Switch assembly with reciprocating cams

Abstract

An improved switching assembly includes a housing which is made of two parts which snap together, a stationary contact member, a movable bifurcated contact member and a springbiased plunger. The plunger includes a separator for maintaining the contact members in a spaced relationship when the assembly is in an open position, and a cam member for coacting with the movable contact member to move the latter into contacting relationship with the stationary contact member when the assembly is in a closed position.

Description

The present invention relates to switching devices and more particularly to switching devices of the crossbar type.

Electronic keyboards, which include any of various types of switches, are useful as interface devices between an operator and many types of electronic equipment, such as computers, displays, data entry and date communication devices, computer printers, etc. One type of switch which can be used in these keyboards is the crossbar switch. Prior to the present invention, however, many of these crossbar switches suffer from one or more disadvantages. Some of the known switches, for example, suffer from the disadvantage that they contain several parts which not only make them relatively expensive to manufacture and difficult to assemble, but increase chances of premature switch failure. Some switches are necessarily relatively large in size and thus are undesirable when they are to be used where space is at a premium. Many switches have been found to be undesirable since they inherently provide considerable contact bounce introducing transient signals in the signal passing through the switch when the switch is initially opened or closed, or when the switch is subject to certain mechanical vibrations. Since crossbar switches usually include one contact member which is movable with respect to another, foreign matter, such as dirt, can collect between the members hindering the switch operation. Further, movable parts in these type of switches are subject to fatigue which can also cause premature switch failure.

It is therefore an object of the present invention to provide an inexpensive compact crossbar switch which is constructed of a minimum of parts and which overcomes, or at least reduces the effects of the aforementioned problems.

It is another object of the present invention to provide a positive acting crossbar switch which has improved reliability as well as a reduction in contact bounce.

Still another object of the present invention is to provide an improved crossbar switch having a preloaded moving contact member for reducing fatigue and improving switch longevity.

Yet another object of the present invention is to provide an improved crossbar switch having means for positive wiping action of the contact members.

Still another object of the present invention is to provide an improved crossbar switch which is easy to assemble and disassemble.

Generally, the foregoing and other objects are realized by a switch assembly comprising a housing made of two integrally formed snap fitting parts; a stationary contact member and a movable bifurcated contact member, both of which are mounted in the housing; and a spring-biased plunger. The plunger includes means for maintaining the contact members separated when the plunger is in a first position and means for moving the contact members into engagement with one another when the plunger is in a second position.

Other objects of the present invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the article of manufacture possessing the construction, combination of elements, and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the attached claims. For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description when in connection with the accompanying drawings wherein:

FIG. 1 is an exploded perspective view of an embodiment of the invention;

FIG. 2 is a cross-sectional side elevational view of the embodiment of FIG. 1, assembled for use with the switch in the open position; and

FIG. 3 is a cross-sectional side elevational view of the embodiment of FIG. 1, assembled for use with the switch in the closed position.

In the drawings, wherein like numerals refer to like parts, the switch assembly shown generally at 10 includes housing 12 which in a preferred embodiment includes case support member 14 and case cover 16 designed to interlock with one another to form a substantially rectanguloid hollow enclosure. The case support member and cover are each preferably pre-molded, integrally formed elements made of any substantially electrically insulating material such as a high molecular weight polymer, for example, polytetrafluorethylene, polyethylene or the like.

Case support member 14 is generally a U-shaped member, somewhat similar to an open box with only two upstanding side walls 20 and 21. A support well 22 is located substantially centrally in the bottom portion or flat base 18 from which walls 20 and 21 extend. Walls 20 and 21 are respectively provided, approximately centrally thereof on their interior surfaces with vertically extending parallel keyways 24 and 26. Each of the exterior surfaces of walls 20 and 21 are provided centrally with vertically directed slots 28 and 30. Resilient tabs 31 and 32 are respectively integrally formed or attached to the bottom of respective slots 28 and 30 adjacent base 18 so that the tabs are normally biased outwardly at about a 10.degree. to 15.degree. angle to the wall. Because the tabs are resilient, they can be forced or pivoted into the corresponding slot and are dimensioned so that when so forced into the corresponding slot they will be substantially flush with the outside surface of the respective wall. Each of tabs 31 and 32 is provided with a flange 34 along the top exterior edge and a horizontal groove 35 disposed immediately below the flange.

