US1376893A - Telephone switching apparatus - Google Patents

Description

J. L. McQUARRIL TEL'EPHONE SWITCHING APPARATUS.

APPLICATION FILED MAYl3,,I9I8.

1,376,893. Patented M y 3, 1921.

elements, such as the contact brushes, which UNITED STTES PATENT OFFIQE.

JAMES L. MCQUABRIE, OF MONTCLAIR, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATI OF v YORK.

' Application filed May 13,

To all whom it may concern I Be it known that I, JAMEs L. MGQUARRIE, a citizen of the United States, residing at Montclair, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Telephone Switching Apparatus, of which the following is a full, clear, concise, and exact description.

This invention relates to automatic telephone exchange systems, and particularly to a novel arrangement in the construction and operation of the switching apparatus used therein for establishing conversational connections between subscribers lines.

It is the customary practice in automatic telephone systems to arrange the subscribers lines and the switches used for interconnecting the same in groups, each group and the subdivisions thereof being arbitrarily assigned a suitable numerical designation. Where all switches of a. group, whether finders, selectors or connectors, are common to the use of all lines in one or more groups of lines, it is necessary to provide as many switches to serve a group of lines as is required to handle the largest number of simultaneous calls that is expected to arise in such group. Experience shows that in systems operating under the average traffic conditions, the maximum number of calls likely to appear in a group is about ten per cent. of the number of lines in the group.

Considering the type of selective switches generally used heretofore in automatic telephone systems in which the selectively controlled movable element, as the switch shaft, has fixed thereto and movable therewith form an actual part of the conversational circuit established, it is seen that on the above assumed basis of trafiic it-'becomes necessary to employ ten switches to serve a group of one hundred lines. VVhena call is initiated, one of the switches will be-operated to its set position to extend the connection and will remain in this position until the conversation has been terminated. On the occurrence of a second call in the same group, one of the nine remaining switches is similarly operated and held in use to the exclusion of other lines during the conversational period, and hence where switches of this type are used the necessity Specification of Letters Patent.

TELETHONE SWITCHING APPARATUS.

v Patented May 31921. 1918. Serial No. 234,180. 7

of employing ten switches to give ,a certain group of one hundred lines a proper grade of 'serv1ce,'results not only from the fact that a switch must beheld to the exclusive use of the calling line during the connecting period, but also from the more important fact that the switch must be maintained busy and non-available to other lines during the entire talking period. This is true since, as above stated, the switch after having performed its primary function of selecting the desired circuit must remain out of use durmg the talking period merely because the directively controlled movable. part of the switch carries elements which are essential to the maintenance of the connection established.

In view of the foregoing, this invention 7 has as its general object, the provision of a switch which may be .directively. operated to select the proper circuit in a vdesired numerical group, effect the necessary connections with such circuit, and thereupon restore immediately to its normal position where it again becomes available to all other lines in the group. By this means the busy period of the switch is greatly reduced with the result that the number of switches needed to afford a group of lines a given grade of service may likewise be reduced.

A feature of the invention consists in a novel arrangement of the contact bank whereby a plurality of incoming circuits are arranged to have a crossing or intersect ing point with each of a plurality of outgoing circuits, together with means such as deposit members provided at each of the intersecting points, and which serve, when operated, to effect a connection between the view of a switch embodying this invention showing a portion of the contact bank, together with the switch operating mechanism; Fig. 2 is a side view of the switch, certain parts being removed to afford a clearer understanding of the operation; Fig. 3 is a bottom plan view illustratingthe releasing mechanism; Fig. 4 is. an enlarged cross-sectional detail showing the relative arrangement of some of the operating parts; Fig. 5 is an enlarged detail in perspective showing the manner of controlling the sliding bar which operates the plunger for depositing a contact making member; and Fig. 6 is an enlarged view in perspective showing one of the deposit members and the circuit contact springs which it controls.

lVhile the principle of this invention is adapted to any class of automatic telephone switch it will be considered for the purpose of the present discussion as embodied in a selector switch, the function of which is to connect incoming trunks from finders or other selectors to trunks outgoing in the proper "direction to selector or connector switches. I

