US2290823A - Double carrier facsimile - Google Patents

Description

y 1, 1942. R. R. HAUGH 2,290,823

' DOUBLE CARRIER FAGSIMILE Filed June 12, 1940 3 Sheets-Sheet l l i ilmmlmllll WIIIIIHIII FIGH I a FIGZ.

Patented July 21, 1942 UNITED STATES PATENT orrlcs DOUBLE CARRIER FACSIMILE Raymond B. Haugh, Chicago, Ill.

Appiication June 12, 1940, Serial No. 340,067

9 Claims.

This invention relates to a method of and means for transmission of shaded pictures and reception of the images over a signalling channel and particularly to refinements in the methods thereof.

It is the object of my invention to provide and improve the method of transmitting shaded pictures and improved apparatus for carrying out the method which is simple and efiicient, low in cost and requiring no adjustments at the recorder.

Another object of my invention is to provide means for balancing the curve characteristics of a facsimile transmitting system.

Another object of my invention is to increase the speed for transmitting pictures.

Another object of my invention is to definitely control the duration of the signal impulses according to the shading of the scanned picture elements.

Another object of my invention is to transmit both the synchronizing and the picture-signals simultaneously in such a way that they will not interfere with each other.

Another object of my invention is to provide for transmitting a picture or other image in such a way that the reception will not be unfavorably effected by static.

These objects are achieved in part by employing a simple electric generator with four separate stator windings. One of said windings produces a control wave train consisting of a series of increasing wave train groups, these successive wave train groups are used to divide the scanned picture into a series of picture elements. wave train is used as a unit for accurately measuring the shading intensity of the picture element being scanned by a photoelectric cell over a very wide range of shades and also for controlling the duration of the black and white picture carriers. The length of these two carriers of different frequency represents the shading intensity of the picture element being scanned. These two carriers are used to operate or key the receiving recorder to the frequency of the wave train groups. Another winding of the said generator produces one of the above carrier waves which carry the black picture signals, consisting of a series of wave trains of constant amplitude but skipping a cycle at regular intervals. This carrier wave will be called the black keying carrier. The control wave train and the black keying carrier are in synchronism. Another winding of said generator produces the other car- Each 11 rier wave which is of constant amplitude but of 55 different frequency than the black keying carrier. The function of this carrier is to carry the white picture signals. These two picture carrier waves have constant amplitudes and approximately the same signal strength. The said generator also produces a synchronizing signal which is of much lower frequency than any of the other three frequencies.

My invention contemplates the transmitting of three generated frequencies plus the change in duration of time that two of the frequencies are transmitted which represents the shading of the picture elements. The duration of the black keying carrier depends on the blackness of the picture element being scanned and the white carrier wave filling in the rest of the time. If the section of the picture being scanned is pure black, the black keying carrier is so arranged that it produces its own keying frequency by dropping a cycle at regular intervals.

In the transmission of pictures by radio it is desirable that all the energy capable of being radiated from a given transmitting station be employed, because the recorded picture depends in a large measure on the ratio of the signal energy level to the static interference energy level at the receiver. In my system the reduction of this interference is accomplished in two ways. First, by transmitting continuously with either one or the other of the two said carriers of different frequency which correspond to the shading of the picture element being scanned. (At the present time facsimile pictures are being broadcast by sending out a carrier wave for the lack picture signal and no carrier wave for the white portion or vice versa. This reduces the transmitted energy level.) Second, in receiving the black and white carriers are filtered out by separate filters, rectified, and amplified and then connected to a signal amplifier so that one signal would oppose the other if they were both on at the same time, and if the signals had the same strength they would cancel out, but the two carriers are never on at the same time. When static goes through the receiver it will go through the two filters and rectifiers with the same amount of energy in each circuit and will balance out because the output of the filters and rectifiers oppose each other in the signal amplifier. This will be explained in more detail later.

There have been quite a number of different methods invented for synchronizing and framing pictures in facsimile transmission. One method sends only a framing impulse each time the picture is being scanned and this impulse releases a clutch which allows the motor to move the recorder through one cycle or line and then waits for another impulse to come along for the next line or cycle. This system has the disadvantage that its releasing time varies with friction and signal strength and the inertia of the moving parts tends to prevent the absolute synchronism of the recorded picture elements from line to line. Another disadvantage of this system is that the synchronizing impulses have to be very much stronger than the picture signal. Another facsimile system depends on the local power circuit for holding the recorder in synchronism with the transmitter after the picture has been framed. This system works fairly well on the same power circuit but does not work well when the transmitter gets its synchronization from one power system and the recorder gets its synchronization from a different power system. Some facsimile systems use involved complicated electrical vibrators depending in most cases upon the impulse synchronizing signals sent by the transmitter to control the vibrator.

My present invention depends simply upon transmitting a continuous synchronizing frequency which controls a synchronous alternator which is driven by a local motor at-the recorder in step at all times. This is accomplished by using this synchronizing signal to continuously modulate the black and white picture signal carriers about 25%. The framing signal at the end of each line is attained by modulating the white and black carriers 50% with the synchronizing signal for a very short time, which allows the framing clutch to release if the picture is framed and if not, it frames it. When the pictures are being changed at the transmitting station the synchronizing signal modulations are again changed 50% for fifteen seconds or more. This operates a delay relay at the receiving recorder which is set for this time delay and operates a paper cut-off. It can be seen that the same synchronizing frequency is used to keep the motor and recorder in step, frame the picture, and to cut off the paper.

