Stand Alone Laser Tracking System

Standalone Laser Tracking System (LTS) is a kind of coordinate measuringmachine which possesses high precision and large measuring range up to more than100meters. This dissertation focuses on researching key technologies of standaloneLTS including system modeling, parameter calibration, error analysis andcompensation, high performance servo controller etc. Main findings of thedissertation can be summed as following:A standalone LTS with precise rotation shafts and accurate mechanical structureis produced. A method for adjusting the laser path and tracking mirror’s positionaccording to the trace of reflected light is developed. A digital servo platform takingDSP as the core is set up and PC application software is programed for theconvenience of developing various control strategies. All of this lays a goodfoundation for subsequent researches.A new mathematical model for standalone LTS which only contains twounknown parameters is proposed. Simulation studies prove that this new model iscorrect.A new calibration method with spherical constrains is proposed to calibrateunknown system parameters. It overcomes the shortcomings of big original error,significant error transmission factor, low noise resistance and narrow convergencedomain that exist in calibration methods with planer or liner constrains.Experiment installation is designed to calibrate LTS, which utilizes CMM andRenishaw QC20-W ball bar to build precision spherical constrains. LTS is calibratedby spherical constrains and planer constrains respectively. Contrast measurementexperiments show that the new calibration method can provide more accuratecalibration results.System errors are analyzed and error compensation is carried out. An errorcompensation model containing the misalignment of two rotation axis and theeccentricity of the tracking mirror is presented. Simulation and experimental resultsshow that system measuring accuracy increases by38%after error compensation.Transformation matrix between the coordinates on the PSD’s surface of the lightspot and the displacements of the target reflector is derived out, which realizes the decoupling of the tracking errors of the two shafts.Combining the compound controller and fuzzy controller together, a compositivecontroller is proposed. Tracking experiments show that the compositive controllerdecreases the tracking error by80%and increases the tacking speed by35%.In order to test the performance of the LTS, experiments for testing themeasuring range, repeatability, single shaft measuring accuracy and volume accuracyare carried out. The results show that the LTS which is built in our laboratory cantrack a target with a speed of no faster than0.5m/s in3.2m radius range. Contrastspatial length measuring tests show that the measuring error of the LTS is±8.5μm.