Mechanical impedances distributed at the fingers and palm of the human hand in three orthogonal directions

Abstract

The objective of this study is to investigate the basic characteristics of the three axis mechanical impedances distributed at the fingers and palm of the hand subjected to vibrations along the three orthogonal directions (x h , y h , and z h ). Seven subjects participated in the experiment on a novel threedimensional (3-D) hand-arm vibration test system equipped with a 3-D instrumented handle. The total impedance of the entire hand-arm system was obtained by performing a sum of the distributed impedances. Two major resonances were observed in the impedance data in each direction. For the hand forces (30 N grip and 50 N push) and body postures applied in this study, the first resonance was in the range of 20 to 40 Hz, and it was primarily observed in the impedance at the palm. The second resonance was generally observed in the impedance at the fingers, while the resonance frequency varied greatly with the subject and vibration direction, ranging from 100 to 200 Hz in the x h direction, 60 to 120 Hz in the y h direction, and 160 to 300 Hz in the z h direction. The impedance at the palm was greater than that at the fingers below a certain frequency in the range of 50 to 100 Hz, depending on the vibration direction. At higher frequencies, however, the impedance magnitude at the fingers either approached or exceeded that at the palm. The impedance in the z h direction was generally higher than those in the other directions, but it became comparable with that in the x h direction at frequencies above 250 Hz, while the impedance in the y h direction was the lowest. The frequency dependencies of the vibration power absorptions for the entire hand-arm system in the three directions were different, but their basic trends were similar to that of the frequency weighting defined in the current ISO standard. The implications of the results are discussed.

A Proposed Theory on Biodynamic Frequency Weighting for Hand-Transmitted Vibration Exposure

“…Therefore, W1 ISO represents the frequency-dependency of the biodynamic response of the entire system. This has been confirmed from the fact that the frequency-dependency of the total vibration power absorption of the entire system is similar to the ISO frequency weighting, disregarding the vibration direction [49][50][51] . On the other hand, the frequencydependency of the total VPA (W VPA ) approximately represents the maximum profile of the weightings of the VPAs distributed in the major substructures of the hand-arm system, as also shown in Fig.…”

“…However, the frequency of peak transmissibility could be reduced to below 25 Hz in a grip-only action with a low grip force 52,58) . Because the shear stiffness is usually less than the compression stiffness, the resonance frequency in the direction along a handle axial direction is usually less than those in the other directions 46,51) .…”

A Sequential Approach to the Biodynamic Modeling of a Human Finger

“…The AM was chosen for this study since it emphasizes the low-frequency components of the biodynamic response [11], which are typically found in the fingers' dynamic response. Generally, the AM is defined as [5] AM =̃,…”

“…A comparison was made between the standard and biodynamic methods in [7] and the biodynamic method was found to be practical since it removes the need for the standard handheld palm adapter. The biodynamic-response method originally measured the dynamic responses of the palm only [5,8], but it was recently upgraded to finger-response measurements [9][10][11] as well. The biodynamic-response method is based on the biodynamic parameters, for example, apparent mass, mechanical impedance, and apparent stiffness, which are derived from measurements made on a device subjected to vibration.…”

“…The experimental data used in the models was derived in the form of the apparent mass using a purpose-built measuring device. The device was developed based on our previous research [9,10] as well as the current state of the art from other researchers [11,27,28]. The parameters for each of the models were obtained by data fitting and the search was conducted sequentially: the distal phalanx parameters were derived first, followed by the middle and proximal phalanx parameters.…”