Haptic Interaction Stability With Respect to Grasp Force

This paper addresses the contact instability of admittance control of a haptic interface. A high level of rigidity of the grasp of a subject operating the haptic interface will result in unstable behavior of the haptic interaction. Experiments with a system dedicated to measuring grasp force were performed to explore the conditions when grasp force has reached the critical grasp force that destabilizes the haptic interface. The critical grasp force was quantified for various values of virtual environment parameters. The experimental results are compared to simulation results obtained with a model of haptic interaction. To improve stability, two methods were applied: one with virtual coupling, the other with a compensator filter. A model was used to define the structure of the compensator filter and to determine the parameters of the virtual coupling and the compensator filter. Experimental and simulation results confirmed an improvement of stability. Both methods allow higher grasp forces of the human operator, and experiments show that the compensator filter allows higher grasp forces than the virtual coupling.