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1、Ultrasonic distance meterDocument Type and Number:United States Patent 5442592 Abstract:An ultrasonic distance meter cancels out the effects of temperature and humidity variations by including a measuring unit and a reference unit. In each of the units, a repetitive series of pulses is generated, ea
2、ch having a repetition rate directly related to the respective distance between an electroacoustic transmitter and an electroacoustic receiver. The pulse trains are provided to respective counters, and the ratio of the counter outputs is utilized to determine the distance being measured.A.BACKGROUND
3、 OF THE INVENTION This invention relates to apparatus for the measurement of distance and, more particularly, to such apparatus which transmits ultrasonic waves between two points. Precision machine tools must be calibrated. In the past, this has been accomplished utilizing mechanical devices such a
4、s calipers, micrometers, and the like. However, the use of such devices does not readily lend itself to automation techniques. It is known that the distance between two points can be determined by measuring the propagation time of a wave travelling between those two points. One such type of wave is
5、an ultrasonic, or acoustic, wave. When an ultrasonic wave travels between two points, the distance between the two points can be measured by multiplying the transit time of the wave by the wave velocity in the medium separating the two points. It is therefore an object of the present invention to pr
6、ovide apparatus utilizing ultrasonic waves to accurately measure the distance between two points. When the medium between the two points whose spacing is being measured is air, the sound velocity is dependent upon the temperature and humidity of the air. It is therefore a further object of the,prese
7、nt invention to provide apparatus of the type described which is independent of temperature and humidity variations. B.SUMMARY OF THE INVENTION The foregoing and additional objects are attained in accordance with the principles of this invention by providing distance measuring apparatus which includ
8、es a reference unit and a measuring unit. The reference and measuring units are the same and each includes an electroacoustic transmitter and an electroacoustic receiver. The spacing between the transmitter and the receiver of the reference unit is a fixed reference distance, whereas the spacing bet
9、ween the transmitter and receiver of the measuring unit is the distance to be measured. In each of the units, the transmitter and receiver are coupled by a feedback loop which causes the transmitter to generate an acoustic pulse which is received by the receiver and converted into an electrical puls
10、e which is then fed back to the transmitter, so that a repetitive series of pulses results. The repetition rate of the pulses is inversely related to the distance between the transmitter and the receiver. In each of the units, the pulses are provided to a counter. Since the reference distance is kno
