US3770921A

US3770921A - Snap-action switch

Info

Publication number: US3770921A
Application number: US00262052A
Authority: US
Inventors: L Wilbrecht
Original assignee: L Wilbrecht
Current assignee: MIDWAY NATIONAL BANK OF ST PAUL
Priority date: 1972-06-12
Filing date: 1972-06-12
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06

Abstract

A snap-action slide switch for micro-circuitry incorporates a slidable drive plate for closing the switch contacts in a quick, positive manner by means of a slide actuator which picks-up the drive plate and rapidly moves it to a contact closing position at the exact instant that the slide actuator is snap-released by detent springs positioned in its slide path. The location and configuration of contact engaging shoulders on the drive plate may be selectively changed so as to permit a plurality of circuits to be closed in a desired sequence and combination.

Description

O United States Patent 1 1 [111 3,770,921 Wilbrecht Nov. 6, 1973 y SNAP-ACTION SWITCH [76] Inventor: Lester L. Wilbrecht, 45 Mid Oak Pmnary Emmmer DaY1d.

Ln St. Paul, Minn 55113 Attorney-George F. wllhamson et al.

[ PP 262,052 A snap-action slide switch for micro-circuitry incorporates a slidable drive plate for closing the switch con- [52] CL 200/68 200/16 200/78 tacts in a quick, positive manner by means of a slide ac- [51] Int CL H01h 13/28 tuator which picks-up the drive plate and rapidly moves [58] Field of l c 153 CA it to a contact closing position at the exact instant that 300/78 68 68 the slide actuator is snap-released by detent springs positioned in its slide path. The location and configura- [56] References Cited tion of contact engaging shoulders on the drivehplate may be selectively changed so as to permit a pl rality UNITED STATES PATENTS of circuits to be closed in a desired sequence and com- 2,488,670 11/1949 Koenig 200/16 c binatiom 1,986,527 1/1955 Rach et al 200/153 CA I 3,146,330 8/1964 Miller 200/16 0 7 Claims, 7 Drawing Flgures BRIEF SUMMARY OF THE INVENTION This invention is directed to a switch particularly characterized by positive, snap-action closing of electric contacts by a slide switch mechanism capable of being readily adapted to the closing of a plurality of circuits in a predetermined sequence.

The basic objectives are realized by utilizing a slide actuator to engage and shift a contact-closing driver member under the impetus of at least one detent spring which is positioned to restrainably engage the slide actuator and impart a snap-action spring release to it. Of special significance in achieving the positive, rapid closing of the spring contacts is the particular cooperative relationship of the contact-closing member with the slide actuator in accordance with which the contact-closing member is not shifted into engagement with a contact to urge it towards a closed position until after the slide actuator has been moved to an overcenter position against the detent spring for snap release by it.

In a preferred embodiment of the invention the aforesaid driver member for closing the switch contacts advantageously takes the form of a separate slide plate which is engaged by spaced apart pick-up elements on the slide actuator as it is shifted back and forth to make and break circuits in a desired sequence. The slide actuator and the contact closing slide plate areso constructed and arranged with respect to each other that a lost motion space is provided through which the actuator moves to an over-center position against a detent spring before picking-up the slide plate, thereby insuring that the slide plate is quickly snapped into a contact-closing position by the spring release of the slide actuator.

A further beneficial aspect of my invention resides in the flexibility of circuit combinations and contactclosing sequences which may be achieved by utilizing a contact-closing member, preferably in the form of a slide plate, with a plurality of contact engaging surfaces formed thereon at predetermined locations. The contact engaging surfaces which can simply be recesses or shoulders forme on the slide plate, can be so spaced and located as to engage and close different contacts at predetermined points in the path of the slide actuator.

Positive contact closing and firm holding of contacts in a closed position is realized by using movable contacts in the form of spring strips or leaf springs positioned under a contact-closing slide plate and having upstanding lobes thereon in the path of the slide plate. As the plate slides over the lobe, it urges the spring strip downwardly and firmly holds it in a closed position by exerting downward pressure on it.

