US3898402A

US3898402A - Snap switch with actuating tongue

Info

Publication number: US3898402A
Application number: US391639A
Authority: US
Inventors: Anthony R Ford
Original assignee: Airpax Electronics Inc
Current assignee: Airpax Electronics Inc
Priority date: 1973-08-27
Filing date: 1973-08-27
Publication date: 1975-08-05
Anticipated expiration: 1992-08-05

Abstract

An electrical switch having an elongated, resilient, conductive blade having upper and lower legs whose end edges are mounted in vertically spaced seats formed in a dielectric switch body. The seats are closer together than the unstressed length of the blade, and one or more terminals abut one face of the central portion of the blade and impose thereon upper and lower bows of opposite curvature. When the switch is actuated by decreasing the curvature of the upper bow, the blade snaps so that its opposite face abuts a second set of one or more terminals. The upper blade leg includes a pair of laterally spaced leg segments, joined by an upper yoke adjacent to the upper edge, and an integrally formed tongue projects downwardly from the yoke into the opening between the leg segments. Deflection of the tongue by an actuator creates stress in the yoke and leg segments tending to decrease the curvature of the upper bow and simultaneously increase the curvature of the lower bow until snap action occurs. A second identical switch is symmetrically disposed in the switch body. The blade may include a pair of laterally projecting arms midway of its length to serve as a shorting bar between laterally spaced abutment terminals. Spring means bias the actuator toward normal position, and releasable latching means maintain it in its actuated position, including a cardioid trackway formed in the actuator sidewall, the trackway being provided with a pair of vertically spaced locking indentations. A ball detent, resiliently biased partially into the trackway, is permitted to move laterally in order to follow the cardioid trackway, which is ramped to insure unidirectional movement of the ball around the trackway.

Description

United States Patent 1 1 3,898,4Q2

Ford Aug. 5, 1975 SNAP SWITCH WITH ACTUATING end edges are mounted in vertically spaced seats TONGUE formed in a dielectric switch body. The seats are closer to ether than the unstressed len th of the [75] Inventor: ig Ford west Covma blade, am? one or more terminals abut one face of the a l central portion of the blade and impose thereon upper [73] Assignee: Airpax Electronics Incorporated, and lower bows of opposite curvature. When the Cambridge, Md. switch is actuated by decreasing the curvature of the P Filed g 27 1973 upper bow, the blade snaps so that its opposite face abuts a second set of one or more terminals. The [Zl] Appl. No; 391,639 upper blade leg includes a pair of laterally spaced leg segments, joined by an upper yoke adjacent to the U 5 Cl 200/67 74/100 P upper edge, and an integrally formed tongue projects [Sl] H 01h 13/36 downwardly from the k mm the Openmg between 581 Field of Search 200/67 DA, 67 DB; 337/89, the leg Segments" peflecton of the tongue by 337/135 136' 74/100 P ator creates stress in the yoke and leg segments tendmg to decrease the curvature of the upper bow and simultaneously increase the curvature of the lower [56] References cued bow until snap action occurs. A second identical UNITED STATES PATENTS switch is symmetrically disposed in the switch body.

2,133,309 10/1938 Schmidinger 200/67 DB The blade may include a pair of laterally projecting 1167543 7/1939 Bflgenhflgen 200/67 DB arms midway of its length to serve as a shorting bar 2395'698 2/1946 200/67 DB between laterally spaced abutment terminals. Spring 2444'529 7/1948 Puster 200/67 DB means bias the actuator toward normal position, and FOREIGN PATENTS OR APPLICATIONS releasable latching means maintain it in its actuated 58.739 10/1922 Sweden 200/67 D position, including a cardioid trackway formed in the Primary Examiner-David Smith, Jr. Attorney, Agent, or Firm-Miketta, Glenny, Poms & Smith 5 7 ABSTRACT An electrical switch having an elongated, resilient, conductive blade having upper and lower legs whose actuator sidewall, the trackway being provided with a pair of vertically spaced locking indentations. A ball detent, resiliently biased partially into the trackway, is permitted to move laterally in order to follow the cardioid trackway, which is ramped to insure unidirectional movement of the ball around the trackway.

10 Claims, 21 Drawing Figures PATENTED AUB 5l975 SHEET PATENTED AUG 5 I975 PATENTEU AUG 5 SNAP SWITCH WITH ACTUATING TONGUE BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates generally to electrical switches, and more particularly to a switch of the snap action type employing a switching blade of resilient conductive material which is maintained under longitudinal compressive stress in the body of the switch whereby to impose on the blade oppositely bowed portions. which may for convenience be referred to as convex and concave bowed portions.

In a preferred form of the present invention, the resilient conductive blade constituting the switching element in the present switch is generally cruciform in shape, having upper and lower legs and a pair of laterally extending arms substantially midway of the blade. The upper leg of the blade is provided with a central opening, and an integrally formed tongue projects downwardly into the opening. When the blade is mounted in its housing seats, a pair of abutment terminals abut the arms, and impose on the blade the oppositely bowed configuration mentioned above. A second pair of abutment terminals lies on the opposite side of the arms from the first named pair. Actuation of the switch consists of decreasing the curvature of the upper bowed portion of the blade and simultaneously increasing the curvature of the lower portion of the blade until a point is reached when the blade snaps from its rest position with its arms in contact with the first pair of abutment terminals into an actuated position with its arms in contact with the second set of abutment terminals. Thus the arms constitute a shorting bar between the terminals of each pair. Actuation of the switch is effected by slidable abutting contact of an actuator element against the blade tongue, whereby stress is built up in the tongue and in the adjacent portions of the leg until the snap action results. Such movement of the actuator element is accomplished by depressing a pushbutton in accordance with the present illustrative embodiment of the invention.

In an alternative form of the invention, the blade arms are eliminated, one end of the blade is in electrical contact with a common terminal, and one abutment terminal is provided on either side of the blade, approximately midway of its length. The blade is otherwise the same as the cruciform blade first above mentioned, and includes an actuating tongue in its upper leg.

Releasable latching means are desirably provided in accordance with the present invention, whereby a sin gle depression of the pushbutton or otherwise actuating the actuator element. serves to maintain the switch in its actuated condition until a second depression of the pushbutton. Under these conditions the switch is of the type referred to as alternating. If the releasable latching means are omitted, then the switch is of the momentary type, being actuated only so long as the pushbutton is maintained depressed.

