US2318734A - Snap action switch - Google Patents

Description

May H, 1943. A. E, BAAK SNAP ACTION swITcH Filed Deo. 7, 1939 Ameri E. cmk

, Gorngg Patented May l1, 1943 Albert E.

Baak, Minneapolis, Minn., assignor to Minneapolisdioneywell Regulator C Minneapolis, Minn., a corporation of Omlmny, Delaware Application December 7, 1939, Serial No. 307,991

19Clalms.

This invention relates to switching devices which are actuated with a snap action.

One oi.' the main objects of the present invention is to design a small, compact, and unitary snap action switch which is inexpensive to manufacture and eiliclent in operation.

A further object is to design a snap action switch of the self return type and completely enclose the structure in an insulating housing having anactuating pin extending therethrough.

Another object is to provide a simple method of changing this switch from aself return type to a push-pull type by inserting a small additional spring inside of the cover.

Another object is to providel an open contact switch lever which is rotated by means of a resilient actuating member and further to provide spring means acting on the lever for over-compensating the spring rate of the actuating member to produce a snap action. 'I'he lever may' carry one or more movable contacts by means of press back blades and in this case the spring rates of the press back blades must also be overcompensated by the spring means.

Still another object is to provide a switch of the above type wherein means are providedfor adjusting the angle at which the spring means exerts its force on the switch lever and also means for adjusting the force exerted bythe spring means.

Another object Vis to provide a double throw switch having two press back blades normally having zero tension and on rotation of the lever one of the blades starts being pressed back just as all of the press back has been relieved from the other blade. 'Ihus the two blades as v tive spring rate and the switch can '-be actuated with a smaller driving force.

These and other objects will readily become apparent as the following specication is read in the light of' the accompanying drawing, in which Figure 1 is a sectional view of va preferred embodimentof my invention, the section being taken along the line of Figure 2.

Figure 2 is a along the line 2-2 of Figure 1.

Figure 3 is an elevation of a modified form of my invention.

Figure 4 is a view of and e Figure 5 is a `detail view 'of a spring which may be added to each of the modications disclosed in the first four iigures.

a further modification,

so arranging them that a unit have a constant eiecf plan view taken partly in section The holes areof such enoy for the contacts Referring now to Figure 1 of the drawing, the reference numeral indicates an insulating base in which are mounted a pair of tacts I2 and I4 which are in the form of sleeves and have at their upper ends special contact surfaces. These sleeves screw terminal screws I5 and I6. l

A metallic frame I1 is mounted on the base and is retained thereon by means of the sleeve I8 which extends'through a hole in the base and also through a hole in the frame I1 and which is turned over to secure the frame to the base member. 'I'he frame -I1 is arms I9 between which is mounted an axle 2|). Lever 2| is pivotally mounted on the axle 20 and carries a pair of press back blades 22 and 23 by any suitable means such as the rivet 24. Each end of the lever 2| is provided with a turned down portion 25 provided with a hole through which 'the ends of the press back blades extend. size as to permit the ends of the blades a predetermined amount of movement relative to the lever and the blades 'are izen-l sioned downwardly against the lower ends of the lever. The press back blade 22 carries a contact 26 which is adapted to cooperate with stationary contact I2 and the blade 23 carries contact 21. which is adapted to cooperate with the stationary contact I4. As seen in Figure 1 the contacts I4 and 21 are in engagement and the blade 23 has been pressed back. Contacts 26 and I2 are separated and the end of the press back blade is tensioned downwardly against the downwardly turned end 25 of @the lever 2|.

A stop 29 is mo ted in the base for limiting the rotation of the lever 2| in a counter-clockwise direction as seen in Figure 1. 'I'hus the lever 2| is not pressing on the movable contact 21 and the pressure between the contacts 21 and I4 is determined by the tensionin the press back blade 23. A similar stop shownin dotted lines in Figure 2 limits the'rotation of the lever 2| in a clockwise direction. Iidesired these stops may be eliminated so that the engagement of the lever with thecontacts themselves limit the rotation of the lever. 'I'his provides for a greater contact pressure for a given switch actuating force but with this-arrangement there is a greater tendto bounce as they come together. Therefore in the preferred embodiment of my invention I employ the stops 29 to limit the movement of the ency toward contact bounce.

stationary conthreadedly receive provided with a pair of lever and reduce the tendwhich one end of a toggle 3| noted that the contact lever 2| is symmetrical about the axle 29. This is so the lever may be assembled on the base without regard to which end is which. The other end of the toggle 3| seats in a depression in an L shaped leaf spring 32, the other end of which is adjustably connected by means of the screw 33 with a horizontally extending portion 34 of the frame I1. The lower end of the leaf spring 32 in which the toggle 3| seats is biased toward the left as seen in Figure 1, and in this position of the parts it biases the lever 2| for rotation in a counter-clockwise direction thereby tending to hold the contacts 21 and I4 in engagement.