11、wn, the ratio of the counter outputs is utilized to determine the desired distance to be measured. Since both counts are identically influenced by temperature and humidity variations, by taking the ratio of the counts, the resultant measurement becomes insensitive to such variations.C.DETAILED DESCR
12、IPTION A.principle of ultrasonic distance measurement 1, the principle of piezoelectric ultrasonic generator Piezoelectric ultrasonic generator is the use of piezoelectric crystal resonators to work. Ultrasonic generator, the internal structure as shown in Figure 1, it has two piezoelectric chip and
13、 a resonance plate. When its two plus pulse signal, the frequency equal to the intrinsic piezoelectric oscillation frequency chip, the chip will happen piezoelectric resonance, and promote the development of plate vibration resonance, ultrasound is generated. Conversely, if the two are not inter-ele
14、ctrode voltage, when the board received ultrasonic resonance, it will be for vibration suppression of piezoelectric chip, the mechanical energy is converted to electrical signals, then it becomes the ultrasonic receiver. 2, the principle of ultrasonic distance measurement Ultrasonic transmitter in a
15、 direction to launch ultrasound, in the moment to launch the beginning of time at the same time, the spread of ultrasound in the air, obstacles on his way to return immediately, the ultrasonic reflected wave received by the receiver immediately stop the clock. Ultrasound in the air as the propagatio
16、n velocity of 340m / s, according to the timer records the time t, we can calculate the distance between the launch distance barrier (s), that is: s = 340t / 2 B.Ultrasonic Ranging System for the Second Circuit Design System is characterized by single-chip microcomputer to control the use of ultraso
17、nic transmitter and ultrasonic receiver since the launch from time to time, single-chip selection of 8751, economic-to-use, and the chip has 4K of ROM, to facilitate programming. Circuit schematic diagram shown in Figure 2. Draw only the front range of the circuit wiring diagram, left and right in f
18、ront of Ranging Ranging circuits and the same circuit, it is omitted. 1,40 kHz ultrasonic pulse generated with the launch Ranging system using the ultrasonic sensor of piezoelectric ceramic sensors UCM40, its operating voltage of the pulse signal is 40kHz, which by the single-chip implementation of
19、the following procedures to generate. puzel: mov 14h, # 12h; ultrasonic firing continued 200ms here: cpl p1.0; output 40kHz square wave nop; nop; nop; djnz 14h, here; ret Ranging in front of single-chip termination circuit P1.0 input port, single chip implementation of the above procedure, the P1.0
20、port in a 40kHz pulse output signal, after amplification transistor T, the drive to launch the first ultrasonic UCM40T, issued 40kHz ultrasonic pulse, and the continued launch of 200ms. Ranging the right and the left side of the circuit, respectively, then input port P1.1 and P1.2, the working princ
21、iple and circuit in front of the same location. 2, reception and processing of ultrasonic Used to receive the first launch of the first pair UCM40R, the ultrasonic pulse modulation signal into an alternating voltage, the op-amp amplification IC1A and after polarization IC1B to IC2. IC2 is locked loo
