DESIGN AND MANUFACTURE OF THE COMPOSITE FLEXSPLINE OF A HARMONIC DRIVE WITH ADHESIVE JOINING

Abstract

The harmonic drive, which is composed of a circular spline, a wave generator and a flexspline, is a compact, light-weight, and precise torque transmission mechanism with little backlash. From these components, the flexspline is the key element for motion transmission. It must be flexible in the radial direction but stiff in the tangential direction to accurately transmit rotational motion. In order to satisfy this dual role, the conventional steel flexspline is usually manufactured as a thin cup shape which requires a large amount of machining using special jigs. Because of the thin cup shape, the steel flexspline produces noise and vibration when operated at high speed. Since the dual role cannot be satisfied effectively with conventional isotropic materials, anisotropic composite materials have been considered. In this paper the cup section of the flexspline was manufactured with carbon-fiber epoxy composite material and the tooth section using steel. Then the two components were joined by adhesive bonding. Also, in order to make the manufacture of the steel flexspline easy and reduce the noise and vibration of the harmonic drive, the cup and tooth sections were manufactured separately and adhesively bonded. The static torque transmission capabilities and the vibration characteristics of the composite flexspline with adhesively bonded steel teeth and the steel flexspline with adhesively bonded steel teeth were experimentally tested. From these tests it was found that the flexspline manufactured with adhesive bonding had sufficient torque transmission capabilities and both the composite flexspline and the bonded steel flexspline had better dynamic characteristics than the conventional one-piece steel flexspline.