The operation of the framing clutch is unique in the fact that it does not function except when the recorder is out of frame and then it brings the recorder into frame in one revolution. The framing clutch is always energized, except when the framing signal is being transmitted at which time the clutch releases and if the picture is in frame it will pass the clutch spring before the framing clutch is energized again. In this system once the picture has been automatically framed the continuous synchronizing signal, which controls the speed of the driving motor and the recorder, also holds the recorder in frame indefinitely.

Certain other objects and advantages will be apparent and the invention will be more readily understood by referring to the following specifications and the accompanying drawings.

Fig. 1 shows a diagram of a fragmentary section of an alternating current generator with two special stator windings.

Fig. 2 curve A shows the increasing wave train groups generated by the winding A of the generator. These wave train groups are called the control wave train. Curve B shows the constant amplitude carrier wave which drops a cycle at regular intervals. This voltage is generated by winding B of the generator and is called the black keying carrier.

Fig. 3 shows schematically the diagram of the amplifier circuit and the wave forms in various parts of the circuit.

Fig. 4 illustrates graphically the output carrier waves corresponding to the picture elements being scanned for one cycle of the synchronizing frequency.

Fig. 5 shows a schematic diagram of Fig. 4 showing more definitely the time that the white and black signals are operating.

Fig. 6 is a schematic diagram of the receiving amplifying circuit showing its connection to the recorder as shown in Fig. '7 and Fig. 8.

Fig. 7 shows a cutaway top view of the paper and the facsimile recorder with the typewriter ribbon and its operating mechanism removed.

Fig. 8 is the left end view of the facsimile recorder showing schematically a cutaway section of the speed control alternator.

Fig. 9 is the right end view of the facsimile recorder showing electrical recorder, paper outoff and typewriter ribbon.

Fig. 10 is a schematic diagram of a modified form of a facsimile circuit showing the wave forms in different parts of the circuit.

Fig. 11 is a schematic diagram of a modified form of a facsimile receiver showing how it is connected to the recorder.

Referring to Fig. 1 the laminated iron rotor H is secured to shaft 52 by key [3. On the circumference of rotor l l are small poles E4 equally spaced. On the face of the main pole l5 are stator poles It, ll, l8, l9, and 22'! on which are wound coils with the same numbers which are connected in series and will be called winding A. On the main pole 2! is field coil 22 which is used to magnetize the poles, making the pole 2| north and the pole I5 south. Field coil 22 is connected to a source of direct current not shown. The air gap 23 under the pole 2! changes from a wide gap to a very narrow gap as the pole piece I la moves across the pole face, thus changing the reluctance of the entire magnetic circuit. As the pole piece I ib passes under the stator poles I6, I1, l8, I9, 20, and due to the changing of the air gap 23 at the same time, it will produce an increasing voltage in each of the succeeding coils. The five voltages generated in winding A are the results of the separate voltages generated in the stator coils It, If, l8, l9, and 22 as shown by curve A in Fig. 2. These increasing voltages !6, l1, l8, l9 and 2t correspond to the voltages generated in stator winding A in Fig. 1. These voltages represent one group in the control wave train.

On the face of the main pole 2d are small stator poles 25, 25, 27, and 28 on which are wound coils of the same numbers. These coils are connected in series. On the face of pole 29 are small stator poles til, 3!, 32, and 33 on which are wound coils of the same numbers and these coils are connected in series. Coils 39, 3|, 32, and 33 are wound in the opposite direction of coils 25, 26, 27, and 28. These two sets of stator coils are connected in series and will be called winding B. Main poles 24 and 29 are excited by coils 3d and 35 which are connected to a direct current not shown. These exciting coils make pole 24 south and pole 29 north.

As the pole pieces I l-c and Mid sweep under coils 25 and 30 the two voltages generated will add, and similarly voltages generated in coils 26, 27, and 28 will add to the voltages generated in coils SI, 32, and 33 respectively. The stator poles that should come after stator poles 28 and 33 are left out so that the voltage generated in winding B will look like curve B in Fig. 2. There will be four complete cycles of constant voltage generated and then one cycle will be dropped in this carrier wave.

The voltages generated in windings A and B in Fig. 1 are in phase with each other as shown by the curves A and B in Fig. 2, which illustrates graphically the waves as they occur in their respective windings in Fig. 1. The cycle that is dropped in curve B corresponds to the lowest voltage cycle in curve A. The voltage increase in curve A for each wave train shown is linear but for balancing the curve characteristics of some other part of the amplifier or receiver circuits the expanding voltage may be made to vary as a convex or concave curve by changing the air gap 23 in Fig. 1 or changing the number of turns on the stator poles l6, l1, l8, l9, or 20.

By way of illustration it will be assumed that the frequency of the voltage generated in winding A in Fig. 1 is 10,000 cycles and that there are cycles in each expanding wave train. A 5 cycle group will represent a single picture element. Therefore there are 2,000 wave trains per second generated in winding A. Winding B will also generate a 10,000 cycle carrier Wave. In this carrier 4 cycles will be a constant voltage and the fifth cycle will be dropped. Therefore there will be 2,000 wave trains per second of 4 cycles each synchronized with the 2,000 expanding wave trains produced in winding A. On the same shaft of this generator but not shown is a winding producing a 5,000 cycle constant voltage carrier Wave. Also on the same shaft of this generator but not shown is a winding producing a 200 cycle synchronizing frequency.

