Two-axes tilt sensing using circular gratings moiré

Pei Ying Tan; Kin Sam Yen; Fauziah Ahmad; Mani Maran Ratnam

doi:10.1117/1.OE.58.4.044103

25 April 2019 Two-axes tilt sensing using circular gratings moiré

Pei Ying Tan, Kin Sam Yen, Fauziah Ahmad, Mani Maran Ratnam

Author Affiliations +

Optical Engineering, Vol. 58, Issue 4, 044103 (April 2019). https://doi.org/10.1117/1.OE.58.4.044103

Abstract

A circular grating moiré method is proposed for sensing the tilt magnitude (θ) and tilt direction (α) for tilt about two orthogonal axes. A device consisting of a pair of fixed (upper) and semifloating (lower) circular gratings inside a water-filled acrylic container has been developed. The moiré pattern images for tilt angles ranging from 0 deg to 7 deg are captured using a webcam, processed by low-pass filtering and transformed from Cartesian-to-polar coordinates. This is followed by column-wise fringe center localization using polynomial fitting, unwrapping of the extracted fringe centers, and sine-curve fitting. The peak-to-valley height (h_pv) and phase shift (φ) of the unwrapped and fringe centers were determined from the fitted sine curve. The relationship between h_pv and θ is found to be parabolic with the y-intercept at its minimum point, whereas that between φ and α is linear. From the tilt sensing experiments, the mean absolute errors in θ and α are found to be 0.16 deg and 3.1 deg, respectively, with uncertainty of ±0.027 deg and ±0.5 deg at 95% confidence level. The proposed device is capable of sensing tilt magnitude and direction along two orthogonal tilt planes and can potentially be applied in landslide monitoring.

Citation Download Citation

Pei Ying Tan, Kin Sam Yen, Fauziah Ahmad, and Mani Maran Ratnam "Two-axes tilt sensing using circular gratings moiré," Optical Engineering 58(4), 044103 (25 April 2019). https://doi.org/10.1117/1.OE.58.4.044103

Received: 3 January 2019; Accepted: 5 April 2019; Published: 25 April 2019

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