CA1221720A - Electric switch - Google Patents

Abstract

ABSTRACT

An electric strip switch for safety and similar application comprising a pair of metal strips 1, 2 of stainless steel separated, except at their overhanging long edges, by a foam tape 3. Electrical connections (not shown) are taken from the strips 1, 2 to provide a normally open switch. The switch is actuated by means of a U-section strip 17 of foam material whose legs 19, 20 touch, or nearly touch the overhanging edges of strips 1, 2. Pressure applied in any one of the three directions P1, P2 or P3 will cause the legs to cause one or both of the overhanging edges to contact, thus closing the switch.

Description

I

"ELECTRIC SWITCH"

This invention relates to electric switches, particularly, but not exclusively, strip switches.
British Patent specification 13519~1 of PUP. Engineering, Published May 1, 197~, describes a mat-type switch having a wide variety of uses, in-eluding security and safety applications. The described switch basically comprises a pair of thin metal, for example stainless steel, sheets between which is sandwiched a sheet of insulating material which separates and thus electrically isolates the sheets from one another. Apertures are formed in the insulating material whereby pressure in the area of an aperture causes electrical contact between the sheets to be made through the aperture. The present invention is related to this general mat-type of switch but has the advantage over the earlier type that it can be actuated from several differ-en angles, using a suitable actuator, making it particularly suitable in safety applications. However, a variety of other uses for the switch will become apparent.
According to the invention there is provided an electric switch made up of a laminate comprising two strips of conducting material and, sand-wicked between the strips to normally electrically isolate the strips from one another, an elongate layer of electrically insulating material, said layer extending lengthwise of the strips in the approximate geometric center thereof such that the elongate edges of the strips overhang the layer, and an actuator comprising a U-section strip of resilient material, whose legs are positioned in such a way as to overlay said overhanging edges of the strips.

q I

Various arrangements are possible for example the sheets could be of rectangular or square shape and overlay one another in registry, with said resilient layer positioned centrally so that the edges of the sheets overhang all around. Alternatively, the resilient layer could extend across the sheets from the central part of one straight side to the central part of the opposite straight side, with opposite edges of the two sheets over-hanging. in the preferred embodiment, the sheets are in strip form, the layer of resilient material taking the form of a foam tape extending length-wise along the strips in the geometric center thereof, thus lo I

2 --leaving the elongate edges of the strip sheets overhanging.
The overhanging edges could be covered in self-adhesive insulating tape to prevent ingress of moisture and dirt. Alter-natively, the whole assembly could be fitted in a suitably-shaped sleeve of flexible plastics material.
With a suitable actuator, the switch of this invention can be actuated from several angles, thus making it very suitable for use in safety cushion switches found around potentially dangerous machinery. Thus in an embodiment, the switch further includes an actuator comprising a sel~-supporting U-section strip of resilient material, for example foam rubber or plastics material whose legs are fitted in positioned in such a way as to overlay said overhanging edges of the laminate. In a preferred embodiment, the legs are fitted into an open channel-section housing in the bottom of which is situated said laminate. The switch is operated by applying pressure to that part of the strip which protrudes from eke housing and which forms a self-supporting resilient cushion. Pressure may be applied either directly down-wards - i.e. in a direction towards the channel - or to one or the other side of the cushion. In all three of these instances either one or both legs of the U-section strip will move towards the bottom of the channel to actuate the switch by pressing one or both of said overhanging edges together. It will be understood that the switch of this invention could be used in any orientation and references to "downwards" and "bottom" should be construed accordingly.
In a preferred embodiment of the invention, a bridge member, being a block of, preferably, resilient material is attached between the legs of the U-section strip near the bottom thereof.
In order what the invention may be better understood, an embodiment thereof will now be described by way of example only and with reference to the accompanying drawings in which-Figure I is a transverse cross sectional view of a strip switch made in accordance with the invention;
Figure 2 is a diagrammatic transverse sectional view of an actuator suitable for the switch of Figure l; and Figure 3 is a diagrammatic transverse section of another actuator suitable for the switch of Figure 1.
Referring to Figure I the switch comprises a laminate made up of two strips 1, 2 of metal for example stainless steel, 5 beryllium copper or phosphor bronze between which is sandwiched a layer 3 of resilient insulating material in the form of a double adhesive foam tape. The strips l, 2 are aligned in resist rye with one another and are typically 1 in. to 3 in. wide and of indefinite length. Typically the strips are of I thou to 15 thou 10 thickness, the foam strip of 1/16 inch thickness. Electrical connections (not shown) are made to the respective strips 1. 2 and are taken away via conventional means to the device being switched.
The foam material is positioned down the center of the 15 two strips to leave overhanging areas 4, 5 at each side. As is clear from Figure 11 the sheets 1, 2 are normally electrically isolated from one another by virtue of the layer 3, but pressure on either side, as illustrated by the arrows Pi, Pi will cause contact to be made due to movement of one strip with respect to the 20 other. Obviously contact could equally well` be effected by upwards pressure. if the switch were to be restrained in the upwards direction, or by a squeezing action near one of the edges.
The free edges of the switch are lightly bound with tape 6 to prevent ingress of moisture and dirt between the over-25 hanging edges.
A switch such as that shown in Figure I could be used directly by being mounted on a surface against which pressure may be applied to actuate the switch, possibly providing only a simple cover to protect and insulate the mechanism. Direct uses include 30 safety equipment and security applications and vehicle detection -in this latter connection it will be noted that the passage of a vehicle across the switch in a direction across the page in Figure I will result in the switch being actuated twice. with an interval between successive actuations governed by the speed of 35 the vehicle.
The switch may also comprise a suitable actuator, for example those shown with reference to Figures 2 and 3. In Figures 2 and 3, the same reference numerals have been used where appropriate. The switch shown in Figure 2 is protected not by tape 6 along its edges, but by being totally enclosed in a sleeve 7 of plastics material.
Referring to Figure 2. the actuator comprises an elongate actuator bar 8, for example of nylon. The bar 8, which is seen in section in the drawings has an actuator portion 9 and splayed-apart legs 10 which extend downwards as shown. The bar 8 is attached to the top of the switch by means of a strip 11 of foam material. Protection of the mechanism is afforded by a housing 12, for example of nylon, comprising a base portion 13 attached by means of screws 14 to a suitable surface, and a shroud portion IS
which has free ends which bear against the bar 8 to seal the assembly.
The switch is operated by moving the bar 8, any one or more of three motions in different directions causing the switch contacts, as represented by strips 1, 2, to close. Pressure in direction Pi or Pi will cause the bar to locally tip over in the appropriate direction about an axis approximately in the area of the strip 11. As a result the appropriate leg 10 will bear against and close the overhanging edge of the strips I and 2, thus effecting an electrical connection. Pressure in a vertical direction.
as represented by the arrow Pi will cause the bar to move down-warmly, thus causing both legs 10 to likewise move downwardly, eventually causing contact, as before.
Although the illustrated switch has a "dead zone"
before contact takes place, it will be clear that the switch can be made very sensitive, should this be desired.
The switch as described with reference to Figure 2 may be attached around dangerous machinery to protect the operator by de-activating the machinery if the operator places himself in a hazardous position. The switch is actable over a wide range of angles, and is thus particularly advantageous in safety applications where the switch is probably only actuated in accidental or panic conditions.

