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TECHNICAL PAPERS: Soft Tissue

Estimation of Vibration Power Absorption Density in Human Fingers

[+] Author and Article Information
Ren G. Dong

Engineering and Control Technology Branch,  National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, West Virginia 26505rkd6@cdc.gov

John Z. Wu, Daniel E. Welcome, Thomas W. McDowell

Engineering and Control Technology Branch,  National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, West Virginia 26505

J Biomech Eng 127(5), 849-856 (Mar 23, 2005) (8 pages) doi:10.1115/1.1992526 History: Received July 13, 2004; Revised March 23, 2005

Abstract

The absorption of hand-transmitted vibration energy may be an etiological factor in vibration-induced disorders. The vibration power absorption density (VPAD) may be a better measure of energy than the total power absorption of the hand-arm system. The objectives of the present study are to develop a method to estimate the average absorption density in the fingers and to investigate its basic characteristics. Ten healthy male subjects were used in this study. The biodynamic response of the fingers in a power grip subjected to a broad-band random excitation was measured under three grip forces (15, 30, $50N$) and three push forces (35, 45, $50N$). The response was used to estimate the total finger energy absorption. The response, together with the finger volume, was also used to estimate the amount of tissue effectively involved in the absorption. Then, the average VPAD under constant-acceleration, constant-power density, constant-velocity vibration spectra, and 20 tool vibration spectra were calculated. The correlations between the VPAD and the unweighted and weighted accelerations (ISO 5349-1, 2001) were also examined. The VPAD depends on both the characteristics of the vibration spectrum and the biodynamic response of the finger-hand-arm system. The biodynamic response generally plays a more important role in determining the VPAD in the middle frequency range $(31.5–400Hz)$ than those at the low and high ends. The applied force significantly affected the VPAD. The finger VPAD was highly correlated to the unweighted acceleration. The average VPAD can be determined using the proposed experimental method. It can serve as an alternative tool to quantify the severity of the vibration exposure for studying vibration-induced finger disorders.

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Figures

Figure 7

Correlations among the finger vibration power absorption density and two acceleration measures: (a) frequency-weighted acceleration vs unweighted acceleration, (b) finger VPAD vs weighted acceleration, and (c) finger VPAD vs unweighted acceleration. The results are calculated using 20 tool vibration spectra reported by Griffin (32) and the data are normalized to the values for one of the tools (rock drill).

Figure 1

Measurement of the finger biodynamic response for the estimation of average vibration power absorption density in the fingers: (a) definition of the finger response in a hand power grip on a tool handle, and (b) instrumented handle used for the measurement (28)

Figure 2

Hand posture in the measurement of finger grip volume. The subject grasps a short section of pipe with a diameter equal to that of the instrumented handle. The hand is then immersed to a level marked on the index finger that is in-line with the crease at the base of the subject’s third proximal phalange.

Figure 3

Apparent mass at the fingers measured with ten male subjects: (a) the imaginary component (Mai) of apparent mass (imaginary mass); (b) the real component (Mar) of apparent mass (real mass), and the estimated mass (MFE) effectively involved in the response. Three combined grip (G) and push (P) actions were used in the experiment.

Figure 4

Power absorption coefficient functions under three combined grip (G) and push (P) actions

Figure 5

Accelerations with constant-acceleration, constant-velocity, and constant-source power density, which are normalized to the value at 16Hz

Figure 6

The relative frequency weightings of the four vibration measures [unweighted acceleration, ISO-weighted acceleration, average finger vibration power absorption density (VPAD), and finger vibration power absorption (VPA)] for the three different types of idealized vibration inputs: (a) constant-acceleration; (b) constant-source power density (SPD) acceleration; and (c) constant-velocity acceleration. The weightings are normalized to the value at 16Hz.

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