'A resilient arm 36 is connected at one end to an arm 31 on the frame I1 and its other end is formed with a reduced portion which extends within the slot 35 in the end of lever 2|. The reduced portion of arm 36 forms shoulders which bear on the surface of lever 2| to rotate the lever. A cover 38 seats on the base II and forms therewith a housing for the entire switch mechanism. A pin 39 extends through an opening in the cover 38 and seats on the rounded projection 40 on the resilient member 36.

When no external force is being applied to the pin 39 the parts will assume the positions shown in Figure 1. At this time the press back blade 23 is attempting to rotate the lever 2| in a clockwise direction but this tendency is overcome by the leaf spring 32 acting on the lever 2l through the toggle 3| and holding the lever in the position shown. In order to actuate the switch an seats. It will be external force is applied to the pin 39 pushing it downwardly. This force tends to bow the resilient member 36 and build up a force therein until it is sufllcient to start the lever 2| rotating in a clockwise direction. As this rotation starts it will be noted that the angle between the toggle 3| and the lever 2| changes in such a manner that the effective force opposing rotation of the lever 2| and exerted by the leaf spring 32 is decreasing. The rate at which this force decreases must be so related to the spring rate of the resilient arm 36 that it decreases faster than the decrease in the force exerted by the resilient arm 36 as this arm rotates the lever 2|. It will also be noted that as the lever 2| rotates, the press back blade 23 straightens out and the force exertedby this blade tending to rotate the lever 2| also decreases until the end of the press back blade engages the end of the lever 2| at which time this force suddenly becomes zero. As the lever 2| continues to rotate contacts 23 and I2 engage at being lfiexe'd'a'nd this iiexure further opposes'ro. tation of the lever 2|. Therefore, in order that the lever snap completely from one position to the other, the force exerted by leaf spring 32 which resists lrotation of the lever 2l must decrease at a rate greater than the combined effect of the spring rate of the resilient arm 36 and the effect of thecpress back in blade 23 being relieved and the effect of picking up the press back blade 22. In Aother words, the spring rate of the resilient arm 36 must be such that when a force is stored in this arm sufficient to start the lever 2| to rotate in a clockwise direction it must decrease at a rate sufficiently low to continue to rotate the lever 2| to its other/position. This can only be accomplished as long as the force exerted by the leaf spring 32 resisting rotation of the lever decreases at a sufciently rapid rate to over-compensate the spring rate of thel resilient arm 33,

which time the press-back blade 22 is electrical connection the press back blades 22 and 23 and to overcome the effect of the initial tension in each of the press back blades as the resisting force of blade 23 is reduced to zero and the resisting force of blade 22 is picked up and increased from zero to a value depending upon the initial tension of the blade.

As set forth above the stop 29 limits rotation of the lever 2| in a clockwise direction and at this time the lever 2| has not passed over center. or even up to dead center, with respect to the` toggle 3|.` This being the case the leaf spring 32 is still tending to rotate the lever 2| in a counter-clockwise direction although with a much smaller force than it was before the'lever 2| was rotated. At this time therefore there is still sufficient force being exerted by the resilient arm 36 to hold contacts 26 and I2 in engagement and to press back the blade 22. As the external force on the pin 39 is removed to a point where the resilient arm 36 cannot hold the lever 2| the lever will start to rotate in a counter-clockwise direction. As it does so the angle at which the toggle 3l presses against the lever 2| is changed to increase the rotative elect which the leaf spring 32 has on the lever 2| and here again this change must increase more rapidly than the increase in resistive force due to the spring rate of the resilient arm 36 and must also increase at pensate for the effect of the press back blades 22 and 23 so that once the lever 2| starts to rotate in a counter-clockwise direction the leaf spring 32 will continue that rotation until thc lever has returned to its original position.

