Vibration energy absorption in the hand–arm system of hand tractor operator

Several investigators have suggested that vibration energy absorption (VEA) may provide a better indication of vibration-induced injuries than would a measure of the handle vibration spectrum. An investigation was conducted to determine the VEA per unit time (absorbed power) of hand tractor in actual field conditions during transportation on tarmacadam road, rota-tilling in dry land and rota-puddling in wet land condition. A force transducer was designed and fabricated to measure vibration force in all the three axes of the hand tractor. Parameters such as vibration velocity in root mean square (rms), force and the phase difference between these two quantities were evaluated. The average absorbed power was computed for various operations. The results indicate that the absorbed power was maximum during rota-tilling operation, followed by rota-puddling and transportation with the mean values 422, 346 and 253 mW, respectively. Furthermore, it was highest in the X-axis (189, 346 and 257 mW during transportation, rota-tilling and rota-puddling, respectively) and lowest in the Y-axis (34, 57 and 45 mW during transportation, rota-tilling and rota-puddling, respectively). The absorbed power was maximum in the frequency range from 6.3 to 80 Hz, which lies within the resonance frequency of hand. A linear relationship was observed between absorbed power and body weight of the operator in all the three operations. However, it was highly correlated with hand volume with coefficient of correlation of 0.845, 0.886 and 0.692 on X-, Y- and Z-axes, respectively.