Patent GB-809208-A (GB)
Title: Telescribing apparatus
IPC: G08C21/00
Filed: 1956-12-06
Abstract: 809,208. Telescribing apparatus. TELAUTOGRAPH CORPORATION. Dec. 6, 1956 [Dec. 12, 1955; Oct. 15, 1956], No. 37312/56. Class 40 (1). A telescribing system uses frequency modulation for representing the movements of a stylus at a transmitting station and controlling the movement of the reproducing pen at a receiving station. First embodiment. General description, Fig. 1. The movements of the stylus 18 are resolved into movements along two diagonal axes at right angles to vary the frequencies of oscillators 10, 12 on either side of 2300 and 1700 cycles per second. Oscillator 14 produces frequencies of 1400 or 1300 c/s. according to whether the stylus is on or off the tablet. The outputs of the oscillators are mixed at 16 and fed to line. At the receiving station the signals are separated by filters 22, 24, 26. A pen lifter detector 40 controls a pen-lifting solenoid 42. The variable-frequency signals supplied by filters 22 and 26 are converted at 28 and 30 into signals of correspondingly variable amplitudes to control motors 36 and 38 controlling the movements of the reproducing pen. Detailed description. Transmitting apparatus, Fig. 2. The movement of stylus 18 varies capacitances 58, 82 through linkages 60, 105 to vary the frequency of oscillator 10 between 2250 and 2350 c/s. and oscillator 12 between 1650 and 1750 c/s. The oscillatory signals are repeated by cathode followers 92, 102 to transformer 98 and so to line. Oscillator 14 operates at a frequency of 1400 c/s. when switch 114 is closed and at 1300 c/s. when switch 114 is opened at the lifting of the stylus. When transmission is to take place switch 134 is depressed to discharge capacitor 136 through solenoid 132 which operates its related contacts and selfholds. When 132 is normal the grids of 92, 102, 122 are at low potential and no signals are sent to line. With 132 operated this low potential is removed. Manual operation of the ganged contacts 112, 120 supplies operating potential to the grid of 122. Transmission can then take place. Receiving apparatus, Figs. 3 and 4. Filter 206 passes the band 1500-1900 c/s. to tubes 208 and 222 in cascade. These tubes are both over-driven and produce inverted signals. Tube 222 therefore produces signals of the same phase as those produced by filter 206. The primary 230 of a discriminating transformer 234 forms part of a circuit resonant at an intermediate frequency of 1700 c/s. The upper and lower parts of the secondary winding resonate at 1730 and 1670 c/s. respectively. The discriminator comprising diodes 236, 238 is biased by tube 250 so that zero voltage appears only at the lower extreme of the range of frequencies. Therefore a direct voltage difference is produced across capacitance 262 proportional to the variation of frequency from the lower extreme. This voltage is amplified by 266. When no message is being transcribed no signal is received by tube 222 so that tube 250 does not bias the discriminators. The voltage produced across resistance 274 represents the movements of the stylus along the one axis and produces a corresponding flow of current through tubes 278, 280 and motor 300 to actuate pen 44 (Fig. 7, not shown). The pen 44 can be adjusted initially by varying potentiometer 272. When a message is being transcribed so that switch 290 is depressed a frequency doubler 293 applies a 120 c/s. frequency to the cathodes of 278, 280 to shake up the bearings of the motor 300, so overcoming static friction in the linkage operating the pen. Filter 210 and the related apparatus operate in similar manner in respect of the signal for the other axis. Filter 208 passes signals of 1300 c/s. when the transmitting stylus is off the tablet. After amplification at 319, 320 the signals are phaseshifted at 330 and rectified at 350 to control the flow of current through solenoid 362, Fig. 4, which lifts the pen from the paper (Figs. 6-8, not shown). The solenoid can be energized only when switch 358 is in lower position, i.e. when a message is being sent. Switch 358 is operated when motor 316 is energized by the reception of signals by filter 210 resulting in the energization of relay 374. At the end of a message relay 374 restores to operate a buzzer 360. During the release time of 374 motor 384 energizes and selfholds for one revolution of cam 401 to advance the paper and operate pump 388, so supplying ink for the pen 44. Second embodiment, Figs. 10, 11. Whereas in the first embodiment the position of rest of the receiving pen is in the middle of the paper, in the second embodiment the receiving pen is withdrawn to one side and clear of the paper. When signals are received from the transmitter a control voltage shifts the operating point of the discriminators as in the first embodiment but signals are necessary on the frequencies of both writing axes, a control circuit responding to both signals to produce a fixed potential. To condition the apparatus for transmission the stylus depresses momentarily a switch 552, Fig. 10, to one side of the tablet. The oscillators 410, 412, 414 then operate substantially as in the first embodiment with oscillator 414 controlled by an under-platen switch 516. The tubes 606, 608, 610, 612 in the receiving circuit form a compander supplying filters 422, 424, 426. For the band with a mid-frequency of 2300 c/s., a positive, zero, or negative voltage is developed across resistors 696, 698 according to the frequency shift. A portion of the signal is applied to diode 682 and appears as a negative potential at the grid of 812. Normally 812 is highly conductive and produces negative potentials across potentiometers 830, 832. If signals are received from both oscillators 410 and 412 tube 812 is cut off. Cathode follower 824 then becomes highly conductive and large positive potentials are applied to the potentiometers 830, 832. These potentials are applied to the lower ends of resistors 698, 706 to shift the operating axes of the pen so that all positions of the pen other than at the origin are represented by positive voltages. If the signal from either of oscillators 410 or 412 disappears the bias voltage from tube 812 also disappears, 824 becomes non-conductive and no current is supplied to the pen motors. When signals from both oscillators are received the pen motors are energized in substantially the manner described in connection with the first embodiment. Current through motor winding 762 closes switch 823 to energize relay 819 and operate pen lifter solenoid 442 until the stylus at the transmitter is placed on the tablet. At the end of transmission the stylus at the transmitter depresses switch 552 momentarily to release the appropriate switches.