Patent GB-655058-A (GB)
Title: Telecommunication switching system
IPC: H04M1/515
Filed: 1948-01-16
Abstract: 655,058. Impulse transmitters. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). Jan. 16, 1948, No. 1369. Addition to 624,557. [A Specification was laid open to inspection under Sect. 91 of the Acts, July 22, 1948.] [Class 40 (iv)] A straight pull impulse transmitter for use in an exchange system as described in Specification 605,049, in which the digits are represented by combinations of positive and negative impulses derived from an alternating current exchange source, has two separate trains of linked finger pull keys for the digits 1 to 5 and 6 to 0 respectively, each set of keys controlling an associated rectifier which is connected in series with the line in alternating directions by the movement of its connections over a commutator device. Two embodiments are described. General arrangement, Fig. 2. Finger pull keys 35 and spacing units 36 are arranged in two parallel slots 34 in the base cover 33 of a telephone set, the keys and spacers being flexibly linked together. The displacement of any key is restricted by a finger stop 65 and the keys are returned to normal by spring control.  Impulsing circuit, Fig. 10. Movement of a right-hand key to the finger stop displaces rectifier brushes 112, 113 into contact with a commutator 115, contacts C1, C2 and C3 remaining inoperative. On release of the key, contact C1 short-circuits the telephone receiver and contact C2 opens the line circuit a, b. Contact C3 then closes and connects a rectifier 92 in series with the commutator and line, the conductive direction of the rectifier alternating as the brushes move over the commutator. The number of impulses transmitted is determined by the displacement of the key train to a maximum of five and they always end with a positive pulse. The left-hand key train is identical in arrangement except that the last impulse is negative. The contacts of an operated key train are released when the keys reach their normal position. First embodiment, Figs. 3 and 9. Each key train assembly is constructed as a separate and similar unit. As shown, the keys and spacers of the right-hand train are connected to a plunger 57 of a speed control dashpot 59 by links 55 and are urged towards their normal position by a spring 58. The links, keys and spacers are flexibly connected by pins 50 fitted with wheels 51 which engage guide slots 52 in supporting frame members 53, 54. Movement of the keys is transmitted to a spindle 75 by an arcuate member 83 fitted with studs 81 which engage corresponding recesses 80a in the base of each key and the adjacent spacer member. A rectifier 93 is clamped on the spindle between insulating washers 96 and has extension arms 94, 95 provided with brushes 112, 113 which engage a commutator 115 fitted within a circular opening in the frame member 54. A sector 103 is clamped on the end of the spindle and drives a loosely mounted sector 101 by a pin and slot lostmotion connection 105, 106. A number of spaced pins 107, 108, secured to the sectors 101, 103 respectively, control the operation of contacts C1, C2 and C3 which are mounted on springs 141-146. Springs 141 and 145 are provided with inclined extensions which are deflected to the right by the pins 107, 108 when the key train is operated so that the contact positions remain unchanged. The inclined extensions however cause a deflection of springs 141, 145 to the left when the key train is released. Spring 141 closes contact C1 which opens contact C2 by deflecting an insulated pin 153. Contact C3 is closed at a later stage by spring 145 due to the lost-motion connection between the two sectors. The angular spacing of the pins 107, 108 on the sectors ensures that the contacts remain operated throughout the return movement of the key train. In the normal position the pins disengage from the inclined extensions and the contacts are released. Second embodiment, Figs. 12, 13, 16 and 17. The keys and spacers of each train are moulded on to a webbing strip 50c which is secured at one end to a pulley 83c, either directly or by the use of a thin metal band 81c. The two key train assemblies are supported on either side of a central support 29c. As shown, the righthand pulley is secured to a spindle 75c which is supported by a bearing 79c in the central support. The webbing strip is guided by troughs 52c and is speed controlled by an adjustable friction plate 57c. A spring 58c fitted between the pulley and a fixed bracket 101c urges the key train back to its normal position against a buffer 66c. A rectifier 93c is clamped on the spindle between insulating washers 96c and has extension arms 94c, 95c provided with brushes which engage a face plate commutator 115c secured on the side of the central support. Contact springs 141c- 146c are controlled by a pin 106c mounted on a hub 105c which is frictionally positioned on the spindle between fixed hubs 102c, 111c by a spring washer 109c. The normal position of the pin is determined by a stud 129c and its angular forward movement is restricted by a stud 134c. During its forward movement, the pin 106c engages inclined extensions 181c, 175c of the springs 145c, 141c in turn and deflects them inoperatively to the right. In the reverse direction the pin engages the inclined extension 175c and deflects it to the left, closing contacts C1c which in turn close contacts C2c by displacing an insulated button 176c. Further deflection of the extension 175c by the moving pin then closes contact C3c by an insulated button 178c. At this point the friction driven pin 106c engages a latch 170c and is held in this position until the latch is released by an arm 104c secured to the hub 102c. The pin 106c then releases contacts C1c and C2c but holds contact C3c closed during its movement past the inclined extension 181c. A cranked arm 128c secured to the hub 111c ensures the return of the pin to its normal position. Specification 624,557 is referred to.