Development of cycloidal planetary reducer

A cycloidal planetary reducer, which fulfils both high reduction ratio and low vibration in a thin and small body, had been proposed to cope with the further downsizing of DC motors. The reduction mechanism is inspired by the intellectual toy ‘Spirograph’ and structurally based on a planetary reducer. Instead of the internal gear of the planetary reducer, output plate with skid epitrochoid groove is introduced. The sun gear is connected to the input shaft and the planetary carrier works as a stator. The planetary gear has a pin that fits in the groove of the output plate. According to the rotation of the planetary gear, the output plate revolves in the counter direction with a speed in inverse proportional to the number of the skid epitrochoid. The prototype can realize higher reduction ratio compared to the planetary reducer without unpleasant vibration that is unavoidable in the cycloidal reducer. It is confirmed that the idling torque is very small with 0.006Nm, and the torque transmission efficiency is acceptable with 73%. But the torque fluctuation caused by the cam motion by the pin and groove is remarkable, which will be forthcoming challenges.