汽车倒车测距仪外文文献翻译.docx

1、汽车倒车测距仪外文文献翻译汽车倒车测距仪外文文献及翻译(文档含中英文对照即英文原文和中文翻译)汽车倒车测距仪的设计摘要本文介绍了汽车倒车测距仪的功能确定、测距原理、设计方法及技术实现,介绍了汽车与障碍物间距离测量的信号处理方法。论述了如何有效地测出并实时地显示出汽车与障碍物的距离,规定了各种不同的报警类型,对于相关类测量系统设计有一定的参考意义。关键词超声单片机测距信号调理随着汽车产业的发展和人们生活水平的不断提高,汽车的数量逐年增加,例如1999 年,我国的汽车年产量已突破了180 万辆,造成公路、街道、停车场、车库等越来越拥挤不堪。汽车驾驶员越来越为车的安全担心了,其中倒车就是一个典型,在

2、繁忙、拥挤、狭窄的地方倒车时,驾驶员即得“瞻前”,又要“顾后”,往往一不小心,就会与汽车尾部障碍物发生碰撞事件。经过调查,对绝大部分非职业汽车驾驶员都希望有一种能发现汽车尾部障碍物的“后视眼”倒车测距仪,因此我们设计了一种经济实惠的汽车倒车测距仪,可以解决驾驶员的“后顾之忧”。1 汽车倒车测距仪的功能指标确定经过对许多汽车驾驶员的调查,确定主要功能指标如下:(1) 最大测距5. 00 米,最小测距0. 35 米,实时数字显示测得距离,显示分辨率0. 01 米;(2) 超过5. 00 米为溢出,仅显示小数点,当距离小于0. 35 米时,显示为0. 00 ,表示很危险;(3) 灯光报警:当距离小于

3、0. 60 米时,报警指示灯亮;(4) 声音报警:当距离小于1. 20 米时蜂鸣器发出间隔频率为1 Hz 的Bi Bi 声,当距离小于0. 90米时蜂鸣器发出间隔频率为2 Hz 的Bi Bi 声,当距离小于0. 60 米时蜂鸣器发出间隔频率为5 Hz 的Bi Bi 声,当距离小于0. 35 米时蜂鸣器连续发出BiBiBi 声。2 测距原理根据声音传播过程中遇到障碍物会发生反射这一原理可以测量距离,超声波测距也是这个原理,即用超声脉冲发射和接收其回波之间的时间差来计算距离,计算公式如下:V = 331. 5 + 0. 607 T式中:V 超声波在空气中传播速度,其单位为米/ 秒,T 环境温度,单

4、位为。D = V t/ 2 = V (t1 - t0) / 2式中:D 被测距离,单位为米,t 超声脉冲发射与接收其回波的时间差,单位为秒,t1 超声回波接收时刻,t0 超声脉冲发射时刻。利用单片机的定时器/ 计数器可以较方便地实现该测距原理,设单片机的T0 端为起始发射同步定时器(确定起点t0) ,单片机的T1 端为回波测量定时器(确定起点t1) ,单片机的P1. 0 (称F 端) 输出窄脉冲串,各端工作波形如图1 所示。测量出t1 和t0 ,就可以算出障碍物和超声探头之间的距离。3 技术实现3. 1 系统框图说明系统框图如图2 所示,采用AT89C2051 单片机作为智能处理部件,配有各种

5、接口电路可实现实时时间差采样、距离运算、显示及声光报警等功能。由于系统的一项重要任务是测量超声脉冲发射与其回波的时间间隔,故单片机与超声信号处理部分的连接端的工作时序是关键,而超声信号处理部分主要由超声脉冲发射、超声回波接收两部分构成,超声信号处理部分的工作受单片机控制的,那么单片机是怎样控制超声信号处理电路呢?图1 测量原理时序图图2 系统框图单片机需要和超声信号处理电路共同完成测量过程,一次测量的全过程定为38. 5 毫秒(见图1 所示) 。首先通过T0 端给超声信号处理电路发出一个1. 8 毫秒的同步负脉冲信号,超声信号处理电路开始新一轮的测量过程。单片机将此时刻定为初始时刻t0 ,而且

