Research On The Motion Performances And Evaluation Methods Of 4-SPS Tensegrity-Based Parallel Mechanisms

Tensegrity-based parallel mechanisms have the characteristics of light-weight,high-strength,easy modeling,deployable,compact structure,geometric nonlinearity,etc.They are widely used in architecture,aerospace,biology,bionics,motion simulation,etc.Compared with traditional parallel mechanisms,tensegrity-based parallel mechanisms contain elastic components such as cables and springs.The introduction of elastic components improves the motion accuracy of the mechanism and enables such mechanisms to have the ability to automatically compensate for motion pair gaps and under drive.Tensegrity-based parallel mechanism has gradually become a hot field of the research of mechanisms.This thesis systematically studied the kinematics,workspace,dynamics and control of 4-SPS(Spherical joint Prismatic joint Spherical joint)tensegrity-based parallel mechanism.The main work and research conclusions are as follows:1)Kinematic analysis of the tensegrity-based parallel mechanism.When the tensegrity-based parallel mechanism is in equilibrium,its potential energy is at a minimum.Based on the principle of minimum potential energy,the kinematic model of the 4-SPS tensegrity-based parallel mechanism is established.Different from the traditional rigid parallel mechanism,the forward and inverse kinematics of the 4-SPS tensegrity-based parallel mechanism are both nonlinear and strongly coupled.In order to solve the forward and inverse kinematics,the kinematic model is reasonably equivalent to an optimization model of the kinematics solution of the mechanism.Based on the artificial fish swarm algorithm(AFSA),the optimization model is numerically solved,and the solutions to the forward and inverse kinematics of the 4-SPS tensegrity-based parallel mechanism are obtained.The results show that the forward and inverse kinematics solutions of the4-SPS tensegrity-based parallel mechanism are not unique,and the artificial fish school algorithm can effectively solve the forward and inverse kinematic solutions of such kind of mechanism.2)The workspace and sensitivity analysis of a tensegrity-based parallel mechanism.The workspace of a tensegrity-based parallel mechanism is not only constrained by geometric scale,but also by energy constraints introduced by elastic components.Taking into account these two constraint conditions,a model for computing the workspace of the 4-SPS tensegrity-based parallel mechanism was established.The workspace of the mechanism was calculated using a polar coordinate search algorithm,and the sensitive characteristics of the workspace to scale parameters such as rod length,rod diameter,spherical pair rotation angle,and upper to lower platform radius ratio were systematically studied.3)The dynamic characteristics and control algorithms of the tensegrity-based parallel mechanism.Based on the Lagrangian equation,a dynamic model of a 4-SPS tensegrity-based parallel mechanism was established,and the dynamic model was numerically solved using the Runge Kutta algorithm.Given the driving force,the under-actuated and fully actuated motion laws of the mechanism were studied separately.A method on the basis of neural network and PID control was proposed to study the motion error of the mechanism.The research results indicate that the 4-SPS tensegrity-based parallel mechanism has a certain motion law for the given four inputs.By learning and adjusting PID parameters through neural networks,the motion error of the mechanism can be reduced to 0.01%.Tensegrity-based parallel mechanisms have considerable application potential in the fields of motion simulation and spatial docking.The work of this thesis can provide basic analytical methods and numerical experimental data for the design and application of 4-SPS tensegrity-based parallel mechanisms,which lays a theoretical foundation for the further wide application of such mechanisms.