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Study on Ultralow Frequency Standard Vibration Metrology System

Author: ZuoTianLi
Tutor: YangXueShan
School: China Seismological Bureau, Institute of Engineering Mechanics
Course: Disaster Prevention and Reduction Engineering and Protective Engineering
Keywords: ultralow frequency calibration vibration isolation negativefeedback a fuzzy PID self-tuning controller uncertainty
CLC: TB533
Type: PhD thesis
Year: 2012
Downloads: 109
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Abstract


The ultralow frequency vibrations are widely applied to engineering,which people has been an increasing interest in. The present research status ofultralow frequency was analyzed in the dissertation. By theoretical analysis,simulation and experiments, a system was designed to reduce the THD (TotalHarmonic Distortion) of an ultralow frequency vibration table effectively,which was based on an ultralow frequency vibration calibration system. Andthe system got a good actual effect. A new controller was presented andstudied. The main contents of the dissertation are arranged as follows:Firstly, the vibration sources were studies. Based on the theory ofvibration isolation, a new active vibration isolation method was presented.According to different feedback parameters, several kinds of feedbackmethods were introduced and simulated with MATLAB. By discussing them,an optimal method was found. The vibration isolation method was studied ofan ultralow frequency vibration table. A new method was given that passivevibration isolation is combined with the active. And the new method caneffectively solve the foundation isolation of an ultralow frequency vibrationtable.Secondly, the principle of an ultralow frequency vibration table wasdiscussed in the dissertation. And its dynamic characteristics were showedwith its mechanical model. Several key technical problems on an ultralowfrequency vibration table were pointed out and discussed, such as its nonlinearTHD, stability, vibration interference of the ground and background noise.Compared with relative velocity feedback and absolute velocity feedback, thecombination feedback method of the relative and the absolute was introduced.With the combination feedback, an ultralow frequency vibration table can beeffectively reduced its THD. Then we can conclude that negative feedback isnecessary and effective in an ultralow frequency vibration calibration system.For the system, the negative feedback can improve the dynamic characteristics,reduce its THD and implement calibration on ultralow frequency vibrationsensors.Thirdly, according to the modern PID control and fuzzy control theory, afuzzy PID self-tuning controller of the digital system was designed based onnegative feedback technology. The traditional analog servo control system isoften difficult to debug, easy to drift what ambient temperature can lead to,poor capacity of complex algorithm, lack capacity of realizing control algorithm based on modern control theory. The digital servo control systemcan avoid the defects what the analog one has. By programming withMATLAB and simulating, the initial values of three main parameters:K_D,K_P和K_I, were confirmed. And the selection rules and relationship of them weregeneralized, as well as the effect of the error on the three parameter valuesduring the self-tuning. The simulation of step response showed that the fuzzyPID self-tuning controller made the system better dynamic characteristics thana traditional PID controller. Also with the controller, the system had bettersinusoidal signal tracking effect. The controller was implemented on anultralow frequency vibration table with a DSP unit. The results show that thesystem can effectively reduce the THD with the feasible and effectivecontroller.Fourthly, the causes of A type uncertainty were discussed in thedissertation, as well as its computational formula. B type and composeduncertainties were also studied by analyzing vibration displacement error,measurement error of output voltage, the lateral motion error of the tableboard, frequency measurement error and so on. Then the judgment andrejection standard of exceptional value were probed during the measurementdata processing. A method was pointed out in the dissertation that the averagevalue of multimetering can effectively reduce the random error of the system.Lastly, a summation is made to generalize the study work in thedissertation. Also the dissertation puts forward the further research work whatwill be carried out in the near future.

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