US2894096A - Rotary switch - Google Patents

Description

July 7, 1959 G. H. SCHACHT 2,394,096

ROTARY SWITCH Filed June 25, 1957 4 Sheets-Sheet 1 ll H INVENTOR. GUNTERI H. SCHACHT ATTY.

July 7, 1959 s. H. SCHACHT ROTARY SWITCH 4 Sheets-Sheet 2 Filed June 25, 1957 L Ifllavl'l... I I l I] I i I I ll BWANW WU INVENTOR. )f" GUNTER H. SC CHT ATTY.

July 7, 1959 Filed June 25, 19s? G. H. SCHACHT ROTARY SWITCH FIG. 7

' 4 Sheets-Sheet 5 INVENTOR.

GUNTER H. SC ACHT 'YfQ I ATTY.

July 7, 1959 G. H. SCHACHT 2,894,096

ROTARY SWITCH Filed June 25, 1957 4 Sheets-Sheet 4 F l G 9 FIG. 13

IIIIIHIII lll lllll 55 fi====== 63 f:

.5 H H 65 5 H 2 52o 52w 52 52X FIG I IG. IO 52 INVENTOR.

GUNTER H. SCHACHT BY 6 a) ATTY.

United States Patent ROTARY SWITCH Gunter H. S'chacht, Vestal, N.Y., assignor to General Telephone Laboratories, Incorporated, Chicago, 111., a corporation of Delaware Application June 25, 1957, Serial No. 667,933

12 Claims. (Cl. 200-105) 1 The present invention includes many of the features shownin such patents as 2,522,715 and 2,710,896 both issued to K. W. Graybill, et al. dated respectively September 19, 1950 and June 14, 1955. These patents show the general construction of a rotary switch and its mechanisms; however the present application, of course, has many features not included in these patents which features will be'pointed out and amplified.

'A major object of the present invention is to provide a switch having its driving pawl and holding detent each formed from a length of music wire into U-shaped element.

Another object of theinvention is to provide a ratchet wheel to be contacted by these U-shaped elements, which wheel is molded or machined from fabric base phenol, linen bakelite or nylon material. Further, between each of the teeth of the wheel is formed separated by a U-groove to firmly nest the music wire elements.

A further'object consists in the use of hook shaped metallic wiper arms molded as part of the wiper assembly.

To each of these arms may be attached demountable individual wiper tips which can be firmly locked into place and yet be readily removed if required.

- Another object resides in the use of an armature bearing pin of simple, loose tolerance construction. This is accomplished by welding the bearing pin directly to the armature and providing a pie-stressed leaf spring or shim as one of the surfaces in contact with the bearing pin. Thus the only surface of the hearing which will be subject to wear is the surface of contact with the holding bracket or yoke.

A major feature of the invention consists-of the use of a solid semi-circular conductingring bonded to each bank level insulator. Through the use of twin contactors on the wiper tip, one of which contacts the ring and the other the successive terminals of the level, a

circuit is completed from the terminals to the ring con-.-

The usual wiper brush arrangement for :com-

ductor. pleting the series circuit is therefore unnecessary.

Another feature of the invention consists of forming a series equally-spaced, raised elliptical prisms on each level insulator during the insulator for blanking operation. The raised prisms serve as a means forpositioningthe terminals of the level in assembly. In operation, the prisms serve as a means for maintaining a level path of travel for the wiper tips across the normal valleys between the contacts. I

These features, objects and many others will become apparent when reviewing the drawings. Fig. 1 shows a side view of the switch as assembled and Fig. 2 shows a top view. Fig. 3 shows thedriving mechanism of the switch while Figs. 4, 5 and 6 show in more detail some of the elements in the construction of the armature assembly of the driving mechanism. Fig. 7 shows a representative bank level with some of the contacts shown in detail so that the construction of a bank level may be more clearly understood. Figs. 7a and 7b show in detail the section of a typical contact. Fig. 8 shows a typical bank spacer or insulator. Fig. 9 shows generally the construction of a wiper assembly. Fig. 10 shows in more detail the wiper to bank contact relationship. Fig. 11 shows a wiper arm and Fig. 12 a wiper tip in position for mounting to the wiper arm of Fig. 11. Fig. 13 shows an end view of the wiper of Fig. 12.

