Research And Implementation Of Control Strategy For BRDF Measurement System

Bidirectional Reflection Distribution Function(BRDF)can reflect the light scattering characteristics of an object’s surface and has important research significance in the detection of the surface of optical components.In order to obtain information about the scattering light from the surface of an optical component,it is necessary to establish BRDF measurement system.However,BRDF measurement system is a complex integrated system with the requirements of high angular positioning accuracy and a large amount of test data.At present,there are some problems in BRDF measurement system,such as complex device,long measurement time and low degree of automation.Therefore,the control strategy of BRDF measurement system is studied.In order to realize the automation of BRDF measurement system,the research status of BRDF and BRDF measurement system are summarized.The basic theory of BRDF and motion control system is expounded in detail.According to the hardware structure of BRDF measurement system,the motion control of sample stage and detector module is studied in detail,and the control scheme of measurement system is designed with system combination control,scanning trajectory and trapezoidal speed planning.In the system combination control,the structure of BRDF measurement system is described specifically,and the coordinate relationship between the two rotating platforms in the detector module and the scattering angle and scattering azimuth angle are established.In the trapezoidal velocity planning,the trapezoidal velocities is analysed and velocities from 100 to 256 levels are selected in order to reduce the measurement time.In the scanning trajectory planning,two types of scanning trajectories along the latitude line and longitude line are designed,and the scanning trajectory along the latitude line is selected through the study and analysis of the two types of scanning trajectories.On the basis of the hardware of BRDF measurement system,the software of measurement control system is designed.Combining the characteristics of the measurement system and the experimental conditions,the overall design plan of the measurement system control software is determined and each functional module is designed.The human-machine interface of the measurement control system is designed using the Laborary Virtual Instrument Engineering Workbench(LabVIEW)development platform,including the design of communication serial port,displacement motion,rotation motion,compensation of photoelectric encoder compensation and scanning motion function module to realise the automatic measurement of the BRDF.According to the overall scheme of BRDF measurement system,the experimental device is built.Firstly,the measurement control system is tested for positioning compensation and the stability.The experimental results show that the measurement control system has good positioning repeatability and stability.Scattering distribution measurement experiments are carried out on standard defective samples with scratched and pockmarked surfaces and smooth surfaces by device of BRDF measurement,and the experimental errors are analysed.The experimental results show that when the scattering azimuth is 0°,BRDF measurement curve generally show a trend of increasing and then decreasing under different incidence angles,and the repeatability standard deviation of BRDF measurement is less than 0.02sr-1 for smooth surfaces and less than 0.04sr-1 for surfaces with scratched and pockmarked surfaces.The research and experimental results show the feasibility of BRDF measurement and control scheme,and provide a research foundation for BRDF measurement devices with higher precision in the future.