Vehicle collision Prevention system based on Ultrasonic Wave

Abstract

In the existing automobile collision prevention system, radar is mainly used for ranging, and the price of this kind of system is high, so it can not be popularized in a large area. The range finding algorithm is optimized on the existing automobile anti-collision system, the ultrasonic sensor is used to measure the distance, the relevant anti-collision model is established, and different alarm information is sent out according to the different measuring distance. The experimental results show that the alarm information is accurate within a certain range.

Keywords: Automotive collision prevention system, Ultrasonic sensor, Ranging algorithm

With the development of city economy and the increase in population, as of 2013, the national vehicle retains the quantity to 137 million, nearly an average annual increased more than 11 million cars in the past decade, however, the rate of mortality caused by traffic has increased meanwhile.In recent years, the traffic accidents happen frequently, which directly threats the public safety and causes huge loss of property.The cause of the serious situations follows:speeding or drunk driving and the uselessness of the system of automobile anti collision.With the development of the embedded technology and related hardware, the embedded vehicle monitoring system starts to enter the automotive industry at the same time.Internationally, such as Germany, Japan, the United States and other counties of advanced car producers began to research and develop the safe mechanism of active anti-collision more than a decade ago.January 6, 2014, TOYOTA and Audi showed independent researches and developments of unmanned vehicles in the United States.The research on automotive anti-collision system technology is relatively rare.There are two companies, Tai Yuan and Chao Yue, which research and develop the management system.The automotive anti-collision device of Tai Yuan, is the most advanced products in China at present.Its technical content has been at the top of the world's advanced technology, but the cost is expensive.According to the above situation, this article optimizes the vehicle model based on the ultrasonic ranging system in a wide range.By the ARM development platform, a system of vehicle anti collision is designed, which is suitable for modern vehicle.The function of the system is simple and practical, the price is reasonable, and the system has the advantage of universal.

In this paper, we choose a kind of embedded system based on ARM processor, and build the necessary peripheral equipment, with the ARM11 processor as CPU combined with ultrasonic distance measurement device, speed sensor, alarming device and related device interface.A typical embedded devices is built.The system uses the mainstream Linux operating system.

OK6410 development board based on Samsung ARM11 processor, which is a RSIC processor with low power consumption and high performance.It is based on ARM11 kernel (ARM1176JZF-s) and can be widely used in mobile phones, general processing and other fields.S3C6410 2.5G and 3G communication service provides optimized hardware performance and built-in powerful hardware accelerators, including motion video processing, audio processing, 2D acceleration, display and scaling and so on.

In the study of the system of automotive anti-collision, for distance measuring device, radar, laser, ultrasound and others are commonly used.Millimeter wave radar is most widely favored, but its high price is not conducive to be spread.Laser radar and high-precision camera are greatly affected by the environment, so the development of ultrasonic anti-collision system with a large range of applied intelligent vehicle systemsis necessary.Ultrasonic Ranging, from the principle, can be divided into two:resonance type and pulse reflection type.Since functional requirements, we use pulse reflection, namely use the ultrasound reflection characteristics in this system.At room temperature environment, we usually take the ultrasonic speed of 340 m/s.By the formula, the distance from the obstacle emitting dot pitch L, can be calculated, this is the propagation time, is the speed of ultrasonic waves.

Ultrasonic transmission circuit includes two parts:ultrasonic control circuit and ultrasonic wave generating circuit.We choose DY150 high-power transducer as ultrasonic probe model, and the central frequency of the transducer is 15 k Hz, maximum range is 50 meters.Its biggest characteristic is to transmit and receive integrated together.

This article adopts the way of interrupt signals to receive the signal.Ultrasonic sensor reflects a bunch of ultrasonic signal which spread through the air, and return when it encounters some obstacles.Ultrasonic receiving device receives the echo signal.Due to the amplitude of received echo signal is small, it will be further processed by amplification, detection and filtering.Finally, a pulse signal is output through a voltage comparator, and then is input to the MCU external interrupt input end, causing SCM interrupt.

In the vehicle driving process, if the distance between two vehicles is less than the safe distance, the alarming module of the ARM development board is used to light the LED alarming circuit with the anti-collision algorithm.

In order to make the system be able to effectively serve as warning to the driver and be unable to interfere with the driver for normal driving by too many reminders, the establishment of model should follow.

(1) The distance of reminder and alarm should be left for enough reactive time to the driver.When the driver hears the alarm, he can prepare to decelerate following the normal habits.

(2) The danger alarming distance (emergency braking critical distance) is set up without consideration of the driver's reactive time and the preparative time.When the driver is alarmed, he has been ready to brake.Secondly, it should prevent frequent warning from disturbing the normal operation of the driver.

(3) The model should be able to reflect the most dangerous situation of cars under different motion state, and has good robustness to judge the dangerous distance under different conditions.

