Research On Virtual Decomposition Control Of Redundant Serial-parallel Mechanism Based On Tension Network

The structure based on the tension network has a certain flexibility,and there is no direct contact between the mechanical rods,so the friction between the components is reduced,and the mechanical efficiency is better.Some scholars have designed the serial-parallel mechanism by combining the tension network and the parallel mechanism as a joint.This design is easier to realize the large-scale organization and variable stiffness research,and has great potential.However,the complexity of the structure of the serial-parallel mechanism also brings difficulties in its control research,which is also the difficulty in the research of the serial-parallel mechanism.Virtual decomposition control theory decomposes a complex system into subsystems,and connects each subsystem through the concept of "virtual power flow" to achieve decoupling and reduce modeling complexity.This is to solve the control complexity problem of serial-parallel mechanisms Provides ideas.In this paper,the virtual decomposition control method is used to study the double-layer redundant serialparallel mechanism with tension network.The double-layer redundant serial-parallel mechanism studied in this paper has a total of four degrees of freedom,each of which is connected to the upper platform by a rigid link and a tension network composed of steel ropes to form a tension joint,and is composed of eight pneumatic The artificial muscles are driven to achieve two rotational degrees of freedom.Virtual decomposition control is a model-based control method,so this paper first establishes its mathematical model for the double-layer redundant serial-parallel mechanism to be studied.In view of the complex structure of serial-parallel robots,each layer of the parallel mechanism based on the tension network is regarded as a flexible joint in the kinematics analysis.The kinematics analysis of the parallel mechanism of the flexible joint is performed first,and then the kinematics analysis of the serial-parallel mechanism.Thus,the relationship between the position and posture of the end of the mechanism and the length of each actuator,and the working space of the experimental table are obtained.Newton's Euler method was used to establish the dynamic model of the mechanical system of the experimental platform,and the simulation analysis was carried out,which laid the foundation for the research of the virtual decomposition control of the redundant serial-parallel mechanism.Gravity has an important influence on the large-scale design of the experimental table of the redundant serial-parallel mechanism.Considering the correspondence between gravity and the load characteristic curve of each layer of pneumatic artificial muscle,and the characteristic that the pneumatic artificial muscle can only output in one direction,a force distribution algorithm,at the same time,it proposes the realization method of the degree of freedom of the double-layer redundant serial-parallel mechanism and the overall control strategy of the mechanism.The computational complexity of the dynamic algorithm of the redundant serialparallel mechanism increases sharply with the increase of the number of joints.To solve this problem,a virtual decomposition control method is introduced to reduce the computational complexity and improve the scalability of the model.The concept of "virtual power flow" is used to analyze the stability of the control system.At the same time,the virtual decomposition controller and the inertial parameter adaptive identification module of the double-layer serial-parallel mechanism were built,and related simulation analysis was carried out,which verified that the virtual decomposition control method can be applied to the redundant serial-parallel mechanism.Through analysis of relevant indicators,it is believed that the method can achieve good control effects.