US1439427A - Automatic telephone exchange - Google Patents

Description

Dec. 19., 1922.

F- A. LUNDQUIST. AUTOMATIC TELEPHONE EXCHANGE.

ORIGINAL FILED JULYIQ. 1917- 3 SHEETS-SHEET l.

w IIIIIIII-IIII- 5? Dec. 19, 1922. 1,439,427 F. A. LUNDQUIST. AUTOMATIC TELEPHONE EXCHANGE.

ORIGINAL FILED JULYl9..I9I7- 3 SHEETS-SHEE1 2.

Dec. .19, 1922.

F. A. LUNDQUIST.

AUTOMATIC TELEPHONE EXCHANGE.

'ommm. man JULYI9. 1917.

3 SHEETS-SHEE'I 3- Patented Dec. 19, 1922. p

il fitlifi rarest fii l ltlth CI-IICAGO ILZ LINOIS, ASSIGNOR, BY MNSNE ASSIGNMENTS, TO 'HENBY S. CONRAD, TRUgTEE. I I

AUTOMATIC TELEPHGNE EXCHANGE.

Application fi1ed'j'u1y 19, 191", Serial No. 181,5536. Renewed May '13, 1922. :Serial No. 560,819.

1 0. all whom it may concern:

1 Be it known that I, FRANK A. LUNn Uisr, a citizen of the United states of America, and a resident of the city of Chicago, county of Cook, and State of Illinois, have invented certain new and useful Improvements in Automatic Telephone Exchanges, of which the following is a specification.

My invention relates to automatic telephone exchanges and has for its object improvements which will reduce the amount of mechanism involved inthe construction and operation of such exchanges.

The improvements in mechanical construc- 5 tion are restricted to the line switches which are individual for the different subscribers, I but these changes in construction bring about changes in the organization as a whole. lhe apparatus at each subscrihers local station is assumed to be the same as that in ordinary use and, as a, consequence, the draw ings show only the wires leading to such stations. Similarly, the selectors and connectors in the exchange are assun'ied to be the same as those now in use, and to be operated in the same way. Consequently, the drawings do not go beyond showing the line switches making connection to the bank contacts which lead to first selectors. In thesaid drawings l Fig. 1., which is largely diagrammatic, represents, at the left, the first or uppermost line switchof a sub-group of one hundred such switches and, at the right, the first line 5 switch of a second subgroup of one hundred such switches.

sand subscribers who have common connec tlons to fifty (more or less) trunks leading to a corresponding number of first selectors- Consequently, Fig. 1 represents simply two line switches at the upper left hand corner oi a group of one thousand such switches,

*ig. 2 is an enlarged plan of part of the 4 apparatus shown in Fig; l, but with the contact makers advanced. from normal position and moved into contact with a pair of terniinals leading to a first selector.

' Fig. 3 5-9 shown in 2. I I 4 is a side elevation of the same parts for the three uppermost switch s in one subgroup, together with the shaft upon which they are mounted and the means for jcperat ing the shaft.

There is intended to be ten such sub-groups to form a group of one thou is a side elevation of the parts inent after arm 19 is stopped.

Fig. 5 isa plan, partly broken away, of i the apparatus for moving and holding the shaft of a subgroup. c i

Fig. 6 is-a plan of one of the springs used to return the contact makers to normal position when released. v

Fig. 'Tis anvenlarged face view of a tape having flexible conductors insulatingly imhedded therein. a

Fig. 8 is a transverse section still more .enlarged, of the tape shownin Fig; 7.

9 is an enlarged detail of one of the contact springs together with a partof the disk to which it is connected.- v

In said drawings, 10 is ashatt on which are secured one hundred disks 11 each having thereon two or more contact springs 12- which also serve as abutmentsv as will be hereinafter. described.- These parts are so arranged that the springs 12 are lOSi'LtQCldlrectly, above each other ina vertical plane 0n the lower end of each shaft 10 area'atch'e-t wheels 13 and 14 controlled bydogs l5 and 16. A magnet 18 operates upon armature lever 17 to, advance the ratchet wheels and consequently'shatt 10 and disks '11 step 'by step as impulsesflow thru m'agnetlg Loosely mounted upon each shaft l0 adjacent to each disk 11 is an arm 19 which iS connected to a spring ZO which acts to normally hold the arm' against a fixed stop 21 (Fig, 1) secured to any convenient part of the stationary frame work. Secured to the hub 22, which connectsspring and partlywrapped around saidhuh, is a tape 23. A sprin 24: connects the 'ovtherend of the tape witha rod 25, which rodihas its outer end connected to a piston 26 in theairv cylinder 2?.

