| Tractors are important basic equipment for national economic construction and their ergonomics is an important direction and research hotspot in international ergonomics research in agricultural engineering.However,the ergonomics issues of agricultural machinery has not yet attracted sufficient emphasis,and investigation on the study and evaluation of tractor seats comfort is particularly rare.The existing research mainly carries out qualitative analysis and evaluation of the driver’s static driving posture comfort through subjective evaluation or kinematics methods such as joint angle,which cannot reveal the impact mechanism of the comfort of the human-chair system and the internal mechanism of human comfort/discomfort.Based on this,this study takes the driver’s lumbar musculoskeletal system as the research object,takes the degree of muscle activity,lumbar intervertebral joint pressure and body pressure distribution as indicators,and uses the seat backrest inclination,horizontal distance and vertical height as the main factors to systematically study the influence of seat position parameters on the internal physiological and external characteristic information of the human body,and to determine the optimal seat position parameters.The relevant research results can provide a new idea for the optimization of seat position parameters of agricultural equipment.The main research contents and results are as follows:(1)Tractor operator-operation environment coupled biomechanical model.In this study,a three-dimensional model of the driving environment was established with reference to the internal layout of the cab of Dongfanghong LX804 tractor.Firstly,the driver musculoskeletal model was modified on the GB/T 10000-1988 Chinese Adult Body Size standard,and three typical small,medium and tall human musculoskeletal models were established in accordance with the Chinese adult body size.Secondly,based on Any Body,the human musculoskeletal model H-point was used as the reference point to import and locate the environment model step by step.Support points were added at the thoracic spine,lumbar spine,thigh,ischial tubercle and feet of human skeletal muscle to realize the couple of musculoskeletal model and environmental model and force transfer.Then the ball joint constraints were added to the hand to balance the degree of freedom,and glove joints were added to avoid abuse of rigid body strength.Finally,add the driver’s own gravity load to realize the model load definition.Based on the above methods,the tractor-operation environment coupled biomechanical model that consistent with the actual driving environment and the typical human body size of Chinese adults was constructed.(2)Simulation analysis of the biomechanical properties of the driver’s lumbar musculoskeletal system.In this study,the tractor seat backrest inclination,the horizontal distance of the seat SIP point from the steering wheel SWC point and the vertical height of the seat SIP point were used as research factors.The degree of activity of the driver’s lumbar multifidus,erector spinae,external oblique abdominal,rectus abdominis muscles and the pressure of the lumbar intervertebral joints were used as muscle and joint comfort evaluation indexes.Single factor and response surface tests were designed to systematically analyze the effect of seat position parameters and their interaction on the driver’s muscle and joint comfort.The test results show that under the same operating conditions,the larger driver’s body size,the smaller the overall lumbar muscle activity.Lumbar L1-L5intervertebral pressure gradually increases from top to bottom,in line with the results of the normal physiological structure of the human lumbar spine.The backrest inclination is a key factor that affects the lumbar intervertebral joint pressure.When the backrest angle is optimal,the lumbar intervertebral joint pressure of the three body types of drivers is reduced by about 41.9%,43.2%and 41.6%respectively compared with the initial sitting position.With the minimum overall activity degree and the minimum L4-L5 intervertebral joint pressure as the optimization objectives,the optimization scheme for seats of all types was obtained.For small types,the backrest inclination is 9.7°,the horizontal distance is472.1 mm,and the vertical height is 465.3 mm.Middle type:backrest inclination 13.9°,horizontal distance 495.6 mm,vertical height 485.3 mm.Large body:backrest inclination14.8°,horizontal distance 526.4 mm,vertical height 520.7 mm.The minimum relative error between the simulation test results of the optimal seat parameters and the budget results of the Design-expert response data is 0.368%,and the maximum relative error is 2.785%,reveal that the simulation results are consistent with the budget results,and the seat optimization results determined by the response surface method have high accuracy.(3)Test and analysis of biomechanical characteristics parameters of driver’s lumbar muscle groups.In this study,the surface EMG test technology was used to calibrate the MVC of the driver’s lumbar muscle,which provided a prerequisite for the comparison of muscle activity data.Referred the simulation test design,the EMG signals of the four lumbar muscle groups under various seat parameters were obtained,and the overall activity degree of the driver’s lumbar muscle was calculated through preprocessing and time domain analysis.To prove the reliability of the seat parameter optimization,the activity of the lumbar muscle groups of the three body types of drivers with the optimal parameters of the corresponding seats were collected and compared with simulation consequence for consistency.The comparison revealed that the test results of tall drivers are lower than that of simulation,and the test results of small drivers are higher than that of simulation.Each muscle group has certain error,the minimum relative error is 1.131%and the maximum relative error is 11.632%.The reason is that the EMG signal actually measured by non-invasive surface EMG test method has the effect of muscle overlapping cross interference,and considering the sensor sticking position,ECG signal,external environmental interference and artificial deviation of adjusting seat parameters,there is 5%～15%inherent relative error,It shows that the optimization results of seat position parameters have high reliability and credibility.(4)Research on driver-seat adaptability based on body pressure distribution.To explore the impact of seat position on the driver’s external body pressure comfort,the body pressure distribution method was used to obtain the driver’s body pressure distribution on the backrest and seat-pan.The single-factor and orthogonal tests were designed to study the effect of seat position parameters on the driver’s body pressure distribution with the maximum pressure,average pressure,contact area and seat pressure distribution uniformity evaluation indexes.The optimal combination of parameters for the medium driver’s seat:backrest inclination is 15°,horizontal distance is 485 mm,and vertical height is 490 mm,coincide with the seat optimization parameters selected in the previous study and within the range of the preferred seat parameters.Under this combination of seat parameters,the maximum body pressure is 15.3 k Pa,the average pressure is 3.2 k Pa,the contact area is1446.78 cm~2,the seat pressure distribution uniformity is 6.06,the body pressure distribution cloud map shows that the driver has good contact with the backrest and seat-pan,the overall contact area is larger,the body pressure is evenly distributed,the pressure concentration phenomenon is weak,and the overall comfort is better. |
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