Design Of Automatic Crash Notification System Terminal Based On Dynamic Discrimination Threshold

Automatic Crash Notification System(ACNS)is a post-accident safety technology aimed at improving the response speed and rescue efficiency of rescue agencies and improving the survival rate of passengers.After a vehicle accident occurs,ACNS can help reduce the death rate after the crash by promptly notifying emergency medical services providers.The accident information sent by ACNS can help rescue centers to quickly lock down the accident site,judge the severity of the accident and predict the injury conditions of the passengers,so as to quickly rescue the passengers from the accident site and transfer them to an appropriate hospital or trauma center.Discrimination threshold plays an important role in the anti-interference and accuracy of ACNS triggered by acceleration signals.Therefore,this paper studies the dynamic matching of ACNS threshold according to road conditions,and designs the software and hardware of ACNS terminal.According to the vehicle longitudinal acceleration peak value under different working conditions and road surface conditions as well as the velocity variation in the crash process corresponding to different threshold thresholds,the influence of discrimination thresholds on anti-interference and accuracy of the ACNS is analyzed.The main trigger algorithms of ACNS are analyzed and compared.The moving window integration method is selected.The acceleration of sled crash test at 30km/h is movably integrated with 8ms window width.The peak value of velocity variation within 8ms window width of 1.91m/s is set as the trigger threshold of ACNS.According to the correlation between Power Spectral Density(PSD)and International Roughness Index(IRI),the linear relation between IRI and root mean square of acceleration PSD is deduced.Based on road surface and vehicle simulation models in CarSim software,the root mean square value of the PSD of the vehicle vertical acceleration corresponding to different IRI and the peak value of the longitudinal acceleration of the vehicle corresponding to the IRI value of A~F grade standard road surface are obtained,the correlation models of "root mean square value of the PSD of the vehicle vertical acceleration-IRI" and "IRI-discrimination threshold " are developed,and the discrimination threshold dynamic matching algorithm is designed.The functional requirements of ACNS terminal are analyzed.The terminal hardware is designed by selecting the suitable products and models of microprocessor,triaxial acceleration sensor,GPS module,SD card,GSM module and LCD display screen.The interfaces of each module and microprocessor,microcontroller peripheral circuit and the terminal power supply circuit are designed.The functions of ACNS terminal are implemented by software,and the initialization of each module,acceleration signal acquisition and storage,GPS information reception,transmission and display of accident information are completed.And the trigger algorithm and threshold dynamic matching algorithm program are written.The real vehicle road test is implemented.The ACNS terminal collects acceleration signals in three directions of the vehicle that running on different roads.At the same time,an acquisition system including a high-precision sensor,a data acquisition card and an upper computer are built to verify the accuracy of acceleration data collected by the ACNS terminal.The trigger conditions are tested after the sled impact data in the SD card are read.When triggered,the ACNS terminal can send information such as geographic position,occur timing and speed variation,and display the information on the LCD screen.The tests results show that the ACNS terminal designed in this paper can dynamically match threshold values according to road surface conditions,and can identify collision severity,send accurate collision information when triggered,with high reliability.