In more detail the switch will be analyzed by component units as. follows: first, the driving mechanism; second, the driven mechanism (wiper assembly) and third, the stationary or bank assembly. The operation of the switch will complete the description.

Driving mechanism The driving mechanism generally consists of a motor magnet and armature assembly. As shown in Figs. 1, 2 and 3, the operating coil 33 is provided with an inverted U-shaped coil core 32. One leg of the U extends through the center of the coil and the other leg serves as a heelpiece. By the use of this type of core, the number of air gaps-in the magnetic circuit is reduced and a more eflicient magnetic path is produced.

The armature assembly is indirectly pivoted to the heelpiece leg of core 32. This pivoting is accomplished by the use of yoke 35 which is mounted to core 32 by using standard round head screws. At its lower end the yoke has an open semi-circular section to retain the armature bearing pin- 36 in place. Bearing pin 36, which is shown in more detail in Fig. 4, is spotwelded to the projections of armature bracket'34- To complete this end of the assembly a shim or leaf spring 37 is mounted between the core 32 and bearingpin 36. This spring is pre-stressed so that it maintains pressure against bearing pin 36. The shim is mounted under the screws which retain yoke 35 to the heelpiece leg of core 32 and maintains bearing pin 36 away from-contact with the core leg 32. 1 Armature bracket 34 is of a magnetic material so that it will be drawn into contact with the coil leg of core 32 on energization' of the coil 33. This energized position is the one shown in Fig. 3.

Attached to the armature bracket 'by screws .44 is I the armature, extension 31 which will be called the arma ture hereinafter. The. armature is a channel shaped length of aluminum or other light weight material. The channel shape and the light weight material are combined to produce an armature having a low mass for the length necessary. Along the'length ofthe armature toward its free-end is mounted pawl bracket 38. Held, in placeagainst this bracket 38 by holder 39 and leaf-springl42 is the driving pawl 40. This pawl is mounted astraddlethe armature as shown in Fig. 5. This pawl 40-is made of a single length of music wire formed into the shape shown. By using -music. wire, three or more effects are achieved. First, the pawl can be mounted in a simple arrangement as shownin Figs. 3, 5, and 6 and no bearings.

, are necessary. ;Second, since the music wire isia high ping pawl 41 whose transverse width, is aboutequal to,

gradespring steel, it isrigid yet has inherentspring serves a secondary purpose by serving as the actuator for interrupter springs 43 which may be provided as required.

At the outermost tip of armature 31 is secured stopthe width of armature 31. By this construction th e s'tOp ping pawl has enough width to engage the entire face of a tooth on the ratchet wheel and thus minimize wear on the teeth. A backing rod 45 which has tapped holes to accommodate holding screws 46, one of which is shown in Fig. 3, is mounted through the channel armature substantially as shown, to hold stop pawl 41.

In viewing Fig. 2, it can be seen that the center-line 47 of coil 33 and core 32 coincides with the center of action of the armature, its driving pawl, the hold detent, and the effective center of the contacting teeth. By this construction a direct straight line linkage is used which allows a maximum of the developed energy to be trans mitted into effective work.

Driven mechanism The driven mechanism or wiper assembly contains the ratchet wheel, the rotary shaft, the wiper block carrying the wiper arms and the wiper tips. These elements are shown in Figs. 1, 2, 3, 9, 10, 11, 12 and 13. The ratchet wheel 54 consists of a circular disc of nylon, linen or other fabric base phenolic material. Along its periphery are formed by machining or molding 102 equally spaced teeth 56, 56a, etc. having the shape shown in Fig. 3. The shape shown includes a rearward- 1y sloped leading face and a radial trailing face on each tooth. Between successive teeth are U grooves having a sufiicently large circular section to fully nest driving pawl 40.

