US1344822A - Selective switching mechanism - Google Patents

Description

R. G. RICHARDSON.

SELECTIVE SWITCHING MECHANISM.

APPLICATION FILED MAYIO, 1916.

1,344,822. Patented June 29, 1920.

3 SHEETS-SHEET l.

5 [ZZUEZZZUF W QM R. G. RICHARDSON.

SELECTIVE SWITCHING MECHANISM. APPLICATLON FILED MAYIO, 1916.

1 344;, 822. Patented June 29, 1920.

3 SHEETS-SHEET Z.

I nwnrm UNITED STATES PATENT OFFICE.

RODNEY e. RICHARDSON, or CHICAGO, ILLINOIS, ASSIGNOR 'ro AUTOMATIC ELECTRIC 7 COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

SELECTIVE SWITCHING MECHANISM.

' Application filed May 10,

To all whom it may concern Be it known that I, RODNEY G. RIGH- ARDSON, a citizen of the United States of America, and a resident of Chicago, county, of Cook, and State of Illinois, have invented certain new and useful Improvements in Selective Switching Mechanisms, of which the following is a specification.

My invention relates to selective switching mechanisms and I have elected to illustrate the same as performing the functions of a trunk selecting device in an automatic telephone system. The principles of my invention, however, are susceptible of em.- bodiment in various other forms to accomplish other objects than the ones here mentioned.

In telephone systems in general and in automatic telephone systems in particular it 7 has been found desirable and even necessary. to divide the subscribers lines into groups and to assign to each group a certain number of trunks accessible to the lines of the group when calling. To this end each individual line may be provided with a line switch or trunk selector which is operated when the associated line is calling to establish connection with an idle trunk line.

When used to perform the functions of a trunk selector of the above character my invention comprises preferably a magnet for each line, each magnet being provided with a plurality of armatures, and each armature being adapted to connect the associated line with a certain trunk line. The magnetic circuit through the magnet core and the several armatures in parallel normally includes a wide air gap for each armature. Means is provided, however, for selectively short-circuiting these air gaps in accordance with idle trunk lines or, more specifically, there is provided means for maintaining at all times a path of low reluctance through one of the armatures corresponding to an idle trunk line while the paths through the remaining armatures remain of very high reluctance.

When a call is initiated over a line, an energizing circuit is completed for theselecting magnet associated therewith, whereby the pre-selected armature is operated to connect the calling line with the corresponding trunk line. A circuit is then closed by which theoperated armature is retained in operated position, after which the original Specification of Letters Patent.

Patented June 29, 1920.

1916. Serial No. 96,496.

energizing circuit is broken. Common mechanism is then operated whereby armatures corresponding to the next idle trunk line are pre-selected in the remaining trunk selectors of the group.

The foregoing is a general description of the preferred method of carrying out my invention. Further details concerning the operation and the particular means em-' ployed will appear hereinafter, reference being had to the accompanying drawings, in

whichFigures 1 and 2 represent diagrammatically a complete circuit connection between a calling and a called substation in an automatic telephone system embodying the principles of my invention, while Fig. 3 is a diagrammatic showing'of certain mechanical details. I

Referring now to Fig. 1, the substation A may be of any suitable type or construction, such, for example, as is shown in British patent to Martin, No. 1419 of 1910. As represented herein, it comprises among other details the receiver 2, transmitter 3, switch hook 1,.ringer 5, and condenser 6. Being an automatic substation, there is also provided a pair of impulse springs 7 and 8 controlled by the impulse wheel 9 through the medium of a finger hole dial '(not shown).

Allotted to the line conductors '12 and 13 at the central exchange are the line and cut-off relays 17 and 18 whose functions are very similar to the usual functions of the same named relays in other. well known indicated by reference character C, which is provided with a plurality of'armatures, one of which is shown and indicated by reference character 21. The magnet C, and armatures 21, together with other associated parts, comprise the trunk selecting mechanism hereinbefore mentioned, and will be described more fully hereinafter.

