| 摘要: | 本研究以窄頻超音波換能器之系統鑑別為目的，其中系統鑑別所指的是以實驗數據推算出換能器的頻譜包括振幅響應及相位響應。由本計畫主持人新近開發出來超音波峰谷到達時間數列(Peak Time Sequence, PTS)測距超音波峰谷時間序列測距方法，已可用簡單數位電路及演算法達到次公釐等級精度測距，較可惜的是缺少Phase delay值時，仍只能量測相對距離，本研究目標在於鑑別出之換能器頻譜有助於計算Phase delay 差，以祈將PTS測距法進一步推展至可以量測絶對距離。窄頻超音波換能器的系統鑑別有幾個須要克服的困難：包括有可以量測頻段狹窄，接收訊號相對發射訊號有純延時的成分影響了頻譜響應的相位變化。本研究配合PTS量測距離的應用及其量測電路，系統鑑別所使用的量測數據也使用訊號過門檻的時間數列(COTS)，而不使用一般以類比數位轉換所取得的波型數列，這讓量測電路簡化但郤增加了系統鑑別的困難度。本研究以方波激發窄頻超音波發射器，透過窄頻超音波發射器的慮波效果，發射出其頻寬範圍內同基頻之弦波。經過超音波在空氣中傳遞時延時及衰減後，以窄頻超音波接收器接收訊號，並以訊號過門檻來偵測過門檻時間並記錄為過門檻數列( COTS)。在接收波為弦波的假設下，我們利用過門檻數列COTS，以及門檻值共同重建接收波波型，取得振幅，並計算出該頻率下測得之頻率響應。將超音波換能器帶通頻寬內不同頻率之頻率響應代入兩個零點四個極點之動態模型，從而鑑別出包含發射器、接收器以及純時間延遲之動態系統模型。因為本研究使用了COTS訊號而不用ADC取樣，比起ADC 取樣，COTS訊號所需的電路和運算能力都簡單許多，配合PTS測距電路並量測PTS電路的頻率響應相位曲線，讓PTS測距法可以進一步量測絕對距離。ultrasonic transducer. System identification is to construct mathematical model based on experimental data referred to calculate the spectrum, including the transducer amplitude response and phase response. Developed by the project leader, the new ultrasonic ranging method, peak arrival time series (PTS) ranging approach, is able to achieve sub-mm level precision ranging with simple digital circuits. Unfortunately, for lack of Phase delay information, current PTS method can only be used to measure relative distance. This aim of this project, to identify the spectrum of the transducer Phase Delay helps to calculate the difference of two frequencies, and to extend the PTS ranging method to measure the absolute distance. To identify narrowband ultrasonic transducer system is required to overcome several difficulties. A narrow band can be measured. Received signal contains pure delay in addition to the phase change. In this study, in order to be consistent with the PTS measured method, measurement data used are the cross over time series (COTS), instead of the wave-type series generated with analog to digital converter. This keeps the measurement circuit simple, but increases the difficulty of identification. In this research, square wave excites narrowband ultrasonic transmitters. For the narrowband filter effect of ultrasonic transmitter, the emitted wave is sinusoid wave with the fundamental frequency of the square wave within the bandwidth of the ultrasonic transmitter. Ultrasound waves pass through the air with time delay and attenuation. With the narrow band ultrasonic receiver, the signals received and compared to the threshold to detect and record the cross over threshold time to construct the cross over time series (COTS). Under the assumption that the received waves are sinusoidal wave, we use COTS as well as threshold lever joint to reconstruct the received sinusoid waveform, to obtain the amplitude, and to calculate the frequency response. The frequency responses of ultrasound transducer pair at different frequencies are fitted to the dynamic model of two zero, 4 poles in order to identify the dynamic system model that include transmitters, receivers, and the pure time delay. Because this study used a COTS rather than the ADC sampling, the circuits are much simpler. With the identified phase response curve, the PTS ranging Method can measure the absolute distance further. 研究期間：10008 ~ 10107 |
