Push-switch With Spring Biased Plunger

Abstract

A highly electrical Electrical switch suitable for keyboards and the like. A pair of resilient contact members are mounted within a housing such that a plurality of contact portions on one of the members are biased to normally contact corresponding portions on the other member. The contact portions are formed from a suitable contact material. When the switch unactuated, a contact separating member on a switch actuating plunger forces apart the corresponding contact portions on the contact members. When the plunger is moved against a spring to an actuated position, the contact separating member moves to allow the corresponding contact portions to come into electrical contact.

Description

BACKGROUND OF THE INVENTION

This invention relates to switches and more particularly to an improved highly reliable switch suitable for use in keyboards and the like.

Many push button switch designs are not suitable for use on keyboards of electronic calculators, electric typewriters, and the like. Keyboard switches must be designed for long trouble-free life. Closure of the switch must require a minimal force and electrical contact must be positive. For ease and speed of operation, keyboard layouts must have a compact arrangement. The keyboard switches therefore must have a small physical size. An electric typewriter may, for example, have as many as 40 or more keyboard switches mounted in an area of less than 8 inches by 3 inches. In view of the large number of switches involved in an average keyboard, the individual switch cost must be as low as possible for the switch to be competitive.

SUMMARY OF THE INVENTION

According to the present invention, an improved electrical switch is provided which is inexpensive to manufacture, small in physical size, reliable and particularly suitable for use in keyboards.

A switch housing having a generally cylindrically-shaped opening is formed from a suitable synthetic resinous material. The single switch housing may be formed as a single unit or a plurality of switch housings may be formed as a unit for an entire keyboard. At the bottom of the cylindrical opening in the housing, a pair of slots are formed for mounting a pair of resilient contact members which are inserted into the slots and held in place by locking tabs on the contact members. The contact members project from the housing for defining external terminals. Within the cylindrical opening, a plurality of contact portions on one or both of the contact members are biased to normally electrically contact corresponding contact portions on the other of the contact members. By having a plurality of contact points, a positive electrical contact will be obtained even though dust or dirt prevents electrical contact between some of the corresponding contact portions. Contact is maintained between the corresponding contact portions by means of the resiliency of one or both contact members. The contact portions are formed of a suitable contact material, such as gold, silver, platinum, tungsten or an alloy of one of these materials.

A switch actuating plunger is mounted to slide within the cylindrical housing opening between an unactuated position and an actuated position. The plunger is keyed such that it will not rotate in the housing. A spring urges the plunger towards the unactuated position while a key button is attached to an exterior end of the plunger for moving the plunger to the actuated position. Within the housing opening, a contact separating member is attached to the plunger such that it extends between the contact members. When the plunger is in a released or unactuated position, the contact separating member forces the corresponding contact portions apart. Actuation of the key button moves the plunger and the contact separating member to a non-interfering position wherein the corresponding contact portions of the contact members are biased into electrical contact with each other by the resiliency of the contact members.

Accordingly, it is a preferred object of the invention to provide an improved keyboard switch.

Another object of the invention is to provide an electrical switch which is highly reliable and inexpensive to manufacture.

Other objects and advantages of the invention will become apparent from the following detailed description, with reference being made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view in partial section of a switch constructed in accordance with the present invention and showing the switch in a released position;

FIG. 2 is an enlarged cross-sectional view taken along line 2--2 of FIG. 1;

FIG. 3 is an elevational view in section of the switch of FIG. 1 and showing the switch in an actuated position;

FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 3;

FIG. 5 is a cross-sectional view taken alone line 5--5 of FIG. 4 and showing the bottom of the switch;

FIG. 6 is a perspective view showing contact members for a switch constructed in accordance with the present invention; and

FIG. 7 is an enlarged cross-sectional view showing the switch housing with the contact members mounted therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1-4, an electrical switch 10 constructed in accordance with the present invention is shown in detail. The design of the switch 10 makes it particularly suitable for use as a keyboard switch where a large number of switches of small dimension are mounted as a unit to form a keyboard such as is used in an adding machine or in an electric typewriter.

The switch 10 includes a housing 11 having a base 12 and a generally tubular wall 13. The wall 13 is integral with and projects from the base 12 to define a cylindrical opening 14. An integral pedestal 12' projects upwardly from the base 12 into the opening 14. The base 12 may have any suitable exterior configuration for use in mounting the switch 10. Or, any number of housings 11 for an entire keyboard arrangement may be molded from synthetic resinous material as an entire unit with the base 12 interconnecting all of the housings 11. In such an arrangement, a tubular wall 13 will project from a single base 12 at the location for each of the switches 10.

