Analysis And Control Of Kinematics Characteristics Of Spatial Mechanism With Clearance Considering Gravity

With the rapid development of space technology,humans had become more and more demanding on the accuracy of space agencies.As one of the main factors causing the nonlinear dynamic characteristics of space agencies,joint clearance had gradually become the focus of domestic and foreign scholars.It was known to all that space agencies were installed and commissioned under the ground gravity environment,but operated under the space microgravity environment.When it was transferred from ground to the space environment,the existence of clearance would affect the kinematics characteristics of the space mechanism and destroy the accuracy.This paper considered both gravity and clearance to study the kinematics characteristics of the driverless clearance hinges and belt-driven clearance hinges respectively.Then,taking a two degrees-of-freedom(DOF)manipulator as the research object,a dynamic model of space manipulator with clearances was established under different gravity environments.And a control algorithm was designed to complete the trajectory tracking control of the space manipulator.The main contents are as follows:Firstly,the simulation of clearance-containing mechanism was carried out.The continuous contact equivalent model and the two-state equivalent model were used to establish the crank-rocker mechanism and the two-linkage mechanism model with clearance.Based on this,the kinematics characteristics of the driverless clearance hinge and belt driven clearance hinge were analyzed under different gravity environments.Secondly,the space mechanism with clearance was correspondingly manufactured as the simulation.The strain measurement method based on flexible cantilever and the laser displacement measurement method based on sensor were used to complete the clearance measurement.The different gravity orientation platform was used to carry out experiments on mechanisms with clearance under different gravity environments and different speeds.And experimental data was processed to analyze the kinematics characteristics of driverless clearance hinges and belt-driven clearance hinges under different gravity environments.Finally,according to the simulation and experimental results of kinematics characteristics clearance joint,the two-state equivalent model was selected to establish the two DOF space manipulator dynamic model under gravity environment and microgravity environment.In addition,a non-singular terminal sliding mode control algorithm was designed and a trajectory tracking control simulation study was performed to verify the effectiveness of the control algorithm.