Referring to the drawing, there is shown in Figs. 2, 3 and 6 themanner in which the incoming and outgoing trunk circuits are arranged in the contact bank. There are ten incoming two- conductor trunk circuits 1, 1, arranged in a plane surface, and disposed along the arcs of concentric circles. Arranged in a plane immediately below that of trunks 1, 1 is a plurality of outgoing two-conductor trunk circuits 2, 2. The trunks 2, 2each extend radially toward the common center of the arcs of trunks 1, 1, whereby each of the incoming trunks 1.1 has an intersection or a crossing point with each of the outgoing trunks 2, 2. Preferably the outgoing trunks 2, 2 comprisev a total of one hundred circuits, which may be divided into ten groups of ten trunks each, each of the successive groups consist ing of ten adjacent trunks 2, 2, and occupying a portion or sector of the contact bank. With this arrangement any one of the ten incoming trunks 1, 1 has a crossingpoint with each of the trunksof ten groups of outgoing trunks 2, 2. Each of the incoming circuits 1, 1 is provided, at the points whereit crosses the outgoing. circuits 2, 2, with spring contact members 3 and 4. Likewise the outgoing trunks 2, 2 are provided at these points of crossing with contact springs 5 and 6. The springs 3, 4, 5 and 6 are firmly secured to an insulating supporting plate 7 with their free ends extending upward into a position to cooperate with each other, as best seen in Figs. 2 and 6. Slidably mounted in plate 7 at the points of intersection are the deposit pins 8, 8. The pins 8 areprovided with cam gage the lower notch in cam 9, whereby said springs are out of contact with springs 5 and 6. When, however, pin 8 is deposited and assumes its lower position with the upper notch thereof in engagement with springs 3 and 4 said springs are flexed into contact with outer springs 5 and 6 respectively. To economize in space, the springs 5 and 6 are arranged to be en gaged by springs 3 or 4, as the case may be, at two adjacent radial positions in the bank as shown in Fig. 2. In this way the springs 5 and 6 of one set may be common to two different trunk intersecting points.

A description will next be given of the step -bystep impulse operated switching mechanism, which cooperates with the contact bank to first select a group of incoming and outgoing trunk intersecting points,then to select a single row of intersections of an idle outgoing trunk with the incoming trunks, then to select the intersection of this chosen outgoing trunk with a particular one of the incoming trunks, and lastly to deposit the pin 8 at such intersection. Rotatably mounted in the upper shelf 10 of supporting frame 29 is a gear member 11, provided at its upper end with gear teeth 12, and at its intermediate portion with an enlargement 14, around the periphery of which gear teeth 13 are arranged. Interposed between the enlargement 14 and the upper surface of shelf 10 is a ratchet wheel 15 which is journaled for rotation about member 11 as a bearing, and which also serves as a guide or stop' to limit member 11 against downward movement. threaded on the lower end of member 11 retains the same against displacement in the opposite vertical direction. Supported on the upper surface of the enlargement 14, and iournaled for rotation about gear memher 11, is a combined plunger bar carriage and gear member 17 A nut 1.8 screwed upon a threaded portion of member 11 holds carriage 17 in proper vertical 'alinement. The carriage 17 is in general of a circular shape, its largest portion being provided with peripheral teeth to form the ratchet wheel 19. Just below ratchet wheel. 19, the

carriage 17 has its diameter considerably reduced, the reduced portion so formed being provided with gear teeth 20.

The carriage 17 is also provided with a rectangular boss 21 which rises above the ratchet wheel 19, and is located to one side of the center thereof, Fig. 1. Boss 21 has extending longitudinally therethrough a rectangular slot or channel 22, in which there is slidably mounted a plunger carrying bar A nut 16" 23. A plunger 24 is mounted on the working end of bar 23, a bracket 25 serving as a guide therefor, while a coiled spring 26 acts to normally retain the plunger in the position shown. On the other end of bar 23 is cut a series of teeth 27 which constantly engage the gear teeth 12 on member 11. A coiled spring 28, one end of which is attached to bar 23, and the other end to boss 21, exerts its tension to hold the plunger bar in its normal innermost position, as seen in Figs. 1 and 2. By this arrangement when the carriage is held stationary with respect to the switch frame, and member 11 rotated about its axis, the gear teeth 12, meshing with teeth 27 cause bar 23 .to be thrust radially outward to carry plunger 24 over the deposit pins 8 in the contact bank. Also mounted on the supporting shelf 10 is a ratchet wheel 30 and a gear wheel 31 which are preferably formed integral with each other. These wheels are rotatably supported on a stud 32, and are held in position by a nut hen assembled on its bearing stud 32, the gear wheel 31 is adapted to mesh with teeth 20 on gear member 11. A clock spring 34, one end of which is fastened to ratchet wheel 30, and the other end to shelf 10, acts through gears 31 and 20 to maintain the carriage '17 and its plunger bar 23 in their normal rotary position with respect to the contact bank, as seen in Fig. 1.

