Development of a six degree-of-freedom laser measurement system for machine geometric error measurement.

Abstract

This dissertation presents the measurement principles, theoretical analysis and experimental results of a laser measurement system for machine geometric error measurement. This system can measure all six error components of a machine axis simultaneously. This dissertation is divided into four parts. The first part of the dissertation presents a literature survey on the development of the sensing technologies relating to machine geometric errors. The second part describes the development of an optical fiber laser beam delivery system. This beam delivery system can stabilize the spatial pointing stability of a light source to better than ${\pm}0.03\ arcsec$ in a period of half hour by utilizing the optical fiber technique. The frequency of a diode laser is stabilized to within $10\sp{-7}$ in a 30 minute test with an interferometer. A prototype combining these two features is built and tested in the laboratory. The third part focuses on the development of a new method of roll error measurement for which there are serious limitations in currently available instruments. This new method is based on the detection of the small change of optical polarization. A novel method for differential detection is also proposed and implemented into the prototype for roll error measurement. The calibration results show the accuracy of the roll prototype is in the range from +0.17 to -0.08 arcsec over a measurement range of 120 arcsec. The last part of the dissertation describes the development of a six degree-of-freedom (6D) laser measurement system for machine geometric error measurement. Several different measurement methods are integrated together in this system and share the same light source presented in the second part. Laser alignment technique is used for straightness measurement; an autocollimator is used for pitch and yaw measurement; optical polarization method is employed for roll measurement; and a Michelson laser interferometer is applied for displacement measurement. Calibration results show that the accuracy is about ${\pm}0.1\ \mu m$ for translational movement and ${\pm}0.2\ arcsec$ for angular movement. The 6D system is also tested in shop floor environment and compared with a Hewlett-Packard interferometer with satisfying results.