The first 10,000 cycle winding produces 2,000 wave trains with 5 expanding cycles in each train or group which is called the control wave train. The second 10,000 cycle winding produces a 2,000 cycle keying frequency of 4 cycles each with one cycle missing which is called the black keying carrier. The third 5,000 cycle winding produces a carrier of constant amplitude which is called the white carrier Wave. The fourth 200 cycle winding produces a carrier which is called the synchronizing frequency.

Referring to Fig. 3 the light from the exciter lamp 40 is focused 'by lens 4! on the picture 42 which is wrapped around the rotating drum 43 which is driven by a 200 cycle synchronous motor 44 which is connected to the 200 cycle synchronous winding of the generator. The intensity of the reflected light corresponding to the shading of picture 42 on drum 43 operates the photoelec tric cell 45 and the amplifier tube 46 in such a manner that the current flowing through the plate resistance 47 has the characteristic shown by curve 43, for the white and black shading intensity of picture 42. The negative side of resistance 41 is connected directly to the two screen grids of the vacuum tubes 40 and 49 and the positive side is connected to their cathodes. The primary winding of transformer 50 is connected to generator winding A shown in Fig. 1 which 1 The plates of these voltage from transformer which is impressed on the control grids. This Voltage is shown by the schematic wave form A. This screen grid method of modulation is described in detail in Patent #1066065. When the White portion of picture 42 is being scanned the current in the plate circuit of tube 45 and through the resistance 41 puts a negative bias on the screen grids of tubes 40 and 49 so that the output voltage will be low and is represented by the wave form A"! which is a schematic drawing of a group voltage curve A shown in Fig. 2. As the current in tube 45 decreases due to the dark shading of picture 42 the negative screen grid bias voltage across resistance 41 becomes less and the output of tubes 48 and 45 becomes gradually greater as shown by the increasing of wave forms A"2, A"3, and A"4.

The center tap of the secondary of transformer 5| is connected to a filter, consisting of choke 52 and condensers 53 and 54, which are connected to the cathode of the double diode triode tube 55. The outside wires of the secondary of transformer 5| are connected to the diodes of tube 55. The resistance 55, the discharge tube 5'! and the voltage 58 are connected in series across condenser 54. The grid of tube 55 is connected through a potential and a high resistance 59 to resistance 50 and the anode of tube 51. The resistances B0 and 6! are connected in the plate circuit of tube 55. The rectified voltages across resistance 56 due to the change in transformer 51 secondary voltage caused by the scanning of picture 42 are shown by wave forms RI, R2, R3, and R4. The cutofi regulating voltage 58 is so adjusted that when the voltages get above the values indicated by dotted line 62 the tube 5] will conduct and a current will flow through resistance 56 which places a large negative voltage on the grid of tube 55 cutting the plate current through resistances 50 and 0| to zero. The value of these negative voltages on the grid of tube 55 is indicated by curves El, E2, E3, and E4. The dotted line 63 indicates the negative voltage that is required to bring tube 55 to its cutoff point. When the voltages drop slightly below the value indicated by dotted line 62, the tube 5i will cease to carry a current and the negative voltage across resistance 55 will disappear and the plate current of tube 55 will go back to its normal value indicating that a lighter portion of picture 52 is being scanned. When a darker portion of picture 42 is being scanned the output voltage of transformer 5! will be greater and the rectified voltage will begin to rise above dotted line 62 and the more it rises the longer the time tube 51 will discharge through resistance 55 and hold the plate current of tube 55 to zero indicated by II, I2, 15, and I4.

The resistances 50 and H are connected to the control grids of tubes 04 and 55 respectively. The common resistance point is connected to the cathodes of these tubes. The primary of transformer 00 is connected to the generator winding that produces the 5,000 cycle white carrier Wave. The secondary output of transformer 66 is connected through a variable resistance 61 in the grid circuit of the tube 05. The primary of transformer 50 is connected to the generator winding B in Fig. 1 that produces the black keying carrier of 10,000 cycles. The secondary output of transformer 08 is connected through a variable resistance in the grid circuit to tube 55. The primary of transformer '80 is connected to the generator winding that produces the 200 cycle synchronizing frequency. Across the secondary of transformer i is connected a re sistance H which by means of a single pole double throw switch 12 the resistance ll is entirely or in part connected in series with the screen grids of the tubes 6 and and the plate potential. The cam switch 72 is operated by cam 73 which rotates with the scanning drum B3 and once each revolution this cam 13 through cam switch l2 sends a framing signal by connecting the full output voltage of transformer F0 to the screen grids of tubes 64 and 05 thus modulating the carrier wave from the controlled grids about 50%. The rest of the time the switch 12 connects only a small part of the total voltage across resistance H to the screen grids of tubes 54 and 65. This only modulates the carrier waves from tubes 64 and 65 about 25%. This modulation is used to keep the recorder in synchronism with the transmitter. The effect of this 25% synchronizing modulating voltage on the two carrier frequencies from tubes 64 and 65 is shown in Fig. 4.

When a white portion of picture 02 is being scanned the plate current in tube 55 is set at a predetermined high value so that the current flowing through the resistance 50 places a positive potential on a control grid of tube 64 making it operate at maximum efficiency passing the white carrier wave of 5,000 cycles from transformer 05. As this carrier goes through tube 64 it is modulated by the 200 cycle synchronizing voltage placed on the screen grids by transformer about 25%. The same plate current from tube 55 also flows through resistance 0! biasing the tube 05 so far below the cutoff point that the carrier wave from transformer St cannot get through the tube 55.

