以多進制灰階編碼原理研製絕對式線性光學編碼器

Abstract

光學編碼器是一種用來迴授位置訊號的光機電整合裝置，主要由三個元件構成：光源、碼盤或光柵尺（提供位置訊息之編碼）以及光偵測器元件（量測到的位置訊息轉換成電子訊號）。依不同碼盤(光柵尺)的設計，可將光學編碼器分為增量式編碼及絕對式編碼。裝置剛啟動時，增量式光學編碼器必須先將系統回歸至參考點，作為當次量測之起始位置；而絕對式光學編碼器因每一個位置皆設計不同的編碼訊息，因此可省略回歸起始位置的步驟。然而，在傳統的絕對式光學編碼器中，基於編碼的複雜度及安裝的困難度，相較之下不符合成本利益，故本研究發展一絕對式光學編碼器來突破此困境。 本研究以多進制灰階編碼作為編碼設計之出發點，透過多種不同反射率之灰階光柵條紋及透過量測多條光柵條紋之方式將編碼單元擴增，並以類似格雷碼的編碼方式，將連續兩位置之編碼編篡成僅有一位元的差異，利用此方法降低粗誤差的發生機率。簡而言之，完整的編碼內容為各軌道依不同週期地將灰階數值按順序再倒序的方式排列，成功地排列出一多軌道的絕對式編碼。 本研究將位置訊號利用影像感測器擷取絕對式編碼尺的圖樣，並從擷取的影像中進行處理與分析。而輸出的訊號相較於傳統的二進制絕對式編碼，因以多進制的編碼方式，可以於相同的軌道數量中編排出更多的絕對位置，再經數值運算後得到最終的位置訊號。也因多進制的編碼方式更容易地將編碼數量提升，因此適用於長距離之位置迴授系統。而實驗以九進制絕對式編碼之測量結果探討本研究之多進制絕對式光學編碼器的可行性，並分析誤差產生的原因及影響，奠定此編碼方式的理論基礎。

An encoder is an opto-electro-mechanical device that reads the motion and converts the motion into electrical signals. It is made up of a light source, a designed code disc to represents position information and a sensor to convert the coded information into electrical signals. Depending on the design of code disc, there are two main type of encoders: incremental and absolute. In operations, when an increment encoder is started, the system has to move to a reference mark as a home position and an absolute encoder indicates the current position so it does not require home operations. However, absolute encoders are usually more expensive than incremental encoders, because of the complicated code disc and the difficulty of installation. Therefore, the research develops an absolute encoder to break through the situation. The research based on the q-ary absolute coding method, and the coding units increased by using many of different reflective grating fringe and multi-fringe measuring method. Like Gray code, this q-ary absolute code’s adjacent code number differ in only one bit (binary digit). This means that, it can prevent the coarse error from the measurement. The research develops an image absolute encoder based on the image texture. The captured image consists of pixels which differ from gray level then converted into position data by using image processing algorithm. The output signal is a kind of q-ary code that could involve more code number compared to the traditional binary code. Therefore, it would be applied to the long distance applications. Experimental results verified that q-ary absolute coding’s feasibility and mapped out the explanation to the detecting error of the image.