On the Ability of Humans to Apply Controlled Forces to Admittance-Type Devices

Abstract

Human–robot collaborative systems have the potential to dramatically change many aspects of surgery, manufacturing, hazardous-material handling, and other dextrous tasks. We are particularly interested in precise manipulation tasks, which are typically performed under an admittance-control regime, where the controlled velocity of a non-backdrivable robot is proportional to the sensed user-applied force. During fast movements, there is a noticeable degradation in control precision and prior results have indicated that system velocity, and not system admittance, is the factor that is most correlated with force control precision. In this paper, we report evidence that system admittance is more important than velocity in determining the user's ability to control applied force and that both factors are less important than the force level itself, and we provide an explanation as to why prior results might have indicated otherwise. We find the conditions under which human force control performance is best when operating under admittance control. We also report the conditions under which human force control on a moving admittance-type device is indistinguishable from isometric force control, which can be used to design better device controllers.