One of the trunk lines accessible to the line of substation A through the medium of the selecting device 0 is shown as extending to the selector switch E. The selector E may be of the general type of selector switch disclosed in U. S. Letters Patent No. 815,321, granted March 13, 1906, to Keith, Erickson, and Erickson; being, however, of the particular type disclosed in British patent to the Automatic Telephone Mfg. 00., No. 2,543 of 1914. Such a selector switch, as is well known, may be operated in response to the first digit of a called number to select one of the groups into which the lines of an exchange are divided. For this purpose the selector switch E, in common with other selectors, may be given access to a number of groups of trunk lines, the trunk lines of each group extending to a group of connector switches which are adapted to complete connections to a group of individual lines.

Oneof these trunk lines is shown extending from contacts 73, 74, and 75 in the bank of selector E to the connector F (Fig. 2). The connector F may be of the general type of connector switch disclosed in U. S. Letters Patent No. 815,176, granted March 13, 1906, to Keith, Erickson, and Erickson;'being, however, of the particular type disclosed in British patent to the Automatic.

Telephone Mfg. 00., No. 2,270 of 1914. A connector switch of the foregoing type may be operated in response to the two last digits of a called number to connect with an individual line in the group to which it has access.

One of the lines accessible to the connector F is the line extending to substation A which substation may be similar to substation A, already described. The line of substation A is provided at the exchange with line and cut-off relays 17' and 18' and selecting device C, which equipment is similar to that shown in connection with the line of substation A.

Referring now to Fig. 3, I have shown at C and C two of the trunk selecting devices stripped of their contact springs for the sake of clearness, and a common mechanism D for controlling the magnetic circuits through the several armatures of the said devices. The showing in Fig. 3 is a diagrammatic representation, intended only to illustrate the principles of the invention.

The common mechanism D is known in the automatic telephone art as a master switch and may be similar to the master switch shown in British patent to Martin, No. 1,419 of 1910. The function of a master switch of this type, when used in connection with an automatic telephone system such as is described in the above mentioned British patent, is to maintain the plungers of all idle line switches in position before a contact set which is the terminal of an idle trunk line. Similarly, when used in connection with my invention, the master switch serves to maintain the vertical bar 53 in position before the armatures of the several selecting devices C G etc, which correspond to an idle trunk line.

Considering more in detail how this is accomplished, the shaft 43 carrying the rectangular offset bar 47 is pivoted at 44, 45,

and 46. In the operation of the master switch the rectangular bar 47 is given a reciprocating motion through the medium of the ratchet wheel 59 and lever 58. It will selecting device C or C are in a straight line,the circular motion of the bar 47 must necessarily be translated to a rectilinear motion in the case of the vertical bar 53. To this end two cross pieces 48 and 49 are rigidly mounted in suitable manner a short distance below and above the horizontal portions of bar 47. The cross piece 49 is provided with a slot 50 while the cross piece 48 is provided with a similar slot 50. The up per horizontal portion of bar 47 is provided with a slot 51 while the lower horizontal portion is provided with a similar slot 51. The bar 53 is carried at the intersection of these slots in a manner readily apparent. That portion of the bar 53 which passes through slots 50 and 50 is preferably made rectangular in cross sections so as to prevent turning of the bar, while that portion which passes through slots 51 and 51 is made round. It will now be clearly seen that as the rectangular bar 47 is moved back and forth by the master switch D the vertical bar 53 will travelin a straight line past the ends of the armatures 21 of the different selecting devices C C etc. The various parts are so "proportioned that when the pin in the end ofarmature 57 of locking relay 41 is in the hole 56 of locking plate 54 the bar 53 will stand in front of the right hand armatures of the several selecting devices. Also when the said pin is in hole 55 of the locking plate the bar 53 will stand in front of the left hand armatures. Evidently the intermediate holes in the locking plate mark the intermediate positions of bar 53 corresponding to the remaining armatures.

It will be seen that the bar 53 carries a projecting pole piece for each selecting device which pole piece in the case of selecting device C is indicated by reference character 22. As the bar 53 assumes its successive positions corresponding to idle trunk lines, the pole piece 22 afiords a magnetic path of relatively low reluctance through the corre sponding armatures in an obvious manner. The fixed pole piece 20 is of such height that when an armature is operated the end thereof is prevented from actually coming in contact with the movable pole piece 22, whereby the bar 53 may be freely moved to its next position.

