This paper describes the mechanical structure of a friction drive system and its traction characteristic. The system consists of a DC servomotor, a friction reduction device (planetary roller type) and a friction drive elements (a pinion roller and a slider). The linear scale measures the slider displacement, which is fed back to the servomotor by way of a micro computer. Since the friction drive system is mechanically easy to make and has small non-linear factors, it is thought that this system is good for precision positioning. In case of usual friction drive, a traction characteristic is easily obtained by measuring the torques of two friction wheels, but in this study it is very hard to obtain it because the slider moves longitudinally. Therefore, the traction characteristic is obtained by a frequency response method between two velocities of the pinion roller and the slider. It is shown that the traction between the pinion roller and the slider is estimated by using an exponential function of the slip ratio.
