Research On Wheel-Step Mobile System And Wriggling Crawl Strategy Of A Six Wheeled Rocker Type Mars Rover

The surface of Mars is varied and the soil is complex.The large-scale easysinking ground and large-angle soft soil slopes has high probability of occurrence.The existing planetary rover lacks sufficient traction capability and is difficult to complete inspection tasks.In order to obtain a better Rover mobile system,it is necessary to explore new ideas,new theories and new methods.The purpose of this paper is to provide theoretical basis and technical support for the development of Chinese mars rover.The successful planetary rover in the past are all wheeled rover,mostly with spring torsion suspension and rocker suspension.American Mars and Chinese lunar rover all use a six-wheel rocker-type mobile system.Practice shows that this type of mobile system has excellent rugged ground driving performance.Considering the technical inheritance and reliability of aerospace products,this paper develops a Mars wheel-step hybrid mobile system based on a six-wheel rocker mobile system.In this paper,the differential output shaft are no longer consolidated,but are connected by two active walking joints.In order to drive the two joints synchronously using one motor,the two joints are linearly related.The suspension geometry parameters must meet the constraints related to the original wheeled movement function,and wheelstep hybrid movement function.The change in the pitch attitude of the car during suspension deployment is important.The Pearson linear correlation function is as the optimization target of the suspension geometric parameters.The optimization is based on the single objective genetic algorithm.The core of the walking actuator mechanism is a special designed planetary gear train.The performance of the wheel-step hybrid mobile system depends on the interaction between the wheel and the ground,in addition to the suspension deformation performance.The wheels in the wheel-step hybrid movement include driving wheels,wheels getting out of sinkage and anti-return wheels.Existing ground mechanics models can be used for drive wheels and wheels getting out of sinkage.The difference between the brake anti-return wheel and the rotate anti-return wheel is given.Based on the soil shear stress-positive stress relationship,the Rankine soil stress and the Taisha base elastic compaction core idea,the maximum resistance model of brake anti-return wheel is proposed.Through the tests,the difference between the rotate anti-return wheel and the brake anti-return wheel was determined quantitatively,and the influence of soil flow and the accumulation of ground soil is considered.According to the test results,the control expectation of the wheel slip rate for the three types of wheels are given.For climbing large slope and getting out of large sinkage autonomous through the wheel-step hybrid movement,the kinematic model and static model of the mobile system on the rugged terrain are established,and the suspension deformation and wheel-ground interaction in the wheel-step composite movement are integrated.The range of suspension deformation during wheel-step hybrid movement is proposed.The distribution principle of the force from ground to wheels when climbing soft slope and getting out of large sinkage is proposed.The performance of mobile system during creep crawling in front and rear directions is analyzed.Then,the creep crawling control strategy of mobile system in two working conditions is proposed.In order to realize the control strategy,a wheel speed control method based on the wheel slip rate is proposed.In addition to allow the anti-return wheel to enhance the creep crawling performance,it can also enhance the creep crawling performance by improving the wheel-ground contact state.This paper presents a method that lifting the wheel to reduce the subsidence depth.The prototype is built from three aspects: mechanical subsystem,electronic control subsystem and control software.The wheel-step hybrid movement strategy and wheel rotation control algorithm are embedded into the control software.The prototype was used to carry out the wheeled climbing slope test,the wheel-step climbing slope test,the wheel-step getting out of sinkage test,the wheel lifting for reducing sinkage test and the suspension deployment test.The experimental results show that the mobile system meets the design requirements and functional requirements.The traction performance of the wheel-step hybrid movement is much larger than the wheeled movement.The strategy of the creep crawling ability is effective,and the methods for enhancing the creep crawling is feasible.During the suspension deployment process,the change of pitch is small,it meets the task requirements.This paper is based on the main line of prototype development and testing,the development of mobile systems-ground mechanics analysis-system performance analysis-control strategies and methods.The research results can be extended to other wheel-step hybrid mobile systems,and has theoretical guiding significance and engineering practice value for the development and control of Chinese Mars rover.