A pair of openings or slotted perforations 36 and 37 are provided extending through plate 18, each perforation being disposed adjacent the corresponding one of walls 20 and 21 and positioned in common to one side of respective keyways 24 and 26. Adjacent the top edge of one wall such as 21, and positioned above perforation 37 so as to extend into the interior of member 14 is convexly curved elongated lip 38. Lip 38 preferably extends in elongation from keyway 26 to the side edge of wall 21 parallel to base 18. The top edge of each of walls 20 and 21 is provided with a step or interior, horizontally extending shelf 40.

Case cover 16 is also a substantially U-shaped element intended to nest or interlock with member 14, and to that end also resembles an open box with only two sides 42 and 44 depending from opposite edges of and perpendicularly to top section 46. Disposed substantially centrally in top section 46 is aperture 47, the edge of which is reinforced by beading 48.

Case cover 16 is constructed, as noted, to interlock with support member 14 to form an enclosed hollow rectanguloid box. In order to accomplish this end, walls 42 and 44 are dimensioned to snugly and slidingly fit perpendicularly to and in between walls 20 and 21 of member 14. Similarly, walls 42 and 44 are spaced in dimension so that walls 20 and 21 can respectively snugly be fitted perpendicularly thereinbetween.

The molded portions of the switch include only one additional member, plunger 50. The latter is preferably integrally formed as a single unit and comprises a cylindrical central shaft 52 having a cross sectional diameter slightly less than the diameter of aperture 47 so that central shaft 52 can be freely movable axially through aperture 47. Extending in one direction from cylindrical shaft 52, and coaxially therewith is elongated portion 54, typically having a cruciform cross-section so that a key or button (not shown) can be securely fitted to the extreme end thereof. Extending in the opposite direction from central shaft 52 and coaxially therewith is a spring retaining shaft 56 which is of somewhat lesser cross-sectional dimension than the internal diameter of well 22. Attached to plunger 50, adjacent the junction of shafts 52 and 56 are a pair of keys 58 and 59 extending oppositely to one another from and perpendicularly to the axis of elongation of shafts 52 and 56. Keys 58 and 59 are dimensioned to fit simultaneously snugly but slidingly within respective keyways 24 and 26, so that the movement of the plunger is constrained purely to a vertical or unidirectional movement up and down the keyways. Connected to key 59 adjacent the juncture of the latter with shaft 52 and extending perpendicularly to the axis of elongation of shaft 52 and to key 59 is an elongated member or first contact cam 60. Also extending from key 59, parallel to cam member 60, but spaced further outwardly along key 59 from shaft 52 is a second contact cam or separator rod 62. In one embodiment of the device, as further described hereinafter, a similar cam member shown as 64 and a corresponding rod 65 extend outwardly from key 58 in an opposite direction to cam member 60 and rod 62.

The switch assembly of the present invention includes only three metallic parts: spring 70 and contact elements 72 and 74. Spring 70 is preferably a helical compression spring having an external diameter small enough to snugly fit within well 22 and an internal diameter large enough to snugly fit around shaft 56. Spring 70 is normally mounted on shaft 56 and emplaced in well 22 when plunger 50 is positioned with keys 58 and 59 fitted into keyways 24 and 26, wherein plunger 50 will be biased outwardly from aperture 47 of case cover 16.

Contact elements 72 and 74 are each preferably formed from a continuous strip of material. Stationary contact element 74 is provided at one end 76 thereof with an extension so shaped that the latter can be inserted through perforation 37 and extended outwardly from the opposite side of base 18 to provide an electrical contact. Means such as spring detent 77 are punched or indented in a portion of contact 74 adjacent end 76, the detent being adapted to releasably lock within perforation 38 so that element 74 is supported by base 18 at a position extending substantially upwardly parallel to wall 21 with the upper extremity of contact element 74 in contact with lip 38. Thus, it will be seen, particularly as shown in FIGS. 2 and 3, that stationary contact element 74 is supported at one end by base 18 and at the other end by lip 38.

