GB2293272A

GB2293272A - Push button switch

Info

Publication number: GB2293272A
Application number: GB9518311A
Authority: GB
Inventors: Paul Man
Original assignee: Arcolectric Switches PLC
Current assignee: Arcolectric Switches PLC
Priority date: 1994-09-14
Filing date: 1995-09-07
Publication date: 1996-03-20
Also published as: GB9418520D0; GB9518311D0

Abstract

A push button switch comprises a housing (10) within which are located opposing fixed terminals (11) and resilient contacts (32). A spring biased actuator is movable into and out of the housing (10) and includes a cam surface which biases the contacts to their respective terminals (11). A cam (40) is located within the housing (10) so as to be freely movable therein. The cam (40) includes a profiled surface within which a cam follower (27) on the actuator can move. A holding position of the cam (40) holds the actuator in a closed or open circuit position. <IMAGE>

Description

PUSH BUTTON SWITCH This invention relates to push button switches, in particular of the push-push type.

There is a need for a switch of simple construction which is robust and cheap to manufacture. Such switches are used in particular, for example, in portable computers.

According to an aspect of the present invent ion, there is provided a switch comprising a housing; an electrical terminal secured within the housing; a resilient contact within the housing movable between an open circuit position in which it does not contact the terminal and a closed circuit position in which it contacts the terminal; an actuator movable relative to the contact and including biasing means for biasing the contact from its open circuit position to its closed circuit position; and a cam movably disposed within the housing, the cam being operable to control the position of the actuator.

Preferably, the cam is free to move within a part of the housing and includes a profiled surface co-operable with a cam follower provided on the actuator, the profile being operative to hold the cam follower into one of the open or closed circuit positions.

In an embodiment, the cam is reciprocably slidable in a direction substantially perpendicular to the direction of movement of the actuator, the cam follower being operative to cause the cam to slide relative thereto and thereby to move within the profile into and out of a holding position of the profile.

The cam may include cam biasing means for controlling the position of the cam within the housing.

The contact is preferably normally biased in the open circuit position and the biasing means includes a cam surface operative to urge the contact towards the terminal to the closed circuit position.

In the preferred embodiment, the switch comprises first and second facing terminals and first and second resilient contacts, the actuator being operative to bias the first and second contacts towards a respective terminal.

The simplicity of the invention and its reliability will be apparent from the following description of an exemplary embodiment of a push-button switch, given in relation to the accompanying drawings, in which: Fig. 1 shows an axial longitudinal section through a complete switch; Fig. 2 shows an axial longitudinal section through the switch in Fig. 1 at right angles to the latter; Fig. 3 shows a sectional view on the line ZZ in Fig. 2; Fig. 4 shows a top plan view of the switch body with its cover and all internal parts removed, to a larger scale than previously; and Fig. 5 shows a front view of the cam to the same scale as Fig. 4.

The embodiments of the push-button switch shown has a hollow body 10 containing two fixed contacts 11. A cap 12 has a central aperture 13 through which slides an actuator 14. The cap is held in position by four spring fingers 15 which clip into small recesses 16 in the hollow body 10.

The actuator 14 has an actuating head 20 which projects through the aperture 13 and a switching portion 21 which extends within the body 10. The actuator 14 moves in and out in a straight line indicated by arrow 22 against a spring 23, and its position is controlled by a cam and cam-follower mechanism to be described. The actuator is constrained in its linear motion by a key 24 on the inside of the hollow body 10 (see Fig.4), the key engaging a grooved projection 25 fixed to the actuator 14. On the other side of the actuator 14 is a guide plate 26 carrying a cam follower 27.

The switching portion 21 of the actuator 14 has a lower part 28 of narrower cross-section and an upper part 29 of wider cross-section. The portion 21 is embraced by a generally U-shaped spring contact 30, and the position of the arms 31,32 thereof is determined by the vertical position of the switching portion 21. In its upper position as shown In Fig.l, the spring contact arms make no electrical contact. In its lower position (not shown) the arms 31,32 make contact with the two fixed contacts 11 since they are forced apart by the wider upper part 28 of the actuator. This consequently completes the circuit between the two fixed contacts 11.

