Strain wave gearing (SWG), also known as harmonic drive gear, has been used in many space applications. In 2003, a development of grease-lubricated-type SWG for space flight applications was begun. The life tests of the SWG exposed to vibration test and thermal vacuum test were performed in vacuum. The life test results showed that the in-vacuum operating life of the SWG was significantly short compared with the in-atmosphere life, which is normally corresponding to a rolling fatigue life of wave generator bearing. This may be mainly caused by the severe wear at the wave generator-flexspline interface, where the lubricant is not supplied easily into the clearance in vacuum.

This paper describes a new concept for linear motion based on the similar theory of strain wave gearing, which has been used for more than forty years by Harmonic Drive Systems Inc. Gear teeth are replaced by screw threads and rotation of the input side generates linear translation at the output. Besides design flexibility and reasonable costs, the new rotary-to-linear harmonic drive® has shown promising potential in positioning accuracy as well as in high load capacity. It is able to compete (and to surpass in some features) with ball screw or lead screw systems.

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