At the center of the wheel 54 is a shaft 55 about which the wheel is driven (shown in Fig. 9). The shaft 55 has the wheel end threaded and has a spacing ring nut 61 placed inward of the threaded portion. At the opposite end of shaft 55 is a recessed slot outward of which the shaft has a smaller diameter faced surface.

The wiper block 51 is a molded rectangular solid through the center of which has been molded bushing 58 of suitable bearing material. The bushing has a series of circumferential oil grooves on its inner surface to circulate the shaft lubricant. A pair of studs 59 are also molded into the block. These studs have radial holes tapped in their side to receive screws 64 which are used to mount ratchet wheel 54 and metallic spacer 60 to the wiper block. Shaft 55 protrudes through the far end of wiper block 51 and retaining ring 57 slides into the shaft recess locking the shaft in position to the wiper block.

Also molded into block 51 are extension wiper arms 52 a, b j and k. These arms are aligned in pairs along the length of the block. These arms are embedded such that emboss 65 as shown in Fig. 11 is facing rearward in the direction of rotation of the ratchet wheel. An identical second set of wiper arms 52 m, n y and z protrude from the opposite end of the block. These also have embosses 65 facing rearward in the direction of rotation. Each of these extension arms is insulated from all the remaining arms on the block by means of the material in the block proper. In the present embodiment sixteen levels can be accommodated. With minor revisions more or less wiper levels could naturally be provided.

Referring to Figs. 11 and 12 can be seen a representative extension arm 52 and wiper tip 53. Emboss 65 on arm 52 is faced rearwardly in the direction of rotation of the ratchet wheel. Arm 52 has a hook shape which can readily be squeezed by pressure on boss 65. The wiper tip 53 has a notch 66 which is of proper size to retain boss 65. The wiper tip is slid onto the extension arm until boss 65 catches in notch 66 to lock the tip onto the arm. The outer end of the wiper tip has a pair of bifurcated contactors 67 and 68 which are pre-tensioned to the approximate shape shown in Fig. 13. These wiper tips may be detached individually by squeezing boss 65 on arm 52, toward the back surface of the arm and the wiper tip may be slid off the arm.

-As can be seen in Fig. wiper tips are of two basic shown as 53a and that shown as 53b. The

difference between these is simply that one, 53a, is made for contact on its left side and the other, 53b, for contact on its right side. With this exception, the wipers are otherwise identical.

As shown in Fig. 2, each wiper arm contains a wiper tip. This assembly is used for 16 levels of 50 points each. For eight levels, points operation, alternate wiper tips on each end of the wiper assembly are removed. An example of this would be to remove alternate Wiper tips such as 53a, 53n 53 53z. With the replaceable wiper tips of the present invention the switch could be changed from 50 point to 100 point operation by removal of the wiper tips as exemplified above, or in the reverse direction from 100 point to 50 point by the addition of these wiper tips and proper wiring of the bank to agree.

Stationary assembly The stationary assembly consists of the contact bank levels of the switch and the stationary frame mechanism The bank assembly is composed of a number of pairs of levels of arcuate rows of bank contacts. Each pair of levels may be considered as including a right hand level and a substantially identical left hand level. Each level consists of a number of contacts equi-angularly spaced, as shown in a representative manner in Fig. 7. The general shape of the contacts may be seen in this figure also. A contact such as 94b consists of an inner contacting portion, a holding body having holes 98 and the outer terminal leg. The holes 98 along circumferential band it of Fig. 7 are holes which are pierced to form a ragged shoulder or edge as is shown in Fig. 7b. The contacts are placed in the proper alignment on an insulator 95 which extends past the contacting portion of the contacts. The contacts are then squeezed onto the insulator, the ragged edge firmly embedding the contacts into the insulator.

In Fig. 7 may also be seen elliptical prisms which are formed into the structure of the insulator when the insulator is being blanked. These prisms have a height slightly lower than the height of a contact. The contacts in assembly are placed between the prisms. The minor diameter of the ellipse is substantially the proper between-contact distance so that when the contacts are placed on the insulator, they are automatically spaced evenly.

