a direct'connection of the motor terminal |89 to ground 4l through the governor, but rather any connection of the motor terminal |83 to ground must now be through the resistor element |23, or by way of the vibrating contactor |3I hereinabove explained to be driven and asvaoss moved between the contact points |33 and- |34 due to the rotation of the motor shaft lil.

It was above explained that when the relay 33 became closed, so that the armature 31 moves to the contact 33, current would also flow through the current regulator tube Il and thence through the conductor Ill to the coil |03, which was to drive the vibrator so that when the coil |33 is energized it will draw `the vibrating amature |31 away from the contact point |33 and thus instantaneously open contact also between the vibrating armature |31 and the contactor |33, which latter contactor connects to the contact point |33 by way of the conductor |34.

'I'he operational frequency of the vibrating armature 31 is so regulated that it may herein be assumed to vibrate at substantially 60 cycles. which frequency is determined by the voltage applied to the vibrator coil which can, in turn, be regulated by the adjustment of the variable resistors 33 and l! which are connected to the terminal of the current regulator corresponding to that at which the conductor ||II connects.

It can be seen, generally speaking, that the vibrator frequency will tend to increase with any increases in voltage without the use of the current stabilizer. The current regulator tube 33 overcomes this effect and the vibrator tends to stabilize regardless of voltage changes in conductor 8|. Generally speaking, the current regulator is such that the current can increase at an established rate with increases in voltage in conductor 9|. This variation in current is chosen to cause the vibrator 31 to remain at substantially constant frequency. Due to the heating of the vibrator itself, the increase in temperature tends to make the vibrator frequency become slower, but if the voltage across the coil |33 increases, the vibrator will tend to return to the desired frequency. 'I'he resistance value of the variable resistors 33 and 33 will tend to increase with temperature and, accordingly, the voltage across the coil will tend to increase, and this will tend to return the vibrator to the desired frequello?.

The vibrating amature |31 alternately contacts the contactors |33 and |33 in its movement due to current in coil lll. Similarly, due to the vibration of the contactor |3|, it contacts the contactors |33 and |34. The connecting conductor |34 between the contactors |33 and |35 and the connecting conductor |35 between the contactors |34 and |34 provide such connections that it can be seen, if the position of the armatures |3| and |31 is such that there is a closed path to ground 43 through either conductor |34 or |85 at any instant, from the conductor 33 which connects to the motor terminal |33, the motor will tend to speed up because the same eifect has been obtained as if the motor had not already been brought up to speed and the contact points |81 and |33 of the governor |2| were making contact. However. if there is lack of coincidence in phase relationship in the vibration of the vibrating armatures |3| and |31, it is apparent that the motor terminal |33 can connect to ground only through the resistance |23, which is shunted by the capacity |21. so that the tendency is for the motor to slow down. Obviously. the resistor |23 also has the function of preventing excessive current flowing through the contactors hereinabove referredeto at any instant, in addition to that of providing for maintaining the motor speed constant.

Accordingly, it can be seen that due to the lack or possibility or' any anamnesi einem@ in phase relationship of the armatures |8| and iti extending over any considerable period of time,

the motor speed may be held quite constant and the motor may .thus be driven at a speed commensurate with that desired to maintain proper synchronism between the record drum (not shown) at the point where recording is to take place. and the record drum or scanning prism or other suitable device at a remote point when once the desired phasal position has been established.

In order that the apparatus herein described may be controlled, a switch unit, generally riesig nated, |48, has been provided. This switching unit consists essentially of two separate switch sections iti and M2, or which the former will be assumed to be operated for the purpose ci' scanningj while the latter will be assumed te be operated for purposes of recording To this end, a switch element |48, in the nature of a toggle, has been provided, so that by means of the cam surface |48 on the switch, a clockwise mction'of the toggle |48 will cause the complete switch unit |4| to move to the right from the position shownfto close a series ci contacts later herein to be explained, and likewise, a counterclockwise motion of the toggle arm |48 will cause the switch section |42 to move to the left from the position shown, to establish certain new con nections and to break certain other connections. Each switch, section moves independently oi the other.

asraoss As herein illustrated in a schematic form, the

switch comprises a series oi armatures through |5i inclusive, and a series ci contacts |68 through |88 inclusive.

In the position shown, the switch is represented in what may be termed a standby operational state, so that contact is established between the amature |41 and the contacter |82, and also between the armature |48 and the contactor |83, as well as between the amature |48 and the contacter |85. Therefore. by reason of the connection established through the contact |63 and the armature |48, a connection to ground 48 is made by way of the conductor |85 for the conductor 68 connecting to the switch element 81 in the cathode circuit of the rst half of the tube 88.

All of the armatures |46, |48, |48 and |58 are preferably connected to ground 48 througnthe common conductor |85.