Mounted at suitable locations on the shelf 10 of frame 29, as shown in Fig. 1 of the drawing, are the primary, secondary and tertiary operatin electromagnets 35, 36 and 37 respectively. 1 agnet 35 is provided with an armature 38 having a pivoted pawl 39 arranged to engage the long tooth ratchet wheel 30, which operates through gears 31 and 20 to rotate carriage 17 and plunger bar 23 by long steps in a clockwise direction as viewed from the top. Each one of these lon steps advances the plunger 24 through an arc corresponding to a numerical group of one hundred trunk intersecting points, or in otherwords, through an arc comprising ten radial rows of deposit pins 8. Magnet 36 is provided with an armature 40 having a pawl 41 which-engages the short tooth ratchet wheel 19v to rotate the plunger bar 23 by short steps in a clockwise direction. Each short stop serves to advance plunger 24 through an arc corresponding'to the distance between two consecutive radial rows of trunk intersection points. The tertiary magnet 37 is equipped with an armature 42 having a pivoted pawl which is arranged to engage and rotate the ratchet wheel 15. spring held pawl 44 is pivoted on ratchet wheel 15, and cooperates with gear teeth 13 on member 11 in such a manner that when magnet 27 steps ratchet 15 in a clockwise directicn, the pawl 44 engages teeth 13 to im- Par a'sira rot tion to the member 11.

Rotation of gear member 11 operates as above described to advance plunger 24 radially through the distance corresponding .to

two circular rows of pins 8 for each step of the magnet 37 I Coming now to a discussion of the mannor in which the plunger 24 is operated to deposit the pin '8 at a selected trunk crossing point there isseen in Fig. 5, a detailed showing of the mechanism for accomplishing this purpose. The boss 21 is provided with twolugs-45 which support a rotatable pivot pin 46. A yoke piece 47 is securely mounted on pin 46, and at its upper endis pivotally attached to the hollow guide and supporting block 48. A plunger'operating bar 49 is pivoted at one end to an arm of the bell crank lever 95. The lever 95 is pivotally secured to bar 23with theother arm thereof extending into operative relation to plunger 24. The plunger operating bar 49 is disposed parallel tobar 23, its free end being guided by and slidably supported in the hollow block 48. By this arrangement the bar 49, which is'forced to participate in the thrusting movement of bar 23, slides through the block 48 a distance correspond, ing to the number of steps taken in the'tertiary operation of the mechanism. Thebar 49 is provided with a series of notches 50, one for each circular row of pins 8. A

spring catch 51 secured to block 48 con 'member 56. A spring 57 acting between the frame and member 56 serves to hold rod 54 and lever 52 in the lowermost position, thus preventing the spring catch 51 from engaging notches 50. The bell crank member 56 also carries the armature of an electromagnet 58. which magnet when energized forces rod54 upward to permit catch 51 to engage a notch 50 in bar 49 for a purpose to be more fully explained hereinafter A release magnet 59 is provided with an armature 60which controls a pair of holding dogs 61 and 62. These dogs engage re.- spectively the ratchets 15 and 1.9 to hold the switch mechanism in its advanced position.

In order to restore to normal a deposited pin 8, and thus disconnect the two trunk circuits concerned, mechanism about to be described is arranged to be operated-step by step to pick outthe radial row of pins con taining theone desired to be restored, and

going trunk 2 with the ten incoming trunks 1, 1, and normally rests in a horizontal plane just below the lower ends of deposit pins 8. A pin 75 has its lower end pivoted to pro jection 76 on rod 7 3. and extends up through the ratchets 66 and 65 to pivotally engage the tail piece 77 of armature 78. A spring 7 9 normally holds pin 75 and rod 7 3 in the position shown, but when the magnet 80 is energized to attract armature 78, rod 73 is rotated in its supporting lugs 71 and 72.

'Rod 73 rotates the apron 74 into engagement with the particular pin 8 that is depressed and restores the same to normal.

