Abstract

A series of experiments are conducted to study the influence of mass unbalance, feed force and the presence of an autobalancer. The measured data are analyzed to derive the eight-hour energy equivalent vibration and the number of years of exposure that may cause vascular symptoms in 10% of the worker's population. The results suggest that exposure to hand-transmitted vibration under 510 gm-mm mass unbalance at a speed of 7500 rpm could cause vibration-induced white finger among 10% of the exposed population in approximately 2.8 years. The addition of autobalancer, however, could reduce the eight-hour energy equivalent value to nearly 20%. A preliminary attempt is made to derive a simplified model of coupled hand-grinder system. The model assumes rigid shaft-disc assembly, rigid tool body, linear bearing properties and the handles being attached rigidly to the tool body. A single-degree-of-freedom model of the hand and arm is also integrated along the y and z-axis of the basicentric axis system used in the study. The model results under varying degrees of mass-unbalance suggest that the magnitude of hand-transmitted vibration increases considerably with increasing mass-unbalance and angular speed. The results of the parametric study suggest that bearing damping does not influence the magnitude of transmitted vibration due to considerably higher natural frequency of the shaft-disc assembly. Increasing the damping properties of the hand-handle interface by introducing anti-vibration gloves or handle grips, however, could reduce the magnitude of transmitted vibration. From the results obtained from the analytical and experimental studies, it is concluded that the use of an automatic-balancer is vital to reduce the magnitudes of hand-transmitted vibration.