A small traction drive that diverted a tapered roller bearing was developed for trial purposes, and the performance was evaluated. We expect that gears as a small transmission cause some problems with decrease of their size, deterioration of accuracy on hobbing, grinding, and heat treatment, tooth profile and lead measurement method and their accuracy, decreasing permissible transmission torque and so on. Authors developed the small size transmission system named a micro traction drive in consideration of these situations. Micro traction drive is a transmission by using of modified rolling bearings in so much transmitted power 70 W. The traction force is easily generated by pre-load between inner race and outer race as thrust force. The driving force is transmitted by the contact of retainer combined output shaft with the rolling element in rotating direction. Authors reported on the traction drive that based on the angular contact ball bearing with retainer as an output shaft, and it has succeeded in the deceleration from a super-high velocity revolution about the 2-stage micro traction drive. However the micro traction drive based on the angular contact ball bearing is easy to drive at high speed, the risk of seizure increase along with torque because the contact area between retainer and rolling element is in condition with point contact and pure sliding. Authors developed a micro traction drive, which can transmit larger torque using tapered roller bearing with line contact between retainer and rolling element, and operating behaviours were compared under large torque conditions. As a result, tapered roller bearing type micro traction drive transmits torque bigger than 1.5 or more times of angular ball bearing type micro traction drive after taking consideration for difference of outer diameter. Efficiency was also satisfactory at 80%～90%. The contact surface of roller, retainer, inner race and outer race was good after operation, and so we report that possibility of utilization of a micro traction drive using tapered roller bearing.
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