US2173548A - Selector switch - Google Patents

Description

l 1939. w. w. CARPENTER ET AL 2,173,548

SELECTOR SWITCH Filed June 15, 1938 5 Sheetsheet 2 ,w W CARPENTER WVENTORSR. F. MALL/NA )4 T TORNE Y Sept. 19, 1939. w, w, CARPENTER r AL 2,173,548

SELECTOR SWITCH Filed June 15, 1938 5 Sheets-Sheet 3 aw J FIG. 7

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90 W WCARPENTER INVENTORS? F MALL INA ATTORNEY Sept. 19, 1939.

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SELECTOR SWITCH Filed June 15, 1938 5 Sheetsheet 4 FIG. /0

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ATTORNEY P 1939- w. w. CARPENTER ET AL ,173,548

SELECTOR SWITCH Filed June 15, 1938 5 Sheets-Sheet 5 FIG/5 .W WCARPENTER INVENTORSR. F MALL/NA By @am ATTORNEY Patented Sept. 19, 1939 UNITED STATES PATENT OFFICE SELECTOR SWITCH Warren W. Carpenter, Garden City, and Rudolph F. Mallina, New York, N. Y., assignors to Bell Telephone Laboratories,

Incorporated, New

12 Claims.

This invention relates to selector switches applicable for use in dial switching telephone systems and more particularly to switches of the terminal hunting type which may be driven at high terminal hunting speeds.

The switch of the present invention is of the general type disclosed in the Patent No. 2,123,229, .granted on July 12, 1938, to W. W. Carpenter and R. F, Mallina, in which a single brush set is advanced from a normal position in a hunting move ment over either one of two panel banks by a motor driven tape belt and is moved back to a marked terminal in the event the brush set overruns the marked terminal in its hunting movement and in which a magnetically controlled brake is provided for quickly arresting the movement of the tape and the brush set controlled thereby. This switch has, however, been modified in accordance with the present invention with respect to several deno tails thereof.

It is the object of the present invention to provide a high speed selector switch which is economical to manufacture and maintain in a high state of mechanical and electrical efiiciency.

This object is attained by providing a switch unit comprising two line or trunk finders mounted vertically on a switch frame and having access to two panel banks of terminals disposed one above the other on the Switch frame with their rows of terminal sets vertically aligned. Each switch unit comprises three main assembly structures two of which are identical upper and lower motor and brake assemblies and the third of which is an intermediate assembly interconnecting the two other assemblies.

Each motor and brake assembly comprises a mounting bracket, which may be secured to a cross member of the switch frame, on which is mounted a driving motor the rotor of which is geared to a tape driving pulley for driving the tape of one of the switches of the unit, an idler pulley for the tape of the other switch of the unit, a magnetically operated brake mechanism cooperative with the tape of the first switch, a spring pile-up comprising springs operable by the brake magnet and oil-normal switch springs and an off-normal switch operating mechanism operated by the tape of the latter switch. The intermediate assembly which is attachable to the mounting brackets of the other assemblies comprises guide rods upon which the brush carriages of the two switches are slidably positioned, flexible cables of conductors attached to the respective brush carriages and channel members within which the depending loops of the flexible cables are guided.

The oil-normal switch operating mechanism comprises a member pivoted on the mounting bracket, one end of which is provided with cam 5 rollers of insulating material for camming the springs of the off-normal switch into engagement and the other end of which is notched for engagement by a lug secured to the tape. The movement of the tape in one direction from its 10 normal position, in which position the brush set controlled thereby is maintained midway between the two banks of terminals, is operative to rotate the off-normal switch operating member in a direction to close certain of the oil-nor- 5 mal springs and the movement of the tape in the opposite direction is effective to rotate the member in a reverse direction to cause a closure of other of the oil-normal springs. The off-normal switch is eiiective to control circuits to restore 20 the operated brush set to its normal position upon the release of a connection established by the switch.

To reduce the eilect of vibrations either transmitted to the switch frame from the building or 25 incident to the operation of other switches mounted on the switch frame, provision is made for cushioning the ends of the guide rods on which the brush carriages slide at their points of attachment to theend plates of the intermediate assembly structure by sleeves of live rubber and to cushion the brush carriages with respect to the guide rods by means of tubular rubber bushings.

