A decentralized digital model-reference adaptive manipulator trajectory controller was tested using a distributed multiprocessor architecture and a PUMA 560 industrial robot. The controller is composed of a nominal model-based component and an auxiliary model reference adaptive component. The purpose of the model reference adaptive control signal is to compensate for deviations of the model parameters from their actual values. Nonlinear interaction and coupling between joints is treated as a disturbance torque that is tuned and compensated for. The motivation for decentralized control is the ease and speed of parallel implementation of the developed control algorithms using relatively inexpensive hardware.>

A simple decentralized time-varying digital trajectory controller for robot manipulators, based on manipulator dynamics and a parameter identification scheme, is developed and tested using multiprocessor architecture and a PUMA 560 robot arm. A discretized equivalent model of the continuous manipulator system is used to design the necessary model-based digital feedback and compensation filters for this purpose. Time schedules of parameters of these filters are generated offline when the desired trajectory is planned. An identification scheme based on output measurements is developed and used to compute the actual values of the model parameters. The nominal parameter values computed offline are used to compensate for timing delays. The performance of the controller is very encouraging and compares very favorably with experimental performance of other controllers, considering that the manipulator was driven very close to its maximum speed.>

Computing manipulator joint velocities and accelerations, given the end-effector Cartesian rates (velocities and accelerations), is complicated by the singular positions the manipulator can assume along a trajectory. At such configurations the Jacobi matrix that relates Cartesian end-effector rates to joint rates cannot be inverted. Geometric approaches in solving for joint rates yield expressions that are indeterminate at such configurations. It is shown that exact solutions for the joint rates can be obtained in most singularity situations if the system of differential kinematic relations is properly partitioned. A solution methodology is developed and illustrated by an example.>