AIRBAG DEPLOYMENT CONTROL SYSTEMProject reportSubmitted inPartial fulfilment of Credit Of Course

AUTOMOTIVE ELECTRONICSIn Mechatronics Engineering

By

DEPARTMENT OF MECHANICAL ENGINEERING NITK, SURATHKAL SRINIVASNAGAR 575025 KARNATAKA INDIA

ABSTRACTAirbag systems have been introduced to supplement the seat belt system primarily to reduce head injuries. Most of the present airbag systems use distributed mechanical sensors, which are costly, not easy to calibrate, and not effective to trigger the airbag on time for different types of crashes. An electronic sensor is more effective in the sense that the signal from the accelerometer can be digitized and analyzed to study the behaviour of the signal for different types of crashes.Airbags are subject of serious government and industry research. My project report on Airbag deployment control presents a new method for Airbag deployment control. The presented method is based on a MEMS Accelerometer (MPU-6050) and an IR Sensor for occupant detection. The deployment control has been shown for two directions Frontal crash and Side impact.

ContentsIntroduction5Components Of Airbag Control System61.MEMS Accelerometer (MPU-6050)62.Infrared Sensor Module83.Arduino UNO(Airbag Control Unit)9Block Diagram10Control Algorithm11Fault detection12Conclusion14References14

Introduction

AIRBAG systems to supplement seat belt systems primarily systems are used in many current vehicle to reduce head injuries. Recent studies show that the airbag reduces head and chest injuries significantly. In the crash sensing system, in order to detect a crash, if the change in velocity is greater than or equal to the threshold value, then a crash detection decision is made. The threshold value is determined from the lowest speed of an effective crash define by NHTSA i.e., 22.54 km/h. However, if is less than, then the decision is that there is no crash.An airbag can be used only once. Since replacing a used airbag costs at least $500, it's obviously critical for the airbag to inflate only when absolutely necessary. Thus, the airbag should not be deployed when a car moves through a very rough or bumpy road, or when it hits a small traffic sign pole, e.g., stop or yield sign pole. Most of the present airbag systems use distributed mechanical sensors. All the mechanical sensors work almost on the same principle. In a typical mechanical sensor a stainless steel ball is held by a magnet at one end of a closed cylinder. The crash impact overcomes the precisely calibrated magnetic bias and the ball moves through the cylinder to close electrical contacts and complete the airbag triggering circuit. Mechanical sensors can be designed to take the above mentioned specifications into consideration, but the necessary calibration for the sensors is not that simple. A MEMS Accelerometer is expected to overcome the limitations of the current distributed mechanical sensors which are costly and ineffective in triggering the airbag on time for different types of crashes. An electronic sensor is more effective, because the accelerometer signal can easily be digitized and analyzed in order to study the characteristics of different types of crashes. The presented hardware implementation of Airbag deployment control depicts some of the control strategies which are being tested on modern cars.

Components Of Airbag Control System

1. MEMS Accelerometer (MPU-6050)2. Infrared Sensor Module3. Arduino UNO(Airbag Control Unit)4. Two LEDs(Actuation signal)5. A Mini Push Button and buzzer

1. MEMS Accelerometer (MPU-6050)

Fig-1(a) MPU 6050 1(b) interface of MPU 6050 with Arduino

MPU-6050 sensor contains a MEMS accelerometer and a MEMS gyro in a single chip. It is very accurate, as it contains 16-bits analog to digital conversion hardware for each channel. Therefor it captures the x, y, and z channel at the same time. The sensor uses the I2C-bus to interface with the Arduino. The MPU-6050 is not expensive, especially given the fact that it combines both an accelerometer and a gyro.The triple-axis MEMS accelerometer in MPU-6050 includes a wide range of features: Digital-output triple-axis accelerometer with a programmable full scale range of 2g, 4g,8g and 16g Integrated 16-bit ADCs enable simultaneous sampling of accelerometers while requiring no external multiplexer Accelerometer normal operating current: 500A Low power accelerometer mode current: 10A at 1.25Hz, 20A at 5Hz, 60A at 20Hz, 110A at 40Hz Orientation detection and signalling Tap detection User-programmable interrupts High-G interrupt User self-test

Fig-2 Example of accelerometer data taken and plotted in MS-excelThe above figure shows the raw data taken from accelerometer to MS-excel for plot curves to determine the acceleration threshold.

2. Infrared Sensor Module

Fig-3 IR sensor ModuleIR Sensors work by using a specific light sensor to detect a select light wavelength in the InfraRed (IR) spectrum. By using an LED which produces light at the same wavelength as what the sensor is looking for, we can look at the intensity of the received light. When an object is close to the sensor, the light from the LED bounces off the object and into the light sensor. This results in a large jump in the intensity, which we already know can be detected using a threshold. Fig-4 Showing working principle of IR sensorAs shown in first figure shows that when no object is present the reciever does not detect any signal and no output is given .In figure second as object comes infront of emitter the reflected reys are detected by reciever of IR sensor and it gives high output.Here in project the IR sensor module has been used to detect occupant present on seat and it is decided by ACU whether to fire ot not fire Airbag.

