| In a complex environment with obstacles, crosstalk is one of the main reasons that affect the accuracy of an ultrasonic ranging system. Besides, with an increase in the measuring range, the length of ultrasonic emission sequence is normally required to increase, and thus it inevitably leads to the reduction of ultrasonic ranging resolution capacity. Therefore, increasing the measuring range and improving the ranging accuracy are contradicted to each other. To solve this problem, the idea of exciting the ultrasonic transducer with sine coded spread spectrum sequences is proposed in this thesis, and the correlation processing technique at the receiving end is adopted to measure the distance. The main research work of this thesis is summarized as follows.The hardware of an ultrasonic spread spectrum ranging system excited with sine signals is built on the basis of the previous pulse coded ultrasonic ranging system. The established hardware system has stable performance and moderate power, and it provides a good platform for constructing sine coded spread spectrum sequences.The amplitude-frequency characteristic of each major part in the ranging system is analyzed and validated first, and then the amplitude-frequency characteristic of the whole ultrasonic ranging system is fitted using the measured distance data.Sine coded spread spectrum sequences have been constructed. To achieve good correlation results, pseudorandom sequences including m-sequence, Gold code and chaotic sequence combined with spread spectrum modulation are used to excite ultrasonic transducers. The feasibility of the sine coded spread spectrum method for crosstalk inhibition has been verified. Offline correlation method is used to calculate the measured distance. Experiments show that a high ranging accuracy can be obtained when the duration of the ultrasonic exciting sequence is long. It effectively alleviates the contradictions between the measuring range and ranging accuracy. |
PDF Full Text Request