Research On Accurate Location Of Dual View Field Focal Plane Array Imager

These days, our air defense forces mainly rely on radars to detect targets while fighting at night. However, Radars installed in our country are generally lagging behind the performance, susceptible to electromagnetic interference at work and vulnerable to enemy missile attack. Therefore, research and design of the infrared low-attitude early-warning system with the uncooled focal plane array imager as its core is of great significance.Dual view field imager can be used to observe the large scenery regional, searching suspected targets in the large view field mode and carefully observing or enlarging targets in the small view field mode. Furthermore, it can recognize, track and aim targets and finish the tasks that the imagers with fixed focus are not able to achieve. The traditional method of manual focusing depends on people's visual and manual adjusting, and has lots of shortcomings, such as time-consuming and having little reproducibility. However, in real application, it is required to locate the "image preset points" quickly and accurately. Consequently, the research about focal length of the positioning and dual view field switching of the uncooled focal plane array imager is carried out.The paper firstly analyses the basic principles involved dual view field switching and focal length of the positioning of the uncooled focal plane array imager , taking into account the restriction of the hardware and the structure of space, and then puts forward the design scheme of achieving accurate location by means of nonlinear shift integral PID closed-loop position feedback, using optical encoder to provide the position feedback of motors, easy detection and high precision.In this paper, the actual demand and design cost are both considered, and low power 16-bit MCU MSP430F157 and CPLD EPM1270T144C5 of Altera corporation are chosen to design the hardware circuits of the focal length of the positioning control system of the uncooled focal plane array imager. The blocks of quadruplicated frequency and filtering algorithm of anti-dithering which improves the positioning accuracy and anti-interference ability are realized by hardware description language (VHDL) on CPLD. Compared with traditional methods of adopting RC circuits and gate circuits to complete a deal with the encoder feedback signal, it improves the system stability and flexibility. To solve the problem of deterioration of positioning accuracy and poor image quality induced by gear wear, this paper launches a research on the algorithm of the automatic focusing , selecting a suitable focusing evaluation function and detailed introducing the principle and realization of the optimized mountain-climb-searching algorithm which can get rid of the disturbance of local extremum effectively, improving the reliability of auto-focusing.In this paper, the designed system is tested in the end, including the nonlinear shift integral PID algorithm test and the optimized mountain-climb-searching algorithm simulation test, the focal length of the positioning and dual view field switching functional test. The system can complete the stable dual view field switching and precise positioning control (positioning error is less than two pulse), and is good to meet the actual demand.