STABILITY OF A SET-POINT CONTROL SYSTEM OF TENDON-DRIVEN MANIPULATORS

摘要

Tendon-driven manipulators are robotic manipulators where joint torques are delivered from motors mounted on the base part through tendons (wires). So far such manipulators were often controlled using multi-looped feedback controllers, where the inner loop takes the responsibility of the tendon tensile force control, and the outer one calculates the desired tendon tensile forces to correct the error from the desired trajectory. In this case, it is assumed that the inner loop converges so fast that we can ignore the effect of the inner loop dynamics when we design the outer loop controller. Therefore the total stability is not assured strictly. In this paper, a set-point PD controller is applied to a tendon-driven manipulator and the Lyapunov stability is investigated. The stability analysis of a tendon-driven manipulator is rather complicated than that of conventional manipulators, because the manipulator has tendons more than the number of joints, the tendons have nonlinear elastic property, moreover they cannot generate negative tensile force. We derive a set of sufficient conditions for the Lyapunov stability and show a numerical simulation result.