Patent GB-252934-A (GB)
Title: Automatic telephone exchange system
IPC: H04Q3/00
Filed: 1925-07-29
Abstract: 252,934. Brander, B. July 29, 1925. Automatic and semi-automatic exchange systems and selectors.-Selectors are constructed in the form of small carriages which are driven along rails by individual electric motors mounted on the carriages. Numerical selectors of this type are controlled by reverting impulses sent back to the subscriber's number-setting device which comprises sets of contacts, one set for each digit, with means for covering any portion of'each set so that the number of " active " contacts represents the required digit. The invention is described with reference to a 10,000-line system, Figs. 4 and 7, in which call-finders, groupselectors, and 3-digit final selectors are constructed as motor-driven carriages. The reverting impulses are generated by special contacts arranged in the path of the test wiper at the beginning of each group of lines, this arrangement permitting the size of groups in a group selector to be varied at will and to be unequal. Further, if desired, the group selector may have more than ten groups of lines, for example, 20 or 25, the corresponding set of contacts in the subscriber's number device being denoted by letters. The last group in the group selector may lead to an operator who is reached if a subscriber removes his receiver without setting his number device. In a modified call-finder arrangement, Fig. 8, the lines accessible to a number of no-normal callfinders are divided into groups and only those idle finders are started which happen to be resting in the group containing the calling line, whilst if there are no such finders, those in adjacent groups are started. The Specification also states that the group selectors may be arranged to function as call-finders and that the arrangement shown in Fig. 8 may be used in this case. In order to shorten the selecting time in a group or final selector of large capacity, the track may be divided into two or more sections each containing a carriage, the carriages running in synchronism and sending back impulses alternately. Construction of selectors; driving arrangements. A triangular metal frame 34 carrying the field coils 33 and armature 35 of a small three-phase motor is fitted with wheels 1, 2 which run on rails 5 and with guide rollers 3, 4 which engage a depending edge on the rail above, the drive being effected by a pinion on the armature shaft engaging teeth on the rail 5. Current is supplied to the field coils 33 and to the brushes 7 . . 9 by rollers 13 . . 18 engaging with feed conductors 19 .. 24, each roller comprising two sheet-metal halves, which embrace the conductors and are pressed together by springs 25. The armature coil has one end connected to the frame and the other to an insulated pin 40 engaged by an insulated spring 41. The brushes are carried on an arm K pivoted in a bracket 26 and controlled by a centrifugal device C so that at high speeds of the carriage the rod 31 is forced inwards and lifts the brushes clear of the contact bank. Alternatively the arm K may be controlled by a magnet which only operates under the strong current supplied when the motor is driven at a high speed. The armature of the motor may be polarized by continuous current or by the phase current, or a continuous current motor or an induction motor for phase current may be used. The centring of the brushes may be effected by polarized relays as described later or, in a continuous current motor, by means of slide rings and brushes connected to the armature. Instead of such centring means, the selector may be stopped mechanically by a magnet which inserts a pin into holes in the carrying rail. and in this case the pinion and toothed gearing may be replaced by a friction drive. The contact rails may, with small-capacity selectors, be replaced by stretched cords, and the contact rollers may be replaced by sliding springs. Subscriber's number-setting device. A contact arm 50, Fig. 4, normally resting on contact 55 is caused to make one complete revolution when a crank arm 61 is similarly rotated once. The arm 50 is mounted on a wheel 56 geared to a pinion 58 carrying a small steel magnet NS mounted between the poles of an electromagnet 59 so that when the latter is energized the gearing and arm 50 are prevented from rotation. The contact segments 51 .. 54 are provided with means by which the number of " active " contacts may be varied. For example, the segments may have a concentric movement so that they can be moved to be more or less covered by fixed insulating segments. The arm 50 during its rotation thus wipes over varying lengths of conducting contacts depending upon the four digits in the number of the wanted line. In the following description, it will be assumed that the exposed portions of the segments 51 .. 