Quasi-passive Biped Walking Robot And Its Control Strategies Study

To achieve human-like stable,efficient and natural gait is always the goal of biped walking robot research.Passive dynamic walking provides a new idea for the realization of high efficiency and natural human like walking and designing more human-like robots.At the same time,the study of passive walking is helpful to understand the human walking mechanism,and it also has a great significance for the rehabilitation of the injured limbs.However,due to the passive robot is extremely sensitive to the initial value and the external disturbance,th e walking stability and diversity of the passive robot need to be further strengthened.The related passive dynamic walking mechanism and the corresponding control strategies need to be further studied.This paper aimed to develop a quasi-passive biped walking robot with stable,high efficiency,natural and diversity gait.The building of dynamic model,mechanical parameters optimization based on walking performance and stability analysis,mechanical structure design and walking control strategy are studied in depth.Build a dynamic walking model with double stance phase which contains body,knee joints and ankle joints.The model contains the double support phase that both feet are in contact with the ground at the same time,and its walking phases are similar to that of human's,so the gait is more natural.To solve the problem that the double stance phase dynamic system is a nonholonomic system with redundant coordinates,the dynamic equations of the double support phase and swing phase are established based on the virtual power principle and Lagrange first equation.Based on the angular momentum theorem and the differential form of the constraint equation,the dynamic equation of the collision phase is established.To solve the problem that the fixed point is more difficult to searching when the number of the state virables is big,using the instance just before heel strike as the Poincare cross section to constructing the Poincare mapping function is proposed.The number of independent variables of the system is reduced from 5 to 3 based on this method,which will improve the success rate of fixed point searching,and reduce the searching time of the cell mapping method which is a traversal method to search the basin of attraction.The fixed point of the model is obtained based on this method,which provides the necessary conditions for the study of the mechanism of passive dynamic walking.Analyze the influence of mechanical parameters on walking performances based on the established dynamic model.Since the length of the foot has a great influence on the cycle of the double stance phase,we combine the foot length and other parameters to analyze their impact on the step length,walking speed,walking cycle,double support phase cycle,knee lock cycle and mi nimum foot clearance.Parametric modeling method is used to model the location and quality of the center of mass,which garantees the correspondence between the results of theoretical analysis and the design process of passive robot.The single step analysis method is proposed to eliminate the influence of the change of the fixed point on the walking performance,which makes the result more accurate.The general rules of the influence of model parameters on walking performance are given,which provide theoretical support for the design of robot structure,and provide effective ideas for the design of control strategy.Using the gait sensitivity norm method to model the location and quality of the center of mass parameters.Based on the gait sensitivity norm method,the influence of structural parameters on the local stability of the passive robot model is studied.Based on the cell mapping method,the influence of structural parameters on the global stability of the passive robot model is studied.Based on walking stability analysis and walking performance analysis results,the parameters of multiple degrees of freedom complex walking model are optimized.Based on the analysis results,the optimal mechanical parameters are obtained,which lays the foundation for the structural design of the passive robot.Design the mechanical structure of the quasi-passive biped walking robot.Give out the design criteria and concrete implementation scheme for the hip joint bisecting mechanism,flexible joint based on the series elastic actuator,knee locking mechanism,and flat ankle joint feet.The correctness of the results of mechanical parameters optimization and the rationality of the design of the quas-passive biped walking robot are verified by dynamics simulation.The control electrical system of the quasi-passive biped walking robot with a data acquisition system and motion control system is designed based on the control requirements.Since the passive robot contains a number of passive joints on which to accurately track the time-varying trajectory of all joints is impossible,design the hip joint and ankle joint control strategies of the passive robot based on the principle of time invariant virtual constraint control principle and flexible joint cascade PID control method.Design the open loop and closed loop control strategy of the hip joint based on theof virtual force constraint principle,which controls the angular velocity of the swing leg and the step length of the passive robot,and reduce the possibility to fall backward or forward of the robot.At the same time,this control strategy makes the swinging leg of the passive robot fully uses its own dynamic characteristics,and reduces the energy consumption of the walking as a result.Design the stance ankle push off control strategy in double stance phase and swing ankle angle control strategy in swing phase in order to adjust the initial angle and angular velocity of the stance leg in swing phase to coordinate the swing leg motion,which will make the passive robot obtain more universal walking gait.Analyze the effects of each control strategy parameters on walking speed,energy consumption and walking stability.The performance of the disturbance rejection and capability of walking speed adjusting of the control strategy are verified by Adams/Matlab co-simulation.Design and build the prototype of quasi-passive biped walking robot and design the control system software.Study the effects of different control parameters on walking performances and determine the proper values for each parameter by several groups of experiments,and verify the effectiveness of each control strategy.Achieve the diverse walking with natural,efficient and stable gait that can reject the external disturbance on some level and adjust the walking speed in a relatively big range finally.