When a black portion of picture i2 is being scanned the plate current in tube 55 is reduced to zero. The positive potential due to a current flowing through resistance 60 is reduced to zero and the battery voltage biases the tube 64 so far below the cutoff point that the carrier wave from transformer 60 cannot get through the tube 64. The negative bias due to the current flowing through the resistance 0| is reduced to zero allowing a more positive potential to develop on the control grid of tube 05 making it operate at maximum efficiency, and passing the black keying carrier of 10,000 cycles from transformer '68. As this carrier goes through the tube 55 it is modulated by the 200 cycle synchronous voltage placed on the screen grid by transformer 10 about Therefore across the output terminals 10a and 151) will be either the white carrier or the black keying carrier and both being modulated by the 200 cycle synchronizing signal.

Fig. 4 shows one cycle of the modulating 200 cycle synchronizing signal. The white carrier 5,000 cycle wave is shown by carriers Wl, W2, W3, W4, and W5.

The number of cycles in each group indicates the length of time that the white signal is being transmitted. The black keying carrier 10,000 cycle Wave is shown by carriers El, B2, B3, B0, B5, B6, B1, and B8. The 200 cycle synchronizing signal modulates both the 5,000 and 10,000 carriers the same amount.

As the gas discharged tube 5'! is either conducting or non-conducting, the plate current of tube 55 will be either on or off so that either tube 04 will be on and 05 off or tube 55 will be on and tube 64 off, so that either the white or black carriers will be on continuously, and both in turn will be modulated by the 200 cycle synchronous signal. It will be noted when a continuous black section is being scanned the tube 65 will continuously amplify the black keying carrier which contains four complete cycles and then drops one cycle. These dropped cycles are shown as Si, S2, and S3 in Fig. 4. The object of dropping a cycle on a continuous black signal is to produce and transmit a keying impulse to operate the receiving recorder instead of producing a keying impulse in the receiver amplifier. Fig. 5 shows a schematic diagram of Fig. 4 showing the length of time that the white and black signals are on, and When no carrier is transmitted.

Fig. 6 shows a schematic diagram of the radio receiver and amplifier for receiving the double carrier wave picture signals which are modulated by a synchronizing signal. The radio facsimile carrier wave is received and amplified by tube and then detected by tubes 8| and 82. The audio output of tube 8| is connected by transformer 83 to the two filter circuits 84 and each consisting of an inductance and a capacity connected in series. The filter circuit 84 which is tuned to the 10,000 cycle black keying carrier is connected by rectifier 8% to the resistance 8'! so that the positive end of the resistance 81 is connected through a high resistance 88 to the grid of tube 89. The filter circuit which is tuned to the 5,000 cycle white carrier is connected by rectifier 00 to resistance 9! so that the positive end of resistance 9| is connected through the high resistance 92 to the grid of the tube 03. The output of the tubes 80 and 93 is connected in pushpull arrangement to a standard electro-magnetic speaker unit 94 in Fig. '7 which operates the recording stylus 85.

When a black keying carrier of 10,000 cycles is being transmitted there will be voltage generated in filter circuit 84 which will be rectified by rectifier 80 and will cause a drop in voltage across resistance 8'! which will put a positive bias on the grid of tube 89. The resistance 83 is used to keep the grid current down when it goes positive. A heavy plate current due to this positive grid voltage will result, which will cause the recording stylus 95 in Fig. 9 to move forward against the typewriter ribbon 93 and mark the inside of the circular paper cylinder segment 91.

When the black keying carrier of 10,000 cycles is being transmitted continuously due to the scanning of a black section of a picture, the dropping of a cycle in this carrier causes the grid voltage to become negative again and reduces the plate current to normal value, allowing the stylus 05 to move back from paper 91 reducing the pressure on the typewriter ribbon 96 and the paper 01. Thus a 2,000 cycle keying frequency is impressed on the recording stylus 95 when a continuous black signal is being transmitted.

When the white carrier of 5,000 cycles is being transmitted continuously due to the scanning of a white section of the picture there will be a voltage generated in filter circuit 85 which will be rectified by tube and will cause a drop in voltage across resistance SI which will put a positive bias on the grid 03. The resistance 02 in the grid circuit of tube 03 is for the purpose of keeping the grid current down when the grid goes positive. A. heavy plate current due to the positive grid bias will result, which will cause the recording stylus 05 to move away from the typewriter ribbon 96 and the paper 91. As long as this white carrier is on the recording stylus will be drawn away from paper 91.

For sending shaded pictures the white and black carriers will alternate at the rate of 2,000 times a second due to the fact that the control wave train is operated at that frequency. The length of time that either carrier is transmitted depends on the shading of the picture being scanned. The darker the picture being scanned the longer the time that the black keying carrier 10,000 cycle wave is transmitted, and the lighter the picture being scanned the longer the 5,000 cycle white carrier is transmitted. The sum of the time that any white and black carriers are transmitted equals the time to scan one picture element or .0005 of a second.

The voltage across the resistances 81 and 9I and the grids of the tubes 89 and 93 are of such values that the plate currents will have reached their maximum value for about 70% modulation of the carrier current, so that the modulation due to the synchronizing signal of 25% will not effect the plate currents of the recording tubes 09 and 93. When either carrier is reduced to zero the battery bias in the grid of the tubes 99 and 93 reduces the respective plate currents to zero.

