Estimator-based optical path difference velocity control for handheld FTIR spectrometers

This paper presents the design, implementation, and experimental validation of a scan motion controller for a compact scanning interferometer intended for handheld FTIR spectrometers. A novel optical path difference (OPD) velocity estimator is introduced, capable of robust real-time velocity control without requiring an additional quadrature output or offline calibration. The proposed two-degree-of-freedom (2DoF) control strategy combines a model-based feedforward approach with a PID velocity feedback controller, significantly improving robustness against external disturbances. Experimental validation on a custom-designed interferometer demonstrates a reduction in OPD velocity error by a factor of 14.1 in handheld operation, highlighting the system's effectiveness for real-world applications.