Linear modeling of human hand-arm dynamics relevant to right-angle torque tool interaction

Area of Science:

• Biomechanics
• Human Factors Engineering
• Occupational Health

Background:

• Powered torque tools are essential in manufacturing but pose risks of upper extremity musculoskeletal injury due to repetitive operator exposure to impulsive forces.
• Understanding the dynamics of the human hand-arm system during tool use is crucial for mitigating these risks.

Purpose of the Study:

• To evaluate a novel protocol for identifying stiffness, mass, and damping parameters of the human hand-arm system during right-angle torque tool use.
• To assess the accuracy and applicability of a linear model for human hand-arm dynamics in this context.

Main Methods:

• A new testing apparatus was developed to simulate biomechanical exposure during torque tool operation.
• Forty experienced operators were tested to determine model parameters and validate the protocol for physical capacity assessment.
• A second-order hand-arm model was employed, with parameters extracted using time-domain system identification.

Main Results:

• The time-domain parameter extraction method met a 5% accuracy criterion for time-to-peak displacement error in 93% of trials, outperforming the frequency-domain method (75%).
• Average errors for time-to-peak handle displacement and relative peak handle force were minimal (0.69 ms and 0.21%, respectively).
• Identified model parameters were significantly influenced by operator gender and working posture.

Conclusions:

• The developed protocol and numerical procedures offer a viable alternative for assessing mechanical parameters in right-angle torque tool use.
• Time-domain system identification demonstrated superior performance for parameter extraction compared to frequency-domain methods.
• Future applications include in situ parameter identification and simulation for developing safer torque tools focused on operator health.