Mechanical data acquisition and analysis system based on ARM

Rock mass mechanical property testing is an important part of rock mass mechanical property testing technology. Its main purpose is to provide necessary physical and mechanical parameters for rock mass deformation and stability analysis and calculation [1]. This paper designs an ARM-based mechanical property testing system to automatically test, collect and analyze the test data of rock block mechanical property testing, so as to accurately predict the deformation and stability of rock mass under various stress fields, and then provide rock mass mechanics basis for reasonable engineering design.

1 System composition

The system is an embedded platform based on the S3C44B0X processor, using μC/OS-II as the operating system. On the one hand, the system design must meet the requirements of rock mechanics property testing, and on the other hand, more functions must be realized on the limited resources of the embedded system. It is mainly composed of data acquisition, data storage, data transmission, etc. By cooperating with rock mechanics test instruments, real-time data acquisition and display are performed, and the test data can also be transmitted to the host computer for further analysis and storage. The basic structure of the system is shown in Figure 1:

First, the mechanical properties of the rock specimen are tested by the mechanical test instrument. The data is obtained by the sensor on the instrument, and then the embedded data acquisition system collects the data and displays the data on the LCD. At the same time, in order to effectively save the data during the test, the storage unit of the system is expanded. The system can communicate with the remote host computer using Ethernet or CAN bus, or it can be connected to the host computer through the serial port. The data processing and analysis system processes and draws the data, and the experimental data obtained can be stored, analyzed, and printed.

2 System application software design

Each module of the system performs different functions. Based on the μC/OS-II operating system, it realizes data acquisition, display, storage and network transmission through task scheduling. The overall design principle is modular design of the system. Each functional module is independent of each other, and the interface is as simple as possible to achieve high cohesion and low coupling of each module, so as to facilitate system maintenance and further expansion.

The system application is mainly written in C language and assembly language, and its functions include: (1) sending a test start signal through an I/O port; (2) collecting and converting real-time data of multiple test parameters through the system's built-in ADC; (3) using the LCD display interface to dynamically display parameter curves using a line graph; (4) when data input is required, the processor scans the keyboard input and output ports to obtain the input value, so that the test process can be monitored in real time and corresponding control can be performed; (5) S3C44B0X can conduct tests independently from the host computer, or communicate with the host computer through Ethernet or CAN bus to transmit test data to the host computer. The specific implementation of the program is to establish multiple tasks of different priorities in the operating system, and then synchronize them through message queues and global variables [5] [6]. The main program flow chart is as follows:

The host computer program is mainly written based on Delphi language. The host computer is connected to the test system to control the test instruments, obtain test data, display the test data curve, and can also conveniently query each set of test data through database technology and compare the test data result files through the PC display interface.

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3 System Testing

In order to debug the performance of the developed real-time data acquisition and analysis system, multiple uniaxial compression, uniaxial tension, triaxial compression, direct shear and other tests were carried out on the rock mechanics test instrument. The corresponding analog signals of three pressure sensors and two displacement sensors were collected to record the pressure, displacement, deformation and other parameters of the entire specimen during the test.

Example (triaxial test (force--travel)):

3) Transmit data to the host computer through the network and display

The test data is stored in the embedded system during the test and can be transmitted to the host computer at the same time. The host computer can take advantage of the large storage space to store the test history data and display the history data at any time.

The host computer receives network data as shown in Figure 4.

4 Conclusion

The test system can automate and intelligentize a series of processes in rock mechanics test, from obtaining measurement data, drawing mechanical property curves, printing reports, to comparing, analyzing and storing experimental data, so that the rock mechanics test and calculation analysis system can be miniaturized, intelligent, and efficiently realize the problem of data collection and analysis in the test. It also has the advantages of low coupling, high cohesion, scalability, portability, good stability, small size and low cost.

The author's innovations in this paper are as follows: (1) Implemented a practical real-time data acquisition and analysis system. (2) Ported the real-time embedded operating system μC/OSII to the ARM7 platform. (3) Ported the TCP/IP protocol stack.