A precise reference position detection method for linear encoders by using a coherence function algorithm

This paper proposed a new method for reference position detection with high precision for linear encoders by using a home designed scale grating and a coherence function algorithm. Differing from the traditional methods, in which the reference position alignment and calibration of reference position was achieved by detecting the peak of the signal with a negative pulse at the reference position, the method in this paper no longer detects the single peak of the signal, but matching and aligning the integral shape of reference position signal through the algorithm based on the coherence function. The proposed method does not require a complex design and precision manufacturing of reference position. Due to the coherence function algorithm, a multi-pulse reference position signals design is available, which not only reduces the difficulty of reference position design and manufacturing, but also shortens the length of reference position area so that the negative effect on the grating diffraction efficiency is limited. What is more, robustness of the reference detection method introduced here is greatly enhanced. Experimental results show that the accuracy of reference detection can still achieve 2 times of resolution even under the low signal to noise ratio (SNR) of 2dB.