The switch unit |48 will, for the first part oi its operation, be assumed to be moved counterclockwise. so that the switch section |42 is moved to the left from the position shown, (that is to the assumed record position) so that the contact between the armature |41 and the contacter |82 is broken, and contacts are now established between the armature |45 and the contactor |88, andlbtween the amature |46 and the contactor 5 It is accordingLv Seen that a connection is at once established from the point 88, which was the terminal connection ior the positive anode voltage to be applied to the tube 88, to the midpoint |81' of the printer coils |88 and |82. 'I'his connection is established by way of the conductor 85 and the armature |45, and the contactar |88 through the conductor |81, so that suitable voltage is now applied to the printer ampliiler unit connected to the terminals |88 and |88 at the outer ends of the printer coils |88 and |82. Suitable damping resistor elements 288 and 28| have been provided across the printer coll units |88 and |88.

At the same time that the energy is supplied to the printer cous, a connection to ground e8 is also established through the conductor |85, the amature |48, the contactor IBI, conductor 288 and conductors 285 and 288, through the relay winding 288 to the power switch 88 and the en= ergy source 88, and thence to ground again at 48. Current ilow through the circuit last described causes the relay armature 2|8 to move down against its lower contact 2|| and away from the upper contact 2i?, and provides a connection to Ya dynamotor, conventionally represented at 858,

to be connected between ground 48 through the conductor 2|8, the contacter iii, armature anti. conductor 82 through the closed power switch 88 to the source 88 and thence to ground, which path is open-circuited in the absence of operation of the record switch section M8., This, it will be seen, starts the generator for the high voltage for various tubes, which generator forista a part ci the dynamotor combination 869i.

When the switch |48 is in the record position, so that the switch section |42 has been moved to the left from the position shown, and ii a white signal has operated the relay 82 through the energization of the coil 88 causing thearmature 81 to make contact with the contactor 88, it is apparent that a closed circuit between ground 48 and the voltage source 88 exists. This circuit may be traced from ground 48 through the energy source 88, the closed power switch 88, the conductors 82 and 88, the armature 8l and con tactor 88, and thence through the current regula-n tor tube 88 and the conductor s'i through either of the variable resistors 88 or 88, depending upon the position of the switch arm Hi8, and thence through conductor |8'i to the contacter G88 and the armature |48, back to ground 48 through the conductor i882 Next, if it is assumed that the device is to be placed in a scanning position, the switch is rotatecl clockwise so as to move the switch section |4| to the right, which will have the eect of breaking the contact previously established be tween the contacter |88 and the armature its. as weil as between the contacter |88 and the amature |48, and new contacts will be estais-a lished between the amature |48 and the contac-I tor |88, the armature |58 and the contactar |873, and the armature |5| and the contactor |68.

Under the conditions when the switch has been moved so that the right hand section |4| is placed in the scan position, as last described. the monitor switch 2|8 is closed if it is desired to monitor an outgoing transmission. It will be seen that a connection is established to the printer amplier unit through the conductor 88. the armature |5|. the cont-actor |68 and conductor 2|| through switch 2|8 to the midpoint |81 of the coils |88 and |82. Likewise, with the armature |58 having been moved to the contactor |51, it is evident that the connection of the relay coil 288 to ground is maintained by virtue of the connection through the conductors 285 and |85, through the contacter |51 and the armature |58. Likewise, due to the fact that the armature |48 has moved over against the contactor |88, it is apparent that a ground connectionto resistor 88 is established by way of the conductor through the said armature |48 to the conductor |85, so that there shall be a ground connection from the current regulator tube 85 through the variable resistor 88.

plained. 'Since the relay is to provide for open circuiting, the exciter lamp 22|, when the armature 2H) moves away from contactor 2I2 and over to contact 2| to energize the B'namotor 2 I l, the relay preferably shouldv be of the relatively slow operating type in order that the exciter lamp 22| in the current path last above explained shall be short circuited initially by way of the connection established through the amature 2||| and the contacter 2 I2, but upon energization of the relay` 208, the exciter lamp will form a part of the circuit last described.

Connection to the transmitter amplifier output is established by way of the conductor 2|! and is indicated only in schematic form.

From the above description, it becomes apparent that the general instrumentality hereinabove explained provides for maintaining the desired motor speed for scanning or recording and holding the said speed rsubstantially constant within moderate limits of hunting, which are not detrimental to the recording action.

Furthermore, it is apparent that the connections herein shown provide for the standby position for transmitting the signals, and at the same time provide for energizing the printer unit coils so as to scan or to record.

Various other modifications and changes may be made without departing from the spirit or scope of what is herein shown and set forth.

, Having described my invention, what I claim as new and desire to have protected by Letters Patent is:

1. A control circuit comprising an electric motor whose speed is to be controlled, a voltage source for energizing said motor, a ilrst switching device driven by said motor and operated at a rate proportional to the motor speed, a. second switching device. an electro-mechanical vibrator to drive the saidl second switching device at a predetermined and substantially constant rate. and a resistance element controlled as to its period of operation by the phasal identity and difference of the said switching devices for varying the voltage applied to the motor between two predetermined limiting values.