For a complete understanding of the invention reference may be had to the following detailed description taken in connection with the accompanying drawings of which:

Fig. 1 is a front elevational view of a switch frame showing two switch units or four selector 40 switches embodying the invention installed thereon;

Fig. 2 is a front elevational view of one switch unit;

Fig. 3 is a side elevational View of the switch 45 unit shown in Fig. 2;

Fig. 4 is a side elevational view of the intermediate assembly of a switch unit;

Fig. 5 is a bottom plan view of the intermediate assembly with certain parts omitted to clarify 50 the disclosure;

Fig. 6 is a detail view partly in cross-section of a brush carriage showing the cushioned mounting thereof on the guide rod;

Fig. 7 is a detail view of a modified cushioned 55 attachment of a guide rod to an end plate of the intermediate assembly;

Fig. 8 is a cross-sectional view of the flexible cable guide channels of the switch unit;

Fig. 9 is a front elevational view of the brake magnet and spring pile-up comprising the magnet operated springs and off-normal springs;

Fig. 10 is a side elevational view, partly in cross-section of the brake magnet taken along section lines Ill-l of Fig. 9;

Fig. 11 is a side'elevational view of off-normal spring operating mechanism;

Fig. 12 is a detail view taken along section line I2-l2 of Fig. 11;

Fig. 13 shows the lug-link in the tape belt for controlling the off-normal spring operating mechanism;

Fig. 14 is a side view of the lug-link disclosed in Fig. 13; and

v Fig. 15 is a wiring diagram of the two switches of a unit.

Referring now to the drawings, the switch frame, as disclosed in Fig. 1, comprises two vertical angle-iron uprights l and 2 which may be secured at their lower ends to the floor by angle members 3 and 4 and upper and lower cross members and 6, the upper member 5 being secured by lag screws l to the upper ends oi uprights l and 2 and the member 6 being similarly secured to the uprights l and 2 near their lower ends. The upper cross member 5 serves as a mounting plate to each face of which the upper assemblies 8 of a plurality of switch units 9 may be secured by screws ill. The lower cross member 6 also serves as a mounting plate to each face of which the lower assemblies 8 of the switch units are secured by screws ill. Secured to the upper edge of cross member 5, in any desirable manner, is a horizontal channel member H, the downwardly extending flanges of which are disposed on opposite sides of the cross member 5 and serve to support the torminal jacks l2, there being a jack mounted thereon immediately above each switch unit. A similar channel member 13 is secured to the lower edge of cross member 6 to the upwardly extending flanges of which other terminal jacks l2 individual to the switch units are secured.

Secured between the uprights t and 2, one above the other, are two panel terminal banks !4 and i5. Each bank is of the general type disclosed, for example, in Patent 1,127,741 granted February 9, 1915 to A. F. Dixon and comprises two horizontal side members 16 and il between which a plurality of sets of multiple terminal strips and insulating separators are clamped. The banks are secured to the uprights i and 2 by lag screws I 8 which pass through the ends of the side members 96 and H of the bank. Each terminal strip is provided with thirty multiple terminals extending outwardly therefrom on each side of the bank and with soldering terminals at each end whereby accessibility is offered to thirty selector switch units or sixty selector switches, fifteen of such units being mounted on each side of the switch frame. The terminal strips are arranged in sets of four to which the tip, ring, sleeve and metering leads of subscribers lines may be connected, although in some instances, as for example, when the switch frame is being used for some purpose other than a line switch frame, each set might comprise but three terminal strips. The corresponding sets of multiple terminals of the several sets of strips in both banks are aligned vertically and individualized to different selector switches of the several units 9.

Each switch unit 3 comprises two complete selector switches and to simplify manufacture and assembly is constructed in three separate assemblies, two identical end assemblies 8 and an intermediate assembly l9. Each end assembly comprises a substantially channel-shaped mounting bracket 20, one flange 2| of which is provided with screw holes through which screws may be inserted to secure the bracket to a cross member 5 or 6 of the switch frame. The other flange of the bracket 20 is formed in two sections one of which 22 serves to support the brake magnet and the other of which 23 serves to support the spring pile-up 24.

