With the rapid development of China's manufacturing industry, the demand for higher precision and efficiency in machining parts has increased significantly. As a result, the level of automation in production processes has also risen. Bar materials serve as the primary raw material for die forgings, roll forgings, and other rolling components. The bar shearing machine plays a crucial role in preparing blanks for these forging processes. Traditionally, shear systems were controlled using AC contactors and relays. However, over time, aging components and frequent equipment failures have led to maintenance challenges, as the system lacks integration and many faults cannot be resolved quickly, causing inconvenience in production.
To address these issues, PLC-based servo control systems have become increasingly popular due to their high positioning accuracy, fast response speed, strong anti-interference capabilities, and stable operation. However, traditional PLCs are not real-time and struggle with complex timing tasks and network support. Therefore, there is a need for high-speed A/D conversion and real-time processing of sensor signals. When it comes to intelligent, information-driven, and network-managed production, PLCs may not be sufficient. The emergence of ARM-based embedded systems offers a more advanced platform for industrial control. These systems provide rich peripheral resources, multiple interfaces, and expandable options, making them ideal for complex control tasks.
ARM-based embedded systems run on real-time operating systems and offer powerful software processing capabilities. They combine the advantages of PCs with lower costs and greater flexibility in hardware and software customization. Additionally, they support large-screen LCD displays for visual interface interaction and can connect directly to local or remote networks, enabling real-time monitoring and management of production.
Based on this, this paper proposes an ARM-based embedded CNC system for bar shearing production lines. The system uses an ARM processor and runs on an embedded Linux operating system. It features scalable I/O nodes and various fieldbus interfaces, allowing automatic cutting control, marker control, and automatic flip feed frame control, which improves the precision of bar processing. The system supports large LCD displays, networking, and an embedded database, enabling intelligent and real-time management of the production process. The embedded database helps manage processing data effectively and allows for automatic adjustments and control of the processing trajectory, achieving adaptive parameter tuning.
The entire shearing line system consists of a central control unit, a cutting system, a hopper, and an automatic flip feed system. The block diagram is shown in Figure 1. The electrical components include console buttons, display lights, various control Switches, and motors. The operation console includes rotary encoders, self-locking buttons, common buttons, key buttons, two-position rotary buttons, changeover switches, counters, and display lights. Control switches include proximity switches, pressure switches, liquid level switches, travel switches, cam switches, photoelectric switches, solenoid valves, AC relays, and AC contactors. Motors include main motor, discharge motor, baffle motor, and lubrication motor. Additional components like transformers, circuit breakers, and noise filters are also included.
The central control system is based on the ARM9 core board. The GPIO expansion board increases the number of input/output nodes, allowing the system to receive signals from buttons, cam switches, and photoelectric switches. According to the program and preset parameters, the system controls the action of solenoid valves, relays, and contactors and sends pulse signals to the servo driver to control the servo motor. Input and output interfaces use optical isolation modules to reduce interference and convert signal levels. The inverter controls the motor's forward and reverse rotation speed based on the ARM output signal, enabling coil release and recovery. The servo driver adjusts feeding length based on the pulse count and frequency from the ARM board. A 10-inch LCD screen provides a user-friendly interface for setting parameters and displaying system status and motion information. The ARM communicates with the inverter and server via RS232 serial ports for real-time data exchange, ensuring coordinated operation of the production line.
The ARM core board is based on the S3C2410X processor, featuring a 6-layer design with a full-featured MMU, low power consumption, rich interfaces, and small size. It integrates numerous functional units, including internal voltage regulators, memory controllers, LCD controllers, DMA channels, serial ports, SPI, IIC bus, USB ports, PWM timers, and a touch screen interface. The core board includes 64MB SDRAM, 64MB NAND Flash, 1MB Boot Flash, and various device interfaces. It supports operating systems such as Windows CE, EPOC32, and Linux, with this paper choosing the open-source embedded Linux system.
The control motherboard connects with the ARM9 board to enable functions like USB ports, serial ports, voltage conversion, and LCD connections. It includes available GPIOs for inputs and outputs. The switching power supply provides 24V at 4A, converting to 12V, 9V, 5V, and 3.3V for different circuits. The ARM9 core board has three RS232 serial interfaces, and a special conversion module is used to convert RS232 to RS485 for better transmission distance and interference resistance. The USBHOST port is divided into multiple channels for keyboard, mouse, and external devices.
GPIO expansion and isolation circuits are designed as separate boards to increase I/O ports and ensure interchangeability. Each expansion board has 64 inputs and 64 outputs, connected via flat cables. Two methods are used for GPIO extension: one involves CPLD for expanding up to 128 I/Os, while the other uses off-the-shelf I/O expansion chips like MAX6957 to expand more than 100 I/Os. Level conversion and isolation modules are designed to handle non-TTL/CMOS signals and provide sufficient driving current for relays and LED displays. Optocouplers are used for both slow-changing and high-speed signals to improve anti-interference capabilities.
Motor control is managed by the inverter, which controls the motor's direction and speed based on the ARM board's output signal. The inverter receives control signals from the isolated expansion board, allowing forward, reverse, high-speed, and low-speed operations. Speed selection is done via a dedicated port, and other parameters are set through the operator panel.
The CNC system software must support user interface, cut control, fault detection, database management, and networking. With an embedded operating system, tasks can run in parallel, using message passing and queues. The software flow chart shows the interaction between user interface, cut control, and fault detection, while omitting database management and networking modules. Porting the embedded Linux system and developing drivers, application programs, and databases are essential for the system's functionality.
In conclusion, this paper introduces an ARM9-based embedded system that replaces traditional industrial control microcomputers. It utilizes Linux, custom hardware drivers, TCP/IP protocol, a QT graphical interface, and an SQL-compliant embedded database. The system offers high-speed data acquisition, direct I/O control, and PC-like information processing and network capabilities. It meets modern industrial control requirements for high precision, compact size, and low power consumption, representing a technological advancement in existing CNC systems.
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