Effect of vibration isolators in reduction of work stress during field operation of hand tractor

The operators of hand tractors experience high levels of vibration in the hand and arm, which cause early fatigue and result in shorter work hours. Suitable isolators were designed and installed in different strategic locations in the hand tractor with a view to reducing the effect of vibration level, and hence reduce work stress. The isolators were evaluated with regard to their performance during actual field tasks involving rota-tilling, rota-puddling and transportation. Field experiments were conducted in a statistically designed layout. Experienced operators were employed for the field tasks. The data collection included frequency-unweighted and frequency-weighted vibration in rms acceleration, frequency response of the vibration and work-related body pain (WRBP). The results indicated that the engine mounting and the handle isolators reduced the vibration acceleration by more than 50%. The characteristics of the isolators were found to vary considerably below 40 Hz. The average reduction of frequency-weighted vibration acceleration (rms) in the X-axis was the highest (35.2%) followed by those in the Z-axis (30.4%), and Y-axis (18.1%). The stress measured in terms of the WRBP was also found to be lower. The values varied from as low as 32% at the hand to as high as 61% at the upper arm.