| Comfort research is essential to the ergonomic design of tractor pedal control system.However,little effort has been made for the comfort analysis and evaluation of the system.Current related research is mainly targeted at the qualitative analysis and subjective evaluation of the static comfort of the operators,while the influencing mechanism of the system comfort remains largely unknown.Therefore,this study focused on the quantitative evaluation of the comfort of the tractor operator’s lower limb-pedal interaction system.A tractor operator-operation environment dynamic coupling model was established using biomechanical simulation software of Any Body Modeling System(AMS).Based on the model,biomechanical loads of the main active muscle groups and joints of the human lower limb in the dynamic environment were computed.Then the effects of pedal design parameters on lower limb biomechanical characteristics were investigated,and a quantitative relationship model between comfort evaluation index of lower limb fatigue and pedal design parameters was also established.Finally,to realize the optimal match of human-machine relationship,parameter optimization and ergonomic design of the system was performed.This study may provide methodological guidance and technical support for the comfort analysis and ergonomic design of human-machine system of agricultural machineryThe primary findings and results of this study are as follows:(1)According to the Chinese anthropometric dimensions and the design parameters of Dongfanghong LX804 tractor cab,an operator musculoskeletal model and an operation environment model were created with AMS software,respectively.To couple these models,several human-machine interaction points between limbs and torso of operator model and steering wheel,joystick,pedal,and seat of operation environment model were added.After that,to drive the model,a rotation driver with a rotation angle range of 0°-42° and a spring device with a stiffness of 37.85 Nm/rad were installed at the model pedal hinge based on the sensor acquisition results of pedal force and pedal travel.Finally,the surface electromyography(s EMG)test system of Cometa Mini Wave was employed to acquire s EMG signals from the main surface muscles of the operator’s lower limb during pedal operation,and the muscle activity(MA)values were calculated.The comparison between the MA predicted from the model and that calculated from s EMG singles revealed that the relative error range was 5%-14%,with an average relative error of 9.2%,which was within the error tolerance of 15%,indicating the validity of this model for analyzing the biomechanical characteristics of lower limb of tractor operator.(2)The dynamic process of pedal operation was simulated based on the model to calculate the biomechanical loads(muscle activity of the dominant muscle groups and the joint moments of three joints)of human lower limbs in a dynamic environment and analyze the dynamic variation pattern of the biomechanical loads of lower limb.The results demonstrated that:(1)in the early stage of pedal operation(pedal angle <8°),iliopsoas was highly active and decreased with the increase in pedal angle;in the late stage of pedal operation(pedal angle >17°),semitendinosus,rectus femoris,and soleus were greatly active and increased as the increase in pedal angle;(2)with the increase in pedal rotation angle,ankle moment increased continuously from 0 Nm,keeping the moment direction in counterclockwise,whereas hip and knee moment decreased first and then increased,and their moment directions changed;(3)the overall muscle activity of lower limb and the overall joint moment of lower limb showed the same changing pattern(they both decreased and then increased with the increase in pedal rotation angle,reaching the lowest level at the pedal rotation angle of 8°-17°),indicating that muscles and joints of the lower limb maintained a consistent biomechanical state during pedal operation.(3)To investigate the influences of pedal design parameters on the biomechanical characteristics of operator’s lower limb,a single-factor simulation analysis experiment was conducted based on the model,with the pedal-seat horizontal distance L,pedal-seat vertical distance H,and pedal spring stiffness k as factors,and muscle activity of the main active muscle groups and joint moments of three major joints of lower limb as indicators.It was found that:(1)parameters L and H considerably affected the biomechanical characteristics of lower limb;when the parameter L≤82 cm(or H≤42 cm),the semitendinosus muscle activity and hip joint moment decreased with the increase in parameter L(or H),while when L>82 cm(or H>42 cm),the semitendinosus muscle activity and hip joint moment abruptly increased with the increase in parameter L(or H);(2)the effect of pedal spring stiffness k was relatively complex;the increasing value of k caused the gradual decrease in iliopsoas muscle activity,increase in the muscle activity of semitendinosus,rectus femoris,and soleus and ankle joint moment,and tendency of first decreasing then increasing of hip and knee joint moments;(3)In general,the overall muscle activity and the overall joint moment of lower limb exhibited the trend of first decreasing and then increasing with the increases in parameters L,H and k,and reached the lowest levels at 82 cm of L,42 cm of H,and 20 Nm/rad of k,respectively;furthermore,the varying patterns of the overall muscle activity and the overall joint moments of lower limb were quite similar,illustrating the consistent biomechanical state of muscles and joints of lower limb.(4)A response surface experiment with three factors was carried out based on the biomechanical coupling model,with pedal design parameters as factors and lower limb fatigue as index.According to the experimental results,the influencing degree of each factor on lower limb fatigue and the interaction between factors was determined,and a quantitative relationship regression model between lower limb fatigue and pedal design parameters was also established.Subsequently,the optimal combination solution of pedal design parameters was calculated based on the regression model with the optimization objective of reducing lower limb fatigue.The optimal range of pedal design parameters was determined as {(L,H,k)|36≤L≤40,72≤H≤76,14≤k≤22}.Finally,the biomechanical models were adjusted to the standard and optimal conditions,respectively,and the changes in the biomechanical characteristics of the lower limb before and after the optimization were analyzed.It was discovered that the overall muscle activity and the overall joint moment of lower limb were reduced by 14.2% and 51.6%,respectively,after the optimization of pedal design parameters,which indicated that the biomechanical loads of lower limb were effectively alleviated.(5)To compare the simulation and experimental results of the overall muscle activity of the lower limb at different factor levels,according to previous experimental schemes of single-factor and response surface simulation experiments,the single-factor and orthogonal experiments of s EMG test were performed based on a platform for tractor simulation driving,with pedal design parameters as factors and the overall muscle activity of operator’s lower limb(obtained from s EMG)as index.The results revealed that:(1)in the singlefactor experiment,the lower limb overall muscle activity obtained from simulation and that from s EMG test showed a consistent changing pattern,and their relative error and Pearson correlation coefficient were in the range of 8.2%-14.3% and 0.90-0.94,respectively;(2)in the orthogonal experiment,the order of influencing degree of each factor on the overall muscle activity of lower limb was: pedal spring stiffness > pedal-seat vertical distance >pedal-seat horizontal distance,which was in accordance with the results of response surface experiment using simulation method;(3)the optimal combination of pedal design parameters were: pedal-seat horizontal distance L=75 cm,pedal-seat vertical distance H=40cm,and pedal spring stiffness k=20 Nm/rad,which was within the optimal range {(L,H,k)|36≤L ≤40,72≤H≤76,14≤k≤22} predicted by regression model.Overall,the overall muscle activity of lower limb obtained from simulation analysis and that from s EMG test showed great correlation at different levels of pedal design parameters. |
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