Vibration Monitoring And Control Of Main Reflector In Large Antennas

The development of radio astronomy and deep space exploration puts forward the requirements of high frequency band,high gain,and high pointing accuracy for large reflector antennas.However,due to the large aperture and low structural stiffness of large reflector antenna,the wind disturbance and other dynamic loads have a significant impact on its pointing accuracy.In addition,the antenna servo system can only measure and control the angle deviation of the pitch and azimuth shaft,cannot sense the pointing error caused by the vibration deformation of the reflector.Aiming at this thorny problem,this dissertation starts with the main links of dynamic monitoring of pointing error,optimizing the layout of sensors,and designing cable actuator to suppress vibration.The key technology of vibration monitoring and control of main reflector in large antenna is deeply studied to improve the pointing accuracy of large reflector antenna.The main work and achievements of this dissertation are as follows:1.A real-time monitoring method of pointing error based on acceleration measurement is proposed,so as to realize the monitoring of the pointing error caused by the vibration deformation of the main reflector in real time.Based on the best-fitting parabolic theory and considering the measurement noise,the Tikhonov regularization principle is introduced to slow down the morbidity of the inverse problem caused by the measurement noise,then the model for real-time estimation of the pointing error through accelerations of the measurement point is established.In order to further overcome the shortcoming that the integration method cannot obtain the low-frequency pointing error below the cutoff frequency,based on the unbiased minimum variance input and state estimator,a non-integral approach is proposed to monitor the pointing error in real time.The simulation results of 7.3m antenna under wind load show that there are ultra-low frequency components near zero frequency in the azimuth pointing error.The relative errors by frequency domain integration method,high pass filter integration method and non-integral approach are 20.07%,20.18% and 4.83%,respectively.Because the non-integral approach does not perform low-frequency cut-off operation on the signal,it has higher accuracy than the two integration methods.2.A sensor layout optimization method is proposed,so as to realize the better monitoring of the pointing error with low information redundancy.First,in order to avoid the redundancy caused by sensor accumulation,the regional correlation analysis method of node mode is proposed,and the constraint distance between sensors is determined.Then,based on the real-time monitoring model of the pointing error through the acceleration measurement,and considering the symmetry of the antenna structure,the sensor layout optimization algorithm through symmetrical partition in the main reflector is established.Finally,under the sensor constraints,the measurement points are optimized from many main reflector nodes.The simulation results of the 7.3m antenna show that the sensor layout optimization method proposed in this dissertation is more effective than the effective independence method.The redundancies in this method and in effective independence method are 18.4% and 20.4%,respectively.For the monitoring accuracy,the relative error of the estimated pointing error in the elevation direction by this method is 0.4%,and it by the effective independence method is1.6%;the relative error of the estimated pointing error in the azimuth direction by this method is 4.8%,and it by the effective independence method is 5.5%.3.A vibration suppression method for the reflector antenna based on a cable actuation system is proposed,which effectively suppresses the vibration deformation of the large-scale reflector antenna under dynamic load.First,the vibration state of the large antenna under dynamic load and cable tension is observed in real time by an unbiased minimum variance state estimator;then,according to the observed vibration state,the linear quadratic regulator controls the drivers to output the cable tension to suppress the vibration deformation of the reflector.In the simulation example of wind disturbance suppression for a 7.3m antenna,the root mean square of pointing error is reduced to 27.17% of the uncontrollable effect.In order to further verify the effectiveness of the cable actuation system in vibration suppression,a reflector platform of the torsional vibration in the pitch direction is built,and a cable vibration damping system is added.The experiment of vibration control in the pitch direction shows that under the shock excitation of a pendulum,the vibration time of the reflector without control is about 7 s,while the vibration time of the reflector with control is reduced to about 1 s.4.A position optimization method for multiple drivers in the cable actuation system is proposed,which is able to further enhance the effect of cable actuation system to suppress the vibration state of the reflector.Since the multiple drivers located on the single slide rail in the system respectively pull the cable to suppress the vibration of the reflector,some drivers' positions may cause interference between the devices.Therefore,first,according to the spatial geometric relationship between the single slide rail,the drivers,the cables and the antenna,the feasible region of the drivers is determined.Then,a separate optimization method for the driver position,and a joint optimization method for the driver position considering the working conditions are proposed.In the simulation implementation of a 7.3m antenna under the transient wind disturbance,using the joint optimization method at the wind direction of 90 degrees,the control performance is improved by 13.06% compared with the single optimization method;while using the single optimization method,the variance of control performance is smaller than the joint optimization method under unknown wind conditions.