US2172673A - Electric snap switch construction - Google Patents

Description

v Sept. 12, 1939. M. w. EATON 2,172,673

ELECTRIC SNAP SWITCH CONSTRUCTION Filed Nov. 11, 1937 Patented` Sept. 12, 1939 UNITED STATES ELECTRIC SNAP SWITCH CONSTRUCTION Malcolm W. Eaton, Freeport, Ill.,- assignor to Micro Switch Corporation, Freeport, Ill., a corporation of Illinois Application November 11, 1937, Serial No. 174,042

3 Claims. (Cl. 200-67) The present invention relates generally to electric snap switches, and relates more particularly to the details of contact constructions in such switches.

The present invention constitutes an improvement upon the construction of snap switches of the type shown in the patent to Phillip K. McGall, 1,960,020, May 23, 1934. The McGall switch employs a spring toggle type of snap mechanism constructed of thin leaf springs, which mecha.- nism operates a mobile electric contact through a comparatively short distance between fixed or stationary contacts or stops. It is a small, compact precision switch. It is a precision switch in that it operates in response to very slight movements of its operating plunger and in that it operates consistently at the same position of its plunger. One commercial construction of the switch, for example, consists of a switch mechanism in a molded housing of insulating material,

occupiesless than 11/2` cubic inches of space, operates in, response to a plunger movement of the order of one ten thousandth (0.0001) inch between on and "of with only a few ounces of operating force, and yet controls directly loads of the order of a thousand watts on alternating current.

` The McGall switch has found use in a number of` electrical control applications. The precision characteristics of the switch, combined with its high control capacity, and its rugged construction, t it for use in limit switches for machine tools to control the operation of tool carriages and cross feeds within tolerances of a few thousandths of an inch. Its small operating effort and its reliability of operation permit the switch to countsheets of thin paper striking against it as they are expelled from printing presses. Its precision, its small operating effort, and' its high control capacity are all taken advantage of in thermostats for domestic heating systems and industrial automatic controls. The switch also iinds extensive use in other applications, such as other machine applications and manual push button controls in which the small compact structure, of the switch and its high control capacity are of particular advantage.

Because the switch is a precision device, and because it operates in response to such slight motion and pressure, extreme careand accuracy are required in manufacture, and the operation of the switch can be impaired very materially by slight changes or misadjustments of its mechanism. Even slight misadjustments or mislocations of its parts will cause the switch to exhibit operating characteristics far inferior to those of a properly constructed switch.` The switch must be manufactured to close tolerances and protected against any injury which might result in a disarrangement of its operating mechanism.

s While the McGall switch operates satisfactorily for many purposes and has certain desirable characteristics, such as those already enumerated, it has other Acharacteristics which leave it unsuited to other applications and it presents a number of.manufactring diiilculties. 'For 'example, switches made in quantity production have exhibited widelydiiferent operating characteristics, and have even changed their characteristics. in use. Consequently, they could not be made easily interchangeable for replacement purposes, and the switch could not conveniently be fitted into the design of other apparatus, the characteristics of which had to be matched to the characteristics of the switch. These shortcomings have seriously restricted the commercial use and value of the McGall switch, and their correction has required experiment and development looking to structural improvements.

Because the 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 difliculties not encounted in other larger switch structures. The arrangement for supporting the stationary contacts or stops of the switch has presented considerable difiiculty of this sort. The construction shown in the McGall patent already referred to for supporting these contacts has not proved entirely satisfactory. That construction includes a large number of separate small insulators and spacers, which because of their number have proved to be expensve and also diilicult to handie and assemble. Furthermore, the structure has not provided a rigid and secure mounting for the contacts. The contacts have shifted and loosened and have thereby altered the operating characteristics of the switches. strains imposed on the supporting structure in the particular switch disclosed in the McGall patent, have been so great that any of the known insulating materials could not stand up over long periods of time. Rigid materials such as porcelain and the like have been too fragile, and stronger materials such as phenol condensate products have tended to exhibit cold flow. The small space available in the compact switch has limited the size of these insulating supports for the contacts, and it has been undesirable to en- Apparently, the

.tact between each other.

large the switch structure itseli to maire room for larger insulators..

It is desirable in the large quantity production of these precision switches to adjust each switch individually after its assembly. Frequently the adjustments include the bending of certain parts so that closer tolerances need not be imposed upon their dimensions. Thus it has been found that it is much cheaper to bend the stationary contacts of the switch after assembly to adjust their spacing than to attempt to predetermine the spacing from the sizes of the parts themselves, and although the contacts themselves must be fairly rigid to prevent their accidental damage in the use and handling of the switch, still the supports for those contacts must be strong enough and anchored firmly enough in the switch base Objects of the present invention include the provision of an improved switch and contact construction of the general-McGall type, and the provision of a stronger, a more rigid, and a more simple but still compact, supporting structure for the stationary contacts of the'switch. These and, other objects and advantages of the invention will be 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 invention may be used. However, the invention is not limited to any particular details of the example. In the drawing:

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

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

Fig. 3 is a plan view showing the mechanism of the switch of Figs. l and 2 with the cover of housing removed;

Fig. 4 is a cutaway perspective view of a part of the switch of Figs. l, 2, and 3, to illustrate certain structural features of the contacts; and,

Figs. 5 and 6 are plan views of certain of the parts of the switch mechanism.

