Research On Several Essential Problems Of Imaging Seeker Servo Mechanism

Seeker servo mechanism is a key part of precise guiding weapons, the performanceof which directly affects the precision of the weapons. With the development of preciseguiding weapons, the dynamic performance of seeker servo mechanism is demandedhigher and higher. Characteristic indexes are corresponding standards of dynamicperformance of seeker servo mechanism, and how to get the reasonable characteristicindexes is the basis of the research work on seeker servo mechanism. Researching onthe main factors influencing performance of the mechanism and putting forward theeffective methods are the radical approaches to improve the performance of seekerservo mechanism. In this paper, the issue on designing characteristic indexes of imagingseekers is studied firstly. Then the coupled dynamics of seeker servo mechanism withtwo-axes gimbal are studied deeply, and the effect of mass imbalance torque andfriction torque on the control precision of seeker servo mechanism is also analyzed indetail. On the basis of the above works, several effective compensatation controlalgorithms are researched to improve the precision of the seeker servo mechanism fromthe aspect of the engineering application. The main works of this paper are as follows:1. On account of the carrier’s movement is the main factor to influence the imagingperformance of electric-optic (E-O) systems, it is important for the reasonable planningthe stabilization precision index of servo system to study on the influence mechanism ofcarrier’s movement. Firstly, the sources causing dithering of LOS by carrier’smovement are analyzed; then, with means of the geometric optics, the relationshipbetween the carrier’s moving and image’s moving on the focal plane is studied; finally,from the aspects of modulation transfer function, spatial resolution, and NIIRS, theinfluence of the carrier’s movement on imaging performance of E-O system is studied.From the point to satisfying the detecting capability of E-O system, the theoretic basisto confirm the stabilization precision index is put forward.2. As to the issue design the indexes of imaging seeker’s control system forsearching, tracking and stabilizing, the main working principle of the seeker isintroduced, and the integrant techniques of seeker servo system are put forward; therelationship between the searching blind regions with the searching velocity is studied.According to the influence of image moving on the performance of detector, the methodof conforming searching velocity is given. From the aspects of the maximal velocity ofLOS and the real time requirement of the image tracking algorithm, the limit of seeker’stracking velocity is presented. The main factors influencing tracking precision of thesystem are analyzed, and the method of conforming tracking precision indexes isdeduced. Taking account of the requirements of the actual system and the effect of thecarrier’ s movement on the performance of E-O system, a kind of design method of seeker’s stabilization precision index is put forward on the basis of the research work.3. On account of better researching on the influence of mass imbalanced torque oncontrol precision of the seeker servo mechanism, the kinematics model of seeker servomechanism are established; furthermore the dynamics model with mass imbalancedtorque are also constituted based on the theorem of angular momentum. The coupleddynamics among missile’s body, seeker servo mechanism are also researched, whichlead to the direction of structure’s design of seeker’s servo mechanism. Finally thesimulation experiments are taken to validate the established models, the results of whichshow the effect of the external disturbance torque on control precision of the seekerservo mechanism and provide foundations for subsequent research works such asstructure optimizing and disturbance compensatation and so on.4. In order to attenuating the effect of friction torque on the control precision of theseeker servo mechanism, the characteristics of friction torque on coupled movement andfrequency trait of the system are researched, as well as the effects of stabilizationcontrol loop on linear disturbance and nonlinear disturbance such as friction areanalyzed, and the simulation experiments are taken to validate the research work, theresults show:(1) The coupled friction torque ratio has the same change trend with thatof missile’s body acceleration.(2) Friction torque can cause error in systemidentification process, which exhibit decreasing amplitude and leading phase.(3) Theopen control gain of stabilization loop can manifests its attenuating performance onouter linear disturbance, but can’t exhibit the impaction on nonlinear disturbancecoupled with friction torque. Increasing the open control gain and compensating frictiontorque are the basic design rules for stabilization control loop.5. Before the research works of compensating the disturbance torque, a kind ofmethod to test mass imbalance torque and friction torque is presented in this paper. Inorder to eliminating the defects of the threory of the present control algorithm based ondouble velocity loop in series, the describing function method is used to analyzed thevalidity of the double velocity control method. The effect of friction model’s parameterson control precision of the system is studied, which is the foundation of compensatationcontrol algorithm based on friction model in practice. The cooperated use of frictionmodel and disturbance observer is studied deeply, and a kind of modified disturbanceobserver structure is put forward. The experimental results show that the presentedcontrol method with friction compensating model and low pass filter can achieve goodperformance, and can be realized easily in practice.6. The structure of the researched seeker servo mechanism is introduced as well asits constitution, working modes and the servo control circuit with double DSPs. Theissues to design different control loops are brought forward as well as the resolvingmethod. The basic ideas for software programming of the control system are given along with the working flow of DSP’s interrupt programs. Based on dSPACE，a kind ofmethod to testing disturbance attenuation is presented, and the test results of thesystem are also given.