| Summary: | 碩士 === 國立虎尾科技大學 === 光電與材料科技研究所 === 99 === The multi-degrees-of-freedom laser encoder developed in this paper uses a reflection diffraction grating as a transformed medium to deliver the motion error signals of a linear stage. Based on the diffraction principle, the Doppler princilple, and the optical interference principle, the multi-degrees-of-freedom laser encoder simultaneously measures linear displacement, roll, yaw, pitch, and horizontal straightness errors of a linear stage.
Two kinds of laser encoders are developed in this paper. The first encoder uses the phase difference of the ±1 order diffraction rays to measure linear displacement and the directional change of ±2 order diffraction rays detected by two quadrant photodiode detectors to measure other motion errors which can improve the measuring sensitivity of the sensing direction. The encoder is vefrified by Agilent 55292A laser calibration system. The measurement errors of roll, yaw and pitch errors are verified as ±0.8 arcsec and the standard deviation are about 0.5 arcsec. The horizontal straightness error is ±1.5 μm/±50 μm and the standard deviation is 0.06 μm. The linear displacement error is ±1.5 μm/± 500 μm and standard deviation is 13 nm.
The second design uses only ±1 order diffraction rays because the diffracted rays has higher light intensity and better signal to noise ratio. In addition, considering the stabiltiy of the laser diode and preventing the zero order diffraction ray back to the cavity, an optical isolation system and a wavelength measuring system are develpoed in the second design of laser encoder. The verification results show the roll, yaw and pitch errors are less than ±0.8 arcsec and the standard deviations are less than 0.18 arcsec. The horizontal straightness error is ±0.5 μm /±250 μm and standard deviation is 0.05 μm. The linear displacement error is ±1 μm/ ±20000 μm and the standard deviaiton is 12 nm. The verification results showed the second laser encoder is superior to the first laser encoder.
The study of this paper provides a new application of the laser encoder to the multi-axes CNC machine tools. The spatial geometric error measurement, error compensation and error diagnosis can be implemented in the CNC machine tools. Using the multi-degrees-of freedom laser encoder, the time of using laser interferometer calibration is decreased. The developement of an error self-compensation intelligent machine tools is possible.
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