Harnessing the Power of Human Biomechanics in Force-Position Domain: A 3D Passivity Index Map for Upper Limb Physical Human-(Tele)Robot Interaction

In the context of physical human-(tele)robot interaction, passivity-based stabilizers have been used to guarantee the physical or (tele)physical stability. In most of these examples, human biomechanics is considered an inherently passive system that dissipates energy. This assumption may not hold true when the interaction is implemented in the force-position domain, even though such a setting would be needed to boost positional accuracy and avoid the common kinematic drifts in the force-velocity domains. The aforementioned topic is examined in this paper using the concept of shortage versus excess of passivity index for human biomechanics in the force-position domain. We also investigate the compounding effect of the frequency of interaction. The outcomes of this paper will be imperative for the design of force-position domain pHRI stabilizers when the classical assumption of passivity of human biomechanics can lead to serious safety issues. In this work, for the first time, we quantitatively present the passivity margin and, thus, the energetic behavior of the human arm's biomechanics under various interaction scenarios in the Force-Position domain. The outcome of this work includes a three-dimensional passivity index map (3DPiM) that is validated on five healthy participants. The goal is to illustrate the passivity margin of the human upper limb biomechanics for two distinct levels of muscle co-contractions, as indicated by the Electromyography (EMG) signal, across four interaction frequencies and eight geometric directions. This outcome enables the future development of biomechanics-aware stabilizers in the force-position domain, quantifying the passivity margin in real-time and thus significantly reducing the stabilizer's conservatism while ensuring the safety of humanrobot interactions.