Patent GB-320875-A (GB)
Title: Improvements in switching apparatus, particularly applicable to automatic telephone systems
IPC: H01H67/12
Filed: 1928-07-23
Abstract: 320,875. Merk, F. July 23, 1928. Automatic exchange systems and selectors.-An escapementcontrolled selector may be operated step-by-step by incoming impulses or may intermittently pre-operate its escapement so as to hunt with an unchecked movement. As illustrated, a 100- point brush-choosing panel selector comprises a brush-carriage which drops under escapement control in two stages, during the first of which a tripping rod remains stationary and trips the required set of brushes, while during the second the tripping rod drops with the carriage. For a given working speed, the adoption of escapement control in place of direct step-by-step drive greatly reduces the maximum momentary velocities and so permits the use of a robust carriage requiring only top and bottom pairs of pins for its guidance. The descent of the carriage is smoothed pneumatically. On release, the carriage and the tripping rod descend until the latter is in its bottom position, and the upward restoration of the switch is then effected pneumatically. The control and restoring mechanism is mounted as a detachable unit at the base of the switch frame. Construction and operation of selector. A first series of impulses in a magnet M, Fig. 8, controls a double-catch escapement 227 to permit rotation of a shaft 222 geared to a slide 205, 206. The brush-carriage 105 which rests on this slide sinks by gravity, its descent being smoothed by the pneumatic device 233 acting as a dashpot. During this movement a magnet N is energized and disengages a catch 215 from ratchet teeth 212 on the slide 205, so that a second slide 208 (to which the tripping rod 106 is coupled at 120) remains in its top position upheld by a spring 218. Consequently the rod 106 by means of pins 116, Fig. 4, successively tilts prisms 115 to select a particular set of brushes, n impulses causing the nth set from the bottom (excluding d, which is an auxiliary brush concerned with call-finding) to be shifted into reach of the bank. At the end of the tripping movement the selected brushes stand just above the corresponding section of the bank. The magnet N is then de-energized to lock the slides 205, 208 together, and under control of a second series of impulses the magnet M allows the brush-carriage 105 and rod 106 to fall until the required terminals' are engaged. Springs e and f, Fig. 17, are shifted when the carriage 105 and rod 106 respectively leave their normal positions. The 10 sets of brushes, and an 11th set engaging supply strips, are multipled by wires 110, Fig. 4. Hunting-movements. When the magnet M is under control of an interrupter i geared to the shaft 222 it rocks the escapement just ahead of each catching position, so that descent is continuous until the circuit is opened. Restoration. Further impulses are supplied to magnet M to lower the slides 205, 208 until 208 reaches its bottom position, when a tumbler 26, Fig. 17, shifts springs g to open the circuit of M, and a slide 243, 244, Fig. 8, shifts a spring 241 to allow a valve 235 to admit compressed air to cylinder 233. The piston 234 lifts the slide 205. The slide 208 is at first locked by a spring detent (not shown in Fig. 8) so that the prisms 115 are now tilted in the reverse, order, but at this stage the movements of the brushes into reach of the bank occur while they are still below the corresponding bank sections. When the slide 205 regains its normal position relative to the slide 208 it trips the latter away from the spring detent. The two slides move up together until normal is regained, whereupon springs e, f, g, Fig. 17, and the valve-controlling slide 243, 244 are restored. Circuits for the switch acting as a finder and as group and final selectors are shown in Figs. 15, 16. The references M, N, d, e, f, g, i have the same meaning as above. Finder S1. On a call arriving, relay R, A, U pull up, the distributor V finds an idle link, and P is energized over e12 in series with C1. Magr.ets N1, M1 are energized, the latter intermittently. When brush d reaches the marked tens terminal Z pulls up and cut out N1. When the calling line is reached, PI pulls up in series with T; A2, V2, U2, pull up and C1, P are unlocked. Group selector S2. Magnet N2 is energized and the first digit is repeated by A2 to M2. Relay U2 then falls off, cutting out N2 and closing a circuit for M2 over i2. When idle terminals are found P2, C3 are energized, a loop is closed for A3, and V3, U3 pull up. Final selector S3. Magnet N3 is energized and the second digit is repeated by A3 to M3. Relay V3 then falls off and cuts out N3. During the final digit V3 is again energized, and V3, U3 then fall off in turn and a transient test circuit is closed through P3. If the line is idle, P3 is energized and connects up ringing current through Q. When the subscriber answers Q and Y pull up, Y removes a short-circuit from the right winding of Q, which remains' locked in the test circuit, and P3 is shorted. Release. Relays A2, V2, PI, T, P2, C3 fall off, M1 is energized intermittently until g1 opens and M2 until g2 opens. When the called subscriber hangs up, Q is shorted and M3 is intermittently energized until g3 opens. Modified escapement action. If a single-catch escapement is used, Fig. 18, each falling off of the impulse relay A2 is instantly followed by energization of X, so that M is only momentarily energized irrespective of the duration of the impulse. Specification 275,255 is referred to in the Provisional Specification.