When static impulses are received, amplified, and rectified by this amplifying system the voltage impulses across the two filter cricuits 84 and 85 will be the same because static impulses are equally distributed over a wide range of frequencies. Thus the same Voltage will be impressed across the grids of tubes 98 and 93 simultaneously and due to the push pull arrangement in the magnetic recorder 94 the plate currents will balance each other and the effect of static on the recording will be zero.

The two carrier waves which are modulated by a 200 cycle synchronizing signal are all rectified out from the radio carrier by tube 82 and transformer 99. By the use of the rectifier tube 99 and the 200 cycle tuned transformer I00 the 10,000 and 5,000 carriers are filtered out, leaving only the envelope of the 200 cycle synchronizing signal to go through the transformer I00. This 200 cycle signal is impressed on the tubes IOI and I02 which are in pushpull. The 200 cycle amplified output of these tubes is connected by transformer I03 to control the speed of the synchronous alternator I04 in Fig. 8.

In this system of transmitting and receiving pictures with two carrier waves, the received energy level of the two carrier waves varies with the synchronizing signal. To compensate for this loss in energy level in the receiver when the synchronizing signal depresses the two carrier waves, it is possible to add an extra secondary winding on the transformer I00 in Fig. 6 and feed this voltage back in the right phase to the grid of the detector tube 8I so as to increase its amplification when the two carrier waves are being depressed. This smooths out the synchronizing modulation depression and increases the operating energy level of the recorder. Another way to overcome this energy loss is shown in Fig. 10 and Fig. 11 and will be described later.

In the common plate circuit of tubes IOI and I02 is relay I06 so adjusted that the ordinary 25% modulated 200 cycle synchronous signal will not operate it. A framing signal is sent once each revolution by the cam 13 operating the switch I2 in Fig. 3 which increases the 200 cycle modulating synchronizing signal for framing to about 50%. The increasing of modulation of the 200 cycle signal will increase the plate currents of tubes IOI and I02 and the relay I06 will operate single pole double throw switch I07 cutting the current oil the framing clutch magnet I08 and allowing the clutch spring I09 to pass between the pole pieces.

When the cam switch 72 returns to normal the relay I06 will become deenergized enough to close switch I0! so as to energize framing clutch magnet Ifiii so that if the picture was not framed correctly the framing clutch magnet I08 will hold the clutch spring I09 until the next framing signal, thus framing the recorded picture.

When the paper -12 is being changed on drum 03 in Fig. 3 the cam I3 holds switch I2 in its downward position allowing the full 200 cycle synchronizing signal to modulate the 5,000 cycle white carrier which is then on about 50%. This 50% modulated carrier will operate relay I05 and the switch I07, opening the circuit to the framing clutch magnet I08 and also putting a potential on the delay relay IIO which has to be on 15 seconds before it operates and closes the contact III completing the circuit for the paper cutoff magnet |I2 which operates the circular cutoii' wheel H3 which cuts the paper 91 against the circular end I92 of recording casting I20. The ordinary framing signals which are on for about one tenth of a second have no effect on the delay relay III] and the paper cutoif magnet II2.

Fig. 7 shows how the continuous sheet of paper 91 is wrapped around the cylinder H9, the two edges of this paper are folded back lit; and Ill and are slipped into the slots I I8 and I I9 respectively which are in the base of the round record ing casting I20. The round cylinder tube H5 is placed in the round hole I22 in casting I20 so that they are coaxial and with enough clearance between them for the paper 91 to be pulled through by the threads I30 on drum I29. Cylinder IIII is fastened to the base of recording casting I20 by means of screw I2I in Fig. 8. The alternator I06, the motor I23, the gear reducer I20, and the bearing I25 are all fastened in the cylinder I IE to the recorder casting base between the slotted openings IE8 and H9 so that they are coaxial with the cylinder III: and the casting opening I22 by means of the frame I31 and screw 2|.

The motor I23 drives the alternator I04 by means of shaft I26 and also drives the gear reducer I24 which turns the shaft I20 on which is mounted clutch cylinder I27. Around clutch cylinder I2? is wound a square steel wire spring I09, one end of which passes between the pole pieces of the clutch magnet I08 and the other end is secured to shaft I29 which turns in bearing I25. The shaft I20 and the clutch cylinder I21 turns in the direction of the arrow, the steel spring wire I09 will be held when the clutch magnet I00 is energized, the spring I09 will tend to unwind allowing it to slip on the cylinder I2! thus stopping the rotation of shaft I28. When the clutch magnet I08 is deenergized the spring I99 will tighten around the cylinder I2'I and turn the shaft I28 at the same speed. The large threaded drum I29 is fastened to the shaft I28 and turns inside of the recording casting I20 with just enough clearance to allow the paper 91 to pass between them. The paper slides from the cylinder H5 onto the threads I30 on the surface of the rotating drum I29. The bent paper edges H0 and II? in slots H8 and IIO respeotively hold the continuous paper sheet 9'! tight against the thread I30 on the rotating drum I29, and as the drum I29 rotates the paper will be pulled from left to right by thread I30 and kept from rotating and held in a straight line by parallel slots H8 and H9.

On the right end of the threaded drum IE9 is mounted a bracket 535 which holds the electromagnetic recorder so so that the recording stylus 55 moves around the inside of the end surface I52 of the recording casting I25, also mounted on this bracket is the cutoff magnet I I2 so mounted that when the circular cutoif wheel H3 is forced outward and bears against the end surface I32 of the recording casting I25 it will cut the paper as the drum I729 revolves except the portions IIB and I N.

