A Dual-Axis Optoelectronic Inclinometer Based on Wavefront Interference Fringes

With the rapid development of ultraprecision instruments, inclinometers play an essential role in machining and calibration. The current mainstream methods based on capacitance, inductance, or optoelectronic autocollimators can achieve a high resolution but they are not directly traceable. In addition, their systems are relatively complex and large. In this study, a novel dual-axis optoelectronic inclinometer is proposed, the tilt angle can be precisely measured by calculating the spatial frequency of wavefront interference fringes, and the liquid surface is applied as its reference. Compared with other interferometers and autocollimators, the proposed inclinometer is not sensitive to mechanical errors and the air refractive index. Therefore, the measurement result is directly traceable to gravity and the laser wavelength. A compact prototype was fabricated to verify the effectiveness of the proposed method. Our experimental results show that the prototype achieves a low long-term drift of 0.02 arcsec/h and a resolution of greater than 0.1 arcsec, with high sensitivity and stability. Compared with a commercial autocollimator, the linear error of the prototype was less than 0.16%.