Some Ergonomic Considerations in the Design of Materal Handling Devices

Abstract

Material handling devices (MHD's) are being proliferated in factory workplaces to prevent workers from being injured due to the lifting of heavy loads. These devices require exertions which have not been adequately studied from an ergonomic perspective. Jobs with MHDs often require complex 3-dimensional movements and loaded axial rotation. One type of MHD, an articulated arm, was used to investigate the effects of inertial load, arm joint friction, and positioning accuracy requirements. The kinematic variables of peak push and pull hand forces, velocities, and accelerations were measured or computed in both a task that allowed sagittally symmetric postures as well as one in which loaded axial torso rotation was required. Greater inertial loads increased the peak push and pull hand forces in all cases by an average of 20%. The activation of a 40 psi brake at both joints of the articulated arm increased the peak hand forces by about 40% on average and decreased the peak velocities and accelerations in both tasks by about 20% and 15% respectively. The effects of positioning accuracy required were not as universal. There was a 10% decrease in peak velocity and acceleration for smaller target size in the sagittally symmetric task but no significant effect in the torso twisting task. The study generated some guidelines for the implementation of MHD's, and suggests some areas where further research is required.