Lo Referring now to Figure 3, it will be seen that the laminate making up the switch is seated in the bottom of a channel section housing 16 of rigid material, for example hard plastics or, with suitable insulation, metal. The switch actuating S member takes the form of a self-supporting Section strip 17 of resilient material - for example foam plastics or rubber material.
The shape of the U-section may be achieved in practice by folding a length of suitable foam material about an axis extending centrally in a direction parallel to its elongate axis and then heat forming the top portion 18 so that it retains the U-section shape.
The legs 19, 20 of the section extend downwards into the housing 16 and rest on, or possibly just above, the switch laminate. The ends of the legs 19, 20 are chamfered at 21, 22 respectively so that the area of contact between the switch laminate and the bottom of the legs is reduced and moved as near to the edge of the laminate as possible. This improves the operation of the switch since, if the whole width of each leg were to be continued down into contact with the laminate. it would be more difficult to operate the switch because the effective mechanical leverage I would be reduced. The spacing of the legs is maintained by a bridging member I which may take the form of a strip of foam material, similar to that used for the strip 17, which is glued or otherwise adhered to the strip along the abutting edges.
A protective cover 24 of flexible rubber or plastics sheet material completes the assembly. The cover 24 is attached to the edges of the housing 16 and extends loosely over the strip 17 in approximate contact therewith. Some care must be taken in attaching the cover since, if it is too tight it will cause the switch to be continuously actuated. If carefully applied, the cover 24 can be used to retain the strip 17 and so ah element in place in relation to the housing 16 as shown in Figure 3. It is not though necessary to separately attach the strip 17 within the housing.
In order to mount the switch, a base plate 25 may be attached to the underside of the channel section. The base plate extends beyond the channel section to define flanges 26 which may ~22~

be attached by any suitable means to an appropriate surface.
The actuator described with reference to Figure 3 will permit actuation of the switch due to pressure applied in any one or more of three directions. Lateral pressure in directions S Pi or Pi will cause the leg 20 or 19 respectively to move down-wards to press the overhanging edge of sheets I and 2 into contact with one another. Downwards pressure in direction Pi will cause both legs 19 and 20 to move downwards thus similarly resulting in contact being effected between the two sheets I 2. For safety applications, the material of the strip 17 must be chosen carefully since it should be sufficiently rigid to transmit pressure to the switch laminate almost instantaneously but must be capable of collapsing easily if additional pressure is applied such as may occur in safety applications due to overrun of a protected machine.
Foam polyethylene has been found to be suitable.
The switch of the invention could also be actuated over a full 360 range by means of a joystick type control.

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electric switch made up of a laminate comprising two strips of conducting material and, sandwiched between the strips to normally electri-cally isolate the strips from one another, an elongate layer of electrically insulating material, said layer extending lengthwise of the strips in the approximate geometric centre thereof such that the elongate edges of the strips overhang the layer, and an actuator comprising a U-section strip of resilient material, whose legs are positioned in such a way as to overlay said overhanging edges of the strips.

2. An electric switch as claimed in claim 1 wherein the layer of in-sulating material takes the form of a foam tape.

3. An electric switch as claimed in claim 1 further comprising an open channel-section housing in the bottom of which is situated said lami-nate and into which the legs of the U-section strip are fitted.

4. An electric switch as claimed in any one of claims 1, 2 or 3 further comprising a block attached between the legs of the U-section strip near the bottom thereof.

5. An electric switch as claimed in claim 1 wherein the U-section strip is fabricated from foam material.