The ends of flanges 2| and 22 of the bracket 26 are bent inwardly at right angles to form legs 25 and 26 to which the end plate 21 is secured by rivets or other suitable means. Mounted on one side of the web of the mounting bracket is a driving motor 28 having a base plate 33. The motor is preferably of the synchronous reversible type and may be designed to operate on single or polyphase alternating current. The rotor shaft of the motor extends through an opening in the web of the bracket and has on its outer end a pinion 29 which meshes with a gear 30 secured to a driving pulley 3| for driving the tape belt of one switch of the unit. The pulley 3i and attached gear 30 are rotatable on a stub shaft 34 secured to a lug on the base plate 33 of the motor which extends through an opening (not shown) in the web of the mounting bracket. Secured to the web of the mounting bracket on the same side thereof as the motor 28 is a collared stub shaft 35 upon which the idler pulley 35 for the tape belt of the other switch of the unit is rotatably mounted.

Mounted on the flange 22 of the mounting plate is a magnetic brake best disclosed in Figs. 9 and 10. This brake comprises an L-shaped heel-piece 38, the vertical arm of which is secured to the flange 22 by screws 39 which extend through an interposed member 40 channeled as indicated at 4lto permit a traverse of the tape to be threaded therethrough. The core 42 of the magnet, upon which the energizing coil 44 is positioned, lies parallel to the vertical arm of the heel-piece and is threaded through a tapped opening in the horizontal arm of the heel-piece whereby the air-gap between the end of the core and the magnet armature 45 may be adjusted. To hold the core in its adjusted position in the heel-piece the lock-nut 43 is provided. The magnet armature 45 is fastened by screws 46 to a hinge plate 41 having ears 48 through which and the end of member 40, a hinge pin 49 is extended. The hinge plate is also provided with an ear 50 to which one end of the spring 5| is attached. The other end of the spring extends through a hole in an extension 52 of the flange 23 of the mounting plate and is adjustably anchored thereto by a key 53. The hinge plate 41 is also provided with an arm 54 having a member 55 of insulating material thereon cooperating with the springs 56 and 51 of the spring pile-up. With the coil 44 of the magnet deenergized spring 5i holds the member 55 in such a position as to maintain the contact springs 56 and 5'l out of engagement with each other. When, however, the coil is energized, the member 55 moves to such a position as to permit these springs to engage.

Staked into a hole in the flange 22 of the mounting plate and in alignment with the center line of the armature 45 is a cast-iron brake shoe 55 between the face of which and the inner edge of the armature one traverse of the tape 51 is gripped when the armature is in its unattracted position, as shown in Fig. 50. The normal gripping pressure is supplied by the spring 51, the tension of which may be adjusted by moving the end of the spring with respect to the extension 52 of the flange 25. When the magnet coil is energized and attracts the armature 45, the pressure between the inner edge of the armature and the brake shoe 55 is released, thereby freeing the tape for movement.

Secured to the flange 23 of the mounting plate by screws 55 is a plate 55 having two oppositely extending arms 5| and 52. The arm 5| serves as a support for the spring pile-up 24. The spring pile-up includes the brake magnet operated springs 55 and 51, hereinbefore referred to, and the off-normal springs comprising the active or cam operated springs 55 and 54 and the passive springs 55, 55 and 51 cooperating therewith. These springs are all suitably insulated from each other and from the arm 5| of the mounting plate by interposed strips of insulating material and are secured to the arm 5| by screws 55 which pass through the outer clamping plate 55 through the springs and insulating strips into threaded holes in the arm 51. It will be noted by reference to Fig. 11 that the springs 55 and 51 are offset with respect to the oil-normal springs to position them in proper alignment with the insulating member 55 carried by the hinge plate 41 of the magnet armature and to prevent interference with the the operation of the off-normal springs. By mounting all the springs as a unit with the planes of the springs all extending in the same direction or perpendicular to the face of the switch frame, all springs are readily accessible for adjustment.

