Study on Grating-dot Diffractive Optical Encoders

• Main Authors: Yeh, Heng-Yi, 葉恆屹
• Other Authors: Yeh, Sheng-Li
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/35873827985638878201

碩士 === 龍華科技大學 === 工程技術研究所 === 101 === Diffractive optical encoders are often used to precisely control positioning because they can accurately measure the nm-order displacements of an object. The key component of a diffractive optical encoder is a grating, which is used to accurately change the optical-path difference of two laser beams in optical interferometry to make the interference fringes accurately shift. This thesis proposed two setups of grating-dot diffractive optical encoders. According to the shifting of straight interference fringes formed by two planar waves and concentric interference fringes formed by two spherical waves created by diffraction-limit phenomena, one can precisely measure the out-of-plane and in-plane displacements, respectively. The purpose of this thesis is to replace large-area gratings in normal diffractive optical encoders with small grating dots, so reducing cost can be reached. The two proposed setups perform as well as a conventional diffractive optical encoder. Experimental results show that the two proposed setups can measure the nm-order displacements of an object and the displacement errors for all cases are smaller than 0.07μm.