Compound Speckle Interferometer for Multi-Degree-of-Freedom Measurement

• Main Authors: Bo-Yen Sun, 孫柏彥
• Other Authors: Hung-Lin Hsieh
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/t9wxgg

碩士 === 國立臺灣科技大學 === 機械工程系 === 106 === In this study, a compound speckle interferometer for multi-degree-of-freedom measurement is proposed. By combining heterodyne interferometry, speckle interferometry and beam splitting techniques, the system can perform precision displacement and rotation measurement, while having the advantages of high resolution, long-range non-contact measurement and a relatively simple configuration. The basic configuration is a two degree-of-freedom (2-DOF) compound speckle interferometer consisting of a heterodyne light source and an innovative compound speckle optical configuration. This speckle optical configuration combines a symmetrical speckle interferometer system capable of measuring in-plane displacement with a novel asymmetric speckle interferometer system capable of measuring both in-plane and out-of-plane displacement. This arrangement allows for the independent measurement of two modes of surface displacement through signal subtraction, while only requiring three laser beams to converge on a single point on the measured surface, making this a simple yet effective design. The interference patterns formed from the scattered light reflecting off the measured surface is received as intensity signals by photodetectors. When the surface undergoes displacement, the phases of the interference patterns will shift according to the principle of Doppler frequency shifting. The resulting phase variation data can be separated by displacement axis via polarization, then the displacement values can be obtained through phase demodulation. The 2-DOF compound speckle interferometer can be further expanded into 3-DOF, 4-DOF, 5-DOF, and 6-DOF measurement systems, allowing for a wide selection to suit the needs of the required task. In order to verify the performance of the proposed compound speckle interferometer, a series of measurement tests were performed with commercial precision motion stages on all variants of the system. These include displacement and rotation measurement tests with various waveforms and ranges, repeatability and resolution tests, as well as measurement range experiments. By comparing the acquired results with data from the internal displacement sensors of the motion stages, it is demonstrated that all variants of the compound speckle interferometer have the ability to accurately measure displacement and rotation in multiple DOFs, while also possessing the high resolution, excellent repeatability, long measurement ranges and a flexible design.