Compact chromatic confocal sensor for displacement and thickness measurements

Abstract Chromatic confocal sensors are widely used in various precision measurement fields because of their high measurement accuracy, fast response speed, and good stability. Unlike traditional fiber-coupled structures, we propose an integrated compact chromatic confocal sensing system that can overcome the device-integrating constraints met in industrial environments. Aiming at the distortion of the peak waveform caused by the inconsistent spectral response of the system and to accurately extract the peak wavelength, a spectral characteristic compensation algorithm and a peak wavelength extraction method based on Gaussian curve fitting are proposed. Based on these methods, a segmented curve calibration algorithm is applied to achieve accurate mapping between peak wavelength and position. For the thickness measurement of transparent objects, a simple thickness measurement model and its calibration procedure are proposed, which do not need to obtain previous parameters, such as incident angle or refractive index. Finally, the performance of the proposed sensing system is tested by displacement measurement and thickness measurement experiments. The experimental results show that the root mean square error (RMSE) of displacement measurement is less than 0.1 μm, and the RMSE of thickness measurement is less than 1 μm, which verifies the effectiveness and feasibility of the proposed sensing system.