I. Introduction
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With the continuous advancement of society, cars are being used by more and more people, and correspondingly, traffic accidents are increasing. The number of people and property losses caused by traffic accidents every year in the world is staggering. Therefore, vehicle safety issues have attracted people's attention. Analysis of a large number of traffic accidents shows that more than 80% of car accidents are caused by driver's reaction failure. More than 65% of vehicle collisions are rear-end collisions, and the rest are side collisions and frontal collisions. Studies have shown that 90% of rear-end collisions and 60% of frontal collisions can be avoided if the driver is aware of the risk of accidents and takes appropriate measures 1 s earlier.
Modern transportation systems and the upcoming Automated Vehicle System (AVS) require the establishment of Intelligent Transportation Systems (ITS) to facilitate traffic monitoring and tracking of vehicles and multi-sensor information fusion. Future AVS heterogeneous sensors include video sensors, laser scanners, and radar sensors. The purpose of the fusion is to input the target into the path planning and guidance system. The vehicle active anti-collision control system based on multi-sensor information fusion is based on the vehicle front target information received by the multi-sensor and the state information of the vehicle, and uses multi-source information fusion technology to identify the distance and speed of the vehicle in front of the vehicle. Wait for status information and perform collision risk estimation. For example, if the distance between vehicles is close to the critical distance, an alarm signal is sent to the driver for attention;
If the distance between the cars is less than the critical safety distance, the brake system is activated to avoid collisions.
Obviously, the vehicle active anti-collision control system based on multi-sensor information fusion is an active anti-collision and anti-locking vehicle safety system, which can optimize the reaction time, distance and speed. Reducing the driver's burden and misjudging will play an important role in improving traffic safety and effectively avoid most car accidents. At the same time, it has laid a good foundation for improving the use of speed, increasing road capacity and achieving automated driving.
2. Composition and function of vehicle active anti-collision control system based on multi-sensor information fusion
The car anti-collision collision control system is an active safety system. The system is not in operation during normal driving. When the front of the car is very close to the rear of the front car, the system will issue an anti-tailing warning. After the warning is issued, if the driver does not take the brake deceleration, the system automatically activates the emergency brake to avoid a rear-end collision.
Automobile anti-collision collision control system
It has three functions: environmental monitoring function, anti-collision judgment function and vehicle control function.
1. Driving environment monitoring system
The driving environment monitoring system consists of an environmental detection system and a vehicle condition detection system. The environmental detection system consists of a millimeter wave radar, a laser radar, a CCD camera, and a road sensor capable of judging the condition of the road surface, which measures the distance between the workshop and the front vehicle. The peripheral sensing technology of the vehicle is the key technology to realize the anti-collision of the automobile. The performance of the sensor will directly affect the performance of the entire system. Only by improving the reliability of the sensor, it is possible to reduce the false alarm rate of the system. As can be seen from Table 1, the microwave sensor (radar) has a high cost performance. Therefore, a microwave sensor operating in a millimeter wave is generally selected as a main sensor, and an image, a road surface sensor, or the like is used as an auxiliary sensor to detect an obstacle before the vehicle. The millimeter wave radar is installed at the center of the front end of the vehicle. The laser radar is installed on both sides of the millimeter wave radar. Their main function is to measure the distance between the vehicle and the preceding vehicle and the orientation of the vehicle in front, and transmit the measured data to the defense. Collision judgment system; CCD camera obtains image information of vehicles and obstacles ahead, road sensor obtains state information of road surface, vehicle condition detection system detects speed, acceleration and other state information of the vehicle, all information will be sent to anti-collision Judging the system.
2, anti-collision judgment system
The collision avoidance judgment system is composed of a target recognition system and a danger estimation system. The target recognition system fuses the information of sensors such as millimeter wave radar, laser radar, CCD camera, etc., and estimates the distance and relative speed of the nearest vehicle or obstacle in front of the vehicle, and transmits the signal to the risk estimation. system.
The hazard estimation system calculates the "critical workshop distance" based on the road conditions (wet/dry), the condition of the vehicle (such as the speed of the vehicle, the steering angle and the lateral swing speed), the distance and relative speed from the preceding vehicle, and the reaction status of the driver. The actual measured inter-vehicle distance is compared with the critical inter-vehicle distance. At some point when the actual measured inter-vehicle distance is very close to the critical inter-vehicle distance, the alarm sends a warning signal. The brake control system is automatically activated when the actual measured inter-vehicle distance is equal to or less than the critical inter-vehicle distance.