2. A control circuit comprising an electric motor whose speed is to be controlled, a voltage source for energizing said motor, a rst switching device driven by said motor and operated at a rate proportional to the motor speed. a second switching device, means to drive the said second switching device at a predetermined and substantially constant rate, and means controlled as to its period of operation by the phasal identity and diil'erence of the said switching devices for varying the voltage applied to the motor between two predetermined limiting values.

3. A signalling system comprising signal amplifying means for amplifying signalling energy l occurring at different polarities to represent periods of marking and spacing, signal reproducing apparatus, a motor drive for the signal reproducing apparatus, a source of energy, thermionic means responsive to one polarity of signalling impulses for applying energy from the source to the motor to drive the said motor, resistance and capacity means having a relatively long time constant for applying the signalling energy to the thermionic means and for holding over the effects of one polarity oi signal for a relatively long period of time during the period of receipt oi' the other polarity oi signal so as to maintain energization of the motor from the source.

4.A signalling system comprising signal amplifying means for amplifying signalling energy .from the source to the motor to drive the said motor, resistance and capacity means having a relatively long time constant for applying the signalling energy to the thermionic means and for holding over the effects of one polarity ot signal for a relatively long period of time during the period of receipt of the other polarity oi` signal so as to maintain energization oi' the'motor from the source, and vibratory means for maintaining the motor speed at a predetermined substantially constant rate.

5. A control circuit comprising an electric motor whose speed is to be controlled, a voltage source for energizing said motor,y thermionic means in a combination with a resistance and capacity means having a relativelylong time constant for applying the signalling energy for controlling the periods of application of the voltage from the source to the motor under the control ot received signalling energy, a first switching device driven by said motor and operated at a rate proportional to the motor speed, a second switching device, a vibrator means to drive the said second switching device at a predetermined and substantially constant rate, means controlled vas to its period of operation by the phasal identity anddiiierence of the said switching devices for varying the voltage applied to the motor between two predetermined limiting values, and constant current means for controlling the said vibrator means for driving the second switching device whereby compensation for temperature and voltage changes is provided.

6. A signal recording device comprising a signal recording unit, a driving motor, a source of energy for driving said motor, a signal amplifying means for amplifying signalling energy to energize said recording means, said signalling energy being of opposite polarity for indicating marking and spacing conditions, thermionic' means responsive to the signalling energy to be recorded for controlling the periods of energization of said motor. a switching device, means for shifting the said switching device alternately to supply the recording unit with energy from the amplifying unit in accordance with remote and locally developed signals, means responsive to each position of the switching device for applying energizing voltages to the thermionic ampliiler units, and means for driving `the motor at substantially constant speed.

7. A signal recording device comprising a signal recording unit, means for deriving signalling energy representative 'oi' a message to be communicated, a driving motor for driving at least a portion of the recording unit, a source of energy for driving said motor, a signal amplifying means for amplifying the signalling energy to energize said recording means, said signalling energy being of opposite polarity for indicating marking and spacing conditions, a motor control relay element. thermionic means responsive to the signalling energy to be recorded for controlling the periods of energization of said motor control relay element, a switching device, means for shifting the said switching device alternately to supply the recording unit with energy from the amplifying unit in accordance with remote and locally developed signals, means responsive to each position of the switching device for applying energizing voltages to the thermionic ampliiler unit, and a vibratory means for driving the motor at substantially constant speed.

8. A speed control device comprising a motor element, a source of energy, means for applying energy from said source to said motor, a vibratory element driven from said motor at a rate proportional to the motor rotational speed, a pair of contact points positioned relative to the vibrating element alternately to be contacted by said element as it vibrates, a second pair oi' contact points connected individually to the rst pair of contact points, a vibrating device having an ,armature positioned to vibrate between the second pair of contact points and alternately contact said points, means for energizing said vibrating element from said source of energy, means for maintaining the vibration frequency of the said vibrating element substantially constant at a predetermined frequency, and

means i'or changing the effective voltage applied from the energy source to drive the motor in accordance with phasal variances of the two vibrating elements.

9. A speed control device comprising a motor element, a source of energy, means for applying energy from said source to said motor, a vibratory element driven from said motor at arate proportional to the motor rotational speed, a

pair of contact points positioned relative to the vibrating element alternatelyto be contacted by said element as it vibrates, a second pair of contact points connected individually to the Mt pair of contact points, a vibrating device having anl armature positioned to vibrate between the second pair of contact points and alternately contact said points, means for energizing said vibrating element from said source of energy, means for maintaining the vibration frequency oi the said vibrating element substantially constant at a predetermined frequency, means for changing the eiective voltage applied from the source of en-

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