Patent GB-189824-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H01H67/06
Filed: 1921-06-14
Abstract: 189,824. Lenaghan, T. June 14, 1921. Automatic exchange systems and apparatus.- In a system in which subscribers' lines are multipled direct to the banks of single-coordinate switches provided with two wiper-arms, an answering arm which hunts for the calling line, and a calling arm which is set by the dialling impulses upon the contacts of the wanted line, the answering arm in its hunting movement directly moves with it the calling arm, which is then stepped away to the wanted contacts by a series of impulses corresponding to the difference between the calling and called numbers. An impulse transmitter is described which permits these impulses to be dialled in one operation, the movable part of the dial being normally in a position governed by the line number of the associated station. Construction of switching-mechanism. Fig. 1 shows the construction of a single switch having a capacity of 50 lines several of the switches being mounted on the frame 15 side by side and adapted to be controlled by a common driving shaft 4 rotated by stepping mechanism 5. The subscribers' lines terminate in a semicircular bank 1 in which they are arranged in numerical order in an anticlockwise direction, that is, in the reverse direction to the rotation of the wiperarms. The answering wiper-arm 3 is fixedly mounted on a sleeve 7 on the shaft 4, to which the sleeve is normally clutched by a pawl 6, carried by the arm 3, passing through a slot 8 in the sleeve 7 to a similar slot in the shaft 4. The slots in the shaft 4 at the different switches are staggered around the circumference of the shaft in order that the arms will occupy different relative positions in the switch banks. A toothed disc 10 loosely mounted on the sleeve 7 but rotated with it may be arrested by the operation of a magnet 9, thereby causing the pin 11 to withdraw the pawl 6 and declutch the shaft 4. The answering wiper-arm 3 carries round with it the calling wiper-arm 2 which is loosely mounted on the sleeve 7 and may be stepped away from the arm 3 in a clockwise direction by the operation of a magnet 12, the armature of which rotates a toothed wheel 13 integral with or fixed to the arm 2. In operation, when a subscriber calls, the common shaft 4 is rotated and all the arms 3 of idle switches, being normally keyed to the shaft are stepped round, taking with them the arms 2. When an answering arm 3 engages the calling line the shaft 4 is arrested, and the magnet 9 is energized to declutch the sleeve 7 and arm 3. The calling arm 2 is then stepped on to the wanted line by successive energizations of the magnet 12. Electrical connection to the wipers of the arms 3, 2 is effected from the jack 16 over brushes and slip rings 18. Construction of sub-station impulse sender. The impulse sender is of the usual make-and-break type but is provided with an index finger 19, Fig. 2, freely rotatable in either direction and having on its underside a pin 20 which may be inserted against the tension of the finger 19 into any one of 50 small holes in the movable dial plate. A pin 25 is inserted in the hole corresponding to the sub-station at which the dial is situated, the engagement of this pin 25 with a stopping pin on the fixed plate determining the normal position of the dial plate. In operation the pin 20 is inserted into the index hole of the wanted number and the finger 19 and dial plate together rotated in a clockwise direction until the portion of the pin 20 projecting below the dial plate engages the stopping pin on the fixed plate. The finger 19 is then released, the pin 20 is withdrawn from the hole, and the dial plate returns under the action of the usual spiral spring until the pin 25 engages the stopping pin and the dial plate is in its normal position. During the return movement of the dial plate the toothed disc 24 and the pawl 23 operate impulse springs, and a number of impulses is sent sufficient to step the calling wiper arm 2, Fig. 1. on to the wanted set of terminals. General operation. On a subscriber removing his receiver to make a call, a circuit is completed for a common starting relay 37, Fig. 6, over normally closed contacts 38, 39 of the calling line in each switch bank. Starting relay 37 energizes the common shaft driving magnet 5, which rotates the answering and calling arms 3, 2, of all the idle switches until the answering arm 3 of a switch finds the calling line, when the circuit of the starting relay 37 is interrupted by the opening of a pair of contacts 38, 39 and the driving shaft is arrested. The line relay 45 and series relay 41 are now energized over the calling loop, the former energizing the magnet 9 to declutch the arm '3, and earthing the test wiper T, and the latter preparing a circuit 53 for the calling arm stepping magnet 12, and energizing the interrupter relay 47 which transmits dialling tone to the calling party over a circuit S, 49, 51, 71, 85. The wanted number is then dialled, de-energizations of the line relay 45 completing the circuit of the stepping magnet 12 which rotates the calling arm 2 to engage the wanted line. The busy relay 56 also responds and during the transmission of impulses maintains earth on the wiper T over contact 61. If the called line is busy, relay 56 holds energized over its contact 67, and busy tone from the buzzer 69 is sent to the calling subscriber over circuit S, 70, 52, but if the wanted party is free, on the relapse of the busy relay 56 the called line is marked busy by the connection of earth at contact 79 to the test wiper T<1> and ringing current is transmitted over circuit 62, 63, 64, 65, 58, 66, the calling subscriber being signalled that ring- ing is proceeding by dialling tone sent over circuit S, 49, 51, 71, 85. When the called party answers, the switching relay 72 is energized over circuit 73, 66, 58, 64, 63, 62, locks up in series with the line relay 45, and completes the talking circuit, current being supplied to both parties over relays 45, 72. When both subscribers hang up these relays de-energize, causing the relapse of relay 9 and the keying of the arm 3 to the driving-shaft, relay 72 closing circuit 82, 84, for a relay 86, which energises the driving magnet 5. The magnet 5 now rotates the answering arm 3 until it is again adjacent the calling arm 2, when the offnormal contacts 84 are opened and the circuits of the relay E6 and magnet 5 interrupted.