Translated Abstract
Clearance joint widely exists in robot, medical apparatus, engineering machinery, aerospace，biological engineering and any other fields. The contact, friction and wear of clearance joint have a significant impact on the dynamic performance, positioning accuracy, reliability and lifetime of mechanical system. As we all know, the lower limb exoskeleton robot is an important rehabilitation equipment, and the basic structure of the lower limb exoskeleton robot is mainly classified into the direct-drive exoskeleton system and the exoskeleton system based on the slider-crank mechanism. The structure of direct-drive exoskeleton system is relatively simple. Therefore the exoskeleton system based on the slider-crank mechanism is taken as the main research object to conduct the coupling research on dynamics and tribology of clearance joint. The related research achievement has great theoretical significance and socioeconomic value for the design and development of the same-type mechanism. The main content can be divided into three parts.
Firstly, the dynamics analysis of mechanism with clearance joint in lower limb exoskeleton robot is researched. The massless spring damping model (MLSD) is introduced to conduct inverse dynamics analysis of slider-crank mechanism with clearance joint. The perturbation method is adopted to solve the nonlinear dynamics equations. Moreover, the forward dynamics of slider-crank mechanism with clearance joint is also analyzed based on MLSD model. The correctness of MLSD model is verified in comparison with the simulation results based on massless link model and ideal constraint condition. The dynamics analysis under different conditions is conducted based on MLSD model and massless link model respectively, such as different rotation speed and different initial clearance size and so on. The comparison analysis indicates that the MLSD model reflects the contact process between pin and bushing accurately when the initial clearance is large and the rotation speed is high, and the dynamics analysis based on MLSD model has a good calculation accuracy.
Secondly, the contact pressure distribution model under high conformal contact condition and coupling analysis of dynamics and tribology are researched. A non-linear contact pressure model (NLCP) is proposed based on the discretization thought. The NLCP model not only describes the nonlinear deformation characteristics of contact area, but also provides a way for solving the contact pressure under high conformal contact condition. Then, the coupling analysis framework of dynamics and tribology of system with clearance joint is established based on the algorithm of MLSD&NLCP. The correctness of MLSD&NLCP algorithm is verified by simulation analysis and experiment research. Moreover, the MLSD&NLCP algorithm obtains a better accuracy than the massless link model&A-Winkler model. The effect of rotation speed, wear cycles, initial clearance and contact stiffness on the system with clearance joint is studied. The results show that there is a positive correlation between the wear behavior of system with clearance joint and state characteristics, such as the rotation speed and the wear cycles of system. There is negative correlation between the wear area and contact characteristics, such as the initial clearance size and the contact stiffness. The lager the initial clearance, the deeper the wear peak. However, when the contact stiffness becomes large, the wear peak will decrease if the rotation speed is high.
Finally, the simulation analysis and experiment research of mechanism with clearance joint in lower limb exoskeleton robot are conducted. The specific structure of real lower limb exoskeleton robot is studied. Then according to the experiment results of step analysis, the experiment device of lower limb exoskeleton robot is designed in the form of slider-crank mechanism. A comprehensive experimental study on wear analysis is presented with different initial clearances, different speed and different wear cycles. The correctness of MLSD&NLCP algorithm in coupling analysis of lower limb exoskeleton robot is verified by experiment results, which is important to the reliability and lifetime prediction. Then, the effect of clearance on the system performance of lower limb exoskeleton robot is analyzed. And the related research ideas of structure design and control system design are proposed for lower limb exoskeleton robot.
In conclusion, several problems in the coupling analysis of multibody system with clearance joint are studied through dynamics analysis, contact and friction mechanism research and coupling method research. The coupling analysis framework of dynamics and tribology of system with clearance joint is established based on MLSD&NLCP model. The effect of clearance joint on dynamics performance is illustrated. The influence rules of state characteristics and contact characteristics in the coupling analysis of system with clearance joint are revealed. Otherwise, the coupling analysis algorithm presented in this thesis has enhanced the calculation accuracy with a good efficiency. In general, the theoretical research results obtained by this thesis have important significance for the system design and the reliability calculation of lower limb exoskeleton robot.
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