Fig. 9 shows that the stylus 55 can move against or away from the typewriter ribbon 55 and the paper all as it rotates around the inside of the recording casting IZii depending upon the frequency of the keying signals. When the stylus 95 passes between the slot openings I I9 and I I8, and the spring wire IE is passing the framing clutch magnet I58 is the time when the picture is framed. In Fig. 7 the recorder 54 and the paper cutter I I2 were moved 90 degrees out of phase with the framing device N28 to show a side view or both pieces of equipment. Also in Fig. '7 the typewriter ribbon 95 and the typewriter spools I55 and I35 were removed from the bearing posts I33 and I55 for the same reason.

By utilizing the Variations in the length or two to the modulated synchronizing signal upon the recording, is eliminated.

By maintaining the gain of the receiving amplifier at a constant and predetermined Another embodiment of my invention is shown in Fig. and Fig. 11. In this second case the shading of a picture element is transmitted by changing the duration of two audio carriers of different frequency but of the same amplitude and the synchronizing signal is sent by alternately transmitting two radio carriers of different frequency but of the same amplitude.

The motor at drives the generator I52; which produces in its different windings the control wave train in winding was, the black keying carrier in winding yy, and the white carrier in winding 22. These windings are connected to the primaries of the transformer 55, 58 and 55 respectively. The motor also drives a commutator II with shorting and insulating bars. The shorting bars connect the brushes hi2 and I43 together for the purpose of changing the grid potential of tube I l l from a positive to a high negative value. When the grid is near its positive value the current through the plate resistances Hi5 and M5 is very high. Resistance I55 puts a positive potential on the screen grid of tube I IFI bringing it to its best operating point. At the same time resistance I435 is putting a negative potential on the screen grid of tube Hi8 making it inoperative. When the commutator I5I shorts the brushe use and M3 together, it places a high negative potential on the grid of tube led and the plate current drops to zero. The positive potential that was on the screen grid of tube IN is reduced so that it is inoperative, while the negative voltage that was on the screen grid of tube N18 is removed and the screen grid becomes positive due to the battery in the screen grid circuit. Thu tube M8 becomes operative and tube Mil becomes inoperative when the brushes M2 and I 43 are shorted by commutator IM. When the brushes Hi2 and H13 are not shorted the tube I l! becomes operative and tube I43 becomes inoperative. The purpose of alternately placing one and then the other tube in operating condition is to transmit a synchroniz ing signal by alternately transmitting two radio carriers of different frequency but of the same amplitude. The length of time that either radio carrier is transmitted depends upon the length of time that the brushes I 42 and I53 are shorted or not shorted. The frequency of this sychronizing signal depends on the number of segments and the speed of the commutator I4 I.

The motor 44 drives the scanning drum by means of the reducing gear I55 and through clutch I5I. This rotating drum 63 carries the picture 42 which is being scanned by the beam of light from lamp 55 which i reflected from the picture 42 into the photoelectric cell 55. The output of the photoelectric cell 45 controls the balanced modulator consisting of the screen grid tubes I52 and I connected in a bridge circuit. The plates of tubes I52 and I53 are connected together and have a common plate resistor I54. The control wave train voltages are applied to the screen grids of tube I52 and I53 by the center tap transformer 55. The center tap is connected to the common cathode circuit of the two tubes by battery I35. The control grids of the tubes I52 arid I53 are entirely independent of each other, one being controlled by a fixed bias while the other depends on the photoelectric cell output for control. When the twotubes are adjusted to the same bias the alternating current output will be balanced tozero in the common plate resistor I54. This adjustment is made with full light from a white reflecting surface of picture 42 shining into photoelectric cell e5. Any decrease in the light to the photoelectric cell 45 due to shaded or black picture elements will unbalance the bridge and the control wave train will appear in the output resistor I54 in proportion to the blackness of the picture being scanned or the unbalanci'ng of the bridge circuit. In this system the control wave train supplies the 10,000 cycle carrier current and also the 2,000 cycle keying frequency at the same time.

The condenser I55 connects the output of tube I52 to the amplifying tube I56 which amplifies the carrier current and the keying frequency and filters out all the direct modulating frequencies bychoke I51 and condenser I53: Ehe output of tube E55 is fed by transformer I59 to the rectifier tube I50, through the filter consisting of choke line as illustrated by peak voltages RI, R2, R3

and Re the gas tube I55 will conduct causing a current toflow through resistances I54 and I65,

putting a high positive bias on the grid of the tube I59 and a negative bias on tube I79. will ma'ke tube I59 operative and tube I15 inoperative. ture element is being scanned and the balanced modulator tubes I52 and [53' are thrown out of balance allowin the control wave train from transformer 55 to go through and operate the This.

This happens when a black shaded pic-- amplifying tube I58, the rectifier tube I68, raising the voltage above the line I68 and operating the gas tube I88 and putting a positive bias on tube I68 causing it to operate and pass the black keying carrier from transformer 88 which is connected in the plate circuit of tube I89 and at the same time putting a negative bias on tube I 18 stopping all current in its plate circuit.

When a white portion is being scanned the tubes I52 and I53 are in balance and the control Wave train is suppressed and there will be no voltages above the line I88 and the gas tube I68 will not conduct so there will be no current through resistances I84 and I85. The positive potential on the grid of tube I89 due to the current that was flowing through resistance I84 will disappear and the grid will become negative due to the biasing battery in the grid. circuit. This will bring the plate current to zero. The negative potential that was on the grid of tube I18 due to the current that was flowing through resistance I65 will disappear and the grid will become positive making the tube I18 operative and passing the white carrier wave from transformer 69 which is connected in the plate circuit of tube I18.

