祖紹鵬，郭明儒，劉會超，張龍飛，婁文忠

(北京理工大學機電工程與控制國家重點實驗室，北京100081)

Along with the developing economy，the amount and variety of dangerous cargo is growing every day，but most of that is transported by conventional techniques and huge safe link are hidden in circulation.Once accident occurs，the destruction should be massive，and will directly threaten the public safety.According to statistics，the quantity of dangerous cargo transported by road in China by 2010 is more than 300 million tons，accounting for1% oftotalhighway transportation.European studies show that，in the years 1926 ～1997，a total of 3222 accidents involving dangerous cargo occurred，of which 41%happened during transport[1－2].As intelligent microsystem is small，light and low power consumption，a micro logistics state recorder is designed，combined with RFID[3]to form an intelligent monitoring microsystem for logistics，realizing real-time monitor of the dangerous cargo in circulation[4].

1 Overall Design

Dangerous cargo is usually very sensitive to vibration，so highly sensitivity accelerometers are chosen to monitor the vibration caused by rough handling，bindinglose or downhill as the transit vehicle starting，braking or bumps.The safety of dangerous cargo is also affected greatly by external environmental conditions.There might be serious accidents when they are subject to col-lision，friction，heating，fire and water，etc[5].As the temperature and humidity changes will have an impact on the safety of most dangerous cargo，they are chosen as essential monitoring parameters.In addition，as most dangerous cargo are flammable，explosive，toxic and corrosive，the effective safety supervision and management is necessary for the storage，management，transportation and some other links，during which any tiny mistakes may result in a major accident，and make incalculable damages to our country and people’s lives and property.To improve logistics efficiency and reduce operating costs，active RFID is introduced into the system to store the information and realize communication.System architecture is shown in Fig.1.

Fig.1 Intelligent microsystem block diagram

The working process of the micro-monitoring and management system can be divided into three stages:

(1)The system monitors the environmental information of transportation and storage through the internal accelerometer and temperature/humidity sensor.When the parameters exceed the threshold，system will record the acceleration，temperature，humidity and the time，meanwhile send an alarm message to the driver and save the data[6].

(2)When the cargo get in or get out of the warehouse，a reader fixed at the door will identify the active RFID tags automatically，and get the cargo’information stored in the tags，such as categories of items，quantity，production date，owner，etc.With the information，storage records and stock data could be updated automatically and precisely，and the warehouse management could be improved greatly.

(3)If there is an alarm event，the information will be read and uploaded to a background database and an alarm message that the cargo are insecurity will be given out.Cargo information visualization in the supply chain will finally be realized.

2 Monitoring system

2.1 Acceleration acquisition module

The ADXL105 is a high performance，high accuracy and complete single-axis acceleration measurement system on a single monolithic IC.It is developed by MEMS processing technology.The vibration which the vehicle passes to the cargo in the process of movement is mainly below 10Hz broadband random vibration[7].ADXL105 with very good linearity at low frequencies can accurately measure the lowest vibration frequency of 1 Hz.Thus making vibration testing，it can meet the range of test signal frequency well.

ADXL105 includes three parts:temperature sensor，X sensor and UCA.The acceleration output(AOUT)of the ADXL105 is 125 mV/gn(for VDD=3.3 V).Since this scale factor is not suitable for this application the UCA is used to increase the scale factor[8].The simplest implementation is as shown in Figure 2.Adjusting R10 and R11 can change the scale factor(SCALE)，and the formula is shown as equation(1)below.

The 0 g offset is 1.575V(for VDD=3.3 V).A method of changing the 0g offset is to add a resistor R12 and a variable resistor R13(Fig.2).Then UCAOUTexpression is as equation(3).

The formula of acceleration is shown as equation(3).

Fig.2 Acceleration measurement module circuit diagram

2.2 Temperature and humidity acquisition module

SHT10 is a single chip temperature and relative humidity multi sensor module comprising a calibrated digital output.Application of industrial CMOS processes with patented micro-machining ensures its highest reliability and excellent long term stability.This results in superior signal quality，a fast response time and insensitivity to external disturbances at a very competitive price9].The sensor communicates with the MCU by DATA and SCK.Application circuit is shown in Fig.3.

Fig.3 Temperature/humidity acquisition module circuit diagram

2.3 RF communication module

A kind of low-cost，low-power UHF wireless transceiver chip CC1100 is used for RF communication module.By configuring the parameters of peripheral devices，the module works in the frequency of 915 MHz.CC1100 communicates with the MCU via 4-wire SPI bus interface，and works in SPI slave mode[10－11].Wireless transceiver module circuit is shown in Fig.4.The electromagnetic wake-up function of CC1100 can guarantee the wireless chip wake up periodically to receive packets from dormancy in the absence of microprocessor intervention.

Fig.4 RF communication module

2.4 Software

The system must be initialized firstly，and run time/date and ID number chip.And then when there is CNVSTR edge，the date about time，acceleration，temperature and humidity is recorded.If the temperature/humidity data exceeds the threshold，the set of data will be recorded.When the interrupt of wireless module is valid，wireless module begins to send the data.After sending，acquisition continues[12].Program flow chart is shown in Fig.5.

2.5 Prototype machine

The whole system is placed in the plastic case.The degree of protection of this case is IP65.

3 Summary

The system relies on micro-nanometer technology and the Internet of Things core technology.The experiments prove that the system has the features of low power consumption，high accuracy.The system can work long time in a variety of harsh environments，and monitor the state of the dangerous cargo in circulation to improve transportation effectively and reduce dangerous cargo accident rate in transportation.Expanding more types of sensors to the system will be the next aim.

Fig.5 Program flow chart

Fig.6 The picture of the prototype machine

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