IROS2019国际学术会议论文集 1759

Abstract Successful sampling on the surface of asteroids is difficult because of their weightless environment and unknown material mechanical property This work presents an asteroid sampler based on sweeping and grinding methods to improve the success rate of sampling The sampler uses two brushes rotating clockwise and counterclockwise to collect sample particles on the surface of asteroids When encountering the hard rock or sample particles with large cohesion the sampler adopts a drill bit to grind them to loose samples suitable for collecting by the brushes The interaction between the brushes and the regolith is modeled and the sweeping mechanism is designed A simple grinding mechanism is also designed Numerical simulation and prototype experiments at different parameters including blades number rotational speed and feeding speed of the brushes mechanical property of the sample and gravity were conducted for validating the proposed methods The 280g sampler prototype with 8 blades of brushes could collect about 19g regolith simulant in 25s in earth environment The drill bits could work together with the brushes to improve the sampling efficiency through DEM simulation in case of large cohesion among sample particles The sampler will be a good choice for installing into an asteroid rover in exploration I INTRODUCTION Asteroids may carry evidences of the formation of the solar system 1 The concepts and technologies for resources mining on asteroids had been proposed and studied in recent years 2 Moreover some Near Earth Asteroids pose dangers to our planet The significances of asteroid study have drawn increasing interest from research institutes worldwide The famous exploration missions includes NASA s NEAR 3 Dawn 4 and OSIRIS Rex 5 JAXA s Hayabusa 1 6 7 and Hayabusa 2 8 and ESA s Rosetta 9 10 etc Sampling on asteroids could not only provide sample for scientists to reveal the secrets about the beginnings of life on earth but also help human to avoid the disaster happening on our planet There are some sampling methods proposed for Moon and Mars exploration The methods can be applied for asteroids sampling by proper improvement The methods This work was supported in part by the National Key R the grinding mechanism nearly has no effect on the increase of the sampling mass As the cohesion increases the particles are tightened the grinding mechanism can significantly improve the sampling mass as shown in Fig 9 b and c The sample mass can be improved by 40 by adding the grinding motion in the case of cohesion of 20kPa among particles However from Fig 9 c and d we can find that the effect of the grinding mechanism reduces when the cohesion increases from 20kPa to 50kPa This means that the grinding mechanism can effectively improve the sampling mass when the cohesion is within a certain range The simulation results show the grinding can improve the sampling performance of the sampler B Regolith Collection Testing by Sweeping We tested the performance of the sampler prototype using the platform as shown in Fig 7 a in our laboratory earth environment In the experiments the change of the blade number and rotational speed of the brushes the feeding speed and the sample simulants i e millet particles and carbon powder on the influence of the collected sample mass were studied respectively The densities of the millet particle and carbon powder are 0 88g cm3 and 0 68g cm3 respectively which are the ones used in the DEM simulation as shown in Fig 8 h The sampling depth was set as 5mm for all the tests The testing results are shown in Fig 10 Fig 10 a shows that the mass of the sample with 8 blades has the largest value the sampler with 6 blades collects less sample than the sampler with 4 blades The changing trend is a little different from the simulation results The reason may be that the influence of the number of blades on the sampling mass is small in short sampling time and the influence is obvious as the sampling time increases Fig 10 b shows the sample mass at different feeding speeds vf using the two kinds of sample simulants The changing trend of sampling mass increases first and then decreases which is a little different from the simulation results This may be caused by the decrease of the rotational speed of the brushes in the tests when the resistance torque is larger at higher vf While the rotational speed of the brushes were set as the same ones at different feeding speeds in the simulation The results indicate that the vf should be controlled properly to obtain the maximum sample mass in the actual mission Fig 10 c is the sampling results at the different rotational speeds The changing trend in the experiment and simulation are consistent with each other The larger of the 01234 0 5 10 15 20 Mass g a Cohesion c 0kPa With grinding Without grinding 01234 0 10 20 30 Mass g b Cohesion c 10kPa With grinding Without grinding 01234 0 10 20 30 Time s Mass g c Cohesion c 20kPa With grinding Without grinding 01234 0 5 10 15 20 Time s Mass g d Cohesion c 50kPa With grinding Without grinding Fig 9 Comparison simulation results without and with grinding help during sweeping sample collection at different cohesion among sample particles when the gravity is on the asteroid Phobos 468 8 12 16 20 24 28 a Number of blade n Mass g 0 050 10 150 20 250 3 4 8 12 16 20 24 28 b Feeding speed vf mm s Mass g 300400500 4 8 12 16 20 24 28 c Rotation speed rpm Mass g 300400500 0 4 8 12 16 20 24 28 d Sample material rpm Mass g vf 0 05mm s 500rpm Millet particle vf 0 1mm s 500rpm Millet particle vf 0 2mm s 500rpm Millet particle n 8 500rpm Millet particle n 8 500rpm Carbon powder n 8 vf 0 05mm s Millet particle n 8 vf 0 1mm s Millet particle n 8 vf 0 2mm s Millet particle n 8 vf 0 1mm s Millet particle n 8 vf 0 2mm s Millet particle n 8 vf 0 1mm s Carbon powder n 8 vf 0 1mm s Carbon powder Fig 10 Sweeping performance testing results a Sample mass at different number of blades b Sample mass at different feeding speeds c Sample mass at different rotational speeds d Sample mass at different kinds of sample simulants Fig 11 Sampling mass of two different samples in the experiment 534 blade the more samples are collected because the larger makes the larger initial velocity of the sample particles and the particles are easier to be swept into the sample container We also tested the sampling using different sample simulants The testing results in Fig 10 d indicate that the carbon powder sample simulant has lower collecting efficiency than the millet particles sample simulant Because some carbon powder particles are too small and slip down from the small gaps setting on the blades Fig 11 shows the collected 19 1g of millet particles and 13 9g of carbon powder in 25s by the sampler in the experiments VI CONCLUSION AND FUTURE WORK This work provides an asteroid sampler design concept combining of sweeping and grinding methods Modeling and simulations of the interaction between the brush blades and the regolith sample give guidelines for sweeping mechanism design We designed the sweeping mechanism and grinding mechanism carefully making the sampler small sized and compact shaped In order to learn the dynamic process of the regolith collection we also conducted the numerical simulation by using discrete element method DEM Based on the simulations we selected proper parameters for the sampler design and developed the first generation of prototype The experimental results validated the feasibility of the sampling method We also studied the cooperation between the sweeping and grinding by simulation The results indicate that the sampling efficiency of sweeping can be improved by combining with grinding In the next step of work we will make proper simulant to test the cooperation between the multiple sampling methods We also will design the second generation of prototype with optimized regolith transmission mechanism and sample containers to improve the sample collecting rate The drop tower 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