Monochromatic LED-based spectrally tunable light source for chromatic confocal sensors

Abstract

Prior art emission spectra of light sources utilized in chromatic confocal sensors share two disadvantages: the uneven spectral power distribution (SPD) and the fixed distribution characteristic. Consequently, the detected peak signal intensity is regulated by the SPD properties of the light source and the spectrum transmittance characteristics of the dispersive lens. To achieve this, 18 types of monochromatic light-emitting diodes (LEDs) with different peak wavelengths were selected to create a wide-spectrum light source with a tunable SPD. The SPD characteristics of the light source can be modified by adjusting the luminous intensity of each LED. The tungsten halogen lamp, the “white” LED, and the designed light source were selected as the light sources for the chromatic confocal measurement system, respectively. Comparing the peak signals obtained under various light sources. The experimental results show that, in the range of 400 to 700 nm, the peak signal intensity extreme value ratio measured with the designed light source is 1.81:1, and the normalized light intensity standard deviation is 0.118. The corresponding light intensity extreme value ratio of halogen tungsten lamp and white LED is 23.3:1, 300:1, and the normalized light intensity standard deviation is 0.302, 0.228. With the help of the designed light source, a group of wave crest signals with uniform light intensity distribution can be obtained. This can reduce the influence of the SPD characteristics of the light source itself and the transmissivity characteristics of the dispersive objective lens on the measured signal, and ensure the accuracy of spectral detection.