Ergonomics Applications of a Mechanical Model of the Human Operator in Power Hand Tool Operation

Abstract

Applications of a new model for predicting power threaded-fastener-driving tool operator response and capacity to react against impulsive torque reaction forces are explored for use in tool selection and ergonomic workplace design. The model is based on a mechanical analog of the human operator, with parameters dependent on work location (horizontal and vertical distances); work orientation (horizontal and vertical); and tool shape (in-line, pistol grip, and right angle); and is stratified by gender. This model enables prediction of group means and variances of handle displacement and force for a given tool configuration. Response percentiles can be ascertained for specific tool operations. For example, a sample pistol grip nutrunner used on a horizontal surface at 30 cm in front of the ankles and 140 cm above the floor results in a predicted mean handle reaction displacement of 39.0 (SD = 28.1) mm for males. Consequently 63% of the male users exceed a 30 mm handle displacement limit. When a right angle tool of similar torque output is used instead, the model predicted that only 4.6% of the male tool users exceed a 30 mm handle displacement. A method is described for interpolating individual subject model parameters at any given work location using linear combinations in relation to the range of modeled factors. Additional examples pertinent to ergonomic workstation design and tool selection are provided to demonstrate how the model can be used to aid tool selection and workstation design.

Keywords:

• eccentric muscle contrations
• human motion and force
• torque reaction force
• upper extremity biomechanical model
• work-related musculoskeletal disorders

Notes

^A H is the horizontal location measured from the ankles to the hand in centimeters.

^B V is the vertical location measured from the floor to the hand in centimeters.

^C Parameters were not measured at this location; Reference 16.

^A Responses were calculated based on the mechanical parameters estimated using the interpolation method.

^A Interpolated from parameter values measured at adjacent locations, Reference 17.

^B The values were obtained from the study reported in Reference 18.