Factors affecting hand posture and one-handed push force during flexible rubber hose insertion tasks

This dissertation supports the development of better human performance models as a general design utility for analyzing work tasks by evaluating the factors that affect voluntary grasp selection and axial push force during one-handed hose insertion tasks. Specifically, this work investigated the effect of hose diameter, insertion force, and obstruction location on hand posture and push force for one-handed hose insertion tasks. The following new findings were demonstrated using empirical methods: (1) By twisting the hose during the insertion, subjects were able to reduce the required axial insertion force by as much as 26% compared to the straight method. This decrease in axial insertion force is accompanied by a 60% increase in the muscle activity of the forearm. Similarly, rocking the hose results in a 22% reduction in the axial force with a 27% increase in forearm muscle activity. (2) Hand clearance envelopes increased by 54% and 32% over the straight method for rocking and twisting insertions, respectively, during the active insertion time period. For female subjects, the increases were 64% for rocking and 38% for twisting over the straight method. (3) The relationship between hose diameter, required insertion force, and hand posture suggests that during insertions at low force levels hose diameter drives grasp selection. For insertions at high force levels the forceful requirements of the task dictate hand posture. (4) Maximum push force capabilities were significantly reduced when obstructions were located on the lateral side of the hand during insertion tasks. (5) Two new evaluation methods were successfully developed and implemented as part of this research: (a) Results from a new subjective method for assessing object diameter using trained observers were within 3% of quantitative measurements. (b) A new method, using optical motion tracking hardware, was used to measure rotational movement during actual insertion tasks.; A model is proposed to help engineers and designers apply these data in making decisions with respect to the design of work tasks that will accommodate the widest range of workers on jobs that include insertion activities.