US2389571A

US2389571A - Switching apparatus

Info

Publication number: US2389571A
Application number: US413176A
Authority: US
Inventors: Bernard D Willis
Original assignee: Automatic Electric Laboratories Inc
Current assignee: Automatic Electric Laboratories Inc
Priority date: 1941-10-01
Filing date: 1941-10-01
Publication date: 1945-11-20
Anticipated expiration: 1962-11-20

Description

9 B. D. WILLIS 2,389,571

SWITCHING APPARATUS Filed 001;. 1, 1941 3 Sheets-Sheet 1 3O 30 A 3837 33 25 E 5 5 38 43 '3 l2 8 n 29 92a 43 INSULATION 5'" 0 24 r l3 26 :z ,4 INSULATION 35 INVENTOR. 34 BERNARD 0. WILLIS M,M,MM

ATTORNEYS Nov. 20, 1945. B. D. WILLIS SWITCHING APPARATUS Filed Oct. 1, 1941 3 Sheets-Sheet 2 OOOAWMVOOOOMU M\B N D T A L U M II I JJJJJJJJJ INSULATION INVENTOR.

BERNARD D WILLIS lom fwuA m mmxz,

ATTORNEYS Nov. 20, 1945. B. n. WILLIS SWITCHING APPARATUS Filed Oct. 1, 1941 3 Sheets-Sheet 3 m m m M ML R Em Wm m 83 m3 9% 88/ A Exam M am 3? E 36/ f. m B J f mmnwmm n 0 N8 0 0 8w 8%. y 6m 08 222B 0552 o6 I N @883 E E 8 Q:

Patented Nov. 20, 1945 SWITCHING APPARATUS Bernard D. Willis, Oak Park, Ill., assignor to Automatic Electric Laboratories, Inc., a corporation of Delaware Application October 1, 1941, Serial No. 413,176

7 Claims.

The present invention relates to switching apparatus and more particularly to improved automatic switching apparatus for automatic telephone systems of the character of that disclosed in U. S. Patent No. 2,222,131, Bernard D. Willis, granted November 19, 1940.

In a conventional automatic telephone system, the automatic switching apparatus is selectively controlled in accordance with different digits comprisingcorresponding different numbers of impulses. However, in an automatic telephone system of the character of that disclosed in the Willis patent mentioned, the automatic switching apparatus is selectively controlled in accordance with different digits in the form of a single impulse and comprising corresponding different time durations. More particularly, in automatic switching apparatus of the type mentioned, the wiper is advanced continuously with respect to the contacts in the associated contact field acces; sible thereto during the time duration of the impulse.

While an automatic telephone system utilizing automatic switching apparatus of the type mentioned is entirely satisfactory in operation, nice adjustment of the timing mechanism incorporated in the call transmitter disposed at each telephone station in the system is required in order to obtain proper control of the automatic switching apparatus from the telephone station; otherwise the wiper in the automatic switching apparatus may not be precisely centered with respect to the selected contact in the associated contact field when the selecting advancement of the wiper is arrested.

Accordingly, the principal object of the present invention is to provide in automatic switching apparatus of the type mentioned, mechanism for positively centering the wiper thereof with respect to the contact last engaged thereby in the associated contact field after the selecting advancement of the wiper has been arrested.

type mentioned including an improved and simplified circuit arrangement for selectively controlling the operation thereof.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which Figure 1 is a fragmentary front elevational view of switching mechanism embodying the present invention; Fig. 2 is a fragmentary side elevational view of the switching mechanism shown in Fig. 1; Fig. 3 is a fragmentaryplan view of a portion of the switching mechanism shown in Figs. 1 and 2; Fig. 4 is a fragmentary side elevational View of a modified form of the switching mechanism; Fig. 5 is a fragmentary' front elevational view of the switching mechanism shown in Fig. 4; and Fig. 6 illustrates diagrammatically an automatic telephone system embodying the present invention and incorporating switching mechanism of either the form shown in Figs. 1 to 3, inclusive, or the form shown in Figs. 4 and 5.

Referring now more particularly to Figs. 1 to 3, inclusive, of the drawings, there is illustrated switching mechanism Ill embodying the present invention and comprising a wiper set It and an associated contact bank I2, the contact bank l2 including an insulating structure l3 supporting a plurality of vertically spaced-apart contact sets l4 arranged in a row. Also, the mechanism 10 comprises a rotatably mounted shaft I5 having a cam l6 rigidly secured thereto, the cam l6 having the general configuration of an involute and comprising first and second laterally spacedapart cam surfaces I1 and l 8. The first cam surface I] has a plurality of spaced-apart involuted teeth [9 disposed about the periphery thereof; while the second cam surface l8 has a smooth peripheral face. The cam I6 is biased in the counterclockwise direction into a normal position, illustrated in Fig. 1, by an arrangement comprising a surrounding coil spring 2|], one end of the coil spring 20 being, secured to the shaft l5 and the other end of the coil spring 20 being secured to an externally supported pin 21. Also the mechanism H1 comprises a follower 22 which is mounted by two

brackets

23 and 24 for pivotal movement, the bracket 23 being externally supported by an arrangement comprising a screw 25 and the bracket 24 being externally supported by an arrangement comprising two screws 26. The follower 22 comprises an arm 21 which is operatively associated with the cam I6, for a purpose more fully explained hereinafter.

