GB2052158A - Electric switch - Google Patents

Abstract

An electrical switch in which two separated stationary contacts 10a and 10b are connected to an external circuit which can be completed by moving contacts 20a and 20b on a conducting plate 18 into touching contact with the contacts 10a and 10b respectively. A barrier 50 of insulating material is pivoted at 52 on a lever 54 which is pivoted at 56 and carries a permanent magnet 58 attracted by a stationary permanent magnet 60 to maintain the barrier between contacts 10a, 20a to prevent them touching until the barrier is moved by pivoting of the lever in response to third magnet moved into proximity with the magnet 58 to repel it away from magnet 60. The plate 18 is supported on an insulating strip 16 carried on slidable tubular member 14 moveable by a detached component which also carries the third magnet. <IMAGE>

Description

SPECIFICATION Switch This invention concerns electrical switches, and is particularly but not exclusively concerned with stop switches normally used in association with movable guards for machines.

It is known to provide those machines which are considered dangerous, with movable guards which prevent persons having access to the machine whilst it is operating. The power supply to such a machine is controlled by an electrical control comprising a stop switch operated by the movable guard, the arrangement being such that when the guard is in the closed position the switch is held made by the guard and the machine receives operating power. The switch is broken by opening the guard and so the operating power is cut off and the machine stops. This stopping, and subsequent delay in attaining full production speed on re-starting, causes fall in production adversely affecting the pay of operatives dn piece work rates or bonuses based on productivity.

Accordingly, there is a tendency to tamper with the switches or jam them so they remain made even when the guard is open, thus putting the operative at risk.

According to the invention an electrical switch comprises makable and breakable contacts, and an obstruction movable between a first position in which it prevents making of the contacts and a second position in which it allows making of the contacts, said obstruction being movable by the magnetic influence of one magnet on another.

In one embodiment of the invention at least first and second electrical contacts are provided in which at least one is movable relatively to the other so that they can make by touching and break by separating. The obstruction is arranged between the contacts to prevent them touching until the obstruction is moved from between them to a clear position. Until moved into the clear position, retention of the obstruction in the obstructing position is ensured by the force of magnetic repulsion or attraction between first and second magnets. The second magnet is stationary relative to the first magnet which is movable between first and second positions. The obstruction is arranged to follow the movement of the first magnet, the first position of the first magnet corresponding to the obstructing position of the obstruction and the second position corresponding to the clear position.A third magnet is movable into proximity with the first magnet with the effect that the magnetic field between the first and third magnets exerts a force of repulsion or attraction of sufficient strength on the first magnet that it moves from the first position into the second position and thus the obstruction is moved into the clear position. When the third magnet is moved away so that its influence on the first magnet diminishes sufficiently, the effect of the magnetic field between the first and second magnets is able to re-assert control over the first magnet and propel it back to the first position, which latter movement is followed by the obstruction to return it to the obstructing position provided the contacts are separated.

Preferably the obstruction is formed of electrically insulating material.

The obstruction can be provided on a lever arrangement acted upon by movement of the first magnet.

Preferably the third magnet is arranged to repel the first magnet relatively strongly and the second magnet exerts a weaker repulsion or attraction on the first magnet. Accordingly, the second magnet holds the first magnet in the first position, and therefore the obstruction in the obstructing position until such time as the first magnet experiences the stronger repulsion or attraction of the third magnet.

The moving contact(s) may be moved in any desired manner. But to ensure synchronism of operation it is preferred that contact movement to cause making be accompanied by movement of the third magnet into proximity with the first magnet, and the breaking movement be accompanied by retreat of the third magnet. This may be achieved by moving the third magnet in response to movement of an actuating member causing the contact movement.

Therefore the invention is particularly suited to stop switches since the contacts cannot be made merely by using the actuating member because the third magnet is required for moving the obstruction.

