A comparison of two real-time control schemes for redundant manipulators with bounded joint velocities

A comparison of two real-time control schemes for redundant manipulators is presented. Both schemes are developed in the framework of resolved rate control, and were presented by the authors in earlier articles (R.V. Dubey et al., 1988, J.A. Euler et al., 1988, and S.M. Babcock, 1988). The first scheme is the gradient projection scheme, which determines only the direction of the self-motion for the optimization of a scalar performance criterion. The second scheme determines the direction as well as the magnitude of the self motion. However, when the magnitude of the self-motion is limited by the hardware bounds on joint velocities, the results obtained using the two schemes are remarkably similar when the computational frequency is high (above 100 Hz). Therefore, the gradient projection scheme, which is computationally more efficient, is recommended. An explanation for the similarity of results is presented. Scheme 1 was implemented in real-time on a Motorola 68020 VME bus-based controller of the seven-degree-of-freedom manipulator at the Center for Engineering Systems Advanced Research