Research And Application Of Disturbance Observer And Advanced Control In Aerial Camera Position-angle System

As one of the main loads of aerial reconnaissance, aerial camera has the advantagesof flexibility, high efficiency and so on. This thesis is one of the research elements ofthe XX-CCD camera research project. This thesis researches and solves thedisturbance suppression problem in image motion compensation control moderequiring low speed and high-precision and the Anti-Windup problem of the cameraposition-angle mirror in position control mode requiring fast speed. The main workhad important significance in improving the resolving power, lengthways positionprecision and shortening camera work cycle.Around the performance index technical difficulties of the XX-CCD cameraposition angle control system, the main work and contributions are given as followsin this thesis.1. This thesis discussed the research background, topics sources and researchsignificance. The domestic and foreign research actuality in fields of some relativeresearch involved aerial camera, servo control systems, disturbance observer andsuppression technology. Moreover, the research status of the disturbance observerand suppression technology of control systems was focused on.2. Introduction on system configuration, work mode, index analysis and criticalcomponent parameters were given. A number of factors, affecting position-angle control system performance index, such as friction disturbance, torque fluctuations,sensor performance and carrier aircraft conditions, were analyzed. Mathematicalmodeling for elements of position-angle control systems were completed by usingtheoretical mechanism modeling method. Through the frequency characteristicstesting experiment on the open loop system and combining with the previous typicalmathematical model, the mathematical model of generalized open loop system wasobtained after the model was simplified processed.3. Friction disturbance compensation method based on the friction feedforwardwas studied. In order to achieve friction disturbance compensation, a simplifiedmathematical model of systems was implemented. A friction model parametersidentification approach based on the binary-coded genetic algorithm was provided.According to balance principle in the system torque combiner, the parameterequivalence relation between the friction feedforward compensation channelregulator and the identification friction model was established. Aiming at externaltorque disturbance, the disturbance observer based on a combination of normalmodel inverse and low-pass filter was adopted. If the observation was inputted intocontrol terminal, the compensation of external torque disturbance could be achieved.Image motion compensation control based on disturbance observer and adaptivesliding mode control using improved discrete exponential reaching law was designed.Finally, compound control method based on the disturbance observer feedback andfriction model feedforward was proposed. This compound control method caneffectively restrain disturbances and make forward image motion residuals reducedabout two-thirds.4."Windup" phenomenon of the position angle position control system caused bythe saturation nonlinearities was analyzed. The two ideas and methods of theAnti-Windup were proposed as follows. From the view point of compensationmeasures for occurred windup, primary and secondary dual loop cascade PIDposition control based on Anti-Windup variable structure was proposed. AdaptivePID control based on Anti-Windup variable structure was used in secondary speedloop. The PID with adaptive slight adjustments of Windup integral coefficient was used in the primary position loop. To overcome the lagging shortcomings ofcompensation measures for Anti-Windup, the variable integral PID as the integralAnti-Windup measures in the position control loop. From the view point ofpreventive measures for windup, position control scheme based on PID with fuzzyadaptive correction and optimized and tuned basic parameters by genetic algorithmwas proposed. Position control scheme still used primary and secondary loopcascade control. Position outer loop is the primary loop and speed inner loop issecondary loop. Position outer loop adopted the method based on fuzzy adaptivecorrection and optimized and tuned basic parameters by genetic algorithm. Thegenetic algorithm minimum objective function had overshoot punishment. Thesebasic parameters of PID were fuzzy corrected within the neighborhood of basicparameters by fuzzy control. Fuzzy control used2D fuzzy PID control scheme withthe nonlinear quantification and center dense membership function. Under thepremise of accelerating error elimination of the system dynamic response as much aspossible, this method helped to improve the system performance. Compared withconventional PID algorithm, these two methods proposed in this thesis have goodcontrol effect, the settling time reduced by about50%and steady-state accuracyincreased by about60%. The application of these methods effectively improve therapidity，accuracy and robustness of position control systems.5. On the XX-CCD camera experimental platform, various experiments includingdisturbance observer validation experiment, friction feedforward control validationexperiment, image motion speed compensation control experiment, position controlexperiment, laboratory dynamic imaging experiments and flight test experimentwere carried out. The effectiveness of disturbance observer was verified by usingsimulation experiment. The experimental results showed that disturbance observercan be more effectively to torque interference suppression by reasonable setting thenominal model and low pass filter. Friction feedforward control experiment wasconducted. The friction disturbance suppression from the friction feedforwardcontrol was verified in the low speed image motion compensation. Image motioncompensation experiment including the routine experiment without taking the initiative disturbance and the experiment with active disturbance verified the validityand capacity of resisting disturbance of image motion compensation control. Threemethod including fixed parameter PID control scheme, Anti-windup variablestructure adaptive PID position control method and PID control method based onfuzzy adaptive correction and genetic algorithm was used to do position controlexperiments respectively. From the maximum overshoot error, rise time, settlingtime and steady-state error，the performance of three methods were analyzed andcompared. Laboratory dynamic imaging experiment was done under the conditionsof flight speed-high ratio parameter respectively equal to0.00691/s,0.01231/s and0.02301/s. Dynamic imaging resolution reach up to51lp/mm superior to therequirements of laboratory dynamic imaging performance index (45lp/mm).6. Through flight test, camera obtained the effective enough flight image samplesand met all the requirements of flight test performance index. Image has anappropriate contrast, detailed shadow, rich graduation and clearly distinguisheddetails of railway sleepers, road markings, vehicle type, lines of stadiums and so on.The performance of position-angle control systems was fully verified.The main work and contributions in this thesis show that this research methodseffectively solved the camera position-angle mirror Anti-Windup problem in theposition control mode requiring fast speed and high-precision and disturbancesuppression problems in the image motion compensation control mode requiring lowspeed and high-precision. The main work had important significance in improvingthe camera imaging quality, the precision of position control and shortening theimaging cycle of camera.