A preferred form of the latching means includes a cardioid shaped trackway formed in the sidewall of the actuator, and a ball detent element partially received in the cardioid trackway, and retained therein by resilient means carried by the switch body. The trackway is provided with two vertically spaced lock positions for the ball detent, corresponding to retracted and actuated positions of the actuating element. The trackway itself is suitable contoured and provided with ramps to insure that the ball detent, which is permitted limited lateral movement relative to the trackway in order to follow the cardioid path, proceeds always in the same direction around said path.

In the preferred form of the invention, a second blade and associated abutment terminals may be provided, disposed symmetrically to the first about a central vertical axis of the switch, so that movement of the actuator switches two separate circuits substantially simultaneously.

It is accordingly a principal object of the present invention to provide and disclose an electrical switch having a novel conductive blade to accomplish the switching, and releasable latching means to maintain the switch, selectively, in either its make or break position. Other objects and purposes are to provide, in such a switch, a blade of generally cruciform shape, having a pair of laterally extending arms constituting in effect a shorting bar; to provide, in such a blade, an upper leg having an opening formed therein and an integral tongue extending downwardly into the opening, slidably abuttable by an actuator element during actuation; to provide a releasable latching means to selectively maintain the actuator element in actuated position, and including a cardioid track'way having upper and lower lock positions, in which a ball detent is resiliently biased for travel around the cardioid between one lock position and the other; for providing in such a switch a duplicate set of switching elements and terminals by which to double the circuit handling capacity of the switch in compact space; and for other and additional objects as will become clear from a reading of the following description of a preferred embodiment of the invention, taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a switch embodying the present invention.

FIG. 2 is a vertical sectional view taken on line 11-11 of FIG. 1, showing the parts in their normal or rest positions.

FIG. 3 is a fragmentary sectional view similar to FIG. 2, except showing the parts in their actuated positions.

FIG. 3A is a fragmentary sectional view similar to FIG. 3 and laterally aligned therewith, showing the right hand portion of the switch proper in actuated position as in FIG. 3, but with the pushbutton carrier retracted to its rest position.

FIG. 4 is a sectional view taken on the line IVIV of FIG. 2.

FIG. 5 is a developed view of the trackway and, in dotted outline, the successive positions of the ball detent therein.

FIGS. 6a, b, c and d are successive views of the migration of the ball detent around the cardioid trackway, FIG. 6a corresponding to the position of the switch seen in FIG. 2, FIG. 66 corresponding to the position of the switch seen in FIG. 3, and FIGS. 6!) and 6d showing the ball and trackway in intermediate positions.

FIGS. 7, 8 and 10 are sectional views taken along the arrows VIIVII, VIIIVIlI, and X-X respectively of FIG. 2.

FIG. 9 is a sectional view taken on the arrows IX-IX of FIG. 3.

FIG. 11 is a bottom plan view of the switch taken on the arrows XlXl of FIG. 2.

FIG. 12 is a perspective view of the preferred form of blade in accordance with the invention.

FIG. 13 is a schematic diagram showing the wiring of the several terminals of the preferred embodiment of the invention.

FIG. 14 is a perspective view of a switch blade in accordance with an alternative form of the invention.

FIG. 15 is a fragmentary sectional view of a portion of a switch incorporating the blade of FIG. 14.

FIG. 16 is a fragmentary sectional view taken on the arrows XVIXVI of FIG. 15.

FIG. 17 is a fragmentary sectional view taken on the arrows XVIIXVII of FIG. 15, and showing the operative portions of the switch in the left portion of the switch assembly, including a second blade and pair of terminals, disposed symmetrically relative to the corresponding parts in the right half of the switch assembly.

DETAILED DESCRIPTION Referring now to the drawing, in FIG. 1 there is indicated generally at 20 a housing for containing the operative portions of the present switch, the housing 20 being desirably made of metal and including an integrally formed externally threaded boss 21 projecting upwardly from the housing proper, for convenience in mounting the present switch housing on a control panel or the like. A pushbutton carrier 22 is telescopically received within the threaded bore 21 and extends thereabove, and is adapted to have a suitable pushbutton mounted on its upper end for actuation by the user. With continued reference to FIG. 1, the lower portion of the cylindrical wall of the housing 20 is crimped inwardly at 23, in order to be attached to a downwardly extending base 24 of dielectric material, from which outlet terminals project downwardly, there being visible in FIG. 1 a total of four such terminals, arranged in

pairs

25, 26 and 27, 28. As will be later understood in detail, and as a glance at FIG. 11 will show, there are desirably a total of eight downwardly projecting outlet terminals disposed symmetrically about a central vertical plane of the switch, the other four terminals being designated by primed reference numerals.

The internal construction of the elements of the switch will be best understood by reference first to FIGS. 2 and 4, showing those parts in their normal or rest positions.

Thus the lower portion of housing 20 comprises a hollow cylindrical casing indicated generally at 30 which receives in its upper portion a body shell of dielectric material indicated generally at 32. This shell includes an upper annular ring portion 34 and, extending downwardly therefrom and integrally formed therewith, a pair of arcuately extending skirts 36, 37 (see FIG. 4), interrupted by a pair of diametrically opposed

openings

38, 39, seen in FIG. 2. The lower interrupted annular edges 40 of

skirts

36, 37 abut the upper face 41 of dielectric base member 24. At the midpoint of

arcuate skirts

36 and 37, body shell 32 is provided with

support columns

42 and 43 respectively, having

coaxial posts

44 and 45 which extend downwardly into

bores

46 and 47 formed in dielectric base 24.

As will be later understood, after assembly of the switch blades with shell 32 and base 24, the

lowermost ends

48 and 49 of

posts

44 and 45 are heat sealed or welded to adjacent portions of dielectric base 24, so

that the shell and base form an integral dielectric body containing therewithin the operative portions of the switch, including switch blades and abutment terminals to be now described.

In FIG. 12 there is indicated generally at 50 the preferred form of blade constituting the moving contact member in accordance with the present invention. Blade 50 is of generally cruciform shape, having an elongated lower leg 52 terminating downwardly in a lower edge 53 and an upper leg indicated generally at 54 terminating in an upper edge 55 which is parallel to lower edge 53. Upper leg 54 is of substantially greater width than that of lower leg 52, and has formed therein a central opening 56 between a pair of laterally spaced

leg segments

57 and 59 joined by an upper transverse yoke. An integrally formed tongue 58 extends downwardly from the yoke, into the opening 56 with its sidewalls spaced inwardly from the inner walls of

leg segments

57 and 59, so that, as will be later understood, tongue 58 can be flexed away from the plane of the yoke during operation. The blade also includes a pair of

arms

60, 62, extending laterally substantially midway between lower and upper edges 53, 55. The total crosssectional area of

leg segments

57 and 59 is approximately equal to that of lower leg 52.

