The Coordinated Compliance Control Of Dual-arm Space Robot For On-Orbit Assembly

With the development of space exploration in the world,the large-scale space structure is the main trend of the future development of space industry.However,limited by the size of the carrier rocket fairing,such large space structures need to be assembled in orbit by modular truss elements.Dual-arm space robot is widely used in the field of on orbit assembly because of its strong operation ability,large working range and stable assembly.In the process of on-orbit assembly,the dual-arm space robot inevitably needs to complete a lot of alignment and screwing operations.However,on the one hand,the traditional servo alignment is based on the accurate calibration of the model,which will cost a lot of time and money.At the same time,due to the influence of the bad space environment,the calibrated results will degenerate,resulting in poor alignment accuracy.On the other hand,the robot will have direct physical contact with the truss structure.The contact force in the process of screwing may cause the truss to shake or deform,resulting in assembly failure.Therefore,it is of great theoretical significance and practical value for the development of on orbit assembly technology to study the coordinated assembly compliance control method for the alignment and screwing operation of dual-arm robot.In this paper,aiming at the problem of servo alignment and compliant screwing in orbit assembly,key technologies such as uncalibrated visual servo alignment control,space dual-arm robot coordinated screwing compliant control and force feedback based screw position and attitude adjustment strategy are studied.Firstly,aiming at the problem of alignment in the process of on orbit assembly,the uncalibrated visual servo alignment control method is studied.The mapping relationship between image feature space and robot joint space is analyzed and deduced,and the uncalibrated visual servo system model is established.Kalman filter is used to identify the model of visual servo system.Based on the design of the target feature depth estimator,the sliding mode control method is introduced to realize the control of the robot.It solves the problem of low alignment accuracy caused by uncertain load inertia parameters,and enables the system to achieve the alignment of trusses in complex space environment.Then,aiming at the problem of screwing in the process of on orbit assembly,the coordinated screwing compliance control method of space dual-arm robot is studied.The relationship among rotation angle,tightening torque and pre tightening force in the process of screw assembly is analyzed to determine the control input of the main arm in each stage of flexible screw assembly.The control input of the slave arm is determined by establishing the constraint model of the coordinated operation of the dual-arm robot.A force/position hybrid control algorithm of space dual-arm robot coordinated screwing force/position is designed.Through the control of tightening torque and angle in different stages,the stable control of pre tightening force is realized to ensure the flexibility between space dual-arm robot and truss in the process of screwing assembly.In view of the uncertain parameters of the system,the adaptive compliance control algorithm is designed to compensate the control errors caused by the system parameter errors and ensure the control accuracy of the screw assembly under the uncertain system parameters.After that,aiming at the problems of vibration,axis dislocation and jamming in the process of screwing,the paper studies the strategy of screwing posture adjustment based on force feedback.The contact state between the truss and the interface is modeled,and the geometric relationship and the force constraint relationship between them are analyzed.On this basis,a flexible screw assembly posture adjustment strategy is proposed to solve the jam problem in the screw process.ADAMS software is used to analyze the vibration characteristics of the pose adjustment strategy,the pose adjustment strategy of minimizing vibration is obtained.On the basis of minimizing the vibration,the problem of jamming in the process of screwing is effectively solved,and the parallelism between the truss and the interface axis is ensured.Finally,the experiment of the coordinated compliance control of dual-arm space robot for on-orbit assembly is discussed.The ground simulation experiment platform was modified to design the uncalibrated visual servo alignment experiment and dual-arm coordinated screw compliance control experiment.The data collected from the experiment are compared and analyzed to verify the effectiveness and practicability of the proposed algorithm.