These and other objects and advantages of my invention will become readily apparent as the following description is read in conjunction with the accompanying drawings, wherein like reference numerals have been used to describe like elements throughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS lines 2-2 of FIG. 1;

FIG. 3 is a horizontal section view taken along lines 3-3 of FIG. 2;

FIG. 4 is a horizontal section view taken along lines 4--4 of FIG. 2;

FIG. 5 is a transverse, vertical section view taken along lines 5-5 of FIG. 1; and

FIG. 6 is a schematic, plan view of the base of the switch assembly showing the contact and circuit arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, I have shown in FIGS. 1 through 5 a slide switch embodying the snap-action, contact closing mechanism of this invention. This particular switch assembly is designed for use in microcurcuitry and as such is of extremely small size, the entire switch assembly being on the order of three quarters of an inch in length. The improved actuating mechanism of this switch provides positive, fast closing of the switch contacts in a very flat, compact switch assembly as shown which is very important in miniaturized circuits and components. The entire switch assembly is generally indicated by reference numeral 1, and includes an enclosure comprised of a housing 2 made of insulating material, such as bakelite or molded phenolic, and a closure frame 4 of inverted, U-shape which is mounted in closing relation to the open, top end of housing 2. Housing 2 includes a base wall 2a, upstanding end walls 2b and opposed, upstanding side walls 20. Generally planar, top closure wall 4a of closure frame 4 overlies the top, open end of housing 2; and downwardly depending wall segments 4b of frame 4 are disposed in overlying relation to the opposed end walls 2b of housing 2 and cooperate therewith in providing a complete switch enclosure. Closure frame 4 is secured-to housing 2 by means of lock tabs 4c at the bottom of wall segments 4b which engage the underside of base wall 2a of housing 2.

A rectangular slot 6 provided in top, closure wall 4a of closure frame 4 accommodates the outward extension of a slide actuator 8 having a gripping head or knob 10, the opposite ends of opening 6 defining the end extremities of a linear path through which actuator 8 may be slidably reciprocated to open and close contacts contained within housing 2. The length of opening or slot 6 is such as to accommodate a shifting stroke of actuator 8 sufficient to open and close the contacts of the switch mechanism, described below. As may be most clearly noted by reference to FIG. 5, slide actuator 8 is of unitary construction, and includes an elongated driver head 12 having a pair of downwardly depending pick-up

fingers

14 and 15 disposed at opposite ends thereof. Pick-up

fingers

14 and 15 serve to carry a slidably shiftable contact closing member in a manner hereinafter explained. Extending along opposite side walls 20 of housing 2 in abutting contact therewith are a pair of

removable spacers

17 and 18 which provide sliding support for laterally projecting

shoulders

19 and 20 on opposite sides of slide actuator 8.

Spacers

17 and 18 also serve to space and support slide actuator 8 at the desired vertical location within housing 2.

In order to prevent the entry of dust and other foreign matter through slot 6 of closure frame 4 into the switch operating and contact space within housing 2, I have provided a cover structure comprised of a pair of

planar cover members

22 and 24. Cover 22 is a slide cover positioned on gripping knob of actuator 8 and slidably shiftable therewith. Cover 24 is positioned behind or below slide cover 22 and is a stationary cover over which cover 22 slides. The peripheral edges of stationary cover 24 abut against the inside surfaces of

adjacent wall portions

2b and 2c of housing 2 and cooperate therewith, as well as with slide cover 22 to close the open, upper end of housing 2. Stationary cover 24 is providedwith a central aperture or slot 26 in alignment with cover slot 6 in closure frame 4a and of sufficient length to accommodate the full, shifting stroke of actuator 8 to its various operational positions. Stationary cover 24 is preferably of the channel shaped configuration shown in FIG. 5, andincludes upright side wall portions 24a with which slide cover 22 is in sliding engagement. The manner in which slide cover 22 and sta-v tionary cover 24cooperate to prevent the entry of foreign matter into switch housing 2 isexplained in detail in my copending US. Pat. application entitled Dust Cover For Switches, filed on June 7, 1972 under Ser. No. 260,486, new. issued as US. Pat. No. 3,723,692.

