Characterization and control of a screw-driven robot for neurorehabilitation

The characterization and control of a module for a therapy robot is discussed. The screw-driven module expands the workspace of an existing robot used for neuro-rehabilitation from two to three dimensions. The need for low endpoint impedance in such devices is emphasized, and the factors influencing endpoint impedance are considered and evaluated for the new device. We evaluate the actuator and control system bandwidths and discuss a series of experiments to characterize the friction, gravitational force, and effective endpoint inertia. Several methods of active control for reducing effective endpoint impedance are explored and compared. Proportional force feedback was found to reduce impedance more effectively than model-based methods. We are presently developing improved analysis tools for understanding the limits of the modification of endpoint impedance with active control.