A secondary purpose of these elliptical prisms is to provide a raised section between successive contacts in the path of travel of a wiper. Thus the valleys between contacts are eliminated and a level path of travel of the wiper tips across the contacts is insured. In this way the constant flexing and stressing of the wiper tips across contacts is relieved, adding to the life expectancy of the wiper tips Each level insulator has bonded thereto a semi-circular conducting ring 97 whose inner circumference is coplanar with the inner circumference of the insulator. This feature may be seen more readily in Fig. 10. This conducting ring terminates in terminal leg 94x at its upper right extremity. For this reason the level of Fig. 7 would be considered a right hand level. A left hand level would be identical to this with the single exception that a left handed level would have its conducting ring terminating leg at the upper left hand extremity of the level.

To explain a switch bank, it should prove easier to assume a switch being built vertically'with a final result as shown in Fig. 2. To start, end frame 92 is placed in the position shown in Fig. 2 with the screws 87 shown in Fig. l placed in the holes. then placed on the frame with screws 87 extending through the spacer holes 104. Next a left handed level would be placed on the screws 87 with the contacts down so that the conducting ring terminal is at the left side of the assembly. Next a right handed level is placed with its contacts up. A spacer 96 follows,'then another lefthatidi Insulator or spacer 96 'is level, a right hand level, a spacer, etc. until the required number of levels have been included.

Fig. shows a section B from Fig. 2. This section shows in cross section the first regular contact in the bank. Shown in the drawing are a lower spacer 96g, a right hand level including contact 94g, insulator 95g and conductor ring 97g. Above this is a left hand level includ ing insulator 95 contact 94 and conducting ring 97f with spacer 96f and steel bracket 99 atop the assembly. Bracket 99 is essentially the same shape as spacer 96; however the holes, corresponding to 104 on spacer 96 are tapped in steel bracket 99 to receive screws 87. The bank assembly is then tightened and squeezed to comprise a unit having its outer surfaces steel bracket 99 and end frame 92.

To mount the bank to the switch, a spacer 101 is used to space the bank a suflicient distance from outer frame 91 and keep the bank from interference with ratchet wheel 54. The bracket 91 serves as the side frame of the switch at the coil side and is mounted to the bank by means of a series of screws received in tapped holes on steel bracket 99. By the removal of these screws, the bank assembly may be dismounted from the switch frame without disturbing the alignment of the coil side frame 91 and the remaining switch elements.

Stationary frame assembly The stationary frame 81 consists of the mounting to which the coil core and the remainder of the switch elements are mounted. Reinforcing brackets may be added wherever needed to further support the armature assem bly and maintain the proper relative position of the integral units of the switch. The use of a reinforcement such as mentioned would not add patentably to the features shown however. As shown, the stationary frame 81 has mounted to it an interrupter spring pileup 43, operative on movement of the armature as reflected through bracket 38. The frame further contains the backstop and adjusting screw 82 for driving spring 84. Spring 84 is a frusto-conical coil spring of the type frequently used in indirect drive switches as the main operating spring. An arm 85 is provided on the stationary frame for mounting the hold detent spring 86. This detent or dog is made up of a U-shaped length of music wire of somewhat lesser diameter of the driving pawl 40 but having the same basic shape.

Operation As in the operation of any electromagnetic switch, a pair of direct current leads must be provided for the coil. Means for interrupting the direct current must also be provided and these means can be the interrupter springs 43 of the switch.

When the current is applied to the coil 33, armature bracket 34 which is of magnetic material is drawn up against coil core 32 to complete the magnetic circuit. Armature 31 is thereby drawn up compressing spring 84. Stopping tooth 41 is drawn out of contact with ratchet wheel 54 and driving pawl 40 is lifted out of contact with the tooth with which it has been engaged. Pawl 40 is pre-stressed toward the ratchet teeth so that on energization of the motor magnet, the pawl drops into the groove behind the previously engaged tooth.

It should be noted that the gear teeth of ratchet 56a, etc. have a sloped leading edge so that the pawl 40 may slide out of engagement smoothly. Further the groove diameter between the teeth is roughly comparable to the pawl diameter so that the pawl nests comfortably at the base of the groove. Hold detent 86 maintains the ratchet wheel at rest by holding the tooth with which it has been in contact. This is the condition of the switch in Figs. 1 and 3.

