US2181068A - Electric snap switch construction - Google Patents

Description

Nov. 21, 1939. A. L. RICHE 2,181,

ELECTRIC SNAP SWITCH CONSTRUCTION Filed Nov. 26, 1937 J2 1 V /J@ 2 j I 0 I 2 6'6 I 12 2 36' a1 14 36 aa- Patented Nov. 21, 1939 UNITED STATES 2,181,088 7 ELECTRIC SNAP swr'rcn coNs'rnUc'rroN Arthur L. Riche, Freeport, Ill., assignorto Micro Switch Corporation, Freeport, 111., a corporation of Illinois Application November 26, 1937, Serial No; 110,535

15 Claims.

The present invention relates generally to electric snap switches, and relates more particularly to snap mechanisms formed of thin leaf springs for such snap switches.

The present invention constitutes an improvement upon the construction of snap switches of the type shown in the patent to Phillip K. Mc- Gall, 1,960,020, May 23, 1934. The McGallswitch is a precision switch and employs a spring toggle type of snap mechanism constructed of thin leaf springs. In one of its forms its snap mechanism includes a cantilever leaf spring that is flexed by an actuating plunger to induce a snap action of the switch. The McGall switch is a precision switch in that it operates in response to a very slight motion of its operating plunger and operates consistently and reliably at a given plunger position even though the plunger be brought to that position slowly. Certain of the commercial constructions, for example, operate in response to mechanical movements of the order of a thousandth (0.001) inch between on and off with only a few ounces of operating force and yet control directly loads of the order of a thou sand watts on alternating current circuits.

The McGall switch possesses a unique combination of precision of operation, large control capacity and small operating effort which has won its adoption in a large number of electrical control applications. The switch is used for its precision on machine tools to control the operation of tool carriages and cross feeds within tolerances of a few thousandths of an inch. It is used for its small operating efiort to count sheets of thin letter paper delivered at high speeds from printing presses. And it is used for its precision, its small operating effort and its large control capacity in thermostats for controlling domestic heating systems and numerous types of industrial heating apparatus. The switch also finds extensive use in other applications such as other machine applications and where the small compact structure of the switch and its high control capacity are of particular advantage.

Because the switch must operatewith precision and with small operating effort, it must be manufactured to close tolerances, and the forces of its spring mechanism must be balanced with torily for many purposes and has certain dedesirable characteristics, such as those already enumerated, it is entirely unsuited to many other applications and it presents a number of manufacturing difliculties. These shortcomings have seriously restricted thecommercial value and importance of the switch. For example, individual switches made in quantity production have exhibited widely different operating characteristics. Consequently, they could not be made easily interchangeable for replacement purposes, and the switch could not conveniently be fitted into the design of other quantity production apparatus, the characteristics of which had to be matched to the characteristics of the switch. Painstaking care and elaborate adjustments in assembly have failed to eliminate the individual variations in the switches, so that even with high manufacturing costs the McGall switch still is limited in its market. One particularly objectionable variant has been the operating life of the individual switch. Switches made at the same time and in the same manner, and seemingly alike in every detail would show lives, as measured by number of mechanical operations, differing from each other in ratios as high as 10 or 20. Some of the switches would fail in service in a short time while otherswould seemingly perform indefinitely.

I have found that a considerable number of the premature failures of switches has beendue to breakage of the cantilever tension springs, that the breakage resulted from fatigue and not from shock or abuse, and that the fatigue can be allayed by restricting the bending of the springs. I have found that some applications of the switch inherently limit the operating force or motion applied to the switch while others do not. I have found that where a switch is operated manually, or otherwise in such a manner that neither the operating pressure nor the operating motion is limited to that required for the actuation of the switch, and also frequently where the switch is operated by cams or other devices having fixed distances of movement, the plunger may be forced several thousandths of an inch beyond the operating point of the switch mechanism, and that the excess bending of the cantilever spring driven by the plunger hastens the fatigue of the metal of the spring and induces premature breakage. Ordinarily a switch should exhibit a mechanical life far in excess of the life to which it is limited by the electrical load which it is required to control. I have found that a certain commercial form of the switch will execute in excess of ten million operations without showing any mechanical failure if the motion'of the operating plunger be limited to that required for the proper operation of the switch, but if the plunger be operated through a certain greater distance, the resultant excess bending of the cantilever spring will induce breakage as early as a half million operations.