therefrom, is a body ofinsulation 30 in which are embeddedcontact strips 28 and 29 These strips extend longitudinally parallel with the shatt l0 and have-projections extending 20 to arm 19,

advanced by the m g being held. from following it by inward toward said shafts at points on a level with certain contact springs carried on the arms 19. The strips 23 and 29 are arranged in pairs, and the length 01 the inward projections on strips 28 are shorter than those on strips 29. The spacing of these strips around the shaft corresponds to the spacing of the ratchet wheels 13 and 1e, that is the angular distance from "one strip 28 to the next strip 28 is equal to the angular distance from one tooth to the next on either of wheels'lo and 14. These strips form contact terminals, and each strip is provided with an outward projection 31 to which a wire may be connected. In Fig. 1 the contact terminals 28 and29 are represented arbitrarily, as connected to a circle 32.

Pivoted on each arm 19 is a bell-crank lever 33, one end of which is connected to the tape 23, and the other end. of which carries two insulated contact springs 34 and 35 adapted to engage projections on strips 28 and 29, respectively. Also pivoted on each arm 19 is a catch lever 36 which is normally held into engagement with the bell-crank lever 33 by a spring 37 (Fig. 2.) lVhen in this position the springs 34 and 35 are held in a retracted position so that they will not engage eontacts'28 and 29 when the arm 19 is turned on shaft 10. Insulatingly mounted on lever 36 is aYcontact spring 38 adapted to engageja contact spring 12011 the adjacent disk 11,.

and when such engagement occurs, the lever 36 is released from lever 33 so that a pull on tape 23 will turn lever 33 on its pivot tothrust springs 34' and 35 outward into engagement with contacts 28 and 29 as shown in Fig. 2. p

The insulation 30, which contains the fifty pairs of contact strips 28 29, extends one-half or one-third of the ,way around the apparatus on shaft 10,and the disks 11 haveeither two or three springs 12 equally spaced. By this arrangement the shaft 10 does not'need to be released to return to a normal position but can be continuously 1.8, The arm 19, however, returns to normal. position and, in being advanced bythe action air over the piston 26, strikes one or, another of these stopping springs 12. hen one of these springs is in a position corresponding to" the first pair of strips the arm 19 moves only a. very short distance from its normalposition before it engages the stopspring' As will be GXPlnlilGil l'iei.einafter, this engagement with a stop spring 12 closes a circuit for themagnet 18 to move the disk 11 and consequently move the stop spring away from the arm 19 said arm gagement between springs;34-35 and strips 2829. Another arm.f19'bei ng advanced by its piston 26 engages its corresponding stop of compressed spring at the new position and this in turn completes a CUCllli} for the magnet 18 to again advance the stop springs. lit the time when the stop'spring is advanced beproper so that a contact 38 in passing over it toward the left will depress the free end without making electrical contact with the disk 11. i

The tape 23 (Figs?' and S) has imbedded therein certain flexible insulated conductors. The tape with these'conductors in it may be likened to the ordinary telephone cord. The conductors within the tape are connected at one end to the springs 34, 35 and 38, and at the other end to certain other conductors to be hereinafter described.

A shaft 10 has thereon one hundred disks 11' and one hundred corresponding and as soeiated arms 19, each disk with itsassociated arms being special for a particular subscriber. @Iie such shaftwith connected parts forms a sub-group of one llllIlC red line switches for one hundred subscribers, and ten such shafts with their associated parts forms a complete group of one thousand line switches for, one thousand subscribers. Each body of insulation 30 (represented by line 32 in Figs. 1 and 5 has in it (more or less) pairs of contactstrips 28 and 29, and each contact strip has one hundred inward projections for engagement by the contact springs 34 or The projections'on strips 28 and 29 thus furnish one thousandpairs of terminals for each one of fiftytrunk lines leading to fifty first selectors.

