Development of a Wide-Range Precision Positioning Sensor Based on Image Analysis of Diffracted Light

Abstract

We propose a wide-range micro- and nano-positioning sensor based on an image sensor. The intensity distribution of a Moiré signal is measured on the image sensor and used for position sensing via Fast Fourier Transform (FFT) analysis. The FFT returns the frequency spectra and phase characteristics of the image. The frequencies caused by the beam divergence, the order of diffraction, and the Moiré signal can then be identified. The sensor can detect position with high accuracy using the phase shift of the Moiré signal. The results also demonstrate a measurement range of up to 6 mm and an estimated standard deviation of 3.3 nm under specified conditions. Moreover, the target position can be set arbitrarily by automatic PI control. This positioning sensor is characterized as using only one sensor to detect position with a high accuracy over a wide measurement range, making it easy to install in existing industrial machines and tools. Moreover, the accuracy and the measurement range are selectable by choosing the appropriate frequency component.