Motion times, hand forces, and trunk kinematics when using material handling manipulators in short-distance transfers of moderate mass objects

The risk of musculoskeletal injury associated with manual materials handlin g tasks has led in part to the use of material handling manipulators, yet t here is limited empirical data to facilitate selection, design, and evaluat ion of these devices. A laboratory study of two types of mechanical manipul ators (articulated arm and overhead hoist) was conducted of short-distance transfers of moderate loads, and the influence of various task parameters a nd transfer method on motion times, peak hand forces, and torso kinematics was obtained. Use of manipulators increased elemental motion times for symm etric sagittal plane transfers by 36-63%, and asymmetric transfers (in the frontal plane) by 62-115%, compared to similar transfers performed manually . Peak hand forces were significantly lower with both manipulators (40-50%) , and approximately 10% higher for asymmetric versus symmetric transfers. O verall torso kinematics were grossly similar with and without a manipulator . These results suggest that for self-paced job tasks, moderate mass object s will be transferred slower over short distances and with lower levels of external (hand) forces when using mechanical aids. These simple effects, ho wever, were influenced by object mass and transfer height. (C) 2000 Elsevie r Science Ltd. All rights reserved.