The arm 52 of the supporting plate 55 is so bent as to be positioned adjacent to the face of the web of the mounting bracket 25. The outer end of this arm is, for the purpose of accurately positioning the arm and the ofi-normal switch operating mechanism carried thereby with respect to the periphery of the idler pulley 55, provided with a hole 15 through which a stud 1i, staked into the web of the mounting plate 25, extends as most clearly disclosed in Fig. 3. The olfnormal switch operating mechanism comprises a U-shaped member 12 pivoted on a shouldered stud 13 staked to the arm 52 and extending through the two arms of the member 12. The member 12 is retained on the stud by a cotter pin 14 extending through the outer end of the stud, a washer 15 being interposed between the cotter pin and the outer arm of the member. The inner arm of the member 12 is provided with pro jections 15 and 11 which engage with the lug 15 bent up from the edge of the arm 52 to limit the rotary movement of the member 12,

Staked in holes in the end of member 12 are two shouldered studs 15 united at their outer ends by a cross-bar 55 on which are rotatably supported two cam rollers 5| of insulating material. These rollers are positioned as shown in Fig. 11 between the springs 53 and 54 of the of!- normal springs ior cooperating with the cam surfaces thereof and in the normal position of the member 12 engage the portions of the springs between the cam surfaces thereof to hold these springs out of engagement with the passive springs 55, 55 and 51. When the member 12 is rotated into the position disclosed in Fig. 11, the spring 54 is cammed into engagement with -sprlng' 51 and spring 55 is permitted by its initial tension to move into engagement with spring 55. When, however, the member 12 is rotated to the other extreme of its movement, at which time the projection 15 thereof engages the lug 15, both pretensioned springs 55 and 54 are permitted to engage respectively with springs 55 and 55.

For rotating the member," in response to the movement or the tape belt in either direction, a notched member 52, preferably of phenol fibre is secured between the arms or member 12 by rivets 55. With the tape belt in its normal position, at which time the brush carriage to which the ends of the tape are secured is positioned with the brush set carried thereby midway between the two panel banks of terminals l4 and l5, 9. luglink 54 interposed in the tape is engagedin the notch in the member 52, thereby holding the member 12 in its neutral position previously described and disclosed in Fig. 3. As disclosed in Figs 13 and 14, the lug-link 54 is secured to the tape by wire links 55. It will be apparent by reference to Fig. 3 that the movement of the tape in a clockwise direction will rotate the member 12 in a counter-clockwise direction to permit the closure of spring 55 with spring 55 and the closure of spring 54 with spring 55 and that the movement of the tape in a counterclockwise direction will rotate the member 12 in a clockwise direction to permit the closure of spring 55 with spring 54 and to cam spring 54 into engagement with spring 51.

To enable the switch unit to be easily installed on or removed from the switch frame without necessitating the soldering or unsoldering of con-- ductors extending to the various elements of the unit, each end assembly 5 of the unit is provided with a plug 55 secured to the mounting bracket of the assembly for cooperation with a jack I. mounted on a cross member of the frame, the plug carried by the upper end assembly being allocated to one switch of the unit and the plug carried by the lower end assembly being allocated to the other switch of the unit. The plug 55 is secured to an angular extension 51 of the web of the mounting bracket 25 as more clearly disclosed in Figs. 2 and 3 and comprises a plurality of springs insulated from each other and provided with soldering lugs to which conductors extending to the electrical elements of a switc of the unit are soldered. When the switch unit is secured in position on the switch frame as disclosed in Fig. 3, the springs of plugs 55 engage with the springs of jacks 12 to which conductors extending to the external control circuits of the switches are connected.

In order that the conductors extending from the springs of plug 55 may be conveniently positioned in the end assembly, a channel member 55 is secured to the web of the mounting bracket 25 by screws 55, as more clearly shown in the lower portion of Fig. 3, in which the conductors are enclosed.

Interposed between the end assemblies of the switch unit is an intermediate assembly I! having two end plates 95 between which the brush carriage guide rods 51 of the two switches of the unit are secured by the screws 92. Screws 52 extend through holes in the end plates into threaded holes in the ends of the guide rods. For attaching the end assemblies to the intermediate assembly lag screws 55 are provided which extend through holes in the end plate 21 of each end assembly into threaded holes in the end plates of the intermediate assembly.

As an alternative construction to prevent thetransmission of vibration from the switch frame to the brush carriage 94 positioned on the guide rod 9|, a sleeve of live rubber may be interposed between the end of the guide rod and the end plate 90 as disclosed in Fig. '7, with the end of the guide rod 9I supported in a hole in one end of the sleeve and the other end of a sleeve supported in a hole in the plate 90. For retaining the guide rod, sleeve and plate.in assembled relationship, a screw 96 having its head hearing through a washer 91 on the surface of the plate 90 is threaded into an axial hole in the end of the guide rod.

