| Lunar exploration is becoming an important part of national deep space exploration program.Lunar rover is the detection platform,which has been be widely used in in the exploration missions.The environment on the Moon is complicated,such as soft surface and low gravity,and probe rovers has the characteristics of light weight and small size,which made rovers is easy to sink,skid and even get stuck.Therefore,an intensive study on trafficability of exploration rovers under the lunar environment is essential,which is significant for the development and performance evaluation of lunar rovers.Wire mesh wheel(hereinafter referred to as WMW)has reticular structure of tread,which can avoid the dust accumulation when working on the soft terrain.Wire mesh wheel has also been applied to the Moon and Mars exploration missions,because of the advantages of light weight and superior stability.The tractive performance is the important component of the rovers' trafficability,but a comprehensive research on performance of WMW on deformable terrains has not been conduct.Limited to the equipment condition,most studies on wheel-soil interaction of the lunar rover were conducted under ground gravity condition.Hence,it is necessary to investigate the wheel-soil interaction under light weight condition,which is significant to improve the lunar rovers' trafficability,and ensure the success of the exploration mission.Based on the terramechanics theory and preparation method of the planetary simulation regolith,the light weight soil bin testing system was developed.Research on the pressure-sinkage and traction trafficability performance of the WMW has been conducted taken lunar simulation regolith JLU-2b as testing medium,and pressure-sinkage and sinkage models were established under light weight testing condition.A scaling model rover based on similarity theory,and the study on traction trafficability performance of the model rover was conducted based on terrain-machine system theories and methods,and the prediction models of sinkage and drawbar pull were established.The slip ratio and apparent sinkage were extracted from the wheel rut,The influence of lunar simulation regolith state and wheel load on the wheel real and apparent sinkage were analyzed under different slip ratio condition.The study on non-parametric estimation method of lunar simulation regolith mechanics state was carried out,the assessment and verification analysis on the sinkage were conducted based on the mechanics estimation results of the simulation regolith.The concrete research content is as follows.The research on preparation method and impact characteristic of the planetary simulation regolith were conducted,based on the mechanics test of the planetary simulation regolith and wheel-soil experiments.The planetary simulation regolith was classified as three states by non-parametric compactness,and defined as loose,natural and compact state.The preparation estimation method was obtained based on bulk density and penetration resistance.The relative error of bulk density measurement was less than 3.4% in the estimation method tests.The maximum of penetration resistance was 300kPa(loose state)?600kPa(natural state)and 1500kPa(compact state),and its relative error not exceeding 10%.The penetration resistance range of simulation regolith contains the upper and lower value of the lunar soil,therefore,the simulation regolith after preparing can be used in the soil bin experiments.The impact characteristics tests were conducted by using six types of soil under natural and compact state,including lunar simulation regolith JLU-1b,JLU-2b and TJ-1,Gobi sand soil,quartz sand,and Martian simulation regolith JLU Mars-1.The impact depth,acceleration and impact force were compared analyzed between different types of soil,and the impact depth model was established related to the impact depth and footpad diameter.The research on trafficability of the WMW under light weight condition,contrast tests were conducted by using a normal cylindrical wheel(hereinafter referred to as CW).The pressure-sinkage characteristics of the WMW under quasi-static condition was analyzed,found that sinkage of the WMW was larger than that of the CW,and the average increase in the ratio of the static sinkage was 15.2%.The pressure-sinkage curve of the WMW was obviously influenced by soil particle size,shape and distribution.An improved pressure-sinkage model for the WMW was established,and a modified quasi sinkage model was also obtained.The improved pressure-sinkage model verification indicated that the relative error of the model prediction was less than 13.6%.The sinkage characteristic of the WMW was analyzed.The wheel sinkage under loose state was increased by 15.4% as compared with that under natural state.The sinkage increases with the increase of wheel load,and the average increase ratio was 15.2%.The sinkage model was established related to the wheel load and velocity.The traction trafficability of the WMW was analyzed.The simulation regolith state affected the driving torque of the WMW more obvious than that of the CW.The driving torque and drawbar pull of the WMW increased by 14.4% and 16.7%,respectively,when the simulation regolith changed from loose state to natural state.The driving torque and drawbar pull of the CW were larger than that of the WMW,and the average increase ratio were 45.2% and 32.3%,respectively.The maximum tractive efficiency of the WMW was 0.29 when the slip ratio was 21.2%.The maximum tractive efficiency of the CW was 0.21 when the slip ratio was 17.9%.When the slip ratio was up to 60%,the