Principle: 1. Ultrasonic generators In order to study and utilize ultrasonic waves, many ultrasonic generators have been designed and manufactured. Generally speaking, ultrasonic generators can be divided into two categories: one is to generate ultrasonic waves electrically, and the other is to generate ultrasonic waves mechanically. Electrical methods include piezoelectric, magnetostrictive and electric; Mechanical methods include Gao Erdun flute, liquid whistle and air rotating flute. The frequency, power and sound characteristics of the ultrasonic waves they generate are different, so their uses are different. At present, piezoelectric ultrasonic generator is commonly used. 2. The principle of piezoelectric ultrasonic generator The piezoelectric ultrasonic generator actually works by using the resonance of piezoelectric crystal. The internal structure of the ultrasonic generator is shown in figure 1. It has two piezoelectric wafers and a vibrating plate. When a pulse signal with a frequency equal to the natural oscillation frequency of the piezoelectric chip is applied to its two poles, the piezoelectric chip will vibrate and drive the vibrating plate to vibrate, thus generating ultrasonic waves. On the other hand, if no voltage is applied between the two electrodes, when the vibrating plate receives ultrasonic waves, it will press the piezoelectric wafer to vibrate, convert mechanical energy into electrical signals, and then become an ultrasonic receiver. 3. Ultrasonic ranging principle The ultrasonic transmitter emits ultrasonic waves in a certain direction, and starts timing at the same time. Ultrasonic waves propagate in the air, and return immediately when encountering obstacles on the way, and the ultrasonic receiver stops timing immediately after receiving reflected waves. The propagation speed of ultrasonic wave in air is 340 m/s. According to the time t recorded by the timer, the distance (S) between the emission point and the obstacle can be calculated, that is, s=340t/2. This is the so-called time difference ranging method. The principle of ultrasonic ranging is to know the propagation speed of ultrasonic waves in the air, measure the time when the sound waves encounter obstacles after transmission, and calculate the actual distance from the transmitting point to the obstacles according to the time difference between transmitting and receiving. It can be seen that the principle of ultrasonic ranging is the same as radar. The formula of ranging is: L=C×T, where l is the measured distance length; C is the propagation speed of ultrasonic waves in the air; T is the time difference of measuring distance propagation (t is half of the time value from transmission to reception). Ultrasonic distance measurement is mainly used for reversing reminder, distance measurement in construction sites and industrial sites. Although the current ranging range can reach 100 meters, the measurement accuracy can only reach centimeter level. Ultrasonic wave has the advantages of easy directional emission, good directivity, easy intensity control and no direct contact with the measured object, and is an ideal means for liquid height measurement. In precise liquid level measurement, it is necessary to achieve millimeter-level measurement accuracy, while at present, the domestic ultrasonic ranging ASIC only has centimeter-level measurement accuracy. By analyzing the causes of ultrasonic distance measurement error, the measurement time difference is improved to microsecond level, and the LM92 temperature sensor is used to compensate the sound wave propagation speed. The high-precision ultrasonic distance meter we designed can reach the measurement accuracy of millimeter level.
Circuit design:
1, 40kHz pulse and ultrasonic emission are generated. The ultrasonic sensor in the ranging system adopts UCM40 piezoelectric ceramic sensor, and its pulse signal with working voltage of 40kHz is generated by the following program executed by single chip microcomputer. Puzel: MOV 14H, #12h; Ultrasonic emission lasts for 200 ms here: CPLP1.0; Output 40kHz square wave nopnopnoppdjnz14h, here; The input end of the ranging circuit before RET is connected to the P 1.0 port of the single chip microcomputer. After the MCU executes the above program, it outputs a pulse signal of 40kHz at the port P 1.0, which is amplified by the transistor T and then drives the ultrasonic transmitter UCM40T to emit a pulse ultrasonic wave of 40kHz continuously for 200 ms .. The input terminals of the left and right ranging circuits are connected to the ports P 1. 1 and P 1.2 respectively, and the working principle is the same as before. 2. Receiving and processing of ultrasonic wave The receiver adopts UCM40R matched with the transmitter, which changes the ultrasonic modulation pulse into AC voltage signal, which is amplified by the operational amplifiers IC 1A and IC 1B and then applied to IC2. IC2 is an audio decoding integrated block LM567 with a locked loop. The center frequency of the internal VCO is F0 =11.1r8c3, and the locking bandwidth is determined by the capacitor C4. When R8 is adjusted on the transmission carrier frequency, the input signal of LM567 is greater than 25mV, and the pin 8 of the output terminal changes from high level to low level as an interrupt request signal, which is sent to the single chip microcomputer for processing. The output end of the front-end ranging circuit is connected to the INT0 port of the single chip microcomputer, and the interrupt priority is the highest. The outputs of the left and right ranging circuits are connected to the INT 1 port of the single chip microcomputer through the output of the AND gate IC3A, and the single chip microcomputer P 1.3 and P 1.4 are connected to the input of IC3A. The identification of interrupt source is handled by program query, and the interrupt priority is first right and then left. Part of the source programs are as follows: receive1:push PSW push ACC clr ex1; Turn off the external interrupt 1JNB P 1. 1, right; Pin P 1. 1 is 0, and go to the right distance measuring circuit interrupt service program JNB P 1.2, left; When the pin P 1.2 is 0, turn the left distance measuring circuit to interrupt the service program and return: setbex1; Open external interrupt 1
The development course of this method: With the rapid development of robot technology in just a few decades after its birth, its application scope has gradually moved from industrial production to people's lives. Such a wide range of applications makes it particularly important to improve people's understanding of robots. Through its sensing system, the robot can detect the distance between the front obstacle and the surrounding environment, and realize the functions of obstacle avoidance, automatic line finding and ranging. Compared with other ranging technologies, ultrasonic ranging has the advantages of low cost, high measurement accuracy, no environmental restrictions and convenient application. Combining it with infrared and gray sensors, robots can find lines and avoid obstacles. Ultrasonic wave is often used for ranging because of its strong directivity, slow energy consumption and long propagation distance in medium. It is mainly used for the development of reversing radar, rangefinder, level measuring instrument, mobile robot, construction site and some industrial sites, such as distance, liquid level, well depth, pipeline length and flow rate. Ultrasonic detection is often quick and convenient, simple in calculation, easy to realize real-time control, and can meet the requirements of industrial application in measurement accuracy, so it has been widely used. The research of this topic has strong practicability and commercial value.
Because of its strong directivity, slow energy consumption and long distance in the medium, ultrasonic wave is often used for ranging, such as rangefinder and level meter, which can be realized by ultrasonic wave. Ultrasonic detection is often fast, convenient, simple in calculation, easy to realize real-time control, and can meet the requirements of industrial application in measurement accuracy, so it is used in the development of mobile robots.
It is also widely used. In order to make the mobile robot walk automatically to avoid obstacles, it needs to be equipped with a ranging system so that it can get the distance information (distance and direction) from obstacles in time. Ultrasonic ranging system provides the robot with moving distance information, so that it can know the environment in front, left and right.
In order to study and utilize ultrasound, people have designed and manufactured many ultrasonic generators. Generally speaking, ultrasonic generators can be divided into two categories: one is to generate ultrasonic waves electrically, and the other is to generate ultrasonic waves mechanically. Electrical methods include piezoelectric, magnetostrictive and electric; Mechanical methods include Gao Erdun flute, liquid whistle and air rotating flute. The frequency, power and sound characteristics of the ultrasonic waves they generate are different, so their uses are different. At present, piezoelectric ultrasonic generator is commonly used.