The carrier wave from transformer 88 or the carrier wave from transformer 68 will be impressed on the primary winding of transformer I1I. The secondary of transformer IN is connected in the common screen grid return circuit of tubes I41 and I48. The commutator I II alternately makes tubes I41 and I48 operative or inoperative by changing the current flowing through the resistances I45 and thus the tubes I41 and I48 will be alternately modulated by the black and white carrier waves from transformer I'II. When tube I48 is operating the carrier waves from transformer I1I which are impressed on the screen grid of tube I48 will modulate the radio frequency carrier (R. F. 1) from oscillator I12, which is inductively coupled to the control grid circuit of tube I48 by radio frequency transformer I14. When tub-e I41 is operating the carrier waves from transformer I1I which are impressed on the screen grid of tube I41 will modulate the radio frequency (R. F. 2) from oscillator I13, which is inductively coupled to the control grid circuit of tube I41 by radio frequency transformer I15. The two alternated modulated radio carrier waves of the same amplitude are connected to the antenna I11 by radio transformer I16 whose primary is connected in the common plate circuit of the two radio frequency modulating tubes I41 and I48.

In this second modified system it can be seen that the two picture carrier waves are alternately transmitted at constant amplitude as in the first case, but in this instance they alternately modulate two radio carrier waves, while in the first case they only modulate one radio carrier wave. In this second modified system the synchronizing signal is transmitted by alternately transmitting two different radio frequency carriers of constant amplitude, instead of amplitude modulation of the radio frequency carrier for synchronizing as in the first case. In this second modified system the framing cutoff signals are transmitted by shorting the secondary of transformer IN by rotating cam 13 closing shorting switch Ill. The shorting of the secondary I1I stops the modulation of the alternately transmitted radio carriers from oscillator I12 and I13. The framing and cutoff signals are sent as unmodulated radio frequency carrier waves from oscillators I12 and I13.

The receiver and recorder for the above pictures and synchronizing signals are shown in Fig. 11. The grid circuit I88 of the radio frequency amplifier tube I82 is tuned to the radio frequency carrier from oscillator I12 in Fig. 10. The output of tube I82 is connected by radio frequency transformer I84 to the detector tube I 88. The output of tube I88 is connected to the stator winding I98 of the alternator I84 by transformer I89, which is tuned to the frequency of the commutator segments of commutator MI in Fig. 10. The grid circuit I SI of the radio frequency amplifier tube I83 is tuned to the radio frequency carrier from oscillator I13 in Fig. 10. The output tube I83 is connected by radio frequency transformer I to the detector tube I81. The output of tube I81 is connected to the stator winding I8I of the alternator I84 by the transformer I89 which is tuned to the frequency of the commutator segments of the commutator MI in Fig. 10. Th commutator I4I by means of tubes I44, I 41 and I48 alternately impresses radio frequency carrier (R. F. 1) an radio frequency (R. F. 2) on the antenna I11. These two alternated transmitted radio carriers are picked up by the receiver as described and alternately applied to the synchronous alternator I 84 to keep the motor I23 and the recording stylus in ste with the scanning of picture 42 in Fig. 10.

The two radio frequencies from amplifying tubes I92 and I 83 are connected by radio transformer 299 and are combined in detector tube 28I. The transformer 282 connects the output of tube 28E to filters 283 and 284, each filter consisting of an inductance and a capacity connected in series. The detector tube 28I rectifies out the two radio carrier waves leaving the two picture carriers to go through transformer 282 and each carrier is separated out by filters 283 and 284.

The black keying carrier 10,000 cycle voltages are filtered out by filter 204 and are applied to the grid of amplifying tube 289, by the use of rectifier 286 and the resistance 281 which is connected in the grid circuit of tube 289. The white carrier 5,000 cycle voltages are filtered out by filter 283 and are applied to the grid of tube 289 by the use of rectifier tube 285 and the resistance 288 which is connected in the grid circuit of tube 289. The rectified current flowing through resistance 281 due to a black keying carrier places a positive bias on the grid of tube 289 causing a heavy current to flow in the plate circuit and causing the recorder 94 to move the recording stylus 95 against the paper 91. The rectified current flowing through resistance 288 due to a white carrier places a negative bias on the grid of tube 289 causing the plate current to drop allowing the stylus 9'5 to be pulled away from the paper 91 by means of a spring not shown. When there is no current in resistances 281 and 288 the tube 289 is so biased that the stylus 95 will be pulled away from the paper 91 by means of said spring.

The shading of each scanned picture element controls the duration of time that the two picture carriers of different frequencies are on. These two picture carriers of constant amplitude continually modulate the two radio carriers of different frequencies that are alternately transmitted at constant amplitude. One of these radio carriers represents one alternation of a synchronizing signal and the other radio carrier represents the other alternation of the synchronizing signal.

