Several Key Technologies Of High Precision Laser Tracing Measurement

Precision measurement technology is the basic technology of engineering science and the key technology of modern intelligent manufacturing,while precise instruments are the carrier of measurement technology and the only method to achieve major scientific discoveries and basic theoretical research.Nowadays,advanced CNC equipment provides relatively rich means for the processing and measurement of high-precision and complex shape parts,but the calibration technology,methods and means for advanced CNC equipment are relatively weak and lagging.Data research shows that the manufacturing accuracy of CNC machine tools will be increased doubly every 8 years.The manufacturing accuracy of current advanced CNC machine tools has entered the sub-micron era.However,this puts higher demands on exclusive measurement equipment.In the field of calibration for CNC equipment,laser interferometers have become the most accurate practical calibration equipment with ultra-high measurement accuracy and resolution.However,it is an indisputablele fact that laser interferometers are used to calibrate CNC machine tools with long detection cycles and low measurement efficiency.In order to improve the measurement efficiency,it is also an option to use a laser tracker to calibrate the CNC equipment.However,limited by the ranging principle and structural characteristics,the improvement speed of laser tracker measurement accuracy has long been unable to keep up with the increase in processing accuracy of CNC equipment.The LaserTRACER,which is also a laser tracking measurement system,solves the contradiction between "measurement accuracy" and "measurement efficiency" to a certain extent.The measurement accuracy of the LaserTRACER is close to the measurement accuracy of the laser interferometer,but the measurement efficiency is close to the measurement efficiency of the laser tracker,so it is more suitablele for high-precision and high-efficiency calibration of advanced CNC equipment.However,LaserTRACER’s complete reliance on foreign imports and expensive issues limit the application and promotion of high-precision laser tracing measurement technology in China.Through theoretical innovation and technical innovation,this paper addresses the optimization of the structure of the LaserTRACER,the design and analysis of the laser interferometry system,the control scheme of the permanent magnet synchronous motor,the study of rotation error of the LaserTRACER and the system ranging accuracy characteristics,the system error compensation method and provides support for the development of high-precision laser tracing measurement systems.This paper has studied several key technologies of high-precision laser tracing measurement system.The main research contents are as follows:(1)The theoretical basis of high-precision laser tracing measurement is discussed.The tracing algorithm based on PSD module and target displacement measurement is briefly introduced,and the principle of multilateral measurement and motion error compensation of CNC equipment are systematically explained.A spatial straight line fitting method based on the total least squares method is proposed.(2)From the perspective of development of high-precision LaserTRACER,a complete set of LaserTRACER design schemes including optimization design and analysis of key mechanical components,design of optical system and analysis and control system design are presented.A 2-D gimbal mount axes based on a reference sphere is designed to effectively reduce the measurement uncertainty of the spatial distance while increasing the space azimuth measurement range.The system energy analysis method of laser interferometry based on the Jones matrix is studied which guides the design of the key interferometer group and the determination of the prism transmissivity,and improves the contrast of the interference fringe received by the four-way photoelectric sensor.A current prediction algorithm based on the expanded state observer is proposed,which combines the speed loop and position loop control algorithm,constitute a three closed loop motor control strategy with PMAC motion control card as the control unit,which effectively improves the response speed of the motor and shortens the calculation time.(3)A comprehensive study of the rotation error and system ranging accuracy characteristics of the LaserTRACER is conducted.Aiming at the structural characteristics of the 2-D gimbal mount axes of the LaserTRACER,the errors of the axes are divided into systematic geometrical errors and rotation errors,and the axes geometrical errors and rotation errors are analyzed respectively.The transfer function of the influence of the individual geometrical errors of the axes on the system ranging accuracy is given,which lays the foundation for the effective compensation of the system error of LaserTRACER.(4)A systematic error compensation method based on calculation methods and measurement methods are proposed.The system error compensation method based on calculation method needs to measure the individual geometrical errors during the equipment installation phase,establelishes a comprehensive geometrical error model to derive the functional relationship between the individual geometrical errors and the system ranging error,and calculates the system ranging error.The system error compensation method based on the measurement method does not need to measure each geometrical error separately,and directly uses external standard parts to measure its system ranging error in the working environment of the LaserTRACER.(5)A complete test plan is designed to verify the feasibility and correctness of the technical plan and measurement method.The test equipment used in the test of each group is introduced,and the parameters of each equipment meet the test requirements.Based on the thinking of relative motion,the experimental model for the research of the LaserTRACER’s rotation error and system ranging accuracy characteristics is simplified.Aiming at the systematic error compensation method based on measurement methods,external standard parts are designed and the discrete geometrical error map of the LaserTRACER is drawn.