GB2223356A - Magnetic switch mechanism for a torch - Google Patents

Abstract

A switch mechanism (40) suitable for use in a waterproof torch (10) has a permanent magnet (54) mounted inside a slidable operating member (48) which is secured to the outside of a casing (12). Inside the casing (12) a first contact member (30) is fixed and a second contact member (38) is mounted so as to be resiliently biased towards or away from the first contact member (30). The second contact member carries a further permanent magnet (58) which is arranged so that like or unlike poles of the magnets face one another when the operating member is in a first position. The repulsive force between the magnets forces the contact members out of or into contact. When the operating member slides to a second position the force between the magnets (54, 58) is not sufficient to overcome the resilient bias and the contact members close or separate. The first contact member (30) is supported on a partition (66) and the torch batteries are located by internal casing ribs. <IMAGE>

Description

SWITCH MECHANISM The present invention relates to a switch mechanism which is particularly suitable for use with small batterypowered tools, such as flashlights or torches, which are required to have a waterproof casing.

The usual type of switch mechanism used in a flashlight requires an operating member on the outside of the casing which carries a projection which extends through an opening in the casing to co-operate with a contact member inside the casing. The arrangement is such that a sliding movement or depression of the operating member forces the co-operating contact member into contact with a fixed contact member inside the casing to close a circuit. The requirement for the opening in the casing represents a sealing problem if the flashlight is to be effectively waterproof.

The present invention is directed to solving the technical problem of providing a switch mechanism suitable for use in a tool which is required to have a waterproof casing.

The switch mechanism of the invention as defined in claim 1 does not require any opening in the casing for its operation and thereby eliminates the sealing problems associated with such openings.

A flashlight incorporating an embodiment of a switch mechanism in accordance with the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Fig.1 is a perspective view of a flashlight; Fig. 2 is a longitudinally sectioned view of the flashlight of Figure 1; and Fig. 3 is a cross section on the line A-A in Fig.2.

The switch mechanism will now be described with reference to its application in a waterproof flashlight. However, it will be appreciated that it can be used for other battery-powered tools.

The illustrated flashlight 10 has a two-part casing. A rear part 12 of the casing is shaped so as to be conveniently held in the hand and houses two batteries 14. The front part 16 of the casing is connected to the rear part 12 by means of a screw threaded connection 18.

The front part 16 includes a lens 20 and a bulb 21 in a bulb holder 22 which is fitted into a reflector 24. The bulb holder 22 is provided with two terminals 26 and 28.

The terminal 26 is disposed at the base of the bulb holder and is positioned to make contact with a corresponding terminal of the bulb 21 and with one terminal of a battery 14 when the two parts of the casing are screwed together. The other terminal 28 comprises a flange which makes contact with the other terminal of the bulb 21 and with a projecting end of a first contact member 30 which is fixed inside the rear casing part 12.

An O-ring seal 32 is gripped between the two parts of the casing at the screw threaded connection in order to prevent ingress of water through this connection.

A coil spring 33 is seated in the base of the rear casing part 12. One end of the spring makes electrical contact with a terminal at one end of the adjacent battery 14. The other end of the spring is electrically connected to a strip of springy conductor 34. This strip 34 is fixed to the inside of the casing and has a final fixing point 36 on the inside of the casing adjacent the end of the first contact member 30. The free end 38 of the strip 34 is therefore free to flex so that it can be forced into contact with the first contact member 30. In its rest position this free end 38, which defines the second contact member is resiliently biased away from the first contact member and towards the wall of the casing.

A switch mechanism 40, which is the subject of the present invention and which will be described in more detail later, is provided to force the contact members 30 and 38 into contact to close the circuit and thereby illuminate the bulb.

As shown in Figure 3 the inside of the rear part 12 of the casing accommodates the batteries 14 and provides a channel 62 for receiving the switch mechanism. Lugs 64 project from the inner wall of the casing in order to locate the batteries in position. Adjacent the front end of the casing the channel 62 is separated from the battery chamber by means of a member 66 which is secured at its edges to the casing. This member 66 provides a support for the fixed contact member 30 which may be secured to it as by riveting.

It will be appreciated that a series connected circuit is defined by the described components of this flashlight.

The circuit comprises the two batteries 14 which are series connected. One terminal of the rearward battery 14 is connected by means of the coil spring 33 and the strip 34 to the second contact member 38. The other terminal of the rearward battery 14 is connected to the terminal of the opposite sign on the adjacent battery.

