汽车倒车测距仪的设计外文翻译

汽车倒车测距仪的 设计 领导形象设计圆作业设计ao工艺污水处理厂设计附属工程施工组织设计清扫机器人结构设计 外文翻译 汽车倒车测距仪的设计 赵文龙1 苑鸿骥1 万卫强1 许光泞1 万泽亮2 (1. 南昌航空工业学院测控 工程 路基工程安全技术交底工程项目施工成本控制工程量增项单年度零星工程技术标正投影法基本原理 系 江西南昌 330034 ;2. 江铃汽车集团公司江西南昌330001) 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 中图分类号 TB551 文献标识码:A 前言 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 小学单位换算公式大全免费下载公式下载行测公式大全下载excel公式下载逻辑回归公式下载 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,单位为?。 D = V ×Δt/ 2 = V ×(t1 - t0) / 2 式中:D ———被测距离,单位为米,Δt ———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2,3 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) :41,46 。 The Design of Telemeter for Motor Move Backward Zhao Wenlong Yuan Hongji Wan Weiqiang Xu Guangnign Wan Zeliang (Dept . of Measuring & Controlling Engineering ,Nanchang Institute of Aeronautical Technology ,Nanchang ,P. R. China 330034) Abstract : The function confirmation ,meterage distance principle ,design means and technique implementation of telemeter 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 alarm types are prescribed. They are signify ,cant for correlative kind designs of measure system. Key words : Ultrasonic ;Monolithic processor ;Meterage distance ;Signal option. CLC:TB551 Document code:A Preface With the auto industry development and people's living standards continue to provide High number of cars increases every year, for example, in 1999, China's automobile Annual 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 that 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 we designed an affordable car down car range finder, to resolve the driver's "worries." 1 car parking range finder to determine the function of indicators After 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 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 alarm 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 when 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 principle 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 T Where: V --- ultrasonic velocity in the air, in units of m/ s, T --- ambient temperature, the unit is ?. D = V × Δt / 2 = V × (t1 - t0) / 2 Where: D --- the measured distance in meters, Δt --- 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 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 shown in Figure 1. Measured t1 and t0,obstacles can be calculated and the distance between the ultrasonic probe. 3 technology 3.1 System Block Diagram Description System block diagram shown in Figure 2, using AT89C2051 microcontroller as an intelligent processing units, with a variety of interface circuits 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 connection 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 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, ultrasonic 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, 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 ultrasonic 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 treatment by a particular circuit, able to 38.5 milliseconds to get a trigger pulse, the microcontroller's timer to record the pulse falling edge of T1 time t1, SCM According to the initial time t0 (also known as the launch time) and receive time t1 to the distance ultrasonic wave can be calculated, half of the distance measured is the distance. When the range of 6.615 m and 6.924 m echo generated between the obstacles still have a certain intensity, low-side control is not allowed by the T0 trigger pulse generated, and more than 6.924 meters away obstacles resulting echo sound pressure should be lower than the threshold to allow the trigger, so you can ensure that this measure will not affect the issue of the ultrasonic pulse to the next measurement cycle time. Furthermore, because the maximum distance required for the 5.00 m, when calculated from more than 5.00 m, only the display overflow flag, does not show distance, in order to ensure the rationality of calculation, each finished in the hair of 16 40KHz square wave before starting a measurement cycle on the distance calculation, display and alarm processing, within the previous measurement period timer T1 failed to produce the trigger, according from the overflow processing. If the calculated distance is less than an alarm threshold, the corresponding alarm processing, ranging from a safe distance, turn off the alarm. If the ultrasonic probe installed in the rear of the car, you can measure the distance between the vehicle and obstacles. 3.2 Ultrasonic signal processing system The rear of the car wide, in order to effectively detect the distance between the rear and obstacles should be installed in the rear of the car multiple ultrasonic transducer, mounted under the general demand for 2 to 3 more appropriate, we reverse rangefinder design into three measurement channels. For ease of installation and reduced system size, we use transmitter and receiver into one of the air probe (transducer). Actual display of cars and obstacles is the distance between the probe and 3 the minimum distance between obstacles. Consider reversing rangefinder has three measurement channels, the three probes by scanning method, can share a signal processing circuit, to reduce costs. 