The harmonic drive is a compact, light weight, and precise torque transmission mechanism without backlash. Its components are the circular spline, the wave generator and the flexspline. From the components, the flexspline is the key element for the motion transmission. It must be flexible in radial direction as the name implies, but must be stiff in tangential direction. In order to be satisfied with this contradictory dual role, the conventional steel flexspline is usually manufactured as a thin cup shape which requires large amount of boring and hobbing operation using special jigs. The steel flexspline produces noise and vibration because of its thin cup section when operated in high speed.
Since the contradictory dual role can not be achieved effectively with conventional isotropic material, but can be achieved with anisotropic composite material. In this paper the cup section of the flexspline was manufactured with carbon fiber epoxy composite material and the tooth section was manufactured with steel, and finally the two sections were adhesively bonded. Also, in order to increase the productivity of the conventional steel flexspline, the cup and tooth sections of the steel flexspline were manufactured separately and adhesively bonded.
The composite flexspline and the bonded steel flexspline were statically torsion tested and vibration tested. From the test, it was found that the torque capabilities of the adhesive bonded joints were 3 times larger than required, and the composite flexspline and the bonded flexspline had better dynamic properties than the conventional steel flexspline.
