GB2137302A - Overload mechanism - Google Patents

Abstract

An overload protection mechanism for a transmission system comprising a crank (2) and a conrod (4) wherein the conrod includes two relatively slidable contiguously arranged parts (8, 10) which can be slid apart to extend the length of the conrod (4) and biasing means (12) effective to provide a biasing force tending to hold the parts (8, 10) together and against which the crank (2) is constrained to act under overload conditions to extend the length of the conrod, whereby under overload conditions crank rotation is not prevented. <IMAGE>

Description

SPECIFICATION Overload mechanism This invention relates to overload mechanisms and more especially it relates to such mechanisms which serve to protect crank and conrod transmission systems.

Crank and conrod transmission systems are very well known in themselves and they serve to transpose rotary motion to linear motion, the crank being pivotally secured to one end of the conrod which rotates with the crank and the other end of the conrod being supported to permit reciprocating linear motion with a stroke which corresponds to twice the effective length of the crank.

If the operating load applied to the conrod becomes excessive, damage may be done to the transmission system and/or to a motor which drives it and which is normally coupled to the crank.

It is an object of the present invention to provide a crank and conrod transmission systen which incorporates a protection mechanism whereby overload conditions can be tolerated.

According to the present invention an overload protection mechanism for a transmission system comprises a crank and a conrod wherein the conrod includes two relatively slidable contiguously arranged parts which can be slid apart to extend the length of the conrod and biasing means effective to provide a biasing force tending to hold the parts together and against which the crank is constrained to act under overload conditions to extend the length of the conrod, whereby under overload conditions crank rotation is not prevented.

The two parts may comprise a slide tube and a slide rod which is telescopically mounted to slide within the slide tube.

The slide tube may be connected to a further rod which defines one end of the conrod and the slide rod may define the other end of the conrod.

The ends of the conrod may be cranked.

The biasing means may comprise a coil spring.

The coil spring may be arranged to embrace the slide tube and may be secured at each end to respective ends of the conrod.

The crank may comprise at one end a journal within which the conrod is mounted and at the other end means to receive in driving engagement a motor shaft.

The mechanism may form a part of apparatus which embodies an electric motor which includes the motor shaft.

The apparatus may be a part of a vending machine.

The vending machine may be primarily designed for drinks and the conrod may be operable for cup delivery purposes.

Thus it will be appreciated that if in this later case a cup jams the conrod, the drive motor will be protected by the mechanism against overload.

One embodiment of the invention will now be described solely by way of example with reference to the accompanying drawings in which: Figure 1 is a side view of an overload protection mechanism associated with a conrod and crank showing the crank in one position; Figure 2 is a side view of the mechanism shown in Fig. 1 with the crank in a different position; Figure 3 is one end view of the mechanism as shown in Fig. 2; Figure 4 is another end view of the mechanism as shown in Fig. 2; and Figure 5 is a plan view of the mechanism shown in Figs. 1, 2, 3 and 4.

Referring now to the drawings, wherein corresponding parts of the various Figures bear as appropriate the same numerical designation, a crank and conrod mechanism comprises a crank 2 and a conrod 4, the conrod being defined by a fixed link 6 which is secured within a slide tube 8 and a slide link 10 which is slidable within the tube 8. The tube 8 is embraced by a coil spring 1 2 one end 1 4 of which is anchored in the slide tube 8 and arranged to pass through the fixed link 6 so as to secure the fixed link 6 to be slide tube 8. The other end 1 6 of the coil spring is secured to the slide link 1 0. The fixed link 6 includes a cranked arm 1 8 which is journaled in one end of the crank 2 and held in position by circlips 20.A motor shaft 22 is coupled towards that end of the crank 2 which is remote from the bush arm 18. The motor shaft 22 is recieved within a hole formed in the crank 2 and is rigidly secured by means of a set screw 24.

As the motor shaft 22 is constrained to rotate due to operation of a motor (not shown) the crank 2 will rotate correspondingly in a direction indicated by the arrow 26. As the crank rotates, the conrod 4 will be caused to reciprocate in directions as indicated by the arrow 28 and a sliding linear motion will normally be produced with a stroke corresponding to twice the effective length L, as shown in Fig. 5, of the crank 2.

In the event that the conrod 4 becomes jammed, the sliding link 10 will withdraw from the slide tube 8 against the spring 1 2 so that the effective length of the conrod 4 is extended whereby continued rotation of the crank 2 in response to rotation of the motor shaft 22 is permitted.

The mechanism may form a part of a vend ing machine wherein the conrod serves to effect a delivery operation, for example of a drinking cup. Thus it will be appreciated that if the conrod becomes jammed by a cup or other article to be delivered, a motor driving it can continue to rotate together with the crank 2 whereby overload protection is provided.

The vending machines may be such as those designed for vending drinks. It is to be understood however that the invention may be applied to any crank and conrod arrange ment wherein overload protection is required.

For example it may be employed in photograph, cigarette or confectionary vending machines which use such an arrangement.

Claims (11)

1. An overload protection mechanism for a transmission system comprising a crank and a conrod wherein the conrod includes two relatively slidable contiguously arranged parts which can be slid apart to extend the length of the conrod and biasing means effective to provide a biasing force tending to hold the parts together and against which the crank is constrained to act under overload conditions to extend the length of the con rod, whereby under overload conditions crank rotation is not prevented.

2. An overload protection mechanism according to claim 1 in which the two parts comprise a slide tube and a slide rod which is telescopically mounted to slide within the slide tube.

3. An overload protection mechanism according to claim 2 in which the slide tube is connected to a further rod which defines one end of the conrod and the slide rod defines the other end of the conrod.

4. An overload protection mechanism according to claim 3 in which the ends of the conrod are cranked.

5. An overload protection mechanism according to claim 4 in which the biasing means comprises a coil spring.

6. An overload protection mechanism according to claim 5 in which the coil spring is arranged to embrace the slide tube and is secured at each end to respective ends of the conrod.

7. An overload protection mechanism according to any one of the preceding claims in which the crank comprises at one end a journal within which the conrod is mounted and at the other end means to receive in driving engagement a motor shaft.

8. An overload protection mechanism substantially as herein described with reference to the accompanying drawings.

9. Apparatus comprising an overload protection mechanism as claimed in any one of the preceding claims and an electric motor which includes the motor shaft.

10. A vending machine including apparatus as claimed in claim 9.

11. A vending machine according to claim 10 which is designed for drinks, the conrod being operable for cup delivery purposes.