Embedded in base wall 2a of housing 2 are a plurality of conductors 26,..27, 28 and 29 having terminal por-

' tions

26a, 27a, 28a, and 29a which project outside of housing 2 for connection in external circuits. The inner ends of conductors 26-29 are positioned within housing 2 in the manner shown in FIG. 6 to form stationary contacts located to be bridged by a pair of movable contact members 30.and 32. Preferably, contact mem- 32, contact buttons 30:: and 30b for contact spring 30 being-shown in FIG. 2. Buttons 30a and 30b, and comparable contact buttons for contact spring 32 (not shown) serve as contact elements for engagement with the inner ends of

conductors

26, 27, 28 and 29.'With "the particular arrangement of conductors 2629 and contact springs 30nd 32 illustrated herein, contact spring 30 will bridge the inner ends ofv

conductors

27 and 29 and complete a circuit therebetwe'en when its contact buttons 30a and 30b are closed. In like manner,

contact spring 32 can have both of its contact elements moved to a closed position wherein it bridges the inner ends of'conductors 26 and 28 to complete a circuit on driver plate 38 I have provided a plurality of notches or shoulderswhich are shaped and located as desired to engage the raised cam lobes oncontact

springs

30 and 32 in a predetermined sequence as driver plate 38 is shifted back and forth by actuator 8. In the particular embodiment of my invention shown in FIGS. 1 through 6,

shoulders

40 and 41 are formed at only one endof driver plate 38 to provide a simple, two position, on-off switch. With slide .act'uat'or'8 shifted to the left or off position as viewed in FIG. 2,

shoulders

40 and 41 will be shifted out of engagement with cam lobes 34b and therebetween. It will be appreciatedthat the inner ends of conductors 26-29 could be arranged invarious patterns in cooperative relation with the contact buttons on-

contact springs

30 and 32 to provide any desired switch and circuit arrangement between particular conwith up- 36b'by theengagement of pick-up finger 15 with driver plate 38. This will permit contact button 30b of contact spring 30, and the corresponding contact button of contact spring 32, to rise to their open positionsout of contact with conductors 29'and 28 respectively. Thus, both circuits controlled by switch 1 will be open when slide actuator 8, and driver plate 38 actuated thereby are shifted to the left, as viewed in FIG. 2. Upon shifting slide actuator 8 to the right, finger 14 will engage and pick-up the opposite end of driver plate 38 and shift it to the right to a position where

shoulders

40 and 41 engage

cam lobes

34b and 36b of contact springs 30 and 32., This will cause the right ends of

contact springs

30 and 32 to be urged downwardly to bring their contact buttons (30b on contact spring30) into engagement with

conductors

29 and 28 to complete the two circuits through switch 1. In the embodiment shown, the underside of driver plate 38'is in continuous engagement with the cam lobes on the left side of contact springs 30 and 32 (34a on spring '30),with 'the result engagement with vertically extending

ribs

44, 45, 46

and 47 on end walls 2b in the manner shown most clearly in FIG. 3. Driver head l2 has a pair oflaterally protruding lugs49 and 50 on opposite sides thereof and is positioned between

detent springs

42 and 43 as shown with lugs 49 and 50disp'osed at the same level as spring detents 42a and 43a As actuator 8, and driver head 12 thereof, are shifted in either direction froma position of rest, lugs 49'and 50 will engage spring detents 42a and 43a, with the result that these spring detents will be compressed and then quickly release

lugs

49 and 50 witha spring action as driver head 12 moves cam"surfacesarein the form of

lobes

34a and 34b formed on contact springs 30 as shown in FIG. 2, one of the cam lobes 36b on'contact spring 32 being shown in FIG. 4. Contact closing member'38 preferably takes the form of a driver plate slidably positioned on top of base wall 20 of housing 2 as shown in FIGS. 2, 4 and 5. The'location of driver plate 38 as shown in cooperative juxtaposition to slide actuator 8 between pick-up

fingers

14 and 15 permits plate 38 to be intermittently engaged by depending fingers l4 and 15 for sliding movementwith'actuator 8. At predetermined locations to an over-centerposition with respectfto detents'42a and 43d. Driver plate 12 is' substantially-shorter than the space between pick-

upfingers

14 and 15 was to provide aclearance or lostj'motio'n space through which driver head 12 can be shiftedin one direction or the other before one of its dependingpick-up fingers 14 or sion X shown in FIG. 3 through which driver head 12 must move in order to bring its

