US2222131A - Automatic switching system - Google Patents

Description

AUTOMATIC SWITCHING SYSTEM Filed July 5, 195s IN VENTORZ ATTORNEYS. A

Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE AUTQMATIC SWITCHING SYSTEM Application July 5, 1938, Serial No. 217,335 32 claims. (c1. 17a- 16) The present invention relates in general to automatic switching systems, and more in particular to such switching systems as include a socalled dial or calling device at a control station,

a a line extending to a distant switching station or exchange, and one or more auto switches at the latter point which are selectively controlled over the line by the calling device at the control station.

id .lin example of such a switching system is an automatic telephone system, in which each subscribers line is equipped with a. calling device at the s ubscribers telephone, and in which automatic switches are provided at the exchange for it the purpose of establishing connections under subscriber control. The invention is not, however, limited to use in an automatictelephone system, but may be used in a variety of situationsin fact, in practically any situation where it is desired to effect selective action under re-v mote control.

The invention is mainly characterized by the novel principle which is employed for exercis. ing control over the selecting operation. In systems which are in common use, such as automatic telephone systems, control is exercised by the transmission of a variable series of impulses ci equal length which are generated by the cal1` ing device. The number of impulses in a series depends on the digit in accordance with which the dial of the calling device is operated. In my improved system, however, I prefer td use a single impulse of variable length or duration. IThe total impulse period, corresponding to the 35 maximum capacity of the calling device, is divided into time units and each impulse transmitted lasts for a variable number of time units depending on the digit dialled. For instance, ii the digit l is called, the transmitted impulse is of minimum length and has a duration of a single time unit. If the digit 2 is called, then the impulse produced lasts for two time units, while if the digit is called, iiveftime units are involved. a5 As in other switching systems, the .so-called impulses may actually be lelectrical impulses transmitted over an open circuit, or they may be interruptions of a closed circuit. The latter arrangement has a wider range of usefulness and is employed in the illustrative embodiment of the invention shown herein. It will be appreciated then that in such a closed circuit system operat ing in accordance with my invention. the circuit will be opened or interrupted, a single time for cach operation of the calling device and that the itil length of each interruption will correspond to a number of time units equal to the digit dialledt There are other features forming part of the invention which, however, will be pointed out in the course of the ensuing explanation, reference 5 being had to the accompanying drawing, ln which-- i Fig. l is a front view oi' the dial or calling device g,

Fig. 2 is a rear-view of the same;

Fig. 3 is a side view ofthe movable finger lever forming part of the calling device;

Fig. 4 is a section through a portion of a calling device governor, and shows an alternative arrangement for generating a variable length i5 impulse; while Fig. 5 is a diagrammatic circuit drawing of a complete switching system constructed in accordance with the invention.

Referring to Figs. 1, 2, and 3 of the drawing, 20 the calling device there shown will rst be described. In certain respects this calling device is similar to the Well known impulse transmitting calling devices which are in common use in automatic telephone systems throughout the country. An example of such a calling device is the one shown in the patent to Obergfell, No. 1,642,822, granted September 20, 1927. The construction of these calling devices has varied somewhat from time to time, but they all include a base or frame plate and a reciprocating finger hole dial rotatably mounted thereon, together with. impulse sending mechanism which is actuated upon the return movement of the dial. The dial is supported on a central shaft which has bearings in the frame plate and which is con-v nected to the frame through a helical coil spring in which tension is stored when the dial is rotated. The impulse sending mechanism comprises a main gear wheel freely rotatable about im viously mentioned. When the dial is released, 50

the ratchet mechanism immediately engages the main gearwheel so that the gear wheel is driven on the return movement of the dial. The main ,gear wheel drives the pinion shaft and rotates the cam to generate impulses. The governor is also driven at the same time and insures that the dial will return to normal at a constant speed.

In the calling device illustrated in Figs. 1; 2, and il, the parts above described are all utilized in substantially their usual form, with the exception of the impulse cam and the impulse transmitting springs, which are omitted. In lieu thereof there is provided a special impulse transmitting unit which is mounted on the frame plate of the calling device and which accomplishes the purpose of Aopening the line circuit once for each actuation of the calling device dial, the duration of the opening depending on the digit in accordance with which the dial is operated.

The finger hole dial is seen clearly in Fig. 1. where it is indicated at 2. The usual finger stop is shown at 3. In Fig. 2. which shows the rear view of the calling device, the base or frame plate on which the dial and other parts are sup-` ported is indicated at 6. This figure also shows the nger stop 3 and the manner in which it is attached to the frame plate. The remainder of the apparatus, including the helical power spring and the gear and pinion wheels, is not shown in the drawing. A small portion of the governor mechanism may, however, be seen, and includes the cup 35' which is mounted on the upturned member 31 of the frame by means of the bearing screw 38. The complete governor mechanism is illustrated in the Obergfell patent hereinbefore referred to.

The impulse sending mechanism provided in accordance with the invention is mounted on a flat plate I6 which is generally circular in shape and which is supported on the frame plate 6 of the calling device in spaced relation thereto, by means of three hollow studs I'I and three machine screws I8. 'Ihe distance between the plate I6 and the frame plate 6 may be approximately three-fourths of an inch, or just suicient to provide room for the power spring and the governor mechanism. The shaft 23 on which the dial is mounted extends up through a central opening in the plate I6, and a short distance above the plate is r'educed in diameter to form a shoulder. This reduced portion of the shaft is threaded to receive the nut l5. It will be understood, of course, that the shaft 23 is modified from standard construction to the extent indicated.