From the foregoing it will be clear that the bar 53 with its pole pieces 22 affords a means of operating the armatures of the several selecting devices individually. Ob viously' the exact mechanical means by which this result is accomplished may be varied without departing from the principles of my invention. For example, I might arrange the armatures of each selecting device in the arc of a circle instead of parallel to each other with the ends in a straight line. In such case the bar 53 would travel in the arc of a circle also, thus simplifying to some having its positive pole grounded. The generator R supplies current for ringing purposes. Reference characters I and Q indicate, respectively, an interrupter for intermittently controlling the ringing operations, and a busy signaling machine.

Having given a general description of the apparatus I will now proceed to a more detailed description of the operation of the same. For the purposes of this explanation it will be assumed that the subscriber at substation A (Fig. 1) wishes to obtain connection with the subscriber at substation A (Fig. 2) this being the complete circuit connection previously referred to. Inasmuch as the automatic substations and switches shown herein are well known in the art, hav ing been fully described in the publications before mentioned, the operations will be described in a more or less general manner except where my invention is involved.

Referring now to Fig. 1, when the subscriber at substation A removes his receiver to initiate the call. an energizing circuit is completed for the line relay 17 over the following path: ground at G, contact springs 29 and 30, line conductor 12, substation A, line conductor 13, contact springs 27 and 28, winding of line relay 17, and back contact of the locking relay 41 (master switch D) to battery B. It should be assumed here that when the call was initiated the bar 53 and pole piece 22 were standing in front of tlie armature 21 whichcontrols connection to the trunk extending to selector E. Upon attracting its armature, the line relay 17 completes the following circuit for the operating winding 24 of the selecting device: ground at G contact springs 26 and 25, and winding 24 to battery B. Upon, the closure of the above circuit there will be a great many more lines of force set up in the armature 21 shown than in the remaining armatures, due to the position of the pole piece 22. will be operated, the remaining armatures retaining their'normalposition. By the'operation of armature 21 contact springs 31 and'33 are brought into engagement, respectively, with contact springs 32 and 34,

Accordingly, armature 21.

whereby the line conductors 12 and 13 are extended through to the double wound line relay 60 of the selector E. The upper winding of the line relay 60 is thus connected in parallel with line relay 17 in an obvious manner, the lower winding, however, being temporarily short-circuited by the connection of line conductor 12 to ground at G. Line relay 60 closes an energizing circuit from ground at G for the slow acting relay 61. Upon energizing, relay 61 completes a circuit for the holding winding of the selecting device C and the cut-off relay 18 over the following path-z ground at G contact springs 7 6 and 77, contact springs 36 and 35, holding winding 23, and winding of cut-off relay 18 to battery B. The cut-01f relay 18 isoperated upon the closure of the above circuit and disconnects the line conductors 12 and 13, respectively, from ground at G and from the line relay 17. Its energizing circuit having been broken the line relay 17 retracts its armature thereby breaking the circuit of operating winding 24, thearmature 21 being retained in operated position by the holding winding 23. The winding 23 and the cut-off winding 18 are so proportioned that winding23 will be unable to operate any of the armatures of itself but is only able to retain an operated armature in position against holding circuit extends to that contact in.

the master switch bank which corresponds to the trunk extending to selector E.- Vhen.

the relay 61 in the selector E energizes, therefore, a circuit is closed for the starting relay 40 of the master switch as follows: ground at G contact springs 76 and 77, contact spring 36, master switch bank contact 37, wiper 39, common strip 38, and winding of starting relay 40 to battery B. Upon energizing, relay 4O closes an energizing circuit for the locking relay 41, which relay, upon, attracting its armature, withdraws the locking pin from the locking plate 54 (Fig. 3), cutsthe battery B off from all the line relays 17 in the group, and closes an energizing circuit for the motor-magnet 42. The motor magnet interrupts its own circuit and therefore operates in the manner of a buzzer to rotate the ratchet wheel 59, whereby the bar 53 and the wiper 39 are advanced until the latter arrives at an ungrounded master switch bank contact corresponding to an idle trunk line. The relay 40 then deenergizes and breaks the circuit of the locking relay 41 which latter relay allows the locking pin to again engage a hole in the locking plate as soon as a magnet 65 in series.

apparatus will be ready for another call. It should be mentioned here that the line relays such as line relay 17 are quick to retract their armatures so as to insure the opening of corresponding operating circuits such as 24; before the bar 53 shall have been moved by the master switch.

