Manually operable electric switch with movable coil spring contact

Abstract

A light-current electric switch has two parallel wire staples in a printed circuit board as fixed contacts which are electrically bridged by pushing a metal coil spring against them. The axis of the spring is parallel to the staples, and the ends of the spring are constrained so that when the spring is moved to contact the staples, the coils of the spring wind or unwind slightly to give a wiping action on the staples which improves electrical contact.

Description

This invention relates to electric switches.

It is desirable that the contact making surfaces of electric switches be self-cleaning, particularly for low voltage, low current use. It is also desirable that switches should be simple, reliable and economic.

With these objects in view, the present invention provides an electric switch in which a metal wire spring which has a plurality of turns disposed in generally helical form is mounted for movement between a position in which individual turns of the spring electrically bridge a pair of fixed contacts and a position in which there is no bridging of the fixed contacts, the arrangement being such that movement of the spring to the position in which it bridges the fixed contacts winds or unwinds the spring to cause relative movement between adjacent turns thereof and thereby provide a wiping action between the spring and the fixed contacts.

Preferably the spring is so mounted that the axis of the helix is substantially at right angles to the direction of said movement.

A push button or key may be provided for manual operation of the switch.

The spring may be loosely carried on an actuating member that is mounted for movement in the direction of said movement. The helical portion of the spring may loosely embrace a peg projecting from this member. The end portions of the spring may extend away from the helical portion thereof, the spring being tensioned so that the end portions press against the actuating member.

The fixed contacts are preferably elongated in a direction generally parallel to the axis of the helix. The fixed contacts may be staple-like in form and may be secured to a printed circuit board in like manner to a paper staple in paper.

Switches of the kind recited above may be provided with a common mounting structure. In this case a common printed circuit board may carry the fixed contacts of all the switches, these fixed contacts being electrically connected to conductors of the printed circuit board. In such an array of electric switches, the switches may be disposed in a rectilinear matrix.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings wherein:

FIGS. 1 and 2 are respectively front and side elevations (partly in section) of a manually operable electric keyswitch in accordance with the invention;

FIG. 3 is a view, corresponding to FIG. 1 of the keyswitch in its operated position; and

FIG. 4 shows a plan view of a printed circuit board that is part of an array of keyswitches each of which is as shown in FIGS. 1 to 3.

Referring to FIGS. 1 to 3 of the drawings, a helical spring 10 of gold plated phosphor bronze or other suitable spring wire is loosely carried on a peg 12 jutting from an actuating member 14 of the keyswitch. The spring 10 is tensioned so that the end portions 10 thereof press against a part 17 projecting from the main body of the member 14, the end portions 10 lying in channels 18 in the part 17 in which channels the ends of the spring may slide longitudinally. The member 14 protrudes through a hole 20 in a surface plate 22 and terminates in a manually-operable key 24. For the purpose of identification the key 24 or the plate 22 adjacent to the key 24 may carry or be associated with one or more alpha-numeric or pictorial symbols (not shown).

A printed circuit board 26 is mounted substantially parallel to the surface plate 22. A projection 28 on the member 14 is slidable in a hole 30 in the board 26 which together with the hole 20 guides the member 14 for sliding movement in the planes of FIGS. 1 and 2. A further spring 32 embraces the projection 28 and engages both the board 26 and the member 14 so as to bias the member 14 from its operated position (FIG. 3) to its non-operated position (FIGS. 1 and 2).

The board 26 has two metal staples 34 of gold-plated copper wire secured thereto to serve as fixed contacts. It will be seen by a comparison of FIGS. 1 and 3 that as the key 24 is depressed to move the member 14, the spring 10 first contacts the staples 34 while the spring 10 is still lying on the peg 12 and then the body of the spring 10 is lifted off the peg 12 by further downward movement of the member 14. In the final position of the member 14 (FIG. 3) as determined by a stop 36 on the bottom of the member 14, it will be seen that the ends 16 of the spring 10 have slid along the channels 18 and the spring 10 is more tightly coiled. As this winding up of the spring 10 has taken place while the spring 10 is in contact with the staples 34, a wiping action has taken place between the spring 10 and the staples 34, so improving the electrical contact therebetween. The quality of electrical contact is further enhanced by the staples 34 being elongated so that each contacts more than one turn of the spring 10, thus providing a plurality of points of contact which are electrically in parallel. The same benefits can be achieved by causing a contact bridging spring to unwind when touching the fixed contacts, as by inverting the spring 10 and suitably disposing its ends 16.

As shown in the drawings, the staples 34 are mechanically secured to the board 26 in like manner to conventional staples by having their end portions 41 turned over. The end portions 41 are electrically connected to conductors 42 on the side 40 of the printed circuit board 26 in known manner by means of blobs 43 of solder. Fixed contacts other than staples could be used.

The board 26 preferably carries printed conductors only on the side 40 although the board 26 can carry conductors on either or both sides. It has been found that at least one printed conductor can be disposed on the board 26 between the staples 34 thereby enabling an increased conductor path complexity.