lugs

49 and 50 to an over-center position against spring detents 42a and 43a. Thus, at the exact instant that driverhead 12 is shifted to an over-center position with respect to spring detents 42a and 43a, in moving from left to right towards a contact closing position, pick-up finger 14 will engage the left end of driver plate 38. There will be no movement of contact closing driver plate 38, and no movement of the electrical contacts towards each other, until driver head 12 springs past detents 42a and 43a, with the result that the spring action of these detents will quickly snap driver head 12 and driver plate 38 into a switch closing position wherein shoulders 40 and 41 move all of the way across the top of the cam lobes on the right end of contact springs 30 and 32 and force them downwardly into a contact closing position in engagement with

conductors

29 and 28. The same fast, positive contact actuation is realized upon the opening of the button contacts (e.g., 30b) with respect to

conductors

29 and 28 by shifting slide actuator 8 to the left, to its off position. it will be appreciated that when slide actuator 8 has been moved to the right, to its contact closing position, a clearance space equal to dimension Y will exist between pick-up finger 14 and the right end of driver plate 38. Thus, finger 15 will not engage driver plate 38 and move

shoulders

40 and 41 out of contact with

spring lobes

34b and 36b until driver head 12 has again moved to an over-center position with respect to spring detents 42a and 43a. Head 12 wil then be snapped back to the left to its off position to provide a fast, positive opening of the contacts above

conductors

29 and 28.

The primary advantage of this snap-action switch mechanism is that there is a sudden, fast closing and opening of the contacts with no gradual flickering of the contacts as they approach each other. Fluttering of the contacts with respect to each other, and resultant arcing across the contacts which can not be tolerated on many micro-circuit applications, are thereby eliminated. Also, the particular contact closing mechanism disclosed herein, utilizing driver plate 38 overlying contact springs 30 and 32 is particularly advantageous in holding the contacts closed, once they have been moved to a closed position. The engagement of the bottom surface of driver plate 38 with the

cam lobes

34a, 34b, 3612, etc., of contact springs 30 and 32 provides a very positive downward restraint against the contact ends of

springs

30 and 32, thereby preventing the contact buttons from fluttering open.

I contemplate that various structural arrangements for actuator 8 and driver plate 38 could be utilized, other than that shown, wile still achieving the positive, spring-action closing of the switch contacts. For example, actuator 8 and driver plate 38 could conceivably be an integral unit. The rapid, spring-action contact closing objective will still be met as long as driver plate 38 is of such a length and its contact shoulders 40 and 41 are so located that hey do not engage and start closing movable contacts until slide actuator 8 has gone to an over-center position against its detent springs. An alternative drive arrangement between slide actuator 8 and driver plate 38, in lieu of the spaced pick-up

fingers

14, 15 shown, would be a pin and slot design. With such an arrangement a pin depending from the bottom of driver head 12 would extend into an aligned slot in driver plate 38, with a predetermined lost motion or clearance space between the pin and the opposite ends of the slot being utilized to permit driver head 12 to move to an overcenter position against its detent springs before engaging and moving contact closing, driver plate 38.

The particular switch mechanism described above has the further advantage of permitting a plurality of contacts and circuits to be closed in any desired combination and sequence by changing the location and configuration of

shoulders

40 and 41 on driver plate 38. For example, as is illustrated in FIG. 7, a driver plate 38a could have a pair of contact shoulders 52 and 54 located at diagonally opposite corners thereof. When driver plate 380 is shifted to the left when viewing the structure of FIGS. 6 and 7, both of the

contact buttons

36a and 36b on contact spring 32 will be held in a downwardly depressed, closed position by driver plate 38a, thereby bridging and closing a circuit between

conductors

26 and 28 as shown in FIG. 6. At the same time, shoulder or recess 54 will be disengaged from cam lobe 34b, thereby permitting contact button 30b on the right end of contact spring 30 to rise to an open position. When driver plate 38a is shifted to the right, shoulder or recess 52 will become disengaged from cam lobe 36a on the left end of contact spring 32, thereby permitting the contact button over conductor 26 to rise to an open position to open the circuit through

conductors

26 and 28. With driver plate 38a in such a position, it will be engaging and

depressing cam lobes

34a and 34b on both ends of contact spring 30, whereby contact buttons 30a and 30b will both be held in a downwardly closed position to complete a circuit between

conductors

27 and 29. The use of a separate driver plate 38 which is not an integral part of slide actuator 8 permits the convenient substitution of different driver plates having various numbers and locations of contact closing shoulders to achieve flexibility in the sequential closing of various contacts in various circuit combination.