In order to properly adjust the switch a screw 43 is passed loosely through a hole in the base II and screw threadedly engages the frame I1 which is biased upwardly. Rotation of this screw will vary the position of the frame and hence the lower end of the leaf spring 32 thereby changing the angle at which the toggle 3| engages the lever 2|. Also by rotating the screw 33 the force exerted by the leaf spring 32 may be adjusted. Adjustmentof this force will of course vary the differential of the switch.

It will be noted that this switch is a single pole double throw switch having a common terminal screw 44. The electrical connection is from the terminal 44 through sleeve I8 to the frame I1, arm I9, and through parallel paths through the axle 29 or conductor 45 to the switch lever 2|. As the switch is oscillated back and forth the is therefore alternately from the terminal 44 to terminal I5 and from terminal 44 to the terminal I6.

Figure 3 shows a modification of the switch shown in Figure 1 in which the base II, frame I1, switch lever 2| and resilient actuating arm 36 are substantially the same as in Figure 1. In Figure 3, however, a bowed leaf spring 50 takes the place of the leaf spring 32 and toggle The spring 50 seats in a depression 5| in the frame I1 and its other end engages directly on the end of the lever 2|. In this modification as the lever 2| is rotated in a clockwise direction it passes over-center with respect to the spring 50. Therefore a return spring 52 must be provided for returning the lever 2| to its original position. In this modification the press back blades 22 and 23 are under zero initial tension and furthermore, as the lever 2| is rotated; the press back in one 'blade is` first gradually relieved and just as one contact is separating from its stationary contact the other contact is just a rate sulciently great to over-com- Y engaging its stationary contact and the other Another diflerence'between this modication and that of Figures 1 and 2 is that the lever is limited in its with the movable contact after the press back blade has been tensioned its limit. In other words, in Figure 3 the contacts 2l and it are in engagement and the left-hand end of the lever 2i is resting on the upper part of the mov,- able contact 21, so that all of the forces which went to produce the snap action are now taken up in forcing the contacts together. Furthermore, as the press back blade 28 is itself trying to rotate lever 2i, the actual pressure between the contacts is greater than the external force required to actuate the switch.

It is intended that the base ii in Figure 3 shall be provided with a -cover and actuatingr pin the same as the switch in Figures 1 and 2. As an external force is applied to the pin an actuating force will be stored in the resilient arm 36 until the lever 2i starts to rotate in a clockwise direction. This rotation is of course initially opposed by the spring 50 but as the lever starts to rotate this a rate suicient to over-compensate for the spring rates of the resilient arm 36, the return spring 52 and the press back blades 22 and 23. Spring will tend to maintain the contacts 26 and i2 in engagement after the lever 2l has been rotated and therefore the return spring 52 must exert sufcient force to overcome the effect oi the spring 50 when the tension in the resilient arm 36 has been removed. It will be understood that as the lever 2i starts to rotate in a counterclockwise direction that the spring 50 will again over-compensate the spring rates of the resilient arm 36, return spring 52 and the two press back blades to 'snap the lever 2i in the opposite direction.

Figure 4 illustrates a third form. of my invention and comprises a stationary support 60 with which the lever 6i has a knife edge engagement; 'I'he opposite end of the lever 6| is engaged by a toggle 62 which seats in a depression in a pivoted' arm 63. The spring 66 biases arm 63 for rotation in a direction to place a longitudinal compressive force on the lever 6l. The lever 6i carries a movable contact 65 by means of a pressr back blade 66, the contact 65 cooperating with a stationary contact 67. When the lever 6i and toggle 62 are aligned the contacts 65 and 61 are in engagement butwthe blade 66 has not been pressed back. This is actually-anunstable position of the switch yas the lever 6I is snapped between the two stops 68 and 63. The lever 6l is actuated by means of a resilient arm 'i6 which is engaged by an actuating pin 'll similar to the pin 39 shown in Figure 1.

Assuming the lever 6i to be engaging the stop 68 it will be seen that theeiect of spring 66 through the lever 63 and toggle 62 is to oppose rotation of the lever 6i. external force to the pin il therefore stores energy in the resilient arm 'l0 until it exerts a being tensioned. The rethe two press black blades.

opposing force decreases at The application of anA rotation only by its engagement in con-junction with spring also compensate the spring blade 66.

his time the effect of spring @d is to tend to At t hold the lever 6i infengagement with the stop arm 76 is relieved by the pin lli. As the lever 6i starts to rotate in a counter-clockwise direction notch Il 1s shown in the outer end of the pin 39 so that it may be engaged by any suitable actuatit may be both pushed and closed herein.

