Effect of Hand Dynamics on Virtual Fixtures for Compliant Human-Machine Interfaces

In human-machine interfaces with joint/link compliance, human hand dynamics can have a detrimental effect on system performance. This paper investigates the effect of human dynamics on the effectiveness of a virtual fixture implemented on an admittance-controlled robot with joint compliance. Two open-loop control methods are proposed for creating a virtual fixture that prevents the user from entering a forbidden region: one that compensates for hand dynamics, and one that predicts overshoot based on the user’s current velocity. The methods determine a“safe” location of the virtual fixture that prevents the user from entering the true forbidden region. A first experiment was conducted to determine hand dynamic parameters (mass, damping, and stiffness) and evaluate their relationship to the force applied by the user on the interface. A second experiment demonstrated that both methods for creating safe virtual fixtures prevent the user from entering the forbidden region, even when the interface has significant joint compliance.