Foreword
With rapid economic development, the use of steel structure products is becoming increasingly widespread, and these products hold enormous market opportunities and development prospects. Based on market demand and technological development trends, designing an advanced fully automatic steel shearing machine to replace existing processing methods will significantly increase productivity. This is the significance of my research into a fully automatic steel shearing and feeding mechanism.
There are many types of automatic feeding methods used in production and research both in my country and abroad, but some problems exist in these products. For example, robotic arms that feed from the side have complex structures, are difficult to assemble, manufacture, and maintain, and are expensive, making them unsuitable for the feeding requirements of Chinese steel shearing machines. Another option is an independently driven movable conveyor that transports workpieces to a predetermined position via a material separation mechanism. However, this type of mechanism has limitations and cannot be applied to the requirements of Chinese steel shearing machines.
In industrial production, many factories utilize steel structures or lightweight steel structures. In the construction of these steel structure factories, the main frame and auxiliary frames are constructed entirely of structural steel sections, resulting in a very large demand and high market volume. However, the automation level of the production equipment for these structural steel sections is still in its early stages, requiring considerable manual labor. To address this issue, based on the characteristics of structural steel production, this paper designs a control system for a structural steel forming machine using a Siemens programmable logic controller (PLC). A touchscreen is used as the host computer to directly control the PLC and frequency converter via a serial communication cable, thus automating the domestic structural steel forming machine.
1. Working principle of steel forming machine
In the current steel market, the C-shaped steel forming machine is a single-coil forming unit that can produce C-shaped finished products of various specifications using a set of rollers. This machine mainly consists of a passive feeding rack, leveling device, punching device, post-forming cutting device, hydraulic station, and computer control system. This machine features automatic flying saw punching and is easy to operate. The C-shaped steel products rolled by the C-shaped steel forming machine have good tensile, bending, and compressive properties, good straightness, fully automatic fixed-length cutting, automatic punching, a high degree of automation, and quick and convenient installation. The products can be used as the main load-bearing structure of large and medium-sized industrial and civil buildings, such as factories, warehouses, locomotive depots, aircraft hangars, exhibition halls, theaters, stadiums, and market flower sheds for roof load-bearing and wall support.
The working principle of the C-shaped steel forming machine is as follows: steel is placed on the C-shaped steel, and after contact with the rollers driven by the reducer, the clamping handle is tightened, the motor oil pump group is started, and the high-pressure oil output by the electric oil pump passes through the overflow valve. During this process, the required pressure can be adjusted, and it enters the agglomerating block and then the electro-hydraulic valve. The electro-hydraulic valve and the jog switch control the operation of the oil cylinder. The working oil cylinder advances, and the calculation begins when the I-beam is pressed against the three support rollers without bending or deformation. The oil cylinder advances another length of 10mm-15mm each time. The main motor is turned on to rotate forward or reverse, and the main motor drives the I-beam to work. The operation is repeated until the desired result is achieved. Figure 1 is a schematic diagram of the working of the steel forming machine.
Figure 1 Schematic diagram of the steel forming machine in operation
2. System Hardware Design
The control system uses a touch screen in conjunction with a PLC, enabling extensive operation control and monitoring of the equipment and its running information to be implemented through touch screen programming. The PLC and touch screen communicate via a serial interface with simple wiring. The control system structure diagram is shown in Figure 2.
Figure 2. Block diagram of the control system
2.1 Hardware Selection
Because PLCs replace the hardware of traditional electrical control systems with software, the workload of designing, installing, and wiring control cabinets is greatly reduced. Most PLC user programs can be simulated and debugged in the laboratory, shortening the application design and debugging cycle. In terms of maintenance, PLCs have an extremely low failure rate, resulting in minimal maintenance workload; moreover, PLCs have strong self-diagnostic capabilities, allowing for rapid identification of the cause based on fault information displayed on the PLC, making maintenance convenient.
A PLC control system consists of signal input elements (such as buttons, switches, and sensors), output actuators (such as solenoid valves, contactors, and indicator lights), and a PLC. Input elements are connected to the PLC's input terminals, providing command signals and status signals of the controlled object. Output actuators are connected to the PLC's output terminals, controlling the operation of the controlled object.
Considering system scalability and ease of maintenance, a modular PLC was selected for this control system. A Siemens S7-200 PLC was chosen as the control unit.
2.2 I/O Allocation and External Wiring
The Siemens S7-200, as the core component of the entire control system, includes 7 inputs and 4 outputs. These I/Os control the frequency converter, punching machine, and shearing machine, among others. The PLC controls the frequency converter via terminals. Based on the system design requirements and I/O allocation table, the PLC external wiring diagram was drawn, as shown in Figure 3.
Figure 3 PLC External Wiring Diagram
3. Software Design
The control system operates in two modes: Automatic (AUTO) and Manual (MANUAL). The selection between these modes is made via buttons on the touchscreen. Manual mode is primarily used for debugging before starting Automatic mode. The PLC handles the sampling of equipment status inputs and output control functions; its main operation is focused on automatic system operation.
1) The roll motor starts, the photoelectric detector collects the strip forming information, and the PLC's high-speed counter is started.
2) The PLC collects the number of pulses sent by the high-speed counter. When the number of pulses reaches the fixed pulse value preset in the PLC's internal memory, the PLC completes the actions sequentially according to the program flow to complete one production cycle.
3) When the set production quantity is not completed, the PLC program will start the next cycle and repeat the previous steel production process.
This design uses a touch screen as the host computer and MCGS embedded configuration software for editing. Through the various control device libraries, graphical controls, and functional controls provided by the PLC, various dynamic functions and control functions are configured, and fault visualization is achieved.
The host computer communicates with the PLC via an RS232 serial port. After the system control and data acquisition function programs are written on the host computer using Step7-Micro/Win, they are downloaded to the PLC. The human-machine interface developed by MCGS drives the PLC program to run, monitor and control the operation of the steel forming machine system.
4. Conclusion
This design improves upon current domestic steel profile forming machine production technology by developing a PLC-based control system for the steel profile forming machine, achieving the required control accuracy. This control system significantly enhances the automation level of the steel profile forming machine, improves the accuracy of punching and shearing, and increases production efficiency, yielding excellent application results. Furthermore, this system features a compact and simple hardware structure, reliable operation, and ease of maintenance.
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