3. Vehicle control with automatic brake operating mechanism
The International Highway Commission investigated the driver's response time and concluded that the average was 0.5 to 3 s. If the driver's reaction time is 1.5s, then when the car's speed is 40Km/h, the driving distance of the car during the reaction time is 16.7m; when the car speed is 80Km/h, the driving distance will reach 33.4m. The automatic braking system has much less reaction time than the driver, and its response distance is only 0.5 m.
During work, the anti-collision judgment system continuously calculates the safety distance based on the measured distance between the two vehicles, its own vehicle speed, and the relative vehicle speed, and compares it with the actual distance measured by the radar. If the measured distance is less than the safety distance, an alarm message is issued. If the driver has not taken measures and the safety distance is less than the limit safety distance, the system acts on the conventional braking system of the vehicle through the actuator to decelerate the vehicle. When the limit distance is exceeded, the brake mechanism returns to normal.
Third, millimeter wave radar
The most popular sensing method at present is the radar system that uses millimeter waves for measurement. The millimeter wave refers to an electromagnetic wave whose operating frequency is between 30 and 100 GHz and whose wavelength is between 1 and 10 mm. Millimeter wave radar (mainly 9 4GHz) was originally used for short-range anti-armor weapon systems, its function is to accurately measure the distance and relative speed of the target. Millimeter wave radar can work around the clock, regardless of weather conditions, and the harsh climate is one of the main causes of traffic accidents. With the emergence and application of GaAs high-frequency devices and single-chip microwave integrated circuits MMIC, the performance of millimeter-wave radar has been greatly improved, the cost has also decreased, and the size of the radar can be made small, which is convenient for the car. Installed on. Therefore, millimeter wave radar has become the first choice for automotive forward-looking radar. In order to find traffic jams in front of the highway in time, the detection distance of the vehicle with millimeter wave radar must be above 100m; in order to cover the lane lines on the left and right sides, the detection width must be 3.5m; in order not to mark and pedestrian above the road The flyover is also detected. The upper and lower sides should have a detection range of about 3m corresponding to the elevation of the road. The main indicators are as follows:
1 antenna: small size, low cost, high performance, and easy to install and use.
2 Working frequency: The operating frequency of the millimeter wave radar is related to its performance and price. In general, the frequency is increased, the target's reflection effect will be better, but the penetrating power of the signal will be weakened, the ranging range will be reduced, and the device cost will increase. There have been reports of radar prototypes and finished products working at 24 GHz, 60 GHz, and 76-77 GHz. Nowadays, the 76-77 GHz millimeter-wave radar has a good cost performance, and this operating frequency is currently used in foreign countries. Due to the influence of device and cost factors, China currently prefers to use 35GHz operating frequency.
3 Viewing angle: The viewing angle is the scanning range of the antenna beam, including the azimuth and the high and low angles. In order to reduce the false alarm rate, the azimuth is generally selected from 9oC to 12oC, or even larger. The high and low angles are around 3oC.
4 working distance: 100m ~ 150m. For example, the US regulations are 1 to 100 m, and the European regulations are 1 to 150 m. The range of the ranging is determined to ensure that the two vehicles do not have a rear-end collision when the vehicle is braked.
5 Dynamic range of measurement: The radar must have sufficient dynamic range to ensure that both large and small targets can be identified.
6 resolution: Radial distance resolution can reach 1m.
Fourth, multi-sensor fusion strategy
Multisensor Information Fusion or multi-source information fusion is a new technology developed in recent years.
Surgery. Information fusion is an effective method to solve the track prediction and tracking of aircraft and missiles, and it is also the intelligent information office.
One of the most promising research directions in the field of science. In a broad sense, information fusion is ubiquitous in nature. For example, human cognitive world
It is to obtain information through senses such as sight, hearing, touch, taste and smell, and to obtain cognitive conclusions through fusion of the brain. Narrow
From a different perspective, different sensors are used to obtain different measurement data of the same object, and an algorithm is used to obtain a comprehensive information, which is data.
