Wide-range vision-based position measurement for linear servo-motor mover

Linear servo-motor (LSM) plays a vital role in industrial automatic machines. This paper proposed a digital image grating (DIG) method to measure the LSM mover position easily, robustly, and accurately over a wide range. The DIG method uses a narrow camera view for obtaining better accuracy and uses calibrated code marks as references to realize a wide measuring range. Furthermore, a 2P-ICGN algorithm was used for fast, robust, and precise image matching, and a fast interpolation method was used for interpolating image pixels efficiently. Firstly, a pattern with code marks and random speckle was set in the measuring range. Secondly, the code mark positions were determined with the help of image stitching. Thirdly, the rough position of the mover was estimated promptly via code mark recognition. Finally, the accurate mover position was calculated by matching the real-time image with the reference image containing the identified code mark. Experimental results confirm that the DIG method can measure LSM mover positions with an accuracy of 0.0031 mm (MAE) in a range of 450 mm.