Vibration Testing for Validating a Reduced-Order Human Impedance Model in Rotational Haptics Interaction

Abstract

Haptic devices are physically coupled to human users, making the mechanical dynamics of the human body an important factor in system stability, transparency, and controller design. While human impedance has been studied extensively in translational interaction, rotational human impedance remains less experimentally validated, especially for single-axis haptic interfaces such as knobs or rotary handles.

This thesis presents a vibration-testing approach for characterizing the rotational dynamics of a human forearm interacting with a motor-driven haptic knob. A single-degree-of-freedom experimental setup was developed to apply torque excitation while measuring motor-side angular position and distributed forearm acceleration. Frequency response functions were obtained using stepped-sine excitation, and the measured responses were used to identify resonance frequencies, damping ratios, qualitative mode-shape trends, and fitted parameters of a reduced-order human impedance model.

The experimental results show two dominant resonance modes at approximately 4.05 Hz and 5.70 Hz, with estimated damping ratios of 0.163 and 0.067, respectively. A two-degree-of-freedom, five-parameter rotational human impedance model was fitted to the measured torque-to-position compliance response. The fitted model reproduced the dominant magnitude-domain resonance structure of the coupled human–device system within the tested frequency band.

These results support the use of vibration-based frequency-domain identification as a practical method for validating reduced-order rotational human impedance models. The identified model should be interpreted as an effective representation for the tested interaction condition, but it provides a useful basis for future stability analysis and controller design of rotational haptic interfaces.