The invention will now be further described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is fragmentary plan view of a known type of stop switch; Figs. 2 and 3 are fragmentary side views partly in section of the switch in Fig. 1 shown in the break and made positions respectively; Fig. 4 is a diagrammatic fragment of a modification, formed according to the invention, of the switch in Fig. 1 with the obstruction in the obstructing position; Fig. 5 is a similar view to Fig. 4, showing the obstruction moved to the clear position; Fig. 6 is a side view of means for actuating the switch in Fig. 4, and Fig. 7 is a fragmentary perspective view of another embodiment of the switch formed according to the invention.

In the following description like references refer to like or corresponding parts.

Referring to Figs. 1 to 3, the known switch has a casing 2 with an internal partition 4. The casing is covered by a cover 6 having a slot 8 at one end.

The casing contains stationary electrical contacts 1 Oa and 1 Ob each with a pip formation. These contacts are mounted on an insulating support 12 and are for connection (by means not shown) to electrical conducting paths in an external circuit.

Partition 4 supports a sliding tubular arm 14 carrying a rigid insulating strip 1 6 supporting a conducting plate 1 8 provided with mobile conducting contacts 20a and 20b of pip form. One end of the arm 14 is engaged by a compression spring 22 seated in a tubular bore 24 in the support 12. The other end of arm 14 is slidably supported in a stationary tube 26 formed with longitudinally extending diametrically opposed slots 28 through which extend opposite ends of a pin 30 engaging the arm 14. Pivoted on these ends are arms 32 pivoted at 34 on radical sides 36 of notches cut into opposite ends of a cylinder 38 formed with a longitudinally extending groove 40. Cylinder 38 is rotatable about an axle 42 on stationary supports 44.

To make the switch, an L-shaped actuating member or tongue 46 is introduced through slot 8.

This causes foot 48 of the L to push on side 40a of the slot 40 so that cylinder 38 rotates anticlockwise in fig. 3, throwing the arms 32 to the right and forcing arm 14 to move in the same direction to bring the mobile contacts 20a and 20b into touching contact with the stationary contacts 1 0a and 1 Ob and complete the circuit between the stationary contacts. The strip 1 6 is mounted on the arm 14 by formations on the lower part of the strip engaging in longitudinally extending slots (only one shown at 17) in opposite sides of the arm 14.This lower part of strip 1 6 is continuously urged towards the right-hand end of the slots 17 (when viewed in Figs. 2 and 3) by a compression spring 17a within the arm 14, one end of the spring acting on the strip 1 6 and the other end braced against a stop 17b fixed inside the arm. This arrangement allows the arm 14 to continue movement to the right in Fig. 3 relatively to the strip 1 6 for a short distance under the action of tongue 46 after the contacts 20a, 20b are stopped by the contacts 1 0a, 1 Oh, thus avoiding excessive strain on the strip during the final part of the insertion stroke of the tongue into the slot 8. To break the switch, the tongue 46 is withdrawn from slot 8. In so doing, the foot 48 pulls against face 40b of the slot 40 and rotates the cylinder 38 clockwise.This pulls arms 32 to the left in Fig. 3, and thus the arm 14 is pulled leftwards. In this event the right hand ends (when viewed in Figs. 2 and 3) of the slots 1 7 pusn the strip 1 6 leftwards with the arm 14 causing the mobile contacts to separate from the stationary contacts to which they may have become welded by the heating effect of electric current.

The casing 2 can be stationarily mounted, and the tongue 46 mounted on a movable guard of a machine to make the switch when the guard is closed and break the switch when the guard is opened. Unfortunately unauthorised metal wedges inserted in slot 8 to press on side 40a of the groove 40 may hold the switch made when the movable guard is open.

