Comparing series elasticity and admittance control for haptic rendering

Abstract

While feedback control can be used to cause a motorized device to render the dynamic behavior of a virtual environment, this capacity inevitably breaks down at high frequencies where the rendered impedance reverts to the impedance of the device hardware. This situation amounts to a disadvantage for admittance display, for which hardware impedance is high. Series elastic actuators offer an attractive alternative with lower impedance at high frequencies, though stability considerations impose limits on the stiffest virtual environment that may be rendered. In this paper we explore the tradeoffs between admittance control and series elastic actuation with the use of analytical comparisons in the frequency domain backed up by experiments and complemented with a passivity analysis that accounts for an excess of passivity contributed by human biomechanics.