The wiper set I I is operatively connected to the follower 22 by an arrangement comprising an insulating bushing 28, the outer end of the wiper set II straddling the insulating structure I 3 of the associated contact bank l2 in guided relation with respect thereto and the inner end of the wiper set I I being secured to the insulating bushing 28. It is noted that the insulating bushing 28 is supported upon the follower 22 by a connection including a screw 29, which is so constructed and arranged that the follower 22 may be pivoted with respect to the supporting

brackets

23 and 24 without effecting rotation of the insulating bushing 28. A release magnet is operatively associated with the follower 22 and comprises a winding 3|, a core 32 and an armature 33, the armature 33 being slidably supported on the outer end of the follower 22. More particularly, the armature 33 comprises a cylindrical body portion v3 4 surrounding the outer end of the follower 22 and carries an inwardly directed key 35 disposed in a longitudinally extending slot 36 formed in the follower 22, as clearly shown in Fig. 3. This connection between the armature 33 and the follower 22 permit the follower 22 to slide in the vertical direction with respect to the armature 33 without interference therewith; but securely locks the armature 33 and the follower 22 together for rotary movement, for a purpose more fully explained hereinafter. The armature 33 and consequently the follower 22 are biased in the clockwise direction, as viewed in Fig. 3, by an arrangement comprising a coil spring 31, one .end of the coil spring 31 being secured to a pin .38 fixed to the cylindrical body portion 34 of the armature 33 and the other end f the coil spring 3! being fixed to an externally supported pin 39. .Two sets of, switch springs S and SM are .operatively associated with the follower- 22, the

' constantly rotating friction disk by the coil spring into engagement with the friction shoes 53; and the shaft I5 is biased in a counterclockwise direction, as viewed in Fig. 1, by the coil spring 26, whereby the cam I 6 occupies its normal position illustrated. Also, the armature 33 and consequently the follower 22 are biased in the clockwise direction, as viewed in Fig. 3, whereby the arm 21 carried by the follower 22 cooperates with the first cam surface I'I carried by the cam I6. Also, at this time, the follower 22 occupies .its fully elevated or normal position, whereby the wiper set I I occupies its normal position disposed above the row of contact sets I4 carried by the contact bank I2. Also, when the follower 22 occupies its normal position the pin 42 carried thereby operates the set of switch springs S40 to its normal position; and the pin 43 carried by the insulating bushing 28 is disposed well above the set of switchsprings S4I, whereby the set of switch springs SM is operated to its normal position.

Considering now the operation of the mechanism ID to cause the wiper set I I to perform a contact selecting function with respect to the associated contact bank l2, the winding of the set of switch springs S46 constituting an off-normal switch and the set of switch springs S4l constituting a limit switch. More particularly, the set of switch springs S46 is operated by a pin 42 secured to the upper end of the follower 22; while the set of switch springs SM is operated by a pin 43 carriedby the insulating bushing 28.

Further the mechanism IU comprises a motor drive including a rotatably mounted operating shaft 44 which is driven at a substantially uniformspeed by an external source of power, not

shown. Preferably, the operatingv shaft 44 is driven by a constant speed motor f the synchronous type. The inner end of the operating shaft 44 carries a non-magnetic friction disk 45 which is operatively associated with a, magnetic friction disk 46 carried by the inner end of the shaft I5. More particularly, the friction disk 46 includes a cylindrical hub 4'! which is slidably mounted on the inner end of the shaft I5 by an arrangement including a pin 48 fixed to the shaft [5 and a slot 49 formed in the hub 47. This pin and slot connection between the friction disk 46 and the shaft l5 permits the friction disk 46 to be slid along I the shaft I5 toward and away from the associated friction disk 45, in an obvious manner. The fricticularly, the friction disk '46 is biased by the coil face H, in an obvious manner.

electromagnet 54 is first energized. When the winding 55 of the electromagnet 54 is thus energized, magnetic flux is set up in the core 56 and traverses a magnetic circuit, including the field pieces 5! and the magnetic friction disk 46,

whereby the magnetic friction disk 46 is attracted toward the field pieces 51. magnetic friction disk 46 is moved against the bias of the coil spring 50 from the left toward the .right, as viewed in Fig. 2, away from the friction More particularly, the

shoes 53 and into engagement with the friction disk 45, whereby the friction disks 45 and 46 are clutched together. Accordingly, the shaft I5 is rotated in theclockwise direction, as viewed in .Fig. l, with the constantly rotating operating shaft 44 against the bias of the coil spring 20; whereby the cam I6 is rotated in the' clockwise direction away from its normal position and the .coil spring 26 is wound. As the cam I6 is rotated .in the clockwise direction the arm 27 carried by the follower-22 follows the first cam surface I! thereof and successively rides over the teeth I9' disposed about the periphery of the first cam sur- As the arm 21 carried by the follower 22 rides over the teeth I9 disposed about the periphery of the first cam surface I! formed on the cam I6, the follower 22 is moved downwardly away from its normal position by gravity due to the general configuration of the cam l6, previously noted. More particularly, the follower 22 is moved downwardly first gradually and then abruptly repeatedly as the arm 21 rides first over the involuted surface of a tooth I9 and then over the face thereof onto the surface of the adjacent tooth. Accordingly, as the follower 22 is moved downwardly'away from its normal position. theeinsulating 1 bushing 28 and consequently the wiper set II are moved downwardly therewith. More particularly, the wiper set H is moved downwardly away from its normal position into successive engagement with the contact sets I4 disposed in the row in the associated contact bank l2.

After the winding 55 of the electromagnet 54 has been energised for a predetermined time interval corresponding to the desired contact set selection required by the wiper set I I, the winding 55 of the electromagnet 54 is deenergized. When the winding 55 of the electromagnet 54 is thus deenergized the magnetic flux set up in the core 56 subsides; whereby the coil spring 50 returns the magnetic friction disk 46 from the right toward the left, as viewed in Fig. 2, away' from the constantly rotating friction disk 45 and into engagement with the associated friction shoes 53, whereby the friction disks 45 and 48 are declutched. When the shaft I5 is thus declutched from the operating shaft 44, the shaft I5 is rotated in the counterclockwise direction, as viewed in 1, by the wound coil spring 20. More particularly, the cam carried by the shaft [5 is rotated in the counterclockwise direction back toward its normal position until the tooth l3 disposed about the periphery of the first cam surface I] formed thereon, over which the arm 21 carried by the follower 22 last rode, engages the arm 21.. When the tooth 19, over which the arm 21 last rode during the clockwise rotation of the cam l6, engages the arm 21, during the counterclockwise rotation of the cam I6, the cam 16 is locked by the arm 2! in a centered position against further rotation in the counterclockwise direction back toward its normal position. As previously noted, the arm 21 follows the first cam surface I 1 formed on the cam l6 during the rotation of the cam 16 in the clockwise direction; also, the arm 2! follows the first cam surface [1 formed on the cam I6 during the rotation of the cam IS in the counterclockwise direction back toward its normal position to its centered position. Accordingly, when the cam 16 is arrested in its centered position the follower 22 occupies a corresponding centered position; and the wiper set ll carried by the follower 22 occupies a centered position with respect to the one of the contact sets l4 last engaged thereby in the associated contact bank I2. The rotation of the cam 16 in the counterclockwise direction following the rotation thereof in the clock- I wise direction, in order to effect a centering of the cam l8, positively effects a centering of the follower 22 and consequently the wiper set II with respect to the last engaged one of the contact sets II in the associated contact bank l2.

