A lightweight asymmetric compensation framework for continuous MWIR zoom control under direction-dependent load variations
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https://doi.org/10.54939/1859-1043.j.mst.FMC.2026.182-190Keywords:
MWIR zoom lens; DC coreless motor; Asymmetric load compensation; PID control; Preload spring; Nonlinear cam mechanism; Zoom control.Abstract
Continuous zoom mechanisms in mid-wave infrared (MWIR) imaging systems often employ nonlinear cam profiles and preload springs to achieve precise lens-group motion and backlash reduction. However, these mechanical structures introduce significant position-dependent and direction-dependent load variations, resulting in asymmetric dynamic behavior. Such nonlinearities make it difficult for a single globally tuned PID controller to satisfy tracking requirements. This paper presents an experimental investigation of load asymmetry in an MWIR zoom mechanism driven by a DC coreless motor with incremental encoder feedback. Based on these observations, a lightweight asymmetric compensation framework rooted in local feedforward linearization is proposed. To replace manual heuristic tuning and improve system adaptability, the method introduces an automated calibration procedure combined with polynomial curve fitting to systematically generate continuous directional bias profiles. This is integrated with direction-dependent PID parameter selection and startup torque injection without requiring additional sensors or complex observers. Experimental validation demonstrates that the proposed method improves the startup success rate from 85% to 100%, reduces the mean overshoot from 10.3 to 3.4 counts, and decreases the mean settling time from 3078 ms to 330 ms. The results demonstrate that the automated characterization and continuous compensation of directional load asymmetry significantly improve the control performance of MWIR zoom systems while maintaining low implementation complexity.
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