GB2024521A

GB2024521A - Electrical Switch

Info

Publication number: GB2024521A
Application number: GB7924087A
Authority: GB
Original assignee: KAC Alarm Co Ltd
Current assignee: KAC Alarm Co Ltd
Priority date: 1978-04-11
Filing date: 1979-07-11
Publication date: 1980-01-09

Abstract

A call point switch for an alarm system has a plate (16) which can be flexed to release a spring loaded actuator (15) of a switch (14) associated with an alarm signal. Subsequently, the plate (16) restores itself to its initial configuration after the actuator (15) has been reset by a tool inserted through a cover (not shown). <IMAGE>

Description

SPECIFICATION Electrical Switch This invention relates to a manually operable electrical switch and is concerned primarily with switches for use in alarm systems.

A common form of switch which is included in fire alarm systems at the present time comprises a glass plate which can be broken by any one wishing to activate the alarm. There is operatively associated with the glass plate a set of springloaded electrical contacts which are held in a first condition whilst the glass plate is unbroken but moved to a second condition when the plate is broken. In some cases the contacts are open in the first condition and in other cases they are closed in the first condition.

Known switches of this kind have the advantage that the broken glass plate provides an easily observed indication that the switch has been operated. One disadvantage of these known switches is that, once the switch has been operated by breaking the glass plate, it is necessary to replace the broken glass by a new plate before the switch can be restored to a useful condition.

In the case of a switch which is included in a fire alarm system the fact that breaking of the glass plate generates noise is not a disadvantage.

There is a requirement for a switch which can be operated with the generation of less noise. Such a switch is required in a security alarm system where the switch is so positioned as to be accessible to a cashier or other person who is particularly exposed to the risk of being threatened with violence. If a cashier is being threatened with violence, it is desirable that the cashier should be able to operate an alarm system without the sudden generation of any noise.

According to the present invention, there is provided a manually operable electrical switch comprising circuit control means which can be changed repeatedly between first and second conditions and an operating member which is accesible to a user, is movable by the application of a force by hand from a first position to a second position without being broken and is so associated with the circuit control means that, when the operating member is moved from its first position to its second position, the circuit control means is changed from its first condition to its second condition, and wherein re-setting of the circuit control means to its first condition is a more complex operation than is the setting of the circuit control means in its second condition by the application of said force to the operating member.

With this arrangement, the circuit control means will not be returned inadvertently to its first condition, but the control means can be deliberately re-set to its first condition without replacement of the operating member.

The circuit control means may include an input member which is engaged with the operating member and is movable in a direction transverse to the direction of movement of the operating member between a primary position which the input member occupies when the operating member occupies its first position and a secondary position which the input member occupies when the operating member occupies its second position and wherein there is provided on at least one of said members a surface inclined to the respective directions of movement of both members and so engaged by the other member that gradual movement of the input member from its primary position to its secondary position is brought about when the operating member is moved gradually from its first position to its second position.

In contrast with the abrupt operation of the known switches referred to, gradual movement of the input member can be effected without the generation of significant noise and the circuit control means can be changed to its second condition without startling any person who is near to the switch.

Two examples of switch embodying the invention will now be described with reference to the accompanying drawings wherein: Figure 1 shows a perspective view of a first switch in accordance with the invention, a cover being separated from the remainder of the switch and an operating member being in a first position, Figure 2 is a fragmentary perspective view of certain parts shown in Figure 1, the operating member being in a second position, Figure 3 is a plan view of the second example of switch in accordance with the invention, Figure 4 is a fragmentary cross section on the line lV-IV of Figure 3 but on a larger scale, and Figure 5 is a cross section similar to Figure 4 showing parts of the switch in positions which they occupy after the switch has been operated.

The switch illustrated in Figures 1 and 2 of the accompanying drawings comprises a body 10 which includes a base 11 and a cover 12 detachably mounted on the base and secured thereto by a screw. The cover defines a window opening 13 through which certain parts within the body can be seen.

Within the base 11, there is mounted circuit control means for controlling an external electrical circuit. This control means can be changed repeatedly between first and second conditions to set the external circuit in corresponding conditions. In the particular example illustrated, the circuit control means comprises a microswitch 14 having a pair of electrical contacts (not shown) which are biased towards an open position but which can be changed to a closed condition by movement of an input member in the form of an operating button 1 5 which is spring-urged towards a position in which it projects from a casing of the micro-switch.