Another branch of the holding circuit may be traced from contact spring 35 by way of conductor 14: to multiple private bank contacts in the group of connectors which have access to the line of substation A, thereby making the line busy to incoming calls.

The foregoing operations whereby the line conductors 12 and 13 have been extended through to the line relay 60 of the selector E have taken place in response to the removal of the receiver at substation A. The calling subscriber may now manipulate his dial in accordance with the first digit of the desired number, thereby separating momentarily the impulse springs T and 8 a number of times and interrupting each time the circuit of line relay 60 of selector of these interruptions of its circuit the line relay 60 is deenergized a corresponding number of times, sending an impulse at each decnergization from the ground at G to the slow acting relay 62 and the vertical The vertical magnet in response to these impulses, steps up the switch shaft until the wipers T 0, 71, and T2 stand opposite the horizontal level in which are located contacts which are terminals of the desired group of trunk lines. The relay being slow acting, retains its armature during the series of impulses and closes a circuit for the test relay 6%, which latter relay prepares a circuit for the rotary magnet (30 and locks itself to ground at G". At the end of the series of impulses the relay 62 deenergizes, thereby completing the aforementioned circuit of the rotary magnet 66, whereupon the wipers T0, T1, and 72 start rotating in search ct an idle trunk line. As is well known, the rotary magnet interrupts its own circuit and also the locking circuit of the test relay at every cnergization, the contacts in the latter circuit, however, being short-circuited by the test or private wiper 71 while passing over grounded busy contacts. As soon, therefore, as the test wiper 71 arrives at an ungrounded test contact the test relay (it de'e' ergizes and opens the rotary magnet circuit, thereby bringing the wipers to rest upon the terminals of an idle trunk line, assumed to in this case the contacts 73, 7 1 and 75. As a further result of the decnergization of the test relay 6%, a circuit is completed for the line switching relay 63 which relay, upon energizing, disconnects the extended line conductors 13 and 12 from the windings of As a result the line relay 60 and further extends them by way of wipers 7 0 and 72 and bank con-.

tacts 73 and 7 5 to the double wound line relay 100 of the connector F.

The line relay 100 thereupon energizes over the line circuit extending back through tery B, and the other branch extending by.

way of off-normal contact 67 and interrupter contact 81 to wire junction 82 where it joins the previously described holding circuit extending back to the selecting device (1.

The subscriber at substation A may now operate his dial in accordance with the second digit of the desired number, resulting in this case in deenergizations of the line relay 100 of the connector F. At each deenergization the line relay 100 sends-an impulsefrom ground at G to the slow acting relay 107 and the vertical magnet 10% in series, side switch wiper 115 being in its first position. The vertical magnet, in response to these impulses, steps up the shaft until the wipers 120, 121, and 122 stand opposite the horizontal level of bank contacts in which the line of substation A terminates. itelay 107, being slow acting retains its armature during the series of impulses and maintains a circuit from ground at G for the private magnet 108 and the wiper cut-oil relay 111 in parallel. At-the endof the series of impulses, the relay 107 deenergizes and breaks the circuit of the private magnet, which latter controls the side switch wipers in the usual manner to ad.

'ance them to their second position. v

The subscriber at sul station A may now operate his dial in accordance with the third and linal digit of the desired number, resuitingas before in denergizations of the line relay 100. Now, however, side switch wiper 115 being in its second position, the line relay sends impulses to the slow acting relay 107 in series with the rotary magnet 105. The rotary magnet operates in response to these impulses to rotate the wipers 120, 121, and 122 until they rest, respectively, upon bank contacts 123, 124:, and 125, these contacts forming the terminal of the line of substation A in the bank of connector F. The private magnet 10S and the wiper cut-oft relay 111 are energized during the series of impulses as before, the latter disconnecting the line wipers during rotation and the former, upon deenergizing, controlling the side switch wipers to advance them to their third position, it being assumed that the line of substation of A was idle when called.

