On-Orbit Pose Measurement Method Based On Zoom Vision For Space Manipulator

With the increasing frequency of space activities,the space manipulator plays an increasingly important role in spacecraft capture,space rendezvous and docking,and on-orbit equipment maintenance.In order to effectively guarantee the efficiency and reliability of the on-orbit service tasks,the space vision camera is used for target measurement and tracking.It is of great significance to complete orbit task for space manipulator.The mechanism of space manipulator is particularly complex,and the tasks are diverse.the traditional fixed-focus measuring camera cannot solve the problem of working space coverage and image pixel resolution under harsh on-orbit environmental conditions.Therefore,the space zoom camera is used to measure space manipulator end-effector and cooperative target,to adapt to different demands in multi-tasking.At the same time,the method satisfies the high accuracy and real-time requirement of the on-orbit pose measurement.Some key problems of on-orbit pose measurement based on space zoom camera for space manipulator are made,and the main contents include:?.Aiming at the problem of zoom camera measuring modeling and marker parameters,a five-point marker parameter optimization method based on space zoom camera measuring modeling is proposed.The zoom vision imaging model,space coordinate measurement model and single objective pose solution model are established.On this basis,a visual measurement model based on space manipulator is derived,and the parameters of the marker are optimized based on the monte carlo simulation method.Through the simulation experiment,the influence of the marker parameter optimization method on the visual measurement accuracy is evaluated.The results show that the maximal comprehensive measurement error is reduced to 60% of the non-optimal parameter marker.?.Aiming at the problem of space zoom camera on-orbit real-time calibration,a two-step on-orbit calibration algorithm for the separation of internal and external parameters based on space zoom camera is proposed.The coordinate system of algorithm is defined and the related time system conversion method is given.In combination with the visual measurement and celestial measurement method,the internal parameter calibration algorithm of the space zoom camera fixed star image point and the calendar system is established.Based on this,the linear algorithm for the external parameters of the space zoom camera is derived and the optimization iteration of the external parameters can be realized.Finally,the calibration simulation of the space zoom camera parameters is completed.The influence of fixed star image point extraction error,latitude and longitude error,image sampling time error,star quantity and focal length on parameter calibration of space zoom camera is evaluated.Among them,when the fixed star image is 0.1 pixel standard deviation and the number of fixed stars is greater than 20,in the range of focal length,the zoom camera can reach the focal length calibration accuracy of 0.005 mm and the main point calibration accuracy of 4 pixels.?.Aiming at the problem of visual marker imaging wave gate processing based on the dynamic characteristics of space manipulator,a real-time visual marker imaging wave gate prediction algorithm based on model is proposed.In this paper,the pose prediction model of space manipulator end-effector is established by using the space manipulator dynamic model and the unscented kalman filter method.Based on the space circular marker perspective projection model and error analysis theory,the transmission model of the prediction pose of the space zoom camera marker image and the space manipulator end-effector is established.On this basis,the real-time prediction of marking imaging wave gate is realized.The simulation verifies the convergence and the wave gate characteristics of the space manipulator end-effector pose prediction process.Compared with the traditional method without the space manipulator dynamic characteristics,the wave gate prediction method of this paper is better.The marker image points are not easy to overflow.The wave gate is not easy to make overlap and has higher precision.In addition,the image processing area is smaller,which can improve the real-time performance of measurement system.?.The algorithm of the thesis is verified by experiment.An experimental platform based on ground system is set up,and experiments are carried out to verify the parameter calibration algorithm of zoom camera and the parameter optimization algorithm of visual marker.Moreover,measurement of the relative position and attitude of the cooperative target and the space manipulator end-effector is conducted by using the optimized visual marker.Lastly,we give a summary of the correctness and the superiority of the algorithms proposed in this paper.