US3374333A - Pushbutton switches with at least one flexible cantilevered spring leaf contact continually prestressed by a pushbutton - Google Patents

Description

March 19, 1968 F. A. ANDERSON 3,374,333

EAST ONE FLEXIBLE CANTILEVERED SPRING LEAF CONTACT CONTINUALLY PUSHBUTTON SWITCHES WITH AT L PRESTRESSED BY A PUSHBUTTON 2 Sheets-Sheet 1 Filed Feb. 1, 1967 mum INVENTOR FRED A. ANDERSON wya/a,

ATTORNEY March 19, 1968 F. A. ANDERSON 3,374,333

PUSHBUTTON SWITCHES WITH AT LEAST ONE FLEXIBLE CANTILEVERED SPRING LEAF CONTACT CONTINUALLY PRESTRESSED BY A PUSHBUTTON Fi led Feb. 1, 1967 2 Sheets-Sheet 2 F ig-4 ATTORNEY United States Patent 3,374,333 PUSHBUTTON SWITCHES WITH AT LEAST ONE FLEXIBLE CANTILEVERED SPRING LEAF CONTACT CONTINUALLY PRESTRESSED BY A PUSHBUTTON Fred A. Anderson, Collinsville, Conn., assignor to Royal Typewriter Company, Inc., Hartford, Conn., a corporation of Delaware Filed Feb. 1, 1967, Ser. No. 613,225

6 Claims. (Cl. 200-164) ABSTRACT OF THE DISCLOSURE A pushbutton switch having at least one flexible cantilevered movable contact continually normally prestressed by a pushbutton and controlled thereby for movement toward encounter with but short of unstressed condition, a fixed contact having a contact surface angularly disposed relative to the path of movement of said movable contact to effect a bounceless high pressure wiping contact.

This invention relates to electrical switches; more particularly it relates to electrical switches characterized by a wiping contact action; and specifically it relates to an electrical switch wherein a prestressed flexible cantilevered contact is allowed to move toward encounter with and to slide along the sloping surface of a fixed contact to eiiect a bounceless wiping contact.

Sought for characteristics of electrical switches are negligible bounce contact makes and breaks to avoid arcing and consequent pitting of contacts which reduce switch life, and high contact pressure (low contact resistance) makes to reduce contact heat for a given current. These desiderata however are incompatible; low bounce makes in keying switch configuration usually are characterized by low contact pressures. Thus the switch designer must compromise one or the other.

In accordance with the present invention the above desiderata are achieved by allowing a prestressed cantilevered wire contact to move toward a fixed contact surface inclined at an angle to the path of movement of the movable contact. Upon encountering the inclined surface the movable wire contact is deflected thereby, and caused to slide along the fixed contact surface. This positive wiping action provides bounceless low contact resistance makes by preventing accumulation of films caused by oxidation. Further tendencies for contact welding are minimized during makes and breaks since the movement of the cantilevered contact along the inclined surface distributes weld currents over a large area.

Accordingly an object of the invention is to provide a long lived keying switch.

Another object of the invention is in the provision of a keying switch having a positive wiping action between movable and fixed contacts to maintain said contacts free of oxides.

Still another object of the invention is to provide a keying switch characterized by negligible bounce makes and breaks and low contact resistance.

Other objects and many of the attendant advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like or corresponding parts throughout the several views thereof and wherein:

FIGURE 1 is an exploded perspective view with parts in section and with the cover removed of a Form C pushbutton or keying switch in accordance with the invention;

FIGURE 2 is an elevational view showing the elements 3,374,333 Patented Mar. 19, 1968 of the switch operatively mounted in the switch housing;

FIGURE 3 is a cross sectional view taken along lines 3-3 of FIGURE 2;

FIGURES 4 and 5 are cross sectional views similar to FIGURE 3 showing the position of the movable contacts when the switch button or keying element is partially and fully depressed respectively;

FIGURE 6 is a partial enlarged view showing a modified keying element and illustrating the wiping action of the movable contact along the sloping surface of the fixed contact.

