GB2289373A

GB2289373A - Control switches for lifts

Info

Publication number: GB2289373A
Application number: GB9409347A
Authority: GB
Inventors: Alan Dewhurst
Original assignee: DEWHURST PLC
Current assignee: DEWHURST PLC
Priority date: 1994-05-11
Filing date: 1994-05-11
Publication date: 1995-11-15
Anticipated expiration: 2014-05-11
Also published as: DE29508195U1; GB2289373B; GB9409347D0

Abstract

A lift control switch is mountable in a lift shaft such that an operating lever (8) can be engaged by a lift ramp. This causes the lever (8) to pivot with its pivot shaft (14) and to actuate switch contacts of a contact block (20). The operating lever (8) is biased into an initial, central, position by a linear coiled compression spring (22) which has one end in a cut out in a metal plate (26). The metal plate (26) is reciprocable generally longitudinally of a housing (2) substantially parallel to its rear wall (28). A roller (30) journalled to the plate (26) acts as a first cam follower for a cam (32) which is rotationally fixed to the pivot shaft (14). As the lever (8) is pivoted in either direction from its initial position, the roller (30) is caused by a cam surface (36) of the cam (32) to move upwardly and to compress the spring (22). The shape of the cam surface (36) is chosen such that at any position of the operating lever (8) the force needed to further pivot the lever (8) remains constant. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO CONTROL SWITCHES The present invention relates to a control switch.

Lift control switches are mounted in lift shafts for detecting and controlling the movement of a lift. A known lift control limit switch, for example, has a projecting pivotable operating arm carrying a wheel which is arranged to be engaged by a lift ramp whereby the arm is pivoted.

The pivoting of the arm is arranged to break and make electrical contacts connected in control circuits for the lift.

A commonly known lift control limit switch has a compression spring fixed between its operating arm and actuating means for the electrical contacts. As the arm is pivoted, it increasingly compresses the spring such that the force of the spring is increased. This means that the force required to move the arm is greater at the final position than at the initial position, and this extra force causes extra wear and is a potential source of noise. The known unit is also handed in that if it is manufactured such that a right handed force is capable of pivoting the operating arm, it has to be reassembled if it is to be used in a situation where the force is left handed. This is a serious disadvantage in that in a lift shaft the switches at the top are generally mounted with the arm projecting upwardly whilst those at the bottom of the shaft are mounted such that the arm projects downwardly. This means that if two limit switches are mounted in one lift shaft at the top and bottom, for example, they need to be opposite handed.

It is an object of the present invention to provide a control switch, for example, for use as a lift control limit switch, in which the disadvantages of the known units are reduced.

According to the present invention there is provided a control switch having a switch housing, a projecting, pivotable, operating lever supported by said housing for engagement and pivoting by a lift ramp, electrical switch means within said housing arranged to be actuated by pivoting movement of said operating lever, and spring means within said housing biassing said operating lever to an initial position, wherein a camming mechanism is provided between said operating lever and said spring means and is arranged, as the lever is pivoted away from its initial position, to apply a force to the spring means opposing the biassing force.

Preferably, the camming mechanism is arranged such that the biassing force on the operating lever remains substantially constant irrespective of the position of the operating lever. The provision of a substantially constant force is important in ensuring that the forces do not rise above the minimum required throughout the range of operating movement of the operating lever. In this respect, the constant force can be achieved by appropriate shaping of the camming mechanism.

The use of a camming mechanism between the spring means and the operating lever results in a control switch which operates with minimum forces and keeps operating noise to a minimum.

In a preferred embodiment, the spring means comprises at least one compression spring arranged to be compressed as the operating lever is pivoted from its initial position.

In a preferred embodiment, the camming mechanism comprises a cam mounted for movement with the pivoting movement of the operating lever, and a cam follower arranged to cause the application of an opposing force to the spring means.

In a preferred embodiment, the spring means is a linear coiled spring one end of which engages a plate guided for reciprocating movement in said switch housing.

In this case, the cam follower is preferably a roller or pinion carried by and journalled with respect to, said plate.

The plate preferably carries two or more shoes guided in, and slidable with respect to, guide channels carried by said switch housing. Preferably, four shoes are provided to limit friction and wear and they also ensure that there can be no twisting movement of the plate.

In a preferred embodiment, the cam is substantially symmetrical about a central longitudinally extending axis of the switch housing, the longitudinal axis being substantially perpendicular to the pivot axis of said operating lever. The operating lever is arranged such that it can be pivoted to either side of said central longitudinal axis. This means that the operating lever can be acted upon from either side.

Preferably, the cam is provided with a second cam surface with which a second cam follower is engaged. The second cam follower is arranged to actuate said electrical switch means upon pivoting movement of said operating lever.

For example, the electrical switch means may comprise two sets of contacts, the first set being normally closed and the second set being normally open. Pivoting of the operating lever is arranged to cause the second cam follower first to break the normally closed contacts and then to make the normally open contacts. With an embodiment of the invention, the operation of the contacts of the electrical switch means is by way of the second cam follower which provides a positive mechanical drive.