The hollow body 10 includes a generally circular recess 35 with a central knob 36 which locates the bottom of the spring 23. In addition, two internal walls 37 separate a cam compartment 38 from the remainder of the body, leaving a channel 39 between the walls. When the actuator is inserted from above into the hollow body 10, the groove of the projection 25 slides down the key 24, and the guide plate 26 lies adjacent the dividing walls 37 with the cam follower 27 projecting through the channel 39 into the cam compartment 38.

The cam shown in Fig.5 has the shape of a basically square tablet with a small spring finger 41 projecting at its bottom edge. It is of a shape and size to fit loosely on edge within the cam chamber 38, the finger 41 being downwards and a relief pattern forming the cam on its operating face (shown in Fig.5) facing towards the cam follower and the interior of the hollow body 10. The areas marked A are full thickness (projections) and area B is recessed. Its orientation can be clearly seen in Fig.3, the pattern on its operating face in this instance being dashed and seen from the back. Once installed in the cam chamber 38, it can move freely from side to side as shown by arrows 42, but only slightly up and down under control of the spring finger 41.It will normally be kept well lubricated with an oil or grease to ensure that it moves freely within the compartment 38.

Upon assembly, the cam 40 is inserted in compartment 38 first, followed by the actuator 14 and then the cap 12.

Upon insertion of the actuator, the cam follower 27 slides down the channel 39 and its tip enters the cam pattern of the cam 40 through a top aperture 43.

Figure 5 then illustrates the positional relationship between the cam 27 and the cam pattern, the relative positions taken up being achieved by movement of the cam and not the follower (which can only move strictly vertically). The two rest positions of the cam follower 27 are illustrated by + and the relative paths between these two positions are illustrated by dashed lines 46,47.

In the upper position of the actuator 14 as shown in Figs.l,2 and 3 (switch open), the cam follower is at the upper +. The first downward pressure on the actuator causes the cam 40 to be deflected from side to side, thus allowing the cam follower to pass below the central island 44, and when pressure on the actuator is released to rise again to lodge in its lower position +, held in the curve beneath the island 44. At this time the spring contact 30 is spread so as to make contact with the two fixed contacts 11.

A second push on the actuator 10 causes the cam follower to follow the second relative path 47 and after release to move back to its starting position +.

The above described switch has minimum moving parts, is reliable and positive in use, and cheap to manufacture and assemble.

Claims

1. A switch comprising a housing; an electrical terminal secured within the housing; a resilient contact within the housing movable between an open circuit position in which it does not contact the terminal and a closed circuit position in which it contacts the terminal; an actuator movable relative to the contact and including biasing means for biasing the contact from its open circuit position to its closed circuit position; and a cam movably disposed within the housing, the cam being operable to control the position of the actuator.

2. A switch according to claim 1, wherein the cam is free to move within a part of the housing and includes a profiled surface co-operable with a cam follower provided on the actuator, the profile being operative to hold the cam follower into one of the open or closed circuit positions.

3. A switch according to claim 1 or 2, wherein the cam is reciprocably slidable in a direction substantially perpendicular to the direction of movement of the actuator, the cam follower being operative to cause the cam to slide relative thereto and thereby to move within the profile into and out of a holding position of the profile.

4. A switch according to claim 1, 2 or 3, wherein the cam includes cam biasing means for controlling the position of the cam within the housing.

5. A switch according to any preceding claim, wherein the contact is normally biased in the open cIrcuit position and the biasing means includes a cam surface operative to urge the contact towards the terminal to the closed circuit position.

6. A switch according to any preceding claim, comprising first and second facing terminals and first and second resilient contacts, the actuator being operative to bias the first and second contacts towards a respective terminal.

7. A switch substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.