GB2132764A

GB2132764A - Harmonic drives for tool adjustment scales

Info

Publication number: GB2132764A
Application number: GB08324764A
Authority: GB
Inventors: Douglas F Wise
Original assignee: Norbar Torque Tools Ltd
Current assignee: Norbar Torque Tools Ltd
Priority date: 1982-09-16
Filing date: 1983-09-15
Publication date: 1984-07-11
Also published as: GB2132764B; GB8324764D0

Abstract

A tool, such as the torque wrench shown, (Fig. 1) has a fixed tube 2 and rotatable coaxial handle 9 which serves to move a nut (5, Fig. 1) longitudinally by means of a lead screw (6, Fig. 1), thus adjusting the compression of a torque setting spring (4, Fig. 1). The torque value is indicated by a scale 14 rotatable in a housing (11, Fig. 1) and viewable through a window (13, Fig. 1) which includes a cursor. The scale 14 is an extension of the dynamic spline 15 of a "harmonic drive" having a cooperating spline 16 fixed to tube 2 and a wave generator comprising two flats 18, on the end (10, Fig. 1) of handle 9, which press the splines into engagement at two discrete locations. For every revolution of handle 9 the scale on member 14 will be moved a distance corresponding to two tooth pitches where the difference in the number of teeth 16 and 15 is two. <IMAGE>

Description

SPECIFICATION Adjustable torque wrenches This invention relates primarily to adjustable torque wrenches but may be used with other tools and is concerned with an arrangement for indicating by means of a scale the torque value to which the wrench is adjusted. The adjustment being effected by rotation of one member relative another.

Torque wrenches, as are known, have a body forming an arm with a drive at one end which receives a socket or other tool and arranged so that the mechanism "clicks" or otherwise indicates when more than a set torque is applied through the arm. The torque is made adjustable through a spring acting on a lever mechanism associated with the drive and the spring force is made variable through an adjusting nut. The nut is associated with some form of linear scale along the body to indicate the torque value set. Such a scale is too short to read accurately and it is often impracticable to accommodate dual scales.

An object of this invention is to provide in a tool such as a torque wrench with a relatively long scale which can be accurately and easily read, yet which is of simple construction and which can be located around the circumference of a handle or arm of the tool.

According to this invention there is provided an adjustable tool, particularly a torque wrench, including a handle with a coaxial rotatable tube mounted through screw thread means whereby relative rotation between tube and handle produces longitudinal movement of an adjusting member, the tube and the handle being operatively coupled with a harmonic drive the dynamic spline of which is connected with a scale movable relative to a fixed cursor, to thereby indicate the position of the adjusting member.

With such an arrangement the harmonic drive provides a compact means of reducing the number of turns of the rotatable tube by a ratio enabling the scale to be accommodated around the circumference of the body of the handle.

The basis of operation of the harmonic drive is the difference in the tooth pitch between two annular splines, one being movable and flexible (the dynamic spline) and the other being rigid and fixed. The dynamic spline is forced into engagement with the fixed spline at one or more locations by a so-called wave generator. Thus in one revolution of the wave generator which is conveniently connected with the rotatable tube, the scale connected with the dynamic spline is displaced by one tooth pitch.

The cursor and fixed spline are connected with the handle of the wrench with the dynamic spline concentric therewith and having an axial extension forming the scale lying beneath a window in a housing positioned around the handle and connected with the fixed spline. The end of the tube is rotatably received in the housing, and has an inner circumference forming the wave generator which overlies the dynamic spline with a portion of reduced diameter to force same into engagement at one or more discrete locations with the fixed spline.

The invention is further described and illustrated with reference to an embodiment shown in the accompanying drawing by way of example oniy. In the drawings: Figure 1 shows a torque wrench handle in longitudinal section, Figure 2 is a section on ll-ll of Fig. 1, and Figure 3 shows the harmonic drive components in longitudinally exploded view.

Referring to the drawings, a torque wrench handle is shown and this includes a tube 2 which, at the left end, has a square drive D retained against rotation in one direction or other by a ratchet means R and which is pivotally mounted in the end of tube 2 by a pin P. The drive D has an arm A which extends along tube 2 to connect via a knuckle joint J with a further lever arm I having a linkage L carrying a roller 3 which is subject to force from one end of spring 4 which acts on roller 3 via a block 3a. The other end of spring 4 is contacted by a moving abutment nut 5 which can be traversed longitudinally by rotation of lead screw 6. Grooves (not shown) in the nut 5 run on raised flutes (not shown) in the bore of the tube 2, thus preventing rotation of the nut relatively thereto.An outer handle tube 9 is coaxial with the tube 2 and relatively rotatably mounted thereon and connected to screw 6 by a stub 6a with a flange 6b abutting circlip 6c serving to retain the handle and screw in tube 2. Tube 9 may be rotated along with screw 6 to adjust the compression applied to spring 4 by nut 5 and hence the release torque. With this construction torque applied above a value determined by the precompression of spring 4 is sufficient to pivot arm A about pin P by deflection of spring 4 through roller 3 thus providing a physical and audible signal as the lever train A, I, L snaps-over.