I claim as my invention: 1, In a device of the character described, a

tacts being in engagement at a rate said contacts, a resilient .arm engaging said lever, means for building up a force in said arm, said la't named force being of sumcient. magnitude t rotate said lever against the action of said spring means and hence reduce the angle between the direction of said force and said lever, the reduction in the angle at whichsaid spring means exerts itsiorceover compensating the spring rate of said resilient arm, and means limiting the rotation of said-lever to prevent the direction of application o! force by said spring means ever being aligned with said lever whereby said spring means is operative to return said leverto its original position upon 'a reduction of the force applied to said arm.

2. In a device of the character described, a pivoted lever, a resilient blade mounted on said lever, a movable contact carried by of said blade, a stationary contact mounted for cooperation with said movable contact, spring means exerting a compressive force on said lever, the direction of said force being at an angle of less than 45 with respect to said lever and such as to tend to separate said contacts, and a resilient member for rotating said lever against the action of said spring means and hence reduce the angle between the direction of said force and said lever, said rotation causing such a reduction in the angle at which said spring means exerts its force on said lever that the spring rates of both said resilient member and said blade are over compensated engage with a snap, said contacts acting to limit tbe rotation of said lever, said blade acting in a direction to reverse said lever.

3. In a device of the character described, a movable member, a resilient blade mounted thereonl a movable contact carried by the free end of said blade, a stationary contact, said confirst position of said movable member and separated at a second a compressive force on said member, the direction of said force being at 45 with respect to said movable member, said force constantly tending to move said member to one of its positions throughout the entire movement of said member, and resilient means for moving said member against the force exerted by said biasing means and hence reducing the angle between the direction ofsaid force and said movable member, said change in angle over compensating the spring rate of said resilient means and blade to cause said member to move from one position to another with a snap action.

4. In a device of the character described, a vlever pivoted at a mid point, a movable contact carried by said 'lever on each side of said mid point, a pair of stationary contacts mounted for cooperation with said movable contacts, spring means exerting a compressive force on said lever at an angle of less than 45, said force tending to close one pair oi contacts and separate the other pair, and said lever against the force exerted by said spring means, said rotation causing he angle at which said spring means exerts its force on said lever whereby the spring rate of said resilient member is over compensated and the lever moves with a snap action to separate one pair oi contacts and close the others, engagement of one or the other of said pairs of contacts limiting the rotation of said lever whereby substantially all of the force which causes the lever-to snap, acts to hold the contacts in engagement.

the free end.

to cause said contacts to exerts its force on said lever that biasing means applying a resilient member for rotating 5. In a device of the character described, a pivoted lever, a resilient blade mounted onsaid lever, a movable contact carried by the free end of said blade, a stationary contact mounted for cooperation wth said movable contact, spring means exerting a compressive force on said lever at an angle of less than 45, said force tending to separate said contacts, a resilient member for rotating said lever against the action of said spring means, said rotation causing such a rethe angle at which said spring means the spring and said blade are over compensated to cause said contacts to engage with a snap, said blade acting in a direction to reverse said lever, and stop means for limiting rotation of said lever whereby the pressure between the contacts is determined by the blade only.

6. In a device of the character described, a. lever pivoted at a mid point, a pair of resilient blades mounted on said lever with their free ends on opposite sides of said mid point, movable contacts carried by the free ends of said blades, blades being -so arranged that when said lever is rotated in one direction one of said blades is pressed back and therefore tensioned, and' when the lever is rotateddn the opposite direction the other blade is pressed back and tensioned, stationary contacts, spring means exerting a compressive force on said lever at an angle of less than 45 and such as to tend to hold one pair oi contacts closed and the other pair open, and a resilient member for rotating the lever against the action of said spring means and hence reducing the angle between the direction of said force and said lever, the arrangement being such that just as the tension of one oi' said blades is relieved the tension of the other blade starts to become operative whereby the two blades as a whole have a substantially constant eiiective spring rate as said lever is rotated, rotation of said lever causing such a reduction in the angle at which said spring means exerts its force on said lever that the spring rates of said resilient member and said blades are over compensated.

