US2351181A - Electric switch construction - Google Patents

Description

June 13, 1944. L. w. BANGASSER ELECTRIC SWITCH CONSTRUCTION Filed Dec. 21, 1942 My Any/ Patented June .13, 1944 Louis W. Bangasser, Freeport,

Ill.,' asslgnor to Micro Switch Corporation, Freeport, 111., a corporation .of Illinois Application December 21, 1942, Serial 409,651 8 Claims. (01. 200166) The present invention relates generally to elec tric snapfiswitches.

The invention constitutes an improvement upon the construction of switches of the type shown in McGall Patent 1,960,020, May. 22, 1934', and in Riche Patent 2,181,068, Novemberzl, 1939. This construction employs a spring toggle snap mechanism constructed of thin leaf springs, which operates a mobile electric contact througha comparatively short distance between fixed contacts or stops. It is small and compact and has alligh load handling capacity. It is a precision switch in that it operates in response to very slightmovements of its operating plunger and in that it operates consistentlyat the same position of that plunger. v For example, one commercial construction' of the-switch is contained in an insulating housing less than 1 cubic inches in size, operates'in response to a plunger' reclprocation of the orderof one ten-thousandth (0.0001). inch between on and "01! with. only a fewounces.

operation permit the switchto count sheets of thin paper striking against itas they are expelled from printing presses. Its high accuracy, its extreme sensitivity ofoperation, and its high control capacity are all taken advantage of in thermostats and other automatic controls, and the switch also finds extensive use in other applications, such as automatic machinery and industrial controls.

Because this type of switch is small and compact, and because it must operate with a high degree of precision, its construction and arrangement of parts presents a number .of difllculties that would not be encountered in larger and less sensitive switches, and its operation may be seri-' ou sly' impaired have been less sensitive device.

by dimculties which would not noticed,,let' alone appreciated, in a While thaMGall switch operates satisfactorily for many purposes. and

action. For this reasonit is desirable prospective uses, and it still presents manufacturing diiliculties.

One troublesome inaccuracy has been traced to lateral shifting of the operating plunger within its bearing. This plunger, in certain commercial forms, of the switch, has consisted of a metal pin carrying an insulating button molded on the in her end of the pin for engaging the thin leaf spring of the switch mechanism'and reciprocating in a hole in the switch housing. If the switch is to repeat its "operating point accurately, that is, i! it is to snap always at the same depressed position of the actuating plunger, it must not shift the point at which the plunger engages the snap acting spring, because such shifting not only alters the mechanical spacing of the parts, but also gives different characteristics to the snap that the metal pin of the plunger be given a close fit with its bearing surface, and that it maintain this close fit throughout its life. To this end, such pins have heretofore been cut-from polished rod,

' but their high finish has frequently been damaged by the th molded insulating material away from the Its high accuracy,

tools used for cleaning flash of steel pin where it joins the moldedinsulating, button. Such flash if not cleaned off may cause the pin to stick in its bearing or the flash may break or! while the switch is in use and plunger construction of'the class described and then, being loose inside'the switch, may 'get between th electric contacts or it may otherwise interfere with the operation of the switch. In addition, the molded plunger is required to have considerable strength, to resist both high static loads and also impact, because the switch is arranged with internal stops for preventing excess motion of the plunger as disclosed in the aforementioned Riche patent.

, Objects of the invention include the provision 0! a cheaper, yet stronger and more rugged the provision of a construction inwhich the formation of fflash' on the molded insulating ma-; terial is eliminated or made more .easily removableyand which permits the fla'sh" to be removed cheaply, with simple tools, and without while numerous improvements, such as those ot the Riche patent already referred to, have ex-- danger of scarring the polished surface of the guide pin. Other objects and advantages of the invention will become apparent from the following description of a specific embodiment, of the invention, which serves by way of example to illustrate the manner in which the invention may be constructed and used. However, the invention is not limited to the particular details of the example.' -1n.th drawing:

present invention and constitutes a section takenv along the lines i-l of Fig. 2;

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

Figs. 3 and 4 are plan views of certain of the parts of the switch mechanism;

Fig. 5 is a perspective view, partly in section showing the improved plunger construction of the switch of Fig. 1;

Fig. 6 is a partial, transverse, sectionaL elevational view of the switch of'Fig. 1 taken along the lines 6-6 of Fig. 1,and' viewed in the direction indicated by the arrows, for showing additional details of the plunger construction; and,

Fig. '7 is a transverse, sectional elevational view of a mold for forming the plungeroi Fig. 5,

. showing the metal parts of the plunger in place for the molding operation.

