Motion control of tendon-driven rotary actuator using Twist Drive system

This paper proposes a method to achieve high-precision control for tendon driven system by using the Twist Drive. Twist Drive is one of transmission system which is consisted a pair of strings and rotary motor. This transmission system converts torque into a pulling force by using the pair of strings twisted on each other. However, it cannot realize pushing motion. Therefore the Twist Drive needs to be combined with an other actuation system for the realization of pushing motion. The problem is solved by tendon drive using Twist Drive system in this paper. High-precision control is achieved by modal-space disturbance observer. Modal-space disturbance observer is designed to realize the acceleration based control. It also compensates the modal interference. Furthermore work space observer is able to estimate the force in the work space without any force sensors. The proposed method was applied to rotational angle control and torque control of the tendon driven rotary actuator. The effect of the proposal is verified through experiments.