Whole Process Modeling And Similarity Study Of 25m Radio Telescope Servo System

The Radio Telescopes are developing towards large aperture and high frequency band.However,increasing the aperture leads to the decrease of the natural frequency of the structure and the increase of the flexibility,and the mechanical resonance is easy to occur,which affects the pointing accuracy;and high frequency band also requires high pointing accuracy.Therefore,it is difficult to ensure the high pointing accuracy of antenna.For achieving high control precision,the optimal control algorithm has been widely used in the large aperture radio telescopes.But an accurate dynamic model of the controlled object should be required in the optimal control.The traditional mechanical modeling method is not applicable to the large aperture radio telescope because of its structural flexibility.For that reason,the servo system dynamic modeling and the similarity of large aperture radio telescope are studied for predicting physical characteristics by platform experiment results in this paper.Aiming at the dynamic modeling of servo system of large aperture radio telescope,the finite element model and the whole process dynamic model of the 25 m Radio Telescope are established.Firstly,the finite element model of 25 m Radio Telescope is established,and the rationality of the finite element model is analyzed.Secondly,the whole process model of pitching system is established,which is from motor and reducer to big gear and main reflector,from big gear and main reflector to auxiliary support leg and auxiliary surface.And the flexible part of the big gear and the main reflector is based on the finite element model of the 25 m Radio telescope,which is established by the modal coordinate method.The auxiliary support leg and the auxiliary part are derived from the equivalent method of equivalent Euler-Bernoulli beam.Then,the dimensionality is reduced of the whole process model.The modal selection is done for the flexible part of the big gear and the main reflector and the supporting leg and the auxiliary part are simplified as the model.Finally,the block diagram is built and simulated.Aiming at the similarity study of large aperture radio telescopes,the prediction of the dynamic response characteristics of 25 m Radio Telescope neglecting the side support and the side support is completed on the fully similar two-inertia experimental platform,and the prediction of the dynamic response characteristics of the actual 25 m Radio Telescope Based on the distorted similar three-inertia experimental platform is also presented.Firstly,without considering the supporting legs and side-faces of the prototype,the similarity of the two-moment inertia experimental platform was studied by using the self-built two-moment inertia experimental platform.And then,the dynamic similarity law of prototype and model and the parameters needed to be adjusted are obtained by dimensional analysis method.The prediction of the prototype dynamic response characteristics is verified by experiments on two inertia experimental platforms.Secondly,a three-inertia experimental platform of flexible ruler is built based on the existing two-inertia experimental platform with considering the supporting leg and the side face.It is found that the mass cannot satisfy the similarity law through similarity modeling and dimensional analysis,which results in the distortion of the three inertia platform.So,the law of predictive distortion is adopted to get the functional relationship between the distortion law of dynamic response and the distortion coefficient of mass.And the prediction of the dynamic response characteristics of the 25 m Radio Telescope is verified by experiments on the three-inertia experimental platform with combining with the relationship between the complete similarity model and the prototype.