A pair of contact members 15 and 16 are mounted within openings 17 and 18, respectively, which extend through the base 12 and the pedestal 12' into the opening 14. The contact members 15 and 16 are formed from a thin sheet of resilient material. The contact member 15 is bent towards the contact member 16 at 19 and the contact member 16 is bent towards the contact member 15 at 20 such that contact points 21 and 22 on the contact members 15 and 16, respectively, are normally urged through the resiliency of the members 15 and 16 into electrical contact with each other, as shown in FIG. 3.

A plunger 23 is positioned within the opening 14 to slide between an unactuated or released position, as shown in FIGS. 1 and 2, and an actuated position, as shown in FIGS. 3 and 4. A helical spring 24 urges the plunger 23 towards the released position. The plunger 23 is generally tubular shaped and closely engages the walls of the opening 14 such that its motion is restrained to lineal motion. The lower end of the spring 24 extends around, and is maintained centered in the opening 14 by, the pedestal 12'. The upper end of the spring 24 closely engages the walls of an opening 23' in the plunger 23. Thus, the helical spring 24 is confined to axial movement as the plunger 23 is moved and is thereby prevented from touching the contact members 15 and 16. A pair of resilient arms 25 are formed in the lower part of the plunger 23. Hooks 26 project outwardly from the lower end of the arms 25 for engaging a pair of elongated slots 27 formed in the tubular wall 13 of the housing 11. The arms 25 are also each provided with a camming surface 28 for deflecting the arms 25 when the plunger 23 is initially inserted into the housing 11. When the plunger 23 is inserted into the housing 11, the hooks 26 engage the slots 27 for preventing rotational movement of the plunger 23 and for retaining the plunger 23 within the housing 11 when the switch 10 is in a released position. When the plunger 23 is moved to an actuated position, a lower end 29 of the plunger 23 engages a portion 30 of the base 12 to limit movement of the plunger 23.

A key button 31 is adapted to engage an upper portion 32 of the plunger 23 for use in actuating the switch 10. The key button 31 may be attached to the plunger 23 by any suitable method, as by a friction fit or by adhering with an adhesive or glue. The key button 31 is preferably formed from a synthetic resinous material and may have a character or symbol molded into an upper surface 33 for indicating the operation performed by actuation of the switch. If, for example, the switch 10 is a keyboard switch on an adding machine, ten different switches will be provided with the ten different digits molded into the surfaces 33 of the ten key buttons 31.

As previously stated, the plunger 23 has a generally tubular configuration. As a result, the plunger 23 surrounds the upper portion of the contact members 15 and 16. A contact separating member 34 is positioned within the opening 23' of the plunger 23 and may be molded as an integral part of the plunger 23. The contact separating member 34 is positioned to come into contact with the contact members 15 and 16 to force apart the contact points 21 and 22 when the plunger 23 is in the released position shown in FIGS. 1 and 2. When the plunger 23 is moved to the actuated position shown in FIGS. 3 and 4, the contact separating member is moved to a position allowing the resilient contact members 15 and 16 to return to a position with the contact points 21 and 22 in electrical contact. The lower portion of the contact separating member 34 is provided with a wedge-shaped surface 35 to facilitate assemblying the switch 10, as will be discussed in greater detail below.

Turning now to FIGS. 5-7, the contact members 15 and 16 are shown in greater detail along with the method for mounting the contact members 15 and 16 on the base 12. Although the contact member 15 may have a single contact point 21 and the contact member 16 may have a corresponding single contact point 22, it has been found that the reliability of the switch 10 is greatly increased by providing a plurality of associated contact points 21 and 22 on the contact members 15 and 16. The end of the contact member 15 is formed into a plurality of fingers 36, each of which has a contact point 21. Similarly, the end of the contact member 16 is formed into a plurality of fingers 37, each of which has an individual contact point 22. When the switch 10 is in an actuated or closed position, each contact point 21 on a finger 36 will normally come into contact with a corresponding contact point 22 on a finger 37. If contamination such as dust or grit should prevent an electrical contact between one pair of the contact points 21 and 22, the remaining contact points 21 and 22 on the remaining fingers 36 and 37 will still form an electrical connection between the contact members 15 and 16. Thus, it is readily apparent that the reliability of the switch 10 is greatly increased by dividing each of the contact members 15 and 16 into the plurality of fingers 36 and 37.

