IL28533A - Harmonic drive transmission - Google Patents

Description

Harmonic drive transmiBsion GEAR 27089 This invention relates to strain wave soma times termed harmonic drive wherein a radially progressively at spaced circumferential localities with a coc circular particularly this invention is with provision of a modified form of harmonic drive gearing for the attainment certain the degree of radial deflection of a selected within a less or greater than the standard hitherto for cooperation with a given circular For background information reference be had to United States Patent and granted upon applications filed in the name of Walton The first of these discloses drive a pair of coaxial gears one of which is both having teeth of the circular pitch but differing in of teeth and in pitch The second discloses a dynamic spline differing from the foregoing in that the of spline teeth on the deflected gear is to that on the circular While the present invention is especially directed to the deflectible gear or flexspline as will be it will be understood that the wave generating means for effecting its lobar shape and rotating the circumferential radial displacement therein may be any of various or hydraulic types previously utilize more than two lobes about the center of It will also understood is any one of hree basic wave or circular may serve as input another serves with the third usually serving as a reaction purpose of this invention is to a to have more latitude in its design and hence in its Another purpose is to attain advantages which can be derived in operation when the s a circular itch ers from that of cooperating circular j and spline teeth respectively differ in mother purpose to novel harmonic drive design having lowerireduction ratio and one wherein may bo less than in deviated harmonic To ends a main feature of the invention resides in the of a harmonic drive transmission having a circular spline and a radially deflected coaxial having teeth meshing and engaging at spaced circumferential the deflection of the being such that at the localities of full instead of both faces of a tooth engaging the adjacent sides of circula spline teeth as in harmonic drives the tooth engagement is to one or the other side of the apex 1 foregoing and features of the 2 together with a novel method for harmonic in a 3 range of reduction will now be set forth with 4 particularity in connection with an illustrative 5 d with referenco to the 6 in 7 1 an enlarged transversa of fully 3 portions of an elliptoidal and its external 9 circular spline according to known harmonic drive construction 10 2 is a section corresponding to 1 but as 11 applied to similar transmission in accordance with 12 the presen the teeth having positive deviation or 3 is a section corresponding 2 but wherein 15 the teeth are in acement or I f deviation according to the presen and 17 4 is a graphic of tooth 18 notion relative to circular spline for positively and j 19 negatively deviated as contrasted with deviated or drive tooth hitlierto It will be understood although the invention is applicable to arrangements wherein the is of the circular the invention will for convenience now be described only related to the arrangement wherein the is internal of the circular An internal elliptoidal generator as in 1 externally splined which be connected to an output is deflected and meshes with and reacts on an internall stationary spline 1 The tooth engagement illustrated in 1 is that of the known or harmonic drive transmission and may bo termed as at the major axis locality designated the teeth are fully in without having Xn the deflection effected by the wave generator 10 equals the pitch diameter of the output member divided by the reduction further characteristic is that ratio equals the number of teeth on driven divided by the in teeth the driven gear and the of teeth on the fixed difference being equal to a multiple of the number of on the In 2 and as contrasted with the flexspline at the apex along the do not contact the circular spline instead the tooth engagement point is displaced or to the right side and to the left the shown in The distinction is that the teeth of 1 all have the circular whereas n 2 and 3 the circular pitch of the flexspline teeth differs from of the circular spline 2 thus spline and right flank a deviated tooth contacting a circular spline 3 shows deviation teeth and of flexspline having their right flanks respectively circula teet respectively having contacting spline harmonic arrangements are due to modifying the deflection the numbers of of the flexspline and cooperating circular spline different according to one or a multiple the number of lobes on the wave there is a difference in the pitch of the fle spline teeth and of the circular spline teeth along the pitch circle the prior art harmonic the amount of radial deflection imposed on the is a function of the circular is the on both the circular spline and the As the wave generator 10 the circular spline 14 being the flexspline 12 rotates counter to the The curve designated in 4 on an enlarged this flexspline tooth with respect to the circular Torque by the flexspline is generated by the contact surface of its tooth at the major axis practice by the several flexspline tooth surfaces adjacent to the De lection stress in known drives is stress to output torque By deviating the tooth contact position to plus or positions within a range by modifying the flexspline radial bending stress can be and effects such as longe working life By way of with the known flexspline tooth motion shown in the curve 4 wherein the radial deflection is a standard or amount flexspline tooth for a positively deviated harmonic drive such as shovm in 2 is shown by curve b having a corresponding tooth for a negatively deviated drive aa shovm in 3 is illustrated by a curve c of 4 wherein the deflection is With positive radial deflection in excess of standard hitherto flexspline teeth are in contact on way out of when their radial velocity is toward the In the case of negative on the other where the deflection is less than the flexspline teeth are in contact on the into and their radial velocity is then away In either case of deviated tooth thickness is modified the design to allow the teeth to shift a contact position at one side of the apex A to a contact position on the other An advantage of the positive deviation is that it relative advantages includes less stress incurred at locality of teeth a lower reduction ratio to be and allows a angle in the which is usually and hence shortening its axial Aside affording greater latitude in the design of harmonic drive actuators and enabling the characteristics of other as well as steel to be used deviated drive efficiency and in the of reduction gear in a performance as next A single wave for instance an cam having a known radial de may be in large quantities and each employed in drive respectively providing different reduction For this purpose blank and blank circular splines conation to all the would be as the requirement for a specific ratio in the range became the appropriate numbers of teeth would be cut in a pair of circular spline and blanks to be used with the generato difference each blank being selected according to a multiple the number of on the wave generator In this for units having reduction ratios ranging from to can be from a of only the three common the wave Λ insufficientOCRQuality

Claims (2)

1. A deviated harmonic drive transmission having a circular spline and a coaxial flexspline radially deflected symmetrically about its center to provide a plurality of lobes having teeth meshing of circumferentially spaced localities, the circular pitch of the flexspline differing from that of the circular spline, and the flexspline having a different number of teeth from those of the ciroular spline as determined by one or a multiple times the number of said flexspline lobes.

2. A transmission as set forth in Claim 1 wherein the circular pitch of the flexspline exceeds that of the circular spline. 3· A transmission as set forth in Claim 1 wherein the circula pitch of the flexspline is less than that of the circular spline. For the Applicants PARTNERS IS:BH