Decentralized Force/Position Fault-Tolerant Control for Constrained Reconfigurable Manipulators with Actuator Faults

Abstract

This paper addresses the problems of decentralized force/position fault-tolerant control for constrained reconfigurable manipulators. A novel decentralized force/position control method is proposed for constrained reconfigurable manipulators without torque sensing by estimating the joint torques with only position measurements. In addition, a modified sliding mode controller is designed to guarantee force/position tracking performance, and the actuator faults in independent subsystem can be compensated by using an adaptive algorithm. The stability of closed-loop system is analyzed using the Lyapunov method. Finally, simulations are performed to verify the advantages of the proposed method.

Appendix A. Joint torque estimation

Considering the constrained reconfigurable module manipulators consists of n-modules, each module provides an independently rotating joint with harmonic drive transmission. According the Ref. [16], we can obtain the joint torque ${\tau _{fi}}$ by using the torque estimation method based on the motor-side and link-side position measurements along with harmonic drive model for each joint module of constrained reconfigurable manipulators.

By the following formula, one can get the constrained torque, which is obtained by the constrained force on the end-effector of manipulator:

$$\begin{aligned} {\tau _{ci}} = {\tau _{fie}} - {\tau _{fio}}, \end{aligned}$$

where $\tau _{fio}$ denotes the joint torque which is obtained in free space, $\tau _{fie}$ denotes the total joint torque in the constrained space. The total joint torque $\tau _{fie}$ and/or joint torque in free space $\tau _{fio}$ is directly obtained by the method proposed in the Ref. [16] under the condition of constrained space and free space, respectively.