Design of automobile anti-collision system by using ultrasonic ranging transducer

With the continuous advancement of automobile technology, especially the development of autonomous driving technology, more and more distance detection equipment will continue to appear. At present, there are four main methods used in automobile ranging: millimeter wave radar ranging mode; camera system ranging mode; laser ranging mode; ultrasonic ranging mode. The millimeter wave radar has the problem of electromagnetic interference, and the camera system is expensive to make it difficult to popularize in automobiles. Laser ranging has the advantages of short measurement time, large range, high accuracy, etc., adapting to the ranging needs of cars from low speed to high speed, avoiding the phenomenon of ranging inaccuracy caused by slow ranging speed when the car is driving at high speed. Ultrasonic distance measurement sensor is simple in principle, it is convenient to manufacture, and relatively low-cost, but it is only suitable for short-distance and low-speed distance measurement, so it is applied to distance measurement when the car is reversing. The safety alarm system that combines laser distance measurement and ultrasonic distance measurement proposed in this paper is designed to help the driver detect and display the distance between the vehicle and surrounding obstacles in a variety of driving conditions and multiple directions. When the obstacle distance is less than the set distance the driver at a safe distance to avoid a traffic accident caused by the driver's untimely response.

2. Scheme design of anti-collision system

The key to realizing automobile collision avoidance lies in the application of distance measuring and collision avoidance systems. This system is composed of ranging module, control calculation unit, display unit, alarm unit, execution unit, etc. The distance measurement module of accurate ultrasonic transducer includes a laser distance measurement module that works when the car is moving forward and an ultrasonic distance measurement module that works when the car is reversing. The two are respectively connected to the control unit through their respective communication circuits, which can monitor the obstacles around the car in a variety of working conditions such as forward and backward of the car, and transmit the distance between the car and the obstacle to the control unit. The control unit is connected through the execution unit, alarm unit, etc. performing sound and light alarms, active braking and other anti-collision functions.

3. Ranging principle

The principle of ultrasonic ranging is the pulse reflection type, which uses its reflection characteristics to work.

Transmitting ultrasonic waves in a certain direction through the ultrasonic transmitter, and start timing while transmitting. The ultrasonic waves propagate in the air and return immediately when is encountering obstacles on the way. The ultrasonic receiver stops timing immediately after receiving the reflected waves. The propagation speed of ultrasonic waves in the air is C, and the time difference t between the transmission and reception of the echo is measured according to the timer, and the distance S between the transmission point and the obstacle can be calculated, namely: S=Ct/2.

The principle of laser ranging is different from the principle of ultrasonic transducer sensor. It uses the triangulation method for ranging.

The transmitter sends a pulse forward, and the echo reflected back after encountering an obstacle is received by the receiver, and the echo image is converged on the sensor through the lens to form an image point. When the object illuminated by the laser moves, the image point also moves on the sensor. Under the premise that the baseline length is known and the relative position of the light source, sensor and lens is determined, the measured object can be accurately determined by measuring the position of the image point on the sensor.

4. System hardware and its operation

The main body of the control and calculation unit adopts the STC89C52RC single-chip microcomputer, which is a low-voltage, high-performance COMOS8 microprocessor with 8K bytes flash programmable and removable read-only memory produced by STC.

With a smart 8-bit CPU and in-system programmable Flash, it can provide highly flexible and ultra-effective solutions for many embedded control application systems. The buzzer and the led light form an alarm unit, which can give an audible and visual alarm in time.

In addition, this system uses SRF020M01A laser distance sensor. The ultrasonic sensor is designed with a high-performance dedicated chip, with high accuracy and good stability. The single range finding input command is "a/A", and the returned data is packaged and sent in a frame. ultrasonic sensors are commonly used in the market.

When the car is moving forward, the speed is high, and all the systems except the ultrasonic module start to work. The control unit (microcontroller) sends a ranging command ("a/A") to the laser ranging module through the RS232 serial communication circuit to control the laser ranging module to emit light pulses forward, and the module receives the laser reflected back from obstacles Analyze and calculate the distance between the car and the obstacle after the pulse, and send the data to the single-chip microcomputer in a hexadecimal number package through the RS232 communication circuit, the specific value is "ee+06+* * * *+cc", ee is the frame header, cc is At the end of the frame, the third * represents the hexadecimal measurement result.

After the single-chip microcomputer is converted into a decimal system, the display circuit dynamically displays the obstacle distance S, and at the same time, it is judged that if S is less than the set threshold K, the red LED light of the alarm unit will continue to flash, and the buzzer will continue to alarm to remind driving The personnel shall take timely anti-collision measures. When the driver still fails to take effective measures after a certain period of time, the single-chip microcomputer makes the execution unit emergency brake to actively avoid the collision.

When the car is reversing, the speed is low, and the ultrasonic module sensor replaces the laser ranging module. Under the control of the high-level signal with the IO port of the single-chip microcomputer greater than 10US, it automatically transmits 40KHZ square waves backward.

After the ultrasonic wave returns, the single-chip microcomputer measures the ultrasonic round-trip time from the high level duration of the INT0 pin, and obtains the distance between the car and the obstacle through conversion. Afterwards, each unit of the system is used to achieve the same anti-collision work as laser ranging.

5. System software design

It shows the design of the ultrasonic distance measurement software. After the system is started, the ultrasonic module sensor emits ultrasonic waves backwards, and starts the timer while receiving the ultrasonic waves. The obstacle distance S is calculated from the measuring time T, and the display unit dynamically displays the continuously changing distance S. If the distance S is less than the set threshold, the system will give an audible and visual alarm, the LED lights will keep flashing, and the buzzer will keep beeping to remind the driver to take timely measures to avoid collisions. If the distance S is still less than the set threshold after a delay of 1 second, it indicates that the driver has not performed any effective operation. Therefore, the system controls the car to brake emergency and actively avoid collision prevention.It shows the laser ranging software design. After the laser module emits and receives laser pulses, the internal circuit of the module simultaneously completes the calculation of the distance S. If S is less than the threshold, an alarm is issued.

6 Conclusion

The system selects a combined distance measurement method that combines a laser ranging sensor and an ultrasonic transducer for distance measurement. The distance measurement method of a single sensor is greatly restricted by the application conditions of the sensor, and it is difficult to meet the complex driving state and changeable external environment of the car, so the advantages of this system are obvious. In a variety of driving states such as forward, reverse, low speed, high speed, etc., the system can effectively monitor and distance obstacles in the surrounding environment of the car, so that the car can actively prevent collisions and prevent traffic accidents. Research prospects.