Abstract
A roll-pitch seeker has a wide field of view but suffers from a singularity as the sightline coincides with the outer gimbal (OG) axis. In the vicinity of the singularity, the tracking effectiveness is often degraded or even lost due to the high actuation demand on OG, which is known as the zenith pass problem. To solve this problem, this paper first proposes a novel motion model of sightline to predict the singularity in a receding horizon, where the model parameters are identified using a modified recursive least square estimator. And with the singularity predictions as set points, a predictive functional controller is then designed for the OG position control to minimize the tracking error. This novel combination control scheme is validated in MATLAB/Simulink. Simulation results have confirmed that the proposed scheme can significantly mitigate the zenith pass problem and be applied to the real-time tracking process.
Highlights
Taking into account the cost savings and size reduction, a two-axis gimbaled platform has been widely used in optics seekers of precision-guided missiles
Ji et al [16] have analyzed the factors influencing the zenith pass problem and concluded that the tracking performance near the zenith is significantly affected by the approaching degree and the angular rate of LOS
Λref = sin−1ðcos σ sin ðωt − π/3ÞÞ, where for the sake of generality, the elevation and azimuth references to be predicted are expressed in a form of a nonlinear function. ω is the sightline angular rate. σ is the zenith pass angle, of which the sine function determines the proximity to the zenith
Summary
Taking into account the cost savings and size reduction, a two-axis gimbaled platform has been widely used in optics seekers of precision-guided missiles. With the three-axis design, the zenith pass problem can be completely overcome by altering the two rotation axes of three in different tracking scenarios This solution can increase the size and cost and bring some other complex issues like coupling of axes’ inertia. Unlike the previous two solutions to change the hardware structure, the third one, program guidance method, is to tackle the problem by preplanning the boresight trajectory within acceptable error range In this method, the OG angle response of zenith pass is optimized under the actuator constraints, and the singularity is significantly mitigated. The OG angle response of zenith pass is optimized under the actuator constraints, and the singularity is significantly mitigated This method is basically only used in the design of satellite tracking antennas for the geometry trajectory of sightline has to be known a priori in the process.
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