Movable contact element 72 is dimensioned at one end 78 so as to fit within and extend through perforation 36. Thus, an electrical contact can be made with element 72 adjacent the outside surface of base 18. Detent means 79, similar in structure and function to detent 77, are also provided for releasably locking end 78 of movable contact element 72 to base 18. As shown, element 72 has an approximately shallow S-curved configuration, one end of which is end 78 as described. The other end 82 and central portion of contact element 72 is longitudinally centrally slotted to provide a bifurcation 80. Mounted adjacent end 82 of bifurcation 80 is a contact strip 84. Similarly mounted on contact element 74 adjacent the opposite end 86 thereof from end 76 is a similar contact strip 88.

Stationary contact element 74 can be made of any of a number of electrically conductive metals, such as copper, silver and various copper and silver alloys with other metals. Movable contact strip 72, on theother hand, should be formed of a substantially resilient material which is also electrically conductive, typically a bronze alloy or the like. Contact strips 84 and 88 on the other hand should be made of materials not only having good electrical conductivity, but suitable as directed wiping switch contacts, and typically, can thus be formed of copper coated with gold or the like. Contact strips 84 and 88 may be applied to a base metal sheet in one simple operation such as roll welding, and then the contact elements can be directly stamped out of the base material which the contact strips properly emplaced.

FIGS. 2 and 3 show assembly 10 assembled for operation wherein stationary contact member 74 and movable contact member 72 are mounted in perforations 36 and 37, respectively as described above. The plunger 50 is mounted in case member 14 so that the keys 58 and 59 respectively slide in keyways 24 and 26, separator rod 62 is disposed between contact members 72 and 74, and cam member 60 of plunger 50 is disposed on the side of movable contact member 72 opposite contact member 74. Spring 70 is disposed with one end in well 22 and the other end around retaining shaft 56, so as to bias plunger 50 in an upward direction so that separator rod 62 will keep the contact members 72 and 74 apart. The cover 16 engages case support member 14, in a manner as described above, so that the shaft 52 and portion 54 extend through the aperture 47 of cover 16.

Referring specifically to FIG. 2, the switch assembly is shown in a normally open position, wherein separator rod 62 is disposed between contact members 72 and 74.

In order to close the switch to the position shown in FIG. 3, plunger 50 is depressed against spring 70 wherein keys 58 and 59 respectively follow keyways 24 and 26, and well 22 accommodates shaft 56 until keys 58 and 59 reach the end of keyways 24 and 26. As the plunger is depressed, cam member 60, as well as separator rod 62 move with it. As cam member 60 moves, it coacts with the contact member 72 so that the latter pivots toward the contact member 74. As shown in FIG. 3, the separator rod 62 will be disposed well below the strips 82 and 88, when the plunger is depressed, while cam member 60 causes the strips 84 and 88 of the two contact members to contact one another. It will be appreciated that since contact element 72 is of an S-curved configuration, the strip 84 moves at an angle to the normal direction of strip 88 so that strip 84 "wipes" strip 88 as it makes contact. This insures good contact between the two strips.

The assembly may be inserted in an aperture of a keyboard panel or switchplate (not shown) wherein the tabs 31 and 32 will pivot into the grooves 28 and 30 as the assembly is inserted. The flanges 34 will prevent the assembly from being forced through the panel aperture. The edges of the panel aperture will be received by the grooves 35, wherein the compressive forces exerted by the tabs will provide a snap fit. In order to remove the assembly from the panel the two flanges 34 of the two tabs are forced together as the assembly is removed. The ends 76 and 78 of the contact members 72 and 74 are suitably connected into the circuit (not shown) to be controlled by the switch.