But, even though such excess flexing of the spring injures the switch, an excess travel of the driving member must be permitted in many apparatuses such as for example, constructions in which the switches are operated by cams, and an excess plunger travel is frequently desirable in other devices such as for example, certain manually operated switches.

Under certain conditions, it is undesirable to attempt to make the cantilever spring more flexible to accommodate the excess bending or otherwise to alter the characteristics of the spring members of the snap mechanism itself because such changes introduce new and different operating characteristics of the switch.

Objects of the present invention include the provision of means for limiting flexure of the spring of the switch of the McGall type and for doing so cheaply in the quantity production of switches, the provision of means for limiting spring flexure while permitting excess motion of the driving elements, and the provision of improved actuating mechanism for snap switches. The objects also include the provision of an improved switch construction, one that will expand the usefulness and increase the life and reliability of the switch and make individual switches more uniform and dependable. These and other objects and advantages will become apparent from the following description of a specific embodiment of my invention which serves by way of example to illustrate the manner in which the inventions may be used. However, the invention is not to be limited to the particular details of any embodiment or example. In the drawing:

Fig. 1 is a longitudinal sectional elevation of a complete snap switch embodying my present invention and constitutes a section taken along the line l--l of Fig. 2;

Fig. 2 is a transverse sectional elevational view of the switch of Fig. 1 taken along the lines 22 of Fig. 1, and viewed in the direction indicated by the arrows;

Fig. 31s a perspective view of a shim or space which serves to limit the movement of the operating plunger of the switch;

Fig. 41s a.plan view of the support member or anchor for the compression leaf springs;

Fig. 5 is a plan view of the integral spring leaf which includes the thin leaf compression and tension members of the snap mechanism of the switch of Fig. l;

Fig. 6 is an enlarged sectional detail view of a part of the apparatus shown in elevation in Fig. l,

. and constitutes a section taken along the line 66 of Fig. '7; and

Fig. 7 is a detail section drawn to the same scale as Fig. 6 and taken along the line of l--'! of Fig. 6.

In accordance with the present invention I provide a fixed stop for the actuating plunger of the switch and interpose a yielding or resilient connection between that plunger and thedevice which applies the operating force to the plunger. The plunger is made to stop against a fixed part of the switch.

Because the switch operates in 3 9021 5? $9 419 a minute motion of its operating plunger, the stops necessarily must be located within a few thousandths of an inch of a certain position of the cantilever spring member of the switch which position is determined by the operation of the switch after flnal adjustment. 1- have found that it is not feasible in all cases to attempt to control the 'set or normal shape of the spring members or to so limit the tolerances of the dimensions of the various parts of the switch as to locate the stop with the required precision. Accordingly, in order to provide a simple and cheapconstruction and to avoid the necessity for elaborate and expensive manufacturing operations for adjusting the switch, I provide a fixed stop for the plunger, which stop by itself permits an excess motion of the plunger, and then after the switch is completely adjusted for proper operation, I select a spacer of the proper thickness to be inserted loose between the abutting surfaces of the plunger and stop so as to properly limit the motion of the actuating plunger.

The drawing illustrates a switch of the McGall type embodying my present invention. The switch includes an insulating housing comprising a base l0 and a cover i2 for enclosing the switch mechanism. A metal insert I4 in the base it carries a screw 16 which supports an anchor I8 and provides an electric connection between the anchor l8 and an external terminal screw 26. The anchor I8 is generally U-shaped. The ends of the legs of the U are provided with notches 22 which pivotally receive the ends of a pair of compression spring members 24 of the snap mechanism. A tension member 26 of the snap mechanism is fastened under the head of the same screw l6 which clamps the anchor l8.