In accordance with one manner of carrying out my invention, I provide a foot, or enlargement at the end of the plunger pin about'which to mold the insulating button, locate the surfaceboundary of the insulating material on the foot of the pin and well away from the pin itself, and locate it also on the upper face of the button making substantial angles with the axis of the pin. With such a construction, I reduce the possibility of flash forming during the molding operation, make the flash that does occur more fragile, permit the removal of the flash with simpler tools and cheaper machine operations, insure that such cleaning operations will not scar the polished bearing surface of the pin, and not only increase the original strength of the molded structure itself but also insure that the machining operations will not weaken it.

The switch shown in the drawing includes an insulating housing comprising a base l and a cover l2 for enclosing the switch mechanism. A metal insert l4 inthe base l0 carries a screw 16 which supports an anchor l8 and provides an electrical connection between the anchor I8 and an external terminal screw 20.- The anchor ill in turn supports a pair of compression spring members 24 and a tension spring member 26 which are stamped integrally from a single sheet of thin spring material so that they constitute a single piece 28. This piece 28 carries a mobile contact 30, and moves it with a snap motion between two stationary contacts 32 and 34, which 7 are notched 'or L-shaped, and are individually supported on separate metal inserts 36 and 38 which in turn are separately supported in the heavy portion of the insulating base 10, and through which they extend to provide electrical connections to external terminal screws 40 and 42. For example, an electric circuit through the switch will extend as follows: From the terminal screw 20, through the insert I4, tension member 26 of the snap mechanism, mobile contact 30, stationary contact 52, insert 38, and terminal screw 42. 1

The thin leaf compression 'members 24' are pivotally supported in notches 22 in' the ends of the legs of the U-shaped anchor i8. 'I'he'tension member 26 is supported in cantilever fashion under the head of the screw l6 at the base of the U of the anchor l8, and passes near the pivotal axis of the two compression members 24 at the notches 22. When the tension member 26 is flexedto carry its tension center line across the 75 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 of its extreme positions to the other. When the tension member 26 is forced down the mobile contact 30 snaps down into engagement with the lower stationary contact 34 and when this operating force is released the contact 30 snaps back to its nor- I mal position in engagement with the stationary contact 32 As has already been pointed out, the switch will operat in response to a motion of the order of a ten thousandth of an inch and accordingly the actual distance through which the tension member 26 need be deflected to opcrate the switch is exceedingly small.

An operating plunger 45 is supported in the cover l2 for actuating the switch mechanism, and is shown in detai1 in Figs. 5 and 6. In this plunger, a hard, polished, stainless-steel bearingpin 48 has riveted to the lower end thereof a disc '50 of strong, corrosion-resistant material such as brass. This pin-and-washer assembly constitutes an insert in a molded button 52' of insulating material which covers the bottom and sides, and also the outer margin of the top, of

the washer 50. The surface-boundary 54, between the molded insulating button 52 and the washer 50, is kept well clear of the pin 48, and the surface 56 of the insulating button next to this boundary 54 flares upward and outward. Consequently, thissurface-boundary 54 and also the adjacent surfaces of both the disc 50 and the insulating button 52 are easily accessible to a cutting .tool so that any flash can be cut away easily without any danger of scratching or otherwise damaging the polished bearing surface of the pin 48. The outward flare 56 of the insulating material next to this boundary 54 facilitates the flash-removing operation because it is permissible to let the tool cut slightly into-this thin edge of the" molded insulation. Without the flare it would be necessary either to hold a closer tolerance on the cut, or else to take the extra time for cutting oiT more material. Since the disc is non-corrosive, the depth of cut need not be controlled accurately, but rather the tool may be set deep enough to cut slightly into the materia1 of the disc 50.

My present construction actually reduces the 50 formation of flash. Fig. 7 shows a mold for making this button, with the assembled pin'48 and pressure holds the disc 50 flrmly against the lip 58 of the mold cavity so that usually no flash forms at all, and when it does form, it rarely constitutes more than a thin, brittle film of clear resin without any flller. Usually, this flash can .be removed with a rotating wire brush so that no cutting is necessary. Moisture is absorbed into the insulating button less readily 60 through an uncut molded surface than through a machined surface. The use. of a brush is cheaper and faster and spoilage parts, but my construction permits and facilitates the use of a cutting tool when that is necessary or desirable. It is this saving in the cleaning or flash-removing operation, and the practical elimination of spoilage that constitutes the principal cost reduction. The savings here easily absorb the extra cost of adding the washer 50 to the guide pin 48. It is well known that cutting operations set up new strains within the material itself, and therefore it is preferable that highly stressed portions of the insulating button 52- be not subjeotecl to machining operations. In my present involves less accidental inferior in one or more improvedconstruction, and

construction, the surface-boundary 54 between the disc 50 and the molded insulating button 52 is, located where the unit-stresses are comparatively low both in the disc 50 and also in the molded insulating material.

