Design And Research Of Measuring Device Of Star Sensor Auto Focusing System

When the optical star sensor of infinite distance imaging system is assembled,the CCD receiving device is fixed after it.In order to achieve the most clear imaging of the CCD receiver.The image plane position of CCD needs to be coincident with the focus position of star sensor.The existing methods is installing a certain thickness of trim ring between the flange face of the star sensor and the flange face of CCD receiving device.The fixed CCD receiving image plane position can be found through the manual method to trial and test repeatedly.This implementation method is inefficient and the precision can not be guaranteed.In order to change the present situation of the manual test in the development of the optical system in China,improve the production efficiency and precision of the optical system development,it is important to carry out the research of auto focusing measurement technology.So aiming at the actual demand of the alignment process of star sensor,an automatic focusing system is designed to accurately measure the working distance of the sensor based on auto focusing technology and error compensation technology.The system realizes the reasonable control of the error precision based on the coupling error theory,real time compensation of error is done based on PID controller algorithm.And the positioning precision of the system is improved,fast and accurate measurement of the working distance of star sensor can be made.So the accurate size thickness of trim ring required can be gotten.And the system precision reaches the design requirements.The main research contents are as follows:Firstly,automatic focusing system is designed.According to the functional requirements,the system is divided into four modules: target and light source system,infinite distant target generation system,automatic focusing measuring device,automatic focusing control system.The design of automatic focusing system measuring device is focused,the measuring device mainly consists of linear guide rail,precision displacement stage,detection bracket,CCD camera and so on.Three dimensional precision motion of CCD camera and acquisition of imaging can be realized.Linear guide rail,electric control precision displacement stage,manual precision displacement stage and so on is selected.The specific selection basis and detailed parameters of parts are analyzed,the length of linear guide rail 500 mm,the measurement range of precision electronic displacement is 100 mm,and the load torque is 6Nmm.The design of the mechanical structure of the measuring device of the automatic focusing system is designed by using the drawing software.The detailed dimension parameters of the mechanical structure are determined.And the assembly process of the auto focusing system is completed.Secondly,the three-dimensional model of the automatic focusing system for measuring device is established based on statics and dynamics theory,static analysis and modal analysis of CCD support part and star sensor are completed by using MSC.Patran & Nastran analysis software,maximum deformation of CCD support member is 7.98×10-5 mm,the maximum stress is 2.9×10-2 Pa,CCD support member has a good static characteristics;The first 6 order natural frequency and vibration type of CCD support components and star sensor can be gotten through the dynamic analysis,the first order natural frequency of CCD support part of is 892.89 Hz,first-order natural frequency of star sensor is 1674 Hz.The dynamic analysis results show that the CCD support component and star sensor have high fundamental frequency,and the dynamic performance is good.Thirdly,the positioning precision test experiment of auto focusing system is completed,the positioning precision of automatic focusing system is ±20.95?m based on ISO230-2 positioning precision standard,,the main factors which affect the precision of auto focusing system are analyzed,and factors mainly include CCD camera,linear guide rail,precision electric displacement,shape error and assembly error.Through the error analysis and control,linear guide rail precision is ±2?m,driving motor precision is ±675?m,lead screw precision is ±5.28?m,position precision is ±2?m,assembly precision is ±2?m,the positioning precision of automatic focusing system is ±18.29?m by using coupling error theory and precision distribution.And based on PID algorithm,error compensation software is designed in the Labview development environment,real-time error compensation is realized.The positioning precision is ±15.95?m after error compensation,the precision is increased by 24%,and the final precision meets the design requirements.Lastly,the working distance of star sensor is measured by using auto focusing system,the working distance of star sensor is 5.21?m.The experimental results show that auto focusing system meets the basic function of star sensor working distance measurement,and a series of advice of improvement are the proposed.