Alternatively, the contacts of the micro-switch could be biased towards a closed condition and movable to an open condition by means of tl- - operating button. Within the base 11 there are provided terminals (not shown) whereby the micro-switch 14 can be connected in an external electrical circuit.

Within the body 10 there is disposed an operating member in the form of a rectangular plate 1 6. A major part of one face (called herein the outer face) of this plate is exposed within the window opening 13. Marginal parts of the outer face are engaged by the cover 12 which holds the plate within the body. At its opposite face, the inner face, the plate 1 6 is supported adjacent to its ends only on ledges 1 7 and 1 8 formed in the base 11. Between the ledges 17 and 18 and adjacent to the inner face of the plate, there is a clearance space. The plate 1 6 is formed of a resiliently flexible plastics material. In its unstressed condition, the plate is flat and accordingly occupies the position illustrated in Figure 1.The plate can be moved to a second position, illustrated in Figure 2, by the application to that part of the outer face which is exposed in the window opening 13 of a force directed towards the base 1 A force which is sufficiently large to overcome the resilience of the plate and move the plate to its second position can readily be applied by hand. In its second position, opposite end portions of the plate may still be engaged on the ledges 17 and 18 but an intermediate portion of the plate is spaced away from those parts of the cover 12 which border the window opening 13.

When the plate 1 6 is in its first position, the intermediate portion of the plate is engaged at one of its edges with the operating button 1 5 of the micro-switch and retains this operating button in a depressed position in which it does not project, or projects only slightly, from the housing of the micro-switch. As the plate 1 6 is moved from its first position to its second position, it moves out of alignment with the button 1 5 and so permits the button to move to a projected position and allows the condition of the microswitch 14 to change, so providing a signal to the external circuit.

Owing to its inherent resilience, the plate 1 6 tends to assume a flat configuration and so to occupy its first position. The button 1 5 acts as a retaining means for retaining the plate 1 6 releasably in its second position. When the plate is in its second position, the button 1 5 overlaps with a small part of the outer face of the plate 1 6 and so obstructs movement of the plate back to its first position. Whilst the cover 1 2 is present on the base 11, the cover prevents access of a person's hand to the button 1 5 so that the plate 1 6 cannot be returned to its first position without the use of a tool.

The cover 12 of the body 10 is formed with an aperture 19 through which a rod (not shown) can be inserted into the body to engage the button 1 5 and depress that button into the housing of the microswitch 14. When the button is so depressed, the plate 1 6 automatically returns to its first position by virtue of its inherent resilience.

The rod is then withdrawn from the body and the plate 16 will continue to hold the button 1 5 in a depressed position. Thus, the micro-switch can be returned to its initial condition and subsequently maintained in such condition without replacement of any parts. It will be understood that once the plate 1 6 has been moved to its second position by the application of hand pressure to its outer face, the mere discontinuing of such pressure or the application by hand of a further force to the plate 16 cannot result in the micro-switch 14 being re-set to its first condition.

Since the plate 1 6 can readily be observed through the window opening 13, this plate provides a visual indication as to whether the micro-switch 14 has been changed from its first condition to its second condition by movement of the plate. Preferably, the plate 1 6 is formed of a transparent material which bears, at the inner face of the plate, a reflective layer which adapts the plate to reflect light as a mirror. This facilitates distinguishing of the flat and deformed configurations of the plate visually.

The switch illustrated in Figures 3, 4 and 5 is a modificed version of that shown in Figures 1 and 2. Certain parts of the modified switch correspond to those previously described with reference to Figures 1 and 2. Such corresponding parts are indicated in Figures 3, 4 and 5 by like reference numerals with the prefix 1 and the preceding description is deemed to apply except for the differences hereinafter mentioned.

The cover of the modified switch is omitted from Figure 3 and the body 10 is partly broken away to reveal the operating button 11 5 of the micro-switch 114. The micro-switch comprises an input member in the form of a lever 120 pivotally mounted at one of its ends in the casing of the micro-switch and bearing at a position between its ends on a free end of the operating button. An end portion 121 of the lever remote from its pivot projects in a direction from the casing of the micro-switch towards the plate 116.

When the plate 11 6 is in its normal position and is flat, an edge of the plate engages a substantially flat surface 122 of the end portion 121 of the lever, the surface 122 being substantially perpendicular to the direction of movement of the lever. The substantially flat surface 122 merges smoothly with one end of a curved surface 123 on the end portion 121 and at is opposite end the curved surface 123 merges smoothly with a further substantially fiat surface 124. The surface 124 is parallel to the direction of movement of the lever. The curved surface 123 is generally inclined to the direction of movement of the lever, that is towards and away from the casing of the micro-switch 114, and also inclined to the direction of movement of the plate 11 6, that is away from the window opening of the cover of the switch.

