A Variable Structure Approach in Discrete Decentralized Time-Varying Nonlinear Manipulator Control

In this paper a decentralized trajectory controller for robotic manipulators is designed and tested using a multi-processor architecture and a PUMA 560 robot arm. The controller is made up of a nominal component designed using a computed torque approach and a correction component based on a variable structure suction control approach. The second control component is designed using bounds on the difference between the used and actual values of the model parameters. Since the continuous manipulator system is digitally controlled along a trajectory, a discretized equivalent model of the manipulator is used to derive the controller. The motivation for decentralized control is that the derived algorithms can be executed in parallel using a distributed, relatively inexpensive, architecture where each joint is assigned a microprocessor. Nonlinear interaction and coupling between joints is treated as a disturbance torque that is estimated using a nonlinear feedback signal and is compensated for.