Design Of Control System For Swing-Arm Profilometer

Precise measurement of surface shape of large-size optical components is an important part in many regions of optical system development.With the development of science and technology,requirements of surface shape measurement of optical components become higher in many fields such as synchrotron radiation source,EUV lithography,camera,telescope,and X-ray free electron laser light.This paper shows a design of a platform which can measure the surface shape of optical components automatically based on the principle of Swing-Arm Profiler.This platform positions sensor to sample the data of surface shape by polar coordinates.After that,the surface shape can be fitted in computer by using these data.The mechanical design of this platform is rational,not only has the advantages of Swing-Arm Profiler such as high precision,wide range and high speed,but also uses many embedded system and computer technologies to improve measurement speed and degree of automation.This paper mainly discusses the design of control system for the platform.In this aspect,first point is the precise control of swing arm and turntable.Two air-floating brushless DC motors are driven by the UMAC motion controller,and 32-bit circular grating encoders are used as position and speed feedback to complete the control of the arm and turntable to position the sensors.The second is high-speed data transmission and storage.The SOPC system is built on a Xilinx FPGA.Data is sampled by high-speed AD and cached through memory management methods such as ping-pong operations.Finally,the data is stored on the hard disk through the hardware-implemented SATA interface protocol.And the surface shape of optical components are obtained by fitting the measured data in computer.On the other hand,The sensor can be easily replaced to achieve the purpose of measuring different surface shapes and accuracy requirements.The laser triangulation rangefinder is chosen for experiment in this paper.The swing arm profiler has unique advantages in measuring the surface shape of large-sized optical components,such as fast measurement speed and high precision.With the improvement of system material and component processing precision and sensor measurement accuracy,it is expected to achieve higher measurement accuracy.