Research On Collision Detection Method Of Space Modular Manipulator

With the development of aerospace technology,space robot manipulators play an increasingly important role in the process of human exploration of space.As a widely researched and applied space robot,the space manipulator can assist astronauts or autonomously complete complex and dangerous space operations tasks,such as the construction of space stations,extravehicular maintenance,capturing of unknown targets,and planetary exploration experiments,etc..At the same time,in order to get rid of the interference and limitations of ground gravity and launch technology on the manufacture of large space facilities(such as large aperture space telescopes),it is necessary to develop on-orbit manufacturing projects.As a key part of the smooth development of the project,the space manipulator can complete tasks such as space operations,handling,assembly,and assist in autonomous or semi-autonomous processing and manufacturing.In order to ensure the safe,reliable and effective completion of the above-mentioned space operation tasks,in addition to the dexterity and reliability requirements for the structural design and electromechanical system of the manipulator,its control system is also required to meet high motion control accuracy,robustness reliability,and safety.This topic focuses on the requirements of accurate,efficient,and safe movement of the space manipulator in the process of performing tasks,and is supported by the manipulator trajectory tracking control,dynamic parameter identification,disturbance observer and collision detection research.The collision detection method under the following conditions is studied,and strives to achieve a high-precision,high-robust and stable control system,and at the same time detect and eliminate the collision risk between the robot manipulator and the operator,so as to assist in solving the safety problem in physical human-robot interaction(p HRI).The specific research contents include the following aspects.(1)To improve the dexterity of the manipulator and the interchangeability of joint maintenance and reduce the difficulty of design and manufacture,a hyperredundant space modular manipulator was designed.Then,the link coordinate system of the manipulator is established and the kinematics model is deduced.Based on accurate kinematics derivation,the dynamic analysis of the manipulator is carried out,including the acquisition of the link and joint dynamic parameters of the manipulator and the simulation verification of the dynamic model.Finally,the high-precision trajectory tracking control technology of the manipulator is studied,and a continuous fast reaching law is designed.Simulation results show that the algorithm has the advantages of a smooth output signal,fast convergence speed,and high control precision.(2)As the basis and key technology of the control strategy research of the robot manipulator,the accurate dynamic model is indispensable for various high-precision control methods,efficient motion planning,and collision detection research.To this end,the dynamic parameters of the redundant modular manipulator are identified.Given its relatively low design motion speed,which may not meet the persistent optimal excitation conditions,the excitation trajectory optimization method is improved.The experimental results show that the method can identify the parameters of the dynamic model relatively accurately,and the RMS value of the joint maximum identification torque residual remains within 6Nm,ignoring the influence of measurement noise.By designing a disturbance observer and a band-pass filter to suppress the measurement noise and the friction modeling error when the velocity crosses zero,the requirements for the dynamic model of the sensorless robot manipulator collision detection can be met.(3)To realize the effective collision detection of the manipulator,the contact force between each joint and the environment(mainly refers to the human body)needs to be fed back to the motion controller in real time.Adding additional force/Torque sensors would increase the cost of the system and reduce its reliability.In this regard,a sensorless external force detection method(disturbance observer)needs to be studied.At present,the generalized momentum based-disturbance observers cannot process a fast transient response,noise resistance,and observation accuracy at the same time.This study proposes an improved generalized momentum base linear disturbance observer and nonlinear disturbance observer.By adjusting the monitoring bandwidth and damping required by the observer in real time,the nonlinear disturbance observer has a fast convergence rate of observation error,small estimation error,strong noise suppression ability,and low initial overshoot in disturbance observation.Simulation and experiments show that the designed observer can fully improve the disturbance observation accuracy,realize high-precision external disturbance tracking.It could play an important role in robot collision detection and compliance control.(4)In this study,the above dynamic model and nonlinear disturbance observer are applied to collision detection of robot manipulators.Firstly,the collision response strategy of the manipulator is designed,including emergency braking,zero force,and compliance control.How the robot manipulator can return to normal operation after avoiding the risk of collision is also a research content of this strategy.Then,a dynamic threshold is designed to approximate the lumped disturbance model online.At the same time,a band-pass filter with time-varying bandwidth and damping is designed,which can eliminate the outliers of the observed signal when the speed crosses zero and reduce its influence on the sensitivity of the collision response.Finally,a comprehensive experimental study is carried out on a 6-DOF collaborative robot and a space modular manipulator.Dynamic and quasi-static collision detection experiments on 6-DOF robots show that the robot manipulator can detect collisions effectively.Under the moving speed and effective mass of the manipulator specified in ISO/TS15066,the contact force of quasi-static collision can be detected with a minimum of 19.73 N,and the dynamic collision force can be detected with a minimum of 38.4N.A collision contact force of these magnitude is safe for most parts of the human body.Collision detection experiments on modular manipulators(effective mass < 20kg)show that the proposed collision detection method can ensure safe human-robot contact.In addition,the compliance control experiment based on the disturbance observer is carried out,which shows that the disturbance observer can provide real-time feedback on the external torque and reduce the impedance characteristics of the manipulator.