The impulse springs are indicated by the reference characters I9 and 2d and are supported on an upturned portion 24 of the plate I6 by suitable screws and insulators, as indicated in the drawing. These impulse springs are of curved shape, and the longer spring 20 has airixed to it a small block of insulating material 2 I The line circuit is connected to the impulse springs at the stationary ends thereof beyond the insulators.

The finger lever 1 lies flat against the upper surface of the plate I6 and is freely rotatable on the shaft 23. At one end the finger lever has a short upturned portion 8 which extends into the plane of the insulator 2i. At the other end the finger lever has an offset curved portion 4 which lies just underneath the dial 2 of the calling device. The shape of the complete nger lever can best be seen in Fig. 3. From this gure and from Figs. 1 and 2 it will be seen that the main part of the finger lever 1 is connected to the offset curved portion 4 by means of a section 1', extending perpendicular to both of the foregoing portions. This section 'I' lies in a slot 5 which is cut in the frame plate 6. The slot is large enough to permit free movement of the nnger lever to the position in .which it is shown in dotted lines in Fig. 2.

Just above the finger lever l there is provided a control member 9, which is also freely pivoted on the shaft 23, and which extends out radially therefrom with its end abutting against the insulating/,member 2| mounted on the spring 20. The function of the control member 8 is to maintain the impulse springs I9 and 20 in closed position. In explanation of this, it may be stated that the spring 20 is tensioned away from spring I9, so that it tends to open the line whenever permitted to do so. When the control member 9 is in the position in which it is shown in Fig. 2, however, the spring 20 is held in engagement with the spring I8.

Just above the control member 9 there is mounted on the shaft the toothed disk I4. This disk rests on the shoulder with which the shaft is provided and is securely held in place by means of the nut I5. 'I'he disk I4 therefore rotates with the shaft 23. A pin 22 is rigidly secured to the disk I4 and extends beneath it into the plane of the control member 9.

Pivoted to the finger lever 1 is a pawl ID, which is adapted to engage the teeth in disk I4. This pawl ls provided with a tail piece normally in engagement with a stud I2 mounted on plate I6, and is also provided with a spring I3 which is shaped as shown in the drawing. The spring I3 may be spot-welded to the pawl.

vThe parts of the calling device just described can best be understood from an explanation of the operation in calling av digit. It will be assumed for this purpose that the dial 2 is actuated in accordance with the digit I. The dial is rotated in clockwise direction, as shown in Fig. 1, and since the disk I4 is fixed to the shaft on which the dial is mounted, this disk will be rotated 1n a counter clockwise direction, as seen in Figs-2. At the rst movement of the dial, therefore, the pin 22 will pass out of engagement with the control member 9, the latter remaining in the position in which it is shown in the drawing. As the finger of the operator approaches the nger stop 3, it will engage the curved portion 4 of the movable finger lever l, carrying it along with the dial during the further movement thereof. The finger lever is therefore rotated about its pivot on the shaft 23, and when the dial becomes fully set, with the finger of the operator in engagement with the linger stop 3, the curved portion il of the iinger lever will be in the position in which it is shown in dotted lines in Fig. 2. During this movement of the finger lever, the upturned end' portion 8 moves in a counter clockwise direction and passes into engagement with the insulating member 2| on impulse spring 20. Shortly before movement of the finger lever is completed, the upturned portion 8 engages the control member 9 and rotates it out of engagement with the insulation 2i. With lthe finger lever fully operated, the upturned portion 8 thereof will be in approximately the same position as that normally occupied by the control member 9, the latter having been rotated far enough so that it is entirely clear of the insulation 2 I It should be pointed out also that, at 70 the first movement of the finger lever, the tail piece II of the pawl I0 will pass out of engagement with the stud I2, while an instant later the oifset curved portion of spring I3 will come into engagement with this stud and will force the dial.

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pawl into engagement with one of the teeth of the disk I4.

'Ihe operation of the dial as described in the loregoing tensions the power spring in known manner, and when the dial is released by removal of the finger ol' the operator, the dial is rotated back to its normal posi-tion. When the dial returns to normal, the disk I4 secured to shaft 23 rotates in a clockwise direction, and since the pdwl I is now in engagement with one of the teeth on the disk, the finger lever 4 is returned to its normal position along with the As the finger lever reaches the position in which it is shown in Fig. 2, the tail piece of pawl I0 engages the stud I2 which rotates the pawl sufliciently to disengage it from the tooth on disk I4. The linger lever therefore stops in the 'position where it appears in Fig. 2, while the return movement of the dial continues unimpeded.

