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Study on Nonlinear Dynamic Modeling Measurement and Control Problems for Precision Pointing Mechanisms

Author: FanShi
Tutor: FanDaPeng
School: National University of Defense Science and Technology
Course: Mechanical Engineering
Keywords: Line of sight stabilization and tracking Precise pointing mechanism Non-linear Structural dynamics Linear parameter varying system Least squares Genetic algorithm Principal component analysis State observer Disturbance observer μ synthesis
CLC: TP273
Type: PhD thesis
Year: 2012
Downloads: 118
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The precise pointing mechanism is a kind of mechatronic rotary motion controldevice, which has been widely applied in aspects including the reconnaissance,prewarning, guidance, fire control, communication, and other equipments. With therapid development of the equipment technology, the precision and lightweightrequirements on the pointing mechanism are higher and higher. The factors includingthe friction, mass unbalance, and modal are essential to the improvements of theprecision of the lightweight pointing mechanism; and, how to perform modeling to suchfactors, achieve the key parameters testing, and control arising positioning errors havebecome key issues in the research on the design technology. In the paper, the authortakes the enhancement of the pointing mechanism control precision as the objective andfocuses on the variability modeling, key parameter identification, and robustanti-disturbance control in case of nonlinearity and modality specific to the influentialfactors including the friction, mass unbalance, and modal, and puts forward the perfectand practical variability modeling, measurement and control methods in case ofnonlinear pointing mechanism.The study work of the paper includes following parts:1. In order to master the impact of the factors including the friction, massunbalance, and modality on the control performance of the pointing mechanism, thenonlinearity dynamics modeling is studied and researched. In addition, based on thedynamics equation set of the two-axis pointing mechanism, its control principles areanalyzed, thus comprehending the mechanism of the friction, mass unbalance, andmodality impacting the control performance. In order to achieve precise measurementand control of the pointing mechanism, further study is performed to the friction andmodality modeling. By means of study on key kinematic pair friction mechanismsincluding the bearing and motive seal, the friction moment model description isobtained. Also, through research on the finite element method, the constant parametermodel of the modality is also obtained.2. in order to perform effective process quality control to the friction, massunbalance, and other nonlinear factors during the mechanism fabrication andassembling stage, the exact identification methods for the inertia, unbalance mass,friction, and other key nonlinear dynamics parameters are studied and researched basedon the demands of the fabrication and assembling performance detection of the pointingmechanism. In addition, the state expansion and discrete dynamics model is establishedfor the pointing mechanism and three kinds of numerical differentiation algorithms for the instantaneous speed signal estimation are also analyzed and compared; on such basis,one unbiased identification method for the key nonlinearity model parameter of thepointing mechanism is proposed by means of the method of least squares and thenonlinear state observation and control methods and taking the mechanism restrictionsin the project into consideration. In a word, the applied research method can effectivelyimprove the identification precision of the inertia, damp, friction, mass unbalance, andnonlinear dynamics parameter.3. Requested by the lightweight demand of the pointing mechanism, the impact ofthe structure modality characteristics on the precision can’t be ignored. On this account,the author studies and researches the modeling and identification method for themodality parameter variation model under changeable loads. In addition, the author alsoanalyzes the influential mechanism of the load inertia changes on the structure modalityparameter; furthermore, he applies the parameter variation model modeling technologyto establish the linear modality parameter variation model for the pointing mechanism.Also, applying the nonlinear least square optimization technology and the principalcomponent analysis technology, the author raises a kind of identification method for thelinear modality parameter variation model. In a word, the author offers a new thoughtfor the structure modeling and analysis of the high precision lightweight pointingmechanism.4. From the control view, the changes of the friction, mass unbalance, and modalitywill impact the control precision of the pointing mechanism in form of disturbance. Theauthor performs studies and researches to the disturbance characteristics by means ofthe disturbance observation technology; summarizes and analyzes the design essentialsof three disturbance observation technologies including the DOB disturbance observer,state expansion Kalman filter, and time delay disturbance observer as well as analyzestheir own advantages and disadvantages from four aspects of the instantaneity,disturbance annihilation performance, noise annihilation performance, and steadyconvergence of the observation results. In a word, the author forms three schemes forthe disturbance compensation control of the pointing mechanism as well as offer ideasfor the subsequent design research on the nonlinear controller of the mechanism.5. Considering the impact of the model parameter uncertainty and the transientcharacteristics of the friction moment on the control precision, the author studies andresearches a kind of robust and precise servo control design method for the pointingmechanism. In addition, the parameterization uncertainty model is also established forthe pointing mechanism. Moreover, the author also analyzes the instantaneousfrequency characteristics of the friction moment signal; defines the measure of theinstantaneous power of the friction signal and the gains of the servo system to the instantaneous power of the signal, so as to estimate the peak tracing error of the servoaxis arising from the friction and analyze the anti-interference performance of the servocircuit. Based on the above systematical analysis methods as well as applying thesingular value control technology and DOB disturbance observation technology, theauthor proposes a kind of dual-circuit robust tracking servo control strategy. With theimproved singular value controller design method, the singular value position servocircuit includes two integrators; thus, the steady tracking error can be effectivelyannihilated. Furthermore, the author also deduces the comprehensive robust steadyconditions for the dual-circuit as well as gives the DOB circuit design method on suchbasis. In a word, all the proposed control strategies can effectively improve the servoprecision of the pointing mechanism and the circuit robustness.

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