6、T0 端在低电平期间还控制超声信号处理部分工作在超声脉冲发射状态。单片机在T0 端给出同步负脉冲的同时,还通过F 端向超声信号处理电路发出16 个40 KHz 的方波(需0. 4 毫秒) ,该信号经驱动后耦合到换能器最终发射出超声脉冲串。在T0 端的负脉冲结束时,超声信号处理部分自动转变为超声回波接收状态。超声波在空气中传播时不会折返,仅当超声波遇障碍物后才被反射,当返回的超声波通过换能器时会转换成电压信号,如果在气温为20 时,超声脉冲6. 615 米内的遇障碍产生的回波有一定强度(声压) ,经过特定电路处理后,能够在38. 5 毫秒之内获得一个触发脉冲,单片机的定时器T1 记录下该脉冲下降

7、沿时刻t1 ,单片机根据初始时刻t0 (也称发射时刻) 和接收时刻t1 就可以算出,该距离的一半即为所测距离。当介于6. 615 米和6. 924 米之间的障碍物产生的回波仍然有一定的强度时,应由T0 端低电平控制不允许产生触发脉冲,而超过6. 924 米以外的障碍物产生的回波的声压,应该低于允许触发的阈值,这样可以确保本次测量发出的超声脉冲不会影响到下一个测量周期的计时。再说,由于要求的最大测距为5. 00 米,当计算出的距离超过5. 00 米时,仅显示溢出标志,不显示距离,为了确保计算的合理性,每次在发完16 个40KHz 的方波后,才启动上一个测量周期的距离计算、显示及报警处理,对上一个

8、测量周期内未能产生对定时器T1 的触发,则按距离溢出处理。倘若计算出的距离小于某个报警阈值,则处理相应的报警,测距在安全距离,则关闭报警。如把超声探头安装在汽车尾部,就可测量出汽车与障碍物之间的距离。3. 2 系统的超声信号处理部分由于汽车尾部较宽,为了有效地探测出车尾与障碍物间的距离,应在汽车尾部安装多个超声换能器,根据一般需求装23 个较合适,我们把倒车测距仪设计成3 个测量通道。为了安装方便和减小系统体积,我们选用发射和接收合为一体的空气探头(换能器) 。实际显示的汽车与障碍物之间的距离是3 个探头与障碍物之间的距离的最小值。考虑倒车测距仪有3 个测量通道,对3 个探头采用扫描工作法,可

9、以共用一个信号处理电路,达到降低成本的目的。3. 2. 1 超声脉冲发射电路该部分的方框图如图3 所示,由单片机产生的40 KHz 方波电压能量有限,不能有效地推动空气探头工作,为了获得足够的能量,必须先经过反相驱动器前置驱动,再经一级发送驱动后发射出去。通过三路模拟传输开关来控制信号送哪一个探头的发送驱动器输入端。三路模拟传输开关需要一个3 进制脉冲分配器来控制,而脉冲分配器由单片机的T0 端信号反相后触发的。3. 2. 2 超声回波接收电路超声波碰到障碍物会发生透射和反射,其中反射到探头的超声波被换能器变成电压信号。由于超声波在空气中衰减较严重,探头接收到的反射波很微弱,故换能器输出的电压

10、信号也很微弱,所以先对该电压信号进行放大,即设置了一个限幅的前置放大环节。由于发射和接收用同一个换能器,发射时的大幅值电压脉冲会影响前置放大器的正常工作, 故这个环节除放大作用外,还有限幅作用,限幅就是为了避免大幅值的发射电压无约束地回馈到后面的电路。图3 超声脉冲发射电路框图由于有多个探头和限幅前置放大环节组成多个接收通道,各通道电子器件参数存在差异而造成各通道不平衡,会影响测量精度。因此,接下来就要设置一个平衡调节环节。反射波被探头转换成电压信号后经前置放大和平衡调节环节,再通过模拟传输开关,其电压幅度还较小,又设置了二级放大器。为了消除发射电压回馈到信号处理电路而引起单片机误计时,此时需