I anticipate that various other modifications and changes can be made in the structure and configuration of the components of my snap-action switch mechanism without departing from the spirit and scope of my invention as defined by the following claims.

I claim:

1. A snap-action, slide switch mechanism comprising:

a stationary contact;

a movable contact shiftable between an open position in spaced apart relation to said stationary contact and a circuit closing position in contact therewith;

a slidably shiftable switch actuator reciprocally movable through a predetermined path between contact closing and contact opening positions and including an elongated member having a pair of spaced apart pick-up elements thereon;

spring detent means disposed in the path of said switch actuator and having an over-center detent surface thereon for engaging and resisting the movement of said switch actuator and for imparting a snap-action spring release movement thereto; and

a slidably shiftable, non-conductive contact closing plate, separate and independent of said switch actuator and said movable contact, positioned adjacent to said actuator in overlying relation to said movable contact between said pair of pick-up elements with opposite end portions of said plate located for alternate engagement by said pick-up elements as said switch actuator is moved back and forth through said predetermined path between said contact opening and contact closing position, and, with said switch actuator in said contact opening position, there being a lost motion space between one of said pick-up elements on said switch actuator and the end portion of said slidably shiftable plate adjacent thereto through which said switch actuator moves to said overcenter position into engagement with said over-center detent surface of said spring detent means before picking up said slidably shiftable plate and shifting it to a position in engagement with said movable contact, herein said plate urges said movable contact downwardly to said circuit closing position and firmly holds said contacts closed as it slides over said movable contact.

2. A snap-action slide switch comprising:

a plurality of stationary contacts;

a plurality of movable electrical contacts disposed in normally open positions with respect to corresponding ones of said stationary contacts and movable into a closed position in circuit closing contact therewith;

a slidably shiftable switch actuator movable through a predetermined path between contact closing and contact opening positions, and having pick-up means thereon;

a removable, slidably shiftable contact closing plate of non-conductive material, separate and independent of the switch actuator and said movable contacts, positioned adjacent to said switch actuator for engagement by said pick-up means of said switch actuator and sliding movement therewith to contact closing and opening positions, said plate having a plurality of separate, spaced apart contact engaging surfaces at predetermined locations on the peripheral surface thereof positioned to selectively engage predetermined ones of said movable contacts and to urge said movable contacts to said closed positions at a predetermined point in the slide path of said plate, whereby a plurality of circuits having said movable contacts therein may be opened and closed by said shiftable plate in a predetermined manner.

3. A snap-action slide switch as defined in claim 2 wherein:

said movable contacts comprise a pair of spring strips positioned under said shiftable plate at laterally spaced apart positions with respect thereto, each of said spring strips having at least one cam surface thereon disposed in the path of one of said contact engaging surfaces on said plate for engagement thereby, said contact engaging surfaces being laterally spaced apart on said plate to cooperate with corresponding ones of said spring strips and acting to urge one end of each of said spring strips downwardly into a circuit closing position in contact with its cooperating, stationary contact as said shiftable plate slides over said cam surfaces, said plate serving to firmly hold said contacts closed. 4. A snap-action, slide switch as defined in claim 2 wherein:

said shiftable plate is positioned for alternate engagement of central portions of opposite ends thereof by said pick-up means; and said contact engaging surfaces comprise shoulders formed in recesses at predetermined locations laterally offset from said central portions of said plate on opposite, peripheral edge portions thereof. 5. A snap-action, slide switch mechanism as defined in claim 1 wherein:

said slidably shiftable plate is disposed under said elongated member of said switch actuator, and said spaced apart, pick-up means on said switch actuator comprise a pair of downwardly depending fingers located at opposite ends of said elongated member for engagement with said opposite end portions of said plate. 6. A snap-action slide switch mechanism as defined in claim 1 wherein:

said movable contact comprises a spring strip positioned under said shiftable plate and having at least one upstanding lobe disposed in the path of said plate for engagement thereby, said plate urging one end of said spring strip downwardly into said circuit closing position in contact with said stationary contact and firmly holding said contacts closed as it slides over said lobe. 7. A snap-action, slide switch mechanism as defined in claim 1 wherein:

said shiftable plate has at least one contact surface formed on a corner portion of the peripheral edge thereof at a predetermined position for engagement with said movable contact at a predetermined point in the slide path of said plate, said contact surface being a separate surface, distinct from the end portions of said slidably shiftable plate which are engaged by said pick-up elements of said switch actuator.