3.2. 1 Ultrasonic pulse transmission circuit The part of the block diagram shown in Figure 3, generated by the microcontroller 40 KHz square wave voltage energy limited, can not effectively promote the work of the air probe, in order to obtain enough energy, you must first drive through the front driver reversed, and then by a driver fired after sending out. Analog transmission through three-way switch to control the signal sent to the sender which drives the probe input. Three analog transmission switch requires a 3 band pulse distributor to control, and pulse distributor of T0 by a single-ended signal is triggered after RP. 3. 2.2 ultrasonic echo receiver circuit Encounter obstacles occur ultrasonic transmission and reflection, which is reflected to the ultrasonic probe into a voltage signal transducer. Ultrasonic attenuation in the air as more serious, the probe receives the reflected wave is very weak, so the transducer output voltage signal is very weak, we first amplified the voltage signal, which set a link in limiting the preamplifier . The transmitter and receiver use the same transducer, the substantial value of firing voltage pulses will affect the normal operation of the preamplifier. Because there are multiple probes and limiting preamplifier composed of multiple links receive channels, each channel parameters are different electronic devices resulting imbalance of the channels will affect the measurement accuracy. Therefore, the next step is to set a balance adjustment link. Probe reflected wave is converted into voltage signal by the preamplifier and the balance after the adjustment links, and through the analog transmission switch, the voltage magnitude is still small, but also set a secondary amplifier. To eliminate the emission voltage feedback signal processing circuit timing errors caused by single chip, this time need a controllable filter, it is controlled by the microcontroller T0 end, it launched the bypass voltage feedback signal, and the acceptance of the echo signal no right to treatment, 100% backward transmission. In order to reduce noise interference, band-pass amplification system, and ultimately, device, so this part except amplification, but also increase the role of limited, is limiting Large value in order to avoid non-binding emission voltage to the back to back circuit. The strength of the reflected wave, and distance has a lot. Within the measurement circuit should have sufficient gain, the gain adjustable magnification setting part is necessary. The processed signal by a microcontroller can not directly trigger the timer T1 signal, you must first packet cell detector, and then clamp comparison, so as to trigger the formation of the timer T1 signal. Clamp comparator threshold voltage is varied (T0-side control by the microcontroller), again to avoid the firing voltage due to feedback error signals caused by single chip timing. Ultrasonic receiver circuit diagram shown in Figure 4. 4 technical specifications of the system to achieve Design work is completed, according to the function of the circuit, electronic devices between the size and installation location, the system made of two pieces of circuit board, single chip control circuit and the alarm made a part of the circuit board (display board), install the driver front; ultrasonic voltage source driver and another information processing section formed a circuit board (transmitter accepts board), installed in the rear of the car; between the two plates connected by a six-core cable. 3 of the ultrasound probe through a three-core cable is connected with the launching board to accept, in-kind photo shown in Figure 5. In the laboratory, the temperature about 20 ?, through the steel tape measure and reversing the skin rangefinder control measurements, the measured data in the following table: Measuring distance is 3 centimeters resolution digital display, which, reversing most of the measurement data to meet the measurement accuracy of ? 1 cm (at 20 ?), a small part of the data errors are within ? 2 cm , and realized that the proposed car parking rangefinder function and parameters required. To achieve the design purpose. Outstanding issue is the environment temperature of measurement accuracy, for example, environmental temperature is 40 ?, the ultrasonic propagation speed is 355.78 m / s, ambient temperature of minus 10 ?, the ultrasonic transmission speed is 325. 43 m / sec, the ratio is 1.0933, the actual car where the temperature is: the temperature in summer is higher than 40 ?, the temperature in winter is lower than 10 ? lower than zero. Ultrasonic speed of propagation of the ratio can reach 10% or more, so to achieve more accurate distance measurement, the need to increase the temperature compensation.