In accordance with my present invention I provide an independent metal support for each stationary contact of the switch and mount each separate support rmly in the comparatively large 'nase block of the switch. Such a. construction eliminates a large number of the fragile insulating parts of the McGall structure and substitutes therefore a pair of comparatively strong and rigid metal posts or studs. Specifically, I provide a single tubular metal insert in the molded insulating base for supporting each stationary contact and so congure the contacts themselves that they clear each other and avoid electric con- Each insert is separately secured against loosening during the bending of the contacts for adjusting them, against loosening during the use of the switch, andes-1 pecially against being drawn out of the switch when the terminal screw is turned down on a conductor. In addition, the terminal screw is itself utilized for securing the insert against loosening and removal.

The switch shown in the drawing includes an insulating housing comprising a base IIJ and a cover I2 for enclosing the switch mechanism. A metal insert I4 in the base IIl carries a screw I6 which supports an anchor I8 and provides an arranca electrical connection 'between the anchor It and an external terminal screw 2t. The anchor I8 in turn supports a pair of compression spring members 24 and a tension spring member 26 of the snap mechanism of the switch. The two side compression members 24 and the central tension member 26 of the snap mechanism are stamped integrally from a single sheet of thin spring material so that the several spring members together constitute a single piece 28. This piece 28 carries a mobile contact 38, which, when the switch operates, is carried with a snap motion between two stationary contacts 32 and 34.

The thin leaf compression members 24 are pivotally supported in notches 22 in the ends of the legs of the U-shaped anchor I8. The tension member 26 is supported in cantilever fashion under the head of the screw I6 at the base of the U of the anchor I8, and passes near the pivotal axis of the two compression members 24 at the notches 22. If pressure be applied to the tension member 26 to deilect its tension center line 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 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 pressure is released the contact 30 snaps back to its normal position in engagement with the stationary contact 32. As has already been pointed out, the switch will operate 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 operate the switch is exceedingly small. It is to be undern stood, therefore, that the actual position occupied by the tension member 26 generally will not be removed as far from the pivotal support of the compression members 24 as shown in Fig. 6, wherein the parts are shown slightly separated in order to facilitate the description.

An actuator 44 includ-es a steel pin 46 on to which is molded an insulating head 48. Pin 46 is adapted to reciprocate in a hole of the cover I2 to move the insulating head 46 against the tension member 26 to deflect it to operate the switch. The pressure is applied to the tension member 26 between the point of its support under the head of the screw I6 and the point of support of the compression springs 24 in the notches 22. Head 48 of the plunger overhangs the two legs of the anchor i8 so that the anchor serves as a stop to limit the downward motion of the plunger. A spacer 5U interposed loose between the plunger head 48 and the anchor I8 has such a thickness as to limit the downward motion of the plunger to just slightly more than that necessary to deilect the tension 26 to the position in which it operates with its snap action.

As is best shown in Fig. 4, the stationary contacts 32 and 34 constitute notched or L-shaped pieces of laminated flat contact metal consisting of layers of silver and copper. The two stationary contact pieces 32 and 34 are individually supported on separate metal inserts 36 and 38 whichI in turn are separately supported in the heavy portion of the insulating base I0. The notch of each of the two contact pieces 32 and 34 serves to clear the supporting structure of the other contact. 'I'hus the notch of the contact 32 serves to leave the mounting screw 33 of the contact 34 uncovered to provide ample clearance between the two con-v tacts and also to permit access to the screw 33 23 'I'he terminal screw tirely through the floor of the base I0 so as to l 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 28, through the insert 4I, tension member 26 of the snap mechanism, mobile contact 38, stationary contact 32, insert 38, and terminal screw 42.