All of the elements of blade 50 thus far described are integrally formed of a flexible conductive material such as a sheet of copper or copper alloy. To minimize contact resistance during switch operation, as is customary in the switch art, contactor buttons 64 may be provided on the arms, desirably made of any of well known materials of high conductivity such a silver alloy or the like. As shown in FIG. 12, the outer surfaces of the contactor button 64 are desirable slightly convex.

There will now be described in connection with FIG. 2 a switch assembly comprising the blade of FIG. 12, its mounting in the dielectric body within casing 30, and the abutment terminals with which the blade arms make contact during switch operation. As will be evident from FIG. 2, the present illustrative embodiment of the invention includes a pair of identical switch assemblies, disposed precisely symmetrically relative to a central vertical plane through the switch, and for brevity only the switching assembly in the left portion of FIG. 2 will be described in detail. Thus the body shell 32 and base 24, both of dielectric material, define therebetween an operating cavity housing the switch blade 50 and the terminals with which the switch arms are abuttable. The lower face of body shell 32 has formed therein a groove 72, and base 24 of the dielectric body similarly has a groove 74 formed therein. Each groove constitutes a seat for receiving the lower and upper edges 53, 55 of blade 50, and the longitudinal spacing between

grooves

72 and 74 is appreciably less than the distance or height between the edges 53 and 55 of the blade when the blade is in its unstressed planar condition seen in FIG. 12. Blade 50 is thus forced to assume a curved configuration throughout its length, and a pair of abutment terminals 76 and 77 (compare FIG. 10) serve to impose upon blade 50 an oppositely bowed configuration in the upper portion of blade 50 comprising leg 54 from the bowed configuration in the lower portion of blade 50 comprising leg 52. More specifically, and using the terms from the view point of the central portion of the switch, upper leg 54 assumes a convenx curvature, while lower leg 52 assumes a concave curvature. Under these conditions tongue 58 projects linearly from the yoke tangentially to leg 54, since the tongue is unaffected by the stress imposed upon leg 54.

It may be noted that, if the switch blades happen to assume the opposite curvature from that just described after the dielectric body parts have been heat sealed together, it is a simple matter for the operator to correct the situation, before the dielectric body is assembled into casing 30, by inserting a small tool through one or both of the

openings

38, 39 and forcing the upper bowed leg 54 to snap into proper configuration.

In addition to

abutment terminals

76, 77 mentioned above, there is also provided a second pair of

abutment terminals

78 and 79 disposed on the opposite side of contactor buttons 64 from

abutment terminals

76, 77.

Abutment terminals

76, 77 will be referred to herein as normally closed abutment terminals, while

abutment terminals

78, 79 will be referred to herein as normally open terminals. It will thus be seen that the

arms

60, 62 of switch 50, together with their contactor buttons 64, constitute a shorting bar between the abutment terminals with which they are in contact.

Actuator means are provided for moving the blade 50 from its rest position seen in FIG. 2 to its actuated position seen in FIG. 3. In the present embodiment of the invention, such actuator means include an actuator head indicated generally at 80 which is mounted centrally of the switch and vertically slidable between its upper position seen in FIG. 2 and a lower position seen in FIG. 3. As best seen in FIGS. 4 and 9, actuator head 80 has formed in its lower periphery a pair of diametrically

opposed guide grooves

82, 83 for slidably receiving a pair ofinwardly projecting splines or lands 84, 85, respectively, which project radially inwardly from the otherwise cylindrical inner wall of body shell 32, so that the actuator head 80 is permitted non-rotational verti cal movement between its upper and lower positions. With continuing reference to FIG. 9, it will be seen that actuator head 80 is provided with a pair of

nose portions

86, 87, which are bounded by arcuately spaced recesses 88 in the lower periphery of actuator head 80. The

actuator noses

86, 87 are diametrically opposed, and are disposed at 90 from the axes of

guide grooves

82, 83.

A comparison of FIGS. 2 and 3 will show that, as actuator head 80 is moved downwardly by means to be described in detail hereinafter, actuator head nose 86 comes into slidable abutting contact with tongue 58 of blade 50, moving the tongue arcuately about the base of the tongue as a fulcrum, and thereby building up stress in the upper leg 54, tending to decrease the curvature of that leg. A decrease of curvature of upper leg 54 necessarily is accompanied by an increase of curvature of lower leg 52, together with a slight downward movement of conductive buttons 64. At some point in the downward movement of actuator 80, the stresses thus produced in blade 50 will cause the blade to snap from its position of FIG. 2, in contact with normally closed

abutment terminals

76, 77, into its position seen in FIG. 3, with the conductive buttons in contact with normally

open terminals

78, 79.

It is to be particularly noted that the recesses 88 on either side of actuator nose 86 insure that actuator nose 86 touches only tongue 58 in its downward movement, and does not touch the upper leg 54 proper. In a switch of the present type. having a blade under longitudinal compressive stress and forming oppositely bowed curved portions, it is necessary to make certain that actuation of the switch from its rest position to its actuated position does not permit such over-travel as to cause the curvatures of the bowed portions to become reversed. As will be readily understood, the switch blade would then assume a stable position with conductive buttons 64 in contact with

abutment terminals

78, 79, and would remain in that position even after the actuator head is subsequently retracted upwardly into its position of FIG. 2. The switch would then be inoperative for any future actuation. The provision of tongue 58 in the present switch insures that such over-travel of the switch blade cannot occur, regardless of any overrun of the actuator head 80 in its downward movement. Accordingly, in the operation of the present switch, retraction of actuator head 80 upwardly into its FIG. 2 position relieves the stress theretofore imposed on tongue 58, and permits the compressive stress in the lower leg 52 to tend to reduce the curvature of that leg and thus to cause the conductive buttons 64 first to slide upwardly on

abutment terminals

78, 79, and, at some point in the upward movement of actuator head 80, to cause the switch blade to snap back into its rest position of FIG. 2.

As will be readily understood, by reason of the symmetry of the present switch, the same functions are being simultaneously performed by actuator nose 87 on the switch blade in the right hand side of FIGS. 2 and 3.

