Research On Mechanism Synthesis And Clearance Dynamics Of Parallel Lifting Mechanism On Stereo Parking Robot

Along with the rapid development of society and economic in China,the living standard of people is daily increasing,possession quantity of cars is increasing rapidly by years,it leads to a serious parking problem.The stereo garage technology solves this problem effectively.However,accidents occurred on stereo garage make some people give up this technology.Security and stability issues become a barrier that worsen and restrict the development of stereo garage.To improve security and stability,this paper focuses on following aspects:Aiming on the type synthesis of parallel lifting mechanism on stereo parking robot,turn the demand of movement problem to the DOF requirement for parallel mechanism.Through investigation,parallel mechanism with a rotational DOF about X axis and a translational DOF along Z axis satisfy the requirement.Based on screw theory,study all the constraint-4 screw system corresponding to 2-DOF parallel mechanism.Therefore,the constraint-4 screw system corresponding to parallel lifting mechanism on stereo parking robot is obtained,and two kinds of limb kinematic chains are obtained.Limb constraint triangle method is proposed for that the limb kinematic chains have no constraint centroids,and the translational DOF along Y axis is constrained,and two kinds of parallel mechanisms which satisfy the requirement are obtained.Flexibility of limb constraint triangle is proposed to compare the two kinds of parallel mechanism,and a proper parallel mechanism is confirmed.Using failure probability,a more stable actuation form of 2-DOF parallel mechanism is confirmed.Aiming at the dimensional analysis of parallel lifting mechanism on stereo parking robot,the kinematic analysis is adopted,including inverse and forward kinematic analysis.Jacobin matrix is obtained through inverse analysis and workspace is obtained through forward analysis.Based on above analysis,isotropy evaluation index for parallel lifting mechanism on stereo parking robot is proposed,it can reflect the isotropy degree of the mechanism with different limb kinematic chains.Meanwhile,singular degree evaluation index and working space index are also proposed.Combining the three indexes,a group of optimal dimensional parameters are obtained.The dynamic analysis of parallel lifting mechanism on stereo parking robot takes the influence of joint clearance into consideration.The joint clearance modeling method is analyzed,and the characters of different normal contact force derived from different contact theories are analyzed,based on modified Winkler contact theory and Flores contact force model,a modified contact force model with higher accuracy is proposed.The Lagrange dynamic model of the mechanism is established,combining the modified contact force model,the dynamic characters of the mechanism with different variables,different actuation velocity,joint clearance value,joint clearance position,coefficient of restitution and loads,are obtained.Based on above analysis and study,an experimental platform is established and different experiments are carried out.The experiment results show that the parallel lifting mechanism on stereo parking robot is effective and above study about the mechanism is correct.At last,the stereo parking robot system is established,the lifting experiments and moving experiments are carried out.The experiment results show the effectiveness of the robot and robot can help release parking pressure.Through the analysis and study,proper configuration of parallel lifting mechanism,optimal configuration size parameters and dynamic characters are obtained.They provide a strong evidence for the improvement on stability and security of the stereo parking robot.