WO2007110658A1

WO2007110658A1 - Electrical switch

Info

Publication number: WO2007110658A1
Application number: PCT/GB2007/050125
Authority: WO
Inventors: Rupert Stephen Fane De Salis
Original assignee: Rupert Stephen Fane De Salis
Priority date: 2006-03-29
Filing date: 2007-03-15
Publication date: 2007-10-04
Also published as: GB0606205D0; GB2436639A

Abstract

An electrical switch is described which comprises conductive electrodes (12) and (14) embedded within a moulding (10) of an elastomeric material. The electrodes being contact with each other in response to deformation of the moulding.

Description

Electrical switch

Field of the invention

The present invention relates to an electrical switch and is particularly concerned with a switch design that enables the switch to be operated by applying tension.

Background of the invention

A search through the prior art has revealed the existence of EP 0618601, US 4343973, US 6091034, US 4429200, US 4356360 and JP2003157739A. These earlier disclosures all describe small, mechanically operated electrical switches with features to reduce cost of manufacture, while delivering durability, resistance to moisture and dirt, electrical insulation, repeatable actuation and "snap action". Snap action maintains a relatively large contact gap until the point of closure, when the gap closes rapidly, so that a "nearly closed" condition cannot be maintained for more than a very short time.

Each device comprises several separate parts, generally numbering more than six, as is typical of commercially available electrical switches.

GB 2249667 is a switch activated by applying a tension force to one end, and it comprises fewer parts than previous switch designs. However, it does not provide any protection from water or dirt, and it is intended for use within a larger housing.

In US 6495780, switch elements are contained in a cavity which is formed in a moulded body. The cavity contains air and requires sealing of several parts together to ensure that moisture and dirt are excluded. Similarly, in EP0177267, the assembly process takes the contacts, open to air, and positions them opposite similar or different contacts, creating an air gap in between. This air gap contains oxygen which can react with the conductive surfaces of the contacts to form an insulating oxide and impair the operation of the switch. Further to this, there is no means provided to prevent fresh oxygen, and moisture, from entering this air gap. The switch is also reliant on compression as the only means of actuation.

Object of the invention

The invention seeks to provide an electrical switch that is simple and inexpensive to manufacture and capable of being designed for operation by application of tension, pressure or other deformation, which is robust and sealed against contamination.

Summary of the invention

In accordance with the present invention, there is provided an electrical switch comprising conductive electrodes embedded in-situ during moulding within an elastomeric material, the electrodes being operative to make contact with each other in response to deformation of the moulding.

It is preferred to form the moulding such that the gap between the electrodes is initially occupied by the elastomeric material. This simplifies the moulding considerably as no special steps will need to be taken to maintain an empty gap between the electrodes during the moulding process . While it might be thought that this would permanently maintain the electrodes isolated from one another, it has been found surprisingly that by suitably shaping the electrodes they will cut through the elastomeric material separating them and come into contact with one another during initial actuation of the switch. It may be necessary to apply more force during the first actuation of the switch to cut through the elastomeric material than will be necessary for subsequent actuations of the switch.

In one embodiment of the invention, the electrodes are shaped as overlapping hooks that come into contact with one another when the elastomeric material of the moulding is stretched.

The electrodes may suitably be formed of stainless steel wire, carbon material or beryllium copper.

In accordance with a second aspect of the invention, there is provided a method of manufacturing an electrical switch, which comprises forming two electrodes of an electrically conductive material, positioning the two electrodes in a multi-part mould such that (i) contact regions of the electrodes are located within a cavity defined between parts of the mould and (ii) parts of the electrodes which are to form connection terminals are gripped between parts of the mould in regions lying outside the mould cavity, filling the cavity with an elastomeric material, and allowing the elastomeric material to set.

Preferably upon first deformation of the switch, the elastomer between the contacts is ruptured, allowing making or breaking of electrical contact with each subsequent deformation of the switch.

The invention further provides a slipper, or other footwear, having an externally visible light source connected by way of a switch as set forth above to a battery mounted in the slipper, the switch being closed automatically when the slipper is worn to activate the light source. The battery is preferably a replaceable battery concealed with the body of the slipper, for example in the heel .

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a switch of the invention,

Figure 2 is a schematic view of the electrodes of the switch in Figure 1 with the elastomeric material removed, and Figures 3 and 4 are a plan view and a side view, respectively, in which the internal parts of the switch are shown in dotted lines.

Detailed description of the preferred embodiment

The illustrated electrical switch comprises two, preferably identical, bent stainless steel wire electrodes, 12 and 14, similar in appearance to paperclips, which are best shown in Figure 2. The electrodes are encased in a moulded flexible silicon-rubber body 10. Each electrode comprises an oval racetrack shape 16, culminating in an extension 18 towards the centre of the switch. The extensions 18 are bent at their ends 20 to form hooks that interlock around one another in the rest position of the switch, but with a small gap between them so that they do not touch.

Each electrode 12, 14 protrudes outside the silicon rubber body 10 in two places. This is in order to provide mounting points for precise location of the electrodes while the body is being moulded around them. For each electrode, one of the protruding portions is also used to attach an electrical wire by soldering.