The restoration of the linger lever has the efiect ol opening the line circuit including contact springs I9 and 20, as will be appreciated irom the fact that the control member 9 Awas previously rotated out of engagement with the insulator 2|. Under its normal tension, therei'ore, the impulse spring 20 takes up a position in which it is out of `engagement with contact spring I9, and the circuit is opened as stated. This condition continues until, as the dial approaches its normal position, the pin 22 lined to the disk I4 engages the control member il and returns it to the position in which lt appears in Fig. 2. In moving-to this position the control member engages the sloping end of the insulator 2| and restores the impulse spring 20 to its normal position.

in the operation of the dial as just described, the return movement of the dial includes a period in which the nger lever 1 is being restored and in which the impulse spring is held in engagement with the impulse spring I9 by the linger lever, and a period during which the impulse springs are separated, which lasts from the time at which 4the linger lever is restored until the control member 9 is restored just as the dial reaches normal position. 'I'his latter period is equal in length to one time unit. If the calling device is operated in accordance with the digit 2, the same restoration period for the nnger lever is involved, but the subsequent period during which the impulse springs are separated is just twice as long as in the case where titi the digit 1 is dialed. That is, the period during which the impulse springs are separated comprises two time units. Similarly, if the dial is operated in accordance with the digit 3, the irnpulse springs will be separated for a period equal to three time units, and so on.

The governor of the calling device is accurately adjusted to run at a predetermined speed, which l bears a dente relation to the speed of the I out of engagement with the insulator 2I.

The modillcation shown in Fig. 4 will now be brieliy described. In this modification an ordinary calling device of standard construction is used except that it should be of the general type of calling device disclosed on pages 33, 34, and 35 of the book entitled Automatic Telephony, by Smith and Campbell, first edition, published by McGraw-Hill Book Company in 1914. This calling device differs essentially from the calling device disclosed in the Oberglell patent by the angular distance between the first finger hole of the dial and the linger stop. In the calling device disclosed in the Obergfell patent this distance is sullicient so that, if the digit 1 is called, the impulse sending mechanism is rotated lar enough on the return movement of the dial to transmit two impulses, the last impulse being canceled by a special contact mechanism associated with the impulse springs. In the dial disclosed by Smith and Campbell, however, the angular distance between the first linger hole of the dial and the linger stop is such that if the digit 1 is called, only a single impulse will be transmitted.

In accordance with the invention, a calling device ol the type disclosed by Smith and Campbell is modified in order to produce a single variable length impulse at each dial actuation by omitting the impulse springs and by changing the governor as shown in Fig. 4. The modification of the governor which is necessary will now be briey explained.

Referring to Fig-` 4, the reference character 31 indicates the upturned ear on the frame plate of the calling device on which the governor cup 35 is mounted by means of the bearing screw 3B. Inside the governor cup 35 is securely iix'ed a disk 36 of insulating material which is provided with a hub portion 39. This latter is surrounded by a metal band 40. The conductor 4l passes through a hole drilled through the base of the cup 35 and through the hub 39 and has one end secured to the metal band 40 by soldering. The reference character 3U indicates a portion of the governor shaft, the end of which has a thrust bearing in the bearing screw 33. The end of this bearing screw is drilled out slightly larger than the end of the shaft, and there is a small steel ball inserted against which the end of the shalt bears when it is rotated. The governor also includes the springs 3l and 32, the extremities of which are equipped with weights 33 and 34, respectively. The springs 3i and 32 are normally tensioned toward the shaft 30 so that the weights 33 and 34 press against the metal band 43 at al1 times when the governor is stationary.

One of the line conductors incoming to the calling device is connected to the frame at some suitable point, while the other line conductor is connected to the conductor 4 I Suitable binding posts or terminals (not shown) may be provided for this purpose if desired. The circuit will then extend from one line conductor to the frame, thence to the governor through the shaft bearings, and thence by way of springs 3| and 32, weights 33 and 34, the metal band 40, and conductor 4I to the other line conductor.

Describing the operation of this modification brieliy, and assuming that 'the calling device is actuated in accordance with the digit 1, when the dial is pulled around by the operator tension is storedrin the power spring in the usual way, but the other parts, including the governor, remain stationary. When the dial is released, the ratchet mechanism connecting the dial with the main gear wheel becomes effective and the governor mechanism starts to rotate. Instantly the governor springs 3| and 32 separate due to centrifugal force acting on the weights 33 and 34, and these weights leave the metal band 40 and engage the inner wall of the cup 35, whereby they operate to regulate the speed at which the dial returns to normal. The separation of weights 39 and 34 from the band 40 breaks the line circuit, and it remains open until the dial has been restored, at which time the governor ceases its rotation and the springs 3| and 32 again resume their normal position. The result is therefore that the line circuit is opened for a predetermined length of time equal to one time unit. If

the dial is operated in accordance with the digit 2, the distance which the dial has to travel in restoring to normal is Just twice as far and the governor is operated for an interval which is exactly twice asflong, and the line circuit is held open for a period of two time units. Thus, it

will be appreciated that by making use of the governor mechanism modified as shown and described, the line circuit can be opened at each operation of the dial for a variable period which contains a number of time units corresponding to the digit dialed.

The modification shown in Fig. 4 is considerably less expensive to manufacture than the arrangement shown in Figs. 1, 2, and 3, but it is open to the possible objection that it is not foolproof in the sense that the latter arrangement is. That is, a false operation may occur through careless operation of the dial. This objection, however, may be obviated by instructing the persons using the calling device as to the necessity for fully setting the dial each time; and at any rate it is not serious under ordinary conditions for the standard calling devices in common use are subject to the same possibility of false operation.

