Accuracy/Stability Trade-Off and Hybrid Impedance and Admittance Control for Haptic Devices

Abstract

This paper investigates the use of Hybrid Impedance and Admittance controllers for navigating an accuracy/stability trade-off in haptic devices. Typically, sensitivity to modelling error in Impedance control (IC) and force sensor error in Admittance control (AC) is reduced by increasing the desired impedance parameters. This, however, couples the design of the interaction behaviour to the design of a stable and accurate control system. Instead, we propose that interpolating between IC and AC using methods like Unified Interaction Control can balance the relative sensitivities to modelling error and force sensor error, potentially improving stability in AC in the presence of force delays or improving accuracy in IC in the presence of parametric uncertainty and friction. This is particularly applicable when the haptic device has a high physical impedance (in terms of friction, gear reductions, etc), or when the desired impedance is lower than the physical impedance. Interpolation is demonstrated on a high impedance haptic device for the lower-limbs.