Resilient means are provided for retracting the actuator head 80 upwardly from its FIG. 3 position to its FIG. 2 position. In the present illustrative embodiment of the invention, such means include a helical spring indicated generally at 90, resting at its lower end on a cylindrical support plate 92, and bearing at its upper end against an annular shoulder 94 ofa collar indicated generally at 95 which is received in a bore 96 formed in the lower face of actuator head 80. Support plate 92 is formed integrally with a fitting shank 91 embedded in the center of base 24.

Immediately above actuator head 80 is a ball track guide indicated generally at 100, which bears upwardly at its upper end against a stop plate 102 which in turn is in abutting contact at its upper face with the annular bottom 104 of pushbutton carrier 22. An elongated metal sleeve indicated generally at has an annular shoulder 112 in its upper portion, against which stop plate 102 is seated, and the uppermost edge 114 of sleeve 110 projects through a central aperture in bottom 104 of pushbutton carrier 22, and is swaged or crimped outwardly as shown, in order to retain sleeve 110, stop plate 102, and pushbutton carrier 22 in fixed assembled relation.

Within sleeve 110 is an elongated tubular insulator indicated generally at 120, having at its lower end an annular shoulder 122 supporting the lower end of sleeve 110. The tubular insulator is provided with an inner bore 123 throughout most of its length, defined upwardly by an annular shoulder 124, above which extends an internal bore 126 of reduced diameter. A plug pin indicated generally at 130 is received in the internal bore 126, and is provided at its lower end with an enlarged head 132 seated against internal shoulder I24.

Within elongated bore 123 of tubular insulator 120 is provided resilient means in the form of helical spring 136, bearing at its upper end on head I32 and seated at its lower end on the upper face 138 of a locator stud indicated generally at 140 which is an integral extension of fitting shank 91 and projects upwardly therefrom in slidable relation with the internal bore 123 of insulator 120.

It will thus be seen that helical spring 136 serves to urge upwardly the tubular insulator 120 and, by means of the lower shoulder 122 of that insulator, the elongated sleeve 110 and stop plate 102 and pushbutton carrier 22 fixed to the sleeve 110.

Means are provided within boss 21 for limiting the upward movement of the parts just mentioned under the force of helical spring 136. Such means hereinclude a tubular bushing indicated generally at 145 which is seated at its upper end against annular shoulder 146 of casing boss 21, and at its lower end abuts an internal annular shoulder 148 formed integrally with body shell 32. In its upper portion, bushing 145 is provided with a downwardly facing internal annular shoulder 149, againstwhich stop plate 102 abuts, thus limiting upward movement of the stop plate and the parts fixed thereto, including pushbutton carrier 22, elongated sleeve 114 and tubular insulator 120.

Latch means are provided in accordance with the invention for releasably retaining actuator head 80 in its lower or actuated position of FIG. 3 and 3a, regardless of the position of the pushbutton carrier 22 and the parts fixed thereto. Such latch means include the ball track guide 100 previously mentioned, as well as a deis bounded laterally by

shoulders

160, 161 adjacent to the side edges of spring leg 156, thus forming a housing groove for the leg to maintain it in vertical orientation as seen in FIG. 4. Leg 156 terminates downwardly in an enlarged plate 162, which overlies a generally rectangular window opening 164 formed in the recessed side wall 166 of bushing 145, in order to receive the outer spherical portion of detent ball 150. Leaf spring 154 is prestressed so that plate 162 at the lower end of the leg resiliently biases ball 150 leftwardly as seen in FIGS. 2 and 3. The ball is permitted lateral movement by reason of the width of window 164, but is restrained against vertical movement, other than slight mechanical clearance, by the upper and lower walls defining window 164.

The releasable latching means in accordance with the present invention contemplate that detent ball 150 will migrate around a generally heartshaped or cardioid trackway, and means are incorporated in the trackway for preventing migration of the ball in one direction, and thus insuring that its migration occurs only in a predetermined desired direction.

With reference to FIGS. 6a-d, the cardioid trackway is indicated generally at 170 and is formed in a flat 172 provided in the otherwise cylindrical side wall of ball I guide bushing 100. Flat 172 is bounded laterally by edges 174 and, as best seen in FIG. 8, the marginal portions of flat 172 adjacent to edges 174 are in slidable abutting contact with internalbosses' 175 formed in bushing 145. Ball guide 100 is thus permitted vertical movement within the switch, but is restrained by shoulders 175 against rotational movement.

The migration of detent ball 150 around cardioid trackway 170 will now be explained with particular reference to FIGS. 6a-d and FIG. 5, the latter showing in developed form a profile of the trackway, including a complete cycle in the migration of the detent ball. FIG. 6a shows the parts in their position when the switch is in its rest condition shown in FIG. 2, the ball 150 being in position A of FIG. 5. Upon depression of pushbutton carrier 22, the vertically movable parts are forced downwardly against the biasing force of retractor spring and internal helical spring 136, and the parts will continue their downward movement to a position slightly lower than that shown in FIG. 3, with the lowermost shoulder 122 of tubular insulator bottoming against plate 180 at the lower end of stud 140. During that downward movement, the detent ball will migrate from its position of FIG. 6a to its position of FIG. 6b. When downward pressure is now released from pushbutton carrier 22, all vertically movable parts will move upwardly under the force of retractos spring 90 to the position seen in FIG. 3, and detent ball 150 simultaneously moves to its position seen in FIG. 66, where it latches the ball guide 100 against further upward movement. However, the pushbutton carrier and the parts fixed thereto continue their upward movement under the force of internal helical spring 136 to their uppermost positions seen in FIG. 3a.

The actuating parts remain in the actuated position of FIG. 3a until the user again depresses pushbutton carrier 22 and its associated parts. Such depression moves all vertically movable parts to their lowermost intermediate position with shoulder 122 bottoming against plate 180, and detent ball 150 simultaneously moving from its position of FIG. 60 to its position of FIG. 6d. Subsequent release of pressure on pushbutton carrier 22 permits the vertically movable parts to return to their positions seen in FIG. 2, and detent ball 150 simultaneously moves to its rest position seen in FIG. 6a.