'1. In a device of the character described, a lever pivoted at a mid point, a pair of resilient blades mounted on said lever with their freeA ends on opposite sides of said mid point, movable contacts carried by the free ends of said blades, said resilient blades being so arranged that when said lever is rotated in one direction one of said blades is pressed back and therefore tensioned, and when the lever is rotated in the opposite direction the other blade is pressed back 'and tensioned, stationary contacts, spring means exerting a compressive force on said lever at an angle less than 45 and such as to tend to hold one pair of contacts closed and the other pair open, and a resilient member for rotating the lever against the action of said spring means, the arrangement being such that just as the tension of one of said blades is relieved the tension of the other blade starts to become operative whereby the two blades as a whole have a substantially constant effective spring rate as said lever is rotated, rotation of said lever causing such a reduction in the angle at which said spring means exerts its force on said lever that the spring rates of said resilient member and said blades are over compensated, engagement of said contacts limiting the rotation of the lever in each direction whereby substantially all of the force direction, -ed on said base and the other end' operatively asians which causes the snap action, acts to hold the contacts in engagement.

8. a device of the character described, a lever p voted at a mid point, :a pair of resilient blades mounted on said lever with their free ends on opposite sides of said mid point, movable contacts carried by the free ends ofV said blades,

stationary contacts, spring means exerting a compressive force on said lever at an angle of less than 45 and such as to tend to hold one pair of contacts closed and the other pair open, a resilient member for rotating the'lever against the action of said spring means, the rotation of said lever causing such a reduction in the angle at which said spring means exerts its force on said lever that the spring rates of said resilient member and said blades are over compensated, and stop means for limiting theA rotation of said lever in each direction whereby the pressure between the contacts is determined by the tension in the resilient blades.

9. In a device of the character described, a movable member, spring means exerting a compressive force on said movable member at an angle of less than 45 and such as to bias it for movement in one direction, a resilient member for moving said movable member against the force exerted by said spring means, said movement reducing the angle at which said spring means exerts its force on said movable member whereby the spring rate of said resilient member is over compensated thereby causing a snap action of said movable member, means for manually changing the angle at which said spring means exerts'its force on said movable member, and a control device actuated by said movable member.

10. In a device of the character described, an insulating base, a lever pivotally mounted on said base,a movable contact carried by said lever, a stationary contact mounted on said base for cooperation with said movable contact, spring means mounted on said base, saidvspring means exerting a force on said lever at such an angle as to bias said lever for rotation in a given direction, aresilient arm having one end mounted 4on said base and the other end operatively associated with said lever, a cover for said base..

a button extending through said cover and engaging said resilientv arm at a point spaced fromV its other end, the application of an external force to said button building up asuicientforce in. said resilient arm to rotate said lever, said rotation causing the angle at which said spring means exerts its force on said lever to change and over compensate the spring rate of said resilient arm, and means preventing said lever from going over center with respect to said spring means whereby said spring means returns saidlever to its original position.

11. In a device of the character described, an insulating base. a lever pivot-ally mounted on said base, a, movable contact carried by said lever, a stationary contact mounted on said base for cooperation with said movable contact, spring means mounted on said base, vsaidspring meansV exerting a force on said lever at such an angle as to bias said lever for rotation in a givenl a resilient arm having one end mountassociated with said lever, a cover for said base, a button extending through said cover and enggaging' said resilient arm at a point spaced from.

rotation causing the angle at which in said resilient arm to rotate said lever, said said spring means exerts its force on said lever to change and over compensate 'the spring rate oi' said resilient arm, means preventing said lever from going over center with respect to said springy means whereby said spring means would normally returny said lever to its original position when the external force applied to said button is removed, and a second spring means inside said cover applying a force to said button which is suflicient to prevent said rst spring means for returning said lever but insufficient to rotate said lever against the force exerted by said first spring means.

12. ln a'device of the character described, an insulated base, a snap action switch of the shelf return type mounted on said base, an actuating member for said switch, a cover for said base enclosing said switch and actuating member, a pin extending through said cover and engaging said actuating member, and a spring mounted between said cover and said pin and exerting a force on said pin suiiicient to' prevent the return of said snap switch but insumcient to actuate said switch.

