| With its advantages of big gimbal angle and smart size, the Roll-Pitch seeker caneasily cover hemisphere of a seeker. On the contrary, the particular disadvantage ofRoll-Pitch seeker is the zenith pass problem that is when a manoeuvreable target ismoving in the range of small abaxial angle, the calculated servo command willbecome singular which will result in the loss of target. The application of Roll-Pitchseeker in the Air-to-Air is severely restricted by its zenith pass problem. Aimed atsolving the zenith pass problem in a Roll-Pitch seeker, this paper is consist ofmodeling of zenith pass problem, tracking strategy analysis, servo controller design,tracking test and conclusions.The algorithm of getting angle increment command from deviation pixels on theimage plane is presented at the beginning. The presented algorithm is the origin ofzenith pass problem, so the description of zenith pass problem is given in sequence.This section is the theory basis of solving zenith pass problem.For solving the zenith pass problem in Roll-Pitch seeker, roll gimbal controllerand pitch gimbal controller are designed first to satisfying dynamic and steady staterequirement of the servo system. Errors that mainly influent the tracking precision arepresented as follows, gyroscope error, servo error and image error. Gyroscope error isemphatically studied as well as its impact in the servo control system. And then thecontrol strategy for zenith pass problem is introduced, and the strategy is based on three input conditions which are pitch angle, target deviation pixels on image planeand target moving rate. Although the strategy works effectively, but it is notsufficiently effective. There is still risk of loss of target, so the self adaptive Kalmanfilter is designed here to predict the next time position, velocity and acceleration oftarget. With the predicted information target tracking process can be more smoothlyachieved.In order to verify and test performance of the zenith pass strategy controller, aplatform consist of AD/DA conversion card, serial communication card, motor driverand so on is built. With this platform it is convenient to do jobs such ascommunication protocol test, seeker model identification, servo controller design andtest. A target movement manner is set that the target passes through the zenith zoneseveral times. Validity of the strategy for zenith pass problem is tested and the resultindicates that it works well.The whole paper is focused on how to deal with zentith pass problem, andmainly discusses the following content, description of zenith pass problem, gyroscopeerrors, self adaptive Kalman filter and strategy design for zenith pass problem. Thefinal experiment said that without using strategy for zenith pass problem the zenithblind zone is about±2.5°while with using the strategy target can be smoothly trackedand the tracking error in y direction is1.8mrad as well in z direction2.2mrad. It isproved that zenith pass tracking controller can solve the zenith pass problem. |