Attention may now be directed to the complete switching system which is disclosed in Fig. 5. This system includes a control station which is indicated by the dotted rectangle enclosing the calling device. This control station may also be provided with a switch 50 of any suitable type for closing the line circuit.

From the control station a line comprising conductors 5| and 52 extends to the switching station and there terminates in an automatic switch. This switch comprises a number of relays and certain mechanical parts which will now be explained briefly.

The relays 53-51, inclusive, may be ordinary telephone type relays of well known construction. Relays 55 and 51 are what is known as slow acting relays; that is, each of these relays is provided with a copper slug which makes it slow to deenergize. The function of these relays will be explained fully during the description of. the circuit operation.

The mechanical portion of the switch includes a contact disk 14, a wiper or brush shaft |06, a continuously operating power shaft |00, and a clutch comprising disks 98 and |05 and stop and go clutch magnets indicated, respectively, by the reference characters S and G.

The contact disk 14 may be made of Bakelite or other suitable insulating material and carries 11 sets of contacts such as the set comprising contacts 52, 03, and04. Each of these contacts may be a curved strip of metal which lies flat on the face of the disk and which is provided with ears at the ends which pass through perforations in the disk and are bent or riveted over on the back side. Inside the circular row of contact sets there are three continuous conducting rings 15, 16, and 11, which are secured to the face of the disk in any suitable manner; preferably by means of countersunk rivets which pass through the disk and afford means for establishing conductive connection to the rings on the rear. The wiper shaft |08 is supported on suitable bearings (not shown) in axial alignment with the disk 14, and supports at the left a wiper holder 8|, to which the wipers 10, 19, are securely fixed. 'I'his wiper holder may be constructed in any suitable manner, but, as indicated in the drawing, it comprises a molded cylinder in one end of which the wipers are embedded. The other end is drilled out to iit the shaft |06 to which it is adjustably secured by means of a set screw. The wipers extend out farther from the holder 8| on one side than on the other, so that at one end the wipers are in engagement with the contact rings, while at the other end the wipers are adapted to engage the contact sets.

There is also mounted on the wiper shaft |06 a cam 10, which is provided for the purpose of controlling the off- normal springs 61, 68, and 89. In order to simplify the drawing, these oilnormal springs are shown in association with the relays, and the cam 10 is also included in the relay circuit. This simplifies the drawing somewhat, and the departure from the actual con` struction will not cause any confusion.

As previously stated, the shaft |00 is a power shaft and is driven at a predetermined constant speed by any suitable means such as a synchronous motor. connecting the wiper shaft |08 to the power shaft |00, the clutch mechanism previously reerred to is provided. At the left hand end oi the power shaft |00 is fixed a hub |0| to which is secured the disk |05, which is made of non` magnetic material. The go magnet G comprises a core portion |02 which lies behind the shaft |00, and two offset pole pieces |03 and |00. These pole pieces are connected to the core |02 by short sections perpendicular to the plane of the drawing, so that the pole pieces lie in the plane of the shaft |00. The ends of the pole pieces |03 and |04 approach closely to the disk |05 but are not in contact with it at any time. On the wiper shaft |05 is slidably mounted a hub 91 to which is secured the disk 90, constructed of magnetic material such as soft iron. While the hub 91 is slidable on the shaft |06, it is not rotatable on the shaft but drives the latter through the medium of a. pin |01, which lies in a slot cut in the hub 91. This slot provides for a limited longitudinal movement of the hub on the shaft. The stop magnet is of'a construction similar to the go magnet G and comprises a core 94 and two offset pole pieces 95 and 96. In normal position the disk 98 rests against these pole pieces. The operation of the switch will be fully explained in the course of the description of the operation in effecting a desired selection.

y Each of the contact sets with which the contact disk 14 is provided constitutes a terminal of a line adapted for selection through the medium of the switch. One of these lines is shown in the drawing as leading from the set of Vcontacts 82,

For the purpose of temporarilyv Ases iii

iii

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titi

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`contact ci armature 85.

B5, and 84, and comprises the conductors 85, 88, 8l. The two former conductors terminate in the line relay 88, which controls relays 89 and 50, while conductor 8'! leads to contacts on the two latter relays. Relay 88 is equipped with contacts i for closing a circuit over conductors 92 and 93. The relays 88, 85, 90 are representative of any suitable or desired line circuit.

The operation of the system shown in Fig. 5 will now be explained. For this purpose it will be assumed that it is desired to select the line comprising conductors 85, 86, 8l which terminates in the tenth set of contacts comprising contacts di, 85, 85. llt will be understood, therefore, that in order to select this line the calling device must be operated in accordance with the digit 0. lin addition to operating the dial, the switch '55 must iirst be closed.

When the switch 50 is closed, a circuit ls cornpleted over the line conductors 5I and 5i for the Vline relay 5t in an obvious manner. The line relay 5t accordingly energizes and at the iront contact ci armature 82 completes a circuit ior` the slow acting relay 55, which energizes and prepares a circuit for the go magnet G at the iront The line relay 5a on energizing also completes a circuit for the stop magnet S at armature 88, this circuit including also the relay 55. Relay 55 and stop magnet S Vare accordingly energized, but these operations are oi no importance at the moment.