It is known that ten per cent of trunking is ordinarily su'liicient when thesub-I scribers are placed in groups of one hun- 'dred. it also kimwn that a less perceir tage oi trunk 1g is suliiciei'lt :when the groups are larger than one hundred subscribers, but,heretofore there has been considerable difliculty and complication involved in making these larger groups. The present coust-ructim': intros {his tact into consideration and devises :ippz-uatiis by which the sul'n-scribcrs can be placed iii groups of one thousand. in such groups, five per cent of trunki n, .1' is subshinftihlly as eflioient ten per cent of trunking in groups oionehundred. Hence. the system is described as having fifty trunks common for agroup of one thousand subscribers.

Parts of the mechanism have already insane? been described. Other parts need .no particular ClQSCI'IPtlOH as their structure and operation w ll be evident in the description of the operationof the exchange when a call is made. vAmong these other parts is a system of piping and air valves which control asupply o-f-compressed airfor operating the pistons 26 in cylinders 27. There is one such piston and cylinder with-air ,control-. ling devices for each line switch.

The first line switch 1) has lines A and B leading' to a subscribersstation, another line switch (No has similar lines A and B leading to another subscribers station, and so on. -yEach pair, of lines A-B, i- --B, etc, is connected at the subscribers station to an ordinary :callingtdevice which need not be described as its structure and operationare well known. v

Assuming that va subscriber is operating; the line switch E0. 1, .shown at the left in Fig. 1, he operates his local devices so to connectlinesvr-r and B together at the station, whereupon a currentfiows: battery Xl04lrelay 4l2 ;i local station at local station-elk relay The operation of relay 43 breaks connection between contacts 80vand 81, and the operation of relay 4&2 shifts 45 from contact 70 to contact 46. hen this last occurs a current flowsz-batteny Y -444L546-'47 magnet i8- gL0uI1 Cl-Y.

v The action of'mag'net 4E8moves bell-crank lever a9 and link ,50 to swing arm :51 and thus shift the air valves on stem 52 to the right from .the position shown. oi the valves permits compressedair to flow from a suitable source or supply thru the pipe 53 to the space hack ofthe piston 26 in cylinder 27. The consequent outward movement of the piston acts thru rod 25.

spring 24. and tape 23 to turn the attached arm 19 on shaft 10. I When the contact spring'38 strikes a contact spring- 12 on the associated disk 11, the rotary movement of arm 19;is arrested and the catch 36 is released from lever The pull on the tape 23 then acts upon "lever 83 to thrust the contact springs 3e. and outwzu d into engagem'ent with project-ions on the particular strips 28 and 29 which correspond to the position of the spring lQnt thetimo it was engaged byspring 38. p

At the time spring; 38 engages stop spring 12. a current flows: battery l -54?- hrush 55 hearing against any disk on shaft 10 I and then thru the mass :to spring 12--3S56 ii" JG 35T- magnet 18- 5%. The operation-o magnet 18 advances the sl'ia'tt LO one step of. theratehet wheel 13 and consequently moves-the disks 11 and springs 12 forward onestep. This breaks the connectionbctween l2 andBS andconsequently the'circuit for magnet 18.1 It also leaves all of the springs-12in such a position that if of one thousand lineswitches.

This shift that other arm 19 would be projected into contactwi-th the next adjacent strips 28 and spring 38 engage its associated spring: 12 so as to send another impulse thru magnet 18 to ac vance shaft and disks 11 to a of a third arm 19 will operate magnet 18 Also. this other varm 19 would have its advance the parts to a fourthposition. and 4 SO OH.

is a branch 57 running;' to magnet 18 oi the second sub-group of one hundred line switches. and thence back thru line 58 to battery-V. In thesame way thereare other branchesrunningto corresponding magnets in the other subgroups of the general group In other words. when any arm 19 in the thousand. is advanced and selects a trunk by its spring;-

38 engaging the corresponding stop '12, a

circuit is completed which advances all other stops 12 to a position corresponding to the nexttrunk i11.succession.- I

The stopping of arm 19 in the manner described doesnot however stop the movement oi piston 26 under air pressure as spring 24 isinterposed tor the purpose oi permitting-a further movement. At the beginning of the outward movement of piston 26.- the disk 59 on rod .25 permits Contact springs 78 and. '77 to close. but as the circuit in which these springs located is open at 80 by reason of relay 43 being at the time energized. this closure affects nothing at that time. On further advance. a projection 60 on rod presses ona spring 61. on link 50. At this time link is toward the right by action of i'nag net 4:8, and'the hook 64, on link 50 is in enp 'agreinent with pin on arm 51. As a consequence'the spring 61, yields without depressing link 50 so as to release arm 51.