The brush carriage 94 comprises a rectangular frame 98 the ends of which are provided with sleeves 99 which slidably embrace the guide rod 9|. Secured to the front side member of the frame 98 by bolts I00 is a channel member IN and a cable supporting arm I02. To the flanges of the member IOI four brush springs I03 to I06, inclusive, are insulatedly secured by screws I01, two brush springs being secured to each flange and extending forwardly on either side of the guide rod. Each spring is provided with a soldering terminal to which terminals the conductors of a flexible cable I08 may be connected. The frame 98 is also provided with ears I09 to which the ends of the tape belt are secured through the interposed shock absorbing and belt tensioning springs H0. The cable supporting arm I02 extends outwardly from the brush carriage with its end turned at right angles and terminating in a cylindrical portion III in which one end of the flexible cable I08 is supported. The other end of the cable is anchored as will be hereinafter described.

A cable is provided for each brush carriage for the purpose of extending conductors to the brush springs thereof while permitting freedom of movement of the brush carriage along the guide rod. Each cable comprises three or more insulated conductors II2 surrounded by a spirally wound wire sheath H3. At the brush carriage end of the cable the conductors thereof are held in position on the arm I02 by tongues H4 and H5 struck up therefrom, are passed through the eyelet II6 and are soldered to the soldering terminals of the brush springs.

For limiting the movement of the brush carriage along the guide rod 95 in the event of failure of the control circuit of the switch to prop erly arrest the movement of the brush carriage in either direction, collars iii are provided on the guide rod on either side of the brush carriage which may be held in adjusted position by set screws II8.

To guide the depending loops of the flexible cables I08 whereby the cables may not become entangled with each other due to the movement of the brush carriages, two sheet metal C=-shaped channel guides II9 and I20 are provided. These channels are positioned back to back and throughout the major portion of their lengths have the cross-sectional form illustrated in Fig. 8. The channels extend between the end plates 90 with the upper end of channel I20 embracing the arm I2I of the upper plate 90 and with the lower end of channel II9 embracing the arm I2I of the lower plate 90 as disclosed in Fig. 5. Positioned within the upper end of channel II9 and within the lower end of .channel I20 are clamping strips I22. The ends of the channels are secured to the arms I2I of the end plates by rivets I23 which extend through the outer flanges and webs of the channels, through, the clamping strips I22 and through the arms I2I as most clearly shown in Fig. 5.

The fixed ends of the two flexible cablesv I08 are secured to brackets I24 positioned within the outer flanged portions I26 of the channels at approximately the mid-point of their length. These brackets are both secured to the webs of the channels by a bolt I25. The depending loops of the flexible cables are guided during movement of the brush carriage by the outer flanged portion I26 and the inner flanged portion I21 of the guide channels.

Positioned in the outer flange channel, is a channel member I28, these members being retained therein by bolts I29 which pass through ears I30 formed integrally therewith and through the webs of the channel guides II9 and I20. These channel members serve to enclose conductors extending between the upper and lower end assemblies 8 and the conductors II2 of the flexible cables I08 extending to either the upper or lower end assemblies as may be required.

In case it should be found desirable to further prevent the transmission of vibrations from the switch frame to the brushes carried by the brush carriages 94, the construction disclosed in Fig. 6 may be employed. As disclosed in this figure, the sleeves I3I positioned in the ends of the brush carriage frame 98 do not slidably engage the guide rod 9I but are connected by tubes I32 of live rubber to auxiliary sleeves I33 which slide on the guide rod. The tubes I32 are cemented or otherwise secured on the sleeves I3I and I33 and serve to resiliently support the brush carriage on the guide rod whereby vibrations of the guide rod are not transmitted to the brushes of the brush carriage.

With the entire switch unit in assembled position, the tape belt 32 of one switch of the unit passes over the driving pulley 3I of the upper end assembly between the brake shoe 58 and the end of armature 45 of the upper end assembly and over the idler pulley 36 of the lower end assem bly and is secured at its ends through the tensioning springs IIO to one of the brush carriages 94. The tape belt 31 of the other switch similarly passes over the driving pulley 3| of the lower end assembly between the brake shoe 58 and the end of armature 45 of the lower end assembly, thence over the idler pulley 36 of the upper end assembly and is secured at its ends through tensioning springs I I0 to the other brush carriage. The brake mechanism of the upper I26 of each guide end assembly and the off-normal switch operating mechanism of the lower end assembly coomrate with the belt 32 and the brake mechanism of the lower end assembly and the off-norrnal switch of the upper end assembly cooperate with the belt 31.

