US2840656A - Low travel switch mechanism - Google Patents

Description

June 24, 1958 0, ROESER 2,840,656

Low TRAVEL SWITCH MECHANISM Filed Jan. 3, 1955 United States Patent 2,840,656 Low TRAVEL SWITCH MECHANISM John 0. Roeser, Chicago,. Ill., assignor to. Illinois Tool Works, Chicago, 11]., a corporation of Illinois Application January 3, 1955; Serial No. 479,427 6 Claims. (Cl. 200-67) This invention is concerned generally with the art of electrical switches, and more. particularly with a switch mechanism requiring an extremely low travel for actuation.

Switch mechanisms. wherein the actuating member is moved an extremely short distance are useful ornecessary in a great many diverse installations, and are of particular importance in control functions wherein movement of a part must be. stopped upon reaching a certain location, or wherein operation sequences must be controlled by very small movements. Prior art switches for serving this purpose have not been entirely satisfactory. Many of the switches have required too great a degree of movement or travel. required too high an actuating. pressure. Still. others which have been satisfactory from a standpoint of travel distance and operating pressure, have been extremely expensive to produce due: to the necessity ofvery close tolerances, or they havenot'held: up wellin operation.

Accordingly, it is an object of this invention to provide a switch mechanism of the. low travel type; solving the above noted and other difiiculties.

A further object. of. this invention is toprovide a snap switch mechanism of the low traveltype wherein a flexed spring actuating member pivots upon itself, thereby elimi nating. frictionin a pivot.

A further object of this invention isto provide a snap switch mechanismv of the low travel type wherein the spring arms effecting the snap movement assume a serpentine shape substantially from one end to the other.

Yet another object ofthisinventionis to provide a snap switch. ofthelow travel. type wherein the moving switcharmf and the spring. actuating means therefor are made of a uniformlength as a single stamping and the switcharm and spring; means are heldunder stress by mounting corresponding-ends offset from one another.

Other and further objects and advantages of thepresent invention will be apparent from the followingdescription when taken in connection with the accompanying drawings,.wherein:

Fig. 1 is a perspective view of the, outside .of a switch constructed in accordance with the principles of my invention;

Fig. 2 is a longitudinal sectional view through the switch taken substantially along the line 2-2 of Fig; 1;

Fig. 3 is a perspective view with part of the case removed andpart. broken away. and showing the operating parts of the switch mechanism;

Fig. 4is1a cross sectional view taken substantially along the line 44 of Fig; 2; and

Fig. 5 is an exploded. perspective view of the switch mechanism..

Referring now in greater particularity tothe drawings, there .will be seen'aswitch mechanism or unit designated generally'by the.numeralr10. This. switch mechanism includes a. case-.12 of' generally rectangular. configuration. The case is maderofat. suitable 'insulatingmaterial. such as. Bakelite andfis providedwith a. topor lid: 14 ;of the Others of such switches have.

2,840,656 Patented June 24, .1958

angle which greatly lessens fatigue of the switch arm.

as compared tothe right angle on which prior art switch arms have been bent. .On either side of the ramp and projecting upwardly from the shelf 16 there is provided a pair of rounded shoulders 20. At the end of the shelf opposite to the shoulders 20 and adjacent the sides thereof there is provided a pair of holes 22'extendingdown into the shelf only a short distance, and between the holes 22 a stud 30 projects therefrom as at 24 (Fig. 5). The stud 30 is a part of a metallic screw anchor 26 cast or molded into the body of the case or housing and provided with a threaded bore 28 for receiving a terminal screw.

The case or housing further is provided with a floor 32 intermediate the ends of the case or housing and at a lower level than the switch blade mounting shelf 16. A screw terminal receptacle 34 having a threaded bore 36 is'cast or molded into the case or housing beneath the floor and has a stud or rivet portion 38 extending upwardly therefrom. The threaded opening 36 opens outwardly of the case as'does the previously mentioned opening 28.

The case or housing further is provided witha step 40 raise-d from the level of the floor 32, and slightly below the level of the shelf 16. An end shelf 42 rises above the step 40, and is at an elevation substantially higher than the switch blade mounting shelf 16. Another screw terminal receptacle 44 having a threaded bore 46 is cast or molded into the casing below the shelf 42 and has a reduced diameter stud or rivet portion 48 extending above this shelf.

