Fabrication of Compact Laser Diffraction Encoder System with High Alignment Tolerance
Date Issued
2005
Date
2005
Author(s)
Shen, Hsin-Mao
DOI
zh-TW
Abstract
For the development of micro/nano technology, many nano manufacturing and measuring systems depend on the methodologies associated with metrology or positioning in the nanometer displacement scale. Sensors with long measuring distance and high resolution, however, are expensive and easily affected by the unstable environment. Thus, the need to have compact, high resolution, low cost and easy-to-use displacement sensors or sensing systems is becoming even more indispensable.
A newly developed compact laser diffraction encoder system with high alignment tolerance was developed during the course in this thesis. It is one type of the grating interferometer using grating to code the displacement information to the grating pitch by Doppler effect such that the measurement scale takes the place of grating pitch instead of laser wavelength and the errors caused by the unstable environment are reduced.
On the optical frame, the use of light division system and polarized optical components improve the head-to-scale tolerance substantially and produce four interference quadrature signals. The feasibility study to high alignment tolerance is achieved by the simulation of optics analysis software. The position and angle tolerances of each optical component are discussed in order to design the mechanism and furthermore calibrate and fabricate the optical head.
A series of signal processing procedure is also developed in this thesis. Errors in quadrature signals caused by misalignment of optical components or the oscillating of the grating can be compensated through the signal processing circuits. In addition, the count and interpolation methodology and the whole measurement program were accomplished with NI DAQ card and LabVIEW interface.
After the novel optical design, measurement principles, tolerance analysis, signal processing and measurement program were integrated, the compact laser diffraction encoder system was accomplished through several simple and easy adjustment and fabrication steps in an optical table. To verify the theoretical predictions and the overall system specifications of the system, the SIOS MI5000 laser interferometer was adopted as the calibration tool. Within the measuring distance of 10mm, even running the calibration at regular laboratory environment, the maximum error is 53nm and the repeatability is below 29.9 nm.
Subjects
光柵干涉儀
雷射光學尺
對位公差
正交訊號
grating interferometer
laser encoder
alignment tolerance
quadrature signal
Type
thesis
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