The end of tube 9 is received in a housing 11 secured to tube 2 by four raised lugs fitting in grooves 2a of the tube 2 (Fig. 2 and 3) and the housing has a window 1 3 enabling a scale S around the periphery of an annular moving member 1 4 to be viewed. This member 1 4 comprises or is connected to the dynamic or rotatable spline of a harmonic drive and has teeth 1 5 around the inner circumference which normally do not engage and are free of a further set of teeth 1 6 comprising a fixed spline 1 7 mounted on the tube 2 and keyed thereto by lugs 1 7a engaging the grooves 2a of the tube 2.The number of teeth 1 6 on fixed spline 1 7 differ from the number of the dynamic spline 14, and by means of a wave generator defined by two opposed flats 1 8 on the end 10 of the handle 9 teeth 1 5 are forced to engage teeth 1 6 at two opposed points and by virtue of the flexibility of spline 14 as shown more clearly in Fig. 2. In Fig. 1 the teeth are shown engaged at the top and disengaged at the bottom for convenience only, normally the two flats engage the teeth at diametrically opposed points.As shown in Fig. 3 the part of moving member 14 carrying teeth 1 5 is made flexible and connected with the part carrying the scale by a joining bridge 14a which takes up deformation applied to the teeth without deforming the scale carrying part. The scale is fully supported on both sides by the housing 11 which is formed with a cylindrical elongate slot to receive the scale.

For every revolution of handle 9 the scale on member 14 will be moved a distance corresponding to one tooth pitch where the difference in the number of teeth 1 6 and 1 5 is one.

The scale can thus provide an accurate indication of torque settings even when the number of revolutions over the adjustment range is high and is easily viewed.

In the embodiment shown the dynamic spline 1 5 has 48 teeth and the fixed spline 1 7 has 46 teeth. The dynamic spline is of a flexible plastics material and with each revolution is moved by half the tooth pitch and provides an effective gear ratio of 23:1.

Although the invention is described in relation to torque wrenches, it may be equally applied to other devices requiring a scale indication where a number of revolutions of an adjusting nut are provided such as in micrometer type instruments or the like.

Claims

1. An adjustable tool including a body part and a rotatable part whereby relative rotation between said rotatable part and the body part produces longitudinal movement of an adjusting member, the rotatable part and the body part being operatively coupled with respective parts of a harmonic drive the dynamic spline of which is associated with a scale movable relative to a cursor, to thereby indicate the position of the adjusting member.

2. An adjustable tool in accordance with claim 1, wherein the body part comprises an elongate handle and the rotatable part comprises a tube coaxial with the handle and relatively rotatably mounted therewith.

3. An adjustable tool in accordance with claim 2, wherein the tube overlies an end of the handle and is connected with a screw threaded member extending within the bore of the handle, a nut being provided held against rotation relative to the handle but longitudinally slidable therein, the nut constituting the adjusting member.

4. An adjustable tool in accordance with claim 2 or 3, wherein the tube constituting the rotatable part has an end receiving the dynamic spline positioned around a fixed spline carried by the handle, the said end having a flat or flats engaging a peripheral surface of the dynamic spline to force same to engage the fixed spline, the dynamic spline being connected with a scale member rotatable relative to the handle.

5. An adjustable tool in accordance with claim 4, wherein the scale member is a tubular extension of the dynamic spline and is operatively associated with a cursor carried by the tube.

6. An adjustable tool in accordance with claim 5, wherein the scale member is housed within an annular end part connected with the tube, said end part having a window therein to view the scale member.

7. An adjustable tool in accordance with claim 6, wherein the annular end part has two concentric annular portions defining therebetween an annular slot which receives the scale member, the inner annular portion forming a contiguous cylinder with the fixed spline and both being keyed to the tube by complementary engaging formations.

8. An adjustable tool in accordance with claim 7, wherein the dynamic spline is housed within a widened end of the annular end part, said widened end forming a mouth to receive an end portion of the rotatable tube, said end portion receiving the dynamic spline and including the flat or flats.

9. An adjustable tool in accordance with any preceding claim, said tool being a torque wrench, the body part (handle) being tubular and having a drive means with a lever arm pivotally mounted in, and extending along the handle, the adjusting member serving to apply precompression to a spring within the handle and operatively coupled with the lever arm to maintain same in a first stable position.

10. An adjustable tool embodying an indicating scale means said means being constructed and arranged to function as described herein with reference to the drawings.