Evaluation method for measuring mechanical impedance of the human hand-arm system under dynamic interaction forces

This paper introduces a time-resolved evaluation method for determining the mechanical impedance of the human hand-arm system under time-varying force conditions within a single continuous test. The method is intended to support the investigation of dynamic hand-arm interaction conditions, while the present proof-of-concept focuses primarily on continuously varying applied grip-force profiles. Conventional impedance measurements, in contrast, are typically conducted at discrete constant force levels and require multiple separate tests at different force conditions. The proposed approach enables the measurement of mechanical impedance for continuously varying force profiles, resulting in increased test efficiency. Experiments were conducted using a test rig compliant with DIN EN ISO 10819:2022. Test subjects were exposed to multi-sine translational vibration in z-direction at frequencies between 10 and 500 Hz, in accordance with DIN EN ISO 5349-1, while performing time-varying applied grip-force profiles. First, mechanical impedance
was evaluated using an established frequency-dependent impedance evaluation method for constant force conditions as a reference. ... mehrIn a second step, the proposed time-resolved evaluation method was applied to determine mechanical impedance under nonstationary force conditions. The results showed strong agreement between the dynamic method and the conventional approach, with a coefficient of determination of R$^2$ = 0.9925 over the investigated frequency range for static grip-force conditions. These findings indicate that mechanical impedance can be reliably calculated under time-varying force condi-
tions, eliminating the need for separate measurements at each force level. This method reduces experimental effort without compromising accuracy and enables future investigations of force‑dependent, time‑varying impedance behaviour of the human hand‑arm system. Furthermore, it enables the representation of mechanical impedance as a time‑resolved curve for different frequencies and varying interaction forces.