| During the process of the altitude-azimuth telescope tracks the objects,the orientation of the azimuth axis in the receiving end field of the telescope system is remain constant,which will not change with the rotate of the altitude and azimuth axis of the telescope,but,since the earth rotation,the telescope's azimuth axis is not coincident with the earth's polar axis,which lead to the dot's(off-axis)image in the field rotate along with the telescope's azimuth axis,except the dot which located in the telescope's azimuth axis,such that the generate of telescope's object-field rotation.Besides,the folding plane mirror in the telescope's Coude optical path will rotate relatively with the rotate of the altitude and azimuth axis of the telescope,compared with the input vector of the telescope,the output vector of the telescope rotate a certain angle around the axis the telescope,such that the generate of the telescope's view-field rotation.In order to realize the real-time objects identification and subsequent image processing,it's necessary to eliminate the effects of object-field rotation and view-field rotation of the altitude-azimuth telescope.K mirror as the de-rotator of reflection optics elimination rotation,which has advantages of “real-time”,“less energy loss” and “full-band”,is widely used in altitude-azimuth telescope to eliminate the filed rotation.Now,K mirror has been confirmed as the de-rotator of the alt-az telescope designed by Changchun Institute of Optical Fine Mechanics and Physics,Chinese Academy of Sciences,combine the design of servo control system of K mirror turntable,the main contents of this paper are as follows: 1)How to determine the performance index of the K mirror turntable in order to realize the eliminate of filed rotation;2)How to design the drive system of the K mirror turntable;3)How to identify the control model of the K mirror turntable;4)How to improve the position tracking accuracy of the K mirror turntable.The reasons of field-rotation and mathematical calculation formula of the field-rotation angle for horizontal telescope were studied thoroughly,the principle of K-mirror turntable can realize de-rotation is analyzed,the performance index of control in condition of de-rotation is given.Firstly,the reason of object-field rotation caused by altitude-azimuth gimbals is analyzed,the relationship between the angle of object-field rotation and the rate of parallactic angle q is analyzed under the spherical coordinate system,the mathematical calculation formula of the object-field rotation angle is given under the cartesian coordinate system;Secondly,by using the method of matrix optics,the angle of image-field rotation,caused by reflector component when the compose movement of position axis and direction axis is occurred,is analyzed;Finally,by using transformation matrix of object-image and transformation matrix of rotation,the paper analyze the principle of K-mirror turntable de-rotation,combining the actual condition of de-rotation K-mirror of altitude-azimuth telescope,determined the performance index of control when the field-rotation can be eliminated.The permanent-magnet DC torque motor's power driver and digital controller are designed in this chapter.The inverter adopts the intelligent power module,which integrate power switches and drive circuit,over voltage/under voltage/overheat protection circuit,and so on.The servo controller is based on the floating-point DSP and FPGA.DSP is responsible for compute the position/speed control algorithm and external control interface.FGPA take charge of gather the signal of position sensor(photoelectric encoder),PWM modulation and fault treatment.The experiment result demonstrates that the drive system designed can meet the requirement of “real time”.Based on the design of drive system,in order to prepare for the design of servo control algorithm,the identification of K mirror turntable control model's order and parameters are studied.Firstly,using the impulse signal as input stimulus signal,system identification method: the Eigensystem Realization Algorithm which is based on the singular value decomposition of the Hankel matrix,is deduced to identify the system's order and parameters.Secondly,since the sin sweep signal is used as input stimulus signal in the project,the obtain method of Hankel matrix is introduced(from measurements one obtain the input and output time histories,rather than the Markove parameter themselves,the exceptions are impulse response measurements).Lastly,1)Based on the sin sweep input sequence and open loop responses output sequence,adopt spectrum analyzing method to determine the frequency characteristic of K mirror turntable.2)Build Hankel matrix based on the input sequence and output sequence.3)Determine the order of the K mirror turntable by decompose the Hankel matrix through singular value decomposition method.4)Estimate the parameters of the K mirror turntable using Eigensystem Realization Algorithm.The results of experimental indicate that,compared with the hierarchical identification method,the proposed identification method can determine the minimum order of the K mirror turntable is 6 accurately,magnitude phase measurement accuracies of transfer function are improved 50.7% and 23% in middle frequency range,respectively.The balanced state-space representation provides a model basis for analysis and design of control system,control algorithms simulation.On the model basis of the K mirror turntable,double closed-loop lead-lag compensator are designed for the K mirror turntable,and verified by simulation and experiment.In order to overcome the influence of the mechanical friction,torque ripple,parameter variations,external uncertainty disturbance nonlinear factors on control output of the K mirror turntable,one-stage linear active disturbance rejection control is designed in speed loop,and verified by experiment.The results indicate that there are problem of “Control Small Dead Zone” and “Control Big Overshoot”,an adaptive active disturbance rejection control,which design the P-type gain of the feedback control law into a function that can be automatically adjusted with a change in the system input speed,is proposed,and verified by experiment.The results demonstrate that the RMS value of position tracking error is 0.4437'',compared with the traditional lead-lag controller and ADRC controller,the position tracking accuracy are improved by 51% and 37%,respectively.(Note: The three algorithms employ the same positioning controller: lead-lag correction controller)In order to drive the K mirror turntable as half the angle of the field rotation angle,such that to eliminate the filed rotation,two-stage linear active disturbance rejection control is designed in position loop.The disturbance estimation ability of the nonlinear extended state observer(NLESO)is superior to linear extended state observer(LESO),but the parameter tuning of NLESO is very difficult,as an alternative,the position loop ADRC controller based on the linear generalized proportion integral observer is proposed.The results demonstrate that RMS value of location error is ± 0.01'',the RMS value of position tracking error is 0.3536'',compared with the traditional ADRC controller,the location precision and position tracking accuracy are improved by 50% and 8.1%,respectively.(Note: The two algorithms employ the same speed controller: lead-lag correction controller)... |
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