The means in accordance with the invention for insuring that detent ball 150 will migrate in the desired direction around cardioid pathway will be best understood by reference to FIG. 5. As there shown, when ball 150 is in its A position, it rests against a concave shoulder 185, extending approximately 90 of arc and having a radius of curvature substantially equal to the radius of ball 150. When now the switch is actuated by the users depressing the pushbutton carrier 22, ball 150 moves along ramp 186 to its intermediate B position corresponding to the bottoming of the vertically movable parts, and rests against concave shoulder 187. Release of force from the push button carrier will now cause the ball 150 to move upwardly as seen in FIG. 5 along ramp 188 to its C position. In the latter position, ball 150 rests against concave shoulder I89. Subsequent depression of the pushbutton causes the ball to move along ramp 190 to its intermediate D position. where the ball rests against concave shoulder 191. Release of force from the push button now permits ball 150 to move upwardly as seen in FIG. 5 along ramp 192 to its A position. It is to be particularly noted that .the

concave shoulders

185, 187, 189, and 191 serve to prevent movement of ball 150 in the undesired direction, corresponding to downwardly in FIG. 5; the ball is instead caused to move up the ramps as above described,

and thus performs a unidirectional migration around the cardioid trackway 170.

In the embodiment of the invention thus far described and illustrated, the laterally extending

blade arms

60 and 62 serve effectively as a shorting bar between corresponding terminals within the body of the switch. Thus, in this form of the invention the electrical conductivity of the legs of the switch blade is not availed of, and such legs could indeed be made of an electrically nonconductive material, provided that such material had the necessary resilience to perform in the manner hereinabove described and illustrated.

In an alternative form of the present invention,,the switch blade itself is energized to constitute a common terminal of the switch, the electrical conductivity of at least one leg of the switch thus being important to the switch operation. Such a switch blade, and a switch assembly in which it is mounted, are shown in FIGS. 14-17 inclusive.

With reference first to FIG. 14, a switch blade indicated generally at 250 includes an upper leg portion indicated generally at 254, comprising laterally spaced

leg elements

257 and 259 separated by a central open portion 256. An actuating tongue 258 is formed integrally with the blade and extends downwardly into the opening 256. Upper leg 254 terminates upwardly in a narrowed projection 25] having an uppermost edge 255. The lower ends of

leg segments

257, 259 are merged in a laterally extending yoke 260, and the blade includes a lower leg 252 extending downwardly from yoke 260 and terminating in a lowermost edge 253. Central yoke portion 260 is provided on each of its faces with a conductive button, one of which is seen at 264 in FIG. 14. As will be evident, blade 250 is similar in many respects to blade 50 previously described, the major difference being that blade 250 does not include the laterally projecting

arms

60, 62 of blade 50, and only one conductive button 264 is provided on each of the faces of blade 250, rather than the two pairs of conductive buttons 64 on blade 50.

The mounting of blade 250 within the switch assembly, and its operation therein, are substantially similar to the mounting and operation of switch blade 50 heretofore described, and will be understood in detail by reference to FIGS. 15, 16 and 17. Thus the upper pro jection 251 of upper leg 254 is received in a V-shaped groove 72 formed in the lower face 70 of dielectric body shell 32, identical to the correspondingly numbered element in the form of the invention first described in connection with FIG. 2. The lowermost edge 253 of switch blade 250 is received in a V-shaped notch 275 formed in a lower common conductive terminal indicated generally at 280, embedded in a dielectric base member indicated generally at 224. The distance between notch 72 and notch 275 is less than the unstressed length of switch blade 250, and an abutment member 281 is disposed substantially midway of the overall length of blade 250, whereby to impose on the blade oppositely bowed portions in its upper and lower legs. As seen in FIG. 15, and corresponding to the lower right portion of FIG. 2, upper leg 254 has a convex configuration, while lower leg 252 has a concave configuration, both terms being used from the viewpoint of the center of the switch. On the opposite side of yoke 260 from abutment member 281 is another abutment member 285, the

abutment members

281 and 285 being normally closed and normally open abutment terminals 200 in respectively, and communicating downwardly with external normally closed terminal 282 and external normally open terminal 286 re spectively. In the upper portion of FIG. 15, actuator and its actuator nose 87 are identical in construction and operation to the correspondingly numbered elements in FIGS. 2 and 3. Thus, when actuator 80 is moved downwardly into its actuated position in the construction shown in FIG. 15, it will slidingly contact tongue 258, whereby to move switch blade 250 to its actuated position, not shown in FIG. 15, but corresponding to the position of blade 50 seen in the lower right portion of FIGS. 3 and 3a.

As will be seen in FIG. 16, external normally closed and normally

open terminals

282 and 286 respectively are desirably laterally offset from common external terminal 280, to facilitate connecting leads to those terminals. Also, as best appears in FIG. 17, it will be seen that the present form of the invention, similarly to the form of the invention first described and illustrated, contemplates the provision of a second switch blade and set of abutment terminals symmetrically disposed about the center of the switch relative to the switch assembly thus far described in connection with FIGS. 14, 15 and 16.

It is especially to be noted that the form of the invention shown and described in connection with FIGS. 14l7 inclusive incorporates the same advantageous characteristic as the first form of the invention, in that the movement of actuator 80 and its nose 87 is in a direction generally parallel to the general longitudinal axis of the switch blade. Moreover, contact between the actuator nose 87 and tongue 258 permits stress to be built up in the upper leg 254 of the blade, and the amount of that stress is virtually independent of the amount of overrun, if any, of actuator 80 beyond its design limit of travel. By this arrangement, as previously described in detail in connection with FIGS. 2, 3 and 3a, the provision of actuating tongue 258 eliminates the possibility that the switch blade might completely reverse its configuration, with the upper bowed portion becoming concave, and the lower leg becoming convex. As noted previously, this would render the switch totally inoperative for subsequent use, since those positions are stable and the switch would thus remain in that condition.

Modifications and changes from the illustrative forms of the invention hereinabove described and illustrated are witihin the contemplation of the invention, and are intended to be embraced within the scope of the appended claims.

What is claimed is:

1. An electrical switch having a switch body with an internal cavity and provided with upper and lower seats in the cavity, a switch blade of resilient conductive sheet material having upper and lower end edges received respectively in the upper and lower seats, the seats being spaced closer together than the instressed distance between the blade end edges, and a set of first and second fixed abutment means disposed on opposite sides of the blade substantially midway between the seats, the first abutment means being normally in abutting contact with one face of the blade whereby to impose thereon a generally sinuous contour longitudinally of the blade, the second abutment means being spaced slightly from the opposite face of the blade, characterized in that:

said blade includes upper convex and lower concave legs terminating respectively in said upper and lower end edges, the upper leg having formed therein a central opening dividing said leg into a pair of laterally spaced leg segments joined upwardly by a transverse yoke portion, and an actuatin g tongue formed integrally with the yoke and projecting downwardly from the central portion thereof in lateral alignment with said opening and extending tangentially to the convex face of the upper leg;

and including actuator means movable toward actuated position along a path of movement substantially parallel to the plane joining said seats and during said movement slidably flexing said tongue toward the center of curvature of the upper convex leg whereby to create stress in the yoke and and upper leg tending to decrease the curvature of the upper leg and simultaneously increase the curvature of the lower leg, until the blade snaps out of contact with the first abutment means andinto contact with the second abutment means.

