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Step and stare imaging with staring arrays has become the main approach to realizing wide area coverage and high resolution imagery of potential targets. In this paper, a backscanning step and stare imaging system is described. Compared with traditional step and stare imaging systems, this system features a much higher frame rate by using a small-sized array. In order to meet the staring requirements, a fast steering mirror is employed to provide backscan motion to compensate for the image motion caused by the continuously scanning of the gimbal platform. According to the working principle, the control system is designed to step/stare the line of sight at a high frame rate with a high accuracy. Then a proof-of-concept backscanning step and stare imaging system is established with a CMOS camera. Finally, the modulation transfer function of the imaging system is measured by the slanted-edge method, and a quantitative analysis is made to evaluate the performance of image motion compensation. Experimental results confirm that both high frame rate and image quality improvement can be achieved by adopting this method.

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High-performance control of inertial stabilization imaging sensors (ISISs) is always challenging because of the complex nonlinearities induced by friction, mass imbalance, and external disturbances. To overcome this problem, a terminal sliding mode controller (TSMC) based on a novel exponential reaching law (NERL) method with a high-order terminal sliding mode observer (HOTSMO) is suggested. First, the TSMC based on NERL is adopted to improve system performance. The NERL incorporates the power term and switching gain term of the system state variables into the conventional exponential reaching law, and the convergent speed of the TSMC is accelerated. Then, an HOTSMO is designed, which considers the speed and lumped disturbances of the system as the observation object. The estimated disturbance is then provided as a compensation for the controller, which enhances the disturbance rejection ability of the system. Comparative simulation and experimental results show that the proposed method achieves the best tracking performance and the strongest robustness than PID and the traditional TSMC methods.

Transparency is an important indicator to evaluate the performance of a bilateral control system. Uncompensated disturbances in high frequency degrade the transparency in the traditional disturbance observer (DOB) based bilateral control. This paper analyzes the influence of the uncompensated disturbances, and proposes a sliding mode assist disturbance observer (SMADO) to solve the problem. The sliding mode technique helps the original DOB to estimate the disturbances in high frequency by making use of a rapid switching control value. The required switching gain is small in the proposal, which is good for alleviating the chattering. Moreover, to avoid conservative and arbitrary design of the switching gain, a reasonable benchmark is proposed by employing the estimation error between the original DOB and another parallel DOB with a different cutoff frequency. The validity of the proposal is confirmed by experiments. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

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