In view of the foregoing explanation of the mode of operation of the mechanism Ill to effect a selecting operation by the wiper set II with respect to the contact sets l4 in the associated contact bank l2, it will be understood that the winding of the electromagnet 54 is energized for a variable time interval corresponding to the desired contact set 14 in the contact bank l2 which is to be selected by the wipe-r set H, and that during this time interval the wiper set H is moved downwardly away from its normal position slightly past the desired contact set M in the associated contact bank I2; and at the conclusion of the time interval mentioned the ciated contact bank l2 minimizes the necessity for exact timing during the interval in which the winding 55 of the electromagnet 54 is energized, and renders it necessary that the timing referred to be only approximate. More particularly, it will be understood that, in the mechanism ill, the timing of the energization of the winding 55 of the electromagnet 54 may be as much as five per cent. too long or too short without causing false selection by the Wiper set H with respect to the contact sets 14 in the associated contact bank l2. Finally, in this connection, itis noted that, in the mechanism It], the timing of the energization of the winding 55 of the electromagnet 54 should be within the limits mentioned in order to effect proper selection by the wiper set H with respect to the contact sets l4 in the associated contact bank l2. At this time, the wiper set II is positively centered with respect to the selected contact set 14 in the associated contact bank 12 and is locked in its selecting position by the cooperation between the arm 21 carried by the follower 22 and the engaged tooth is disposed about the periphery of the first cam surface 11 formed on the cam I6.

In order to release the mechanism l3 and to cause the Wiper set H to be returned upwardly to its normal position, the winding 3| of the electromagnet 30 is energized for a short time interval. When the winding 3! of the electromagnet 30 is thus energized, magnetic flux is set up in the core 32, whereby the armature 33 is attracted. When the armature 33 is thus attracted it is rotated in the counterclockwise direction, as viewed in Fig. 3, against the bias of the coil spring 37!, whereby the follower 22 is pivoted in the supporting

brackets

23 and 24 in the counterclockwise direction. When the follower 22 is thus pivoted in the counterclockwise direction the arm 21 carried thereby is moved out of engagement with the associated tooth l5 disposed on the periphery of the first cam surface 11 formed on the cam I6 and into engagement with the second cam surface !8 formed on the cam l6, as clearly indicated in Fig. 2; whereby the cam i6 is unlocked and rotated in the counterclockwise direction by the coil spring 20 back into its normal position. When the cam I6 is thus rotated in the counterclockwise direction back into its normal position the arm 21 follows the smooth second cam surface l8 formed thereon, whereby the follower 22 is elevated and returned to its normal position. When the follower 22 is thus elevated and returned to its normal position the wiper set ll carried thereby is thus elevated and returned to its normal position with respect to the contact sets M in the associated contact bank l2.

Subsequently, the winding 3| of the electromagnet 30 is deenergized, whereby the armature 33 is rotated in the clockwise direction, as viewed in Fig. 3, by the coil spring 31. When the armature 33 is thus rotated in the clockwise direction the follower 22 is pivoted in the supporting

brackets

23 and 24 in a clockwise direction; whereby the arm 21 disengages the second cam surface l8 formed on the cam I6 and reengages the first cam surface I! formed on the cam IS, the first cam surface I! and the second cam surface [8 formed on the cam [6 being coninsulating bushing mechanism I0, it is pointed out thatthe set of switch springs S40 is operated from its normal position to its off-normal position when the pin 42 carried by the follower 22 is lowered due to operation of the follower 22 away from its normal position; on the other hand, the set of switch springs S40 is operated from its off-normal position back to its normal position by the pin 42 carried by the follower 22 when the follower 22 is elevated and returned to its normal position. Finally, the set of switch springs SM is operated from its normal position to its off-normal position by the pin 43 carried by the insulating bushing 28 in the event the follower 22 is lowered away from its normal position an amount sufficient to cause the wiper set II to disengage the last contact set I4 in the associated contact bank I2; on the other hand, the set of switch springs SM is operated from its off-normal position back to its normal position when the pin 43 carried by the insulating bushing 28 is elevated due to the elevation of the follower 22 back into its normal position. Finally, it is noted that, in the event the set of switch springs S4I is operated to its off-normal position, circuit control means is governed to deenergize the winding 55 of the electromagnet 54 and to energize the winding 3| of the electromagnet 30, whereby the mechanism i is released, in the manner explained above.

Referring now more particularly to Figs. 4 and of the drawings, there is illustrated a modified form of the switching mechanism IIO embodying the present invention and comprising a wiper set III and an associated contact bank II2, the contact bank II2 including an insulating structure II3 supporting a plurality of vertically spaced-apart contact sets II4 arranged in a row. Also, the mechanism IIO comprises a rotatably mounted shaft II5 having a ratchet wheel H6 and a gear H1 rigidly secured thereto. The ratchet wheel H6 has a plurality of spaced-apart teeth II9 disposed about the periphery thereof. The ratchet wheel IIS and the gear II1 are biased in the counterclockwise direction into normal positions, illustrated in Fig. 5, by an arrangement comprising a surrounding coil spring I20, one end of the coil spring I20 being secured to the gear H1 and the other end of the coil spring I20 being secured to an externally supported pin IN. The gear II1 cooperates with a rack I22 which is mounted by two brackets I23 and I24 for sliding movement, the bracket I23 being externally supported by an arrangement comprising two screws I25 and the bracket I24 being externally supported by an arrangement comprising two screws I26.

