A Study On Key Technology Of Digital Control Of Airborne Electro-optical Stabilization Platform System

Airborne electro-optical stable platform can isolate movement and vibration of the airframe, stabilizes the optic axis of the photoelectric detector, realize the observation and tracking for the object. It has comprehensive application value in army and civil field. Most of present airborne platforms are analogic control system, digital control system can improve the system general performance, digital control is the development direction of platform systems, digital control has especial techonoly, this paper focus on researching the key technologies of digital control of airborne electro-optical stable platform.By gyro detecting inertia velocity of platform to form close-loop, the airborne platform realizes the isolation to the movement and vibration of the airframe. By traction of the helmet or the angle deviation between optical axis and object axis, platform realizes the reconnaissance or tracking. Airborne electro-optical stable platform is two-axis-two-frame platform system of pitch axis and azimuth axis, its main component are mechanism, electronic box, photoelectric detector and sensor.On the aspect of theory, accurate model of the control object is the primary guaranty of high accuracy control system, reasonable system identification model let us understand system inertia structure and working mechanism. Platform system makes up of linear part and nonlinear part, this paper research as nonlinear friction existing, how to get the transfer function of linear part. To the system existing friction, there will be error if directly detect the frequency characteristic of the control object. If excite the servo control object by difference and large amplitude signal and collect the difference response, then get the frequency characteristic, this way can basically eliminate the error. The hierarchical least square iterative (HLSI) identification algorithm can converge the model transfer function parameters to their actual value. Basing on the HLSI the hierarchical identification way can get the high accuracy transfer function of airborne electro-optical stable platform system.Control strategy selection and controller design are key problems of the high precision control system. This paper research the platform control problem by lead-lag + fuzzy complex controller. The lead-lag control system has high accuracy, and the fuzzy controller has the ability of resist to nonlinear, the complex controller has their two merits, so platform system has high isolation performance, smooth step response and the better ability of external perturbation rejection and nonlinear friction rejection.Platform system use DSP to realize the servo controller, it is multi-rate sample control system. Based on lifting, sampling and holding technique, this paper research the transfer function of the feedback control multi-rate close-loop system and controller design, the matrix lifting transfer function changes the multi-rate close-loop system from time-variant system to time-invariant system. Present the concept of filter-holding, and point out that filter design can reject the vibration by sampling, the design of filter should consider the system frequency width, sample frequency and the control frequency.In the way of realization technology, the way of V/F transform + CPLD counter is used to solve the long-distance transmission of the gyro weak signal. The current close-loop is realized by PI analogy circuit, the current close-loop bandwidth is 1.25kHz. DSP is used to realize digital controllers of velocity-loop and position-loop. Analyze and validate that dividing high-level continue controller to several low-level controllers, then discretize the low-level controllers to form series controller can depress the discretization control error. In the end, introduce the experiments and their result.