On further outward movement of piston 26 the insulated extension of rod 25engages spring 4,0110 break itsronnection with spring 41, and immediately thereafter the disk 59 engages'and pas. und .ra hook (it? on spring actuated arm Opening sp ri n as The engagement between hook 1 lee &

projection (7'0 on spring 61 will more link -30 downward so that its hook 66 will engage hook 67 on arm 63. These parts remain in this position during the-further operation of apparatus in the process of calling a subscriber, and during conversation.

\Vhen springs 34 and 35 were projected outward into engagement with a pair of strips 2829 they made connections to a trunk line leading to a first selector. First selectors as now constructed and installed in automatic telephone exchanges have one branch of the trunk leading thereto connected thru a relayto a battery and ground. This connection establishes a circuit for relay 43 so that when the circuit for relay 42 was broken by the opening of springs 4041 there was another circuit previously established for relay 43. This other circuit is as follows: ground43A-telephone -B-68 thru tape 23 to spring selected strip 29 and trunk connected thereto-relay in first selector on end of trunk-battery ground. The relay 43 is of the type known as slow relay and will hold its armature attracted during the time when further impulses are flowing for the operation of selectors and connectors. If the next trunk is busy there will be an arm 19 with its contact spring 38 at that position. Fig. 9 shows a standing spring 38 with the disk 11 and its spring 12 in a position to be moved to the right under the spring 38. In passing under spring38, the spring 12 is deflected downward and then rises making electrical connection with 38 while rising. This electrical connection sends another impulse thru magnet 18 to advance the apparatus another step.

' As previously described, the magnet 48bit line switch No. 1 was operated from battery Y by relay 42 moving armature 45 into contact with 46. In the same way, the magnet of line switch No. 2 would be operated by the relay of that switch moving 45 to contact with 46. To make this possible, armature 45 of switch No. 1 must be against its back contact 70, which in this case is represented a mercury cup to reduce resistance. Similarly, to make it possible for magnet 48 of switch No. 3, if any later one in the entire series of one thousand switches, the armatures 45 of all intermediate switches back to battery Y must be against their back contacts. I

When subscriber No. i is calling, thclirst operation energizes relay 42 to out of? calls by all other subscribers in the thousand un til no, '1. has seized an idle selector and the n'ioreinent of his piston 26 has broken the circuit for relay at -441.. It is during this interval that all disks ll. on the one thousand are being advanced one step, and it .is inadinissable that two subscribers should be simultaneously advancing the same apparatus. As soon asarmature of No. 1 falls back connection is completed so that relay 42 of No. 2 (or any later number) may close for 4.8 of that station. When this occurs No. 2 holds the connection against No. 3. and later numbers by having his connection open at until he has seized an idle selector and opened his contact springs 40 41. Similarly, N o. 3 would hold the connections against No. 4 and later numbers, No. 4 would hold them against No. 5 and later numbers, and so on. I

When No. 2 is calling he holds the con nections against all subsequent numbers by having his contact 70 open, but he does not hold it against No. l in the same way because No. 1 is between him and battery 1.

The same result, however, is accomplished in another way. The battery Y'is made of such strength and relationship to the magnets 48 that it furnishes current eiiough to operate one of them but not two of them at the same time. Thus, if No. 2 calls first and gets current on his magnet 48 from battery Y, then if No. 1 comes in during the brief time while a selector is being selected and the contacts 40-41 of No. 2 are closed, the

closure of the circuit for 48 of No. 1 will i not cause that magnet to operate until 40- 41 of No. 2 is opened. To prevent the relay 42 of No. 1 from breaking the circuit for 48 of No. 2, that switch, and all other switches except No. 1, is provided with a shunt which 48 closes for itself until 42 of N0. 2 is deenergized. This shunt circuit is; Y7172 73 74 75764546-4748-gr0und -Y. The springs 7374 are on all line switches except No. 1.

hen the calling subscriber has finished his conversation he hangs up his receiver. The ordinary local station apparatus is so constructed that hanging up the receiver breaks the connection at the station between lines A and B. The linesA and B form part of the circuit for relay 43, and breaking the connection between them breaks the circuit for this relay. When this occurs the armature 81 falls back against thecontact whereupona circuit is completed as fol.- lows: battery Z 77 7 87 9 80:-81--82 --48 ground-Z. The action of magnet 48 moves link 50 to the right to pull catch 62 switches, more or less, which form aunit stand ata normal position.

but which, for convenience of construction, I divide intotensub-groups of one hundred each; Each subscriber has in the apparatus apair of contact makers which are individual for his use. and which, when not in'use, All of the rest of the apparatus. of the line switches, when not in motion, stand opposite the first idle trunk leadin to an idle selector. When a calling subscriber advances his contact makers they are projected into engagementvvitlijthis trunk and a'circuitisv closed which advances the rest of the apparatus'to a position opposite the next idle. trunk. By providing a plurality of stops 152 foreach subscriber I am enabled to confine. the trunk terminals to a sinall space without making it'necessary to return the general apparatus to. a normalzposition at intervals.