2. The invention as defined in claim 1 including releasable latch means for selectively retaining the actuator in actuating contact with the tongue.

3. The invention as defined in claim 1 wherein said switch includes a second blade, a second pair of upper and lower seats, and a second set of first and second abutment means, all identical respectively to the first named corresponding elements and disposed within the cavity symmetrically relative thereto, and said actuator means is disposed centrally of the switch body and includes symmetrically placed portions for substantially simultaneously flexing the tongues of both blades during actuator movement toward actuated position.

4. The invention as defined in claim 1 wherein one of said seats is conductive and including a common terminal connected to the conductive seat.

5. In an electrical switch, in combination:

a vertically oriented body of dielectric material having formed therein an operating cavity having upper and lower walls, said walls having horizontally extending grooved seats formed therein;

a blade of generally cruciform shape and made of resilient conductive sheet material, including upper and lower legs terminating respectively in upper and lower parallel edges, and a pair of laterally extending arms substantially midway between said edges,

the upper leg having formed therein a central opening dividing said leg into a pair of laterally spaced leg segments joined by an upper yoke,

and a tongue formed integrally with the yoke and extending downwardly therefrom into said opening,

the distance between the blade upper and lower edges, when the blade is in unstressed planar shape, being greater than the distance between said seats,

and the blade being supported by said body with its upper and lower edges in said upper and lower seats respectively;

a first pair of abutment terminals carried by the body in said cavity and abuttable against the outer portions of said arms, whereby to impose on the blade an upper convex bow and a lower concave bow,

said tongue projecting tangentially to the upper convex bow;

a second pair of abutment terminals carried by the body in said cavity on the opposite side of the general plane of said blade from the first named pair of abutment terminals and in general horizontal alignment therewith;

and a vertically movable actuator selectively movable between a retracted position above said tongue, and a lower actuated position and in slidable abutting contact with said tongue during at least the terminal portion of its downward movement,

whereby to flex the tongue toward the center of curvature of the upper convex portion of the blade, and thereby to cause the switch to snap from its first position wherein said arms are in electrical contact with the first named pair of terminals,

to a second or actuated position wherein said arms are in electrical contact with said second pair of abutment terminals.

6. The invention as defined in claim 5 wherein said switch includes selectively releasable latching means for maintaining the actuator in its lower actuated position.

7. In an electrical switch having a switch body provided with a cavity therein, a generally vertically oriented elongated blade consisting of integrally formed upper and lower legs of substantially equal length, and made of resilient conductive material, the blade leg ends being mounted in seats in said body spaced closer together than the unstressed length. of the blade, whereby to impose a longitudinal compressive stress on the blade, a pair of laterally spaced abutment means on opposite sides of the blade adjacent to the juncture of the legs, one abutment means being in contact with the blade under rest conditions and imposing upper convex and lower concave bows on the legs, the provision of:

and opening in the upper leg dividing said leg into a pair of spaced leg segments joined at their upper ends by a transverse yoke,

a tongue formed integrally with the yoke and projecting downwardly therefrom and tangentially to the convex face of the upper leg,

and actuator means for selectively forcing the tongue toward the center of curvature of the upper leg whereby to create stress in the yoke and upper leg tending to decrease the curvature of the upper leg until the blade snaps away from contact with said one abutment means into contact with the other abutment means, the upper and lower legs retaining their respective convex and concave bowed configurations during movement of the actuator means.

8. The invention as defined in claim 7 wherein at least one of said seats is conductive and including an external terminal connected thereto.

9. The invention as defined in claim 8 including a second external terminal connected to one of the abutments.

10. The invention as defined in claim 7 including releasable latching means for selectively retaining said actuator in actuated position.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N 3,898,402 Dated August 5, 1975 C Inventoflg) Anthony R. Ford It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

. I i In the grant (ONLY) insert

columns

1, 2, 3 and 4, as shown on the attached sheets.

Signed and Sealed thls sixth D y of January 1976 [SEAL] Q Attest:

RU-TH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ufParenls and Trademarks FORM Po-1050 (10-69) UsCOMM-DC wave-Pas U.S. GOVERNMENT PRINTING OFFICE: 9

SNAP SWITCH WITH ACTUA'HNG TGNGL'E BACKGROUND AND SUhiMrUtr' OF THE lNVENTlON The present in cntion relates generally to electrical switches. and more particularly to a switch of the snap action type employing a switching blade of resilient conductive material which is maintained under longitudinal compressive stress in the body ot the switch whereby to impose on the blade oppositely bowed portions. which may for convenience he referred to as convex and concave bowed portions.

in a preferred form of the present invention. the resilient conductive blade constituting the su itching element in the present switch is generally cruciform in shape. having upper and lower legs and a pair of laterally cxtending arms substantially midway of the blade. The upper leg oi the blade is provided with a central Opening. and an integrally formed tongue projects downwardly into the opening. When the blade is mounted in its houssng; seats. a pair oi abutment termirials abut the arms. and impose on the blade the oppositely bowed configuration mentioned above. A second pair of abutment terminals lies on the opposite side ol the arms from the first named pair. Actuation of the switch consists ofdccreasing the curvature of the upper bowed portion of the blade and simultaneously increasing the curvature of the lower portion of the blade until a point is reached when the blade snaps from its rest position with its arms in contact with the first pair ol abutment terminals into an actuated position with its arms in contact with the second set of abutment terminals. Thus the arms constitute a shorting bar between the terminals of each pair. Actuation of the switch is effected by slid-able abutting Contact olan actuator element against the blade tongue, whereby stress is built up in the tongue and in the adjacent portions of the leg until the snap action results. Such movement of the tie-- tuator element is accomplished by depressing a pushbutton in accordance with the present illustrative enibotliment of the invention.

