Effects of velocity on human force control

Although many robots and haptic interfaces are of the impedance type, admittance-type devices offer distinct advantages, such as high damping and stiffness display, particularly in applications requiring precise motion control. This study seeks to quantify human force control limitations in admittance control systems, where robot velocity is controlled to be proportional to the force applied by a human operator. Measurements of human force control in both admittance- and velocity-controlled scenarios were used to quantify force control precision, as well as to find a threshold over which a human cannot control a constant force and determine if that threshold depends on admittance gain or velocity. Experimental results show that robot velocity, not admittance, determines force control precision. Thus, velocities in admittance control systems should be limited to ensure that human force inputs remain precise.