When the switch is pulled to a greater length by tension applied to the two holes 22 in the body 10, the wire electrodes 12 and 14 move bodily apart, with the result that they come closer to one another in the central interlocking area. At the required switch elongation, they touch and provide electrical contact.

On the first elongation of the switch, silicon rubber material is ruptured in the small gap between the electrodes 12 and 14, allowing electrical contact to begin. On release of the switch, the gap between the electrodes is opened, and electrical contact is broken. Electrical contact is restored whenever tension is applied to the body 10, and released whenever the tension is released.

It is alternatively possible for the electrodes 12 and 14 to protrude from the body 10 of the switch on one side only. Location of each wire in the mould is provided through clamping the protruding end only. This gives the advantage of halving the number of exposed segments of the electrodes, so that the switch can be more easily isolated from electrical contact with water or other adjacent substances or parts .

In use, connecting leads can be soldered to the electrodes 12 and 14 using special solder suitable for stainless steel. After soldering leads onto the electrodes, the exposed ends of the leads can be covered and insulated by means of a heat shrink material, which is shrunk onto the leads by applying heat, for example with a soldering iron.

This connection method renders the switch and connecting wire assembly completely waterproof and unable to make electrical contact with adjacent moisture or other conductive substances or solid conductive items.

Alternatively, the connection can be insulated with simple constant section heat shrink tubing, or multiple pieces of more than one size, to save the cost of obtaining sleeves to a unique specification.

As an alternative to the projecting loops, the electrodes may have protruding flattened portions for connection to spade terminals on connection leads.

The illustrated switch is particularly advantageous in that it is operated by tension or by stretching. It should be mentioned, however, that by suitable selection of the ends of the extensions 18, and the general shape of the wires and body, the switch may be actuated by compressive pressure, torsion, bending, hydraulic or pneumatic pressure, hydraulic or pneumatic negative pressure, magnetic attraction, gravity, inertia, thermal expansion or other means of force application.

The illustrated switch may be fastened to an adjacent piece of fabric with a fold of fabric provided between the attachment points, such that when tension is applied to the fabric, the fabric applies tension to the switch and causes it to provide electrical contact. Alternatively, to machinery or other moving items to operate in response to changes in position or shape, e.g. brake light switches for bicycles or other vehicles" .

As an alternative, the fabric may itself be elasticated in which case the switch will only close when a preset tension is applied to stretch the switch and the fabric.

There are several applications for a switch that detects when a fabric is stretched or placed under tension. One such application is in slippers or other items of footwear having externally visible LED's that are illuminated automatically when the slippers are worn, the LED's being connected by way of the switch to a replaceable battery concealed in the body of the slipper, such as in the heel. For an attractive novelty item, the uppers of the slippers may be made of a furry material and the LED's concealed within the pile. When lit, the LED's shine like eyes and give the slippers the appearance of little furry animals. In other items of footwear, the LED's can help to make the wearer visible at night. A circuit may also be incorporated in the slippers so that the LED's are only operated intermittently, to conserve battery life. If desired, the circuit may for the same reason also include a light sensor to prevent the LED's from being activated in bright light conditions.

The switch is attached to the fabric lining the slippers by means of two fasteners. The fasteners comprise two small mushroom shaped plastic pins, known as trim clips, and two spring steel retaining washers which serve to maintain a clamping force when assembled to the pins. Assembly to the lining is accomplished by punching two holes therein, passing the two pins through the lining from the foot side, fitting the holes of the switch over the pins, then fitting the retaining washers over the pins, and clamping axially to create a clamping force that holds the switch firmly to the inner skin at each end.

The switch may have alternative means for attachment to adjacent components, including button features moulded into the body. It may furthermore be attached by stapling or by the use of a piece of compliant material such as fabric, looped through the switch hole and stapled, glued, stitched, plastic-welded or otherwise attached to the adjacent component. Still further possibilities for mounting the switch include inserting a screw, pin, rivet etc to attach through the hole in the switch.

It is not essential for the body to be formed of silicone rubber it being possible to use other elastomeric material, which may be opaque, translucent or transparent.

It is furthermore possible to modify the manufacturing process and/or materials and/or geometry of the switch and the wire elements.

It is an advantage of the switch that it may be readily adapted for small and large scale applications, and that it can be designed to withstand harsh environmental conditions e.g. industrial processes, extreme climate etc.

Though the illustrated switch contains only one pair of contacts, it is possible to provide several differently spaced pairs so that switch may indicate progressive degrees of movement by sequential activation of the pairs of electrical contacts.

The electrical switch may be manufactured by forming two electrodes of an electrically conductive material. The two electrodes are positioned in a multi-part mould such that contact regions of the electrodes are located within a cavity defined between parts of the mould. Parts of the electrodes which form connection terminals in the manufactured switch are gripped between parts of the mould in regions lying outside the mould cavity. The cavity is then filled with an elastomeric material, and the latter is allowed to set. _ g -

Advantages of the switch of the invention.

