GB2091941A - Switch utilising toroidal spring - Google Patents

Abstract

A keyboard switch has a post 8 extending upwardly from a base board and carrying a toroidal spring 14 which is forced into engagement or proximity so as to provide a capacitative coupling with electrically conductive members 15 and 16 by depression of an operating member 2. The conductive members 15 and 16 are in the form of rings each of which has fingers interdigitated with the fingers of the other ring. The conductive members 15, 16 are surrounded by an insulating sheet 20. <IMAGE>

Description

SPECIFICATION Switch utilising toroidal spring This invention relates to switches and in particular to switches which may be used in keyboards or the like and which include a toroidal spring for bridging electrical contacts.

Switches utilising expanding toroidal springs are already known; two examples are illustrated by United States Patent Specification No. 3735058, which discloses a toroidal spring held on a tapered post and capable of bridging two semi-circular contacts, and United States Patent Specification No.

4088855 which discloses a switch in which a toroidal spring is held on a conductive, tapered post and, when depressed against the bias provided by the taper's cooperation with the toroidal spring, can make contact between the post and an encircling contact on a base board.

The present invention particularly relates to an improved construction of switch. In a preferred form, the switch comprises a board bearing conductive electrical members, an insulating post which is upright with respect to the board and has an upward taper, a toroidal conductive spring disposed on the post, and an operating member for pressing the spring down the post against the taper so that the spring is forced into proximity with the said conductive members, which extend, one inside the other, around the post. Preferably the said conductive members are substantially in the form of rings, each of which has fingers extending between fingers of the other ring.

In a particularly preferred form, the said fingers curl in a direction across successive turns of the spring. The contacts may be surrounded by a guard ring or other protective non-conductive member which is raised from the surface level of the electrical members.

There follows a description by way of example of one embodiment of the invention with reference to the accompanying drawings, in which: Figure 1 is a part-sectional view of a switch embodying the invention; and Figure 2 is a plan view of a preferred form of contacts forming part of the embodiment which is shown in Fig. 1.

The switch which is illustrated in the drawings is adapted for use in a keyboard of which the top plate 1 has an aperture 1 a for accommodating an operating member 2 which is preferably translucent. The operating member 2 is circular in cross-section and has at its underside a central cylindrical recess 3. The outer periphery of the member 2 has a deep annular groove 4 bounded at one side by the main body of the member 2 and bounded at its lower side by an annular flange 5.

Spaced from, and underneath the top plate is an insulative board 6 which has, centrally of the aperture 1 a and aligned with the central recess 3 of the member 2, an aperture 7 for the accomodation of an insulating post 8.

For the convenience of manufacture and for a purpose which will be mentioned later, the post is made of polytetrafluoroethylene and has annular flanges 9 and 10 space apart by approximately the thickness of the base board. The flanges 9 and 10 serve to maintain the post upright with respect to the base board.

The post 8 is hollow, having a central passageway 11 which may accommodate a lamp 12, which is received in the recess 3 when member 2 is depressed.

The outer surface 1 3 of the post has an upward taper of which the slope lessens towards the top of the post. Disposed on the post is a toroidal spring 14 which may be gold plated. This spring has a self-constricting action which, by cooperation with the taper of the post, causes the spring naturally to maintain itself around the upper part of the post, spaced substantially away from the base board 6. The lower part, namely the flange 5 of the member 2, engages the toroidal spring.

On the board 6 is a pair of electrically conductive members 1 5 and 16, which are particularly illustrated in Fig. 2. As illustrated by the Figure, the members 1 5 and 1 6 are generally in the form of rings, the member 1 6 being inside the ring 1 5. These members may be formed in a manner known in itself on the surface of the board 6.

The rings 1 5 and 1 6 could be entire, but for the purpose of making electrical contact from other conductive members on the board 6, the ring 1 5 has a gap in which is disposed a terminal tag 1 7 for the inner ring 1 6. In the particular embodiment, the two rings each have a multiplicity of fingers 1 8 and 1 9 respectively, the fingers of each ring extending between adjacent fingers of the other ring.

It is preferred that the fingers have a slight clockwise curl which is opposite the helical pitch of the toroidal spring.

The electrical members 1 5 and 1 6 extend around the post; they themselves are surrounded by an insulating sheet 20 which has a circular aperture 21 of approximately the same diameter as the outer periphery of the outer ring 1 5. The sheet 20 is disposed on the base board but may overlap the outer member 1 5 slightly. The purpose of the insulating sheet is to protect against the shortcircuiting of the members 1 5 and 1 6 if the toroidal spring is broken.It will be appreciated that in practice the switch may form part of a large keyboard containing a multiplicity of switches which all share the same base board; the sheet 20 provides some protection against the disabling of the complete keyboard merely by the failure of any one switch.

The purpose of the recess 4 is to accommodate the margin of an aperture in an insulat ing flexible sheet 22 disposed underneath the top plate 1. This insulating sheet may protect the inner workings of the switch and the associated electrical circuit from dust, dirt, water splashes and the like.

The switch is operated by depression of the member 2 so as to force the toroidal spring downwardly against the taper into proximity with electrically conductive members 1 5 and 1 6. If the switch is intended to provide a direct electrical connection between the members 1 5 and 16, the concentric arrangement of the members 1 5 and 1 6 facilitates the contact of the toroidal spring with large areas of the members 15 and 16 and thereby facilitates the provision of a switch with low contact resistance. That purpose is aided by the interdigitation of the fingers. However, the physical engagement of the spring with the members 15 and 1 6 is not necessary if the switch is or can be used to provide a capacitive coupling, by way of the spring 14, between the members 15 and 16.

The use of polytetraflouoroethylene for the central post 9 facilitates the provision of a smooth action for the spring and the reduction of wear on the spring.

Claims (4)

1. A switch comprising a board bearing electrically conductive members, a post which is upright with respect to the board and has an upward taper, a toroidal spring disposed on the post and an operating member for pressing the spring down the post against the taper so that the spring is forced into proximity with the said electrically conductive members, which extend, one inside the other, around the post.

2. A switch according to claim 1 in which each electrically conductive member is in the form of a ring which has fingers extending between adjacent fingers of the other ring.

3. A switch according to claim 1 or claim 2 in which there is an insulting member which encircles the contacts and covers part of the said board and the conductive members.

4. A switch substantially as hereinbefore described with reference to the drawings.