The wiper set III is operatively connected to the rack I22 by an arrangement comprising an I28, the outer end of the wiper set III straddling the insulating structure II3 of the associated contact bank H2 in guided relation with respect thereto and the inner end of the wiper set II I being secured to the insulating bushing I28. It is noted that the insulating bushing I28 is secured to the lower end of the rack I22 by a connection including a screw I29. An electromagnet I30, constituting a release magnet, is operatively associated with the ratchet wheel H6 and comprises a winding I3I, a core I32 and an armature I34 mounted upon an externally supported pivot pin I35. The ar- 'mature I34 carries an outwardly and upwardly projecting arm I36 constituting a pawl cooperating with the teeth II9 disposed about the contact bank I I2.

periphery of the ratchet-wheel IIG. Thearmaiture I34 and consequently the pawl I36 are biased in the clockwise direction, as viewedin Fig. 5, by an arrangement comprising a coil spring I31; one end of the coil spring I31 being secured to a pin I38 fixed to the outer end of the armature I34 and the other end of the coil spring I31 being fixed to an externally supported pin I39.

Two sets of switch springs SI40 and SIM are operatively associated respectively with the ratchet wheel H6 and the rack I22, the set of switch springs SI40 constituting an off-normal switch and the set of switch springs SI4I constituting a limit switch. More particularly, the set of switch springs SI40 is operated by a pin I42 fixed to the side wall of the ratchet wheel IIIS; while the set of switch springs SI4I is operated by a pin I43 carried on the lower end of the rack I22.

Further, the mechanism I I0 comprises a motor drive, including a rotatably mounted operating shaft I44, which is driven at a substantially uniform speed by an external source of power, not shown. Preferably, the operating shaft I44 is driven by a constant speed motor of the synchronous type. The inner end of the operating shaft I44 carries a nonmagnetic friction disk I45 which is operatively associated with a magnetic friction disk I46 carried by the inner end of the shaft II5. More particularly, the friction disk I46 includes a cylindrical hub I41 which is slidably mounted on the inner end of the shaft II5 by an arrangement including a pin I48 fixed to the shaft H5 and a slot I49 formed in the hub I41. This pin and slot connection between the friction disk I45 and the shaft I I5 per! mits the friction disk I46 to be slid along the shaft II5 toward and away from the associated friction disk I45, in an obvious manner. The friction disk I46 is normally biased away from the associated friction disk I45 by an arrangement comprising a spring motor or coil spring 150 surrounding the shaft II5, one end of the coil spring I50 being secured to a pin I5I fixed to the ratchet wheel I I6 and the other end of the coil spring I50 being secured to a pin I52 fixed to the hub I41. More particularly, the friction disk I46 is biased by the coil spring I50 away from the associated friction disk into engagement with a number of externally supported friction shoes I53. Finally, the motor drive comprises an electromagnet I54 including a winding I55 and a core I56, the core I56 being provided with field pieces I51 disposed adjacent the friction'disk I45 and forming a part of a magnetic circuit, including the magnetic friction disk I 46.

When the mechanism ,I I0 is fully releasedthe friction disk I46 is biased away from the associated constantly rotating friction disk I45 by the coil spring I50 into engagement with the friction shoes I 53; and the shaft H5 is biased in the counterclockwise direction, as viewed in Fig. 5, by the coil spring I22, whereby the ratchet wheel H6 and the gear II1 occupy their normal positions illustrated. When the gear I I1 occupies its normal position the rack I22 occupies its fully elevated or normal position, whereby the wiper set III occupies its normal position disposed above the row of contact sets II4 carried by the Also, the armature I34 and consequently the pawl I36 are biased in the clockwise direction about the pivot pin I35, as viewed in Fig. 5, by th coil spring I31; whereby the pawl I36 engages one of the teeth II9 disposed on the periphery of the ratchet wheel I I6 in order positively to lock the ratchet wheel H6 in its normal position. Further, when the ratchet wheel I I6 occupies its normal position the pin I42 carried thereby operates the set of switch springs SI4II to its normal position; and when the rack I22 occupies its normal position the pin I43 carried on the lower end thereof is disposed well above, the set of switch springs SI4I, whereby the set of switch springs SI4I is operated to its normal position.

Considering now the operation of the mechanism IIII to cause the wiper set I I I to perform a contact selecting function with respect to the associated contact bank II2, the winding I55 of the electromagnet I54 is first energized. When the winding I55 of the electromagnet I54 is thus energized, magnetic flux is set up in the core I56 and traverses a magnetic circuit including the field pieces I51 and the magnetic friction disk I46, whereby the magnetic friction disk I46 is attracted toward the field pieces I51. More particularly, the magnetic friction disk I46 is moved against the bias of the coil spring I50 from the right toward the left, as viewed in Fig. l, away from the friction shoes I53 and into engagement with the friction disk I45; whereby the friction disks I45 and I45 are clutched together. Accordingly, th shaft H5 is rotated in the clockwise direction, as viewed in Fig. 5, with the constantly rotating operating shaft I44 against the bias of the coil spring I20; whereby the ratchet wheel H6 and the gear II! are rotated in the clockwise direction away from their normal positions and the coil spring I20 is wound. As the gear II! is rotated in the clockwise direction the rack I22 is driven at a substantially constant speed downwardly away from its normal position. Accordingly, as the rack I22 is moved, downwardly away from its normal position the insulating bushing I28 and consequently the wiper set III are moved downwardly therewith. More particularly, th wiper set II is moved downwardly away from its normal position into successive engagement with the contact sets II4 disposed in the row in the associated contact bank H2. Also, as the ratchet wheel H6 is rotated in the clockwise direction the pawl I36 rides over the teeth II9 disposed about the periphery thereof.