Preferably, stop means are provided in said switch housing to limit the movement of said cam. The stop means may comprise a rubber pad at each end of the movement profile of the cam.

Other profiles may be added to the camming mechanism to operate further switch contacts, if required. For example, the camming mechanism may be arranged to provide for operation of switch contacts in sequence to provide slow down and then stop control signals for a lift. The camming mechanism may alternatively be arranged to operate appropriate switch contacts to form a direction switch.

Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a front view, partly broken away, of a control switch of an embodiment of the invention, Figure 2 shows a side elevation of the control switch of Figure 1, Figure 3 shows a section taken along the line A-A of Figure 1, and Figure 4 shows a rear view of the control switch illustrating the range of movement of an operating arm thereof.

The control switch shown in the drawings is intended for use as a lift control limit switch. It has a one piece housing 2, injection moulded from plastics material, which is formed to have two spaced lugs 4 for mounting the control switch in a lift shaft. The housing 2 also has bores 6 through which electrical cables and connectors therefor (not shown), may extend as required.

An operating lever 8 is fastened to the housing 2 for pivoting movement as indicated by the arrows B-B. At its far end, the operating lever 8 carries a wheel 10 for engagement by a lift ramp in conventional manner. In this respect, the wheel 10 is connected to the lever 8 by way of a shaft 12, for example, as can be seen in Figure 2.

At its end spaced from the wheel 10, the operating lever 8 is fixed to a pivot shaft 14 and is secured thereon by way of a fixing bolt 16. If it is required to adjust the hand of the control switch, this can be done simply by loosening the bolt 16, resetting the lever 8 and thereafter refixing the fixing bolt 16. In this respect, in the embodiment as illustrated, the operating lever 8 extends in its initial position along a substantially central, longitudinal axis A-A' of the housing 2 and is pivotable, to a substantially identical extent, to either side thereof as indicated by arrows B-B. However, in use in a lift shaft it would be usual to set the lever 8 to extend initially at an angle, for example, of the order of 30 , to the central axis A-A' to facilitate engagement with the lift ramp. Not only can the operating lever 8 be simply set in the orientation required by use of the fixing bolt 16, but, as is described in more detail below, the force necessary to operate the control switch remains substantially the same irrespective of the initial orientation of the lever 8.

In known manner, a lift control limit switch as illustrated is fixed in a lift shaft such that the wheel 10 of the operating lever 8 can be contacted by the lift ramp.

This causes the lever 8 to pivot the lift together with its pivot shaft 14, and this pivoting is arranged to actuate switch contacts. For example, individual contacts may be made or broken, and/or a series of contacts may be made or broken in sequence in dependence upon the amount of pivoting movement of the lever 8 and of the pivot shaft 14 to thereby indicate the position of the lift. In the embodiment illustrated, a substantially conventional contact block 20 mounted in the housing 2 has a first pair of normally closed contacts and a second pair of normally open contacts (not visible). As the operating lever 8 is pivoted from its initial position it is able first to cause opening of said normally closed contacts, whilst further pivoting movement thereof is subsequently enabled to cause closing of said normally open contacts.

The operating lever 8, and its pivot shaft 14, are biased into their initial positions, for example the central position of the lever 8 as shown in Figures 1 to 3, by way of a linear coiled compression spring 22. This spring 22 extends within a recess moulded in the housing 2 and one end thereof abuts against an abutment face 24 provided in the moulding. The other end of the spring 22 is received in a cut out therefor in a metal plate 26. The metal plate 26 extends generally parallel to a rear surface 28 of the housing 2. At a number of locations thereof, preferably four locations, the plate 26 is provided with plastics material shoes (not visible) which are guided in guide channels (not visible) moulded in the rear surface 28 of the housing 2. The shoes and guide channels cooperate to guide the plate 26 as it is reciprocated generally longitudinally of the housing 2 substantially parallel to its rear wall 28.

A roller 30 is journalled to said plate 26 and acts as a first cam follower for a cam 32. As can be seen, the cam 32 is rotationally fixed to the pivot shaft 14 of the operating lever 8. The cam 32 is shaped to have two cam surfaces 34 and 36, spaced along the shaft 14, which are substantially identical in shape. Thus, each cam surface 34, 36 has a centrally arranged indent from each side of which a curved cam surface extends. Each cam surface 34, 36 is substantially symmetrical about the central longitudinal axis A-A' of the housing 2. This means that the movement of the cam follower roller 30, for example, as the operating lever 8 is pivoted in one direction B away from its initial position is substantially identical in profile to its movement if the operating lever 8 were to be moved in the opposite direction B.