When the dial i is operated in accordance with the digit i), the line circuit is interrupted in the manner previously explained, for a period equal to ten time units. At the beginning oi this interruption in the line circuit the line relay 54 deenergizes and breaks the circuit ci relay 55, which, however, is slightly slow to fall back and remains in energized position long enough for a circuit to be established through the bach contact of armature 52 and the front contact oi armature 55 to the go magnet G. On energization oi the go magnet, the disk 98 is instantly attracted and moves to the right into engagement with the disk H55, thus coupling the wiper shaft iiiii to the power shaft |00. The wipers "it, i9, til now start to rotate in `a clockwise direction and at a speed which carries them past one set oi contacts per time unit. Relay 55 falls back after an instant and breaks the circuit of the go magnet G at armature E5, but before this taires place a new circuit is established through the oit-normal springs 58 and 69. When the wiper shaft starts to rotate the cam 'lll rotates with it, with the result that off-normal spring 5l is allowed to separate from spring 69, and the latter comes into engagement with spring 68. The circuit ior the go magnet then extends from ground by way of armatures 60 and 82, off-normal springs 5,8 andV 68, and the winding of relay 5l to the go magnet. Relay 51 is energized, but its operation at this time performs no function.

At the end of the interruption in the line vcir-- cuit, ten time units vwill have elapsed and the wipers i8, 19, will have been rotated into'engagement with the tenth set of contacts, or the contact set comprising contacts 82. 83, 84 in which the desired line is terminated. The closure of the line circuit at the end of the interruption brings about the re-energization of the line relay 54, which breaks the circuit of the go magnet G at armature 62 and closes the circuit ofthe stop magnet S at armature 53. 'I'he latter circuit extends from ground by way of armatures 6| and 63, and winding of relay 56, to the stop magnet,

and is instantly effective to move the disk 98 out of engagement with the disk |05 and to bring it against the pole pieces 95 and 98, with the result that the movement of the wiper shaft |86 is stopped with the wipers in engagement with the tenth set of contacts.

Relay 58 is energized in the circuit oi the stop magnet S and now closes a circuit for the switching relay. 53, which extends from ground at the normally closed contact of relay 58 by Way oi conductor 81, contact t2, wiper 'I8 in engagement therewith, contact ring l5, conductor lli, armature E4 and its front contact, and the winding of relay 53 to battery. Relay 5t is energized over this circuit, and at armatures 5t and 5i brealrs the circuit of relay 55 and also the original circuit for the stop magnet. At the :iront Contact of armature 8|, however, an alternative circuit is y established for relay 55 and ior the stop magnet which includes the resistance r. This resistance permits enough current to flow over the circuit to maintain relay 56 energized. in addition to the foregoing operations, relay 55 disconnects the incoming line comprising conductors 5i and 5i from the winding of relay 5i, which deenergizes, and extends it to the line conductors 'i2 and i3. A circuit is accordingly established over the line and over the conductors i2 and i3. contact rings 1B and 1T, wipers 'i9 and til, contacts t5, and di, and conductors 85 and 85, to the windings oi relay 88. Relay 88 is accordingly energized and completes a circuit ior the slow acting relay 55, which energizes also and closes a circuit for slow acting relay Bil. Relay 85, on energizing, places ground on conductor 8l before the original ground connection through which the circuit was first'established is opened at the armature ci relay 50. Relay 88 also closes a circuit over conductors 92 and 53 at armature di.

The desired selection has now been effected,

' used for any desired purpose, depending on the situation in. which the selecting system is used. The details of the operations which are performed after the connection is established, however, i'orm no part of the invention and are not shown herein.

In order to release the connection. the switch is opened, causing relay di to deenergize. Relay 88, on deenergizing, opens the circuit ci' relay t9, which deenergizes after an instant and opens the circuit oi relay When relay 55 deenergizes, it alsodisconnects ground from conductor 81, and this conductor is therefore ungrounded for an instant until relay 50 deenergizes. Relay 53 accordingly deenergizes and opens the circuit including relay 56 and the stop magnet S, whereupon relay 58 deenergizes and opens the circuit of relay 53 at armature 64. Relay 53 therefore cannot again energize when ground is applied to conductor 81 by the deenergizatlon of relay 90.

On deenergizing, relay 53 also closes a circuit for the go magnet G, the circuit including ofi'- normal springs 69 and 88 and the relay 5T. The go magnet G is accordingly energized to couple the wiper shaft |06 to the power shaft |00 and the wipers are rotated toward their normal position. Relay 51 is energized in series with the go magnet and prepares a circuit for the stop magnet S at armature 86. When the Wipers reach their normal position, where they are shown in the drawing, the cam 10 engages olf-normal spring 61 and said spring is shifted into engagement with spring 69, the latter spring being distid engaged from spring at the same time. The circuit of the go magnet G is broken by this restoration of the off-normal springs, and a circuit is established for the stop magnet' S. the circuit including off-normal springs 00 and 01 and amature 66 of relay 51. The circuit of-'relay 01 has already been broken, but the relay is slow acting and remains in operated position long enough to provide for a momentary energization of the stop magnet as described, which prevents overrun of the wipers due to inertia of the moving parts, and insures that the wipers will bc brought to rest in normal position. The switch is now fully restored and ready for use in a second selecting operation, which may be the same as the iirst or in accordance with any other digit.

