GB2269428A - A torque limiting device - Google Patents

Abstract

A torque limiting device for operating gates has a sleeve 54 arranged to fit over an output shaft 34 of a motor gearbox 33 and an actuator 50 having a socket 53 for receiving the sleeve 54. The socket 53 squeezes the sleeve 54 onto the output shaft 34 to produce a frictional contact between the output shaft and the actuator whereby torque applied between the output shaft and the actuator above a predetermined level will cause the output shaft to rotate within the sleeve. The degree of the frictional contact between the actuator and the output shaft is adjustable by screws 55. The sleeve 54 is optional. <IMAGE>

Description

A TOROUE LIMITING DEVICE The invention relates to a torque limiting device for limiting the torque applied between an actuator and an output shaft of a motor or gearbox. The invention has particular application to drive mechanisms for operating gates and the like and it is within this context that the invention will be described.

Motor/gearbox combination units are well known for opening and closing gates and while they generally operate quite satisfactorily, there are at least two main drawbacks of the common types. In the common type, the motor is connected to the actuator for the gate via a gearbox and can be termed a rigid or direct connection as any movement of the motor is directly transmitted to the gate actuator. The first problem arises in controlling the motor in that should the gate be obstructed for any reason, the motor will stall which may lead to the motor being damaged and/or may result in an unusually high force being applied to the gate. This may be of particular concern if the obstacle is a person.

Apart from the safety aspect, the standard drive mechanisms do not allow manual operation of the gate which may be required during times of power failure or outage of the operating motor (e.g. for maintenance or repair) as the gate actuator cannot drive the motor due to the geartrain.

In U.K. Patent No. 2153004, there is disclosed a gearbox for a gate drive mechanism in which a clutch arrangement is incorporated into the gearbox. The clutch arrangement comprises a boss fitted to the output shaft, on which the main drive cog is able to rotate but the drive cog is held in frictional contact with the boss by a series of springs and a pressure plate urging the boss and drive cog into contact. While this arrangement works satisfactorily, it does require a special purpose built gearbox and is expensive to manufacture while there is no adjustment to the loading at which slippage occurs apart from replacing the springs which requires disassembling the gear box.

Accordingly, the present invention provides a torque limiting device comprising a sleeve arranged to fit over the output shaft of a motor or gearbox and an actuator having a socket for receiving the sleeve, wherein the sleeve provides frictional contact between the output shaft and the actuator.

Preferably, the frictional contact between the output shaft and the actuator is adjustable.

According to a second aspect, the present invention provides a drive mechanism for a gate or the like comprising a gearbox having an output shaft, a motor connected to the gearbox for driving the gearbox to rotate the output shaft, and an actuator having a socket into which the output shaft extends for frictional contact therebetween, whereby torque is transmitted between the output shaft and the actuator below a predetermined torque limit and relative rotation of the shaft with respect to the socket occurs above the predetermined torque limit.

Preferably a sleeve is provided between the output shaft and the socket to provide the frictional contact between the shaft and the socket.

Preferably the frictional contact is adjustable by reducing the internal diameter of the socket.

One advantage of the torque limiter according to the present invention is that it can be post-fitted to the output shaft of a standard or existing motor/gearbox combination.

One preferred embodiment of the invention will now be described by way of example, only with reference to the accompanying drawings, in which Figure 1 is an exploded pictorial representation of a drive mechanism according to the present invention showing the parts thereof; Figure 2 is a cross-sectional view of the assembled mechanism of Figure 1; and Figure 3 is a plan view of the actuator of the mechanism of Figure 1.

As shown in Figures 1 and 2, the drive mechanism indicated generally by 10 comprises and electric motor 20, a gearbox 30, and an actuator or drive arm 50. The motor and gearbox are enclosed within an outer cover 11 which is fitted to a top cover or lid 12.

The electric motor 20 is of the standard type in which the end of the rotor shaft is fitted with a worm cog (not shown) to drive a pinion gear 22. The housing 21 of the electric motor includes means for mounting the motor to the gearbox casing 31. The pinion gear 22 mates with the input shaft 32 of the gearbox. The input shaft drives the main cog of the gearbox 33 via a worm gear connection. The main cog is fitted to the output shaft 34 of the gearbox and is keyed for rotation with the output shaft by key 35. The output shaft extends through the top cover 12 to mate with the actuator 50. The gearbox also includes various bearings 41 and oil seals 42 as usual.

The actuator 50 is shown in the form of a bar with a socket at one end. Typically the bar would be rigidly connected to the gate and the output shaft of the gearbox would be coaxially aligned with the hinges of the gate with the actuator and output shaft forming one hinge.

Screw 51 and screw holes 52 are used to diagrammatically represent connection of the actuator to the gate which may in practice be connected by an actuator arm.