In the initial position of the operating lever 8 and of the pivot shaft 14, the roller 30 is received within the indentation provided centrally of the rear one 36 of the two cam surfaces. As the lever 8 is pivoted in either direction from its initial position, the roller 30 is caused to ride out of the central indentation of the cam surface 36 and to move along its surface. As the roller 30 moves along the surface, it is effectively moved upwardly in the direction of arrow C of Figure 3. This upward movement of the roller 30 acts to compress the spring 22 and thus to oppose the biassing force thereof. However, the shape of the cam surface 36 is chosen such that at any position of the operating lever 8 the force needed to further pivot the lever 8 remains constant. That is, at any instant the spring force biassing the lever towards its initial position remains constant.

Figure 4 shows the full range of positions of the operating lever 8 with the two end positions thereof shown in dash dot lines and the initial position shown in full lines. With the embodiment of this invention the spring force acting on the lever 8 at any of its positions pivoted from the initial position is substantially the same. It will be appreciated that if the operating lever 8 is set at an initial position in which it extends at an angle to the central axis A-A', the operation of the control switch remains the same. Thus, in the initial position of the lever 8 the roller 30 remains centrally of the cam surface 36, and pivoting movement of the lever 8 to either side of its initial position pivots its pivot shaft 14 and hence causes the roller 30 to follow the appropriate part of the cam surface 36.

We have seen that the cam 32 has a second cam surface 34 which is arranged axially in front of, and is substantially identical in shape to, the first cam surface 36. A second cam follower 40 engages with this second cam surface 34. The second cam follower 40 comprises a switch actuating lever which is pivotally mounted at a pivot axis 42. A surface of the lever supports an operating rod 44 of the contact block 20. We have already seen that the contact block 20 contains two pairs of contacts. The arrangement is such that initial movement of the operating lever 8 from its initial position lifts the rod 44 a short distance whereby normally closed contacts of the contact block 20 are broken. Continued movement of the lever 8 lifts the rod 44 further and subsequently makes normally open contacts within the contact block 20.

As in a control switch of the invention there is always a substantially constant force on the operating lever 8, the operation of the control switch is generally also much quieter than conventional units. The reduction in operating noise comes from the provision of the camming mechanism, which is preferably made from plastics material, within the housing 2 and between the lever 8 and the parts actuated thereby.

It would, of course, be possible for the contact rod 44 to be mounted to be actuated directly by the cam 32.

However, the interposition of an actuating lever 40 to act as a cam follower is preferred as this reduces any tendency of the contact block to click as it is restored to its normal position.

To prevent over travel of the cam 32 two rubber stops as 50 are mounted in the housing 2, one at each end of the travel of the cam 32.

The plastics material of the housing 2 is preferably made of a translucent or transparent plastics material so that the contents thereof are readily visible. The housing preferably has a front cover 60 for easy access when required.

It will be appreciated that modifications in and variations to the embodiments described and illustrated may be made within the scope of this application.

Claims

1. A control switch having a switch housing, a projecting, pivotable, operating lever supported by said housing for engagement and pivoting by a lift ramp, electrical switch means within said housing arranged to be actuated by pivoting movement of said operating lever, and spring means within said housing biassing said operating lever to an initial position, wherein a camming mechanism is provided between said operating lever and said spring means and is arranged, as the lever is pivoted away from its initial position, to apply a force to the spring means opposing the biassing force.

2. A control switch as claimed in Claim 1, wherein the camming mechanism is arranged such that the biassing force on the operating lever remains substantially constant irrespective of the position of the operating lever.

3. A control switch as claimed in Claim 2, wherein the constant biassing force is achieved by the shaping of the camming mechanism.

4. A control switch as claimed in any preceding claim, wherein the spring means comprises at least one compression spring arranged to be compressed as the operating lever is pivoted from its initial position.

5. A control switch as claimed in any preceding claim, wherein the camming mechanism comprises a cam mounted for movement with the pivoting movement of the operating lever, and a cam follower arranged to cause the application of an opposing force to the spring means.

6. A control switch as claimed in Claim 5, wherein said spring means is a linear coiled spring one end of which engages a plate guided for reciprocating movement in said switch housing, and wherein the cam follower is a roller or pinion carried by, and journalled with respect to, said plate.

7. A control switch as claimed in Claim 6, wherein said plate carries two or more shoes guided in, and slidable with respect to, guide channels carried by said switch housing.

8. A control switch as claimed in any of Claims 5 to 7, wherein said cam is substantially symmetrical about a central longitudinally extending axis of the switch housing, the longitudinal axis being substantially perpendicular to the pivot axis of said operating lever, and wherein said operating lever is arranged such that it can be pivoted to either side of said central longitudinal axis.

9. A control switch as claimed in any of Claims 5 to 8, wherein said cam is provided with a second cam surface with which a second cam follower is engaged, said second cam follower being arranged to actuate said electrical switch means upon pivoting movement of said operating lever.

10. A control switch as claimed in any of Claims 5 to 9, wherein stop means are provided in said switch housing to limit the movement of said cam.

11. A control switch substantially as hereinbefore described with reference to the accompanying drawings.