基于数字解调的对射式超声波测距方法研究

发布时间：2018-06-02 16:33

本文选题：数字解调 + 正弦拟合　；参考：《湖北工业大学》2017年硕士论文

【摘要】：超声波测距技术在汽车倒车雷达、机器人定位系统、金属探伤等工业测控领域应用广泛。科研生产中对超声波测距的精度和测量盲区及测量速度提出越来越高的要求。为此,本文设计了一种基于数字解调的对射式超声测距系统,降低了测量电路的复杂性。针对绝对测距和相对测距两种模式,提出了两种直接数字的信号处理算法,提高了系统的测量精度。通过嵌入式系统软件算法的的编程实现,完成了超声信号的数字解调,并进行了大量实验和数据分析,验证了算法的可行性。具体研究内容如下:首先,在查阅国内外大量关于超声波测距文献的基础上,进行了系统方案设计,构建测量系统的总体框架,设计了超声波测距的主要电路。其次,应用飞行时间检测原理,针对脉冲瞬态激励模式下的超声接收信号,提出了一种基于移动正弦拟合的包络曲线快速提取算法。运用这种算法,分别对传统的单段式脉冲激励与本文提出的三段式正反交替脉冲激励条件下的超声接收信号实现了包络曲线的提取。实验表明,这种包络提取算法速度快,结果可靠。第三,分别实现了两种激励模式下的飞行时间的计算。单段式脉冲激励下,应用二分之一包络峰值点作为位置特征进行飞行时间计算;三段式正反交替激励下,应用过渡谷点作为位置特征实现飞行时间的计算。并通过实验比较发现,三段式正反交替激励模式具有更大的精度优势。第四,应用相位差检测原理,针对超声连续激励模式,提出一种基于最小二乘法的数字椭圆拟合算法,实时获取激励参考信号与超声采样信号的实时相位差,并通过相位解包裹算法将实时相位差扩展为绝对相位差。通过绝对相位差的变化与声波波长成正比的关系,计算出相对距离值。最后,完成了绝对测距实验和相对测距实验。实验发现改进的三段式正反脉冲交替激励模式绝对测距精度达到1mm,测量盲区低至3mm,量程为800mm,基本满足了设计要求和达到了相关测量技术指标。对于相对测距,在现有STM32单片机的极限采样频率下,每周期采样21点,被测对象能够达到的最大移动极限速度为/83.2sm,椭圆拟合误差小于0.2mm,满足超声相对测距的要求。
[Abstract]:Ultrasonic ranging technology is widely used in automobile reversing radar, robot positioning system, metal inspection and other industrial measurement and control fields. In scientific research and production, the accuracy, blind area and measuring speed of ultrasonic ranging are demanded more and more. Therefore, this paper designs a digital demodulation based on the ultrasonic distance measurement system to reduce the complexity of the measurement circuit. In this paper, two direct digital signal processing algorithms are proposed for absolute distance measurement and relative distance measurement, which improve the measurement accuracy of the system. The digital demodulation of ultrasonic signal is accomplished through the programming of embedded system software algorithm, and a large number of experiments and data analysis are carried out to verify the feasibility of the algorithm. The specific research contents are as follows: firstly, on the basis of consulting a large number of domestic and foreign literature on ultrasonic ranging, the system scheme is designed, the overall framework of the measurement system is constructed, and the main circuit of ultrasonic ranging is designed. Secondly, based on the principle of time-of-flight detection, a fast algorithm for extracting envelope curves based on moving sinusoidal fitting is proposed for ultrasonic signals received in pulse transient excitation mode. By using this algorithm, the envelope curves are extracted from the traditional single-segment pulse excitation and the three-segment positive and negative pulse excitation proposed in this paper. Experimental results show that the algorithm is fast and reliable. Thirdly, the calculation of flight time under two excitation modes is realized respectively. The flight time is calculated by using the 1/2 envelope peak as the position feature and the transition valley as the position feature under the three-segment positive and negative excitation. The experimental results show that the three-segment positive and negative alternating excitation mode has more precision advantages. Fourthly, based on the principle of phase difference detection, a digital ellipse fitting algorithm based on least square method is proposed to obtain the real time phase difference between the excitation reference signal and the ultrasonic sampling signal. The real time phase difference is extended to absolute phase difference by phase unwrapping algorithm. The relative distance is calculated by the relation between the absolute phase difference and the wavelength of sound wave. Finally, the absolute ranging experiment and the relative ranging experiment are completed. The experimental results show that the absolute ranging accuracy is 1 mm, the measurement blind area is as low as 3 mm and the measuring range is 800 mm, which basically meets the design requirements and the related technical specifications. For relative ranging, at the limit sampling frequency of existing STM32 microcontroller, the maximum moving limit velocity of the measured object is 83.2 smm and the ellipse fitting error is less than 0.2 mm, which meets the requirement of ultrasonic relative ranging.
【学位授予单位】：湖北工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB559

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