Socket 53 may fit directly over the end of the output shaft 34 for frictional contact therewith but in the preferred embodiment, a sleeve or bush 54 is used to provide the frictional contact between the socket and the output shaft. The sleeve would normally be made of nylon or a plastics material and is replaceable should excessive wear occur. The sleeve fits over the output shaft and within the socket.

Preferably, a locating and locking key 61 formed on the bush 54 cooperates with a corresponding keyway 62 formed in the socket 53 to restrict relative rotation or movement between the shaft 34 and the socket 53 to between the shaft 34 and bush 54.

The frictional contact between the actuator and the output shaft is adjustable by reducing the internal diameter of the socket 53. This squeezes sleeve 54 onto the output shaft 34 thereby increasing the frictional contact. Socket 53 is split to allow screws 55 receivable in holes 56 which span the split to vary the diameter of the socket.

The holes 56 are threaded on one side of the split so that tightening of the screws 55 urges the sides of the split together reducing the internal diameter of the socket.

Washer 36 and circlip 37 hold the actuator onto the output shaft while allowing relative rotation of the output shaft with respect to the actuator. Circlip 37 engages a groove 38 formed in the end of the output shaft.

A cover 57 encloses the actuator 50 to improve its appearance and to protect the connection between the output shaft and the socket from debris. Holes 58 in the cover allow access to screws 55 for adjustment of the frictional contact between the actuator and the output shaft.

In operation, rotational movement of the output shaft is transmitted to the actuator via the frictional contact between the output shaft and the socket. Provided the torque applied by the output shaft is below the limits set by the frictional contact, the actuator will rotate with the output shaft. Should the torque applied by the output shaft exceed the limit set by the frictional contact, the output shaft will rotate within the socket. The level of the frictional contact between the output shaft and the socket is adjustable by tightening or loosening the screws 55. By tightening the screws, the internal diameter of the socket is reduced which in turn, squeezes the sleeve more tightly onto the output shaft increasing the frictional contact between the socket and the output shaft. In this way, the level of torque at which slippage occurs can be adjusted. The adjustment to the present torque limit can be carried out when desired as it is a simple procedure and does not require disassembling the gearbox.

The torque between the output shaft and the actuator is of course relative and this torque limit may be exceeded by either the motor trying to drive an obstructed actuator or by the actuator being manually moved with respect to the output shaft, i.e., by manual opening or closing of the gate.

The sleeve 54 is optional and the socket may be fitted directly onto the output shaft. However, the sleeve is preferred as it can be easily replaced should excessive wear occur.

Claims (17)

1. A drive mechanism for a gate or the like comprising a gearbox having an output shaft, a motor connected to the gearbox for driving the gearbox to rotate the output shaft and an actuator having a socket into which the output shaft extends for frictional contact therebetween, whereby torque is transmitted between the output shaft and the actuator below a predetermined torque limit and relative rotation of the output shaft with respect to the socket occurs when the predetermined torque limit is exceeded.

2. A drive mechanism as defined in claim 1 wherein a sleeve is provided between the socket and the output shaft to provide the frictional contact between the shaft and the socket.

3. A drive mechanism as defined in claim 2 wherein the sleeve is split.

4. A drive mechanism as defined in claim 2 or 3 wherein the sleeve is made of nylon or plastics material.

5. A drive mechanism as defined in any one of the preceding claims wherein the frictional contact between the output shaft and the actuator is adjustable.

6. A drive mechanism as defined in claim 5 wherein the internal diameter of the socket is adjustable to vary the frictional contact.

7. A device as defined in claim 6 wherein the socket is split and clamping means is provided across the split to vary the internal diameter of the socket.

8. A device as defined in claim 7 wherein the clamping means comprises at least one screw extending across the split and arranged to reduce the width of the split as the screw is tightened.

9. A torque limiting device comprising a sleeve arranged to fit over an output shaft of a motor or gearbox and an actuator having a socket for receiving the sleeve, wherein the sleeve provides frictional contact between the output shaft and the actuator.

10. A device as defined in claim 9 wherein the frictional contact is adjustable.

11. A device as defined in claim 10 wherein the internal diameter of the socket is able to be changed to adjust the frictional contact.

12. A device as defined in claim 11 wherein the socket is split and clamping means is provided across the split to change the internal diameter of the socket.

13. A device as defined in claim 12 wherein the clamping means comprises at least one screw extending across the split and arranged to reduce the width of the split as the screw is tightened.

14. A device as defined in any one of claims 9 to 13 wherein the sleeve is made of nylon or plastics material.

15. A device as defined in any one of claims 9 to 14 wherein the sleeve is split.

16. A torque limiting device substantially as hereinbefore described with reference to the accompanying drawings.

17. A drive mechanism for a gate or the like substantially as hereinbefore described with reference to the accompanying drawings.