In an alternative form of the invention. the blade arms are eliminated. one end of the blade is in electri cal contact with a common terminal. and one abutment terminal is provided on either side of the blade, approximately midway of its length. The blade is otherwise the same as the cruciform blade lirst above mentioned. and includes an Zttjltlitlltlg tongue in its upper leg.

Releasable latching means are desirably provided in accordance with the present invention. whereby a single depression ol" the pushbutton or otherwise actuating the actuator element. sen es to maintain the switch in its actuated condition until a second depression of the actuator. and a lkzll dt-tt-nt clement i"--.lllt;tli}. receiwd in pt sitioi'is ol the actuating: t'ltniicnt. lln' il-li lt v'riy ii aylt cm y rtr ilient.

(ill

is suitable contoured and provided with ramps to insure that the ball detent. which is permitted limited lateral movement relative to the traclzway in order to follow the cardioid pa h. proceeds always in the same direction around said path.

in the preterrt-cl form ofthe invention. a second blade and associated abutment terminals may be provided. disposed symmetrically to the first about It central vertical axis of the switch. so that movement of the actuator switches two separate circuits substantially simultaneously.

it is accordingly a principal object of the present invention to provide and disclose an electrical switch havi g a novel conductive blade to accomplish the switching. and releasable latching means to maintain the switch. scle tively. in either its make or brcal; position. Other objects and purposes are to provide. in such a switch, a blade or generally cruciform shape. having a pair of laterally extending arms constituting in effect a shorting bar. to provide. in such a blade, an upper leg having an opening formed therein and an integral tongue extending downwardly into the opening. slidably abuttable by an actuator clement during actuatitm: to provide a releasable latching means to selectively maintain the actuator element in actuated position. and including a cardioid tracliway having. upper and lower lock positions. in which a ball detent is resiliently biused (or travel around the cardioid between one lock position and the other; for providing in such a switch a duplicate set of switching elements and terminals by which to double the circuit handling capacity of the switch in compact space; and for other and additional objects as will become clear from a reading of the lol lowing description of a preferred embodiment oithe invention, taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWlNGS FlG. l is a side clevational view of a switch embodying the present invention.

HO. 2 is a vertical sectional vie taken on line llll ofl lG. 1. showing the parts in their normal or rest positions.

HG. 3 is a fragmentary sectional view similar to H6. 2, except showing the parts in their actuated positions.

llG. 3A is a fragmentary sectional view similar to FIG. 3 and laterally aligned therewith. showing the right hand portion of the switch proper in actuated position as in l-l-Zj. 3. but with the pushbutton carrier retracted to its rest position.

HO. 4 is a sectional view taken on the line lV-l\/ oi FIG. 2.

H0. 5 is a developed view of the trackway and, in dotted outline. the successiye positions of the ball detcnt therein.

FlGS. (m.!1.canddare successive views of the migration of tin: ball detent around the cztrdioid trackway'. H0. (in corresponding to the position of the switch seen in l-'l(i. 2. Hi (ncorrcs ondin to the position of the switch seen in i ti. 3. and HUS. n!) and fut slime hi the ball and trackway' in intermediate positions.

l" (i.-2, 7. 8 and ill trc sectional \lt h taken along: the arrows \'ll --\'ll. \llll \'lll. and iv respectively of l-l(i. 2.

l-lt'} i :1 sectional view taken on the arrows l.\' ---lX (it Hi 3,

FIG. ll is a bottom plan view ol the switch taken on the arrows Xl-Xl ol FIG. 2.

FIG. I2 is a perspective view oi the preferred form of blade in accordance with the invention.

FIG. I4 is a perspective view of a switch blade in accordance with an alternative form of the invention.

FIG. 15 is a fragmentary sectional view of a portion of a switch incorporating, the blade of FIG. 14.

FIG 16 is a fragmentary sectional view taken on the arrows XVl--X\/l of FIG. 15.

FIG. 17 is a fragmentary sectional view tal-zcn on the arrows XVli-XVII ol FIG. 15. and showing the operative portions of the switch in thclet't portion ol the switch assembly, including a second blade and pair of terminals, disposed symmetrically relative to the corresponding parts in the right hall of the. switch assembly.

DETAILED DESCRIP'IION Referring now to the drawing, in FIG. I there is indicated generally at 20 a housing for Z'ontaining the operative portions of the present switch. the housing 20 being desirably made of metal and including an integrally; formed externally threaded boss 21 projecting upwardly from the housing propsr. for convenience in mounting the present switch hr rsing on a c ntrol panel or the like. A pushhutton carrier 22 is telescopically received within the threaded bore 2! and extends thereabove, and is adapted to have a suitable pushbutton mounted on its upper end for actuation by the user. With continued reference to TIC. 1, tin. lower portion of the cylindrical wall of the housing 2 is crimped in wardly at 23, in order to be attached to a downwardly extending base 24 ol dielectric material, from which outlet terminals project downwardly. there being visible in FIG. 1 a total of four such terminals, arranged in pairs '25, 26 and 27, 2-3, As will be later understood in detail, and as a glance at FIG. I! will show, there are desirably a total of eight downwardly projecting outlet terminals disposed symmetrically about a central vertical plane of the switch, the other four terminals being designated by primed reference numerals.

The internal construction of the elements of the switch will be best understood by reference first to FlGS. 2 and 4-, showing those parts in their normal or rest positions.

Thus the lower portion of housing 20 comprises a hollow cylindrical casing indicated generally at 30 which receives in its upper portion a body shell of dielectric material indicated generally at 32. This shell includes an uppc r annular ring; portion 3-4 and, extend-- ing downwardly therefrmn and integrally formed therewith, a pair of arcuatcly extending sldrts 3s. 37 (see FIG. 4), interrupted by a pair ol diametrically opposed openings 3?! 3), seen in ll i, 2. 'l be lower interrupted annular edges we or Slill'iS an, 37 a ut the upper face 41 ol dielcclric base member 24. .-\t lll\' midpoint olarcuate skirts 3-!" and 37, body shell 52 is provided with support columrc-z 4?. and -ll rcs'icctivcly, having coaxial posts -14 and 45 which extend downiurdly into

bores

46 and 47 l'orrncd in dielectric base 34.

