Telehaptic Perception of Delayed Stiffness Using Adaptive Impedance Control: Experimental Psychophysical Analysis

Telehaptics is the science of transmitting touch-related sensations over computer networks. With respect to robot teleoperation, telehaptics emphasizes more on reliably reproducing physical properties of a remote environment, as mediated over a network through the use of appropriate haptic interfacing technologies. One of the main factors that can cause degradation of the quality of a telehaptic system is the presence of time delays. Inspired by concepts such as impedance-reflection and model-mediated telemanipulation, an adaptive impedance control scheme has been proposed aiming to mitigate some of the problems caused by network delays in a telehaptic system. This paper presents an experimental analysis, which has been conducted to assess the actual performance of the proposed telehaptic scheme in terms of both control and human perception objectives. Firstly, a set of comparative numerical experiments is presented aiming to analyze stability and characterize transparency of the telehaptic system under large time delays. The results show the superior performance of the proposed adaptive impedance scheme as compared to direct force-reflecting teleoperation. Then, a series of psychophysical experiments is described, to evaluate the performance of the telehaptic system with respect to human perception of remote (delayed) stiffness. An analysis of the obtained results shows that the proposed adaptive scheme significantly improves telehaptic perception of linear stiffness in the presence of network delays, maintaining perceptual thresholds close to the ones obtained in the case of direct, nondelayed stimuli. A comparative experimental evaluation of psychometric transparency confirms the superior robustness with regard to time delay of the adaptive impedance telehaptic scheme as compared to state-of-the-art position/force transparentizing methods.