Research On Opposite-Type Ultrasonic Ranging Method Based On Digital Demodulation

The ultrasonic ranging technology is widely applied to industrial automatic control,such as parking sensor,robot localization system,metal detection and so on.There is an increasing demand on the ultrasonic distance measurement accuracy and measurement of blind area and measurement speed in research and production.This paper designs a kind of ultrasonic ranging system based on digital demodulation,which reduces the complexity of the measurement circuit.For the absoulte ranging and relative ranging,two kinds of direct digital signal processing algorithms which improve the precision of the system are proposed in this paper.The ultrasonic signal has been digital demodulated with the above algorithms.A large number of experiments and data analysis are carried out to verify the feasibility of the algorithm.The main contents are arranged as follows:Firstly,the system scheme is designed and the overall framework of the measurement system is constructed based on referring to large numbers of domestic and international aspects of the basic references of ultrasonic ranging.Secondly,a fast algorithm of envelope curve extraction based on moving sine fitting about time-of-flight is proposed.Using this algorithm,the extraction of the envelope curve of the ultrasonic pulse signal under the condition of the traditional single segment pulse excitation and the three section positive and negative alternating pulse excitation is presented.The experimental results show that the algorithm is fast and reliable.Thirdly,the flight time of the two excitation modes are calculated.Single pulse excitation,1/2 envelope peak position as characteristics of flight time calculation;three segment reciprocal excitation,calculated as the feature position of flight time transition Valley point.Compared with the experimental results,it is found that the three section positive and negative alternating excitation model has a higher accuracy.Fourthly,using the phase difference detection principle,the ultrasonic continuous incentive model,this paper proposes a digital ellipse fitting algorithm based on least square method,real-time acquisition and real-time sampling phase reference signal excitation signal,and the phase unwrapping algorithm of real-time phase difference for the expansion of the absolute phase difference.The relative distance value is calculated by the relation between the absolute phase difference and the sound wave length.Finally,the experiment of absolute distance measurement and relative distance measurement.The experimental results show that the absolute range accuracy of the improved three section positive and negative pulse alternating excitation mode is 1mm,the measurement blind area is as low as 3mm,the measurement range is 800 mm,which meets the design requirements and achieves the relevant measurement technical specifications.The relative location,sampling frequency in the limit of the existing STM32 MCU,sampling 21 points per cycle,the measured maximum moving speed limit object can reach to 2.83m/s,the ellipse fitting error is less than 0.2mm,meet the requirements of relative ultrasonic ranging.