When the edge of the plate 11 6 is engaged with the surface 122 of the lever, the plate holds the lever close to the casing of the micro-switch 11 4 so that the operating button 11 5 is maintained in a depressed position and the electrical contacts of the micro-switch are maintained in a first condition. If pressure is exerted on the centre of the surface of the plate 11 6 which is accessible through the window of the switch cover so that the plate is gradually moved to its second position, the edge of the plate which bears against the end portion 121 of the lever travels across the curved surface 123 until it engages the flat surface 124. This allows the lever gradually to move away from the casing of the micro-switch so that the operating button is permitted to project from the casing of the micro-switch and the contacts assume a second condition. As shown in Figure 5, when the plate 11 6 is engaged with the flat surface 124 of the lever, the lever retains the plate in its second position. Once the user's hand has been removed from the plate, the plate will exert on the end portion 121 of the lever a force directed towards the cover of the switch but, as seen clearly in Figures 4 and 5, a part 125 of the body overlies the end portion of the lever to constrain the lever against movement in this direction.

There is formed in the cover of the switch an aperture which permits a tool to be engaged with the end portion 121 of the lever so that the lever can be returned to its normal position without the cover being removed.

Claims

1. A manually operable electrical switch comprising circuit control means which can be changed repeatedly between first and second conditions and an operating member which is accessible to a user, is movable by the application of a force by hand from a first position to a second position without being broken and is so associated with the circuit control means that, when the operating member is moved from its first position to its second position, the circuit control means is changed from its first condition to its second condition, and wherein re-setting of the circuit control means to its first condition is a more complex operation than is the setting of the circuit control means in its second condition by the application of said force to the operating member.

2. A switch according to claim 1 so arranged that neither discontinuing the application of said force to the operating member nor applying by hand a further force to the operating member results in the circuit control means being re-set to its first condition.

3. A switch according to claim 1 or claim 2 adapted to provide a visual indication as to whether the circuit control means has been changed from its first condition to its second condition by movement of the operating member from its first position to its second position.

4. A switch according to any preceding claim wherein the operating member is resiliently biased towards its first position.

5. A switch according to claim 4 wherein biasing of the operating member arises from inherent resilience of the operating member.

6. A switch according to any preceding claim comprising means for retaining the operating member releasably in its second position.

7. A switch according to claim 6 wherein the means for retaining the operating member is inaccessible by hand, in the assembled switch.

8. A switch according to claim 6 or claim 7 defining an aperture to provide access for a tool to the means for retaining the operating member.

9. A switch according to any one of claims 1 to 5 wherein the circuit control means includes an input member which is engaged with the operating member and is movable in a direction transverse to the direction of movement of the operating member between a primary position which the input member occupies when the operating member occupies its first position and a secondary position which the input member occupies when the operating member occupies its second position and wherein there is provided on at least one of said members a surface inclined to the respective directions of movement of both members and so engaged by the other member that gradual movement of the input member from its primary position to its secondary position is brought about when the operating member is moved gradually from its first position to its second position.

10. A switch according to claim 9 wherein said surface is curved and merges smoothly with a second surface substantially parallel to the direction of movement of the member bearing the curved surface and the second surface.

11. A switch according to claim 10 wherein said curved surface also merges smoothly with a third surface which is substantially perpendicular to the second surface.

12. A switch according to claim 9 or claim 10 wherein the input member is arranged in its secondary position for retaining the operating member releasably in its second position.

13. A switch according to any preceding claim wherein the operating member has the form of a flexible plate.

14. A switch according to claim 13 as appendant to any of claims 1 to 8 wherein the plate is normally aligned with a movable input member of the circuit control means to limit movement of said input member and there is provided clearance for the plate to flex out of alignment with said input member and thereby permit movement of the input member.

1 5. A switch according to any preceding claim wherein the circuit control means is biased to its second condition.

1 6. A switch according to claim 1 5 comprising means for maintaining the circuit control means in its first condition whilst the operating member remains in its first position.

17. A switch according to any one of claims 1 to 8 wherein the operating member is deformed when it is moved from its first position to its second position.

18. A switch according to claim 3 wherein the operating member is adapted to reflect light as a mirror.

1 9. Any novel feature or novel combination of features disclosed herein and/or in the accompanying drawing.

20. A switch substantially as herein described with reference to and as shown in the accompanying drawing.