GB2175358A

GB2175358A - Slip-drive assembly

Info

Publication number: GB2175358A
Application number: GB08610366A
Authority: GB
Inventors: Andrew Kennedy
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-04-26
Filing date: 1986-04-28
Publication date: 1986-11-26
Also published as: GB8610366D0

Abstract

A slip-drive assembly has a zig-zag spring (Figs. 3 and 4) contained in an annular chamber 44 whose curved walls are defined by driving and driven members 31, 41. The spring provides friction between the members, which friction may be adjustable by adjusting pressure on the spring and is overcome if the torque exceeds a predetermined maximum (Fig. 1) depicts an alternative chamber construction. <IMAGE>

Description

SPECIFICATION Drive assembly A drive assembly connects a driving shaft to a driven shaft. When the driven shaft is likely to be stopped from rotation or at least encounter high resistance to rotation, overloading of the motor driving the driving shaft can be avoided if the drive assembly allows slippage between the two shafts.

A simple form of such drive assembly comprises a pair of facing clutch plates connected to respective shafts, the plates having facing surfaces in contact, the friction between the facing surfaces providing a drive between the driving shaft and the driven shaft until the resistance to rotation of the driven shaft exceeds a pre-determined value according to the friction coefficient between the two facing surfaces.

According to the present invention, there is provided a more sophisticated drive assembly, and in one embodiment an adjustment of the pre-determined resistance can be adjusted.

The invention provides a slip drive assembly comprising a driven member and a driving member, one member comprising a cylinder and the other member defining an annular chamber with said cylinder, and a spring which extends around the annular chamber in a zig-zag shape so that it contacts spaced points on the cylindrical surface of one member interspersed with spaced points on the cylindrical surface of the other member. When it is desired to adjust the pre-determined value, an adjusting member may be introduced into the annular chamber to adjust its radial width, thus adjusting the compression of the zig-zag spring.

Examples of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diametral section through a drive assembly.

Figure 2 is a diametral section through another drive assembly, and Figures 3 and 4 are plan views illustrating alternative springs which can be used in the apparatus of Figs. 1 and 2.

In Fig. 1 a driving member 11 which is generally cylindrical with a central bore 12 for a driving shaft not shown. A flange 13 is provided at the outer end of the driving member 11. The mid section 14 of the member 11 is cylindrical and the inner end 15 has an outer surface which is frusto-conical. The inner portion of the inner end is recessed at 16.

The driven member 21 is also generally cylindrical, with a central bore 22 for engaging a driven shaft. The member 21 is provided with a cylindrical recess 23 whose bore is slightly larger than the flange 13 of the driving member. The recess continues past the midportion 14 of the driving member, forming therewith an annular chamber 24. The base of the recess is stepped at 25 and its narrower portion 26 receives the inner end 15 of the driving member. A journal bearing 27 is located between the base of the recess 26 and within the recess 16 of the driving member.

In Fig. 2 the driving member is an annular pinion 31. It is enclosed by housing members 32, 33 which are cut away in one region for the application of a driving gear (not shown).

The driven member 41 has a central cylindrical portion 42 which defines with the bore of the pinion 31 an annular chamber 44 corresponding to the chamber 24 of Fig. 1. The member has a shaft 43 and a base disc 45, the parts 42, 43 and 45 being co-axial. The lower edge of the chamber 44 is defined by the disc 45 and the upper edge by the housing member 33.

As shown in Figs. 3 and 4, a zig-zag spring is located in the annular chamber, with first portions in contact with the inner walls and second portions in contact with the outer walls. The spring 51 of Fig. 3 has first and second portions which are arcuate and in extended contact with the curved walls of the chamber, and intermediate portions which are straight and are inclined at a small angle (about 30 ) to the radius, alternately in one direction and the other. The spring 52 of Fig.

4 has straight second portions, contacting the outer wall at its ends only, and curved first portions joining adjacent second portions, contacting the inner wall at their mid-points only.

Each spring may be continuous or may be a strip bent into a loop with or without overlap of its ends. The cylindrical walls are smooth, but there is friction between them and the spring. When a drive shaft turns the driving member about its axis, the friction between the cylindrical surfaces and the spring will cause the driven member to rotate about the axis until the drive shaft engaged thereby encounters a torque greater than a pre-determined maximum. When this happens, the friction between the spring and the cylindrical walls of the chamber 24 or 44 will be insufficient and slippage will occur. The journal bearing 27 of Fig. 1 keeps the drive member supported above the base of the recess 26 of the driven member and allows free relative rotation when slippage at the spring occurs.

A screw (not shown) may be mounted in the wall of the recess of the driven member so as to extend into the chamber thus reducing the width of the chamber at the point of mounting the screw and squeezing the spring 51 or 52 so that it presses with greater force on the cylindrical surfaces of the chamber.

This will have the effect of increasing the maximum torque resistance to be applied to the driven member before the drive assembly will slip. A plate may be mounted on the end of the screw within the chamber to assist compression of the spring.

The driven member of Fig. 1 may be provided with a pair of dogs 28 extending into the central bore 22 to engage a recess or a pair of recesses in the driven shaft so that the driven shaft is positively driven by the driven member.

Claims

1. A slip drive assembly comprising a driven member and a driving member, one member comprising a cylinder and the other member defining an annular chamber with said cylinder, and a spring which extends around the annular chamber in a zig-zag shape so that it contacts spaced points on the cylindrical surface of one member interspersed with spaced points on the cylindrical surface of the other member.

2. An assembly as claimed in claim 1 wherein the spring contacts the inner wall of the annular chamber along lines parallel to the axis.

3. An assembly as claimed in claim 1 wherein the spring contacts the inner wall of the annular chamber over extended areas.

4. An assembly as claimed in any one of claims 1 to 3 wherein the spring contacts the outer wall of the annular chamber along lines parallel to the axis.

5. An assembly as claimed in any one of claims 1 to 3 wherein the spring contacts the outer wall of the annular chamber over extended areas.

6. An assembly as claimed in any one of claims 1 to 5 wherein one member is an annular pinion.

7. An assembly as claimed in any one of claims 1 to 6 comprising a stationary housing which defines an end wall of the annular chamber.

8. A slip drive assembly substantially as herein described with reference to and as illustrated in either Fig. 1 or Fig. 2 together with either Fig. 3 or Fig. 4 of the accompanying drawings.