Attention may now be directed to certain features of the system which it was not convenient to discuss in detail in the course of the general 'explanation It has already been stated that the speed of the power shaft |00 bears a predetermined relation to the speed of the calling device dial and is such that the switch wipers are moved past one set of contacts per time unit. 'Ihe length of a time' unit therefore determines the speed of shaft |00`in revolutions per minute. While the speed may be varied between fairly wide limits, I propose for convenience to so regulate the governor of the calling device ythat the dial illustrated in Fig. 1 will return to normal in exactly one second, when the dial is operated in accordance with the digit 0. Of this period of one second, one-eleventh is consumed in restoring the ilnger lever and the remainder, tenelevenths, is divided into ten time units corresponding to the ten digits. Each time unit, therefore, is equal to one-eleventh of a second.

Now, since there are eleven sets oi' contacts on the contact disk 10, and since the switch wipers o are required to pass over one set of contacts per time unit, the wipers require eleven time units to make a complete rotation, or exactly one second. The shaft |00 therefore rotates at a speed of 60 R. P. M.

45 As mentioned hereinbefore, the shaft |00 may be driven by a synchronous motor which can be operated from any current source of constant frequency. An ordinary 60-cycle commercial power supply will be found to have the necessary con- 50 stant frequency characteristic, as is demonstrated by the fact that commercial power is universally used in recent years for' the operation of clocks. The driving of the power shaft |00 at the proper speed therefore presents no difliculty.

55 The maintenance of the dial speed at the proper value is a somewhat more diilicult problem, but the satisfactory operation of the system is insured nevertheless by an accurate regulation of the governor, and by the contact arrangement at 60 the switch which permits variations in dial speed within certain limits without resulting in any error in selection. As regards the governor, it is well known that very accurate regulation is possible, and that when once properly adjusted the 55 speed will be maintained constant for long periods. As to the switch, it will be appreciated that if the dial runs too fast, the switch wipers will lag and will fail to reach the exact centers of the contacts, while if the dial is too slow, the

70 wipers will advance farther than they should. This result is due to the decrease and increase in the time units caused by fast and slow dials, re-

spectively. The error thus introduced is cumulay tive and becomes increasingly serious as the nu- '15 merical value of the digits dialed increases. That is, the total error is greatest when the digit 0 is dialed. The danger of a false selection which is thus introduced is eliminated (assuming that the dial speed is regulated within prescribed limits) by restricting the number of contact sets to eleven and by distributing the contact sets over a complete circle. With this arrangement each contact set has an angular length of about and the wipers may lag or lead by about 15 without causing a wrong selection. It is entirely feasible, therefore, to provide for the full number of ten digits as required in thevdecimal system. Of course, if less than ten digits are employed, the number of contact sets is correspondingly reduced, and as they will still be distributed over a complete circle, the factor of safety will be increased.

The invention having been described, that which is considered to be new and for which it is desired to secure the protection of Letters Patent will be pointed out in the appended claims.

What I claim is:

1. In an automatic switching system, a calling device having -a reciprocating dial, a line circuit including said calling device, means included in said calling device for altering said line circuit at the beginning of the return movement of the dial and for maintaining the altered condition until the return movement is completed, an automatic switch, and means controlled over said line circuit for continuously advancing said switch during the time said line circuit is in altered condition at a speed bearing a predetermined relation to the speed of the return movement of said dial.

2. In an automatic switching system, a calling device, an automatic switch, a rotating power shaft, a line circuit extending between said calling device and switch, means included in said calling device for continuously holding the line circuit open fora variable period of time depending on the digit dialed, and means responsive to the opening of the line and reclosing of the same for coupling and uncoupling said switch to and from said shaft.

3. In an automatic switching system, a calling device, an automatic power driven switch, a line circuit extending between said calling device and switch, means included in said calling device for opening the line circuit for a period comprising a number of time units equal to the digit dialed, means controlled over said line circuit responsive to the opening thereof for continuously operating said switch throughout the period during which the line circuit is open and for stopping it when the circuit is closed, and wipers in said 'switch having different selective positions equal in number to the capacity of said calling device in time units.

4. In an automatic switching system, a calling device, an automatic switch, a line circuit extending from said calling device to said switch, means included in said calling device for continuously opening the line circuit for a period comprising a variable number of time units, wipers and Contact sets included in said switch, a shaft associated with said switch and rotating at a speed which will drive the said wipers past one contact set per time unit, and means controlled over said line circuit responsive to opening thereof at said calling device for coupling the switch wipers to said shaft.

5. In an automatic switching system, a calling device provided with a reciprocating dial, means in said calling device for producing a single impulse at each actuation o! the dial, said impulse having a variable length dependingon the digit dialed, an automatic switch, and means including a line circuit extending between said calling device and switch for advancing the switch a distance proportionate to the length of said impulse.'

6. In an automatic switching system, a calling device provided with a reciprocating dial, normally closed impulse springs, means for opening said springs during each return movementl oi said dial and for closing them only at the end oi such return movement, whereby said springs are opened for a variable time interval depending on the digit dialed, means including a movable finger lever for insuring a complete setting operation of the dial in order to effect opening of said springs upon the return movement, an automatic switch, and means including a line circuit extending between said calling device and switch for advancing said switch throughout the time said impulse springs are open.

