本研究主要提出一套創新的Wollaston雷射光學尺量測系統，用以進行六自由度線性位移及旋轉角位移之精準量測。此套光學尺系統主要結合外差干涉術、光柵剪切干涉術、Wollaston prism共光程光路及分光技術等設計概念進行開發，使系統具備高穩定度、高解析度及六自由度的量測能力。
此套雷射光學尺系統主要由一氦氖雷射、電光調變器、擴束鏡組、Wollaston prism、繞射光柵及其他光學元件所組成。首先利用電光調變技術來產生外差光源，同時透過Wollaston prism及光柵的使用來建構出共光程光路架構，使參考光及量測光在空間中行進的路徑皆相同，當系統遭受外界環境擾動影響時，兩道光將感受到相同的擾動訊息，其影響量將於干涉訊號中相互抵消，如此即可有效地降低外界環境擾動對量測結果造成的影響。而後，透過分光技術的使用，建構出三組具備雙自由度(一線性位移及一旋轉角)量測能力的偵測架構，使此套系統擁有六自由度(x, y, z, θx, θy, θz)的精準量測能力。
為了驗證本研究所提出之Wollaston雷射光學尺的可行性及系統性能，本研究使用商用的六軸定位平台及長行程步進平台進行多項實驗，並後將Wollaston雷射光學尺的量測結果與平台內建的電容式位移計與光學編碼器所得到的結果相互比較。由實驗結果證明，此套Wollaston雷射光學尺可在不改變光學架構下，同時提供六自由度線性位移及旋轉角位移的量測訊息，其線性位移與旋轉角位移的量測解析度分別可達2 nm與200 nrad，穩定度於五分鐘內分別為10 nm及1000 nrad，系統量測速度極限可達1100 μm/s，具備優異的量測性能，可廣泛應用於應用於奈米科技、半導體、自動化光學檢測及精密機械等場合中。

In this study, a novel laser encoder for measuring six degree-of-freedom (DOF) displacement and rotation angle information is proposed. This laser encoder is developed by combining heterodyne interferometry, grating shearing interferometry, the design of common-optical-path (COP) configuration by using Wollaston prism, as well as the technique of separating the beams from the same light source. It possesses six DOF measurement ability with high resolution and high stability.
The proposed laser encoder consists of a He-Ne laser, electro-optic modulator, beam expander, Wollaston prism, diffraction grating, as well as other optical components. First, the heterodyne light source is generated via electro-optic modulation, and the COP configuration is constructed by combining the Wollaston prism and grating components. The proposed COP configuration relies on the fact that the propagation paths of the two orthogonally polarized beams (beams s and p) are almost the same and as a consequence undergo similar surrounding disturbances that will be compensated in the interference signal. Therefore, the unanticipated influences from the surrounding disturbances of the measurement result are reduced effectively with COP configuration. Last but not least, the proposed laser encoder has six DOF (x, y, z, θx, θy, θz) precise measurement ability while using a single light source.
In order to verify the performance of our proposed laser encoder, a six DOF precise position stage and a long stroke stepper stage are being used to perform several experiments. The measurement results obtained from our proposed laser encoder are compared with the results acquired from the commercial capacitive senor built in the six DOF precise position stage as well as the linear encoder built in the stepper stage. As can be verified from the results of our experiments, the proposed laser encoder has the ability to precisely measure displacement and rotation angle in six DOF without modifying the optical configuration. The resolutions of displacement and rotation angle are 2 nm and 200 nrad, respectively. The stabilities of displacement and rotation angle are about 10 nm and 1000 nrad over minutes. The measurement speed can achieve 1100 μm/s.

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