Upper-limb Geometric MyoPassivity Map for Physical Human-Robot Interaction

TL;DR

This study introduces the Geometric MyoPassivity (GMP) map, a novel real-time measure of the upper limb's energy absorption capacity during physical human-robot interaction, based on electromyographic feedback and passivity concepts.

Contribution

It is the first to analyze the frequency-dependent passivity map of the upper limb with real-time muscle co-activation control using EMG feedback.

Findings

Correlation between EMG and EoP was observed.

Increasing frequency altered the energetic behavior.

GMP map can quantify passivity margin in real-time.

Abstract

The intrinsic biomechanical characteristic of the human upper limb plays a central role in absorbing the interactive energy during physical human-robot interaction (pHRI). We have recently shown that based on the concept of ``Excess of Passivity (EoP)," from nonlinear control theory, it is possible to decode such energetic behavior for both upper and lower limbs. The extracted knowledge can be used in the design of controllers for optimizing the transparency and fidelity of force fields in human-robot interaction and in haptic systems. In this paper, for the first time, we investigate the frequency behavior of the passivity map for the upper limb when the muscle co-activation was controlled in real-time through visual electromyographic feedback. Five healthy subjects (age: 27 +/- 5) were included in this study. The energetic behavior was evaluated at two stimulation frequencies at eight interaction directions over two controlled muscle co-activation levels. Electromyography (EMG) was captured using the Delsys Wireless Trigno system. Results showed a correlation between EMG and EoP, which was further altered by increasing the frequency. The proposed energetic behavior is named the Geometric MyoPassivity (GMP) map. The findings indicate that the GMP map has the potential to be used in real-time to quantify the absorbable energy, thus passivity margin of stability for upper limb interaction during pHRI.