The contact members 15 and 16 are preferably formed from a thin sheet of resilient material such as a sheet of spring phosphor bronze. The lower portion of each contact member 15 and 16 which engages the base 12 of the housing 11 is bent to define wing portions 38 which add rigidity to the lower portion of the contact members. The wing portions 38 confine flexing of the contact members 15 and 16 to the fingers 36 and 37 and to the upper portions of the contact members 15 and 16. A tab 39 projects from the upper portion of each of the wings 38 to retain the contact members 15 and 16 within the housing 11. As best seen in FIGS. 4 and 7, when the contact members 15 and 16 are inserted into the openings 17 and 18, respectively, in the base 12, the tabs 39 come into contact with an upper surface 40 on the housing base 12. A resilient locking tab 41 is also formed in each of the contact members 15 and 16. The locking tabs 41 are initially deflected when the contact members 15 and 16 are inserted into their respective housing openings 17 and 18. When the contact members 15 and 16 are inserted completely into their respective openings 17 and 18 such that the tabs 39 contact the surface 40, the locking tabs 41 engage notches 42 on the base 12 to prevent removal of the contact members 15 and 16 from the openings. Each of the contact members 15 and 16 may also be provided with an opening 43 adjacent its lower end for use in making electrical connection to wires 44 leading to external circuitry.

The contact points 21 and 22 may merely consist of the two points on the contact members 15 or 16 which come into contact with each other. However, as best shown in FIG. 7, the contact points 21 and 22 preferably consist of suitable contact material applied to the contact members 15 and 16, respectively, at the location in which the contact members 15 and 16 are urged into contact with each other. The contact material may comprise, for example, gold, silver, platinum, tungsten or an alloy of any of these materials. Other known contact materials and alloys may also be used.

Referring still to FIG. 7, the end of the contact member 15 extending past the contact point 21 is bent outwardly or away from the contact member 16 to form a surface 45. Similarly, the contact member 16 is bent away from the contact member 15 to form a surface 46. The bends forming the surfaces 45 and 46 impart a slight curve to the contact points 21 and 22 such that a point contact is achieved when the switch 10 is actuated. The bent surfaces 45 and 46 also form a camming or guide surface to facilitate assembly of the switch 10.

As is readily apparent from the drawings, the switch 10 consists of the pair of contact members 15 and 16 and the spring 24 which are both of metal and the housing 11, the plunger 23 and the button 31 which may be inexpensive moldings from a suitable synthetic resinous material. Thus, the cost of the components for the switch 10 is very low. Assembly of the switch 10 is also simple, keeping the cost at a minimum. The two contact members 15 and 16 are mounted within the housing 11 merely by insertion into their respective openings 17 and 18 in the housing base 12 where they are locked in place by the tabs 41. The plunger 23 is then attached to the housing 11 merely by insertion into the housing 11. As the plunger 23 is inserted into the housing opening 14, the camming surfaces 28 on the arms 25 deflect the arms 25 inwardly out of the way of the housing wall 13. The bent surfaces 45 and 46 at the ends of the contact members 15 and 16 guide the wedge surface 35 on the contact separating member 34 between the contact points 21 and 22. When the plunger 23 is inserted a sufficient distance into the housing opening 14, the hooks 26 on the arms 25 engage the slots 27 in the tubular housing wall 13 to retain the plunger 23 within the housing 11. Assembly is completed by attaching the button 31 to the plunger 23, which may be accomplished merely by pressing the button onto the plunger 23 for a friction fit. From the above, it is readily apparent that assembly of the switch 10 is a fast and an inexpensive manufacturing operation.

It will be appreciated from the above description of a preferred embodiment of the switch 10 that various changes and modifications may be made without departing from the spirit and the scope of the claimed invention.

Claims

What I claim is:

1. An electric switch comprising, in combination, a generally tubular housing having a wall defining an interior chamber that has an open upper end and a generally closed bottom, a plunger having an exterior complementary to the interior chamber of said housing to be axially movable therein and having an interior opening, a pedestal extending upwardly into said chamber from the center of said housing bottom, said pedestal having an upper surface, a pair of contact receiving slots extending from said upper pedestal surface in said chamber through said pedestal and said housing bottom, a pair of generally flat contact members having elongated bodies with lower connection ends and contact portions adjacent upper ends, means on said members near said connection ends and in said slots cooperating for retaining said members in said slots with their bodies extending upwardly in the central region of said housing chamber, said members having inwardly directed bends with the contact portions of said members resiliently urged together, said upper ends terminating at an upwardly and outwardly directed flare, a helical spring spaced from and surrounding at least a portion of said members in said chamber, said spring having a first end positioned around said pedestal and a second end extending into and closely engaging an interior wall of said plunger opening whereby said spring is prevented from moving into contact with said members, said spring biasing said plunger from an actuated position to a released position, resilient means on said plunger for retaining said plunger in said housing chamber when said plunger is inserted into said housing chamber without interfering with movement of said plunger between the released position and the actuated position, and a contact separating member extending across said plunger opening, said contact separating member extending between said contact members to separate said contact portions when said plunger is in the released position and not to interfere with contact between said contact portions when said plunger is in the actuated position, said separating member having a wedge-shaped lower surface located to separate and pass between said flared upper ends when said plunger is inserted into said housing chamber.