As will be later utnlctstood. alter assembly of the switch blades with she l AP. art-i l-iiwc .54, the lowermost ends 4;"; and -55" ol post" l-l and -35 .li'i l'.:.-.n seated or welded to llLllLlt'Clll portions ol' dielectric base 24. so

(til

Pa e 3 that the shell and base form an integral dielectric body containing therewithin the operative portions of the switch, including switch blades and abutment terminals to be now described.

leg segments

57 and 59 joined by an upper transverse yoke. An integrally formed tongue 58 extends downwardly from the yoke, into the opening 56 with its sidewalls spaced inwardly from the inner walls of leg seg ments 57 and 5). so that, as will be later understood, tongue 58 can be flexed away from the plane of the yoke during operation. The blade also includes a pair of

arms

60, 62. extending laterally substantially midway between lower and upper edges 53, 55. The total cross sectional area

ol leg segments

57 and 59 is approximately equal to that of lower leg 52.

All of the elements of blade 50 thusl ar described are integrally formed ofa flexible conductive material such as a sheet of copper or copper alloy. To minimize contact resistance during switch operation, as is customary in the switch art, cont-actor buttons 64 may be provided on the arms, desirably made of any of well known materials ofhigh conductivity such a silver alloy or the like. As sh wn in FIG. .2, the outer surfaces of the contactor button 64 are desirable slightly convex.

There will now be described in connection with FIG, 2 a switch assembly comprising the blade of FIG. 12. its mounting in the dielectric body within casing 30, and the abutment terminals with which the blade arms make contact during switch operation. As will be evident from FIG. 2, the presentillustrative embodiment of the invention includes a pair of identical switch assemblies, disposed precisely symmetrically relative to a central vertical plane through the switch. and for brevity only the switching assembly in the left portion of FIG. 2 will be described in detail. Thus the body shell 32. and base 24, both of dielectric material, define therebetween an operating cavity housing the switch blade 50 and the terminals with which the switch arms are abuttable. The lower face of body shell 32 has formed therein a groove 72, and base 24 of the dielectric body similarly has a groove 74 formed therein.

Each groove constitutes a seat for receiving the lower and upper edges 53, 55 of blade 50, and the longitudinal spacing between

grooves

72 and 74 is appreciably less than the distance or height between the edges 53 and S5 of the blade when the blade is in its unstressed planar condition seen in FIG. 12. Blade 50 is thus l'orccd to assume u curved configuration throughout its length, and a pair of abutment terminals 76 and 7'7 (compare HG. l l) serve to impose upon blade Si) an oppositely bowedconfiguration in the upper portion of blade 50 comprising leg 54 from the bowed conligtxrtv lion in the lower portion othladc 5t) comprising. leg 2. More specifically. and using the terms from the viewpoint oi the central portion of tluswitch, upper leg 54 ir-sinncs it converts curvature. while lower leg 53. assumes a concave curvature. lndcr thcsc conditions

Claims

1. An electrical switch having a switch body with an internal cavity and provided with upper and lower seats in the cavity, a switch blade of resilient conductive sheet material having upper and lower end edges received respectively in the upper and lower seats, the seats being spaced closer together than the instressed distance between the blade end edges, and a set of first and second fixed abutment means disposed on opposite sides of the blade substantially midway between the seats, the first abutment means being normally in abutting contact with one face of the blade whereby to impose thereon a generally sinuous contour longitudinally of the blade, the second abutment means being spaced slightly from the opposite face of the blade, characterized in that: said blade includes upper convex and lower concave legs terminating respectively in said upper and lower end edges, the upper leg having formed therein a central opening dividing said leg into a pair of laterally spaced leg segments joined upwardly by a transverse yoke portion, and an actuating tongue formed integrally with the yoke and projecting downwardly from the central portion thereof in lateral alignment with said opening and extending tangentially to the convex face of the upper leg; and including actuator means movable toward actuated position along a path of movement substantially parallel to the plane joining said seats and during said movement slidably flexing said tongue toward the center of curvature of the upper convex leg whereby to create stress in the yoke and and upper leg tending to decrease the curvature of the upper leg and simultaneously increase the curvature of the lower leg, until the blade snaps out of contact with the first abutment means and into contact with the second abutment means.

5. In an electrical switch, in combination: a vertically oriented body of dielectric material having formed therein an operating cavity having upper and lower walls, said walls having horizontally extending grooved seats formed therein; a blade of generally cruciform shape and made of resilient conductive sheet material, including upper and lower legs terminating respectively in upper and lower parallel edges, and a pair of laterally extending arms substantially midway between said edges, the upper leg having formed therein a central opening dividing said leg into a pair of laterally spaced leg segments joined by an upper yoke, and a tongue formed integrally with the yoke and extending downwardly therefrom into said opening, the distance between the blade upper and lower edges, when the blade is in unstressed planar shape, being greater than the distance between said seats, and the blade being supported by said body with its upper and lower edges in said upper and lower seats respectively; a first pair of abutment terminals carried by the body in said cavity and abuttable against the outer portions of said arms, whereby to impose on the blade an upper convex bow and a lower concave bow, said tongue projecting tangentially to tHe upper convex bow; a second pair of abutment terminals carried by the body in said cavity on the opposite side of the general plane of said blade from the first named pair of abutment terminals and in general horizontal alignment therewith; and a vertically movable actuator selectively movable between a retracted position above said tongue, and a lower actuated position and in slidable abutting contact with said tongue during at least the terminal portion of its downward movement, whereby to flex the tongue toward the center of curvature of the upper convex portion of the blade, and thereby to cause the switch to snap from its first position wherein said arms are in electrical contact with the first named pair of terminals, to a second or actuated position wherein said arms are in electrical contact with said second pair of abutment terminals.

7. In an electrical switch having a switch body provided with a cavity therein, a generally vertically oriented elongated blade consisting of integrally formed upper and lower legs of substantially equal length, and made of resilient conductive material, the blade leg ends being mounted in seats in said body spaced closer together than the unstressed length of the blade, whereby to impose a longitudinal compressive stress on the blade, a pair of laterally spaced abutment means on opposite sides of the blade adjacent to the juncture of the legs, one abutment means being in contact with the blade under rest conditions and imposing upper convex and lower concave bows on the legs, the provision of: and opening in the upper leg dividing said leg into a pair of spaced leg segments joined at their upper ends by a transverse yoke, a tongue formed integrally with the yoke and projecting downwardly therefrom and tangentially to the convex face of the upper leg, and actuator means for selectively forcing the tongue toward the center of curvature of the upper leg whereby to create stress in the yoke and upper leg tending to decrease the curvature of the upper leg until the blade snaps away from contact with said one abutment means into contact with the other abutment means, the upper and lower legs retaining their respective convex and concave bowed configurations during movement of the actuator means.