The member 14 (including the peg 12, the part 17, the projection 28 and the stop 36) is preferably a unitary plastics moulding.

The surface plate 22 may have lip 38 round the hole 20 to reduce the chances of spilled liquids contaminating the switch and printed circuit board.

A plurality of the above described switches may be assembled in rows and columns to provide a manually operable keyboard, e.g. for a telephone subscriber's apparatus or for a PBX. The layout of conductors of part of a common printed circuit board for such an array of switches (in place of the printed circuit board 26 in FIGS. 1, 2 and 3) is shown in FIG. 4.

Referring now to FIG. 4, those portions of the conductors on the printed circuit board 45 that are designated 46A to 46L are each associated with one of said switches. Considering now the portion 46B, for example, the board 45 has a pair of holes 47 to receive a fixed contact staple (corresponding to one of the staples 34 in FIGS. 1 to 3) and adjacent to those holes there are a pair of printed lands 48 to which the end portions (corresponding to the portions 41) of that staple are soldered after they have been bent over to hold the staple captive on the board. Similarly another pair of holes 49 is provided to receive the other fixed contact staple and there are a pair of printed lands 50 adjacent to the holes 49 for solder connection to the end portions of that staple. The hole 30' corresponds to the hole 30 in FIGS. 1 and 3.

It will be noted that in the complete array of switches, the conductors 51 and 52, for example, connect one fixed contact of one switch to the corresponding fixed contacts of the two switches that lie in the same line as that switch one on either side thereof. Furthermore, the fixed contact staples in the holes 47 and 49 effectively bridge the conductor 53 which passes between the pairs of lands 48 and 50. During use of the array, operation of any one of the switches causes a connection to be provided between a unique pair of contacts 54 and the features just mentioned enable this to be achieved with printed conductors on only one side of the board 45.

Claims

I claim:

1. An electric switch comprising an electrically insulating member, a pair of fixed contacts mounted on said member, a metal wire spring which has a plurality of turns disposed in generally helical form, means to mount said spring for movement between a position in which individual turns of the spring electrically bridge said fixed contacts and a position in which there is no bridging of the fixed contacts, and spring tensioning means operable upon movement of said spring to the position in which it bridges the fixed contacts to cause relative movement of adjacent turns of the spring and thereby provide a wiping action between the spring and the fixed contacts.

2. An electric switch according to claim 1 wherein said spring is so mounted that the axis of the helix is substantially at right angles to the direction of said movement.

3. An electric switch according to claim 1 wherein said means to mount said spring comprises an actuating member having a peg which projects from the body of that member and which is loosely embraced by the helical portion of the spring.

4. An electric switch according to claim 3 wherein said spring has two end portions which extend away from the helical portion thereof and generally tangential respectively to the two end turns of the helical portion and which press against part of said actuating member, the spring being tensioned so that when it is in the non-contact bridging porition the helical portion presses against said peg while in the contact bridging position the helical portion is lifted off said peg.

5. An electric switch according to claim 1 wherein said fixed contacts are elongated in a direction generally parallel to the axis of the helix.

6. An electric switch according to claim 5 wherein said fixed contacts are staple-like in form.

7. An electric switch according to claim 1 wherein said electrically insulated member is a printed circuit board and said fixed contacts are electrically connected to conductors thereof.

8. An electric switch according to claim 7 wherein said pair of fixed contacts are provided by a pair of staples each of which has a centre portion lying adjacent one side of the printed circuit board and two leg portions which pass through the printed circuit board and at least one of which is electrically connected to a conductor of the printed circuit board on the other side thereof.

9. An electric switch according to claim 8 wherein another conductor of the printed circuit board passes between the two leg portions of each of two staples.

10. An array of electric switches each according to claim 8 wherein the fixed contacts of all said switches are mounted on a single printed circuit board.

11. An electric switch comprising a printed circuit board having a plurality of conductors on one side thereof, a pair of metal staples mounted on said board and each having a centre portion and two leg portions which extend one from either side of the centre portion, the centre portions of the two staples lying parallel to one another adjacent the opposite side of the printed circuit board to that on which said conductors are provided and the two leg portions of each staple passing through the board with leg portions of the two staples electrically connected respectively to two of said conductors an actuating member, a metal wire spring which comprises a centre portion having a plurality of turns disposed in generally helical form and two end portions which extend away from the centre portion and generally tangential respectively to the two end turns of the centre portion, means to mount said actuating member for movement in a direction perpendicular to the plane of said board between a position in which individual turns of the centre portion of said spring electrically bridge the centre portions of the two staples and a position in which there is no bridging of the staples, and means to apply force to the end portions of said spring upon movement of said actuating member to the bridging position and after the centre portions of said spring first makes contact with the staples so as to cause relative movement between adjacent turns of the centre portion of the spring and thereby provide a wiping action between the spring and the staples.