13. In a device of the character described, a substantially rigid pivoted lever, a movable contact carried by said lever, a stationary contact mounted for cooperation therewith, a support, a bowed leaf spring seated at one end on said support and engaging said lever lat the other end to exert a force on said lever at an angle with respect thereto, a resilient member for rotating said lever against the force exerted by said leaf spring, the change in angle at which said spring exerts its force on said lever over compensating the spring rate of said resilient member, and means for adjusting said support along a line substantially parallel to the movement of said movable contact.

le. In a device of the character described, an elongated lever, pivot means pivoting said lever for rotary movement, a stationary contact, a movable contact carried by a free end of said lever for cooperation with said stationary contact, spring means exerting a compressive force on said free end of the lever at an angle of less than 45 and such as to tend to separate said contacts, a resilient arm acting upon said lever at which it acts on said sucient to cause said resilient arm to rotate said lever in a contact closed direction, rotation movable contact carried by a free end of said lever for cooperation v tact, spring means exerting a compressive force with said stationary conon said free end of the lever at an angle of less than 45 and such as to tend to separate said contacts, a resilient arm acting upon said lever at a point between said pivot means and movable contact, and means for exerting a force on said resilient arm at a point remote from the point at which it acts on said lever, -said i'orce being suflcient to cause said'resilient arm to `on said lever, said 6 rotate said lever in a contact closed direction, rotation of said lever causing a reduction in the angle at which said spring means exerts its force spring means exerting sutilcient force to overcompensate the spring rate of said resilient arm. said stationary contact being so positioned as to stop rotation of said lever by its cooperation with the movable contact before said lever` has reached its dead center position with respect to said spring means.

16. In a device of the character described, an elongated lever, pivot means pivoting said lever at a mid point for rotary movement, a first stationary contact. a first movable ,contact carried by one end of said lever for cooperation with said first stationary contact, a second stationary contact, a-second movable contact carried by the other end of said lever for cooperation with said second stationary contact, spring means exerting a compressive force on one end of said lever at an angle of less than 45 and such as to tend to separate said first contacts, a resilient arm acting upon said lever at a point between said pivot means and one of said movable contacts, and means for exerting a force on said resilient arm sufllcient to cause it to rotate in a direction to close said iirst contacts, rotation of said lever causing a reduction in the angle at which said spring means exerts its force on said lever, said spring means exerting sumcient force to overcompensate the spring rate of said resilient arm.

17. In a device of the character described, an elongated lever, pivot means pivoting said lever at a mid point for rotary movement, a rst stationary contact, a ilrst movable contact carried by one end of said lever for cooperation with said first stationary contact, a second stationary contact, a second movable contact carried by `the other end of said lever for cooperation with said second stationary contact, springmeans exerting a compressive force on one end of said lever at such an angle of less than 45 and such as to tend to separate said first contacts, 'a resilient arm asrsfzsa tion with said first movable contact before said lever has reached its dead center position with respect to said spring means.

18. In a device oi.' the character described, a movable member, means for limiting said member for movement between two positions, spring means, a toggle link carried at one end by said spring means and at the other end by a free end of said movable member, said toggle link transmitting said spring force to said movable member at an angle thereto for biasing said member for movement to one of its positions, a resilient member for moving said movable member against the force exerted by said spring means, the resultant reduction in the angle between the toggle link and movable member over compensating the spring rate-of said resilient member so as to cause a snap action of said movable member, and means for adjusting the position of said spring means in the direction of movement of said free end of said movable member and over a suflicient range to change the action of said toggle link from a non over center action in which said spring means makes said device a device of the self return type, to an over center action with respect to said movable member whereby said device is changed from a self return.

19. In a device of the character described, a movable member, means for limiting said member for movement between two positions, spring means, a toggle link carried at one end by said spring means and at the other end by a free end acting upon said lever at a point between said pivot means and one of said movable contacts,

and means for exerting a force on said resilient arm suillcient to cause it to rotate in a direction to close said first contacts, rotation of said lever causing a reduction in the angle at which said spring means exerts its force on said lever, said spring means exerting sufllcient-force to over compensate the spring rate of said resilient arm, said first stationary Acontact being so positioned as to stop rotation of said lever by its cooperaof said movable member, said toggle link transmitting said spring force to said movable member at an angle thereto for biasing said member for movement to one of its positions, a resilient member for moving said movable member against the force exerted by said spring means, the resultant reduction in the angle between the toggle link and movable member over compensating the spring rate of said resilient member so as to cause a snap action of said movable member, and means for adjusting the position of said spring means in the direction of movement of said free end of said movable member and over a sufficient range to change the action of said toggle link from a non over center action in which said spring means makes said device a device of the self return type, to an over center action with respect to said movable member whereby said device is changed from a self return, and means for adjusting the magnitude of the force exerted by said spring on said toggle link.

ALBERT E. BAAK.

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