Maximal acceptable forces for manual insertions using a pulp pinch, oblique grasp and finger press

Abstract

The purpose of this study was to investigate the human limitations for electrical connector tasks common to automotive manufacturing. The study employed a psychophysical and biomechanical methodology and included 24 female participants from a wide range of working ages. Each participant was provided with a total exposure of 27 h to a variety of simulated electrical connector tasks, with at least 18 h of training before final testing. The independent variables in this study were grip type (Oblique Grasp, Finger Press, Pulp Pinch), insertion frequency (2, 7 and 12/min) and wrist posture (Extended, Neutral, Ulnar Deviated). For each trial, participants were asked to exert the maximal force that they would find acceptable at the tested frequency for full eight hour work day. For each trial, the dependent variables were maximal acceptable peak force and impulse. There was a main effect of grip type and frequency for both variables, with no significant effects of wrist posture or age. Oblique Grasps had higher acceptable efforts than both the Finger Press and Pulp Pinch, and the acceptable efforts were observed to decrease with increasing insertion frequency. At the lowest frequency (2/min), the recommended peak force TLVs for Oblique Grasp, Pulp Pinch and Finger Press were 41.7, 28.2 and 26.0 N, respectively. On average, participants selected acceptable peak forces that were 62–63% of their absolute maximum for Pulp Pinch and Finger Press grips and 48% of maximum for the Oblique Grasps. Relevance to Industry Many insertion tasks, like electrical connections, are made in industry using various interfaces between the hand and a part. It is anticipated that the results of this study will further contribute to our understanding of the limits of the hand and arm to acceptably perform such tasks repetitively in manufacturing environments.