Fusion. Data fusion is the simplest and most practical method of information fusion. This method is based on estimation theory, especially Bayes estimation.
Theory, and mainly for the same type of data information. A typical application is the track prediction in target tracking, which comes from different monitoring.
The device's data is fused to get the best estimate. The data fusion method is divided into a centralized processing method and a distributed processing method.
In the tracking research, the distribution processing method has its special importance.
The working environment of the automobile anti-collision system is harsh, and there are many interference factors. It is easy to generate false alarms only by using a single radar sensor.
To improve the ability to identify and estimate targets, it is necessary to introduce multi-sensor information fusion technology. Among them, the sensor includes a radar sensor, laser scanning
Instruments and video sensors, etc. Multi-source information provided by multiple homogeneous or different types of sensors distributed in different locations for comprehensive processing
The purpose is to reduce the uncertainty of detection and form a relatively consistent perceptual description of the system environment in order to obtain an accurate and reliable analysis and judgment.
Break the results, thereby improving the system's decision-making ability.
1. Target recognition based on multi-sensor information fusion technology
One of the key technical aspects of automotive anti-collision systems is the target recognition system. Because, when the radar emits electromagnetic waves to the front, the belongings in front of the car
Body such as trees, highway signs, three-dimensional intersections, bridges, overhead wires, etc. will reflect the radar waves. The system must eliminate those false ones,
That is, signals that are not reflected by objects that are dangerous to collision, detect the signals that are real, that is, the risk of collision, and then process them.
Work accurately without malfunction.
In order to eliminate or reduce the occurrence of false alarms, in addition to ensuring certain technical indicators when designing and selecting sensors (such as requiring radar
The angle of view is within a certain range), and the information of other sensors is used for comprehensive analysis and judgment.
2. Distance estimation based on multi-sensor information fusion technology
From the above description, the distance between the vehicle and the preceding vehicle is an important parameter of the anti-collision system of the car. When calculating the critical safety distance,
According to it, the speed and acceleration of the preceding vehicle are estimated. Therefore, the accuracy of the distance will directly affect the reliability and accuracy of the anti-collision system.
Sex.
The sensors used for measuring distances are laser sensors and millimeter wave sensors, each of which has its own characteristics. Their measurement range, pair of rings
The ability to adapt to the environment and the ability to reflect on the target are not the same, but no matter which sensor is used to ensure measurement over the entire measurement range.
Accuracy and reliability must use fusion technology so that appropriate mathematical operations can be performed based on the complementarity and redundancy of sensor information.
Rational, get a more accurate distance value.
3. Risk assessment based on multi-sensor information fusion technology
The core of the risk assessment system is to make a judgment based on the road condition, the running condition of the vehicle, the distance and relative speed from the preceding vehicle, and the reaction status of the driver. Calculate the “critical workshop distance†and the actual measured workshop distance and criticality. Workshop distance comparison.
The determination of "critical workshop distance" must take into account the impact of various aspects. If the driver's response is more sensitive, or the road conditions are better, or the brake system of the vehicle is working well, the "critical workshop distance" can take a smaller value; "Critical Workshop Distance" needs to take a larger value to prevent collisions from occurring.
V. Summary
The main content of vehicle active anti-collision control system based on multi-sensor information fusion is to explore the real-time fusion method of multi-source information, including real-time target recognition algorithm for real-time fusion of multi-source information and real-time parameters of real-time fusion of multi-source information. Estimate, real-time risk assessment of real-time integration of multi-source information, and apply these methods to engineering practice. The technical indicators that can be achieved by the vehicle active anti-collision control system based on multi-sensor information fusion include online real-time data acquisition, and complete target recognition and multi-sensor information fusion processing; target recognition accuracy reaches industrial application standards; The current state and the state of the obstacles are judged against collisions; in particular, warnings can be made for dangerous situations, and an alarm signal is sent to alert the driver when approaching the target. The implementation of vehicle active anti-collision control system based on multi-sensor information fusion can greatly improve the safety of vehicle operation and minimize the occurrence of traffic accidents. In particular, if this method is applied to an automatic vehicle system (AVS), it can bring about a great improvement in vehicle safety.
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