When a lineiremains busywtor some time and a dislrll; advances far enough for a spring contact 12 to pass under the spring 38 of the busy line, the said spring 88 touches the contact 12 and completes a -circuit tor the magnet 18 to advance the dish 11 another step. In thiscase theadvanceeach. line, a common shaft carrying all of said-line switcl'ies, a master stop for each line switch mounted on said shaft automatic means. for rotating said shaft to maintain said stops in alignment With l(lle' tlI1I1l lines, and a pneumatic device for operating each line switch to connect with the trunk preselected by its stop.

8. shaftyhaving, a stepping device secured thereto, a magnet and devices for advancing the "shaittand stopstep by step, a series of contact terminals. adjacent to the path of the stop and spaced to correspond to the step by. step movement oi? the stop, an arm pivoted upon the shaft and movable from a normal position teengagement with the stop, devices on the arm arranged to be automatically projected into engagement-With contact terminal when the stop is. engaged, and an el ctric circuit for said magnet closed by engagement with said step. m"

i. it plurality-of stopping devices v and means for moving them step by step about a central point, contact'terminals adjacent to, the. pathof the. stops and extending over a distance'equal'to the angular distance between one stop and the: next-,an movableabout the center to contactwith a stop, and means by which suchcontact .causes the arm to'..engage: and be held: byan adjacent terminal. 'i I l V A shaft hrwing a plurality. of disks secused thereon, devices for advancing the shatt step by step, a stop-.on each disk, said stopsibeing, in line Wi-theach other, contact strips arranged 3 around; said: shaft and each progectmg inward. flClJLCGHt to said d sks, an

'independently movable arm pivoted upon the shaft adprcent to the face of each dish,

devices for each'arm for moving it; from: its normal position to contact with a stop on the adjacent disk, and means by Whichsuch contact causestheniovedarni to engagethe contact strip corresponding to the. position of the stop, at the time the armwvas moved.

6'. The combination with a large number 0t; independentlymovable: contact makers and a less number of tr ink lines each having a contact terminal adjacent to thepath of each contact maker, ofmeans for moving any contact maker from its normal position ovcra space represented by terminalslfor all trunklines, means for arresting the moving. contact ."maker opposite the terminal oi the idletrunk andlfor causing a'turther movement to bring about engage-- mentbet veen thetWo, and means-for prc venting asecond contactmalrer-being simila rly moved prior to the completion ofsuch .engagement. 1 I Y '1'. Theflcombination with a l'a rge number of contact makers-each normally held at a normal position, and a less number of trunl: lines each having terminals located at varying distances it'romtthe normal posit'ion ot" each contact maker, of meansto)? movingv any contact makerfromits. normal position tov engagement with a terminal oi? an idle trunlnand means forprevent ing any other contact matter being moved from its normal position during. the inten val in which the first contact maker Was moving. 1 I

8. The combination ith a large number oi. pairs of contact makersseach normally held a normal position, and a less number oi? pairs ottrunl; terminals adjacent toxthe path of each contact maker, of independently opcrable. devices for. moving each pair contact maker from its normal position to engagement with the terminals of an idle trunk, means assoc1ated with the beginning of the operation of each or said de vices "for breaking the operating connections for the other "devices, and means asso ciated with the completion of a movement oiiqa. pairotcontactmakers for re-estab-. iishing the operating. connection-s for 'th'e said other devices. A

9. In atelephone"exchange, the combination with a large number of contact carriers, and a less. number oftrunk lines hav ing terminals adjacent to the path of each carrier, of a separate power device for moving'each carrier from its normal position to engagement of its contacts with the terminalsot an idle trunk, lines leading to subthe other power devices will be restrained from operation until the first power device has completed the movement ot'its carrier to establish connections with an idle trunk.

