切換式電路應用於超音波感測器訊號控制與效能提升

Abstract

本研究以車用倒車雷達的超音波測距感測器為電路負載，利用切換式電路驅動超音波測距感測器，了解壓電材料在電能與機械能之間的轉換特性。依據超音波測距感測器電訊號的變化可分為驅動、殘響及回波三大階段。驅動電路由切換式主動開關與中週變壓器所組成，本研究將完整建立感測器及中週變壓器的等效電路模型，加以分析中週變壓器等效電路參數與超音波測距感測器驅動訊號之間的關係。 因壓電材料具有力、電耦合特性，本論文設計阻尼控制電路，以消散在驅動訊號結束後的機械振動能量。自適性速度控制阻尼電路將整併於倒車雷達驅動電路中，設計開關訊號切換倒車雷達的驅動與殘響抑制階段。以外加電容做為自適性電源因此不需額外電壓源，且電容電壓值可隨著振動訊號改變，當結構的振動較小時，自適性電容的電壓值同時變小。論文中將以理論與模擬分析，建立最佳化的自適性電容參數，使受控結構在振動停止時電容電壓亦完全放電。由實驗結果可知，當選取自適性電容值過大時，將造成電壓能量回流使得受控系統不穩定。 在倒車雷達的回波訊號擷取階段，當倒車雷達發射超音波訊號經過空氣衰減後，使得回波訊號振幅減小，容易被雜訊覆蓋。實驗以資料擷取卡(DAQ)採集回波訊號，同時設計虛擬儀控軟體(LabVIEW)進行數位訊號處理，進而獲得與驅動訊號相同頻率的回波訊號，超音波在空氣中傳遞所需的時間以及殘響時間皆可以利用此LabVIEW計算而得，藉此提升判斷倒車雷達效能的準確性。 本論文目標為改善超音波測距感測器的驅動電路效能及減小殘響時間，首先以理論分析各階段的電路設計及驗證其可行性，接著透過電路模擬軟體PSIM進行實驗結果的預測，最後以實驗驗證其可達成超音波測距感測器控制與效能提升的結果。

This thesis dedicated on investigating the ultrasonic ranging sensor driving circuit which is used in surrounding obstacles detection for automobiles. The driving circuit of ultrasonic ranging sensor is mainly constructed by full-bridge switches. The characteristic of piezoelectric transducer is the mechanism of converting electrical energy to and from mechanical energy. The ultrasonic ranging sensor driving and sensing operation is composed of three phases, which are driving stage, reverberation stage, and ultrasonic echo receiving stage. The driving stage in the circuit is consisted of active switches and intermediate frequency transformer. This research will demonstrate the equivalent circuit of the sensor including the intermediate frequency transformer, and will show the relevance of intermediate frequency transformer and ultrasonic ranging sensor. In the reverberation stage, the adaptive velocity controlled piezoelectric active switching damping circuit (Adaptive VPSD) is used to dissipate the vibration energy of structure in the transient stage after the driving signal is stopped. In addition, Adaptive VPSD exhibits no requirements of additional power supply and offers advantages of adaptive voltage source with variation of vibration levels. In order to maximize power dissipation and attenuate the instabilities of Adaptive VPSD, the complete theoretical and simulation model will be proposed and verified. The key parameters of the system include the capacitance value for adaptive damping control will then be derived with this model and verified by simulation. In the ultrasonic echo receiving stage, the amplitude of ultrasonic echo is much smaller than the transmitted wave in the driving stage. The echo signal can be accesses through a data acquisition (DAQ) card on a computer from the output of operational amplifiers. This experiment will acquire and further process ultrasonic echo signal with a computer program written with LabVIEW. The reverberation time, time-of-flight of the echo signal can all be obtained from the LabVIEW program. The purpose of this work is to improve the efficiency of driving circuit and reduce the reverberation time of ultrasonic ranging sensor. In this thesis, theoretical analysis will first be conducted to explain the feasibility of design. PSIM, a circuit simulation software, was used to predict the experimental result. The theoretical models, simulation results, and experiment verification will all be detailed and discussed in this study.