In order to ensure driving safety, the car which is at high speed on the highway must keep a certain distance S from the front vehicle.The anti-collision system based on the size of the distance between the two vehicles is divided into three stages:namely remind distance St, alarming distance Sw, and forced braking distance Sd.In the same situation the expressions are as follows:St>Sw>Sd.When the distance between test car and the car in front is in remind distance St, the range finder will issue a warning signal to remind the driver that the distance between two vehicles is too short.At this time the driver has enough reactive time to hear the reminding calm and be ready to slow down according to normal habits.When the distance between test car and the car in front is within reminding alert distance Sw, there is a risk factor of two vehicles, which is relatively low.After hearing the alarm, the driver should be vigilant and pay attention to the situation of the front car to ensure the safety of driving.When the distance between test car and the car in front is in alert distance Sd, the risk factor is high, and the driver has no enough time to make a judgment.The system will exceed the driver, because the vehicle will be forced to send a deceleration signal and decrease the car's speed to increase the distance between two cars, which reduces the driving risk factor.

In order to determine St、Sw、Sd, the specific values of three kinds of distance in the braking model, we need to analyze the condition of two vehicles during braking, through calculation the distance needed in the process of braking to determine the collision risk.For car in the actual car braking process, in case of the tire does not lock up, the braking resistance comes from the friction between the tire and the ground, and the friction depends on the friction coefficient.From energy conservation we can get power of friction force on the body which is equal to the variation of the kinetic energy of the object:μNS=1/2 mv2, where N is the number of cars on the ground pressure, μis the ground friction coefficient for car, S is the braking distance, m is the mass of the car, v is the speed of the car, and the pressure of car to the ground is equal to the gravity of the car F=mg, so that we get mgμs=1/2mv2, namely s=v2/ (2μg) .

The common accident on the highway happens since the speed of the car behind is higher than the car front.In this condition the distance between the two cars is too short with a greater risk.Assuming there are two cars on the coincide road, the car behind is A, the speed of A is va, the car front is B, the speed of B is vb, va>vb, and the distance between two cars is S.

If S is greater than Sa, in this case, even if the vehicle in front instantaneously stops due to the occurrence of an accident, the car behind also has enough distance to brake until stop.So we consider the distance between the two cars.

If driver B found an accident in front of him, and he has enough distance to brake the car until stop, the bra-king distance of the car is Sb=v2 b/ (2μg) , assuming that the two cars distance is Sa-Sb, to make sure the safety, the car behind should completely brake.At this time, the accident probability is very high, we now set the risk coefficient as 1.

Anti-collision system not only must remind the driver in relatively safe distance between vehicles, but also can't send a wrong braking signal, which can affect the normal driving, so we can reference the increase of risk to determine the set.

There is Maintain Safe Distance principle in the safe driving knowledge that people should maintain a distance for one over one thousand of the driving speed.For example, the car's speed is 50 km/h, we should keep the 50 m distance, and the speed is 120 km/h, we should keep the distance 120 m.We will base on the basic driving knowledge to set the remind distance as St=vt

It will alarm as long as there is a dangerous situation.The alarming distance is the distance S0when the risk factor is 0, where Sw=S0=v2 a/ (2μg) .

It will be dangerous, if the driver does not make the braking measure.We will put the risk factor of 0.5 for safety reasons, so we set Sdas the distance between S0and S1, where Sd= (S0+S1) /2.

If we consider the reactive time of the car as t2+t3, usually the total time required is about 0.5-0.6 s.Because of safety, we will set t2+t3as 1 s.The time required is short and can be used as the reactive time of the vehicle braking system.Then St, Sw, Sdneed to increase the delay distancet×va.

If two cars running at a larger speed, such as the speed of the vehicle in is 0 km/h, another car is50 km/h, then it will appear the extreme situation s0=s1, when the absolute safety distance is not enough, under this circumstance we need a speed difference coeffi-cient to guarantee to give the driver a judgment.In this model, we introduce a speed difference coefficient kv=1+0.8 (vref/va) , vrefis the relative speed of two vehicies, the speed difference coefficient will be based on the two car speed difference, the safety factor has been increased from 1 to 1.8.

Since the braking distance is inversely proportional to the friction factor, the reminder distance is also related to the coefficient of friction, so Stshould increase the ratio of the friction factor.As the friction factor is generally around 0.8, so the coefficient is set to 0.8/μ.

Firstly, Ok6410 development board implement module performs initialization, including a LED driver initialization and serial receiving procedures, through the way of interrupting to receive ultrasonic range data which is sent by AVR microcontroller.Thus the data are substituted into the alarming algorithm as alarming information, then the information is written to the LED driver to complete alarm.

The ultrasonic launch program initializes the initial parameter, and then sends the 15 k Hz ultrasonic pulse signalper 60 ms.By comparison with the timer, the time of delay of sending ultrasonic signalis 50 ms.So we enable the interruption and initialize the timer to wait for the signal.Only when the echo is received, the waiting program is shut, the interruption is off and the timer starts to count.Otherwise, the waiting program continues.According to the difference between the read echo and the transmitted wave, the distance is calculated every 1 s.

In this paper, the ultrasonic distance measurement device obtains travel distance between vehicles and calculates the speed information about the front vehicle, then using the computer to simulate the speed of the current car.The distance from the two vehicles that will speed the automotive anti-collision warning information were substituted into the model.System design is mainly dominated by the ultrasonic ranging.It calculates the traffic data by the analysis of theory and practice and ARM processor.At the same time, it uses LED light to send alarming information for the automobile anti-collision.With the improvement of the system, it will be used more widely.