Research On Motion Control Methods For 6-DOF Space Manipulator

Space technology has become an important standard to measure the overall strength of a country,which attracts the world to strive,and draws more and more attention.Aerospace powers have built their own space stations,as a basis for deep space development,"three-step" strategy of China's space is also being successfully implemented.Space manipulator,as one of the basic space technology,is the foundation to ensure the smooth progress of China's aerospace industry.To develop reliable and practical space manipulators is significant and valuable to the development of both space technology and civilian technology greatly.This paper relies on the project "a small space manipulator prototype",cooperating with the China Aerospace Science and Technology Corporation,to conduct a full range research on 6-DOF(Six Degrees of Freedom)space manipulator motion control;meanwhile,solutions were proposed and verified to solve two existing problems in controlling space manipulators.Considering the lack of efficient and practical space manipulator motion control software system architecture,a software architecture for space manipulator control system based on multithreading and round-robin queue is proposed under the C/S(Client/Server)structure.This architecture is composed of Client part and Server part,respectively taking on different functions.Using the 6-DOF small space manipulator of independent research and development as a platform,details of the architecture implementation process are introduced,and simulation verifications are conducted,which showed that the architecture can meet the actual demand for space manipulator motion control;at the same time,this architecture has nothing to do with platforms or operating systems,and needs little prior knowledge,which can greatly shorten the period and difficulty in development.In view of the lack of economic and effective wide range compliance control methods in gravity environment,a wide range compliance control method in gravity environment based on end F/T sensor is put forward.A real time compensation of the end's gravity with the manipulator kinematics is conducted,to remove the influence of the end's gravity on the F/T sensor measurements,and control the stress of robotic arm's end through the joint space position impedance control strategy.Taking the 6-DOF small space manipulator as an example to introduce the implementation process of this method fully,first of all,the D-H(Denavit-Hartenberg)method is adopted to build the mathematical model of the space manipulator,to establish the position and speed forward/inverse kinematic equations of this manipulator,at the same time,an optimization method for inverse kinematics is proposed to solve the problem of multiple solutions of the position inverse kinematic equation,which is verified in detail,the calculation precision of the position forward/inverse kinematic equations as well.Then,the single node and multi-node space manipulator path planning schemes were designed and verified based on three fundamental manipulator path planning interpolation algorithms.Finally,a real-time gravity compensation algorithm of the end of the space manipulator based on the kinematics was introduced in detail,also,the computer implementation process of this wide range compliance control method,meanwhile,based on the work above,the real-time gravity compensation algorithm and wide range compliance control method in gravity environment are verified.Results show that the proposed method could track the external force in any end position or posture on a large scale,giving the manipulator compliant ability during the whole process of motion control,and remaining stable statically,which makes the operation process of mechanical arms more like biological arms.