Referring now to the drawings wherein like reference numerals designate like or corresponding parts throughout the several views there is shown in FIGURE 1 a switch housing generally designated by reference numeral 10, prefereably of molded construction, formed to accommodate the movable and fixed contact and terminal ele ments of a Form C switch, and a pushbutton or keying element generally designated by reference numeral 11. The switch elements are adapted to be retained within the housing by a cover plate 12 (FIGURE 3) held secured as by rivets 13 (FIGURE 2) to the housing.

As viewed in FIGURES 1 and 2 the substantially rectanugular housing 10 has a central cavity 14 defined by upper and lower walls 15 and 16, and by relatively thick left and right end walls 17 and 18 through which rivet holes 19 extend for securing the cover plate 12 to the switch housing.

The forwardly facing upper and lower edges of the upper and lower walls of the switch housing are also formed with outwardly extending projection 21 adapted to cooperate with complementary cut-outs in the cover plate 12 to assure proper mounting of the latter. The left end wall is formed with slots 22 which converge inwardly towards one another from the upper and lower left corners of the switch housing into the cavity of the switch housing. The walls of the slots 22 are formed with undercuts to form locking abutments 23 and 24 for terminal lugs as will hereinafter appear, and the ends 25 of the slot 22 opening into the cavity are rounded off. The cavity midway between end walls is formed with spaced partitions 26 parallel to the end walls to accommodate and support as will hereafter appear a fixed contact. The partitions 26 are formed with rearwardly extending recesses 27 to permit flexible wire contacts to extend therethrough and to permit them to be deflected vertically and laterally, as will hereinafter appear. The cavity of the switch liousing to the right of the partitions 26 is adapted to accommodate the push button or keying element 11; the upper wall of the switch housing having a rearwardly extending cutout 28 to permit vertical movement of the keying element relative to the housing. As viewed in FIGURES 1 and 2 the keying element, preferably of one piece molded construction, is E-shaped and is mounted with the edge of the horizontal bar 29 of the E facing leftwardly toward end wall 17. The upper bar of the E is vertically elongated and its upper portion 31 extends upwardly through the cutout in the upper wall. A vertically extending rectangular slot 32 in the upper portion 31 of the keying element cooperates with a projection 33 extending forwardly from the back wall 34 of the housing into the slot to guide, and with the upper and lower walls of the slot, to limit the movement of the keying element. Another projection 35 extending forwardly or outwardly from the forward side of center bar of the E cooperates with a recess 36 (FIG. 3) in the cover plate 12 to guide the vertical movement of the keying element. As viewed in FIG- URES 2 and 3 a coiled spring 37 located in the cavity beneath the keying element 11 serves to normally bias the keying element to its upper limit position.

As best viewed in FIGURES 3-5 the upper surface of ICC the center bar 29 of the E of the E-shaped keying element, viewed from the edge, is formed with a V-shaped notch whose downwardly inclined or sloping sides 41 and 42 serve to guide and prestress or flex Form A wire contacts 43 and in conjunction with the fixed contact serve to virtually eliminate bounce as will hereinafter appear. Similarly the lower surface of the center bar of the E of the keying element is formed with an inverted V-shaped notch whose upwardly sloping surfaces 44 and 45 serve to guide and prestress or flex Form B wire contacts 46. With par ticular reference to FIGURE 1 the Form A and Form B movable switch contacts 43 and 46, each comprising in a preferred embodiment a pair of parallel flexible wires, are secured to switch terminal lugs 43 and 49 as by bending a section 51 of the terminal lugs over and crimping the wire ends. The terminal lugs are adapted to be received into the slots 22 formed in the left end wall 17 with the bent over sections 51 of the terminal lugs located within and locked between the abutments 23 and 24 formed by the undercut slots 22.

