The passivity of natural admittance control implementations

Natural Admittance Control (NAC) has been proposed as a means of implementing responsive force control that is both gentle and rapid while maintaining an end-effector admittance that is passive. Practical implementations, however, must deviate from the ideal NAC formulation, impacting the passivity of the manipulator. Issues arise particularly in the case where NAC is retrofitted to an existing industrial robot controller. Command input may be restricted to only position commands, and the servo algorithm may be fixed. Direct torque control is often not possible, precluding the use of torque feed-forward. Finally, the feedback sensors signals themselves often contain filters. Each of these three effects is examined and their effects on NAC implementations are identified by considering a simplified, continuous-time model of a typical NAC implementation.