Mounted on the under side of shelf 64 are the stepping magnets 67 and 68. Magnet 67 has an armature 69 and pawl 70 adapted to engage ratchet wheel 65 to rotate the rod 73 in a counter-clockwise direction, looking from the bottom, over the contact bank. Magnet 68 likewise has an armature 81 and a pawl 82 arran ed to engage ratchet wheel 66 to rotate rod 3 in the opposite direction. A flexible holding dog 83 exerts sufficient pressure upon ratchet 66 to hold rod 7 3 in properposition while being stepped around in either direction. Arranged on the under side of supporting shelf 64 and insulated therefrom is a circular conducting strip 84, concentrically disposed with respect to the axis of the releasing mechanism. A series of conducting segments 85 are similarly arranged along the arc of a circle in proximity to strip 84, being insulated from each other and from the supporting shelf 64. A pair of brushes 86 and 87, insulatedly mounted on ratchet wheel 65, are arranged so that the former makes engagement with the continuous strip 84, while the latter successively engages the segments 85 during rotation of the deposit pin restoring rod 73. The purpose of these circuit controlling members will be considered hereinafter.

A description of the operation of the.

group; thirdly, it must hunt automatically to n t e crossing point a t Pa t ula incoming trunk 1 on which the call appears with the selected outgoing idle trunk 2; and lastly it must then deposit the circuit connecting pin 8 associated with this crossing point. To accomplish these functions, the group selecting series of impulses is sent to primary magnet 35. Magnet 35 operates its stepping pawl 39 to advance ratchet 30 and gear 31 against the tension of spring 34. The gear 31 acting upon. gear 20 operates to rotate carriage 17 together with bar 23 and plunger 24 through an arc corresponding to a group of ten outgoing trunks 2, 2 for each impulse sent to magnet 35. It is evident that, if while carriage 17 and toothed bar 23 are thus being rotated in a clockwise direction as seen in Figs. 1 and 2, the gear member 11 remains stationary with respect to the frame of the switch, rotation of the toothed bar 23 about gear teeth 12 will cause said bar to be simultaneously thrust outwardly. This, however, is prevented by spring 28, whose tension opposes the tendency of such a thrusting motion of bar 23 sufiiciently to overcome the inertia and friction of the comparatively lightmember 13, thereby causing said member 11 to rotate and maintain its normal relation with the teeth 'on bar 23. Rotation of the gear member 11 at this time is also in a clockwise direction, so that the pawl 44 carried on ratchet 15 rides loosely over the teeth 13 on said member 11. The holding dog 62 engaging the ratchet wheel 19 serves to hold the operated parts in advanced position against the spring 34.

An operating circuit is next established for the secondary magnet 36 which engages its pawl 41 with ratchet wheel 19 to advance the'same through the distance of one tooth for each energization of said magnet. Each step of ratchet 19 carries the bar 23 and its plunger 24 through an arc corresponding to the distance between two rows of outgoing trunk intersections. This operation con- 110 tinues until the plunger 24 is positioned in radial alinement with an idle outgoing trunk 2 in the selected group, at which time the circuit of magnet 36 may be opened to render the same inactive. The holding dog 62 11 acts as in the case of the primary motion to retain the adjusted parts in their advanced position against spring 34.

A circuit may now be closed for the tertiary magnet 37, which operates through its 120 pawl 43 to step the ratchet 15 around in a clockwise direction as seen in Fig. 1. The pawl 44, therefore, engages ratchet teeth 13, whereby the gear member 11 is forced to rotate in a similar direction. Since the 125 spring 34, acting through gears 31 and 20 resists with considerable force any rotation of the carriage 17, rotation of the gear 12 consequently operates to slide the plunger ba .2 out ar y agai st the ten ion of 130 spring 28. Hence, for each energization of magnet 87, the plunger 24 is advanced along the selected trunk 2 through a distance equal to that between two adjacent deposit pins 8. As soon as the plunger 24 is stepped I thereby permits catch 51 to drop into the particular notch 50 in bar 49 that corresponds to the adjusted position of plunger 24. As the rod 54 reaches its full upward position it engages and rotates a lever 88.

Lever 88 like the lever. 47 is securely fas-- tened to pivot pin 46 so that rotation thereof by rod 54 causes a corresponding rotation of lever 47. The lever 47 by rotating carries the supporting block 48 forward slightly and since catch 51 is now engaging a notch 50, the plunger operating bar 49 is simultaneously advanced with the block 48. This movement of bar 49 relative to the bar 23 operates the bell crank lever 95 to press plunger 24 down against the selected deposit pin 8. Pin 8 thereupon causes the springs 3 and 4 to respectively engage springs 5 and 6 to complete the desired connection. The magnet 58 may now be deenergized, whereupon the rod 54 by disengaging lever 88 permits spring 26 to restore plunger 24 and plunger operating bar 49 to normal position. 1

The switch having thus performed its function, a circuit is immediately established in any suitable manner for the release magnet 59. Magnet 59 operates to withdraw both holding dogs 61 and 62. from engagement with ratchets l5 and 19 respectively. Upon the withdrawal of dog 61 the spring 28 acts to pull the toothed bar 23 back through the channel 22 to its normal radial position. The dog 62 being also removed from engagement with ratchet wheel 19, the spring 34 is at the same time operating through gears 31 and 20 to rotate carriage 17 and its associated parts back to thei normal rotary position. By such an arrangement a very simple releasing operation is made possible, it not being .I18C6Sf sary for the releasing movement to be completed in one direction before it may begin in another direction as is theusual case in directively operated switches; The switch operating mechanism is now restored to its normal position and. is again available for I setting up other connections.

