GB2054271A - Electric switch - Google Patents

Abstract

In an electrical switch, particularly for use as a safety device, having a housing (2) and a switching mechanism including a rigid arm member (22) providing a direct, non-elastic link between an actuating button (8) and a fixed first terminal member (10) whereby depression of the button (8) moves the arm member (22), against the bias of resilient means (34), out of contact with the terminal member (10), a barrier means (40) within the housing (2) ensures that the resilient means (34), on inadvertent displacement thereof from a normal location within the housing (2), cannot effect electrical continuity between the arm member (22) and the terminal member (10). The barrier may be a plastic insert (40) shown or may be provided by wide portions of the arm 22 or of the arm support terminal 16 extending across the interior of the housing. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electric switches This invention relates to electric switches, particularly such switches for use as safety devices to ensure that, on actuation thereof, the electrical supply to associated equipment is cut off.

It is often advisable, if not essential, to provide safety switches on certain electricallyoperated equipment, such as office machines, paper shredders, spin dryers and the like, such that when a mechanical component part of the equipment is moved, said equipment is automatically stopped.

In order to ensure effective and consistent operation of such switches, they should incorporate positive-action mechanisms therein i.e. mechanisms which incorporate direct, non elastic linkages between an actuating button of the mechanism and the contact element with which electrical contact is to be made and broken-as opposed to snap-action mechanisms.

Heretofore the only switches satisfying these requirements have been somewhat cumbersome in construction, while the majority of switches used in this particular application include mechanisms incorporating a spring or energy store so arranged that, if said spring broke, depression of the associated actuating member may not result in the required interruption of the associated electrical circuit.

Clearly it would be advantageous if there could be provided a compact, positive action switch which, even if an associated coil spring or like resilient means within the actuating mechanism broke, ensured effective operation of said switch.

It is currently well-established practice to provide snap-action microswitches which include any one of a number of different types of snap-acting mechanisms but all of which are contained within housings adhering to established dimensions. These dimensions are laid down in British Standard BS 9578N001 as well as in DIN 41635. A housing according to these standards is of generally rectangular section and includes a pair of diametrically-opposed mounting holes therethrough, the spacing of said holes being 22.2mm + 0.2mm in the front to rear direction of the housing and 1 0.3mm + 0.1 mm in the top to bottom direction of said housing. The housing has mounted therein to project therefrom an actuating button depression of which operates a switching mechanism within the housing against the action of resilient means of said mechanism.

Such a housing will herein after be referred to as 'a housing of the type described'.

According to the present invention there is provided an electrical switch comprising a housing of the type described, said housing containing a switching mechanism including a rigid arm member, and resilient means having a normal location within said housing urging said arm member into a rest position in which one end of the arm member abuts the actuating button and the other end of the arm member makes electrical contact with a fixed first terminal member, depression of the actuating button pivoting the arm member about an intermediate region thereof against the bias of the resilient means into a displaced position in which the one end of the arm member remains in abutment with the actuating button and in which the other end of the arm member is out of electrical contact with said terminal member, the switch further comprising barrier means within the housing positioned between the resilient means in its normal location and the other end of the arm member whereby, on inadvertent displacement of the resilient means from its normal location within the housing, said barrier means prevents inadvertent contact of the displaced resilient means with both the arm member and the first terminal member.

The switch may comprise a further fixed terminal member, the intermediate regions of the arm member engaging with, to make electrical contact with, said further terminal member whereby said arm member is, on depression and release of the actuating button, pivotal on the further terminal member to break and make an electrical circuit between the first and further terminal members.

The barrier means preferably comprises an insert of a plastics material extending substantially the full width of the interior of the housing and located in the housing at a position at or adjacent the intermediate regions of the arm member to define, with the walls of the housing, a first compartment within the housing containing the one end of the arm member and the resilient means, and a second compartment within the housing containing the other end of the arm member and the terminal member.

In such a case, the resilient means may comprise a coil spring normally located to react between a fixed point on the insert and the one end of the arm member.

