Abstract
The purpose of this paper is to design nonlinear control systems for tendon-driven robotic mechanical systems.
Tendon-driven mechanisms are appropriate especially for force-controlled robotic arms as well as robotic hands, because they allow to locate actuators away in the robot bodies and make them small in size and light in weight. In the dynamic aspect of the mechanisms, one of the most important features is the joint stiffness adjustability using the redundancy of actuators and nonlinear elasticity of tendons.
A conventional control system for a tendon-driven robotic mechanism is a double looped control system, which consists of an inner loop for tendon force control and an outer loop to generate the desired tendon forces for position and stiffness control. In this control system, the inner loop has to converge to much faster than the outer one does. Thus the inner loop feedback gains become relatively large and the system tends to be vibrative.
In this paper, a nonlinear control system that can control the joint angles and the joint stiffness separately is proposed using an exact input-output linearization approach. A necessary and sufficient condition under which we can design such a contoller is given. Classes of tendon-driven robotic mechanisms which satisfy the condition are also investigated. Finally some numerical results will be given to show the efficiency.
