Study On The Pointing Error Modification Methods Based On Three-axis Gimbal With Collimation Axis Eccentricity

The three-axis optoelectronic tracking system is widely used because of itsadvantages of tracking goals in zenith blind zone. The pointing accuracy is one ofthe important performance indicators. In the case of manufacturing accuracy islimited, it would rely largely on the improved the software algorithm to improve thepointing accuracy. Therefore, it would need to analysis in depth the reasons of thepointing error affected the measurement of photoelectric tracking system to establishthe high-precision and high stability of pointing modifying model, in order toimprove the pointing precision of photoelectric tracking measurement system.However, there is no effective pointing error-modified model of the three-axisgimbal yet. To this end, this paper researched the various factors effecting thesystem’s pointing accuracy and the theory and deficiency of the existing error modelbased on analyzing the measuring principle and frame structure of the three-axisphotoelectric tracking system to establish the separate-item modification modelhaving actual physical meaning and high modifying precision. What’s more, thepointing modifying system adopted the separate-item modification model wasproved to be feasible and effective by using simulated data and field measured data.Firstly, the pointing modification system’s overall structure was analyzed indetail and the measurement principle of normal three-axis gimbal was studied in thispaper. It put emphasis up on analyzing quantitatively the measurement error thateffected by the deflection distance of the deflecting three-axis system. Then, theerror source effecting on the pointing precision of the three-axis photoelectrictracking system, which was divided into static and dynamic error sources, wasanalyzed and described in this paper. The static error mainly included spindle error,shaft encoder error and bearing error, the dynamic error was mainly producedbecause of the dynamic deformation and motion tracking. It pointed out thatpointing modification methods could be effective for static system error.Secondly, after studying the fundamental and merits and drawbacks of pseudospherical harmonics model and parameter improved model in the three-axis pointingmodification system, it pointed out the necessity of establishing the pointing modelbased on the frame structure and principle of measurement of the three-axis. Then,the relation of the axis-error and encoder’s error effected on the elevation angle and heeling angle of three-axis frame was analyzed by using the method of quaternionrotating transformation, and establishing the three-axis separate-item modificationmodel having actual physical meaning based on the mapping relation. In the end ofthis part, it used the Monte Carlo method to simulate the model, the simulationresults showed that the separate-item modification model has better correctioncapability. And in the case of known azimuth axis tilts, the model could be appliedto the pointing modification at anywhere of azimuth axis.Finally, using the three-axis separate-item modification model in the pointingmodification system and field experiments showed that in the case of fixed azimuthaxis, the error precision of three-axis system could be controlled in3.5″. Under thecircumstances of fewer stars, the model could also keep higher pointing accuracyand stronger stability. During the three kinds of model, the separate-itemmodification model was better than the parameter improved model, and the pseudospherical harmonics model was worst.