Development of a Four-Degree-of- Freedom Common Path Linear Encoder

• Main Authors: XIANG-AN ZHAN, 詹翔安
• Other Authors: Hung-Lin Hsieh
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/a5369s

碩士 === 國立臺灣科技大學 === 機械工程系 === 107 === An innovative four-degree-of-freedom common path linear encoder with the ability to simultaneously measure both in and out of plane displacements and rotations is proposed in this study. This linear encoder combines the advantages of interferometry, grating interferometry, beam splitting techniques and common optical path design to develop a system with high sensitivity, high stability, high tolerance, precise displacement measurement and self-correction capability, and has been successfully miniaturized. The four-degree-of-freedom common path linear encoder has the advantages of simple configuration, quick set up and low cost. In addition, only one set of prism and grating is needed to obtain both in-plane and out-of-plane displacement information. The system is designed around the core of a common optical path configuration, focusing mainly on the angle of the prism. This causes the laser light source entering the prism to split into a transmission P beam and a refracted R beam. The P and R beam are then incident onto the optical scale (grating) at an oblique angle and diffracted, causing the diffracted P and R beams to overlap forming interference. When the grating is displaced in and in-plane or out-of-plane direction, the phase change of the interference signal received by a photodetector can be used to obtain the grating displacement value. To further enhance the measurement capability of this system, beam splitting was utilized to form two detection points on the grating, allowing the linear encoder system to measure displacement and rotation simultaneously, while compensating for measurement alignment errors, and give the system the ability to self-correct. The experimental results show that the resolution of the displacement and rotation angle of the four-degree-of-freedom common path linear optical scale can reach 10 nm and 200 nrad, respectively. The repetition rate can reach 3.6 nm and 71 nrad, and the stability is within 30 minutes. Under the condition of better than 30 nm and 1000 nrad, the speed limit can reach 8800 μm/s. It has excellent measurement performance and potential of commercial development, and can be widely used in various occasions where precision measurement is required.