; After the conversation period has expired or if for any other reason it becomes desir able to disable the established connection, the restoring mechanism operates as follows to restore the deposit pin 8 to its normal.

position. The stepping magnets 67 and 68 may be arranged to operate the restoring rod 73continuously forth and back over the contact bank, magnet 67 acting first to step the rod to its extreme forward position, and

magnet 68 thereupon acting to step it back agaln. As soon then as ltbecomes necessary to restore the operated deposit pin 8, a discriminating condition may be placed on the particular conducting segment 85 individual to the trunk circuit 2 with which the oper ated pin 8 is associated, there being a seg'-' ment 85 fo each of the one hundred outgo-. ing trunks 2. l/Vhen the brush 87 arrives on.

this identified segment 85, suitable circuit means may be operated to. open the cir cult of the magnet 67 or 68 as the case may be. At thesame time the magnet .80 is momentarily energized, and by attracting its armature 78 rotates the rod 78. The apron 74 is thereby carried into engagementwith the deposited pin 8 and the latter is restored to normal. Either the magnet 67 or 68 may now be operated to again start the contin uous movement of the restoring mechanism.

lVhile in the drawing the switch disclosed illustrates a contact bank in which two-con' ductor trunks are used, it is apparent that of inco ing circuits and a plurality of out goin circuits terminating in said contact bank, a plurality or" contact making members, each adapted to establish a connection between one of the incoming and one of the outgoing circuits, a switching mechanism arranged for a plurality of selective movemerits, means for operating said mechanism toselect one of said contact making members, and means for operating theselected contact making member.

2. Ina. switch, a contact bank, a plurality of incoming circuits and. a plurality of outgoing circuits terminating in said contact bank,'a plurality of contact-making members each adapted to establish a connection between one of saidincoming circuits and mechanism arranged for a plurality'ot'selective movements, means for operating said mechanism to select one of said comet-man ing members, means. foroperating the selected contact-making members, and means for restoring the switching mechanism to its normal position.

3. In a switch, a contact bank, a plurality of incoming circuits and a plurality of outone of said, outgoing circuits, a..switchi;ng

of incoming circuits and a plurality of outgoing circuits terminating in said contact bank, a plurality of contact-making members each adapted to establish a connection between one of said incoming circuits and one of said outgoing circuits, a switching mechanism arranged for a plurality of selective movements, means for operating said mechanism to select one of said contactmaking members, means for operating the selected contact-making member, means for restoring the switching mechanism to its normal position, and means for restoringthe selected contact-making member to its normal position.

5. In a switch, a contact bank, a plurality of incoming circuits and a plurality or" outgoing circuits appearing in said contact bank, a plurality oi' contact making members, each adapted to establish a connection between one of the incoming and one of the outgoingcircuits, a switching device, means for advancing said device in a plurality of selective movements to select any one of said contact making members, means for operating the selected contact making member, and means for releasing the switching device, to normal while said contact making member remains in its operated position.

6. In a switch, a contact tank, a plurality of incoming circuits and a plurality of outgoing circuits terminating in said contact bank, said circuits being arranged such that each incoming circuit has a crossing point with each outgoing circuit, a switching device, means for selectively operating said device in a plurality of directions to select one of said crossing points, and means for establishing a connection between the circuits at the selected crossing point.

7. In a switch, a contact bank,'a plurality of incoming circuits and a plurality of outgoing circuits terminating in said contact bank,said circuits being arranged such that each incoming circuit has a crossing point with each outgoing circuit, contact members at each of said crossing points for establishing a connection between an incoming and an outgoing circuit, a switching device, means for advancing said device to select any one of said crossing points, means for operating the contact members at the selected crossing point, and means for restoring said switching device to normal.