The compression members 24 and the central tension member 26 of the snap mechanism are stamped integrally from a thin sheet 28 of spring material, as shown in Fig. 5. Each separate tension and compression member constitutes in itself a thin leaf spring strip joined. to the others at its unsupported end. The member 28 carries a mobile contact 30 at the joined unsupported ends of the several spring members 24 and 26.

Apair of fiat stationary electric contacts 32 and 34 are individually supported on separate metal inserts 36 and 36 in the base Ill. Ternnnal screws 40 and 42 are provided in the lower ends of the inserts to permit electrical connections to be made to the stationary contacts 32 and .34. For example, an electric circuit through the switch will extend as follows: from the terminal screw 20, through insert l4, tension member 26,'mobile contact 30, stationary contact-32. insert 38, and terminal screw 42.

The spring members 24 and 26 are adapted to move the mobile contact 30 between the two stationary contacts 32 and 34 with a snap motion. The thin leaf compression members 24 are pivotally supported in the notches 22 of the anchor 18 and the'tension member 26 is supported in cantilever fashion under the screw i6 at the base of the U-shaped anchor i8, and passes near the pivotal axis of the two compression members 24 at notches 22. If the tension center line of the member 26 be deflected across the pivotal axis. of the two compression members 24 the spring members 24 and 26 will co-act to snap the mobile contact 30 from one stationary contact to the other. The anchor l8 and the stationary contacts 32 and 34, which serve as stops for the snap mechanism, are so aligned and positioned, and

the set of the several leaf springs are so adjusted 10 the pressure is released, the contact 30 snaps back to its normal position. As has already been pointed out, the switch will operate in response to a motion of the order of a thousandth of an inch and accordingly the actual distance through.

15 which the tension member 26 need be deflected to operate the switch is exceedingly small. It is to be understood therefore that the actual position occupied by the tension member 26 generally will not be removed as far from the pivotal support 20 of the compression members 24 as is shown in Fig. 6, wherein the parts are shown slightly separated in order to facilitate the description and illustration.

Referring particularly to Fig. 6, an operating 25* plunger or actuator 88, having a molded piece of insulating material 44 at its lower end, bears down against the upper surface of the cantilever tension leaf spring 26 at a point intermediate its support under the head of the screw l5 and the 0 pivoted support of the compression members 24 for applying pressure to the tension member 25 for operating the switch. The insulating member 48 is so supported (as will be described presently) that it can move up and down to operate 35' the switch, and is provided with a circular shoulder 56 overhanging the leg portions of the U- shaped anchor member 58 as is best shown in Fig. '7. Accordingly, the shoulder .portions as V are adapted to stop against the legs of the U- 40' shaped anchor E8 to limit the deflection of the cantilever leaf spring 26.

A spacer 18 interposed between the abutting surfaces of the shoulder 45 of the member dd and the legs of the anchor l8, has just sufficient 45 thickness to stop the actuator plunger 63 just below the position at which it causes the switch to operate. It would be exceedingly costly to attempt to predetermine within small limits the relative positions of the legs of the anchor i8 and the surface of the-shoulder $6 of the insulating member Ad to accurately predetermine the limit of deflection of the cantilever tension spring 26. The comparatively large economical limit of manufacturing tolerances in the dimensions of 55- the individual parts, and the necessity for making some adjustment of the set" of the springs in the final adjustment of the switch introduce too much variation in the final relative positions of anchor 58, tension spring 25, and actuator Q3. Accordingly, the dimensions of the anchor i8 and actuator 63 are so chosen as to separate those surfaces by a distance sufiicient to permit the insertion of the spacer 48 between them. A spacer of the proper thickness is selected and ggjpserted after all other adjustments have been completed. The cover l2 and the actuator 43 are removable for this purpose. The spacer 58 lies loose over the anchor l8. As may be seen in Fig. 3, it consists of a thin rectangular sheet 7 having a central elongated perforation 49 separating a pair of spaced apart legs and having also a turned down edge 53. As is shown in Fig. 7, the spacer is slightly narrower than the anchor i8 and so fits loosely between the side walls 3-! 7 and 33 of the base Ill. The turned down edge 58 lies between the base of the 'U of the anchor l8 and end wall 85 of the base Ill. The perforation 49 clears the screw l6 and the central extension of the plunger 48. Thus, while the'spacer 48 is loose it nevertheless is held in place between the 5 plunger 43 and anchor 18. Being loose, the spacer 48 is free to assume the alignment of the surfaces which stop against it, and accordingly it cannot cock to hold the plunger 43 andanchor l8 farther apart than its own thickness.

