Ergonomics design of tractor clutch pedal based on biomechanical model

Abstract: Aiming at the problem of driver fatigue caused by insufficient ergonomics design of tractor clutch pedal, the driver-clutch pedal human-computer interaction test system was built in this paper to reveal dynamic characteristics of pedal manipulation and biomechanical characteristics of driver's lower limb. The test results showed that knee and hip joint movement drive pedal rotation, while ankle joint remained in the neutral position with no foot pronation and eversion. In the process of pedal rotation, feedback force of pedal increases approximately linearly. Muscle activation of thigh muscle was significantly greater than that of calf muscle, and calf muscle was mainly used to maintain ankle joint in the neutral position, while thigh muscle drive pedal rotation. Based on characteristics of human-computer interaction of clutch pedal, the tractor driver-pedal musculoskeletal biomechanical model includes main bones and muscle of human body was built in AnyBody biomechanics software. GB 10000-1988 "Human Size of Chinese Adults" and the Scaling-Length-Mass-Fat body size/weight scaling method were used to build tractor driver musculoskeletal biomechanics model. Based on the considering of parallel passive elasticity of muscle, serial elasticity of tendon and fibre angle, Hill muscle model was adopted. In order to solve problem of redundant muscles, inverse dynamics method and maximum/minimum optimization model of muscle activity were used to calculate muscle stress, which considere that the distribution of muscle strength follows the principle of maximum activity minimum optimization. In simulation process of driver's pedal manipulation, kinematics constraints of driver's pedal manipulation motion characteristics were applied to the model, and reliability of the model was verified by the surface electromyography test. Lower limb joint output was put forward to describe comfortable of clutch pedal handling process for different pedal layouts and pedal resistance condition. The influence of pedal ergonomics parameters on driver's pedal handling comfort was analyzed by simulation. With the increase of pedal pretightening torque, driver's driving comfort decreased first and then increased, and the optimum pedal pretightening torque of pedal increased with the increase of vertical/horizontal distance between pedal and seat. The pedal resistance coefficient also directly affected driving comfort of pedal handling. When pedal pretightening torque was less than 7.8 N·m, the maximum limb joint output level decreased firstly and then increased with the increase of pedel resistance coefficient, when pretightening torque was greater than 7.8 N·m, the maximum limb joint output level decreased and then increased with the increase of pedel resistance coefficient. If a driver operated pedal only through knee and hip joint movement, the greater distance between pedal and seat was the more conducive to reduce lower limb joint output. However, when pedal layout exceed the range of lower limb movement, maximum lower limb joint output level increased sharply because of ankle movement. An application case was used as an example to show the correctness of clutch pedal ergonomics design method proposed in this paper. The clutch pedal resistance and its resistance coefficient could be changed by optimizing geometrical size of link between pedal and clutch. Through application case, maximum feedback force of pedal was reduced from 154 to 120 N, and maximum lower limb joint output level was reduced by 20.89%. In next research process, the multi-disciplinary optimization model of clutch pedal mechanism will be studied to obtain the optimal value of clutch pedal design and further improve the driving comfort. The research methods and results presented in this paper will provide reference for ergonomic design of tractor clutch pedal.