When the armature is drawn up, the pawl bracket 38 causes the spring of pile up 43 to break, opening the circuit to coil 33 (assuming self-interrupted operation).

The armature is released due to spring 84 discharging its compressed force. Pawl 40 is forced against the radial trailing edge of tooth 56 and pushes the ratchet wheel forward. When a finite angle of revolution has passed, stopping tooth 41 mates with the tooth adjacent its prior position, stopping the motion of the ratchet wheel. The relationship between the driving surface (the base of the U of the pawl 40 and the tip of stopping tooth 41 is such that one tooth and only one tooth is passed before stopping tooth 41 is engaged with ratchet Wheel 54. Hold detent is slid out of its contact during this movement of the wheel and falls into the next groove.

A circuit is then completed between ring conductor such as terminal 94x, ring conductor 97, wiper tip ground arm 67, wiper tip 53, contact arm 68 to the contact such as 94m as shown in Fig. 1. Successive steps are made in the same manner to traverse the bank contacts sequentially.

What is claimed is:

1. In an indirect drive rotary stepping switch, a rotatable wiper assembly and driving means for rotating said wiper assembly, said driving means including an energizable electromagnet, an armature actuated in response to energization of said electromagnet, a driving pawl secured astraddle said armature, said driving pawl comprising a U-shaped length of longitudinally stifi, transversely flexible music wire, said rotatable wiper assembly including a ratchet wheel having a plurality of teeth spaced equally around its periphery, the base of said U-shaped driving pawl being impelled against one of said teeth on deenergization of said electromagnet to cause said ratchet wheel to rotate, means for holding said ratchet wheel stationary between impellations of said driving pawl, said holding means comprising a U-shaped length of music Wire disposed to contact said wheel between said teeth, means coupled to said driving pawl for stopping said ratchet wheel after said wheel has rotated through a predetermined acute angle, said coupled means comprising a rigid tooth, said driving pawl compensatorily flexible for misadjustments in said tooth-to-pawl distance when said ratchet wheel is stopped by said rigid tooth.

2. In a rotary stepping switch having a frame, a plurality of contacts aifixed to said frame, said contacts arrayed in a plurality of arcuate tiers, each of said contacts having an individual external terminal, each of said tiers having an equally spaced, identical plurality of said contacts, each of said tiers having associated therewith a solid arcuate sector of a conducting ring, a rotatable wiper assembly axially mounted to said frame, said wiper assembly having a plurality of pairs of opposed contacting arms, each one of said contacting pairs of arms being adjacent a different one of said tiers, each of said arms detachably bearing a pair of conductively connected wiper tips, one of said pair of tips capable of conductively contacting the contacts in the said adjacent tier, the other of said pair of tips capable of contacting said conducting ring, a terminal connected to said conducting ring, driving means for rotating said wiper arms in a series of steps, each of said steps comprising a finite sector of a circle, said sector of circumferential are equal to the spacing between the contacts in a tier, said one wiper tip consecutively contacting the contacts adjacent said wiper arm on said steps, said other wiper tip on contacting said ring sector completing from said conducting ring sector terminal, through said conducting ring sector, said other wiper tip, said one wiper tip to consecutive contacts and their external terminals.

3. In a rotary switch having a frame with a plurality of arcuate rows of equally spaced terminals secured to said frame, means axially linked to said frame for rotating in a series of finite steps to traverse said terminals, said axial means comprising a base unit, a plurality of hook shaped arms parallelly aligned in said base, each of said arms individually adjacent one of said rows of terminals, each of said arms having a shoulder outwardly embossed at'the tipofsaid hook'shaped arm, individual contacting means removably mounted in a slidable manner to each of said'arms, each of said contacting means having a notch therein for encircling said shoulder thereby cooperatively locking said contacting-means to said arm, each of said contacting means disposed to conductively contact consecutively the individual terminals in a row during saidseries of finite steps.

