Oscillation Element Optimization And Circuit Design Of Tapered Element Oscillating Microbalance

The micro mass sensor of oscillating balance uses the inherent relation between the resonant frequency and the mass of the oscillating element to weigh the micro mass.The upper end of the hollow micro-mass sensing element is covered with a filter for obtaining particulate matter in the soot gas and weighing the particles online.In order to further improve the sensitivity of the micro mass sensor and simplify the drive circuit,this thesis carries out the simulation optimized design of its core component—micro-mass sensing elements,and designs the digital closed-loop drive circuit based on STM32.The main work of the thesis is as follows:(1)Motion analysis of micro-mass sensing elements.The oscillation state of the micro-mass sensing elements is analyzed by mathematical model,and the emphasis is placed on the analysis of the damped oscillation and forced oscillation,which will provide a theoretical basis for the optimization of micro-mass sensing elements and digital drive circuit design.(2)Simulation optimization of micro-mass sensing elements.The model components of the micro-mass sensing elements are worked using Solid works,and the model is modally analyzed using the finite element analysis software ANSYS.In terms of material selection,simulation experiments are carried out on commonly used materials.The results show that the magnesium alloy is excellent in performance and durable,and the magnesium alloy is finally selected as the material for the micro-mass sensing elements.In the aspect of type selection,the size design of the composite double-tube micro-mass sensing elements is improved,and the simulation experiment analysis of the composite double-tube oscillating element with different angles is carried out.The relationship between the angle between the double-tube and the overall performance of the oscillating element has been explored.The overall design of the composite double-tube oscillation sensing element is further improved,and the preliminary optimization of the oscillating element is completed.(3)Further optimization of the oscillating element.The Evolutionary Structural Optimization method is used to further optimize the oscillating element,and the excitation force is added to analyze the stress-strain results of the oscillating element.The elimination of excess material of the component is achieved while ensuring that there is almost no loss in the overall structural performance of the component.The modal analysis of the material removal schemes for different parts of the oscillating element is carried out.The experimental comparison shows that the Evolutionary Structural Optimization method can effectively realize the weight reduction of the oscillating components.Finally,the weight loss of the oscillating component is 9.8%,and the mass sensitivity and frequency drop ratio are increased by 58.1% and 43.6% respectively.The overall performance of the oscillating element is significantly improved.(4)Design of digital closed-loop drive circuit based on STM32.Taking STM32 as the core,the AD9833 chip is used to form the frequency generating circuit,which realizes the initial forced driving of the oscillating element.The automatic gain control circuit is used to achieve a stable output of the drive signal.The capture of the resonant frequency takes advantage of the phase-frequency characteristics of forced oscillations,and the fast capture of the resonant frequency is achieved at-90 degrees using the dichotomy algorithm.In view of the phenomenon that the phase frequency characteristic curve of the oscillating element is abnormal in the experiment,by changing the detection method of excitation signal,the voltage measurement method directly measures the magnetic field intensity of the other end of the exciter with the inverse-phase linear hall element.The phase error from frequency characteristic curve caused by the detection has effectively reduced.A square wave conversion circuit effectively solves the problem of abnormal output waveform of the Hall element.In this thesis,the micro-mass sensing elements in the oscillating balance are optimized,and the effect has been improved obviously.The effectiveness of the Evolutionary Structural Optimization method in realizing the weight reduction of the oscillating components is verified.The digital closed loop drive circuit is designed to avoid the traditional analog closed loop circuit vibration difficulties and easy to stop the defects.Moreover,it is not necessary to add a frequency measuring circuit,because the designed drive circuit can greatly simplify the complexity of the circuit and has certain practical value.