As side switch wiper 114 comes into engagement with its third position contact point, a circuit is completed for the cut-oif relay 18 as follows: ground at G side switch wiper 1141 (in third position), wiper 121, bank contact 124, holding winding 23 of the selecting device C, and winding of cut-off relay 18 to battery B. The cut-off relay 18 upon energizing, disconnects the line conductors 12 and 13, respectively, from ground and from the line relay 17. The holding winding 23 is not sufficiently powerful to operate any of the armatures of the selecting device C, as already mentioned in the case of selecting device 0. Ground at G also extends to multiples of bank contact 124 in the banks of other connectors of the group, thereby making the line of substation A busy to other calls.

By the engagement ofside switch wipers 112 and 113 with their third position contact points the connection between the calling and called substations is completed, relay 111 being deenergized. By the engagement of side switch wiper 115 with its third position contact point, a circuit is completed for the ringing relay 109 in series with the interrupter 1, whereby ringing current is projected intermittently out over the line of substation A to operate the signal in bridge thereof.

The subscriber at substation A has now established the required connection with substation A and the bell at the latter substation is being rung to attract the attention of the called subscriber. When the called subscriber removes his receiver from the hook a circuit is completed for the double wound back bridge relay 102 in the well known manner. 'Upon attracting its armature, relay 102 closes a circuit for the ring cut-off relay 110 which relay locks itself to ground at G and also opens the circuit of the ringing relay 109, thereby stopping the ringing operation. As a further result of the energization of relay 102 the incoming line conductors are reversed as regardstheir connection with the windings of line relay 100. The latter operation is without importance in the system shown here, although it is provided in case it is desired to operate meters or similar apparatus.

The calling and called subscribers may now converse without further effort. Current for the transmitter at substation A is supplied through the windings ofthe line relay 100, while current for the transmitter -at substation A is supplied through the windings of the back bridge relay 102. The voice currents follow the path shownin the heavy lines which, it is thought, will be apparent without further amplifying the explanation.

ergizing, relay 100 breaks the circuit of slow acting relay 101. Upon the denergization of relay 101, the connector F is restored to normal in the regular manner through the medium release magnet 103, and as a further result ground is removed from the holding trunk extending back to selector E and the selecting device C. By the removal of ground from the holding trunk, relay 63 of the selector E is restored to normal in the usual manner through the medium of release magnet 69. As a further result of the removal of ground from the holding trunk, the holding winding 23 of the selecting device C and the cut-off relay 18 are deenergized, the former allowing the armature 21 to resume its normal position and thus break connection with selector E, vand the latter connecting the line relay across the line in series with the battery in preparation for another call.

The operation ofa connector switch such as the connector F when connection is attempted with a busy line is well known and has been described in the publications previously mentioned. My invention involves nothing new in connectiongwith this feature, consequently it is thought to be unnecessary to describe such operation here.

It will be seen from the foregoing that I have invented a simple and highly efficient selecting mechanism whose operation depends on the selective directing of magnetic fluX through a plurality of circuit con trolling armatures.

\Vhile I have found it convenient in explaining my invention to show a certain specific embodiment thereof, I am Well aware thatmany modifications may be made, some of which will no doubt adapt my invention for uses other than the one herein .of an energizing circuit for said magnet,

means for concentrating the magnetic flux in any one of said armatures to operate the same independent of the others, and means for retaining any operated armature in operated position after said energizing circuit is broken.

2,. In a selective switching device, a mag net provided with a plurality of circuit controlling armatures, an energizing circuit for said magnet, means for producing a magnetic circuit of relatively low reluctance through the core of said magnet and any one of said armatures, whereby upon the closure of said energizing circuit such armature may be operated independent of the others, and means for retaining any operated armature in operated position after said energizing circuit is broken.

3. In a selective switching device, a plurality of normally open contact sets, a magnet provided with a separate armature for closing each set, an energizing circuit for said magnet, means for directing the magnetic flux through one armature to the exclusion of the others, whereby one of said contact sets may be closed independent of the others, and a holding circuit completed by way of the closed contact set for retaining the associated armature.

4. In a selective switching device, a plurality of normally open contact sets, a magnet provided with a separate armature for closing each set, an energizing circuit for said magnet, means for directing the magnetic flux through any one of said armatures, whereby said contact sets may be closed selectively, and means responsive to the closure of any contact set for breaking the circuit of said magnet.

5. In a selective switching device, the combination with a plurality of circuit controlling contact members, of an elcctro-m agnet having a plurality of armatures for operating said members, an energizing circuit for said magnet, means for controlling the magnetic flux to operate said armatures selectively, and independent means for retaining any operated armature in operated position.