The barrier means may comprise an extent of the arm member itself the width of which is substantially equal to that of the interior of the housing, or, alternatively, may comprise an extent of the further terminal member the width of which is substantially equal to that of the interior of the housing-in both cases the resilient means are located to the side of the extent of the arm member or further terminal member remote from the first terminal member.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawing which shows the interior of a switch according to the invention.

Referring to the drawing, the illustrated switch comprises a housing indicated generally at 2 the dimensions of which conform with those laid down in B.S. 9578N001, said housing having formed therethrough a pair of diametrically opposed mounting holes 4, 6 and being provided with an actuating button 8 slidably mounted therein to project therefrom.

A first terminal member 10 is fixed in, to extend from one end of, the housing 2, said member having a contact button 1 2 mounted thereon within said housing.

A further terminal member, indicated generally at 14, is fixed within the housing and includes an intermediate portion 1 6 projecting through the intermediate regions of the base of the housing and a terminal portion 1 8 outside the housing forming a right-angled extension of said portion 1 6. The member 14 further includes an uppermost, substantially Lshaped portion 20 within the housing. Said portion 20 extends substantially the full width of the housing and includes a central aperture therethrough defining a pair of opposed leg members thereto, said aperture being extended downwardly into the upper regions of the intermediate portion 1 6 for reasons to be detailed below.

The switching mechanism includes a rigid arm member indicated generally at 22 and including a one end portion 24, an intermediate extent 26 and a further end portion 28 carrying a contact button 30.

The arm member 22 extends through the part of the aperture through the upper regions of the intermediate portion 1 6 of the terminal member 14, the intermediate extent 26 of said arm member seating on a transverse peak 32 integrally formed on the inner surface of the base of the housing. The arm member has a normal rest position within the housing 2 in which the contact button 30 engages with, to make electrical contact with, the contact button 1 2 of the terminal member 10 and in which the one end portion 24 of the arm member abuts the lower surface of the actuating button 8.

The arm member 22 is retained in this rest position by means of a coil spring 34 extending through the aperture in the portion 20 of the terminal member 1 4 and reacting between the one end of the arm member and a fixed point within the housing.

With the switch in the illustrated condition, electrical contact between the terminal members 10 and 14 is established through an increased-width part 36 of the intermediate extent 26 of the arm member 22 being resiliently urged by the spring 34 into engagement with the left-hand side, as viewed in the figure, of the intermediate portion 1 6 of the terminal member 14 and through the abutting buttons 12 and 30.

This circuit can be broken by depressing the actuating button to pivot the arm member 22, against the bias of the spring 34, about its line of contact with the terminal member 1 4 and on its seating on the peak 32, thereby to move the contact button 30 away from and out of engagement with the button 1 2.

It will be appreciated that such a switching action is positive in nature in that the linkage between the actuating button 8 and the fixed terminal member 10 comprises the rigid arm member 22 and does not include any elastic or resilient means.

The pivoting movement of the rigid arm member 20 is, as mentioned above, against the action of the coil spring 34 and, on release of the button 8, said spring 34 returns the mechanism to its illustrated rest position.

In the event of the coil spring 34 breaking or coming loose from its mounting within the switching mechanism, depression of the actuating button 8 will still result in movement of the contact button 30 away from the contact button 1 2 and breaking of the associated electrical circuit-the switch is therefore fail safe in this respect.

However, in order to ensure that there is no electrical continuity between the terminal members 10 and 14 in such a situation, it is necessary to ensure that the spring 34, once broken or loose, cannot short between the disengaged buttons 12, 30.

In the illustrated arrangement, this is achieved by the provision of barrier means in the form of a plastic insert indicated generally at 40 between the coil spring 34 and the buttons 12, 30.

More particularly, the insert 40 includes a sidewall 42 of a width substantially equal to that of one of the legs of the portion 20 of the terminal member 14 and integrally formed with which sidewall 42 is an end wall extending perpendicularly from said sidewall 42 and of a length substantially equal to the width of the interior of the housing 2. A raised boss 46 is formed on a face of said sidewall 42 adjacent and just in front of the end wall 44.

