Design And Multi-mode Motion Analysis Of Reconfigurable Spatial Close-chain Wheel-Leg Mechanism

Wheel-leg ground mobile robots have been widely studied and applied because of the stability and high speed of wheel-leg robots and the mobility and obstaclesurmounting of legged robots.However,the existing wheel-leg robot is generally a rigid combination of wheel-type moving mechanism and leg-type moving mechanism,and the complex mechanical structure makes it more difficult to control the robot in actual operation.Based on the above problems,combined with the design method of single ring reconfigurable mechanism,this paper proposes a reconfigurable wheel-leg mechanism with mode switch based on bifurcation characteristics,which reduces the complexity of the mechanical system and control system of the traditional wheel-leg mechanism.In this paper,the bifurcation characteristics,kinematics analysis,DOF calculation,dynamics simulation and prototype experiment of the reconfigurable wheel-leg mechanism are studied.Firstly,based on the single-ring reconfigurable mechanism design method,the Bennett mechanism was evolved into a reconfigurable Bricard mechanism with bifurcation characteristics through investigation and analysis.Combined with the special geometric constraints of the two mechanisms,the parameters of the mechanism were adjusted so that the mechanism contained bifurcation branches which could realize the target trajectory in the period of motion.Then,the two bifurcation branches in the motion cycle were designed as leg mode and wheel mode respectively,and the bifurcation point position between the two branches was designed as the switching point position of mode switching.Secondly,D-H parameter method and SVD numerical method were used to study the kinematics,bifurcation characteristics and multi-mode analysis of the designed Bricard mechanism.Because the mechanism is a single loop over-constrained mechanism,the degree of freedom of the mechanism at bifurcation branches and bifurcation points is analyzed by combining screw theory.Then,the serious interference problem between the connecting rod and the rotating pair under each bifurcation moving branch is solved by means of hierarchical design and adjusting the deviation distance of the rotating pair.Combined with the analyzed degrees of freedom and the trajectory of the rotation pair,the rod model was designed.After completing the model design,the moving performance of the two motion modes was analyzed,including the moving speed and the obstacle crossing expectation of the mechanism in the leg mode.Thirdly,taking the designed reconfigurable wheel-leg mechanism as a mobile unit,a six-legged reconfigurable wheel-leg ground mobile robot is designed.The steering performance,longitudinal slope climbing performance,pose and dynamics of the whole machine are analyzed.The dynamic simulation software was used to simulate and test the whole machine,including linear speed test,steering performance test,vertical wall climbing test and longitudinal climbing test.Through the post-processing function of the software,the motor torque,centroid velocity and centroid fluctuation of the whole machine in each movement mode are measured and compared,so as to summarize the movement mode that the robot should adopt when facing different ground environments.Finally,prototype production and bench test of the designed reconfigurable wheelleg mobile mechanism were carried out,including parameter design and strength check of each connecting rod,rotary joint design,selection of control components,connecting rod processing and assembly and prototype test,so as to verify the feasibility of the design.