An overtravel mechanism carried by a tubular guide 50 on the cover l2 serves to support and operate the actuator 43. As is shown in Fig, 6, a second generally tubular member 52 recipro cates within this guide 50, but has its upward motion limited by its own bottom shoulder 54 which abuts against the lowerend of the guide 50. This tubular .member 52 has a small bore in its lower end and a somewhat larger bore in its upper portion. The small bore at the lower end of the member 52 reciprocally carries a rod or pin 56 having at its lower end a head 58 which is molded into the insulating piece 44. The pin 56 and molded piece 44 together constitute the actuator plunger 43. The upper or large bore of the tubular member 52 contains aheaded pin 60. The head is at the lower end of the pin 60 and fits the larger bore of the tube 52 and stops against the shoulder between the large and small bores.

A coil spring 62 surrounds the pin 60, bears at its lower end against the head of the pin 60 and at its upper end against a cap 64 which closes the upper end of the tubular member 52. Thetubular member 52 is adapted, with its cap, 84, to be moved down and to thereby apply actuating force to the pin 56 through the spring 62 to operate the switch. The set of the spring 62 is suflicient'to maintain the head of the pin 60 firmly in its lower-most position in the bore of the tubular member 52 when operating the switch. When the insulating member 84 of the actuator d3 stops against the spacer 48 and the legs of the anchor l8, continued downward motion of the tube 52 compresses the spring 62 to permit overtravel of the member 52 beyond the limit of motionof the switch mechanism itself. The overtravel is limited by the pin which, extending through the coils of the spring 62, strikes against the cap 6d.

The force exerted on the plunger 43 for flexing 50 the coiled overtravel spring 62, and for finally limiting the overtravel when the cap 64 engages the pin 80, is supported by the legs of the U- shaped anchor i8 and not by the thin leaf spring 28 of the snap mechanism of the switch.

Inasmuch as the actuator is carried by the cover i2 of the switch housing, it can be readily removed to permit the insertion or removal of the spacer 48 without disturbing any adjustment of the snap mechanism. When the switch is finally adjusted and a spacer 48 of the proper size is in place, pins 68 may be inserted to hold the complete assembly together.

Thus, while the motion of the switch mechanism itself isprecisely limited to avoid undue 5 fatigue and mechanical strain of the parts, a member applying actuating force to the cap 84 of the reciprocating tube 52 may move an appreciable distance beyond the operating point of the switch. This overtravel arrangement permits 70' greater tolerance in the'location of the switch with respect to the mechanism which must operate it in applications where precise operation is not of prime importance, and in all cases guards against damage to the switch mechanism from 7'5" accidental or other occasional excess motion of the member which operates the switch.

It is thus seen that I have provided an improved switch construction, one that does not require elaborate or expensive manufacturing or adjusting operations, but which limits the flexing of the cantilever leaf spring of the switch to prolong its life, which at the same time permits the member actuating the switch to execute an overtravel motion without injuring the switch, and which insures that all similar switches made in ordinary production will show uniformly long mechanical life.