The insert 38 extends entirely throughvthe insulating material of the base I0 of the switch, and has a headed or enlarged portion 39 at its upper end. 'I'his enlarged portion 39 provides a shoulder which bears against the upper surface of the insulating base I0 so as to prevent the insert 38 from being drawn out of place downward by the terminalscrew 42. A wire conductor 4| is shown in Flg. 2 clamped under the terminal screw 42 in such'a manner that the terminal screw 42 might act to draw the insert 38 down through the base I0. I'he wire 4I is so small and its loop is suiiiciently large that it does not rest against the end of the insert 38, but rather rests directly against the insulating material of the base I0. While a connection made in this manner might be considered unsatisfactory and improper for certain purposes, it is a type of connection encountered frequently in practice. The shoulder 38 tends to sustain the clamping force of the terminal screw 42 and keep the insert 38 tight. It is undesirable to enlarge the insert because such a change would reduce the thickness of the insulating material and thereby weaken the switch base. Furthermore, I prefer actually to use the terminal screw 42 for preventing the insert 38 from being displaced upward while the contact 32 is being adjusted and in the event that user of the switch applies pressure to the terminal screw 42. 'I'hus the insert 38 is securely held in place by its shoulder 39 and the terminal screw 42, and the "terminal screw 42 not only serves to clamp connecting Wires to the switch but also constitutes a structural element of the switch itself for giving the insert 38 added strength.

Insert 38 is just long enough to extend through the insulating base l0 from one surface to the other. 'Ihe vcontact member 34 is fastened to the upper end thereof by means of screw 33 and overhangs the insert 36 so as to bear directly against the upper surface of the-insulating base.- 40, like the terminal screw 42 is adapted to clamp against the lower surface of insulating materialA so as to provide a safeguard against the loosening of the insert 38.

Thus it will be seen-that I have provided an improved compact, rigid, and strong construction for supporting the contacts in the comparatively small space of a switch of the McGall type.

that I have eliminated all fragile insulating constructions and have provided instead a substantial metal support construction anchored firmly 'in the comparatively large insulating base por-A The construction is suflition of the switch. ciently strong to permit the contact pieces 32 and 34 to be bent in situ for adjusting their positions and it is proof against damage from slovenly or otherwise improper terminal connections. Furthermore, the entire construction is extremely simple, has very few parts, and can be easily manufactured and assembled at low cost.

vCertain'speciilc structural details of the switch mechanism herein shown and described are described and claimed in the McGall patent already referred to and, in the copending applications of Arthur L. Riche, Serial No. 126,789, filed February 20, 1937, and Serial No. 176,535, filed November 26, 1937.

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 descriptionof the particular embodiment the more complete and explicit and the invention is not limited to such details. Therefore, I wish to be limted only by the scope of the appended claims.

I claim:

1. In combination in a switch construction of the class described, an elongated insulating switch case, a pair of generally cylindrical metal inserts placed symmetrically lateral to each other at one end of said case, andextending substantially vertically through the bottom of said case substantially parallel -to each other and insulated from each other by said case, one of said inserts extending higher within said case than the other, a pair of generally L-shaped switch contact members each having a horizontal contact portion lying transverse said case and a lug portion extending longitudinally of said case from said contact portion the lug portion constituting one leg of the L, each lug portion being fastened atop one of said inserts and clearing the other, said contact portions being vertically opposed to each other, said inserts and contact members providing shoulders engaging said switch case for preventing said inserts from moving downward, axial switch terminal screws at the lower ends of said inserts adapted to prevent said inserts from moving upward in said case, and a switch mechanism in said case including a mobile switch contact movable between said opposed contact portions of said L-shaped plates.

2. In combination in a switch construction of the class described, an elongated insulating switch case, a pair of generally cylindrical metal inserts placed at one end of said case, symmetrically lateral to each other with respect to said case, said inserts extending substantially vertically through the bottom of said case, and substantially parallel to each other, said inserts being insulated from each other by said case, one of said inserts extending higher within said case than the other, said high insert having an integral shoulder engaging said switch case for preventing said high insert from moving downward, a pair of' flat switch contact plates each having the general shape of a rectangle with a portion notched from one corner thereof, that is, the general shape of the letter L, each contact plate having a horizontal contact portion lying transverse said case and a lug portion extending longitudinally of said case from said contact portion, said lug portion constituting one leg of the L, each lug portion being fastened atop one of said inserts, and clearing the other insert, each contact plate having a width approximately equal to that of said case, so that 4- armere the walls of said case serve to obstruct any ma contact movable between said opposed contact terial misalignment of said contact plates in said portions of said contact plates.

case, the high insert providing the solo support 3. The combination of the immediately prem for its contact plate, the .other insert and its con ceding claim wherein each contact plate is `iastact plate providing shoulder 4portions engaging tened to its insert by o, single screw threaded into said switch case for preventing soiclother insert the insert, wherein the notch of the lower plate from moving downward, terminal means at the provides the clearance for the high insert, and lower ends of said' inserts adapted to prevent the notch of the upper plate serves to leave exsaid inserts from moving upward in said cose., posed from above the head of the screw in the said contact portions oi said plates imm;y vorm lower insert tically opposed to eacii other, and a sventola mocha MALCOLM W. EATGN. snism. in said case :including o moisilo switch

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