tractive efficiency of the WMW was below 0.13.Hence,the slip raio should be controlled at about 20%,which make ensure that the lunar rover has a better trafficability.The research on the traction trafficability of the scaling model rover based on similarity theory was conducted.The sinkage and traction characteristics of the scaling model rover on the different type soil were analyzed.When the model rover drove on the simulation regolith,the sinkage and maximum drawbar pull were larger than that on the quartz sand.Based on terramechanics theory,this study adopted linearization technique of the wheel-soil contact stress,a new prediction model of the drawbar pull was established.The average relative error between predicted and experimental value was 8.6%.The influence of the velocity and slope on the traction trafficability of the model rover was analyzed.The wheel slip ratio of model rover increased with the increased of the slope,and there existed a quadratic relationship between the slip ratio and slope.The velocity affected the slip ratio significantly smaller than the slope.The average error fluctuations of the slip ratio caused by the velocity were 9.0%(front wheel)?8.9%(middle wheel)and 8.7%(rear wheel),respectively.The sinkage of the front and middle wheel increased with the increased of the slip ratio,and their changing rule were basically consistent.The maximum sinkage of the rear wheel was 13.6mm(18.1% of the wheel radius),which was obviously smaller than that of the front and middle wheel.When the slope value was 20 degrees,the slip ratio of the front and middle wheel were up to 65%,the simulation regolith on the slope presented landslip phenomenon,the trafficability of the model rover performed worse and it was at risk of getting stuck.When the slope value was 25 degrees,the sinkage of the front and middle wheel was 33.1mm(44.1% of the wheel radius)and 33.9mm(45.2% of the wheel radius),respectively,and the slip ratio reached 90%.In the tests,the ultimate climbing slope of the rover was 25 degrees,therefore,the maximum exploration slope within 25 degrees was safe,when considered reasonable power consumption and trafficability of the rover.The research on the sinkage of the scaling model rover based on the rut non-contact measurement was conducted.The sinkage tests on the soil bin under different slip ratio were conducted,and this study was focused on the rut of the rear wheel.The slip ratio and apparent sinkage were derived from the non-contact measurement of the rut morphology.The influence of the simulation regolith state,wheel load and slip ratio on the real and apparent sinkage of the front and rear wheel were analyzed.The results indicated that the real and apparent sinkage affected more obviously by the wheel load than that of the simulation regolith state.The real sinkage models of the front and rear wheel were established related to the load and slip ratio,the root-mean-square error between predicted and experimental sinkage value was less than 2.4mm,and the average relative errors were within 10%.The real sinkage models of the front wheel was established related to the apparent sinkage and slip ratio,and the real sinkage models of the rear wheel was established related to the apparent sinkage,the root-mean-square error between predicted and experimental sinkage value was less than 2.1mm,and the average relative errors were within 15%.The influence of evaluated error on prediction accuracy of the models was analyzed,including the load,apparent sinkage and slip ratio.The results indicated that the prediction error caused by the load was less than 9.9%,and for slip ratio was 12.1%.The estimation method on mechanics and sinkage characteristic of the simulation regolith was studied.The remote measurements which influenced the wheel real sinkage of the lunar rover were analyzed,including the apparent sinkage,wheel load and slip ratio.Twenty binary and ternary identify parameters for the simulation regolith estimation was derived,and estimation criterion was also established.Non-parametric estimation for the mechanical state of the simulation regolith was carried out,corresponding estimation method was derived based on the remote measurements.The identification accuracy and conservation ratio were analyzed,and the optimal terrain identify parameters and criterion were obtained.Results show that the identification accuracy and conservation ratio was 50% and 67%,respectively,when the identify parameters contained the slip raio.The identification accuracy and conservation ratio was up to 83% and 100%,respectively,when the identify parameters formed by the wheel load and apparent sinkage.The process of the real sinkage estimation was analyzed,the estimation method of the sinkage was carried out.The deviations between models prediction and experimental value ranged from-6.3mm to 3.0mm,and the relative errors were less than 18.5%,and the root-mean-square errors were within 3.2mm.The sinkage models and its estimation method could well predict the sinkage of the rover in current region.In this paper,the sinkage models on the simulation regolith were established,the prediction method on mechanics and sinkage characteristic of the simulation regolith was studied,and the model and method successfully applied in parameter identification of the lunar soil,the prediction for trafficability of the planetary exploration rovers.This research results provided technical guidance for ground test,performance evaluation and technical support of the planetary exploration rovers. |
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