11、要一个可控滤波器,它由单片机的T0 端控制,它对发射电压回馈的信号进行旁路,而对回波的接受信号无权处理,100 %向后传输。为了减少噪声的干扰,系统中少不了带通放大装置。反射波的强弱,与距离有很大关系。在测量范围内的电路应有足够的增益,设置增益可调放大环节是必要的。经上述处理的信号不能直接作为单片机内定时器T1 的触发信号,必须先包格检波,再钳位比较,这样才能形成定时器T1 的触发信号。钳位比较器的阈值电压是变化的(由单片机的T0 端控制) ,再一次避免了因发射电压回馈信号而引起单片机误计时。超声波接收电路框图如图4 所示。图4 超声回波接收电路框图4 系统达到的技术指标设计工作完成后,根据电

12、路的功能、电子器件的体积及安装位置关系,将系统电路制成两块电路板,单片机控制电路及显示报警部分做成一块电路板(显示板) ,安装在驾驶员前面;超声电压源驱动及信息处理部分做成另一块电路板(发射接受板) ,安装在汽车后部;两板之间通过一根六芯电缆相连。3个超声探头各通过一条三芯电缆与发射接受板相连,实物照片如图5 所示。在实验室内,气温约为20 时,通过钢皮卷尺与倒车测距仪对照测量,测得数据如下表所:测量距离是以厘米为分辨率的3 位数字显示,其中,绝大部分倒车测量的数据满足1 厘米的测量精度(在20 左右) ,少部分数据的误差也在2厘米的范围内,并且实现了提出的汽车倒车测距仪的功能及参数的要求。达

13、到了设计的目的。图5 汽车倒车测距仪的实物照片尚待解决的问题是,环境气温影响测量的精度,例如, 环境气温为40 时, 超声波传播的速度是355. 78 米/ 秒,环境气温为零下10 时,超声波传播的速度是325. 43 米/ 秒,两者之比为1. 0933 ,实际用车场合的温度是:夏天的气温比40 还高,冬天的气温比零下10 还低。超声波传播的速度的快慢之比可以达到10 %以上,故要实现较精确的测距,还需增加温度补偿。参考文献1吴正毅,测试技术与测试信号处理M,北京:清华大学出版社,1995 ;2方佩敏,新编传感器原理应用电路详解M,北京:电子工业出版社,1994 ;3王福瑞等,单片微机测控系统

14、设计大全M,北京:北京航空航天大学出版社,1998 ;4赵文龙,高精度可编程流量积算仪的设计J,南昌航空工业学院学报1998,15(1) :4146 。 The Design of Telemeter for Motor Move Backward Zhao Wenlong Yuan Hongji Wan Weiqiang Xu Guangnign Wan ZeliangAbstract : The function confirmation ,meterage distance principle ,design means and technique implementation of t

15、elemeter which is for motor move backward ate introduced. The method of signal processing of the measured distance between the motor and the obstruction ,and method to effectively measure and real time display ,the distance between the motor and the obstruction are discussed. All of the different al

16、arm types are prescribed. They are signify ,cant for correlative kind designs of measure system.Key words : Ultrasonic ;Monolithic processor ;Meterage distance ;Signal option.PrefaceWith the auto industry development and peoples living standards continue to provideHigh number of cars increases every

17、 year, for example, in 1999, Chinas automobileAnnual output has exceeded 1.8 million, resulting in roads, streets, parking lots,Garage more and more crowded. More and more car drivers car security concerns, among them the reverse is a typical, busy, crowded,Reversing the narrow places, the driver th

18、at was forward looking and also taking care of after , often accidentally, it will collide with the car rear obstacle collision event.After an investigation, the majority of non-occupational car drivers have hope there is a hope to find car rear obstacle post as the eye - back car range finder, so w

