IJAT Vol.18 No.2 pp. 249-256
doi: 10.20965/ijat.2024.p0249

Research Paper:

Design of an Optical Head with Two Phase-Shifted Interference Signals for Direction Detection of Small Displacement in an Absolute Surface Encoder

Ryo Sato ORCID Icon, Tao Liu, Satoru Maehara, Ryota Okimura, Hiraku Matsukuma ORCID Icon, and Wei Gao ORCID Icon

Department of Finemechanics, School of Engineering, Tohoku University
6-6-01 Aramaki Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8579, Japan

Corresponding author

May 31, 2023
January 15, 2024
March 5, 2024
absolute encoder, surface encoder, variable line space grating, mode-locked femtosecond laser

This paper presents the design and construction of a new optical head with two phase-shifted interference signals in an absolute surface encoder by using a mode-locked femtosecond laser. A series of discrete absolute positions of the scale grating is obtained from a series of peak wavelengths of the spectrum of the +1st- or -1st-order diffracted beam. The two beams at a specific wavelength λi interfere with each other to generate an incremental interference signal for high-resolution displacement measurement over a small interpolation range around the corresponding discrete absolute position xi. In the previous design of the optical head, the two beams were guided by optical fibers into a fiber coupler for the interference. This fiber optics design was simple and stable but could not identify the moving direction of small displacement within each interpolation range because only one interferential signal could be generated. The aim of this study is to develop a new design of the optical head, where two interference signals with a phase difference of π/2 are generated. For this purpose, free-space optics, instead of fiber optics, is adopted in the new optical head. Experiments are conducted to confirm the generation of the two phase-shifted interference signals. A Lissajous figure is plotted to verify the phase difference between the two signals.

Cite this article as:
R. Sato, T. Liu, S. Maehara, R. Okimura, H. Matsukuma, and W. Gao, “Design of an Optical Head with Two Phase-Shifted Interference Signals for Direction Detection of Small Displacement in an Absolute Surface Encoder,” Int. J. Automation Technol., Vol.18 No.2, pp. 249-256, 2024.
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Last updated on Jul. 23, 2024