Vibration measurement system for monitoring logistics transportation processes

0 Introduction
Modern logistics industry has become one of the main driving forces for economic development and is the main industry for promoting economic development. Logistics is the physical flow process of goods from the supply place to the receiving place. According to actual needs, the basic functions of transportation, storage, loading and unloading, handling, packaging, circulation processing, distribution, and information processing are organically combined. Transportation is one of the most important links in the modern logistics industry. Through transportation, production materials are continuously delivered to producers to ensure the smooth progress of production, and at the same time, goods are continuously delivered to the consumer market to meet the needs of consumers.
Due to the diversification of production needs, the transported goods are diverse, and the requirements for transportation are diverse. The transportation of ordinary goods has no special requirements for the transportation process. However, the transportation of fragile or dangerous goods requires monitoring of vibration parameters during the transportation process to ensure the integrity or safety of the transported goods.
This paper proposes and implements a vibration measurement system for monitoring the logistics transportation process, using vibration sensors to collect vibration information of transportation vehicles. The vibration information collected by the system can be stored for analysis of the logistics transportation process. At the same time, the vibration system can also be connected to the alarm system to issue an alarm prompt when the vibration data exceeds the safety range.

1 Measurement system and hardware design
1.1 Measurement system design
The structure of the vibration measurement system proposed in this paper is shown in Figure 1. It is based on the ATmega16L microcontroller and the acceleration sensor MMA7260, and is equipped with peripheral circuits. If an alarm is required when the vibration exceeds the standard, the system can be connected to the corresponding alarm system.

1.2 MMA7260 acceleration sensor module
The system uses MMA7260 acceleration sensor to measure vibration parameters. MMA7260 is produced by Freescale, USA. It is a low-cost, low-power, fast-starting, fully functional and highly shock-resistant three-axis acceleration sensor. There are four measurement ranges to choose from, namely 1.5g, 2g, 4g, and 6g. Among them, 1.5g has the highest accuracy, reaching 800 mv/g; MMA7260 has a sleep mode, and the current in sleep mode is 3μA. [page]

The MMA7260 acceleration sensor outputs an analog voltage signal to characterize the acceleration of a moving object. The output analog voltage signal is proportional to the acceleration. The analog signal is calculated and processed by the microcontroller after A/D conversion. Figure 2 shows the pin diagram of the MMA7260, where Xout, Yout, and Zout are the X, Y, and Z analog voltage output pins, respectively, G1 and G2 are range selection pins, VCC is the sensor power supply pin, and VSS is the sensor ground pin.

When using the MMA7260 accelerometer, it is necessary to select the appropriate range by assigning different values ​​to pins 4 and 5 according to actual requirements. The specific selection method and the corresponding range and sensitivity are shown in Table 1.

1.3 Controller and acceleration data acquisition
This measurement system uses the ATMEL MCU ATmega16L as the main controller. ATmega16L is a high-performance, low-power 8-bit MCU with 16 kB programmable Flash, 0.5 kB E2PROM, 1 kB on-chip SRAM, and an internal successive approximation ADC circuit with 10-bit accuracy, 13-260μs conversion time, and 8 selectable single-ended input channels.
The connection between ATmega16 and MMA7260 is shown in Figure 3. PA0, PA1, and PA2 in the MCU PA port are used as the input terminals of the analog voltage of the three axes X, Y, and Z of the MMA7260 vibration sensor. The received analog voltage signal is converted into a digital signal by the A/D converter inside the MCU, and then the data is processed. The PC3 and PC4 pins of the MCU are used as the control terminals for the range selection of the vibration sensor. G1 and G2 of MMA7260 are connected to PC3 and PC4 of the microcontroller respectively. The required range is selected by controlling the output level of PC3 and PC4. The range of 1.5g is used in this system, so both PC3 and PC4 output low level. The Sleep Mode pin of MMA7260 is connected to PC1 pin of the microcontroller. Let this pin output high level, allowing the sensor to enter sleep mode, which has energy-saving effect.

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2 Measurement system software design
The measurement system software mainly includes hardware initialization and data processing. Initialization includes initialization of the ADMUX register of the microcontroller and initialization of the I/O port of the microcontroller. Data processing includes vibration information acquisition and data processing after A/D conversion. The system software is designed in C language programming, and the software flow chart is shown in Figure 4. After the system is powered on, it is initialized first, and then the system starts data acquisition and processing. The main controller works in an interrupt mode, reading vibration information from the MMA7260 vibration sensor at regular intervals. The microcontroller performs A/D conversion on the analog data, processes it, and then enters a low-power sleep state.

When collecting voltage information of the three axes of the vibration sensor, the A/D converter is set to free conversion mode, and the voltage information of the X, Y and Z axes are collected respectively by polling, and then enter the sleep state. A time is set by the timing counter, and when the timer reaches the time, it wakes up from the sleep state and continues to collect voltage information of the X, Y and Z axes. [page]

3 System Implementation and Experiments
The vibration measurement system implemented in this paper is shown in Figure 5. The MMA7260 vibration sensor realizes vibration information collection, and the microcontroller performs A/D conversion and processing on the data. It should be pointed out that an RS 232 serial port is added to the implemented sample system to input the measurement data to the PC for easy system debugging.

In order to verify the system designed in this paper, a transport vibration simulation test was carried out in a laboratory environment. During the experiment, the vibration sensor MMA7260 was fixed on the toy car, and the car was shaken to generate vibration, while the data output by the vibration sensor was collected. Some experimental data are shown in Figure 6. It can be seen that when the car is vibrated, the sensor can clearly detect the vibration information.

4 Conclusion
This paper studies and designs a vibration measurement system for monitoring the logistics transportation process, so as to monitor the transportation process of fragile items or dangerous goods. The system composition, hardware design and software flow are introduced, and the implemented system is given. The vibration measurement experiment is carried out based on it. The results show that the system runs well and can accurately record vibration parameters. It can be widely used in logistics transportation monitoring systems as an effective means of vibration monitoring in vehicle transportation processes.