Research On Target Offset Measurement Of Low Gravity Simulation System Based On PSD

The sling suspension method is a ground low(zero)gravity simulation method.Compared with falling tower method,parabolic flight method,water float method,air float method,exoskeleton method and robotic arm lifting method,the system is simple and easy.Realization,good real-time performance,and greater comprehensive advantages.In the suspension method low gravity simulation system,it is very important to collect the inclination angle of the sling or the displacement information of the experimental target and feed it back to the two-dimensional follow-up subsystem.The feedback information is used to track the experimental target in real time to ensure that the sling is vertical and eliminate interference forces.Highprecision sling inclination or target displacement measurement technology is the key to improving simulation accuracy.Aiming at the motion of the experimental target in the suspended low gravity simulation system,this project carries out the research on the experimental target offset measurement technology based on one-dimensional position sensitive sensor(PSD).The main research content includes: PSD-based sling inclination measurement program research and neural network-based measurement system calibration research.In terms of measurement program research,in response to the high-frequency and high-precision measurement requirements of the low-gravity simulation system,a scheme of sling inclination measurement based on dual one-dimensional PSD shadow method is proposed.Based on the principle of PSD measuring the center of gravity of the spot,a mathematical model of the PSD output and the position of the center of gravity of the sling projection and an analytical model of the twodimensional inclination of the sling are established.According to the measurement requirements,the various modules of the measurement system are selected and determined,and the PSD output characteristics based on the shadow method are explored through experiments.It is obtained that there is a certain linear relationship between the PSD output and the inclination of the sling,which proves that the measurement scheme is feasible.In order to realize the high-precision mapping between PSD output and sling angle information and experimental target displacement,neural network method is used to predict sling angle and experimental target displacement,and the performance of the measurement system is tested.First,set up a calibration experiment platform and perform measurement experiments.The adaptive Kalman filter is used to preprocess the PSD output and the calibration data of the experimental target displacement.The least square method,BP neural network and GRNN neural network are used to fit the relationship between the PSD output value and the experimental target displacement.Compared with the fitting results,GRNN with higher accuracy is selected to solve PSD output.The accuracy test,repeatability test and noise test of the measurement system are carried out,and the factors affecting the measurement results are analyzed.The performance test experiment shows that the measurement system can achieve 1KHz measurement frequency and 0.01° sling inclination measurement,which meets the low gravity simulation system The demand is a realtime,high-precision measurement system.