Patent GB-139900-A (GB)
Title: Improvements in automatic switching apparatus for telephone exchange systems
IPC: H01H67/12
Filed: 1919-03-25
Abstract: 139,900. Western Electric Co., (Western Electric Co.). March 25, 1919. Automatic exchange systems and apparatus.- Relates to an improved selector of the type described in Specification 131,106, the primary object being to increase materially the number of sets of fixed terminals from which a selection is to be made. For this purpose, it is provided that the first set of numerical impulses received by the selector causes a selection of a particular set of brushes which is to be operative, the second set of impulses causes all the sets of brushes to rise to a particular level, and the third set of impulses causes the chosen set of brushes to move outwards step by step to make contact with some particular set of fixed terminals, in the group and at the level so determined. The selection of the required set of brushes is determined by a rotary movement of an inner shaft of the selector. The inner shaft and the outer or hollow shaft which carries the sets of brushes then rise together in selecting the level, and the inner shaft finally rises within the hollow shaft in effecting the outward movement of the chosen set of brushes. Construction of selector and side switch. The hollow shaft 4, Figs. 5 and 9, supports guides 37 for the carriages 3 of the various sets of brushes 2, which are capable of being moved outwards by the action of levers 40 against the tension of spring 3<1>. The first set of impulses is received by the magnet 24, Fig. 10, and causes a partial rotation of the ratchet-wheel 19 and inner shaft 17. The shaft 17 has slots 31 spaced angularly apart, so that when the shaft has been turned through some angle depending on the number of impulses received, some particular slot 31, and the latch 32 pivoted within it, will register with a slot 39 in the hollow shaft 4. The latch 32 remains, for the time being, within the slot. The second set of impulses is received by the magnet 12, the armature of which carries the stepping- pawl of the rack 9. All movements of this rack are communicated to the inner shaft 17, but they are or are not communicated to the hollow shaft 4 according as the rotary locking-member 15 engages the rack 9 to lock the shaft 4 to it, as shown in Fig. 10, or engages a fixed rack 9<a> to lock the shaft 4 in any position to which it has been raised. At the time when the second, set of impulses is received, the locking-member 15 is in engagement with the rack 9, with the result that the inner and outer shafts rise as one, and the sets of brushes 2 all move to some selected level. The rack 9 moves up two teeth for each step made at this stage. A third set of impulses then energizes the magnet 12. These impulses may either be a numerical set directed by the calling-subscriber, or, as in the system shown in Fig. 10, may be automatically produced with a view to causing the set of brushes that has been selected by the rotary movement of the shaft 17 to hunt for a disengaged line in the level of fixed contacts 1 against which it is alined. Before this third set of impulses takes effect, the locking-member 15 has disengaged the hollow shaft from the rack 9 and locked it to the rack 9<a>. Consequently, the further upward stepping of the rack 9, which takes place one tooth per step, causes the shaft 17 to move within, and relatively to, the shaft 4. A pin 38, acting upon the tail of the particular latch 32 that has been brought opposite a slot 39, causes the latch to issue from the slot and to hook on to the lever 40 as soon as the shaft 17 begins to rise. Consequently, the third set of impulses effects an outward step-by-step movement of the selected set of brushes, which continues, in the case of automatic control, until an idle line is formed. The side switch 47 is operated by a cam 45 under the control of a magnet 41. Another cam 46, also controlled by the magnet 41, acts upon a lever 50 which actuates the locking-member 15 and is also concerned with release. Release. This is effected by the movement of the cam 46, which causes a detent pawl to be withdrawn from the rack 9. The shaft 17 then falls within the hollow shaft 4 until the notch in the bar 9 comes opposite the locking-member 15. This is only symbolically represented in Fig. 10, but the locking-member is actually so constructed that a small rocking movement due to a helical spring disengages it from the rack 9<a> and engages it with the rack 9. The shafts 17, 4 then continue to fall together, and just as they are reaching the normal position, a detent pawl of the ratchet-wheel 19 is released, and the spring 20 rotates the shaft 17 into normal angular position. Circuit arrangements. The calling-subscriber A, on removing his receiver, is automatically connected with the contacts 112 by means of a call. finder, with the effect that the relay 115 is ener. gized through a circuit established over the sideswitch wipers 116, 117 and the line. The slowrelease relay 123 is consequently energized, thereby grounding the test-lead 124 and preparing circuits of the relav 125<1> and slow-release relay 126. When the calling-subscriber operates his sender, the relav 115 intermittently de-energizes, but the slow-release relay 123 remains energized. Impulses therefore pass through the slow-release relay 126 to the magnet 24, which steps round the shaft 17. The relay 126 closes a circuit through sideswitch wiper 128 and the magnet 41. which operates the cams 45, 46. At the end of the first set of impulses, the magnet 41 releases, and the sideswitch wipers are advanced to the second position. The side-switch wiper 127 being now in the second position, the second set of impulses effects the intermittent energization of the magnet 12, stepping up the shafts 17. 4 together. When these impulses cease, the magnet 41, on de-energization, moves the side switch into third position. In moving into the third position, the cam 46 unlocks the member 15 from the rack 9 and engages it with the fixed rack 9<a>. In the system as shown in Fig. 10, the subscriber does not send a third set of impulses, the outward movement of the selected set of brushes 2 being a hunting one. If, by premature release or otherwise, the relay 115 becomes permanently de-energized at this stage, the magnet 41, through its armature 42 and sideswitch wiper 129, becomes self-acting, and steps the side switch right round to normal or release position. If, however, the call proceeds normally, the magnet 41 energizes in the third position of the side switch through the contact 135 of the relay 131, which is primarily energized through the side-switch wiper 123 and locks up by a circuit including the wiper 133 and normal contact 134. The magnet 12 now becomes self-acting over a circuit which includes its own armature and the front right-hand contact of relay 131. The first upward step of the rack 9 breaks the contact at 134, the shaft 4 being now fixed, and the holding- circuit of the relay 131 is transferred to the testbrush 2, being broken as soon as that brush finds a non-earthed or idle test-contact, when the magnet 12 ceases to step the brushes farther. The magnet 41 now de-energizes, and the side switch passes into the fourth position. In this position, the relay 125' energizes, and the talking circuit is extended to the trunk found bv the brushes The side-switch wipers remain in the fourth position until the calling-subscriber hangs up his receiver, when relays 115, 123 de-energize, breaking the circuit of the relay 125<1> and making the magnet 41 self-acting through contact 42 and wiper 129, so as to step the cams 45, 46 right round to the eighth position, during which time release of the switch takes place as already described. The contact 136 is closed on restoration of the switch, and the magnet 41 is once more energized to bring the side switch into its normal or first position. This takes ground off the test-lead 124 and causes release of the call-finder. Busy signal. The last set of fixed terminals 1 hunted by the brushes 2 may be provided with any suitable means by which, if the brushes fail to find an idle trunk, the switch mechanism is caused to advance to such position that, when the calling-subscriber, who will have received a busy signal, hangs up his receiver, the switch mechanism is returned to normal as above described.