Claims

1. A snap-action, slide switch mechanism comprising: a stationary contact; a movable contact shiftable between an open position in spaced apart relation to said stationary contact and a circuit closing position in contact therewith; a slidably shiftable switch actuator reciprocally movable through a predetermined path between contact closing and contact opening positions and including an elongated member having a pair of spaced apart pick-up elements thereon; spring detent means disposed in the path of said switch actuator and having an over-center detent surface thereon for engaging and resisting the movement of said switch actuator and for imparting a snap-action spring release movement thereto; and a slidably shiftable, non-conductive contact closing plate, separate and independent of said switch actuator and said movable contact, positioned adjacent to said actuator in overlying relation to said movable contact between said pair of pick-up elements with opposite end portions of said plate located for alternate engagement by said pick-up elements as said switch actuator is moved back and forth through said predetermined path between said contact opening and contact closing position, and, with said switch actuator in said contact opening position, there being a lost motion space between one of said pick-up elements on said switch actuator and the end portion of said slidably shiftable plate adjacent thereto through which said switch actuator moves to said overcenter position into engagement with said over-center detent surface of said spring detent means before picking up said slidably shiftable plate and shifting it to a position in engagement with said movable contact, herein said plate urges said movable contact downwardly to said circuit closing position and firmly holds said contacts closed as it slides over said movable contact.

2. A snap-action slide switch comprising: a plurality of stationary contacts; a plurality of movable electrical contacts disposed in normally open positions with respect to corresponding ones of said stationary contacts and movable into a closed position in circuit closing contact therewith; a slidably shiftable switch actuator movable through a predetermined path between contact closing and contact opening positions, and having pick-up means thereon; a removable, slidably shiftable contact closing plate of non-conductive material, separate and independent of the switch actuator and said movable contacts, positioned adjacent to said switch actuator for engagement by said pick-up means of said switch actuator and sliding movement therewith to contact closing and opening positions, said plate having a plurality of separate, spaced apart contact engaging surfaces at predetermined locations on the peripheral surface thereof positioned to selectively engage predetermined ones of said movable contacts and to urge said movable contacts to said closed positions at a predetermined point in the slide path of said plate, whereby a plurality of circuits having said movable contacTs therein may be opened and closed by said shiftable plate in a predetermined manner.

3. A snap-action slide switch as defined in claim 2 wherein: said movable contacts comprise a pair of spring strips positioned under said shiftable plate at laterally spaced apart positions with respect thereto, each of said spring strips having at least one cam surface thereon disposed in the path of one of said contact engaging surfaces on said plate for engagement thereby, said contact engaging surfaces being laterally spaced apart on said plate to cooperate with corresponding ones of said spring strips and acting to urge one end of each of said spring strips downwardly into a circuit closing position in contact with its cooperating, stationary contact as said shiftable plate slides over said cam surfaces, said plate serving to firmly hold said contacts closed.

4. A snap-action, slide switch as defined in claim 2 wherein: said shiftable plate is positioned for alternate engagement of central portions of opposite ends thereof by said pick-up means; and said contact engaging surfaces comprise shoulders formed in recesses at predetermined locations laterally offset from said central portions of said plate on opposite, peripheral edge portions thereof.

5. A snap-action, slide switch mechanism as defined in claim 1 wherein: said slidably shiftable plate is disposed under said elongated member of said switch actuator, and said spaced apart, pick-up means on said switch actuator comprise a pair of downwardly depending fingers located at opposite ends of said elongated member for engagement with said opposite end portions of said plate.

6. A snap-action slide switch mechanism as defined in claim 1 wherein: said movable contact comprises a spring strip positioned under said shiftable plate and having at least one upstanding lobe disposed in the path of said plate for engagement thereby, said plate urging one end of said spring strip downwardly into said circuit closing position in contact with said stationary contact and firmly holding said contacts closed as it slides over said lobe.

7. A snap-action, slide switch mechanism as defined in claim 1 wherein: said shiftable plate has at least one contact surface formed on a corner portion of the peripheral edge thereof at a predetermined position for engagement with said movable contact at a predetermined point in the slide path of said plate, said contact surface being a separate surface, distinct from the end portions of said slidably shiftable plate which are engaged by said pick-up elements of said switch actuator.