6. In a selective switching device, a plurality of circuits to be controlled, and magnetic means for controlling said circuits, said means comprising a plurality of magnetically operated armatures adapted to be actuated by a common magnet, mechanism for directing the lines of force produced by said magnet through the said armatures to oper' ate them selectively, and means for controlling the operation of said mechanism over any one of said circuits.

7. In a selective switching device, a .plurality of circuit controlling armatures adapted to be actuated by a common magnet, an energizing circuit for said magnet, a magnetic circuit through the core of said magnet and the several armatures in parallel, a movable element for temporarily reducing the reluctance of one of the parallel branches whereby upon the closure of said energizing circuit the magnetic flux is directed through the low reluctance branch to operate the armature included therein, and means for automatically moving said element whenever any armature is operated.

8. In a selective switching device, a plurality of circuit controlling armatures adapted to be actuated by a common magnet, an energizing circuit for said magnet, a plurality of magnetic circuits corresponding to the several armatures, each magnetic circuit including the core of said magnet, an air gap in each magnetic circuit, and automatic electromagnetically controlled mechanism for selectively short circuiting said air gaps, whereby upon successive closures of said energizing circuit said armatures may be 'operated selectively.

9. In a selective switching device, a plurality of circuit controlling armatures adapted to be actuated by a common magnet, an energizing circuit for said magnet, a magnetic circuit through the core of said magnet and the several armatures in parallel, mechanism for temporarily reducing the reluctance of one of the parallel branches whereby upon the closure of said energizing circuit the magnetic flux is directed through the low reluctance branch to operate the armature included therein, and means for then automatically operating said mechanismto reduce the reluctance of another of said branches, whereby upon the next closure of the said energizing circuit another armature may be operated.

10. In combination, a conductor, a, plu rality of other conductors, and electro-magnetic means operated by direct current for connecting said first cmiductor separately with any one of the other conductmrs, said means comprising a magnet with a plurality of armatures each adapted to connect said first conductor with a particular one of the other conductors.

11. In combination, a first conductor and a plurality of other conductors, a magnet having a plurality of armatures each adapted to connect said first conductor with a particular one of the other conductors, an energizing circuit for said magnet, and means for directively controlling the magnetic flux through the several armatures whereby upon successive closures of said circuit said armatures may be operated selectively.

12. In combination, a line, a plurality of trunk lines, and a selecting device for connecting said line to any one of said trunk lines, said device comprising a magnet having a plurality of armatures each of which is adapted to connect said line with a particular trunk line, an energizing circuit for said magnet, and controlling means for altering the magnetic circuit through the several armatures whereby they may be operated selectively.

13. In combination, a line, a plurality of trunk lines, and a selecting device for connecting said line to any one of said trunk lines, said device comprising a magnet having a plurality of armatures each of which is adapted to connect said line with a particular trunk line, means for closing a magnetic circuit of relatively low reluctance through an armature corresponding to an idle trunk line, and an energizing circuit for said magnet whereby the said armature may be operated.

14. In combination, a line, a plurality of trunk lines, and a selecting device for connecting said line to any one of said trunk lines, said device comprising a magnet havinga plurality of armatures each of which is adapted to connect said line with a parti cular trunk line, means for closing a mag netic circuit of relatively low reluctance through an armature corresponding to an idle trunk line, an energizing circuit for said magnet whereby the said armature may be operated, and means for then shifting the magnetic circuit to include another armature corresponding to the next idle trunk.

15. In combination, a line, a plurality of trunk lines, and a selecting device for connecting said line to any one of said trunk lines, said device comprising a magnet hav ing a plurality of armatures each of which is adapted to connect said line with a particular trunk line, an energizing circuit for said magnet, and means for directively controlling the magnetic flux through the sev eral armatures in accordance with idle trunk lines, whereby the said first line may be selectively connected with such trunk lines.

16. In combination, a line, a second line, electro-magnetic means for connecting said lines, said means comprising a magnet and a normally inoperative armature, an energizing circuit for said magnet, and means for decreasing the reluctance of the mag netic circuit through said magnet core and armature whereby upon the closure of said energizing circuit the said armature may be operated, and. a second circuit forsaid magnet for retaining said armature in operated position.

