The Improvement of Ultrasonic Sensor by Switching Circuit Control

• Main Authors: Chia-Wei Hu, 胡家瑋
• Other Authors: 李世光
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/28932471243289927241

碩士 === 國立臺灣大學 === 應用力學研究所 === 99 === 　　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.