My new construction is also stronger. As is shown in Fig. 6, the molded button 52 includes shoulders 60 which overhang the legs of the U- shaped anchor 18 of the switch, and which are adapted to stop against these legs of the anchor 98 to prevent excess flexing of the spring 2Q. Not only will any excess driving force that is applied to the pin 45 be carried by the molded button, 52, but it is likely also that only-one side of the shoulder Gil of the plunger will engage the anchor l8, and thereby impose an eccentric load on the molding ,52. It is this necessity for serving as an overtravel-stop that imposes the severest strains on the molded insulating button 52; I find that my present construction is so much stronger that I am able to make the button 52 from generalpurpose molding material ratherthan from the special, high-strength materials that were needed .in the old, unimproved construction. A general purpose material is one with good molding characteristics, such as small tendency to form flash, small tendency to crack or warp, and small tendency to stick in the mold cavity. Special high strength material is usually acteristics and for that reason.is considerably more expensive to use. Not only does the use of general .purpose molding material reduce the cost of the molded article itself, but it also ac-' centuatesthe reduction of the formation of flash,- the ease of cleaning out any flash that does form,

of these molding char- I scribed, of an operating plunger comprising a guide pin finished for smooth reciprocation in a bearing surface having a foot fixed thereto at one end, said foot having a diameter greater than said pin and extending beyond the radial periphery of the pin on all side of substantially rigid insulating material molded on to said foot with the surface-boundary of said insulating material lying on the side of said foot adjacent said pin and spaced clear of said pin.

2. The combination of claim 1, wherein the face of said foot next said surface-boundary lies at a substantial angle to the direction of the axis ing button,

of said pin.

3. The combination of claim 1, wherein the faces of both said foot and said insulating material next said surface-boundary lie at substantial angles to the directionof the axis of said pin.

4. The combination of claim 1, wherein said surface-boundary of said insulating material lies in a surface of revolution about the axis of said guide pin. I

5. The combination of claim 1, wherein said surface-boundary of said insulating material is so located with reference to the structure and configuration of said guide pin and molded insulatand with respect to the forces applied to said plunger in use, that the insulating material next to said surface-boundary is subjected to a substantially 1ower-unit-stress than the maximum unit stress-in other portions of said molded insulating button.

6; In combination in a device of the class described, a polished guide pinof stainless steel, a

and the reduction in the cost of preparing the plunger for use after it has been molded.

My construction also increases the flexibility and usefulness of the molding tool. It is necessary that these plunger's be made with several different over-all lengths, andheretofore the mold, because it supported the bearing pin at its end, had to be readjusted for each different pin length. Now, with the new construction, one set-up of the mold handles all the different pin lengths because the mold supports my pin-and-washer as-. sembly at the washer 50 as shown in Fig. 7.

Thus, it will be seen that I have provided an improved switch construction, which not only facilitates manufactureby permitting theuse of cheaper materials and less -expensive-machine operations, but which also is stronger and free of defects that. were unavoidable in the older, un-

which therefore may d to a higher degree of accuracy that high accuracy for a be manufacture and-made to retain longer service life.-

It will be readily apparent that the embodiment of my invention herein shown and described, is by way of illustration and example only, and that such embodiment. is capable of numerous variations and-modiflcatlons. Specific -dimensions, also specific orientations are used only to facilitate description and are not intended 6 as limitations on the invention.

1. In combination in a switch of the class debrass disc riveted to one end of said pin, a button of insulating material molded over said disc, covering all the bottom and edges, and the margin of the top of said discso that the only surface boundary of the molded button lies on the top of the disc and clear of the pin, said surfaceboundary being arranged symmetrically around said pin, the surface of said button flaring up and out from said surface-boundary.

7. In combination ina device of the class de-Q scribed, a reciprocal guide pin, a disc of highstrength m'aterial secured'to one-end of said pin so that the axis of said pin is substantially per-- pendicular tonthe plane of said disc, an insulat-- ing button molded onto said disc, so that the surface-boundary of the molded button lies entirely on the disc and clear ,of the pin.

8. In combination in'a device of the class de-' scribed, a' reciprocable guide pin having a foot at its lower end, said footextendlng beyond the radial periphery of the'pin on all sides thereof, a button of insulating material molded on to said foot covering all the bottom and sufficient of the sides of v said insulating material lies 011, said foot next to an exposed surface thereof that faces in a direction that has a substantial component upwards, said surface boundary lying in spaced relation to said pin for access to said surface boundary with a tool without contacting said pin whereby to remove the flash material from the area of said "boundary.

LOUIS -W.

5 thereof, a buttonsaid foot that the surface boundary of

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