Certain of the specific structural details of the switch mechanism herein shown and described are described and claimed in the McGall patent already referred to, in my copending application, Serial No. 126,789, filed February 20, 1937, and in the copending application of Malcolm W. Eaton, Serial No. 174,042, filed Nov. 11, 1937, now Patent 2,172,673, Sept. 12, 1939.

It will be readily apparent to those skilled in the art that the embodiment of my present invention herein shown and described, is by way of illustration and example only, and that such embodiment is capable of numerous variations and modifications. Dimensions and structural details, where supplied are included only to make the description of the particular embodiment the more complete and explicit, the invention is not limited to such details. Therefore, I wish to be limited only by the scope of the appended claims.

I claim:

1. In combination in asnap switch of the class described, a snap mechanism comprising a member adapted to be flexed to operate said snap mechanism, an actuator movable to flex said member, and stop means for said actuator so positioned as to limit to a predetermined value the movement of said actuator beyond the position thereof at which said snap mechanism operates, said stop means comprising an abutment member and a spacer, said spacer being interposed between said actuator and said abutment member, and abutting directly against said abutment member, said abutment, spacer, and actuator being further so constructed and arranged, and said member to be flexed being so positioned with respect thereto that the actuator transmits the actuating force to said member to be flexed independently of said spacer.

2. The combination of the immediately preceding claim wherein said member adapted to be flexed consists of a thin leaf spring supported in cantilever fashion at one of its ends, and is adapted to be flexed to store energy for the operation of said snap mechanism, and wherein said snap switch always snaps at the same flexed position of said thin leaf spring.

3. In combination in a precision snap switch of the class described, a spring snap mechanism including a thin leaf spring adapted to be flexed to store energy for the operation of said snap mechanism, an actuating member movable to flex said spring, said actuating member having a bumper portion adapted to engage a stop, said switch mechanism being so constructed and arranged that said snap mechanism always operates at the same position of said spring flexed under the force of said plunger as aforesaid, a fixed stop adapted to be engaged by said bumper portion of said actuator, but being so positioned and arranged that said flxed stop by itself would allow too great a motion of said actuator in flexing said spring as aforesaid, and a spacer interposed between said bumper and said fixed stop, said spacer being adapted to be inserted and removed after all adjustments of said snap mechanism have been completed, and without disturbing such adjustments, said spacer having such a thickness as to limit the extreme motion of said actuator to the desired terminal position thereof.

4. In combination in a snap switch of the class described, an anchor member, a thin leaf tension spring strip supported on said anchor and extending therefrom with its plane approximately parallel to the surface of said anchor, a compression spring supported on said anchor and acting between said anchor and said tension spring strip, a shouldered actuator adapted to bear against said tension spring to flex it in a direction approximately normal to its plane to operate the snap mechanism, the shoulder of said actuator overhanging the surface of said anchor'so that said anchor surface is adapted to limit the movement of said actuator thereby to limit the flexing of said tension leaf spring, and a spacer of thin leaf material interposed between the shoulder of said actuator and said surface of said anchor, said snap mechanism being adapted to be adjusted for proper snap operation without said spacer in place, and being adapted further to permit said spacer to be inserted and removed after adjustment of the mechanism without disturbing the adjustment said spacer beingof such thickness as to limit to a desired extent the flexing of said thin leaf tension spring strip by said actuator.

5. In combination in a snap mechanism of the class described, an anchor member, a thin leaf spring strip supported on said anchor member and extending away therefrom, said anchor having spaced apart portions flanking said spring strip, an actuator adapted to bear against said tension spring between said flanking spaced apart portions of said anchor to flex said spring to operate the snap mechanism, said actuator overhanging said spaced apart portions of said anchor so that said spaced apart portions limit the movement of said actuator thereby to limit the flexing of said spring strip, and an integral spacer having separate spaced apart portions interposed between saidactuator and the separate spaced apart portions of said anchor, said spacer being retained in place loose, and being of such thickness as to impose a desired limitation on the flexing of said thin leaf spring strip by said actuator.