The case or housing further may have transverse openings or holes 50 extending therethrough, conveniently below the step 40 and below the step 16 for accommodating mounting screws or bolts to hold the switch mechanism or unit in a desired operating position.

A flat contact plate 52 rests on top of the end shelf 42. The stud or rivet projection 48 of the screw receptacle 44 extends through the contact plate 52 and is peened over as at 54 to hold the contact plate in place. The

contact plate preferably is provided with an opening 56 near its outer free end for mounting a contact element 58 on the lower side. The contact element preferably is made of silver or some other metal which is well adapted for make-and-break contacts without undue burning of the material.

Another fixed contact member 60 comprises an intermediate diagonal section or wall 62 and a pair of offset end sections or flanges 64 and 66, the latter being provided with an opening 68. The flange 66 rests on the floor 32 with the stud or rivet portion 38 of the receptacle 34 projecting through the opening 68. The end of the stud or rivet portion is peened over as at 70 to hold the contact piece 60 in place with the flange 66. tight against beryllium copper. The switch blade 72 comprises afiat;

a 1 f 3 'i end piece 74 having a hole or opening 76 therein, and a central longitudinally extending tongue or arm 78. A hole 80 is provided in the tongue or arm 78 near the free end thereof.

The: switch "blade further comprises a pair of side legs .82 which are equal in length withthe' opposite ends with a pair'of punched down sections .90

forming anchoring fingers on the underside of the anchor piece. These punched down portions and fingers are offset from the hole 88 by about .020 inches. Thus, when the fingers associated with the depressed portions 90 are placed through the holes 84 in the ends of the legs 82, and the upwardly projecting stud or rivet portion '30 of the receptacle 26 is placed through the arm opening 80 and through the anchor piece opening 88, and is peened over'as at 92, the ar-in 78 is held in tension and the legs 82 are held in compression.- The downward set of the legs 82 relative to the end pier 1e74, and also the rounded raisedshoulders cause the legs 82 under. compression toassume a serpentine shape as shown in 'Figs. 2 and 3. The geometry of the parts is such that the end piece 74 is raised so that a contact element 94- of silver or the like in the opening 76 is held against the contact element 58. i i

The cover or lid 14 is provided near one end with a raised boss 96, and an opening 98 extends through this bossand through the cover or lid. A plunger 100 extends through this hole into the case or housing 12 and is provided with a rounded insulating head 102. 'A square or rectangular block 104 fits about the plunger 100 immediately below the head and limits the height to which the head and plunger can be raised. T The head 102 bears against the arm 78 between the legs 82, and the arm 78 holds the plunger in raised position.

When the plunger 100 is depressed, the head 102 bears against the arm 78 and moves it toward a dead center position. The switch blade shortly moves through dead center and the arm snaps down to bring the contact element94 into engagement with the flange 64 of the contact piece 60. Upon releaseof the plunger, the switch blade geometry reverts to its original configuration and the switch blade snaps back up through thedead center position. Theinitialmovement of the switch blade toward its dead center position reduces the subsequent force needed for overcentering, and thereby in a sense the applied force and the required force approach each other. As a result, very little force or movement is needed to operate the switch. In fact, and by way of specific example, a movement of about .0005 inch of the plunger will suffice for operation of the switch. Contact gaps may be made from .OlOinch to .070 inch,'or even more. The

contact force is about 30 grams. 7

By varying the relative positions of the lower contact, as the flange 64, the common attachment point for the spring, namely the'shelf 16, and the abutment in the form of the shoulders 20,the switch may be made to function either as a spring return type, or as a maintained contact type. Inthelatter case, the moving contact will remain in position against the lower fixed terminal after i it is snapped and until it is returned by some other force.

This is useful in safety devices of the overpressure or overmovement type. r

i The shoulders 20 help the side'legs to assume their serpentine shape, and in a sense act as fulcrums. However, the legs act ually pivot upon themselves by virtue of their serpentine shape and there is substantially no friction by way of a merit factor.

' 4 between the legs and the shoulders during such pivoting. Snap switch mechanisms can be compared in efliciencies Applying this factor, it has been found that the switch constructed in accordance with the principles of this invention is approximately three times as efiicient as the best prior art switches, and is over twenty times as efficient as many prior art switches.