The common point of resistances 2i 298 is connected by resistance are to the common return of filters 253 and 2%. The resistance 258 is connected in the grid circuit of tube 2M so that any rectified current from filters or 204 will place a positive bias on the grid of tube 26 I. This current will cause the delay relay 212 to keep the switch points 2E3 open and the framing clutch It'd energized. When a framing signal of one tenth of a second is being sent the cam 13 in Fig. 10 closes the switch ill which shorts the secondary of transformer ill cutting off the picture carrier signals from modulating the two alternately transmitted radio carriers so that the radio carrier waves go on the air without being modulated. If the radio carrier waves are not modulated there will be no voltage across the tuned filters 233 and 29 3 and there will be no current through resistance 2H3 and this will allow the grid of tube 2% l to become negative and the plate current through the framing clutch clutch N58 to drop thus deenergizing it and allowing the spring clutch 5% to pass the pole pieces of the framing clutch Hit. The delay relay 2 i2 is so adjusted that it is not effected by this short drop of plate current.

When a picture is being changed the cam i3 is so set that the switch ill is closed and the action as described above takes place only this time if the switch is held closed fo; in seconds or more the delay relay M2 will deo ize and will allow the switch points M3 to come together and this will send a battery current through the cutoff magnet H2 causing the cutoff wheel H3 to move out and cut the paper ill as described in connection with Fig. '7.

When static impulses are received they will be rectified and filtered by the tuned filters 2533 and 284. These two filtered signals will be approximately the same strength and because they are applied to the resistances 2m and 298 in the grid circuit of tube 22bit at the same time, they will balance each other out because they oppose each other with equal strength.

By utilizing the variations in the length of the two different audio carriers of different frequency to carry the shading of the picture elements the response of the receiver and the recording is independent of the amplitude of the signals. By alternately transmitting two radio carriers of different frequency modulated by the above picture signals it is possible to transmit at constant amplitude the carrier wave which contains the white and black picture signals as well as the synchronizing signal so that fading and static will have little or no eifect on the recording and the synchronizing of the picture.

In these drawings only two disclosures of my invention have been shown but certain portions can be changed without destroying the spirit of this invention. For example, the white and black audio carriers in the first case may be changed to radio frequencies carriers. The second method can be changed by using two audio frequency picture carriers of constant amplitude with varying durations to modulate a radio frequency. The two side bands of this radio frequency are separated out, amplified and alternately transmitted. These transmitted side band frequencies will carry the synchronizing frequency as well as the two picture carriers. The receiving system of this method will be described in a later patent.

I claim:

1. A system for transmitting facsimile picture signals, means for generating a series of expanding wave trains, means for generating a carrier of constant amplitude for carrying the white picture signals, means for generating a carrier of constant amplitude but different frequency for carrying black picture signals, means to use said expanding wave trains to divide a picture into series of picture elements, an amplifier to control the amplitude of the said expanding wave trains by the tone value of the said picture element being scanned, said amplifier transmitting one of said carriers of constant amplitude when the amplitude of the said expanding wave train is greater than a predetermined level, said amplifier transmitting the other said carrier of constant amplitude when the amplitude of the said expanding wave train is less than said level.

2. A system according to claim 1, in which the said two carriers of constant amplitude are modulated by a synchronizing signal.

3. A facsimile system of sending pictures and synchronizing signals, comprising transmitting three carrier waves, means to divide all picture elements into two time periods, the first said period is occupied by a constant amplitude white carrier picture signal, and second said period is occupied by a constant amplitude dark carrier picture signal of different frequency, said means measuring the duration of time that either said carriers are transmitted dependent on the shading of each said picture element and means to modulate the said constant amplitude picture carriers by a synchronizing carrier frequency.

i. A system according to claim 3 in which a change in the percent of the said modulation of the said synchronizing carrier transmits a framing signal and a longer change in the said modulation of the said synchronizing carrier transmits a cutoff signal.

5. In an image transmitting system, means for generating three carrier waves, first said carrier consisting of a series of expanding wave train groups, means to control the amplitude of each said expanding wave train by the shading of a picture being scanned, means for transmitting the second and third carriers alternately at double the frequency of the number of said roups and means for controlling the transmitting time of said second and third carriers in accordance with a predetermined level of the said expanding wave train.

6. A picture signaling system including means to generate a series of expanding wave train groups, means to produce electrical variations in accordance with the tone value of the picture elements being scanned, and means to control the amplitude of the said expanding wave trains by the said electrical variations, and means to transmit a carrier when the amplitude of said expanding wave train exceeds a predetermined level, and means to transmit a different carrier when the amplitude of the said expanding wave train is belowsaid level.

'7. In a facsimile receiver and recorder adapted to operate by incoming picture signals composed of two different wave trains alternately transmitted, the duration of one of said wave J trains corresponding to the white tone value of said receiver separating out the two said Wave trains, means to rotate an electromagnetic recording stylus radially inside a lengthwise moving paper cylinder, said stylus axial movement actuated by said wave trains and means for directing the axial movement of said stylus point against a marking surface onto said paper cylinder, and means for separating out said synchronizing frequency to control the speed of rotation of said recording stylus.

8. In a facsimile recorder of picture signals means to rotate an electromagnetic operated recorder stylus concentric with and inside a paper cylinder said paper moving lengthwise, inside and adjacent to a metal ring surface, and means to direct the point of said stylus against a paper marking means as said stylus and said marking means rotate inside said paper cylinder and said ring surface, said marking means coming in contact with said paper cylinder when said electromagnetic operated stylus is actuated by a picture signal.

9. A method of transmitting facsimile picture elements and a synchronizing signal, consisting of generating two different carriers of constant amplitude, alternately transmitting both said carriers at a constant frequency, controlling the percent of time that either said carrier is transmitted by the tone value of a picture element, modulating the amplitude of said controlled carriers to transmit a synchronizing signal.

RAYMOND R. HAUGH.

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