10. In the trunk selecting mechanism of atelephone exchange, a power device havingv a predetermined movement, a contact carrier having a variable movement by which connection is established with one of a number of trunk lines, and ayielding connection between the power deviceland the carrier by which the early stopping of the carrier doesnot limit the movement of the power device.

.11. A contact carrier, a power device for moving said-carrier from its normal position, a series of trunkterminals, a stopping device located in the, path of the carrier, means for shifting the position of the stopping device from time to time so as to maintain it opposite the terminals oi an idle trunk, and a yielding connection between the power device and the carrier.

12. A series of contact-terminals, a contact carrier, a. power device for moving the carrier over the entire series of terminals, means for stopping the carrier at an inter- .mediate point'to bring about engagement with an intermediate terminal, a yielding connection between power device and carrierso thata stoppage of the carrier does not stop the power device, and an electrical controlling device operated bv the terminal part of the movement of the power device.

- 13. A shaft having a'stopping device secured thereto, a power device and connections for advancing the shaft and stop from a position of rest, a series of contact terminals adjacent to the path of the stop, an arm pivoted upon the shaft and movable from a normalposition to engagement with the stop, devices on the .arm arranged to engage a contact terminal when the stop is engaged, and automatically operating means for starting the power device into operation when the stop is engaged by the arm.

14:. Contact makers, a flexible connection serving to move said contact makers, a magnet for controlling their movement, and

an electrical conductor embedded in said flexible connection and serving as partor the electrical circuit for said magnet.

' 1 5. The combination with a contact carrier, and a pneumatic motor for moving it "from normal position, of a stop for arresting the carrier, a. power device for moving the stop so that-it will not arrest some other carrier at the same position, and means for controlling said power device by the stoppage of the carrier.

16. In a switching mechanism, a series of stops movable from position to position, a series of arms each movable to engagement with a stop in stationary position, means by which. upon a stop being engaged by an advancing arm said arm will be arrested and the stop advanced to its next position, and means by which upon a stop overtaking an advanced arm the said stop will be deflected to pass under the arm and will then complete a connection for causing the stop to be advanced to its next position.

17. The combination with a series of contact carriers, and a corresponding series of pneumatic motors: for moving them independently from normal position, of stopping devices for arresting the carriers when so moved, power means for moving the stopping devices so that-two carriers will not be stopped at the same position, and means by which the stoppage of a moved carrier causes an operation of the power means.

18. The combination with aseries of contact carriers, and pneumatic devices for moving them independently from normal position, and automatic means controlled by the stoppage of one carrier for moving thestopping devices so that another carrier will not be arrested at the same position.

19. The combination with a large num ber of contact makers each normally held at a normal position, and aless number of trunk lines each having terminals located at vary ing distancesfrom the normal position of each contact maker, of means formoving any contact maker from its normal position to engagement with a terminal of an idle trunk, means for preventing any other contact maker being moved from its normal position during the interval in which the first contact'maker was moving, and a relay for controlling both of said means. I

'20. The combination with a large number of contact makers each normally held at a normal position, and a less number of trunk lines each having terminals located at varying distances from the normal position oi each contact maker, of means for moving any contact maker from its normal position to engagement with a terminal of an idle trunk, means for preventing any other contact maker being moved from its normal position during the interval in which the first contact maker was moving, a relay for controlling both of said means upon its initial cnergization, means for returning said contact maker to normal position, said, last means controlled by said relay upon its second energizatlon.

21. In a trunk selecting mechanism of a telephone exchange, a contact carrier having a variable movement by which connection is established with one of a number of trunk lines, power device for moving said contact carrier and having a predetermined movement, and a yielding connection between the power device and the contact carrier which permits said power device to continue its movement to its predetermined position after said contact carrier has been stopped.

22. A contact carrier, a power device for moving said carrier from its normal position by a continuous or single movement, a series of trunk terminals, a stopping device located in the path of the carrier, means for shifting the position of the stopping device from time to time by a step by step move- 'ment so as to maintain said stopping device opposite the terminals of an idle trunk, and a yielding connection between the power device and the carrier.

23. A plurality of stopping devices and means for moving them step by step, contact terminals adjacent to the path ofthe stopping devices and extending over a distance equal to the distance between one stopping device and the next, an arm movable to make contact with a stopping device, and means for causing the arm to engage and be held by an adjacent terminal.

FRANK A. LUNDQQUIST.

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