Interaction control for a brake actuated manipulator.

If a passively actuated physical human-robot interaction (pHRI) device could produce the transparency and controllability of an active device, the safety standard of pHRI could dramatically improve. This is critical since pHRI devices are being developed for rehabilitation or assistance where the user may not be able to provide full strength or speed to counteract accidental movements caused by a motor driven robot. This paper demonstrates effective friction compensation and an interaction controller that increases overall transparency of a passively actuated pHRI device, the Brake Actuated Manipulator (BAM). We analyze the friction compensator's stability with passivity theory, and evaluate the proposed interaction control scheme on the BAM with real time experiments during display of virtual environments composed of non-linear Coulomb or viscous friction. Results show excellent force tracking performance during display, and indicate that passively actuated pHRI devices can be transparent despite notions that brakes are poor actuators.