As viewed in FIGURES 1 and 3 the fixed contact 52, in the form C switch illustrated, takes the shape of an E with a downwardly extending tail 53 or terminal lug. As clearly shown in FIGURE 3, the shoulder 54 formed by the terminal lug of the fixed contact is, when the fixed contact is mounted between the partition walls 27, supported by the bottom wall 16 of the switch housing which is provided with an opening 55 through which the fixed contact terminal lug extends.

As viewed in FIGURE 1 the E-shaped fixed contact opens or faces forwardly or outwardly and the upper edge of the center bar 56 of the E has an inverted V-shape forming downwardly inclined or sloping surfaces 57 and 58. Similarly the lower surface has a V-shape forming upwardly sloping surfaces 61 and 62. When mounted in the housing the apexes of the V-shaped fixed contact surfaces and the V-shaped guide surfaces of the keying element are vertically aligned and preferably the angle between the sloping surfaces are the same to most efficiently control the lateral deflections of the flexible wire contacts 43 and 46 as they encounter and are deflected by and along the fixed contact surfaces.

As is evident from FIGURE 2, the flexible wires 43 and 46 extend across the cavity above and below the center bar 56 of the E of the E-shaped fixed contact 52 and the free ends of the first and second pairs of contact wires 43 and 46 extend respectively into the opening above and below the center bar 29 of the E of the E-shaped keying element. The limit positions of the keying element are such that the cantilevered flexible wires are prestressed in that they are not permitted to assume a vertically unflexed position by the keying element. In the Form C switch illustrated, the B contact wires 46 are flexed laterally by and are in contact with the sloping surfaces 61 and 62 of the fixed contact while the A contact wires 43 are unflexed laterally but prestressed vertically to a greater extent by the keying element and are out of contact with the sloping surfaces 57 and 58 of the fixed contact. Thus a circuit from the fixed contact 52 to the terminal lug 49 is normally closed (Form B) and the circuit to the terminal lug 48 is normally open (Form A). Depression of the keying element 11 will allow the A contact wires 43 to move from the FIGURE 3 position toward vertically unflexed condition until they encounter (FIGURE 4) the sloping surfaces 57 and 58 of the fixed contact, and thereafter are flexed laterally as they slide along the sloping surfaces to the FIGURE position. In the FIGURE 5 position the Form A contacts are still vertically prestressed by the keying element. The downward movement of the keying element also forces the B contact wires 46 to slide out of contact with the sloping surfaces 61 and 62 of the fixed contact under control of the sloping surfaces 44 and 45 of the keying element. FIGURE 4 shows the make before break action characterizing a Form C switch. FIGURE 5 shows the switch transferred. Upon return movement of the keying element the opposite 4 sequence occurs, the sloping surfaces 61 and 62 of the fixed contact spreading or effecting lateral flexure of the B wire contacts 46 as they are allowed to move toward and to encounter the fixed contact under control of the keying element sloping surfaces 44 and 45, and the A contacts 43 are forced out of contact with the fixed contact; the return to laterally unflexed but vertically flexed or prestressed condition being controlled by the keying element sloping surfaces 41 and 42.

With reference to FIGURE 6 the keying element is modified by forming at the apex of each of its sloping surfaces a projection 63 to hold the wire contacts of a pair spaced to assure that they will move toward associated sloping surfaces of the fixed contact.

Where the speed of pushbutton depression does not exceed the velocity the prestressed wires 43 would attain if free to do so, contact makes are free of bounce as the sloping surfaces 41 and 42 (FIGURE 4) of the keying element act to prevent bounce and to control lateral deflection. Where the speed of depression exceeds the velocity of the prestressed wires 43 and they are free from control of the keying element as they move toward the fixed contact, bounce on contact may be virtually eliminated by selecting contact wires having a predetermined length and stiffness, and to so prestress them as to match their velocity in moving to unstressed condition to the slope angle of the fixed contact surfaces 57 and 58 such that the resultant force R of the bounce force vector B and the remaining force vector C of the prestressed wire, after contact, is along the fixed contact surfaces 57 and 58 as shown in FIGURE 6.