After the winding I55 of the electromagnet I54 has been energized for a predetermined time interval corresponding to the desired contact set selection required by the wiper set I I I, the winding I55 of. th electromagnet I 54 is deenergized.

When the winding I55 of the electromagnet I 54. is thus dcenergized the magnetic flux set up in the core I56 subsides; whereby the coil spring I50 returns the magnetic friction disk I46 from the left toward the right, as viewed in Fig. 4, away from the constantly rotating friction disk I45 and into en agement with the associated friction shoes I53, whereby the friction disks I45 and I45 are declutched. When the shaft H5 is thus declutched from the operating shaft IMl, it is rotated in the counterclockwise direction, as viewed in Fig. 5, by the Wound coil spring I29. More particularly, the ratchet wheel II6 carried by the shaft H5 is rotated in the counterclockwise direction back toward its normal position until the tooth H6 disposed about the periphery thereof. over which the pawl I36 last rode, engages the pawl I36 mentioned. When the tooth Hi. over which the pawl I36 last rode during the clockwise rotation of the ratchet wheel II6, engages the pawl I 36 during the counterclockwise rotation of the ratchet wheel II6, the ratchet wheel H6 is locked by the pawl I36 in a centered position against further rotation in the counterclockwise direction back toward its normal position. As previously noted, the rack I22 is driven downwardly away from its normal position by the gear II'I during the rotation of the ratchet wheel I I6 in the clockwise direction; also the rack I22 is driven upwardly back toward its normal position by the gear I I1 during the rotation of the ratchet wheel I I6 in the counterclockwise direction back toward its normal position to its centered position.

Accordingly, when the ratchet wheel H6 is arrested in its centered position the rack I22 occupies a corresponding centered position; and the wiper set II I carried by the rack I22 occupies a centered position with respect to the one of the contact sets II4 last engaged thereby in the associated contact bank H2. The rotation of the ratchet wheel H6 in the counterclockwise direction, following the rotation thereof in the clockwise direction, in order to effect a centering of the ratchet wheel II6, positively effects a centering of the rack I22 and consequently the wiper set III with respect to the last engaged one of the contact sets I I4 in the associated contact bank II2.

In view of the foregoing explanation of the mode of operation of the mechanism Hi! to effect a selecting operation by the wiper set III with respect to the contact sets H4 in the associated contact bank II2, it will be understood that the winding I55 of the electromagnet I54 is ener- 5 gized for a variable time interval corresponding to the desired contact set I I4 in the contact bank II2 which is to be selected by the wiper set III; and that, during this time interval, the wiper set III is moved downwardly away from its normal position slightly past the desired contact set H4 in the associated contact bank I I2; and, at the conclusion of the time interval mentioned, the wiper set III is then moved upwardly back toward its normal position to a centered position with respect to the selected contact set H4 in the associated contact bank II2. This arrangement for positively centering the wiper set III with respect to the last engaged contact set H4 in the associated cont-act bank II 2 minimizes the necessity for exact timing during the interval in which the winding I55 of the electromagnet I54 is energized; and renders it necessary that the timing referred to be only approximate. More particularly, it will be understood that in the mechanism II II th timing of the energization of the winding I55 of the electromagnet I54 may be as much as five per cent. too long or too short without causing false selection by the wiper set III with respect to the contact sets H4 in the associated contact bank I I2. Finally, in this connection. it is noted that in the mechanism III! the timing of the energization of the winding I55 of the electromagnet I54 should be within the limits mentioned in order to effect proper selection by the wiper set I I I with respect to the contact sets H4 in the associated contact bank II2.

At this time, the wiper set I I I is positively centered with respect to the selected contact set H4 in the associated contact bank H2 and is locked in its selected position by the cooperation between the pawl I36 carried by the armature I34 and the engaged tooth II9 disposed on the periphery of the ratchet wheel II6.

In order to release the mechanism IIII and to cause th wiper set III to be returned upwardly to its normal position, the winding I3I of the electromagnet I30 is energized for a short time interval. When the winding I3I of the electromagnet I30 is thus energized, magnetic flux is set up in the core I32, whereby the armature I34 is attracted. Whenthe armature I34 is thus attracted it is rotated in the counterclockwise direction about the pivot pin I35, as viewed in Fig. 5, against the bias of the coil spring I31, whereby the pawl I36 is moved out of engagement with the associated tooth II9 disposed on the periphery of the ratchet wheel II6, whereby the ratchet wheel I I 6 is unlocked and'rotated in the counterclockwise direction by the coil spring I back into its normal position. When the ratchet wheel I6 is thus rotated in the counterclockwise direction back into its normal position the gear II1 drives the rack I22 upwardly back to its normal position. When the rack I22 is thus elevated and returned to its normal position the wiper set III carried thereby is thus elevated and returned to its normal position with respect to the contact sets I I4 in the associated contact bank I I2. Subsequently, the winding I3I of the electromagnet I is deenergized, whereby the armature I34 is rotated in the clockwise direction about the pivot pin I35, as viewed in Fig. 5, by the coil spring I31. When the armature I34 is thus rotated in the clockwise direction the pawl I36 reengages the associated tooth I I9 disposed on the periphery of the ratchet wheel I I6. At this time, the mechanism H0 is completely released.

In conjunction with the operation of the mechanism I I0, it is pointed out that the set of switch springs SI40 is operated from its normal position to its oil-normal position when the pin I42 carried by the ratchet wheel H6 is moved in the clockwise direction as the rack I22 is lowered away from its normal position; on the other hand, the set of switch springs SI40 is operated away from its ofi-normal position back to its normal position by the pin I42 carried by the ratchet wheel II6 When the ratchet wheel H6 is rotated in the counterclockwise direction as the rack I22 is elevated and returned to its normal position.

