Study On Method And System For Laser Simultaneously Measuring Six Degree-of-freedom Geometric Motion Errors Of A Linear Guide

A linear guide is the key component in ultra-precision machining and measuring equipment such as computerized numerical control machines and coordinate measuring machines (CMMs). The manufacturing and assembly deviations of the linear guide are main factors that influence the machining and measuring accuracy of the ultra-precision equipments mentioned above. The conventional method for measuring the geometric motion errors of a linear guide employs a laser interferometer. However, the measurement efficiency is extremely low, and the need in multi-error component, high speed and high accuracy calibration of machine tools cannot be satisfied. Therefore, the primary need and development trend in this field is to develop a system that can simultaneously measure 6DOF geometric motion errors to significantly improve the measurement efficiency and accuracy of geometric motion errors of the linear guides of the machine tool.In order to solve these mentioned problems, the relative research background was analyzed in detail and two measurement methods for simultaneously measuring 6DOF errors were proposed according to the principle of miniaturization and high integration in this dissertation. The corresponding measurement instruments were developed and the reliability and effectiveness of the developed instruments were verified by a series of experiments.The primary job and innovative research achievements obtained in this dissertation are as follows:1. A measurement method for simultaneously measuring 6DOF geometric motion errors based on the combination of laser interferometry and laser collimation was proposed. The measurement principle for each error parameter was analyzed. The common path based beam drift measurement and compensation method was introduced. The design of optical configuration, signal processing unit and measurement software was performed according to the measurement principle. The corresponding measurement instrument based on the He-Ne dual-frequency laser and the single-mode fiber-coupled laser diode was developed. The performance of the developed measurement system was evaluated by a series of experiments. The standard deviation of positioning error, straightness error, pitch, yaw and roll are 0.8μm,0.5μm,0.5",0.5", 1", respectively, and the repeatability error are 0.8μm,0.5μm,0.5",0.5",1", respectively. The requirement in calibrating precision machine tool can be satisfied by using the developed system.2. A measurement method for simultaneously measuring 6DOF geometric errors based on the combination of heterodyne interferometry and laser fiber collimation was proposed. The heterodyne interferometry based positioning error measurement, which uses single polarization maintaining fiber transmitting the dual-frequency laser, was performed. The design of optical configuration, hardware unit and measurement software was performed according to the measurement principle. The corresponding measurement instrument using a polarization maintaining fiber-coupled He-Ne dual-frequency laser was developed. The performance of the developed measurement system was evaluated by a series of experiments. The stability error of positioning error, straightness error, pitch, yaw and roll are 31.1nm,60nm,0.04",0.03",0.29". The repeatability error of straightness error, pitch, yaw and roll are ±0.15μm, ±0.18", ±0.24", ±0.35", respectively. The effectiveness of polarization maintaining fiber on improving the measurement accuracy and thermal stability of the developed system was proved by a series of experiments. The measurement system was verified to be effective on measuring ultra-precision machine tool.3. The error factors of system for simultaneously measuring 6DOF geometric motion errors were discussioned, and the systematic error for straightness error measurement was studied in detail. The systematic error of straightness error measurement in simultaneous measurement of 6DOF geometric errors was analyzed in detail. The corresponding error compensation model was established. The influence of systematic error, which is caused by variation of measurement sensitivity, fabrication and installation deviation, error crosstalk and Abbe error, on measurement accuracy can be eliminated theoretically. The experimental set-up of laser collimation based straightness error measurement was developed. The comparison deviation of horizontal and vertical straightness error measurement was reduced from 1.8μm and 2.8μm to 0.9μm and 0.8μm after compensation, respectively. The effectiveness of the error compensation model was thus verified.