The wiring diagram of the assembled unit as disclosed in Fig. 15 schematically illustrates in the upper portion thereof plug 86, motor 28, brake magnet coil 44, the brake magnet operated contact springs and the off-normal springs of the upper end assembly and in the lower portion thereof the corresponding equipment of the lower end assembly. The magnet coil 44, the contact springs 56 and 5'! controlled thereby, motor 28 and off-normal springs 66 and 61 of each end assembly are interconnected or connected to terminals of plug 86 individual to the assembly by local conductors. To the other terminals of the plug 86 and to the off- normal springs 63, 64 and 65 of each end assembly are connected conductors which are run through the channel member 88 individual to the assembly and are then divided into two groups one of which is run through one of the channel members I28 located in channel guide H9 and the other of which is run through the other channel member I28 located in channel guide I20. Some of these conductors then extend through the channel member 88 of the other end assembly to equipment in such assembly, while other conductors extend through the flexible cable I08 to the brush springs of one of the switches of the unit.

The external circuits for controlling the switches of a unit have not been disclosed but might be of the type disclosed in the patent granted to W. W. Carpenter and R. F. Mallina hereinbefore referred to.

What is claimed is:

1. In a selector switch having two banks of terminals, a brush set cooperating therewith normally positioned midway between said banks and a belt for traversing said brush set over either one of said banks, a double-throw off-normal switch and a member secured to said belt engageable with said off-normal switch when said brush set is in its normal position for holding said off-normal switch in its neutral position and for moving said ofi-normal switch into one or the other of its operated positions dependent upon the direction of movement of said brush set.

2. In a selector switch having two panel banks of terminals, a brush set cooperating therewith normally positioned midway between said banks and a belt for traversing said brush set over either one of said banks, a double-throw off-normal switch comprising a movable spring, a fixed spring on either side thereof, a pivoted actuating member engageable with said movable spring to move it into engagement with either one of said fixed springs, said member having a notch in one end thereof and a lug secured to said belt engageable with said notch when said brush set is in its normal position for holding said member in its neutral position and for rotating said member in one or the other direction to engage said movable spring with one or the other of said fixed springs dependent upon the direction of movement of said brush set.

3. In a selector switch having two panel banks of terminals, a brush set cooperating therewith normally positioned midway between said banks and a belt for traversing said brush set over either one of said banks, a double-throw off-normal switch comprising a movable spring having cam surfaces thereon, a fixed spring on either side thereof, a pivoted actuated member having a cam roller engageable with the cam surfaces of said movable spring and having a notch in one end thereof and a lug secured to said belt engageable with said notch when said brush set is in its normal position for holding said member in its neutral position and for rotating said member in one or the other direction to cam said movable spring into engagement with one or the other of said fixed springs dependent upon the direction of movement of said brush set.

4. In a selector switch having two panel banks of terminals, a brush set cooperating therewith normally positioned midway between said banks and a belt for traversing said brush set over either one of said banks, a double-throw off-normal switch comprising first and second pretensioned springs each having cam surfaces thereon, a fixed spring on either side of said first spring and a fixed spring associated with said second spring, a pivoted actuating member having cam rollers engageable with the cam surfaces of said pretensioned springs to control their engagement with their associated fixed springs, a notched member secured to said actuating member and a lug secured to said belt engageable in said notch when said brush set is in its normal position for holding said operating member in a neutral position in which said springs are all maintained out of con tact with each other and for rotating said operating member in one direction to permit the engagement of said first pretensioned spring with one of its fixed springs and the engagement of said second pretensioned spring with its associated fixed spring and for rotating said operating member in the other direction to cam said first pretensioned spring into engagement with the other fixed spring associated therewith and to permit the engagement of said second pretensioned spring with its associated fixed spring dependent upon the direction of movement of said brush set.

