汽車倒車時防撞自動測距警報系統(tǒng)設(shè)計畢業(yè)論文-展示頁
2025-07-04 02:29本頁面
【正文】 性，因此，在下一節(jié)驗證系統(tǒng)B的指向性可以較寬，并提供更適合的障礙檢測。該地圖的制作方法是為將一定范圍的數(shù)據(jù)沿傳感器放置在一個方向測量范圍內(nèi)。A系統(tǒng)使用了一個喇叭，以增加其強度。實驗環(huán)境如圖12，系統(tǒng)A和B的實驗結(jié)果分別顯示在圖13和14中。圖11系統(tǒng)B安裝在移動機器人“YAMABICO”上。傳感器直接連接到電路板，沒有喇叭。傳感器被置于0點 圖13表明系統(tǒng)A只可以檢測到傳感器視線內(nèi)到墻的垂直回聲。作為一個結(jié)果，看來這個系統(tǒng)有一個狹窄的方向性。然后，后來的回聲振幅超過一個閾值水平。與上述相比，圖14表明，系統(tǒng)B可以檢測在每一個方向的回聲，由于在這個系統(tǒng)中的回波信號的強度足夠大。因此，當(dāng)一個機器人移動，障礙是可以檢測到的，即使他們沒有垂直面對到換能器的視線。Ⅴ 結(jié)論從上述結(jié)果可以得到以下結(jié)論：●障礙物檢測的性能隨著不同傳感器系統(tǒng)變化?！裼纱说玫降穆暭{地圖形狀急劇變化，根據(jù)傳感器的特點，如靈敏度，方向性等。如果機器人感知能力與人類幾乎無異，我們可以信任機器人。因此，我們必須小心處理機器人的存在。 (1) where c is the speed of sound, and t is the roundtrip timeofflight (Fig. 1). The TOF method produces a range value when the echo amplitude first exceeds the threshold level after transmitting. In spite of the simple method like this, information obtained by the ultrasonic sensor is influenced by the characteristics of the sensing system, it of environment and so on.In this paper, in order to investigate the influence of the sensor system, we constructed two ultrasonic ranging systems of which characteristics differs from each other and examined their performance such as obstacle detectability and resultant sonar map.In section II, we introduce two ultrasonic ranging systems which we developed. Their availability for obstacle detection is examined in section III, sonar map making using them in section IV. Finally, the conclusions are presented in section V. Fig. 1. The principles of the timeofflight (TOF) methodII. Two Ultrasonic Ranging SystemsFig. 2 shows a model of reflected waves, where there are two objects in a field of view. As an ultrasonic wave attenuates and spreads, the echo amplitude reflected off farther object is smaller (even from the same object[2]). Because we use piezoelectric ultrasonic sensors, we use a transmitter and a receiver separately. So, the received waves include the direct wave from the transmitter which must be neglected.We have developed a ultrasonic range finding system A in which the following fundamental method is employed[4][3]. Ultrasonic waves are discharged from a transmitter given paratively long burst waves in order to vibrate its piezoelectric vibrator fully. A range value is calculated by TOF method using the amplified echo and a threshold level. The threshold level to detect echoes is constant in order to simplify the circuit. The concept of each signal for System A is shown in Fig. 3. However, this system has some problems. First, the rise of echo signal is slow, since the intensity of the echo signal is not so large. So measuring errors result. To reduce such measuring errors, the rise of ultrasonic waves must be quickened. Next, the measuring range is limited by a fixed threshold level. It is impossible to detect far distance objects when the level is set higher, or it is likely to detect noise from near distance objects when the level is set lower. Also, horns are attached to System A to increase the intensity of waves. However, it makes the directivity narrow. Fig. 2. A model of reflected waves.To solve the problems of System A, we improved the transmit and receive circuit, and developed a new ultrasonic sensor system B. The concept of each signal for System B is shown in Fig. 4. In order to enlarge the intensity of echo signal and quicken the rise of it, a high voltage single pulse is employed for transmitting. The peak voltage is about 720V, while it is about 12V in System A. This method has the following benefits. First, themasking time can be shortened by shortening the transmitting time. Thus it is possible to measure near distances. Second, the rise time of transmitting waves is shortened byusing a high voltage for discharging ultrasonic pulses. Therefore the measuring errors can be reduced. For receiving, the threshold level is decreased with time, and is gradually adjusted to the echo amplitude decreasing with the distance. We call this method timethresholdcontrol. This met
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