Finally, the set of switch springs SI4I is operated from its normal position to its oiT-normal position by the pin I 43 carried on the lower end of the rack I22 in the event the rack I22 is lowered away from its normal position an amount sufficient to cause the wiper set I I I to disengage the last contact set I I4 in the associated contact bank II2; on the other hand, the set of switch springs SI4I is operated from its off-normal position back to its normal position when the pin I43 carried.-

an automatic telephone system embodying the present invention and incorporating switching mechanism of either the form shown in Figs. 1 to 3, inclusive, or the form shown in Figs. 4 and 5. In the description of the-circuit shown in Fig. 6, the reference numbers used in describing the form of switching mechanism illustrated in Figs. 1 to 3, inclusive, have been used, as far as possible, but it will be readily apparent that the 39 instrument, not shown.

spending reference numerals used in the description of the form of construction shown in Figs. 4 and 5 may be substituted therefor. The telephone system illustrated comprises a telephone station 606 having a telephone line 605 extending thereto, a selector 6I0 terminating the telephone line 605, and ten telephone lines, including the telephone line 685, accessible to the selector 6I0. The telephone station 600 comprises station equipment including a call transmitter 60I of the construction and arrangement of that disclosed in Figs. 1 and 2 of the previously mentioned Willis patent, a hook switch 602, and a telephone The selector 6I0 comprises a switching mechanism I0 which may be of either of the two forms described above, which includes a go magnet 54, a release magnet 30 and a wiper set provided with the wipers Bill and 692. Also associated with the switching mechanism I0 are two sets of oil-normal switch springs S694 and S695 and a set of limit switch springs S696. Also, the selector 6| 0 comprises a relay group, including a switch-through relay R620, a line relay R630, a hold relay R640, a release relay R650 and two control relays R660 and R610, and a control network connected and arranged in a manner more fully explained hereinafter. Finally, each of the telephone lines 685, etc., is provided with a line circuit including a seizure relay, the telephone line 685 being provided with a line circuit including the seizure relay R680. A better understanding of the connection and arrangement of the telephone system will be facilitated from a consideration of the following description of the mode of operation of the apparatus incorporated therein incident to the extension of a connection from the telephone station 600 to a called one of the telephone lines 685, etc.

Considering now the extension of a call from the telephone station 600, the operator thereat first removes the receiver of the telephone instrument from its associated switchhook; whereby the hook switch 602 is operated to complete a loop circuit for energizing in series the upper and lower windings of the line relay R530 in the selector 6 I 0. The last-mentioned loop circuit extends from ground by way of the lower winding of R630, the contacts 624, one of the line conductors of the telephone line 605, the hook switch 602 and the call transmitter 60I at the telephone station 600, the other line conductor of the telephone line 605, the contacts 622, and the upper winding of R630 to battery. When thus energized the line relay R630 operates to complete, at the contacts 632, an obvious circuit, including the contacts 66I and 62 I, for energizing the winding of the hold relay R640, thereby to cause the latter relay to operate. At this time, the selector 6I0 is rendered responsive to a digit in the form of a single impulse of variable time duration transmitted thereto over the telephone line 605 from the telephone station 600 to select a corresponding one of the telephone lines 685, etc.

Now assuming that the operator at the tele phone station 600 operates the call transmitter 60I in accordance with a given digit having an open-circuit period corresponding to the called telephone line 685, the call transmitter 60I first interrupts the previously traced loop circuit for energizing in series the upper and lower windings of the line relay R630 and, at the conclusion of the previously mentioned time interval, recompletes the loop circuit mentioned. Accordingly, the line relay R630 restores and then, at the GOIlclusion of the predetermined time interval mentioned, reoperates. Upon restoring, the line relay R630 completes, at the contacts 631, an obvious circuit, including the contacts 66!, 621 and 64 I, for energizing the g magnet 54, thereby to cause the latter magnet to operate and initiate operation of the switching mechanism 10, in the and when the set of ofi-normal switch springs S695 is thus operated a circuit traced hereinafter is prepared for energizing the winding of the switch-through relay R620.

Subsequently, when the line relay R530 reoperates it interrupts, at the contacts 631, the previously traced holding circuit for energizing the go magnet 54, thereby to cause the latter magnet to restore in order to arrest further operation of the switching mechanism I0. The wiper set of the switching mechanism is then positively centered with respect to the contact set in the associated contact bank terminating the called telephone line 685, in the manner previously explained. Also, upon operating, the line relay R630 recompletes, at the contacts 632, the previously traced circuit for energizing the winding of the hold relay R640, thereby to cause the latter relay to reoperate in the event it restored during ths transmission of the digit from the telephone station can, the hold relay R645 being of the slow-to-release type. Further, the line relay R680 completes, at the contacts 633, the previously mentioned circuit, including the contacts 621 and 663 and the set of off-normal switch springs S695, for energizing the winding of the switch-through relay R620. When thus energized the switch-through relay R620 operates to complete, at the contacts 626, an obvious holding circuit substantially identical to that previously traced for energizing the winding thereof. Further, the switch-through relay R626 interrupts,

at the contacts 621, the previously traced circuit for energizing the winding of the hold relay R640,

thereby to cause the latter relay to restore shortly thereafter. Also, the switch-through relay R320 interrupts, at the contacts 622 and 624, the previously traced circuit for energizing in series the upper and lower windings of the line relay R630, thereby to cause the latter relay to restore. Finally, the switch-through relay R625 completes, at the

contacts

623 and 625, a loop circuit for energizing in series the upper and lower windings of the seizure relay R660 in the line circuit associated with the called telephone line The last-mentioned loop circuit extends from ground by way of the lower winding of R600, the wiper 662 of the switching mechanism It, and the contacts 625 to one of the line conductors of the telephone line 605; and from battery by way of the upper winding of R683, the wiper 691 of the switching mechanism l0 and the contacts 623 to the other line conductor of the telephone line 605, the line conductors of the telephone line 605 being connected together by way of the bridge at the telephone station 660, previously mentioned. When this loop circuit 18 completed the seizure relay R680 is energized and operates.

