Design Of Laser Tracking System Based On FPGA

With the development of modern industry, people have demand for moreeffective ways to measure3D coordinates, especial in the field of industrialrobots, aerospace, shipbuilding industry etc. The traditional coordinatemeasuring machine can no longer meet the requirement. Compared to thetraditional three-dimensional coordinate measuring method, laser trackingsystem has the advantages of wide range, high-precision, site-survey,non-contact and so on. Based on the principle of the spherical coordinatemethod, laser tracking system used in Field－Programmable Gate Array(FPGA) is designed.According to the principle of spherical coordinates, optical design of thesystem is done, using single-frequency laser as the light source, thecorner-cube prism as the target mirror. We optimize the traditional opticalpath and use Faraday-optical-rotator as the optical isolator. According to themotion characteristics of the laser tracking system, a mirror rotationmechanism is designed and the proper engine is selected.A two-dimensional Position-sensitive Detector is selected to be the sensor tomeasure the position of the center of the light spot of the laser reflected from thetarget mirror. The electrical circuit to convert the intensity of the electric current tothe voltage is designed based on the chip AD820. Then the analog signal is convertedto digital signal by a A-D transition circuit.Based on the FPGA chip cyclone IV, using the Verilog HDL, the software isdeveloped. It is consisted on three parts: AD control module, coordinate calculationmodule and motor controller module. AD control module sends instructions to the ADconvention circuit mentioned above to get the voltage of the PSD electrodes.Coordinate calculation module calculates the coordination of the position of the laserspot and the angle the motors need to rotate. The motor controller module sendssignals to the motors to rotate the mirror.The tracking system is set up according to the scheme mentioned above, theperformance of the system are tested and evaluated. Firstly, the experiments showedthat two-dimensional PSD has a good linearity. Secondly, the experiments show thatthe laser system can smoothly capture the track of the target moving at0.1m/s in the distance of2m from the rotation mirror. Finally, the experiments show that theacceptance angle of the target mirror is-24.9~+25.1.