22、p with audio decoder chip LM567, internal voltage-controlled oscillator center frequency of f0 = 1/1.1R8C3, capacitor C4 determine their target bandwidth. R8-conditioning in the launch of the carrier frequency on the LM567 input signal is greater than 25mV, the output from the high jump 8 feet into
23、a low-level, as interrupt request signals to the single-chip processing. Ranging in front of single-chip termination circuit output port INT0 interrupt the highest priority, right or left location of the output circuit with output gate IC3A access INT1 port single-chip, while single-chip P1.3 and P1
24、. 4 received input IC3A, interrupted by the process to identify the source of inquiry to deal with, interrupt priority level for the first left right after. Part of the source code is as follows: receive1: push psw push acc clr ex1; related external interrupt 1 jnb p1.1, right; P1.1 pin to 0, rangin
25、g from right to interrupt service routine circuit jnb p1.2, left; P1.2 pin to 0, to the left ranging circuit interrupt service routine return: SETB EX1; open external interrupt 1 pop? acc pop? psw reti right: .?; right location entrance circuit interrupt service routine ? Ajmp? Return left: .; left
26、Ranging entrance circuit interrupt service routine ? Ajmp? Return 3, the calculation of ultrasonic propagation time When you start firing at the same time start the single-chip circuitry within the timer T0, the use of timer counting function records the time and the launch of ultrasonic reflected w
27、ave received time. When you receive the ultrasonic reflected wave, the receiver circuit outputs a negative jump in the end of INT0 or INT1 interrupt request generates a signal, single-chip microcomputer in response to external interrupt request, the implementation of the external interrupt service s
28、ubroutine, read the time difference, calculating the distance . Some of its source code is as follows: RECEIVE0: PUSH PSW PUSH ACC CLR EX0; related external interrupt 0 ? MOV R7, TH0; read the time value MOV R6, TL0? CLR C MOV A, R6 SUBB A, # 0BBH; calculate the time difference MOV 31H, A; storage r
29、esults MOV A, R7 SUBB A, # 3CH MOV 30H, A? SETB EX0; open external interrupt 0 POP ACC? POP PSW RETI D.Fourth, the ultrasonic ranging system software design Software is divided into two parts, the main program and interrupt service routine, shown in Figure 3 (a) (b) (c) below. Completion of the work
30、 of the main program is initialized, each sequence of ultrasonic transmitting and receiving control. Interrupt service routines from time to time to complete three of the rotation direction of ultrasonic launch, the main external interrupt service subroutine to read the value of completion time, dis
31、tance calculation, the results of the output and so on. E. CONCLUSIONS Required measuring range of 30cm 200cm objects inside the plane to do a number of measurements found that the maximum error is 0.5cm, and good reproducibility. Single-chip design can be seen on the ultrasonic ranging system has a
32、 hardware structure is simple, reliable, small features such as measurement error. Therefore, it can be used not only for mobile robot can be used in other detection systems. Thoughts: As for why the receiver do not have the transistor amplifier circuit, because the magnification well, CX20106 integ