While pairs of wires 43 and 46 with associated sloping fixed contact surfaces 57 and 58 and 61 and 62 are illustrated, it is to be understood that single wire contacts are within the scope of the invention. Further it is to be understood that the invention is not limited to a Form C contact, which is a Form A and a Form B contact, but may be constructed to incorporate a Form A or a Form B alone, or a break before make or Form D switch. Further the switch configuration shown can be modified to serve as an on-otf switch, i.e. a switch that is stable in either the on or oif state, by extending the push button element through the lower wall of the housing whereby it may be pushed back from the FIGURE 5 to the FIGURE 3 position, and by providing an overcentering spring connected to the push button element and to the housing to hold the keying element in either its on or off position. Such an overcentering spring will be operative after initial movement of the push button element to snap the button to its limit position at a controlled velocity. Further an overcentering spring may be used with or without spring 37. When used with spring 37 it will be stronger than spring 37.

It should be understood therefore that the foregoing disclosure relates to only a prefe rred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention.

The invention claimed is:

1. A bounceless switch comprising:

a fixed contact,

a flexible movable contact,

a housing anchoring said fixed contact and one end of said flexible movable contact, said fixed contact having a sloping surface positioned adjacent the free end of and in the path of travel of said flexible contact from a flexed position operative to deflect said flexible contact,

a keying element guided for movement within said housing between first and second limit positions, said element having an opening into which the free end of said flexible contact extends and is held flexed by a surface defining said opening, movement of said keying element from one of said limit positions allowing the movement of said flexible contact toward, and after encounter its movement along said sloping surface, and from the other of said limit positions carrying said flexible contact out of engagement with said sloping surface, and

spring means normally biasing said keying element to one of its limit positions.

2. A bounceless switch as recited in claim 1 wherein said flexible contact comprises a pair of wires.

3. A switch as recited in claim 1 wherein said keying element surface slopes in a direction opposite that of said fixed contact sloping surface thereby to control the deflection of said flexible contact after its encounter with said fixed contact sloping surface.

4. A bounceless switch as recited in claim 1 further including a second flexible movable contact anchored at one end to said housing,

wherein said fixed contact includes a second sloping surface adjacent the free end of said second flexible contact and in the path of travel of said second flexible contact from a flexed position, and

wherein said keying element includes a second opening into which the free end of said second flexible contact extends and is held flexed by a surface defining said second opening, movement of said keying element from one to the other of its limit positions allowing one of said flexible contacts to move toward encounter and thereafter follow the slope of the fixed contact surface in its path while carrying the other flexible contact from engagement with said other fixed contact sloping surface, and vice versa.

5. A bounceless switch as recited in claim 4 wherein each of said flexible contacts comprises a pair of wires,

wherein each of the associated fixed contact sloping surfaces are V-shaped and diverge laterally from the path of movement of associated flexible contacts whereby each Wire of the flexible contacts are deflected in opposite directions upon encountering said fixed contact.

6. A bounceless switch as recited in claim 5 wherein said keying element surfaces are V-shaped in a direction opposite to that of the V-shaped fixed contact surfaces, the apexes of said V-shaped element and fixed contact surfaces being aligned.

References Cited UNITED STATES PATENTS 2,616,993 11/ 1952 Koehler ZOO-166.1 XR 3,275,963 9/ 1963 Hoel ZOO-166.1 XR

FOREIGN PATENTS 204,988 5/ 1939 Switzerland. 577,778 7/1954 Canada. 752,907 7/ 1956 Great Britain.

ROBERT K. SCHAEF-ER, Primary Examiner. H. BURKS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,374 ,333 March 19 1968 Fred A. Anderson It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, lines 6 to 8, for "assignor to Royal Typewriter Company, Inc., Hartford, Conn., a corporation of Delaware" read assignor to Litton Business Systems, Inc. a corporation of New York Signed and sealed this 1st day of July 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

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