The insert 40 is positioned within the housing 2 with the sidewall 42 lying adjacent and parallel with an interior sidewall of the housing and with the end of said sidewall 42 remote from the wall 44 abutting one of the legs of the portion 20 of the terminal member 1 4. The end wall 44 of said insert thus extends right across the width of the interior of the housing 2, the upper edge of said wall 44 lying closely adjacent an upper interior surface of the housing 2 and the lower edge of said wall 44 lying closely adjacent the transition in the terminal member 14 between the portion 1 6 and the portion 20 thereof.

Thus said insert, in combination with the walls of the housing 2, in effect divides the interior of the housing into separate compartments 48, 50.

One end of the coil spring 34 is in fact hooked onto the boss 46, said spring thus serving to retain the insert in its desired position by urging it from right to left, as viewed in the drawing, against the terminal member 14.

Thus it will be appreciated that, should the coil spring 34 break or come loose from its position within the switching mechanism, the end wall 44 of the insert 40 presents a mechanical barrier to the passage of said spring from compartment 48 to compartment 50 and therefore eliminates the possibility of said spring effecting electrical continuity between the terminal members 10, 14 under any circumstances.

It will be noted that the insert 40 and the interior of the housing 2 are shaped, at 52, 54 respectively, to prevent inadvertent movement of the insert 40 from left to right as viewed in the drawing and therefore to prevent interference by said insert with the switching mechanism should the spring 34 become detached from said insert.

The barrier means may be other than as illustrated. For example, the portion 20 of the terminal member 14 may comprise a linear extension of the portion 1 6 of said member, said portion 20 then forming a suitable barrier to which the coil spring 34 can be attached.

Alternatively, the intermediate extent 26 of the arm member 22, to the right-hand side of the member 14 as viewed in the drawing, may be of width substantially equal to that of the interior of the housing 2 and the spring 34 may be suitably positioned so that said increased-width portion of the extent 26 constitutes the necessary barrier. Other modifications and variations will be apparent to those skilled in the art.

In assembly of the switch, the components 22, 34 and 40 can be sub-assembled externally of the housing 2 and subsequently manoeuvred through the component 14 into position with the housing.

The insert 40 may, if necessary or if desired, be glued or otherwise secured in the housing 2.

Claims (7)

1. An electrical switch comprising a housing of the type described, said housing containing a switching mechanism including a rigid arm member and resilient means normally located within said housing to urge said arm member into a rest position in which one end of the arm member abuts the actuating button and the other end of the arm member makes electrical contact with a fixed first terminal member, depression of the actuating button pivoting the arm member about an intermediate region thereof against the bias of the resilient means into a displaced position in which the one end of the arm member remains in abutment with the actuating button and in which the other end of the arm member is out of electrical contact with said terminal member, the switch further comprising barrier means within the housing positioned between the resilient means in its normal location and the other end of the arm member whereby, on inadvertent displacement of the resilient means from its normal location within the housing, said barrier means prevents inadvertent contact of the displaced resilient means with both the arm member and the first terminal member.

2. An electrical switch as claimed in claim 1 and comprising a further fixed terminal member, the intermediate regions of the arm member engaging with, to make electrical contact with, said further terminal member whereby said arm member is, on depression and release of the actuating button, pivoted on the further terminal member to break and make an electrical circuit between the first and further terminal members.

3. An electrical switch as claimed in claim 1 or claim 2 in which the barrier means comprises an insert of a plastics material extending substantially the full width of the interior of the housing and located in the housing at a position at or adjacent the intermediate regions of the arm member to define, with the walls of the housing, a first compartment within the housing containing the one end of the arm member and the resilient means, and a second compartment within the housing containing the other end of the arm member and the terminal member.

4. An electrical switch as claimed in claim 3 in which the resilient means comprises a coil spring normally located to react between a fixed point on the insert and the one end of the arm member.

5. An electrical switch as claimed in claim 1 or claim 2 in which the barrier means comprises an extent of the arm member itself the width of which is substantially equal to that of the interior of the housing, the resilient means being located to the side of said extent of the arm member remote from the first terminal member.

6. An electrical switch as claimed in claim 2 in which the barrier means comprises an extent of the further terminal member the width of which is substantially equal to that of the interior of the housing, the resilient means being located to the side of said extent of the further terminal member remote from the first terminal member.

7. An electrical switch substantially as described with reference to and as illustrated by the accompanying drawing.