On the discrepancies in the reported human hand–arm impedance at higher frequencies

Abstract

The reported driving-point mechanical impedance (DPMI) characteristics of the hand–arm system exposed to vibration show extreme variabilities among them at higher frequencies. The sources of these discrepancies under z h -axis vibration, particularly above 500 Hz, are investigated using experimental and analytical techniques. Four different handle designs with varying geometric and dynamic properties are considered for characterizing DPMI responses of the handles and hand–arm system using two different measurement methods involving acceleration measurements at the fixture base and in the vicinity of the hand. A split handle design is analytically modeled and integrated with the 3-DOF model defined in ISO-10068 [International Standards Organization, ISO-10068, 1998. Mechanical vibration and shock-free mechanical impedance of the human hand–arm system at the driving point.]. Both the measured and simulation results show that the measurement location and handle natural frequency significantly influence the hand–arm impedance response at higher frequencies. The experiments involving measurements at the fixture base resulted in a sharp increase in magnitude near the resonance, while those near the hand caused the magnitudes at high frequencies to decrease or remain relatively constant. From the model and measured results, it is concluded that reliable impedance responses could be attained up to a limiting frequency that depends upon the measurement location and handle natural frequency. Handle design guidelines are also proposed on the basis of the results. The results also show that the contributions due to handle inertia at higher frequencies cannot be entirely eliminated through mass cancellation. Relevance to industry A good understanding of biodynamic responses of the human hand–arm is essential to effectively control hand-transmitted vibration (HTV) and reduce hand–arm vibration syndrome (HAVS) common among workers. This study systematically investigates the observed discrepancies in the reported impedance response of the human hand–arm at higher frequencies. The study also recommends guideline for the design of simulated handle used in laboratory investigations of hand–arm biodynamic responses to reduce measurement errors caused by handle dynamics and experimental setup.