Design and control of a planar haptic device with passive actuators based on passive force manipulability ellipsoid (FME) analysis

In this paper, we propose an optimal design for a passive haptic device with brakes and its control method. The inability of a brake to generate torque significantly affects the performance of a multi-DOF haptic device, in that a desired force can be generated only approximately in some workspace and, in some cases, the device may become stuck contrary to the user's intention. In this research, these limitations are analyzed by means of the so-called passive force manipulability ellipsoid. Through the analysis, performance indices are developed for evaluating the limitations associated with passive haptic devices. Optimization is conducted for a 5-bar mechanism with redundant actuation, and a coercive force approximation scheme is developed to avoid unsmooth motion during the wall-following task along the virtual wall. It is experimentally shown that the performance in relation to the limitations is greatly improved for the optimized mechanism.