8. In a switch, a contact bank, two groups of trunks terminating in said contact bank, said trunks being arranged such that each trunk of one group has a-orossing point with each trunk of the other group, contact members at each crossing point for establishing connection between a trunk of one group andv a trunk of the other group, a step-bystep operated switching device, means for advancing said switching device to select any one of said contact members, means for operating said device to operate the selected contact member, means for restoring the switching device to normal, and step-by-step actuated means for restoring an operated contact member to normal position.

9. In a switch, a contact bank, a plurality of incoming trunks and a plurality of outgoing trunks terminating in said contact bank, a plurality of contact making members, each ,adapted to establish a connection between one of the incoming and one of the outgoing circuits, said members being arranged ingroups, a switching device, means for advancing said device to select a group, means for advancing said device to select a contact making member in the group, means for operating the selected contact making member, and means for restoring said switching device to normal position.

1.0. In a switch, a contact bank, a plurality of incoming trunks and a plurality of outgoing trunks terminating in said bank, a plurality of contact making members, each adapted to establish a connection between one of the incoming and one of the outgoing circuits, said members being arranged in groups and subgroups, a switching device, means for advancing said device to select a group, means for advancing said device to select a subgroup, means for advancing said device to select a contact making member in the subgroup, means for operating said. member, means for thereupon restoring the swtiching device to normal, and means for restoring an operated contact making member to its normal position.

11. In a switch, a contact bank, a pluralityof incoming trunks and a plurality short steps to select a subgroup, means for further moving said device to select a contact set in the subgroup, means for operating said set, and means for then restoring the switching device to its normal position.

12. In a switch, a contact bank, a plurality I of incoming trunks and a plurality of outgoing trunks terminating in said bank, said trunks being arranged such that each incoming trunk has a crossing point with each outgoing trunk, a contact set at each crossing point for connecting an incoming trunk to an outgoing trunk, a deposit pin for operating each contact set, a plunger, means for selectively advancing said plunger to select any one of said deposit pins, means for operating said plunger to operate the selected deposit pin, means for restoring said plunger to its normal position, and means for restoring an operated deposit pin.

18. In a switch, a contact bank comprising a plurality of sets of spring contacts, said sets of contacts being arranged in groups and subgroups, a switching device arranged to be advanced in a plurality of selective movements to select and operate a desired contact set, and means for restoring said device to normal position while maintaining the contact set operated.

14:. In a switch, a contact bank comprising aplurality of sets of spring contacts, a pin associated with each of said contact sets, a plunger, means for advancing said plunger step-by-step in a plurality of selective movements to select a set of contacts, means for operating said plunger to depress the pin associated with the selected set to close the contacts thereof, and means for restoring a depressed pin to its normal position.

15. In a switch, two groups of conductors, said conductors being arranged such that any conductor inone group may be connected to any conductor in the other group, a switching device, means for operating said device in arcuate and radial selective movements to select a desired conductor in each of said groups, means for establishing a connection between the selected conductors, and means for restoring said switching device to normal position.

16. In a switch, a contact bank comprising a plurality of sets of contact members arranged in a plurality of arcuate rows and radial rows, said contact members arranged to lock in their operated positions, a switching mechanism comprising a bar rotatable into operable relation to any of said radial rows individually and movable radially over said radial rows, an operating plunger for said contact member carried by said bar, an electromagnetic step-by-step mechanism for selectively rotating said bar and plunger into alinement with a desired radial row of contact members, a second electromagnetic step-by-step mechanism for selectively moving said bar and plunger radially into operable relation with a desired contact mem-' ber, means for moving said plunger to operate said contact member, means for restoring said plunger to normal, means for restoring said switch mechanism to its normal position upon completion of an operation, and a common restoring means for said contact members.

17. In a switching mechanism, a row of contact operating members, a bar movable longitudinally .over' said contact operating members, a plunger on said bar for operating said contact operating members individually, an operating bar for said plunger arranged parallel with said first-mentioned bar and movable therewith, means for moving said first-mentioned bar radially to position said plunger int-o operable relation with a contact operating member, means operable to move said operating bar to effect operation of said plunger, said last-mentioned means being operable when said plunger is in any of its operable positions.

18. In a switching mechanism, a plurality of rows of contact operating members, means for operating said contact operating members individually, a restoring device for said contact operating members comprising a rod, an apron on said rod, said rod movable into operable relation to any of said rows of contact, members individually, means for'moving said rod into operable re lation to a row of contact members, and means for rotating said rod to effect a movement of said apron to restore an operated contact member to normal. r

In witness whereof I hereunto subscribe my name this 8th day of May, 'A. D. 1918.

JAMES L. MGQUARRIE.

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