AU602862B2 - Zero backlash gear - Google Patents

Description

COMMONWEAL TH OF AUSTRALIA Patent Act 1952 0 2 CO0M PL ET E S P E C I F I C A T I 0 N

(ORIGINAL)

5.S3-1 Class Int. Class Application Number PHOO 050 Lodged 9 April 1985 Complete Specification Lodged Accepted Published Car j.

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bol I Li V~ fl~.ac 44 t 0 0 o t4 Priority: Related Art

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~ec~ 3N&t) Name of Applicant Address of Applicant Actual Inventor Address .for Sexcvice -R--A-ThAN-- EMM-ERT0N- 22 Railway Road, Meadowbank, New South Wales, Australia ROY ALAN EMMERTON F.B. RICE CO., Patent Attorneys, 28A Montague Street, BALMAIN. 2041.

14 44 44 41£ Complete Specification for the invention entitled: "?ZERO BACKLASH GEAR" The following statement is a full de cription of this invention including the best method of performing it known to me:- 2 The present invention relates to gear boxes used in robotics and other applications where little or no backlash can be tolerated and in particular the invention provides a zero backlash gear for such a gear box.

Prior art zero backlash gear box arrangements, known as harmonic drives, are well known and are commonly used in the robotic industry. These prior art drives rely for their operation upon the combination of a wave generator comprising a thin wall ball race fitted to an eccentric former which serves as a high efficiency torque converter, a flexible steel spline with external teeth which is fitted over the wave generator and elastically deformed by it and an internally toothed circular spline which engages Sthe teeth of the flexible spline across the major axis of °o 15 the wave generator. Typically the flexible spline is c s provided with several teeth less than the circular spline 0o although the teeth of each of the splines are of equal Spitch and about 15% of the total number of teeth are in engagement as a result of the deformation of the flexible j f v20 spline by the wave generator. The gear ratio of the harmonic drive is given by the ratio of the number of teeth on the flexible spline and the difference between the number of teeth on the flexible spline and the number of teeth on the circular spline and this ratio is negative such that with the wave generator as the input and the flexible spline as the output and with the circulaL spline direction to the wave generator and at a greatly reduced rate.

relatively low cost replae f- own zero backlash The present invention consists in a gear wheel comprising a central boss adapted to be rotatably mounted, a flexible, toothed rim pressed onto said boss such that fied f dieto otewv eeatrada ral eue y 1 a e 2a one side of the toothed rim engages the boss, the teeth of the toothed rim being located on the opposite side of said rim to the boss-engaging side portion and a clearance a- 4 #4 aa~ o 0 4 4 I 4 a 40# 00 00 a a, 44 01 0 4 (4

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44 o lo 0-3 4 404 a -3 being provided between the rim and the boss on the toothed side of the rim such that deformation of the rim will occur under pressure applied radially inwardly to the teeth thereof.

Preferably means are provided to limit the deformation of the rim to a fixed predetermined amount and it is also preferable that the teeth of the rim are provided with steeply sloping faces to prevent the teeth from riding over engaging teeth of a meshing gear.

The zero backlash gear wheel of the present invention is suitable for use with both cog gears and worm gears.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 illustrates a zero backlash gear wheel according to the present invention in elevation; and Figure 2 illustrates a half sectional end elevation Fig of the gear wheel of Figure i.

I: The illustrated embodiment of the present invention comprises a central boss 10 having a peripheral recess 11 about one side of its circumference and a peripheral S flange 12 about the other side of its circumference. An annular rim 13 having a generally L-shaped sectional shape is pressed into the recess 11 with a portion of the rim 13 disposed remotely of the recess 11 being spaced by a distance C from the flange 12 of the boss 10. The flexible rim 13 carries an annular projection 14 into which a set of outwardly directed teeth 15 are formed. In operation, the distance between the zero backlash gear of the present invention and a toothed gear or worm gear with which it meshes is adjusted such that the flexible rim 13 is preloaded, thereby reducing the distance C at the point of meshing of the two gears. In this way, the teeth of the meshing gears are held tightly in engagement without any backlash and this tight engagement is maintained -4throughout the rotation of the gears by virtue of the loading provided in the flexible rim 13.

The teeth of the zero backlash gear and the gear with which it is meshed will preferably be designed with steep faces such that there is no tendency for the teeth of the zero backlash gear to ride up on the teeth of the gear with which it is meshed and the teeth of the two cooperating gears will be substantially identical.

The flange 12 is provided under the flexible rim 13 to prevent excessive deformation of the rim under certain circumstances, as for example, under shock load conditions. The flange 12 acts as a buffer, with which the rim will come into contact if excessive deformation of the flange occurs. It will be recognised by persons skilled in the art that the deformation of the rim 13 may be limited by various other methods such as the provision of an inwardly projecting flange on the rim itself or alternatively by reduction of the centrally located gap 16 between the rim 13 and the boss 10, however- the inclusion of flange 12 provides a method of buffing the deflection of the rim 13 which is relatively simple to achieve during the manufacturing process.

Claims (9)

1. A gear wheel comprising a central boss adapted to be rotatably mounted, a flexible, toothed rim pressed onto said boss such that one side of the toothed rim engages the boss, the teeth of the toothed rim being located on the opposite side of said rim to the boss-engaging side, and a clearance being provided between the rim and the boss on the tooth side of the rim such that deformation of the rim may occur under pressure applied radially inwardly to the teeth thereof.

2. The gear wheel as claimed in claim i, wherein means are provided to limit the deformation of the rim to a predetermined maximum atount.

3. The gear wheel of claim 2 wherein the deformation of the rim is limited by providing a clearance between the i tooth side of the rim and the boss which is equal to the predetermined maximum amount of deformation. a

4. The gear wheel of claim 3 wherein the clearance between the boss and the rim is set by a step in the peripheral surface of the boss, the step being located under the tooth side of the rim and the height of the step being selected to set the clearance to be equal to the predetermined maximum deformation.

The gear wheel as claimed in claim 3 wherein the clearance between the boss and the rim is set by an annular projection carried on the rim, under the toothed side thereof, the height of the projection being selected to define a clearance between the rim and the boss to be equal to the predetermined maximum deformation of the rim.

6. The gear wheel as claimed in any one of the preceding claims wherein the teeth are provided with steeply sloping faces to prevent the teeth from riding over engaging teeth of a meshing gear.

7. The gear wheel as claimed in any one of the preceding claims wherein the rim has a substantially L-shaped cross- 6 section.

8. The gear wheel as claimed in any one of the preceding claims wherein the rim carries an annular projection in which the teeth are formed.

9. A gear wheel substantially as hereinbefore described with reference to the accompanying drawings. DATED this 4th day of April 1986 Pee1e P -A L-Tl. RQY--A-LAN--EMM.ER-T-ON Patent Attorneys for the i) Applicant: F.B. RICE CO. Ao4 0 a 0o 00« Si 4 tt4