Characteristics of vibration transmission in the hand–arm system and subjective response during field operation of a hand tractor

Hand–arm vibration, which is transmitted from the handle to the hands, arms and shoulders, causes discomfort to the operator and results in early fatigue. An investigation was conducted to determine the transmission of vibration from the handle of the hand tractor to the metacarpal, wrist, elbow and acromion of the operators under actual field conditions during transportation on a tarmacadam road, rota-tilling in a dry land and rota-puddling in a wet land condition. An aluminium adapter was designed and developed to measure vibration in the hand–arm system of the operators. Parameters such as frequency-unweighted and frequency-weighted vibration acceleration in root mean square (rms) and work-related body pain (WRBP) of operators were evaluated. The vibration transmissibility was computed for various operations. The results indicate that vibration acceleration and posture of operation influenced vibration transmissibility. The maximum transmissibility was observed during the rota-tilling operation with the mean values of 0.91, 0.47, 0.30 and 0.21 at the metacarpal, wrist, elbow and acromion, respectively. The corresponding values during transportation were 0.89, 0.44, 0.24 and 0.12 and during rota-puddling were 0.85, 0.43, 0.22 and 0.18. Resonance at the metacarpal was observed in the frequency range of 31.5–100 Hz. High-frequency vibration (100–1250 Hz) was primarily localised to the hands. The magnitude of vibration was amplified in the dominant axis of vibration, i.e. X-axis during the rota-tilling operation. The average transmissibility in X, Y and Z axes was observed to be 1.01, 0.84 and 0.88, respectively, during rota-tilling. The WRBP was maximum during the rota-tilling operation, followed by transportation and rota-puddling. Maximum pain to the level of 4.9, 3.7 and 3.3 (Borg, CR—10 scale) was observed at the wrist and 4.3, 3.5 and 2.6 (Borg scale) at the hand during rota-tilling, rota-puddling and transportation operations, respectively. Vibration transmissibility and WRBP correlate well during transportation (r2=0.81) as compared to rota-tilling (r2=0.36) and rota-puddling (r2=0.44).