The specific illustrative example of the invention herein shown and described is for purposes of examplifieation of the invention only. Various changes in structure will doubtless occur to'those skilled in the art, and are to be understood as forming a part of my invention insofar 'as they fall within the spirit and scope of the appended claims.'

I claim: 1. A snap switch mechanism comprising a movable switch structure having an elongated switch arm and a leg generally parallel thereto, said arm and leg being of substantially the same length, said arm and said leg tending to be substantially flatfmeans for maintaining a corresponding free end of said arm and of said leg fixed relative-to one another but free for movement, an anchor member separate from and anchoring the opposite ends of said arm and leg adjacent one another, said anchor member maintaining said opposite ends longitudinally offset whereby said arm is maintained in tension and said leg in compression, said leg thereby being deformed into a serpentine shape, a fixed contact toward and away from which said switch structure is snapable, an actuating member engageable with said switch structure for effecting such snapping, electrical terminal means connected to said fixed contact, and electrical terminal means connected to said switch structure. 2 i

2. A snap switch mechanism as set forth in claim 1 and further including a second legsimilar to the first mentioned leg, said legs being integral with said arm and with one another at the free ends of said arm and legs and lying on opposite sides of said arm.

3. A snap switch mechanism comprising an insulating base, a movable'switch structure having an elongated switcharni and a leg generally parallel to said arm,

means for maintaining a corresponding free end of said arm and said leg in fixed relation relative to one another and free for movement relative to said insulating base, means for anchoring the opposite ends of said switch arm and said leg to said base with said arm in tension and said leg under compression, said leg thereby being in a serpentine state, a fulcrumcarried by said base and spaced from said anchoring means longitudinally of said arm and leg, said fulcrum being positioned for engagement by a concave portion of said leg and not being engageable by said arm, a fixed contact carried by said base toward and away from which said switch structure is snappable, said arm pivoting generally in the vicinity of said "anchoring means and said leg pivoting generally in the vicinity of said fulcrum, an actuating member engaging said switch structure for effecting such snapping, electrical terminal means connected to said fixed contact, and electricalterminal means connected to said switch structure.

4. A snap switch mechanism as set forth in claim 3 and further including a second leg similar to the first leg, both of said legs being integral with one another and with said arm atthe free ends thereof and lying on opposite sides of said arm, said legs being similarly anchored by said anchoring means, there being a pair of fulcrurns similarly positioned with regard to said legs, said legs and said fulcrums similarly being spaced apart and clearance space being provided between said fulcru ns for movement of said arm. i

5. A snap switch mechanism comprising an insulating base having an intermediate floor portion, a raised shelf at one end of said floor portion, and a pair of step portions atthe other'end of said floor portion and at different elevations relativeto 'saidfloor portion; a movable 5 switch structure comprising an elongated arm and a pair of legs lying generally parallel to said arm and on opposite sides thereof, said legs and arm being of sheet metal and integrally joined at a free end thereof, said legs and arm being of the same length and having means at the ends opposite the integral connection adapted for cooperation with an anchor member; an anchor member mounting said switch structure at the end opposite said integral ends on said self, said anchor member having parts cooperating with the cooperating parts on the ends of the legs and arm to maintain said arm under tension and said legs under compression, said legs assuming a serpentine shape; fulcrums on said shelf laterally spaced apart and engageable by said legs, a ramp between said fulcrums providing clearance for said arm; a pair of spaced apart fixed switch contacts carried by said step portions and between which the integral end of said switch structure is snappable, said arm pivoting in the vicinity of said anchor member and said legs pivoting generally in the vicinity of said fulcrums; an actuating member engageable with said switch structure for etfecting such 6 snapping; and a plurality of electrical terminal means respectively connected to said movable switch mechanism and to the pair of spaced apart switch contacts carried by said step portions.

6. A snap-switch mechanism as set forth in claim 2 and further including aligned connecting means on corresponding ends of said arm and said legs, and offset con necting means on said anchor member cooperable therewith.

References Cited inthe file of this patent UNITED'STATES PATENTS 1,960,020 McGall May 22, 1934 2,370,479 Meyer Feb. 27, 1945 2,666,836 Stiebel Jan. 19, 1954 2,700,079 Haydon Jan. 18, 1955 FOREIGN PATENTS 567,614 Great Britain Feb. 23, 1945 640,097 Great Britain July 12, 1950

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