Research On Bionic Flexible Joint Design And The Active/Passive Control Strategy

Legged robots can achieve non-contact obstacle avoidance and obstacle crossing by means of a discrete ground support walking mode.Therefore,the legged robot has strong environmental adaptability and motion flexibility,and has broad application prospects in disaster relief,military reconnaissance and other fields of national economy and national defense construction.As the direct carrier of the legged robot,the bionic flexible joint coordinately drives the robot to complete various complex bionic behaviors in order to give full play to its efficiency,which directly affects the overall performance of the robot.However,the existing bionic flexible joints are limited by the structural and control bottlenecks,and the prominent problem of poor joint flexibility is widespread,so the ability of the robot to withstand rigid impact and disturbance from external environment needs to be improved urgently.In order to solve the above problems,a new flexible bionic joint with variable stiffness is designed based on the mechanism of flexible bio-joints and cam mechanism,and an active/passive joint flexible control method is proposed in this paper,which realizes the bionic flexibility in the process of joint dynamic motion.The main innovative work of this paper is as follows:Firstly,based on the study of the mechanism of bio-joint flexibility and the characteristics of its physiological structure,a new type of bionic flexible joint with variable stiffness is proposed,which is based on cam mechanism.From the point of view of realizing the function of bionic flexibility,the joint structure system is divided into joint drive system,stiffness adjustment system and output feedback system,and the detailed design structure of each joint system is completed.Secondly,the stiffness model of the bionic flexible joint is constructed through the force analysis of the spatial cam mechanism.Based on the extraction and analysis of joint stiffness model parameters,the main structural parameters and mechanical parameters affecting joint stiffness characteristics are optimized.The effects of stiffness model parameters on joint stiffness are verified by simulation experiments,and the inherent stiffness characteristics and dynamic stiffness characteristics of joint are obtained.Thirdly,aiming at the problem of joint motion control,the active/passive flexible control method of joint is studied.Considering the practical application of bionic flexible joint,the changing rules of joint target trajectory and target output stiffness are proposed.Through dividing gait period,the joint trajectory control strategy and stiffness control strategy are formulated.Based on the linear transformation of joint system and the control idea of fixed stiffness trajectory control in different phases of gait cycle,an active/passive joint flexible control method is proposed,and the hardware and software control system is built.Finally,the test platform of bionic flexible joint prototype is built.The joint stiffness performance experiment is carried out around the joint stiffness characteristics,which verifies the feasibility of the joint prototype structure design and the accuracy of the analysis of the stiffness characteristics of the variable stiffness mechanism.The joint trajectory and stiffness joint control performance experiment is carried out around joint motion control performance,which verifies the effectiveness of the joint flexibility control method.