33、rated amplifier, but also with automatic gain control level, magnification to 76dB, the center frequency is 38k to 40k, is exactly resonant ultrasonic sensors frequency.超声波测距仪摘要：提出了一种可以抵消温度的影响和湿度的变化的新型超声波测距仪，包括测量单元和参考资料。在每一个单位，重复的一系列脉冲的产生，每有一个重复率，直接关系到各自之间的距离，发射机和接收机。该脉冲序列提供给各自的计数器，计数器的产出的比率，是用来确定被测
34、量的距离。 一、背景发明 本发明涉及到仪器的测量距离，最主要的是，这种仪器，其中两点之间传输超声波。精密机床必须校准。在过去，这已经利用机械设备来完成，如卡钳，微米尺等。不过，使用这种装置并不利于本身的自动化技术发展。据了解，两点之间的距离可以通过测量两点之间的行波传播时间的决定。这样的一个波浪型是一种超声波，或声波。当超声波在两点之间通过时，两点之间的距离可以由波的速度乘以测量得到的在分离的两点中波中转的时间。因此，本发明提供仪器利用超声波来精确测量两点之间的距离对象。 当任意两点之间的介质是空气时，声音的速度取决于温度和空气的相对湿度。因此，它是进一步的研究对象，本次的发明，提供的是独立于
35、温度和湿度的变化的新型仪器。 二、 综述发明这项距离测量仪器发明是根据上述的一些条件和额外的一些基础原则完成的，其中包括一个参考单位和测量单位。参考和测量单位是相同的，每个包括一个超声波发射机和一个接收机。间隔发射器和接收器的参考值是一个固定的参考距离，而间距之间的发射机和接收机的测量单位是有最小距离来衡量的。在每一个单位，发射器和接收器耦合的一个反馈回路，它会导致发射器产生超声脉冲，这是由接收器和接收到一个电脉冲然后被反馈到发射机转换，从而使重复系列脉冲的结果。重复率脉冲是成反比关系之间的距离发射器和接收器。在每一个单位，脉冲提供一个反馈。由于参考的距离是众所周知的声速，比例反产出是利用数学
36、以确定所期望的距离来衡量。由于这两方面都是相同的影响，温度和湿度的变化，采取的比例相同，由此产生的测量变得准确。 三、详细说明一 超声波测距原理 1、压电式超声波发生器原理 压电式超声波发生器实际上是利用压电晶体的谐振来工作的。超声波发生器内部结构如下所示，它有两个压电晶片和一个共振板。当它的两极外加脉冲信号，其频率等于压电晶片的固有振荡频率时，压电晶片将会发生共振，并带动共振板振动，便产生超声波。反之，如果两电极间未外加电压，当共振板接收到超声波时，将压迫压电晶片作振动，将机械能转换为电信号，这时它就成为超声波接收器了。 2、超声波测距原理 超声波发射器向某一方向发射超声波，在发射时刻的同时
37、开始计时，超声波在空气中传播，途中碰到障碍物就立即返回来，超声波接收器收到反射波就立即停止计时。超声波在空气中的传播速度为340m/s，根据计时器记录的时间t，就可以计算出发射点距障碍物的距离(s)，即：s=340t/2二 超声波测距系统的电路设计 系统的特点是利用单片机控制超声波的发射和对超声波自发射至接收往返时间的计时，单片机选用8751，经济易用，且片内有4K的ROM，便于编程。电路原理图如图2所示。其中只画出前方测距电路的接线图，左侧和右侧测距电路与前方测距电路相同，故省略之。1、40kHz 脉冲的产生与超声波发射 测距系统中的超声波传感器采用UCM40的压电陶瓷传感器，它的工作电压是
38、40kHz的脉冲信号，这由单片机执行下面程序来产生。puzel： mov 14h, #12h；超声波发射持续200mshere： cpl p1.0 ； 输出40kHz方波 nop ； nop ； nop ； djnz 14h，here； ret 前方测距电路的输入端接单片机P1.0端口，单片机执行上面的程序后，在P1.0 端口输出一个40kHz的脉冲信号，经过三极管T放大，驱动超声波发射头UCM40T，发出40kHz的脉冲超声波，且持续发射200ms。右侧和左侧测 距电路的输入端分别接P1.1和P1.2端口，工作原理与前方测距电路相同。2、超声波的接收与处理 接收头采用与发射头配对的UCM40
39、R，将超声波调制脉冲变为交变电压信号，经运算放大器IC1A和IC1B两极放大后加至IC2。IC2是带有锁 定环的音频译码集成块LM567，内部的压控振荡器的中心频率f0=1/1.1R8C3，电容C4决定其锁定带宽。调节R8在发射的载频上，则LM567 输入信号大于25mV，输出端8脚由高电平跃变为低电平，作为中断请求信号，送至单片机处理。 前方测距电路的输出端接单片机INT0端口，中断优先级最高，左、右测距电路的输出通过与门IC3A的输出接单片机INT1端口，同时单片机P1.3和P1.4接到IC3A的输入端，中断源的识别由程序查询来处理，中断优先级为先右后左。部分源程序如下：receive1：
40、push psw push acc clr ex1 ； 关外部中断1 jnb p1.1, right ； P1.1引脚为0,转至右测距电路中断服务程序 jnb p1.2, left ； P1.2引脚为0,转至左测距电路中断服务程序return： SETB EX1； 开外部中断1 pop? acc pop? psw retiright： .? ； 右测距电路中断服务程序入口 ? ajmp? returnleft： . ； 左测距电路中断服务程序入口 ? ajmp? return3、计算超声波传播时间 在启动发射电路的同时启动单片机内部的定时器T0，利用定时器的计数功能记录超声波发射的时间和收到反
41、射波的时间。当收到超声波反射波时，接收电路 输出端产生一个负跳变，在INT0或INT1端产生一个中断请求信号，单片机响应外部中断请求，执行外部中断服务子程序，读取时间差，计算距离。其部分源程序如下：RECEIVE0： PUSH PSW PUSH ACC CLR EX0 ； 关外部中断0 ? MOV R7, TH0 ； 读取时间值 MOV R6, TL0? CLR C MOV A, R6 SUBB A, #0BBH； 计算时间差 MOV 31H, A ； 存储结果 MOV A, R7 SUBB A, #3CH MOV 30H, A? SETB EX0 ； 开外部中断0 POP ACC? POP
42、PSW RETI四、超声波测距系统的软件设计 软件分为两部分，主程序和中断服务程序，如图3（a）（b）(c) 所示。主程序完成初始化工作、各路超声波发射和接收顺序的控制。 定时中断服务子程序完成三方向超声波的轮流发射，外部中断服务子程序主要完成时间值的读取、距离计算、结果的输出等工作。五、结论 对所要求测量范围30cm200cm内的平面物体做了多次测量发现，其最大误差为0.5cm，且重复性好。可见基于单片机设计的超声波测距系统具有硬件结构简单、工作可靠、测量误差小等特点。因此，它不仅可用于移动机器人，还可用在其它检测系统中。思考：至于为什么接收不用晶体管做放大电路呢，因为放大倍数搞不好，CX20106集成放大电路，还带自动电平增益控制，放大倍数为76dB，中心频率是38k到40k，刚好是超声波传感器的谐振频率 。