The other terminal of this forward battery is connected to a first terminal of the bulb 21 via the terminal 26.

The other terminal of the bulb is connected via flange 28 to the first contact member 30.

The flashlight as so far described is of a structure which is similar in principle to existing flashlights and it is therefore not considered necessary to describe the components in further detail.

The switch mechanism 40 will now be described.

An elongate channel 42 is defined on the outside of the casing by means of an insert strip 44 secured in a recess 46 on the outside of the rear casing part 12. The channel 42 receives an operating member 48 which has the shape of an inverted cup. The width of the operating member corresponds to the width of channel 42 with just sufficient play to allow free sliding movement of the member 48 along the length of the channel 42. Around the open end of the cup, which faces the casing, there is provided an outwardly projecting flange 50, which engages underneath a corresponding flange 52 of the insert 46.

The flange 52 is defined around the periphery of the channel 42. The interengagement of the flanges 50 and 52 enables the operating member 48 to slide within the channel 42 between a forward, first position, as shown in Figure 2 and in which the contact members 30 and 38 are forced into contact to close the circuit and illuminate the bulb 21, and a second, rearward position, not shown, in which the contact members are apart.

A permanent magnet 54 of flat, annular shape is seated inside the cup shaped operating member 48. The magnet 54 is located by means of a central peg 56 which projects from the base of the cup towards its open end. The permanent magnet is magnetised so as to have its poles on the annular end faces. A similarly shaped permanent magnet 58 is mounted to the free end of the contact member strip 38 as by means of a rivet 60. The magnets 54 and 58 are arranged so that they have like poles facing each other. The magnets are also positioned so that they are substantially in opposition when the operating member is in its first position.

It will be noted that there is no opening in the casing between the magnets. It is, however, necessary that the magnetic flux should be capable of passing through the wall of the casing 12. This requires the casing to be of non-magnetic material such as plastics material. Because of the presence of the insert 46, the thickness of the wall of the casing 12 between the magnets can be made relatively thin.

The described switch mechanism operates by means of the repulsive force created between the magnets when the operating member is in the first position. This force is sufficient to overcome the resilient bias of the mounting of the end of the contact strip, which bias normally holds the contact members apart. The repulsion between the like poles of the two magnets forces the free end of the strip 38 downwardly (as seen in Figure 2) so that the two contact members are brought into electrical contact.

When the operating member 48 is slid rearwardly in its channel 42 the permanent magnets are sufficiently far apart for the force between them to be insufficient to overcome the resilient bias of the mounting of the second contact member. Therefore, the contact members separate under the influence of the bias of the resilient mounting.

The switch mechanism has been described as making use of the repulsive force between like poles of two permanent magnets. It will be appreciated that it is possible to arrange the components so that it is the attractive force between the magnets which is used to move one contact member against a resilient bias. Similarly, although the magnetic force has been described as being employed to bring the contact members into contact, it would also be possible to use the magnetic force to draw the contact members out of contact.

Claims (6)

1. A switch mechanism comprising an operating member comprising a permanent magnet mounted so as to be slidable between first and second positions, a first, fixed contact member, a second contact member which is mounted so as to be resiliently biased away from the first contact member, the second contact member carrying a further permanent magnet, the permanent magnets being brought into overlying relation when the operating member is in the first position, whereby the force between the magnets is sufficient to overcome the bias of the resilient mounting of the second contact member so that the first and second contact members are forced into contact to close the switch, the magnets being separated by a sufficient distance when the operating member is in the second position in order to allow the contact members to separate under the influence of the bias of the resilient mounting of the second contact member.

2. A switch mechanism as claimed in claim 1, wherein the permanent magnets are mounted such that like poles are facing each other in the first position of the operating member.

3. A switch mechanism as claimed in claim 1 or 2, wherein the second contact member comprises a strip of springy conductor fixedly mounted at an intermediate point to leave an end which is free to flex in a direction transverse to the length of the strip and towards and away from the first contact member, the permanent magnet being mounted adjacent the free end.

4. A portable flashlight comprising a sealed casing of non-magnetic material and a switch mechanism as claimed in any one of the preceding claims, wherein the first and second contact members are mounted inside the casing and the operating member is mounted in a channel defined on the outside of the casing, the first and second contact members being part of a series connected circuit including at least one battery and a light bulb.

5. A switch mechanism substantially as herein described with reference to the accompanying drawings.

6. A flashlight substantially as herein described with reference to the accompanying drawings.