54 correspond to the number 5289. Circuit arrangements; initiation of call; callfinder, Fig. 5. The calling subscriber's receiver is not removed until after the number-setting device has been operated and need not be removed until a ring-back signal is heard on the bell. In order to initiate a call, the segments 51 . . 54 are set and the handle 61 given one revolution. Arm 50 moves over segment 51 until an uncovered conducting portion is reached when a circuit is completed for magnet 59 in series with the left-hand winding of the combined line and cut-off relay 70 and the arm 50 is stopped. Relay 70 operates only contact 73 whilst pilot relays 71, 74 close starting circuits for relays 81 in idle call-finders, three-phase current from a generator G being thus supplied to the finder motors M. When the calling line is reached, the test relay 82 energizes in series with the right hand winding of relay 70 which now operates fully. Relay 82 cuts off the three-phase supply and completes direct current circuits over one or two of the armatures 102 . . 104 of polarized relays 95 . . 97 which are included in the three-phase supply circuit. These direct-current circuits pass through corresponding field coils 91 .. 93 and serve to centre the brushes on the calling terminals. Relay 84 extends conductors 107 . . 109 to the group selector, Fig. 6, relays 70, 84 being held in series over resistance 110 and contact 113. The call-finders are of no-normal type the direction of motion being reversed when the end of the contact field is reached by a switch 80 which reverses two of the phases. Group selector, Fig. 6, When the connection is extended to the group selector, magnet 59 remains energized in series with relay 117, the upper conductor 107 being connected to the mid-point of battery CB. Relay 117 energizes relay 119 which connects high-frequency threephase current to the motor M to drive the wipers forward at a high speed. The selector comprises 10 groups each of 50 contacts and for each group passed over the test wiper 126 engages an extended earthed contact 130 which reverses the current in magnet 59 so that the arm advances half a step. When the wiper 126 leaves the contact 130 a second reversal of current advances arm 50 a second half-step. Alternatively, the current reversals may be effected by a pole changing a relay energized from the test wiper. After engaging five such earthed contacts so that the wipers are entering the sixth group, arm 50 leaves segment 51, the line circuit being thereby broken, relay 117 releases and short-circuits itself over offnormal contacts 132 whilst relay 137 energizes to connect up the lower-frequency supply which is fed to, the motor M through polarized relays 147 .. 149. When an idle outgoing trunk is found the test relay 139 energizes, cuts off the supply, and completes direct-current wiper-centring circuits as in the call-finder. These circuits include relay 116 which operates after relay 138 has opened contact 154 and extends the connection. In order to mark the seized trunk busy during the time that the wipers are running beyond and are being brought back. the resistance 163, Fig. 7, may be replaced by a relay which connects battery through a resistance 248 to the test lead. A similar arrangement may be provided in connection with resistance 110 when first and second group selectors are employed. Final selector, Fig. 7. The line conductors 160, 161 are connected respectively over sequence-switch arms 165. 166 to the mid-point of battery (represented by #) and to relay 167 which energizes, arm 50 now having advanced on to the uncovered portion of segment 52. The stepping magnet 168 of the sequence switch energizes over contact 169 and arm 170 moves the switch into its 1st position in which high-frequency current X, Y, Z is supplied to the motor M. The final selector is of 1,000-line capacity comprising 10 hundreds groups each subdivided into ten groups of ten lines. At the beginning of each hundreds group, the test wiper 179 engages a battery-connected contact 183 over which relay 185 energizes and by earthing the lower conductor 161 sends a reversal impulse back to the magnet 59. When the correct number of impulses have been sent back the movement of arm 50 from segment 52 to segment 53 momentarily interrupts relay 167 which de-energizes to cut the drive, to close a motor-braking circuit over arms 192 .. 194 and armatures 195 . . 197 and to close a circuit for driving the sequence switch into its 2nd position. When relay 167 again energizes, the switch moves to its 3rd position, the highfrequency source is again connected up and tenscontrolling impulses are sent back to the sub. station instrument, the tens group contacts 184 being however connected to earth whilst the other side of relay 185 is at this time connected to battery. When arm 50 passes from segment 53 to segment 54 the momentary de-energization of relay 167 drives the sequence switch into its 4th position, and the motor M is disconnected from the source and braked as before, the braking circuit including a differential relay 200 which is at this time energized over its left-hand wind