Adaptive Power Control for Laser Triangulation Measurements on Moving Samples

Abstract

This article proposes an adaptive laser power control approach for laser triangulation measurements on moving samples. Utilizing the obtained image intensities as a feedback signal, the effective sample reflectivity is estimated. Based on this estimation, a digital integral controller is adaptively tuned. The thereby determined laser power setpoint is stabilized by a custom laser driver with a bandwidth of 50 kHz. Implementing the digital controller on an FPGA enables power adjustments between two consecutive exposure times, ensuring stable laser power conditions during the exposure. Experimental evaluation on a sloped sample successfully demonstrates that the proposed method reduces the spot size variation on the detector by 81%, ensuring a constant spot size for arbitrary sample orientations and exposure times.