17. In combination, a line, a second line, a line and a cut-oil relay associated with said first line, an electro-magnetic device and an op rating circuit therefor controlled by said line relay for connecting the two lines, and a second circuit independent ofthe first and including a second winding of said device completed when such connection is established for maintaining said device in operated position and for operating said cut-off relay to disconnect said line relay.

18. In combination, a line, a secondline,

line and cut-off relays for said first line, a

device comprising a magnet with two windings, an armature, and contacts controlled thereby for connecting said lines, an energizing circuit for one winding of said magnet controlled by said line relay for operating said armature, and a second circuit in eluding the other magnet winding and the said cut ofi relay completed thereupon for maintaining said armature in operated position and for operating said cut-off relay to disconnect the said line relay.

19. In a telephone system, a line, a plurality of trunk lines, and a selecting device for connecting said line to an idle trunk line, said device comprising a magnet having a plurality of armatures, each armature adapted to connect the saidline with a par-, v

ticular trunk line, an energizing circuit for said magnet controlled over said line, and means controlled by the idle or busy condition of said trunk lines for directing the magnetic flux set up upon the closure of said circuit through a particular one of said armatures to operate the same.

20. In a telephone system, a plurality of lines, a plurality of trunk lines, and a se lecting device for each line for extending connection to an idle trunk line, each selecting device comprising a magnet having a plurality of armatures each adapted to connect the associated line with a particular trunk line, an energizing circuit for each magnet controlled over the associated line, and means controlled by the idle or busy condition of said trunk lines for directing the magnetic flux set up upon the closure of any energizing circuit through a particular one of the associated armatures to operate the same.

21. In a telephone system, a line, a plurality of trunk lines, a selecting device for connecting said line with an idle trunk line, said device comprising a magnet and a plurality of armatures, each armature adapted to connect said line with a particular trunk line, an energizing circuit for said magnet, and means for reducing the reluctance of the magnetic circuit through any one of the armatures whereby upon the closure of said energizing circuit such armature may be operated without operating the others.

22. In a telephone system, a line, a plurality of trunk lines, a selecting device for connecting said line with an idle trunk line, said device comprising a magnet and a plurality of armatures, each armature adapted to connect said line with a particular trunk line, an energizing circuit forsaid magnet, means for reducing the reluctance of the magnetic circuit through one of the arinatures whereby upon the closure of said energizing circuit such armature may be operated, said means movable relative to said armatures, and a master switch for maintaining the armature corresponding to an idle trunk line.

23. In a telephone system, a plurality of lines, a plurality of trunk lines, and an electro-magnetic device associated with each line for extending it into connection with any one of said trunk lines, each device comprising a magnet having a plurality of parallel magnetic circuits, each circuit including a movable trunk connecting ele ment, a high reluctance gap in each of said parallel circuits, and a common mechanism for lowering the reluctance of one of the parallel circuits in each device in accordance with an idle trunk line.

24. In combination, a line, a second line,

means for connecting said lines comprising a magnet and armature, a plurality of magnetic circuits including a common section, each circuit including also a section individual thereto, an energizing circuit for creating a magnetic flux in one of said circuits to operate said armature, and a second energizing circuit for creating a magnetic flux in the other circuit to retain said armature in operated position.

25. In a telephone system, a plurality of lines, a'lesser plurality of trunk lines, and an individual trunk selector for each of said first lines comprising a switching relay with a plurality of contact sets and a corresponding plurality of electromagnetically controlled actuating members, together with means whereby when a call is initiated over one of said lines the switching relay of the trunk selector associated therewith is actuated to connect the line with an idle trunk line.

26. In a selective switching device, the combination with an electromagnet having a plurality of circuit controlling armatures, of an energizing circuit for said magnet, and automatic electromagnetically operated mechanism for concentrating the magnetic flux in any one of said armatures to operate the same independent of the others.

27. In a selective switching device, the combination with an electromagnet having a plurality of circuit controlling armatures, of an energizing circuit for said magnet, a movable pole piece for concentrating the magnetic flux in any one of said armatures to operate the same independent of the others, means for moving said pole piece to successive positions adjacent the several armatures, and means for preventing the said pole piece from coming to rest in intermediate positions.