5. A switching device comprising a mounting frame, two panel banks of terminals mounted thereon and a switch unit mounted on said frame, said unit comprising two end brackets attached to end members of said frame, a guide rod, the ends of which are secured to said brackets, a brush carriage slidable on said guide rod and carrying a brush set cooperating with said banks, said brush set being normally positioned midway between said banks, a belt for traversing said brush set over either one of said banks, a driving pulley for said belt mounted on one of said brackets, an idler pulley for said belt mounted on the other of said brackets, a double-throw off-normal switch mounted on one of said brackets and a member secured to said belt engageable with said off-normal switch when said brush set is in its normal position for holding said off-normal switch inits neutral position and for moving said elf-normal switch into one or the other of its operated positions dependent upon the direction of movement of said brush set.

6. In a switching device comprising a mounting frame and a terminal bank mounted thereon, a selector switch unit embodying two selector switches comprising identical first and second end assemblies and an interconnecting intermediate ,assembly, said intermediate assembly comprising for each of said switches a brush carriage having a brush set thereon for cooperating with the terminals of said bank and a guide rod on which said carriage is slidable, and each of said end assemblies comprising a driving motor, a driving pulley geared thereto and a brake magnet for one of said switches and an idler pulley and off-normal switch for the other of said switches, a driving belt for one of said switches extending around the driving pulley of the first of said end assemblies around the idler pulley of the second end assembly and attached to one of said brush carriages and a second driving belt for the other of said switches extending around the idler pulley of said first end assembly around the driving pulley of said second end assembly and attached to the other of said brush carriages.

'7. In a switching device comprising a mounting frame and a terminal bank mounted thereon, a selector switch unit embodying two selector switches comprising identical first and second end assemblies and an interconnecting intermediate an switch the other on said bracket, means sci" securing the end plates of said end ssemblies rescectively to the end plates of tern-1e te assembly, a belt one 01 said st" ches extending around the driving pulley oi the first of said end as semblies around the idler pulley of the second end i mounting iounted thereon, a .bodying two selector switches comprising ide tical first and second end erccnnecting intermec assemblies assembly, said for each of sea a brush set tnereon for with the ter Initials of said a guide rod on which said carriage slidable, and each of end assemblies com, ing a ving motor, driving pulley geared tnereto a o a brake magnet or one of said switches and an idler pulley and oilnormal switch for the other of. said switches, a driving belt for one of said switches extending around the driving pulley of the first of said end assemblies around the idler pulley of the second 7 assembly and attached to one of said brush carriages, a driving belt for the other of said switches extending around the idler pulley of said first end assembly around the driving pulley of sa d second end assembly and attached to the other of said brush carriages, channel ducts secured to each of said assemblies and conductors for interconnecting the apparatus of said assemblies ex tending through said ducts.

9. A switching device comprising a mounting frame, a panel bank of terminals mounted thereon and a switch unit mounted on said frame, said unit comprising two end brackets attached respectively to the end members or" said frame, a brush carriage having a brush set thereon for cooperation with the terminals of said bank, guide rod extending between said brackets upon which said brush carriage slidaole and sleeves rod GIZ'lZsilC. rush carriage h carriage co "iiig openings a its ends throug rod extends, a set mounted thereon for cooperation who bani; terminals,

sleeves for carriage s giude rod and sleeves oi resilient material surrounding said guide rod inteioosed between said bearing sleeves ends of said frame for cushioning said brush set from vibration i. parted to said guide rod.

In a switching device comprising a mount-- frame and a pa el bani: oi terminals mounted tnereon, a switch t tv mounted on said frame prising two end oraclzets attached respectively to the upper lower cross members of said frame, a vertically disposed guide rod extending setweezi each said JEECEEGl/S, brush CELL. sliclable on e rod having a b1? .-et cooperating with bani: of terminals, a flea isle cable conduc ors use eh of which. is se-- cured a stationary portion or switch unit and the other end or" wllch is secured to said brush set and a channel guide extending between said brackets which the depending loop oi cable is retained whereby lateral swaying oi said cable loop incident to movement of said brus set is obviated.

12. lo a switching device comprising a mount-- ing frame and a panel bank of terminals mounted thereon, a switch unit -cunted on said frame comprising two end bract ts attached respectively to the upper and lower cross members of said frame, two vertically disposed guide rods said gular frame och. said extending between said brackets, a brush carriage sliclable on each of said guide rods and having a brush set cooperating with said bank of tor-- minals, two flexible cables of conductors individual respectively to said brush sets, one end of each cable being connected to one of said brush

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