Sightline Jitter Minimization and Shaping Using Nonlinear Friction Compensation

Abstract

Friction-induced sightline jitter significantly degrades the image resolution and detection range of a stabilised optical system. Therefore, any controller that can reduce jitter levels in the stabilisation sub-system will have a significant impact on overall electro-optic system performance. This article presents the results of an investigation into several friction compensation models applied to the validated model of an in-service electro-optic turret. The turret test harness, system identification software and friction measurement techniques used in the validation procedure–experimental transfer function analysis–are presented. A worst-case approach was used in setting the sensor noise and base motion acceleration levels. This test data was then used to validate a mathematical model of the turret elevation axis for use in off-line design and tuning of six friction compensation controllers. Three types of friction compensator model were investigated; a linear Kalman filter, an extended Kalman filter with a static friction model and an extended Kalman filter using a dynamic friction model. Additionally, two controller architectures were used. All six controllers were shown to significantly reduce jitter levels overall, but a new controller architecture was shown to also further reduce image degradation due to smearing.