4. In a rotary stepping switch, an electromagnet, an armature of magnetic material and a wiper assembly, said electromagnet comprisinga U-shaped coil core and a coil disposed around one leg of the -U-shaped core, means pivotably securing saidarmature to'the other leg of said U-shaped core, said pivotable means comprising a cylindrical ax-le welded to saidarmature-and a bracket secured to said other leg for holding said axle, said bracket restrictingsaid axle to'rotati-ve motion, said axle restrained to rotation through a predetermined arc, a channel shaped member mounted cooperatively with said armature, said wiper assembly comprising a rotatively mounted ratchet wheel having aplurality of teeth equally spaced along its periphery, pawls aifixed to the channel member for engagement with the teeth of said ratchet wheel, saidelectromagnet energizable to attract said armature against said one leg of the coil core, said channel member'controlled by said'pivotingto draw said pawls out'of engagementwith the teeth of said ratchet wheel, spring means compressed by the energization of said magnet and restored responsive to the deenergization of said electromagnet for driving said pawls into contact withsaid ratchet thereby causing said-wiper assembly'to rotate through a predetermined angle of revolution.

5. In a rotary switch, a stationary frame having a semi-circular terminal bank mounted thereto, said bank comprising a plurality of pairs'of levels,-each level including an inner arcuate conducting band and an outer band having a plurality of equi-angularly spaced contacts, means for insulating each of said contacts from the remaining contacts and from the conducting bands, each of said levels having enantiomorphic relation to the next adjoining levels, means for simultaneously connecting a contact in each level and the conducting ring of the same level, said connecting means comprising an individual wiper for each of said levels, each of said wipers individually detachably mounted to a rotatable member,

each of said wipers sequentially contacting the contacts.

ofzsaid level on rotation of said rotatable member.

6. In a rotary stepping switch, a motorrnagnet having an energizable electromagnetic coil integral thereto, an armature pivotably mounted to said motor magnet, a rotatable ratchet wheel having a plurality of teeth,,said armature having means for tactually engaging teeth of said ratchet wheel, said engaging means slidably moved across a tooth of said wheel on energization of said-coil, said engaging meanstimpellably forced against a tooth of said wheel on deenergization of said core to cause said wheel to rotate through a' predetermined are, said motor magneticoilhaving a plane through its centerline at which plane themagnetic effect of said coil is a maximum, said armature having its centerlinecoplanar with said centerline plane, said engaging means having a centerplane of action incommon with the center plane ofaction of said teeth, said center planes and center lines coplanar with the center plane of saidelectromagneticcoil.

'7. In a rotary stepping switchcomprising a stationary frame, a motor magnet and a rotating wiper assembly, an armature pivotably mounted to said magnet, means forzrotating said wiper assembly in a step-by-stcp man ner, said rotating means comprising a driving pawl secured to said armature and a ratchet wheel having a plurality of teeth, said driving pawl comprising a U-shaped length of music wire, grooves between the teeth of said ratchet for receivingsaid driving: pawl, each of said grooves having a substantially circular bottom fornesting said driving pawl, holding means mounted to said frame, said holding-means comprising a U-shaped* length of music Wire, the wire of said-holding means beingmeans thereafter slidable across-:the teeth of said wheel,

further means afiixed to said armature and having a predetermined spatial relation to said driving pawl'for stopping the rotation of said ratchet-wheel after a predetermined arc of revolutionhasbeen completed, said holding means thereaftennesting in a round groove of said ratchet wheel and holding said wheel stationary.

