Research on error compensation method of reading head spacing variation in linear grating displacement measurement

Abstract To improve the absolute positioning accuracy of image-type linear displacement measurement, this paper proposes a method for error compensation of reading head spacing variation in linear grating displacement measurement. Firstly, the principles behind image-type linear displacement measurement were detailed explanation. Secondly, an error model for the variation of the distance between the reading head and the scale grating was established. Thirdly, the error self correction method within the range of measurement is derived through the error model of spacing change. During the test, the spacing between the reading head and the ruler grating changed significantly through our intentional inclined installation, and succeeded in reducing error range with in a 0–240 mm range from −6.4 μm to 0.2 μm down to −1.3 μm to 1 μm. The results confirm the efficacy of the proposed method. Compared with the traditional compensation technology, this method does not need to calibrate the range error, and does not need to strictly ensure the parallelism between the reading head and the ruler grating, so as to realize the self correction of the spacing change error in real time. This research may provide a sound technical basis for further exploration of high-precision, large-scale linear displacement measurement methods.