Bandwidth performance of a direct drive manipulator under joint torque and endpoint force control

The experimental bandwidth limitations for digitally implemented joint torque and endpoint force control of a one degree-of-freedom direct drive manipulator are discussed. It is shown that an open loop joint torque controller can be used with good results to track endpoint force trajectories, but is limited in bandwidth to the natural frequency of the rigid-body mode. Endpoint force control compensates for the rigid-body mode and is capable of increasing the bandwidth above the joint torque controller (within the limits of the actuator). Both results suggest that a higher natural frequency of the system is desirable. In contrast, it is shown that a lower natural frequency is desirable in the case of contact discontinuity due to the large impulses created during impact