'7. in an automatic switching system, a calling device provided with a reciprocating dial, an au- -tomatic switch, a line circuit connecting said calling device and switch, a governor for regulating the speed at which said dial returns to normal aiter each .setting thereof, means included in the governor mechanism for opening said line circuit throughout the return movement of the dial, and means responsive throughout the time the line is open for advancing said switch.

d. In an automatic switching system, a calling device provided with a reciprocating dial, an automatic switch, a line circuit connecting said calling' device and switch, a centrifugal device operated only during the return movement of the dial and effective to open said line circuit when the return movement attains a certain speed and to close the line circuit again when the return movement is completed, and means responsive throughout the time the line is open for advanc ing said switch.

il. In an automatic switching system, an automatic switch including a wiper shaftfa constantly rotating shaft, an electromagnetic clutch for connecting said shafts, a line incoming to said switch, control means for closing said line and for opening it for a predetermined variable time interval, said line remaining open throughout said interval, means including fast and slow relays energized responsive to closing the line and denergized responsivexto opening thereof to close a circuit for said clutch, and an alternative cir` cuit for the clutch closed upon the initial movement .or said wiper shaft and opened responsive to the reenergization of the said fast relay at the end of said time interval.

1U. In an automatic switching system, an automatic switch including a wiper shaft, a constantly rotating shaft, a go magnet for coupling said shafts, a stop magnet for stopping said wiper shaft, an incoming line, means for placing a control condition on said line and for maintaining it throughout a variable timeinterval, and means responsive to said control condition and effective at the beginning of the said time interval to energize said go magnet and at the end of the time interval to energize said stop magnet.

1i. In an automatic switching system, an automatic switch, a line circuit over which said switch is controlled, means for, continuously driving said switch to a variable set position responsive to a single change in the line circuit of variable duration, means also controlled over the line circuit for continuously driving said switch to normal position, and electromagnet means for positively stopping the switch in any set, position and also in its home position to prevent oiverrun when the driving means ceases to funct on.

12. In an automatic switching system, a calling device having a reciprocating dial, 'means for regulating the return movement of the' dial `to a predetermined speed, a line circuit, means in said calling device for interrupting said line circuit during the return movement of the dial and for maintaining it in interrupted condition for a variable time interval which depends on the digit dialed and upon the speedv to which the return movement is regulated. an automatic switch, wipers in said/,switch and means for advancing them while the line circuit is interrupted, and contact sets in said switch distributed in a complete circle, the contacts in each set being ex- I tended as far as possible around the circle in both directions from the points at which they are normally engaged by said wipers so as to allow for a maximum variation in the speed of the dial without causing said wipers to be positioned on the wrong set of contacts.

13. In an automatic switching system, a rst line, a plurality of other lines, means responsive to the closing of said first line and the subsen quent single opening thereof for a predetermined variable time interval for selecting one of said other lines, and means for connecting the first line to the selected other line responsive to the completion of the selection.

14. In an automatic switching system, a first line, a plurality of other lines, means responsive to the closing of said first line and the subsequent single opening thereof for a predetermined variable time interval for selecting one of said other lines, means for connecting the first line to the selected' other line responsive to the completion of the selection, and a relay energized over the said rst line and the selected other line for controlling the maintenance of said connection.

15. In an automatic switching system, a first line, a plurality of other lines, switching mechanism responsive to closing of said first line and subsequent single opening thereof for a variable predetermined time interval for selecting one of said other lines, a control relay for said mechanism normally connected to said line, and means effective upon the completion of the said selection for disconnecting said iirst line from said relay and for connecting it to the selected other line.

16. In an automatic switching system, a first line, a plurality of other lines, switching mechanism for selecting any one of said other lines and for connecting said first line thereto, and control means for said mechanism responsive to the establishment of current flow over the first line and the subsequent interruption of said current flow for a variable predetermined time interval during which the interrupted condition is maintained.

17. In an automatic switching system, a rst line, a plurality of other lines, a device i'or selecting `one of said other lines, means for supplying current to said first line, means responsive to a single predetermined variable length interruption of the current flow over said first line for selectively operating said device, and means for conductively connecting said first line to the line selected -by said device. i

18. In an automatic switching system, a first line, a plurality of other lines. a device for selecting one of said other lines, means for supplying c rrent to said first line, means responsive to a ingle predetermined variable length interruption of the current iiow over said first line for selectively operating said device, means for conductlvely connecting said first line to the line selected by said device, means for supplying current to said iirst line over the selecting line connected therewith, and means for disconnecting said iirst current supplying means.

19. In an automatic switching system, a rst line, means for supplying current to said line, a switch means for continuously driving said switch responsive to a single variable length interruption of the current fiow over said line, a plurality of other lines, means for connecting said rst line with one of said other lines, the line connected to depending on the length of said interruption and the consequent advance of said switch, means including a relay energized over said iirst line and deenergized by interruption of current ilow therein for controlling said switch, and a second relay energized over said iirst line and the other line connected thereto for controlling the maintenance of the connection.