Upon operating, the seizure relay R660 completes, at the contacts 682, an obvious circuit for energizing the winding of the control relay R610, thereby to cause the latter relay to operate. Upon operating, the control relay R610 completes, at the contacts 612, an obvious multiple holding circuit for energizing the winding of the switchthrough relay R620, thereby to retain the latter relay in its operated position. Also the control relay R610 completes, at the contacts 611, an obvious circuit for energizing the winding of the control relay R660, thereby to cause the latter relay to operate. Upon operating, the control relay R660 interrupts, at the contacts 66I, a further point in the previously traced circuits for energizing the winding of the hold relay R640 and the go magnet 54; interrupts, at the contacts 663, a point in the original holding circuit for energizing the winding of the switch-through relay R620; and prepares, at the contacts 662, a point in an obvious circuit for energizing the winding of the release relay R650.

Also, when the seizure relay R680 operates it interrupts, at the contacts 68I, an obvious bridge connection between the line conductors of the called telephone line 685, whereby the calling telephone line 605 is operatively connected to the called telephone line 665 for telephone communication thereover. More particularly, the line conductors of the telephone line 665 are respectively connected by way of the condensers 663 and 684 to the previously traced loop circuit extending between the telephone station 600 and the seizure relay R680. Also it is noted that, in the event it is necessary to perform further switching operations over the called telephone line 665, this may be accomplished by the seizure relay R680 under the control of the call transmitter 601 at the telephone station 600. More particularly, in the event the call transmitter GM is reoperated in accordance with an additional digit, the seizure relay R680 first restores and then reoperates at the conclusion of the digit mentioned. Upon restoring, the seizure relay R660 recompletes, at the contacts 66| the previously mentioned bridge connection between the line conductors of the called telephone line 665. Subsequently, when the seizure relay R680 reoperates it interrupts, at the contacts 68!, the previously mentioned bridge connection between the line conductors of the called telephone line 665. Accordingly, the call transmitter 60! at the telephone station 600 is operative to transmit additional digits in the form of single impulses of variable time duration over the called telephone line 685 by way of the telephone line 605 and the selector H0, in the event this is necessary. Also, in this connection, it is pointed out that, during the transmission of the additional digits from the call transmitter 601 at the telephone station 600 over the called telephone line 685, the seizure relay R660 occupies its restored position, whereby the previously traced circuit for energizing the winding of the control relay R610 is interrupted during the time interval mentioned. However, the control relay R610 is of the slow-to-release type and has a release characteristic such that the latter relay does not restore during impulsing. Accordingly, at this time, an operative connection is completed between the telephone station 600 and the called telephone line 685, including the telephone line 605 and the selector 6l0, for telephone communication purposes.

The release of the established connection is under the control of the operator at the telephone station 600 and is effected when he replaces the receiver of the telephone instrument thereat upon its associated switch-hook in order to operate the hook switch 602, in an obvious manner. When the hook switch 602 is thus operated the previously traced loop circuit for energizing in series the upper and lower windings of the seizure relay R680 is interrupted, thereby to cause the latter relay to restore. Upon restoring, the seizure relay R680 recompletes, at the contacts 68l, the previously mentioned bridge connection between the line conductors of the telephone line 685; and interrupts, at the contacts 682, the previously mentioned circuit for energizing the winding of the control relay R610, thereby to cause the latter relay to restore shortly thereaften'the control relay R670 being of the slow-to-release type, as previously noted. Upon restoring, the control relay R610 interrupts, at the contacts 612, the previously traced alternative holding circuit for energizing the winding of the switch-through relay R620, thereby to cause the latter relay to restore. Also the control relay R6'l0 interrupts, at the contacts 61!, the previously mentioned circuit for energizing the winding of the control relay R660; however, the latter relay does not restore immediately as it is of the slow-to-release type.

Upon restoring, the switch-through relay R620 reprepares, at the contacts 62I, the previously traced circuit for energizing the winding of the hold relay R640; interrupts, at the contacts 628, a further point in the holding circuit for energizing the winding thereof; interrupts, at the

contacts

623 and 625, a further point in the previously traced loop circuit for energizing in series the upper and lower windings of the seizure relay R680; and prepares, at the contacts 622 and 624, a point in the previously traced loop circuit for energizing in series the upper and lower windings of the line relay R630. Finally,

the switch-through relay R620 completes, at the contacts 626, the previousl mentioned circuit for energizing the Winding of the release relay R650, thereby to cause the latter relay to operate. Upon operating, the release rela R650 completes, at the contacts 651, an obvious circuit for energizing the release magnet 30, thereby to cause the latter magnet to operate. Upon operating, the release magnet 30 unlocks the wiper set of the switching mechanism I0, whereb the switching mechanism I0 is mechanically released by the associated spring motor, in the manner previously explained. When the switching mechanism I0 is thus fully released the sets of off-normal springs S694 and S695 are operated back to their normal positions. Shortly after the switching mechanism It) is thus released the control relay R660 restores, as previously noted. Upon restoring, the control relay R660 interrupts, at the contacts 662, the previously mentioned circuit for energizing the winding of the release relay R650, thereby to cause the latter relay to restore shortl thereafter, the release relay R650 being of the sloW-to-release type. Upon restoring, the release relay R650 interrupts, at the contacts 65 I, the previously mentioned circuit for energizing the release magnet 30, thereby to cause the latter magnet to restore, whereupon the switching mechanism I0 is reconditioned for further operation. At this time, the selector 6l0 is completely released and all of the apparatus utilized in establishing the connection between the telephone station 600 and the called telephone line 685 are completel released and available for further use.