The preferred embodiment has been described as an assembly having a single switch with two contact members. If desirable however, it is possible to make the assembly a multiple switching assembly. For example, two additional slots similar to slots 36 and 37 may be provided in a similar manner in the base 18 of member 14 between the keyways 24 and 26 and the rear edge of the base 18. A second lip similar to lip 38 is then provided along the top edge of the vertical side wall 20 of member 14 above the slot which is similar to slot 37. An additional pair of contact members, identical to member 72 and 74 are disposed in the additional two slots in the same manner as members 72 and 74 are disposed in slots 36 and 37. The additional cam member and separator rod 64 and 65, previously described, which may be provided on the opposite side of plunger 50 from cam member 60 and separator rod 62, will keep the additional contact members separated when the assembly is in the open position, and the additional cam member 64 on plunger 50 will coact with the additional movable contact member so that as the plunger is depressed the additional contact members will come into contact with one another.

A switch assembly made in accordance with this invention has numerous advantages in addition to those mentioned. The use of tabs integrally mounted to the housing eliminates the need for metal clips which add to the costs of manufacturing. The switch assembly can be constructed with a minimum of parts. By using a positive action assembly, the movable parts are allowed to return to their preformed position allowing for (1) relaxation and therefore decreasing the chances of switch failure resulting from fatigue, (2) minimum contact bounce, and (3) the minimum need for close tolerances in the assembly dimensions. Additionally, bifurcation of the movable contact member not only reduces contact bounce, but decreases contact failures, i.e., where switch assembly is closed but no contact is made. The separator rod has the advantage of acting as a damper for the contact members in the open position and prevents the contacts from making accidental contact which might occur when the assembly is subject to certain mechanical vibrations. The shallow S-curved contact element will provide the wiping of the two contact strips as they contact each other, thereby providing improved contact. Finally, by making the housing of two parts which snap together, the housing cannot only be easily assembled, but also disassembled for repair.

Since certain obvious changes may be made in the illustrated embodiment of the device without departing from the scope of the invention, it is intended that all matter contained herein be interpreted as illustrative and not in a limiting sense.

Claims

What is claimed is:

1. A switch assembly comprising in combination:

first and second interlockable housing members which when interlocked form a substantially hollow enclosure having an aperture at one end thereof, and a pair of parallel keyways disposed along the interior walls thereof;

a switch plunger having a portion thereof extending through said aperture, and being mounted for substantially unidirectional motion along said keyways;

spring means for resiliently biasing said plunger outwardly from said aperture to a first position;

a first electrically conductive contact strip mounted on one of said housing members with a portion thereof extending through said one of said housing members, and being supported within said enclosure in a substantially stationary position;

a second electrically conductive flexible strip having a bifurcated portion mounted on one of said housing members so as to extend therethrough and being spaced from said first strip when said plunger is in said first position;

said plunger including first and second cam portions, said first cam portion being disposed between said conductive strips so as to positively maintain said two strips in spaced apart relation when said plunger is in said first position, and being moved out of contact with said second strip when said plunger is moved against the bias of said spring to a second position;

said second cam portion being disposed so that when said plunger is moved toward said second position said second cam portion engages the bifurcations of said second strip and forces the latter into electrical contact with said first strip.

2. A switch assembly in accordance with claim 1 wherein said enclosure includes a convex lip portion and a portion of said first strip contacts said lip.

3. A switch assembly in accordance with claim 2, wherein said second strip is of a shallow S-curved configuration so that the contacting portion of said second strip wipes the contacting portion of said first strip when the former contacts the latter.

4. A switch assembly in accordance with claim 3, wherein each of said contacting portions of said first and second strips is a piece of contact strip secured to each of said first and second strips.

5. A switch assembly in accordance with claim 1, wherein said first and second housing members and said plunger are each integrally formed.

6. A switch assembly in accordance with claim 1, further including a pair of tabs resiliently integrally formed at one end on the exterior of said enclosure at an angle thereto, for mounting said assembly.

7. A switch assembly in accordance with claim 6 wherein said enclosure further includes slots for receiving said tabs said tabs being adapted to pivot into said slots so that said tabs are substantially flush with the surrounding exterior surface of said enclosure.

8. A switch assembly in accordance with claim 7 wherein each of said tabs includes a flange along the exterior edge of the end opposite said one end and a groove disposed adjacent and parallel to said flange.