Abstract: This paper introduces the prevention of road rear-end collision warning system. The system consists of information collection unit, central control unit, alarm circuit and display output unit. The information acquisition unit completes the signal collection of the vehicle running state by four kinds of sensors. The central control unit analyzes and processes the input information to complete the anti-collision prediction and judgment function. The alarm circuit generates an alarm to remind the driver to take measures to avoid the rear-end collision accident. The system also has a display function.
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0 Preface
In recent years, China's economy has developed rapidly, the number of private cars has grown rapidly, and road construction has also developed rapidly. At the same time, traffic accidents are frequent, due to various reasons, such as poor road conditions and high speed, causing driver visual deterioration. Poor climate conditions. Among them, the collision of the rear-end collision in the accident is the first, so the prevention of traffic accidents is mainly to prevent car rear-end collision.
In view of this, this paper discusses how to prevent the design of car rear-end collision warning system.
1. System overall design
As shown in Figure 1, the system consists of an information acquisition unit, a central control unit, an alarm circuit, and a display output unit.
Figure 1, system structure block diagram
1.1 Information Collection Unit
The sensor is an important part of the information acquisition system unit. The sensor refers to a device or device that can sense the specified measurement and convert it into an available output signal according to a certain rule, thereby completing the detection task. It converts object characteristics or state parameters into measurable quantities and sends this signal to the sensor system for processing [1]. Finally, the cause of the change in the control system is converted into an electrical signal and transmitted to the control unit for analysis and processing.
The information collection unit is composed of a distance measuring sensor, a speed sensor, a brake pedal position sensor and a road surface selection switch, and is used for collecting information such as road conditions and running states of the vehicle.
First, the distance sensor
The system uses a pulsed photoelectric sensor to measure the distance. In this paper, the time difference principle of photoelectric sensor is used to work, that is, the distance is measured by measuring the round-trip pulse interval. The method of measuring the pulse interval is to fill the count with the clock pulse between the start and end points of the determination time, as shown in Fig. 2: constant light source The light emitted by D is projected on the object O, and then reflected to the photo element B, and the distance is measured according to the time difference between transmission and reception. This method can obtain higher test accuracy.
Figure 2. Schematic diagram of time difference ranging
Figure 3, distance count schematic
Second, the speed sensor The speed sensor is made using the principle of the Hall effect. That is, in the semiconductor Hall device, when the magnetic field lines pass through the energized Hall element, the charge of the Hall element is shifted, and the Hall voltage UH value is changed correspondingly in the element to form a pulse, and the Hall sensor will The output speed signal is outputted by the amplification shaping circuit, and the moving speed of the vehicle can be calculated by using the external counting interface of the single chip microcomputer to detect the number of pulses. Therefore, the measurement of the vehicle speed is essentially a measure of the frequency of the speed signal.
Figure 4, Hall speed sensor
Third, the brake pedal position sensor
The sensor is used to determine whether the driver has taken braking measures to reduce the speed of the vehicle when it receives an alarm or has recognized the danger. If it is braked, the alarm is suppressed. The brake sensor extracts the potential signal directly from the vehicle brake indicator circuit, and after processing, sends it as a flag signal of the vehicle brake information to the control unit.
Figure 5, brake pedal position sensor
Fourth, the road condition selection switch
The system uses a manual three-contact road surface selection switch to select the road surface friction coefficient, and the road surface friction coefficient varies with the road surface conditions. The driver should select according to the current road conditions and select the corresponding switch position.
Figure 6, road selection switch
V. Sensor measurement error and compensation method
In practical applications, there are many factors that affect the measurement accuracy. There are two main factors that cause measurement errors: one is the inherent characteristics of semiconductors, and the other is a defect in the manufacturing process of semiconductors, which exhibits zero error and temperature. error.
The zero error is mainly caused by the unequal potential caused by the semiconductor manufacturing process problem. In order to eliminate or reduce the unequal potential, the bridge balance principle shown in Fig. 7 can be used for compensation. The temperature error is caused by the temperature change of the resistivity, mobility and carrier concentration of the semiconductor material. The degree of this change varies with different semiconductor materials. The effect of temperature change on the sensor output or input internal resistance can be Use the output loop shunt resistor or the input loop series resistor to compensate. [6]
Figure 7. Unequal potential compensation circuit
1.2 Central control unit, alarm output unit and display device
The central control unit is the central part of the control system and is the information processing part of the system. The sensor input information is processed and analyzed here to complete the anti-collision prediction and judgment function. When the danger occurs, the information is sent to the alarm output device to realize the alarm and remind the driver. Take measures such as deceleration and braking to avoid rear-end collision accidents.
The system adopts ISP-Flash series single chip AT89S8252, which is a low voltage, high performance CMOS 8-bit MCU with 8k bytes of Flash read-only program memory and 256 bytes of random access data memory, compatible with standard MCS-51 command system. It is powerful, it can process the information collected by the information collection unit, and output control signals to the display device and the alarm output unit according to the situation.
The alarm output unit circuit is composed of a peripheral circuit such as a triode plus a speaker. When the central control unit determines through analysis that there is a hidden danger in the front, a certain signal is generated to drive the speaker to give an alarm to remind the driver to take necessary measures. At the same time, the display device in the system can be driven by the chip MCS14495 to display the digital display.
2, the conclusion
The innovation of the article lies in (1) describing in detail the working principle graphics and specific application principles of each sensor in the data acquisition system. The selected ISP-Flash series single-chip AT89S8252 is powerful. (2) Analyze the measurement error of the whole sensor and propose a specific error compensation solution. The whole scheme has better completed the design of the vehicle rear-end collision prevention system. In addition, the virtual alarm situation needs to be considered. In short, car rear-end is a complex system engineering, the occurrence of the rear-end process is subject to subjective and objective factors. Overall, the overall design is more reasonable and can be applied to practical applications.
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