In the modification shown in Figs. 4 to 6, which is an embodiment of the invention, an obstruction or barrier 50 of insulating material is freely pivoted at 52 on one end of a lever arm 54 mounted for pivoting at 56 on an upward extension 1 2a of the support 12. A plate magnet 58 is mounted on the other end of arm 54 and is attracted to a keeper magnet 60 as shown in Fig. 4 so that the barrier 50 is located in the path of mobile contact 20a and is disposed between that mobile contact and the corresponding stationary contact 1 Oa. The keeper magnet 60 is mounted on a stationary partition 4a of non-magnetic material which is an extended version of the partition 4 in Figs. 1 to 3, and the switch is covered by the cover 6 shown in dotted lines in Fig. 4.

Until the barrier 50 is moved clear of the path of contact 20a there are two possibilities. Either (í) neither of the mobile contacts can touch the corresponding stationary contacts, or (ii) the contact 20a is stopped by the barrier from touching the contact 1 Oa and thus the circuit between contacts 1 Oa and 1 Ob is not completed through the plate 1 8 even though the mounting of the strip 1 6 on the arm 14 may allow some skewing of the strip relatively to the arm by which the contact 20b may touch the contact 1 or. To avoid damage to the barrier 50 and arm 54, the pivot 56 is preferably shorter than shown so that the barrier is closely alongside the contact 1 Oa.

Thus pressure of the contact 20a on the barrier 50 will be mainly transmitted therefrom to the contact 1 Oa and not to the pivot 52 or arm 54.

To move the barrier 50 clear (as shown in Fig.

5), a repulsion magnet located externally of the casing 6 is brought into proximity with the magnet 58 which moves away from the keeper 60, thus pivoting the arm 54 clockwise with respect to Figs. 4 and 5. This repulsion magnet is shown at 62 in Fig. 6 mounted in a support 64 carrying the tongue 46. As the tongue 46 is inserted to move the mobile contacts towards the stationary contacts, the repulsion magnet 62 is automatically brought closer to the magnet 58 having a pole face 66 of the same polarity as the pole face 68 of the repulsion magnet. The force of repulsion is so strong it overcomes the force of attraction of the keeper magnet 60 and forces the magnet 58 away from the keeper causing the arm 54 to pivot clockwise before the contact 20a reaches the barrier.

Removal of the tongue 46, automatically removes the effect of the repulsion magnet 62 so that when the contacts break, the keeper magnet 60 attracts the magnet 58 back into the position shown in Fig. 4 causing the barrier 50 to resume its obstructing position.

The support 64 can be mounted on the movable guard. Since at least the contacts 1 Oa, 20a cannot be made by use of an unauthorised wedge, unless an unauthorised repulsion magnet is also used to move the barrier 50, the invention provides another tiresome safety device to be overcome by someone hoping to use the machine without closing the guard. And since the unauthorised repulsion magnet will also be repelled by the magnet 58, it is rather difficult to maintain the unauthorised magnet in the correct position to hold the barrier 50 clear whilst the contacts are being jammed closed.

A stop shown, for example, at 70 may be used to limit swing of the arm 54.

So that the switch may be used in any attitude, it may be preferred to provide the barrier 50 with a guide determining the path of movement of the barrier. This guide may comprise a channel provided on one side face of the barrier 50 so that the contact pip of contact 1 Oa is disposed within the channel which has sides extending alongside opposite side edges of the pip.

If desired pivot 56 can extend between the extension 1 2a and partition 4a or may be mounted solely on that partition, in either case the partition is of insulating material.

Any of the magnets may be a ceramic magnet.

The arm 54 is also preferably of insulating material and both it and the barrier 50 may be of plastics, for example nylon.

Preferably the casing 2 and cover 6 are of nonmagnetic material.