20. In an automatic switching system, a line extending to a switching station, said line being normally open at the distant end, means at said distant end for closing and opening said line at will, a device also at said distant end .effective while the line is closed by said iirst means for opening it and holding it open at another point for a variable predetermined time interval, switching mechanism at said station prepared for operation responsive to closure of said line, means responsive to opening of said line for selectively operating said mechanism in accordance with the duration of said time interval, a connection established between said line and one of a plurality -of other lines responsive to operation of said mechanism, and means for maintaining said connection until said first line is opened by said iirst means.

21. In an automatic switching system, a twoconductor metallic line circuit extending from a control station to a switching station and there terminating in an automatic switch, means at said control station for closing the line and for thereafter opening it and holding it open for a variable predetermined time, a line relay included in said switch and energized over the line when the same is closed, means prepared for operation responsive to energization of said line relay and rendered eiective upon deenergization thereof to advance the switch a variable distance depending on the duration of the open period, a line selected by operation of said switch, and means for connecting the conductors of the said' rst line, respectively, with the conductors of the selected line through the contacts of said switch.

22. In an automatic switching system, an automatic switch provided with a line relay and having access to called lines, a calling line terminating in said switch, a control station on the calling line, means at said station for closing an energizing circuit for said linel relay over the calling line, means at the control station for opening said circuit and holding it open for a variable predetermined time, thereby deenergizing said line relay while the circuit is open, means in. said switch controlled by said line relay for advancing the switch while the line relay is deenergized to select a called line, the line selected depending on the length of time the line relay is deenergized, and

means in said switch for disconnecting the calling line from said line relay and for connecting the calling line to the selected called line. 23. In an automatic switching system, an automatic. switch provided with a line relay and having access to called lines, a calling line terminating in said switch, a control station on the calling line, means at said station for closing an energizing circuit for said line relay over the calling line, means at the control station for opening said circuit and holding it open for a variable predetermined time, thereby deenergizing said line relay while the circuit is open, means in said switch controlled by said line relay for advancing the switch while the line relay is deenergized to select a, called line, the line selected depending on the length of time the line relay is deenergized, means in said switch for disconnecting the calling line from said line relay and for connecting the calling line to the selected called line, and means controlled over the connected calling and called lines for maintaining the established connection.

24. In an automatic switching system, an automatic switch provided with a line relay and having access to called lines, a calling line terminating in said switch, a control station on the calling line, means at said station for closing an energizing circuit for said line relay over the calling line, means at the control station for lopening said circuit and holding it open for a variable predetermined time,.thereby deenergizing said line relay while the circuit is open, means in said switch controlled by said line relay for advancing the switch while the line relay is deenergized to select a called line, the line selected depending on the length of time the line relay is deenergized, means in said switch for disconnecting the calling line from said line relay and for connecting the calling line to the selected called line, a relay reenerof the called line, means in the switch responsive to opening of the line for advancing the switch to select the called line, and means in said switch lfor connecting said lines.

26. In an automatic telephone system, an automatic switch having a bank in which terminate a plurality of called lines, a calling line, means on the calling line for closing the line and for opening it and maintaining the open condition for a variable length of time depending on the position of a desired called line in the bank of said switch, means in said switch responsive to the closing and subsequent opening of the calling line for advancing the switch to select the de sired called line and connect the calling line thereto, and means responsive to reclosure of the line upon expiration of said variable time for maintaining said switch in operated position.

27. In an lautoiinatic telephone system, a calling line extending from a subscribers station to an exchange, a switch at the exchange having access to a plurality of called lines, a calling device-at the said station for effecting a change in the calling line circuit and for maintaining it for a variable predetermined time interval, means controlled over said line for continuously advancing said switch during the period in which the line circuit is in changed condition to cause the said station for effecting a change in the calling line circuit and for maintaining it for a variable predetermined time interval, means controlled over said line for continuously advancing said switch during the period in which the line circuit is in changed condition to cause said switch to select a desired called line, means efiective upon the completion of the operation of said switch for extending the calling line into connection with the called line, and means dependent upon restoration of the calling line circuit at the end of said time interval for maintaining the connection between the calling and called line.

29. In an automatic telephone system, a calling line extending to a switching station, means for closing saidline, switching mechanism at the said station prepared for operation responsive to closure of said line, means for opening said line and for maintaining it in open condition for a vari' ablefpredetermined time interval. means responsive to the opening of said line for selectively operating said switching mechanism in accordance with the length of said time interval, another line selected and connected with the calling line responsive to the operation of said mechanism, and means controlled over the calling line for maintaining said connection.

30. In a automatic switching system, a line, an automatic switch, means responsive to the establishment of current flow over said line and the subsequent interruption thereof for starting said switch, and means for continuing the advance of said switch for a variable time depending on the duration of the interruption.

31. In an automatic switching system, a line, an automatic switch, means responsive to the establishment of current flow over said'line and the subsequent interruption thereof for starting said switch, means for continuing the advance of said switch for a variable time depending on the duration of the interruption, and means for stopping the switch if the interruption is longer than a predetermined time interval.

32. In an automatic switching system, a line, an automatic switch, means responsive to the establishment of current flow over said line and the subsequent interruption thereof for starting said switch, means for continuing the advance of said switch for a variable time depending on the duration of the interruption, means for stopping the switch at the end of the interruption,

and means for restoring the switch responsive to a second interruption of current flow over said line. l BERNARD D. WILLIS.

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