3. Arduino UNO(Airbag Control Unit)

Fig-5 Pin diagram and components of Arduino uno The Arduino Uno is a microcontroller board based on the ATmega328. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with an AC-to-DC adapter or battery to get started. For hardware implementation of Airbag deployment control it has been used as Airbag Control Unit (ACU) and programming has been done accordinglySome of important feature of Arduino UNO has been given belowMicrocontrollerATmega328

Operating Voltage5V

Input Voltage (recommended)7-12V

Input Voltage (limits)6-20V

Digital I/O Pins14 (of which 6 provide PWM output)

Analog Input Pins6

DC Current per I/O Pin40 mA

DC Current for 3.3V Pin50 mA

Flash Memory32 KB (ATmega328) of which 0.5 KB used by boot loader

SRAM2 KB (ATmega328)

EEPROM1 KB (ATmega328)

Clock Speed16MHz

Block Diagram

Fig-6 Showing block diagram of hardware modelAs shown in above figure the accelerometer acts as crash sensor, the crash is being detected in two directions i.e. for Frontal crash and Side impact. The accelerometer reads the change in velocity i.e. acceleration in both X and Y directions .The data is continuously fed to Arduino UNO which acts as Airbag control unit (ACU).The ACU is programmed to detect crash when the acceleration value sent from acceleration sensors exceeds the set threshold value it generates an actuation signal which is shown via two LEDS(Red and White) .The ACU is programmed so that it only gives actuation signal for any crash only when IR sensor acting as proximity sensor get high value .The IR sensor acts as proximity sensor for detecting the occupant.

Control Algorithm

Fig-6 Showing control algorithm used in hardware projectAs shown in above figure, the control algorithm is shown in tabular form. The first column shows the reading from proximity sensor, second and third column shows X, Y-Axis acceleration values. Fourth and fifth column shows whether the acceleration value is greater than threshold value. Sixth and seventh column shows whether the Airbag has been actuated in required direction i.e. front or side Airbag.As the ACU detects HIGH value from proximity sensor (IR Sensor) it sends a signal to ACU that occupant is present on the seat and in case of any crash the Airbags should be deployed. When no occupant is presents the IR sensor gives LOW output.When IR sensor do not detects any occupant it sends LOW signal to ACU and it does not send signal to actuate the Airbag even though acceleration value in X, Y direction is greater than the set threshold value, and no LEDs glow. When IR sensor an occupant it sends A HIGH signal to ACU saying that occupant is present and actuation signals should be sent to actuate the Airbags whenever the acceleration value exceeds the set threshold value. So whenever change in velocity exceeds the set threshold value in any of the direction X or Corresponding LEDs are glow to show actuation signal.

Fault detection

BEEP SOUND

PUSH Fig-7 A mini push button and buzzer used for fault detectionAs shown in above figure a MINI Push button and a Buzzer has been provided to detect the fault in accelerometer. It detects fault and generates beep sound when accelerometer gives constant reading for more than ten iterations.As we press the button it makes the output of the accelerometer constant and as programmed in Arduino .It makes the reading of accelerometer constant. Here fault is being introduced purposely to show its ability to detect fault and warn the driver. FIG-8 Showing serial monitor data and part of program for fault detection

As shown in above figure the first figure shows accelerometer reading constant when button is pressed.the second figure shows program written for fault detection,it simply stores the x,y axis acceleration value in two integers and subtracts from previous value to get Zero defference.when this occurs ,buzzer beeps to alert the driver.

Conclusion

A hardware model has been made to show the implementation of Accelerometer based Airbag deployment control system which also combines the proximity sensor to detect the occupant to prevent unnecessary actuation of Airbags. The MEMS accelerometer based Airbag control system is more reliable compared to mechanical sensor based Airbags control system which are costly, inefficient and difficult to calibrate. While can be digitized and analyzed to study the behaviour of the signal for different types of crashes.Research is going on more advanced systems which detect occupant distance from steering wheel to deploy Airbag accordingly also cameras are being used to classify living and non-living thing for actuations. Some systems are using weight sensor to classify adult and children. So as Airbag deployment is related to safety lots of research is going on to make it safer for passengers.

References

M. A. Hannan, A. Hussain, and S. A. Samad, Sensing Systems and Algorithms for Airbag Deployment Decision Syed Masud Mahmud, Member, IEEE, and Ansaf I. Alrabady, A New Decision Making Algorithm for Airbag Control http://www.safercar.gov/Vehicle+Shoppers/Air+Bags/Air+Bag+Deployment http://www.cvel.clemson.edu/auto/systems/airbag_deployment.html http://playground.arduino.cc/Main/MPU-6050 http://invensense.com/mems/gyro/mpu6050.html

2