6. The combination of the immediately preceding claim wherein there is included a case for said snap switch, said case including a base carrying said anchor and including also a cover separable from said base for carrying said plunger.

7. In combination, in a snap switch of the class described, a U-shaped anchor member, a thin leaf tension spring strip supported in cantilever fashion on said anchor at the bow of the U and extending from its point of support in the direction of the legs of said U and with its plane approximately parallel to the plane of said U, a pair of thin leaf compression spring strips bowed in longitudinal compression, pivotally supported on the ends of the legs of said U, extending out away from said anchor alongside said tension spring on opposite sides thereof, and connected at their outer ends to said tension spring. a shouldered plunger adapted to bear against said tension spring to flex it in cantilever fashion in a direction approximately normal to its plane and to the plane of the U of the anchor to operate the snap mechanism, the shoulder of said plunger overhanging the two legs of the U of anchor so that said plunger extends between said spaced apart portions of said spacer to engage said tension leaf spring, said spacer being retained in place loose, and being of such thickness as to impose a desired limitation on the flexing of said cantilever tension spring by said actuator.

8. The combination of the immediately preceding claim wherein there is included a case for said snap switch and wherein said case has an end wall flanking said anchor at the base portion of the U and two side walls flanking the two legs of the U, said spacer being sumciently wide to be held laterally-fin place by said two opposed side walls of said case, said spacer having a bent down portion hooking over the base end of said anchor and lying between said base and the end wall of said case to hold said spacer in place longitudinally, the movement of said plunger being limited to prevent said bent down portion from lifting onto said anchor.

9. In combination in a switch of the class described, a spring snap mechanism including a member adapted to'ibe flexed to cause an operation or said snap mechanism, an actuator movable to flex said member, and a stop for said actuator so positioned as to limit to a predetermined value the movement of said actuator beyond the position thereof at which said snap mechanism operates, said stop including an abutment member and including also a spacer interadapted to transmit force and motion through said spring to said actuator, said spring being adapted to compress iurther to permit motion of said tube without an accompanying motion of said actuator.

11. The combination of claim wherein there is included resilient means for transmitting force and motion to said actuator.

12. The combination of claim 5 wherein there is included an overtravel mechanism for transmitting force and motion to said plunger, said mechanism including a tube having longitudinally opposed internal shoulders, a spring in said tube adapted to transmit force and motion through said spring to said plunger, said spring being adapted to compressfurther to permit motion of said tube without an accompanying motion of said actuator.

- 13. The combination or claim 1 wherein said member adapted to be flexed consists of a thin leaf spring supported in cantilever fashion at one of its ends, and is adapted to be flexed to store energy for the operation of said mechanism, wherein said snap switch always snaps at the same flexed position of said thin leaf spring, and wherein said spacer is retained loose between said flxed stop and said actuator.

14. In combination in a snap switch of the class described, a snap mechanism comprising a member adapted to be flexed to operate said snap mechanism, an actuator} movable to flex said member, and stop means for said actuator so positioned as to limit to a predetermined value the movement of said actuator beyond the position thereof at which said mechanism operates,

, said stop means including an abutment member and a spacer interposed between said actuator and said abutment member, said abutment, spacer, and actuator being soconstructed and arranged, and said member to be flexed being so positioned and arranged with respect thereto, that said abutment and spacer act independently of said member to be flexed to limit the movement of said actuator.

15. In combination in a switch of the class described, a spring snap mechanism including a member adapted to be flexed to cause an operation oi said snap mechanism, an actuator movable to flex said member, and a stop for said actuator so positioned as to limit to a predetermined value the movement of said actuator beyond the position thereoiat which said snap mechanism operates, said stop comprising an abutment member, and resilient means for-transmitting iorce and motion to said actuator for operating said switch, whereby said stop limits the flexure of said member to be flexed, and said resilient means for transmitting force and motion limits the actuating force exerted by said actuator against said stop.

L. RICHIE.

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