• The switch is suitable for underwater, hot, cold, corrosive, dusty or otherwise harsh environments and also in environments where electrical sparks present a risk, e.g. mining, and for sterile environments where cleaning operations are important.

• Though the switch does not provide a snap action, it provides a simple momentary operation and is suitable, for low current, low voltage applications such as LED switching, as well as some existing microswitch applications such as limit switching.

• With only three separately manufactured parts — of which two may be identical — the switch comprises fewer parts than any previous design of housed switch.

• The gap area is permanently free from oxygen and moisture, both of which are expelled during moulding, preventing oxidation of the contact areas. The switch protects its contacts from ingress of environmental water and dirt, without the use of a complex sealed housing.

Therefore additional contact coatings, such as gold plate, are not required.

• Activation of the switch does not cause any sliding, rubbing or abrasion except in a very small area around the contact gap, giving an advantage for long working life.

• The wire elements can be manufactured very cheaply using readily available stainless steel wire and conventional wire-bending machines, requiring very little unique tooling and very short lead-times.

• For prototype and low-volume production purposes, the wire elements can be manufactured using simple hand- operated bending jigs which can be made at very low cost, with very short lead-times . • The housing can be moulded using conventional injection moulding equipment, requiring only one cavity design . • For prototype and low-volume production purposes, the housing can be manufactured using gravity-poured two- part silicon rubber compound in a non-pressurised mould, allowing very low-cost manufacture and very short lead- times, where small volumes are required.

• The moulding process is very simple and cheap, comprising the placement of the wires, closure of the mould, injection of the elastomer material, high temperature curing and ejection of the finished part. Excess material is then removed from the contacts - without difficulty, as the elastomer material has a weak adhesion to the wire material.

• The wire elements are suitable for soldering to connecting wires where they protrude, with the use of solder and flux that are suitable for stainless steel. • The silicon rubber and stainless steel materials are resistant to soldering temperatures and a wide range of hot and cold temperatures that may be encountered in various industrial applications. They are also highly chemically inert and therefore resistant to corrosive environments. • The switch is suitable for a wide range of uses where a "pull" motion is available for actuation. It can tolerate a significant amount of "over-travel" without damage .

• The switch can tolerate bending into different shapes without unintended activation or damage, making it suitable for applications where flexion is present, e.g. in footwear and other clothing.

• The switch is soft and free from sharp edges, and therefore suitable for applications where comfort and protective surfaces are required, e.g. in footwear and other clothing .

• The switch design can be altered in dimensions and shape to suit different applications, with very little outlay in tooling. • The switch allows waterproof connection to the connecting wires by the use of heat-shrink tubing, which locates on the oval raised sections at the exit point of each wire from the body.

• The switch can be packaged in free bag form for shipping and line side assembly storage without risk of damage - no extra packaging is required. This gives an environmental advantage and a logistics cost advantage.

• The two materials of the switch are non-toxic, non-allergenic, non-staining and non-reactive. This makes them suitable for applications where the switch is in close proximity to the skin.

• The flexibility of the body, and the provision of two fixing holes in compliant elastomer material, makes it possible to mount the switch to a variety of adjacent components without unique modification. • The switch design is optimised for production in emerging-market countries where labour costs are low, with minimal requirement for unique tooling.

Claims

1. An electrical switch comprising conductive electrodes embedded in-situ during moulding within an elastomeric material, the electrodes being operative to make contact with each other in response to deformation of the moulding .

2. An electrical switch as claimed in claim 1, wherein the moulding is formed such that the gap between the electrodes is initially occupied by the elastomeric material and is subsequently ruptured by the electrodes upon first deformation of the moulding, enabling contact between the electrodes .

3. An electrical switch as claimed in claim 1 or 2, wherein the electrodes are shaped as overlapping hooks that come into contact with one another when the elastomeric material of the moulding is stretched.

4. An electrical switch as claimed in any preceding claim, wherein the electrodes are formed of stainless steel wire .

5. An electrical switch as claimed in claims 1 to 3,, wherein the electrodes are formed of carbon material.

6. An electrical switch as claimed in claims 1 to 3, wherein the electrodes are formed of beryllium copper.

7. A slipper or an item of footwear having an externally visible light source connected by way of a switch as claimed in any preceding claim to a battery mounted in the slipper, the switch being closed automatically when the slipper is worn to activate the light source.

8. A slipper as claimed in claim 7, wherein the battery is a replaceable battery concealed with the body of the slipper.

9. A method of manufacturing an electrical switch, which comprises : forming two electrodes of an electrically conductive material, positioning the two electrodes in a multi-part mould such that (i) contact regions of the electrodes are located within a cavity defined between parts of the mould and (ii) parts of the electrodes which are to form connection terminals are gripped between parts of the mould in regions lying outside the mould cavity, filling the cavity with an elastomeric material, and allowing the elastomeric material to set.

10. A method as claimed in claim 9, wherein upon first deformation of the switch, the elastomer between the contacts is ruptured, allowing making or breaking of electrical contact with each subsequent deformation of the switch .