8. In a rotary stepping switch, adriving means for producing reciprocating motion, rotatable 'meansdriven by said reciprocating means and a stationary assembly holding both saidprior mentioned means, saidreciprocating motion impartedtoa driving pawlintegraltosaid driving means, said driving pawl comprising a prestressed fU formed length of steel wire, said pawlsequentially contacting the respective teeth of a ratchet wheel to:rotate said wheelthrough a predetermined arc on'each. of saidreciprocating cycles, said rotatable means including said ratchet wheel and-a wiper block coupled thereto to rotate in conjunction with said wheel, .said stationary assembly having a .U formed length ofsteelwire for holding said wheel stationary between said are rotations, said wiper block havingia first plurality of arms protruding therefrom in aligned array, a second pluralityof arms aligned opposite said firstplurality of arms, each of said arms electrically insulated fromithe remaining of said arms, each of said'arms having a substantially recurved extremity and a shoulder at the tip of said recurve, individual bifurcated contacting means each having a sleeve section 'for detachably mounting to the recurved extremity of one of saidarms, each of said sleeve sections having a slot thereinfor receivingtheshoulder of the 'arm, said shoulder and slot combinedlydocking said sleeve'to said arm,,said recurve manually compressible "to remove said sh'oulderfrom said slot'to release said contacting means, a plurality'of arcuate rows of contacts, each of said rows tactually adjacent one of said contacting means, each of said rows of contacts'havinga solid conducting semi-circularring radially inward thereto, each of said contactingmeans capable of completing a circuit from the ringto individual contacts of the adjacent row,=each' or said-contacting means advancing to successive contacts within arow on each of said reciprocating cycles of said driving means.

9. In a stepping switch comprising a wiper assembly and stepping means for operating saidassembly in successive stepping operations, said assembly comprising a main bodyportion, wiper arms and wiper tips detachably mounted on said wiper arms, said-wiper arms each having a portion thereof molded in said body; portion and a free endextending longitudinally therefrom, said wiper arms each having atdiagonal slot in the .free ends thereof forming acompressible hook, a protuberance on said hook, said wipertips each comprising a pair of wiper fingers on-one-endand a channelportion at the other end slidably positioned on a wiper arm, and a slot in* said channel portion of each said wiper tip cooperatingwith aprotuberance on one of said wiper arms for detachably lockingawiper tip to a wiper anm, said slot in-saidhook permitting manual depression of said protuberance and compression of said hook to enable manual removal of a wiper tip from a wiper arm.

10. In a rotary switclna contact bank having a plurality of levels of equi-spac'ed contacts, each of said levels having an insulator on which said contacts are arrayed in an arcuate path, a wiper individual to each of said levels movable across the level to tactually engage successive contacts, means integral to each of said levels for maintaining said wiper movement substantially' in a plane parallel to the level, said maintaining means comprising a series of raised elliptical prisms along the wiper movement path, one: of said prisms located betweeneach of said contacts, the minor diameter of said elliptic prisms covering substantially the transverse spacing between said contacts in the movement path, said prisms further providing insulation between successive contacts of a level.

11. In a rotary stepping switch, a plurality of arcuate levels of stationary contacts, a wiper assembly having a central core, means for rotating said assembly in a step by step manner, a motive wiper set tactually adjacent each of said levels, each of said motive Wipersets having a sleeve extremity, a series of protruding arms extending from the central core of said wiper assembly, means on each of said protruding arms for mating with one of said sleeve extremities to firmly hold the motive wiperset in position to tactually engage stationary contacts of the adjacent level, each of said arm means individually compressible manually to release the sleeve and thereby release the wiperset held thereon.

12. In a rotary stepping switch, a plurality of levels of axially aligned contacts, the contacts of each level spaced to comprise a semi-circular sector, each of said levels having a solid annular conducting band within the 10 sector of and coplanar to the contacts of the levels, conductive means for completing a circuit from a contact on a particular level to the conducting band of that level, said conductive means comprising a first contactor adjacent the contact, a second contactor adjacent the conducting band and a conductive path therebetween, means external to said completed circuit for rotating said conductive means to cause said second contactor to sequentially traverse successive contacts on that level, said rotating means including a Wiper block having a plurality of arms extending outwardly in one direction from said block, each of said arms having mounted thereto a wiper assembly including said conductive circuit completing means.

References Cited in the file of this patent UNITED STATES PATENTS 1,388,541 Woodbury Aug. 23, 1921 2,559,075 Horlacher July 3, 1951 2,600,938 Thierfelder June 17, 1952 2,699,468 Unk Jan. 11, 1955

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