28. In a selective switching device a magnet provided with a plurality of circuit controlling armatures, an energizing circuit for said magnet, and a movable pole piece for producing a magnetic circuit of relatively low reluctance through the core of said said means in association with magnet and one of said armatures, whereby upon the closure of said energizing circuit such armatures may be operated independent of the others, means for breaking said circuit without releasing the operated armature, and means for automatically moving said pole piece into position before another armature.

29. In a selective switching device, a plurality of normally open contact sets, a magnet provided with a separate armature for closing each set, an energizing circuit for said magnet, a movable pole piece common to said armatures for directing the magnetic flux through one armature to the eX- clusion of the others, whereby one of said contact sets may be closed independent of the others, and means operated automatically upon the closure of any contact set for moving said pole piece.

30. In a selective switching device, a 13111- rality of normally open contact sets, a magnet provided with a separate armature for closing each set, an energizing circuit for said magnet, a movable pole piece for directing the magnetic flux through any one of said armatures, whereby said contact sets may be closed selectively, and an automatic selectively movable switching device for controlling the movement of said pole piece.

31. In a selective switching device, the combination with a plurality of circuit controlling contact members, of an electromagnet having a plurality of armatures for operating said members, an energizing circuit for said magnet, means for operating said armatures selectively, and a separate holding circuit for said magnet for retaining any operated armature in operated position.

32. In a selective switching device, the combination with a plurality of circuit controlling contact members, of an electromagnet having a plurality of armatures for operating said members, an energizing circuit for said magnet, and an automatically operated selecting mechanism for controlling the magnetic fiuX to operate said armatures selectively.

33. In a selective switching device, the combination with a plurality of circuit controlling contact members, of an electromag net having two or more armatures for operating said members, an energizing circuit for said magnet, a movable pole piece com mon to said armatures for controlling the magnetic flux in one of said armatures to operate the same independent of any other one of said armatures, and a relay for clos ing said energizing circuit;

34. In a selective switching device, a plurality of circuits to be controlled, magnetic means for controlling said circuits, said means comprising a plurality of magnetically operated elements adapted to be actuated by a common magnet, a movable pole piece for directing the lines of force produced by said magnet through the said armatures to operate them selectively, a holding circuit for retaining any operated element, and means actuated over any controlled circuit for closing said holding circuit.

35. In a selective switching device, a plurality of circuit controlling armatures adapted to be actuated by a common magnet, an energizing circuit for said magnet, a magnetic circuit through the core of said magnet and the several armatures in parallel, a movable pole piece for temporarily reducing the reluctance of one of the parallel branches whereby upon the closure of said energizing circuit the magnetic flux is directed through the low reluctance branch to operate the armature included therein, and an automatically operated preselecting mechanism for then causing the reluctance of another of said branches to be reduced, whereby upon the next closure of the said energizing circuit another armature may be operated.

36. In combination, a line, a plurality of trunk lines, and a selecting device for con necting said line to any one of said trunk lines, said device comprising a magnet having a plurality of armatures each of which is adapted to connect said line with a particular trunk line, an energizing circuit for said magnet, and a movable pole piece for directively controlling the magnetic fillX,

through the several armatures in accordance with idle trunk lines, whereby the said first line may be selectively connected with such trunk lines.

37. In a telephone system, a line, a plurality of trunk lines, and a selecting device for connecting said line to an idle trunk line, said device comprising a magnet having a plurality of armatures, each armature adapted to connect the said line with a particular trunk line, an energizing circuit for said magnet controlled over said line, and a preselecting mechanism controlled by the idle or busy condition of said trunk lines for directing the magnetic flux set up upon the closure of said circuit through a particular one of said armatures to operate the same.

88. In a telephone system, a plurality of lines, a plurality of trunk lines, and a select ing device for each line for extending con nection to an idle trunk line, each selecting device comprising a magnet having a plurality of armatures each adapted to connect the associated line with a particular trunk line, an energizing circuit for each magnet controlled over the associated line, and a preselecting mechanism controlled by the idle or busy condition of said trunk lines for directing the magnetic flux set up upon the closure of any energizing circuit through a particular one of the associated armatures to operate the same.

Signed by me at Chicago, Cook county, State of Illinois, this 20th day of April, 1916.

RODNEY G. RICHARDSON.

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