| During the operation of the tractor,it will inevitably produce strong vibration due to the operation of the transmission system,its own structural characteristics and the unevenness of the farmland.The vibration transmitted to the driver’s arm system through the steering wheel is called hand-transmitted vibration.The driver’s long-term contact with hand-transmitted vibration is likely to cause obstacles to the peripheral circulation,terminal nerve and bone joint muscle movement system,and even develop into the arm vibration disease,a national legal occupational disease,In addition,the frequent turning of the steering wheel by the tractor driver during driving will also cause the accumulation of arm muscle fatigue.The contact of hand-transmitted vibration and the accumulation of muscle fatigue will not only reduce the driver’s work efficiency and comfort,but also threaten the driver’s driving safety.Based on this,this study takes the tractor driver’s arm system as the research object,and takes the vibration transmission rate and muscle activation degree as the index to study the vibration transmission characteristics and biomechanical characteristics of the driver’s arm.The relevant research results not only provide reference for the structure and parameter optimization of tractor steering wheel,but also provide important reference for the occupational health monitoring of drivers and the early diagnosis and prevention of arm vibration disease.The main research contents and results are as follows:(1)Evaluation of tractor steering wheel manual vibration.Based on the ISO 5349evaluation system,this study evaluates the hand transmitted vibration of the tractor steering wheel.The results show that the daily vibration exposure of the tractor steering wheel is 4.257m/s~2,which exceeds the daily vibration exposure limit of 3.5m/s~2 specified in the national standard,and has a high risk of causing arm vibration disease.(2)Analysis of vibration transmission characteristics of driver’s arm.By collecting the vibration acceleration signals of the tractor steering wheel and arm,the vibration transmission rate of the driver’s arm is calculated,and the vibration transmission characteristics of the driver’s arm are analyzed.It is found that the axial vibration of the steering wheel is the main factor causing the arm vibration disease,and the constraint on the vertical direction between the tractor engine and the steering shaft of the steering wheel should be strengthened.Secondly,the wrist joint and elbow joint can absorb the radial and tangential vibration respectively.Therefore,the radial protection of the driver’s wrist should be strengthened,while the tangential protection of the elbow joint should be strengthened.In addition,by analyzing the vibration transmissibility of different percentile drivers’arm measurement points,it is found that the smaller driver’s palm has a stronger amplification effect on the steering wheel vibration;The wrist of larger drivers has stronger amplification effect on low-frequency vibration.Therefore,in engineering practice,small drivers should pay attention to the vibration protection of the palm,while large drivers should pay attention to the vibration protection of the wrist.(3)Construction of finite element analysis model and steady-state dynamic analysis of driver arm.In this study,the finite element analysis model of the driver’s arm is constructed by reverse engineering technology.Firstly,the soft tissue model of the driver’s arm is obtained by three-dimensional scanning technology,and the driver’s arm bone model is established by the biomechanical modeling software anybody;After that,the soft tissue and bone models are loaded into Geomagic Studio software for point cloud processing,polygon processing and surface fitting,and the reverse engineering model is imported into Creo software for materialization and assembly to establish a three-dimensional solid model of the driver’s arm;Then,the solid model is loaded into Hyper Mesh software,the mesh is divided,the material properties are defined,and the finite element analysis model of the driver’s arm is constructed;Finally,the finite element analysis model is loaded into ABAQUS software for modal analysis and steady-state dynamic analysis,and the natural characteristics and vibration response transmission characteristics of the human arm are studied.The results show that the natural frequency range of the first 10 modes of the arm is about 1hz-5hz,which is in good agreement with the literature.In addition,the human arm is more sensitive to low-frequency vibration.The vibration response of the palm and forearm is larger,and it is more sensitive to the vibration in the frequency range of 0Hz-5Hz and 180Hz-185Hz.During operation,try to avoid the vibration of 0Hz-5Hz and 180Hz-185Hz directly contacting the hand,and take key protective measures for the palm and forearm.(4)Biomechanical analysis of the driver’s arm during tractor steering.In this study,the biomechanical modeling software Any Body was used to analyze the reverse dynamics of the tractor steering wheel torsion process and calculate the driver’s arm muscle activation.Firstly,a biomechanical model is established according to the actual measured size of the driver.Based on the model,the process of the driver twisting the steering wheel is simulated,and the muscle activation degree of the main active muscle groups of the arm is calculated.Then,it is compared with the calculation results of the surface electromyography test at the same part of the arm to verify the reliability of the driver biomechanical model.The comparative analysis shows that the relative error range between the muscle activation degree of s EMG test and its simulation analysis results is8.41%-12.34%.According to the literature research,the relative error between s EMG test and simulation analysis results is less than 15%,so the biomechanical model in this study has high reliability.By analyzing the muscle activation degree of the driver’s arm,it is found that the muscle activation degree of the driver’s right arm is significantly greater than that of the driver’s left arm in the process of turning the steering wheel counterclockwise.In the process of turning the steering wheel,the muscle activation degree involved in wrist activities is much greater than that involved in elbow and shoulder activities.Therefore,the optimization should focus on reducing the muscle activation degree involved in wrist activities.In addition,the degree of arm muscle activation basically decreases with the increase of the driver’s body size,and small drivers are more likely to suffer from fatigue during steering.(5)Optimization of tractor steering wheel position parameters based on biomechanical analysis.In this study,the 50th percentile driver biomechanical model was used to analyze the effects of three position parameters on the driver’s arm muscle activation degree:the steering wheel surface inclination,the front and rear distance from the steering wheel midpoint to the driver’s crotch point,and the upper and lower height.Taking the comprehensive muscle activation degree as the evaluation index,the position parameters of the tractor steering wheel were optimized to determine the best position parameter combination of the steering wheel.The results showed that the steering wheel surface inclination had the most significant effect on the comprehensive muscle activation,followed by the height,and the front and rear distance had the least effect on the comprehensive muscle activation.Considering the interaction between the factors,the regression orthogonal test was designed.It was found that when the disc inclination was31°,the front back distance was 431mm,and the height was 375mm,the comprehensive muscle activation of the driver’s arm was the smallest,and the result was 1.2887. |
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