Patent GB-947011-A (GB)
Title: Printing telegraph apparatus
IPC: H04L19/00
Filed: 1962-04-06
Abstract: 947,011. Typewriters &c. DOW JONES & CO. Inc. April 6, 1962 [June 20, 1961], No. 13296/62. Heading B6F. [Also in Division H4]  A control circuit for a type-printing telegraph receiver (see Division H4) comprises a transistor which amplifies and inverts a string of square input pulses and functions in response to the converted pulses to operate in accordance with the input pulses to operate the various functions of the telegraph, i.e. to select a character to be printed, to print the selected character, to sound a bell, to switch the receiver on or off &c. Current pulses of zero or plus or minus twelve milliamps are fed through the circuit through leads 20, 21 across which is a testing jack 35. The pulses pass through a PNP transistor 30 biased by a battery 41 and emerge from its collector 49 as a string of inverted and amplified pulses of rising from zero to one hundred and fifty or three hundred milliamps respectively. In operation, a long negative pulse fed to the circuit is converted into a long 300 milliamp positive pulse. This operates a slow acting relay 56 to temporarily connect an A.C. motor 95 to an A.C. supply a generator 96. The motor rotates three shafts 136, 137 and 165 through suitable friction drives 135, 135a. The pulse also operates an electromagnet 77 through a normally closed relay 70 to lower a detent member 160 to allow the printing shaft 137 to rotate through almost half a revolution. A cam 172 on the shaft moves a follower against the action of a spring 171 to disengage a worm follower 168 from a rotating worm 166 and thus allow the worm follower to move to right (as shown in Fig. 4) under the action of a spring mounted in a sleeve 169. The worm follower releases its pressure from a spring-pressed contact 115, thus allowing the latter to return into engagement with a contact 108, thus forming a permanent circuit between the motor and generator. A number of short positive pulses are then fed to the circuit, these do not operate the slow-acting relay 56 but pass through a coil 63 of an escapement mechanism 25 to cause it to oscillate to allow stepped rotation of a print wheel 26 mounted on the shaft 136, thus allowing a desired character to be selected. The pulses also pass through a condenser 91 and a rectifier 87, thus energizing the relay 70 to open its contact 71 and thus de-energize the electromagnet 77 allowing the detent to lift so that the shaft 137 completes its half revolution, the cam 172 causing the worm follower 168 to re-engage the worm 166. Next, a long positive or zero pulse is fed to the circuit. The path of this pulse through the relay 70 is blocked by the condenser 91 so the relay 70 is de-energized, thus energizing the electromagnet 77 to cause further rotation of the shaft 137, a cam 150 causing a bar 28 to press a sheet or strip of paper 27 against the type 26. The printing pulse is followed by a further set of short character-selecting pulses or if it is required to repeat a character a short negative pulse is sent through the circuit this does not operate the escapement 25 but operates the relay 70 to temporarily de-energize the electromagnet 77 to allow the printing shift 137 to rotate again. When an extra long negative pulse is fed through the circuit the relay 56 is energized and a bell 128 rings to call attention to the receiver. As the shaft 136 rotates to select a character a follower 176 moves along a worm 175. The follower is normally lifted and returned under the action of a spring 178 during the printing operation. If the shaft 136 is rotated through somewhat more than a revolution by continued pulses the follower reaches a stop member 180 the figure wheel is arrested with a predetermined character in position to set the receiver in unison with the transmitter. A further continuation of these pulses similarly moves the worm follower 168 until it moves the switch contact 115 to switch-off the receiver.