19、e designed an affordable car down car range finder, to resolve the drivers worries.1 car parking range finder to determine the function of indicatorsAfter a survey of many car drivers to determine the main features indicators are as follows:(1) The maximum distance 5.00 m, the minimum distance 0.35

20、meters, real-time figures show that the measured distance, display resolution of 0.01 m;(2) over 5.00 meters for the overflow, only the decimal point, when the distanceless than 0.35 meters, the display is 0.00, indicating very dangerous;(3) Light Alarm: When the distance is less than 0.60 m, the al

21、arm indicatorlights;(4) Sound the alarm: When the distance is less than 1.20 m when the buzzer made a frequency of 1 Hz intervals of Bi Bi sound, when the distance is less than 0.90M interval of the buzzer frequency 2 Hz of the Bi Bi sound, when distance of less than 0.60 m interval of the buzzer wh

22、en the frequency of 5 Hz of Bi Bi sound,When the distance is less than 0.35 m when the buzzer sent straight BiBiBi sound。2 ranging principle According to the sound propagation will occur in the reflection that an obstacle a principle can measure the distance ultrasonic distance measurement is the pr

23、inciple that ultrasonic pulse transmitter and receiver with its echo to calculate the time difference between the distance, calculated as follows: V = 331. 5 +0. 607 TWhere: V - ultrasonic velocity in the air, in units of m/ s, T - ambient temperature, the unit is . D = V t / 2 = V (t1 - t0) / 2Wher

24、e: D - the measured distance in meters, t - ultrasonic pulse transmit and receive the echo time difference, in seconds, t1 - Ultrasound echo reception time, t0 - ultrasonic pulse emission times. Using the microcontroller timer / counter can be more easily implemented Is the ranging principle, based

25、microcontroller T0-side synchronous launch scheduled for the beginning timer (to determine the starting point t0), SCM T1 measurement end time for the echo device (to determine the starting point t1), SCM P1. 0 (called F-side) narrow pulse output red string, each end of the work of the waveform show

26、n in Figure 1. Measured t1 and t0,obstacles can be calculated and the distance between the ultrasonic probe.3 technology3.1 System Block Diagram Description System block diagram shown in Figure 2, using AT89C2051 microcontroller as an intelligent processing units, with a variety of interface circuit

27、s can be realized in real timesampling time difference, distance calculation, display and sound and light alarm.Because the system is an important task is to launch its ultrasonic pulse echo measurement of time intervals, so the microcontroller and the ultrasonic signal processing part of the connec

28、tion end of the work of the timing is the key, and ultrasound signal processing part, by the ultrasonic pulse transmitter, two received ultrasonic echo parts, ultrasonic letter no part of the work handled by the microcontroller, then the MCU is how to control the ultrasonic signal processing circuit

29、 it ？SCM needs and ultrasound signal processing circuitry together to complete the measurement process, a measurement of the whole process as 38.5 ms (see Figure 1). First of all T0-side through the ultrasound signal processing circuitry to send a 1.8 millisecond sync negative pulse signal, ultrason

30、ic signal processing circuit to start a new round of the measurement process. SCM this time as the initial time t0, and T0 in the low end of the period also controls the ultrasound signal processing part of the work in the ultrasonic pulse emission state. T0-side SCM in sync negative pulse is given,

31、 it is also through the F-side issue to the ultrasound signal processing circuit 16 40KHz square wave (to be 0.4 ms), after the signal by the driver coupled to the transducer emits the final ultrasonic pulse train. Negative pulse at the end of the end of T0, the ultrasonic signal processing ultrason

32、ic echo receiver automatically into the state.Ultrasonic wave propagation in the air will not turn back, only after when the ultrasonic wave is reflected obstacles encountered, when the return of the ultrasonic transducer will by converted into a voltage signal, if the temperature is 20 , the ultrasonic pulse 6.615 m in the case of certain obstacles in the echo intensity (sound pressure), after treatme