In the switch in Fig. 7 the insulating barrier 50' is fixed to or formed integrally with the lever arm 54' as a cranked end to the lever arm. The other end of the lever arm 54' carrier a permanent magnet 58' having a lower pole face 70 of the same polarity as an upper pole face 72 of a stationary permanent magnet 60' mounted on the casing 2 below the magnet 58'. The magnet 60' repels the magnet 58' to urge end 74 of the lever 54' about the pivot 56 so that the end 74 is pushed against the underside of the cover 2 and the barrier 50' is located between the contacts 1 Oa and 20a to prevent them touching. The magnet 58' has an upper pole face 66' of the same polarity as the pole face 68 of magnet 62 in Fig. 6.When the tongue 46 is inserted into slot 8 to move the contacts 20a, 20b towards contacts 1 0a, 1 Ob the pole face 68 is brought into proximity with the pole face 66'. The repulsion exerted by the magnet 62 on the magnet 58' is much greater than that exerted by the magnet 60' and the lever 54' pivots in the direction of arrow A to move the barrier 50' from between the contacts 1 Oa, 20a to allow them to touch. This pivoting is terminated either by end 76 of the lever 54' coming into contact with the underside of the casing 2 or until the repulsion force exerted by the magnet 60' on the approaching magnet 58' becomes equal to that exerted on the magnet 58' by the magnet 62. In either case the lever 54' is not pivoted so far that it obstructs contact 20b.

In Fig. 7 the insulating strip 1 6 bearing the conducting plate 1 8 carrying the contacts 20a, 20b is wholly located in the slot 17 in the arm 14.

Claims (18)

1. An electrical switch comprising makable and breakable contacts, and an obstruction movable between a first position in which it prevents making of the contacts and a second position in which it allows making of the contacts, said obstruction being movable by the magnetic influence of one magnet on another.

2. A switch as claimed in claim 1 in which the obstruction is formed of electrically insulating material.

3. A switch as claimed in claim 1 or claim 2, in which the obstruction is movable into the first position by said influence.

4. A switch as claimed in claim 1 or claim 2, in which the obstruction is movable into the second position by said influence.

5. A switch as claimed in claim 3, in which the obstruction is movable into the first position in response to magnetic repulsion between the magnets.

6. A switch as claimed in claim 3, in which the obstruction is movable into the first position by magnetic attraction between the magnets.

7. A switch as claimed in claim 4, in which the switch is movable into the second position by magnetic repulsion between the magnets.

8. A switch as claimed in claim 1 or claim 2, in which the obstruction is movable into the first position in response to movement of a first magnet relative to a second magnet which is stationary, the movement of the first magnet being in response to force exerted on the first magnet by the magnetic field between the two magnets, and after said movement said force acting to maintain the obstruction in the first position.

9. A switch as claimed in claim 8, in which the obstruction is movable from the tirst position into the second position by a movable third magnet which can be moved into a location so that the magnetic field between the first and third magnets exerts a second force on the first magnet which overcomes the first mentioned force exerted on the first magnet by the magnetic field between the first and second magnets such that the first magnet moves in response to the second force and in response the obstruction moves into the second position.

10. A switch as claimed in claim 9, in which the first force is a repulsion force.

11. A switch as claimed in claim 9, in which the first force is an attraction force.

12. A switch as claimed in claim 9, in which the second force is a repulsion force.

13. A switch as claimed in any one of claims 8 to 12, in which the obstruction is provided on a pivotable arm, the first magnet is mounted on the arm, and the obstruction is movable between the first and second positions by pivoting the arm.

14. A switch as claimed in claim 13, in which the obstruction is rigid with said arm.

1 5. A switch as claimed in claim 13, in which the obstruction is pivotably mounted on the arm.

16. A switch as claimed in any one of claims 8 to 15, in which a first said contact and a second said contact are arranged for relative movement therebetween by an amount causing these contacts to touch when the obstruction is in the second position, said movement being in response to movement of a switch actuating member.

17. A switch as claimed in claim 9 and claim 16, in which the third magnet is movable to said location simultaneously with the movement of the switch actuating member.

18. An electrical switch substantially as hereinbefore described with reference to Figs. 4 to 6 or Figs. 6 and 7 of the accompanying drawings.