Development of a tractor operator-operation environment coupled biomechanical model and analysis of lower limb muscle fatigue

For the quantitative analysis and evaluation of tractor pedal operation comfort, this study developed a tractor operator-operation environment coupled biomechanical model in AnyBody Modeling System. First, operator model and operation environment model were generated according to Chinese adult male anthropometric dimensions and Dongfanghong LX804 tractor design parameters. To couple these two models, the connections between operator model's palms, feet, pelvis and operation environment model's steering wheel, joystick, pedals, seat were created. The release scheme of limb joint angle constraints was designed, which allowed limbs to fulfill the kinematic requirement of operating devices. Then, to drive the model, a driver device with a rotation angle range of 0°-42°and a spring with a stiffness of 37.85Nm/rad were added to pedal hinge based on the driving data of pedal force and pedal travel collected by sensors. Subsequently, to validate the model, the surface electromyography signals of lower limb muscles were acquired using the test system of Cometa MiniWave. The average relative error between the lower limb muscle activity calculated from electromyography signals and that computed from the model was 9.2%. Finally, the model was employed to simulate the dynamic process of pedal operation and analyze lower limb fatigue. The results demonstrated that the fatigue exhibited a tendency of first decreasing and then increasing as pedal rotation angle increased, and reached a lower level within the pedal rotation angle range of 8°-17°.