In conjunction with the operation of the selector 6l0 and the switching mechanism l0 incorporated therein, it is pointed out that, should the operator at the telephone station 600 remove the receiver of the telephone instrument thereat from its associated switchhook and then replace the receiver upon its associated switchhook without operating the call transmitter 60l, thereby abandoning the call, the selector 6l0 would be seized and operation of the switching mechanism l 0 incorporated therein would be initiated, in the manner previously explained. However, in this event, the line relay R630 remains restored for an indefinite time interval, whereby the wiper set of the switching mechanism I0 is driven beyond the last contact set in the associated contact bank. When the wiper set of the switching mechanism In is thus driven beyond the last contact set in the associated contact bank the set of limit switch springs S696 is operated. More particularly, the set of limit switch springs S696 is operated to complete, at the contacts 691, and then to interrupt, at the contacts 698, an obvious path for applying ground potential to the control conductor C593 and consequently the circuit for energizing the winding, of the control relay R610. Accordingly, the control relay R610 operates and then subsequently restores, thereby to effect operation of the control relay R660, in the manner previously explained. Upon operating, the control relay R660 interrupts, at the contacts 66!, the previously traced holding circuit for energizing the go magnet 54, thereby positively to arrest further movement of the wiper set of the switching mechanism I0 with respect to the associated contact bank. Also the control relay R660 completes, at the contacts 662, the previously traced circuit for energizing the winding of the release relay R650, thereb to cause the latter relay to operate. Subsequently, when the control relay R610 restores it effects restoration of the control relay R660 and the release relay R650. While the release relay R650 occupied its operated position the release magnet 30 was operated, thereby to effect the release of the switching mechanism I 0, in the manner previously explained. Incident to the restoration of the release relay R650 the release magnet 30 is released, thereby to condition the switching mechanism l 0 for further operation, in the manner previously explained. At this time, the selector Ell) and the switching mechanism [0 incorporated therein are completely released and available for further use.

While one embodiment of the invention has been disclosed, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention.

What is claimed is:

1. In a switching system wherein a single variable digit is transmitted over a line by a timing transmitter, switching mechanism comprising a wiper having a normal position, a plurality of spaced-apart contacts disposed in a row and accessible to said wiper, means controlled during the receipt of said single digit over said line for continuously advancing said wiper away from its normal position along said row into successive engagement with said contacts, means controlled at the conclusion of the transmission of said single digit over said line for centering said wiper with respect to the one of said contacts last engaged thereby, and means controlled in response to the disengagement by said wiper of the last one of said contacts in said row for returning said wiper to its normal position.

2. In a switching system wherein a timing transmitter is selectively operable to alter the circuit condition of a line and to maintain said altered circuit condition during different time intervals, switching mechanism comprising a wiper having a normal position, a plurality of spacedapart contacts disposed in a row and accessible to said wiper, means controllable over said line for continuously advancing said wiper at a substantially uniform speed away from its normal position along said row into successive engagement with said contacts during the time interval through which said altered circuit condition of said line is maintained, means controlled at the conclusion of said altered circuit condition of said line for returning said wiper toward its normal position and to a centered position with respect to the one of said contacts last engaged thereby, and means controlled in response to the disengagement by said wiper of the last one of said contacts in said row for returning said wiper to its normal position.

3. Switching mechanism comprising a cam having a normal position, a follower arranged to ride upon a cam surface of said cam, motor means adapted to advance said cam continuousl away from its normal position, said cam surface having means whereby said cam may be definitely located in one of a plurality of spaced-apart positions by said follower upon reverse movement of said cam toward said normal position, means for selectively controlling said motor means to determine the extent of said advance of said cam from said normal position, means operated when the advancement of said cam away from said normal position is arrested for returning said cam toward said normal position and thereby causing it to be located in one of said positions by said follower, and contact selecting means operatively connected to said follower.

4. Switching mechanism comprising a cam having a normal position and carrying a plurality of spaced-apart teeth disposed about the cam surface thereof, a follower adapted to ride upon the cam surface of said cam, motor means adapted to advance said cam continuously away from its normal position, means for selectively controlling said motor means, means governed when the advancement of said cam away from its normal position by said motor means is arrested for returning said cam toward its normal position to the nearest one of a plurality of spaced-apart centered positions, said one centered position being established when said follower is engaged by the one of the teeth disposed about the cam surface of said cam which was last to ride under said cam, and contact selecting means operatively connected to said follower.

5. Switching mechanism comprising a cam having a normal position, said cam including a first cam surface carrying a plurality of spacedapart teeth and a second smooth cam surface, a follower normally associated with said first cam surface and adapted to be associated with said second cam surface, motor means adapted to advance said cam continuously away from its normal position, means for selectively controlling said motor means, means governed when the advancement of said cam away from its normal position by said motor means is arrested for returning said cam toward its normal position, means governed when the one of the teeth carried by said first cam surface which was last to ride under said follower engages said follower for arresting the return of said cam toward its normal position, thereby to establish a corresponding centered position for said cam, means for disassociating said follower from said first cam surface and for associating it with said second cam surface, means governed when said follower is disassociated from said first cam surface for returning said cam to its normal position, and contact selecting means operatively connected to said follower.

6. The combination in switching mechanism of a rotatable toothed member having a normal position, a follower mounted for linear movement 1 and having a part arranged to ride continuously upon said toothed member, a plurality of spacedapart contacts disposed in a row, a wiper carried by said follower and adapted to engage said contacts successively upon endwise movement of said follower, motor means adapted to rotate said toothed member from its normal position to advance said wiper over said contacts, a spring adapted to be wound by said rotation of said toothed member, means for controlling said motor means, and means including said spring and operative when the operation of said motor means is arrested for returning said wiper and said toothed member to their normal positions,

7. The combination in switching mechanism of a rotatable cam having a peripheral surface including a toothed part and a smooth part, a follower having a part adapted to ride normally on said toothed part of said cam, a plurality of contacts arranged in a row, a wiper carried by said follower for movement over said contacts, motor means for rotating said cam in one direction with said follower riding on said toothed part, a spring adapted to be wound by said rotation of said cam, means for controlling the operation of said motor means, and means actuated when said motor means is arrested for moving said part of said follower into engagement with said smooth part of said cam and thereby permitting said spring to return to its normal position.

BERNARD D. WILLIS.