The CNC milling machine described in this paper is a standard three-axis system, featuring the machine tool operation panel, X, Y, and Z linear axes, an upper axis, and auxiliary functions such as hydraulic pressure, lubrication, and cooling. The electrical system includes a digital control (CNC) system, a digital servo drive, a spindle frequency converter, and a PLC-based input/output control system. This system handles user interaction, coordinate feed, main spindle operation, and control of auxiliary systems like hydraulic, lubrication, and cooling.
The machine uses HEIDEHAIN linear encoders for full closed-loop feedback on all three axes, and the spindle is an electric motor controlled by a Schneider inverter. The electrical control system is based on the NUM1050 digital control system from France's NUM company, paired with a corresponding MDLUNUMDRIVE numerical control servo drive. The PLC program is developed using the built-in PLC function of the NUM1050, allowing for flexible and easy maintenance due to the high performance of the system.
The NUM1050 is an open, powerful 64-bit digital control system with fast processing speed and high precision. It supports graphic display, memory storage, communication via RS232 and network interfaces, axis control boards, internal PLC for machine management, and software that manages programs, data, and axis movement.
The built-in PLC of the NUM1050 communicates through %I and %Q variables, exchanging data with the NC via a swap area. Variables %R and %W are used for specific control tasks, ensuring coordination between the NC and external devices. The PLC program structure includes initialization (%INI), cyclic tasks (%TS0–4), background tasks, and interrupt tasks (%TH). These modules manage different functions such as machine start-up, cycle operations, and emergency responses.
The PLC program for this three-axis milling machine was developed using PLCTOOL, a Windows-based platform that allows programming in ladder logic or C. Ladder diagrams were chosen for their clarity, ease of debugging, and intuitive interface. The program is modular, with each task and subroutine handling specific machine functions, such as cooling, lubrication, tool clamping, and safety checks.
Key modules include %SP2 for custom button controls, %SP3 for coordinate limits, %SP5 for axis enable, and %SP6 for spindle control. These core modules ensure smooth operation and efficient debugging. The modular design improves maintainability and allows for quick problem identification during testing.
After commissioning, the machine operates smoothly and meets all acceptance criteria. The successful implementation of the control software demonstrates its effectiveness, and the basic modules can be adapted for other NUM series CNC machines, providing a solid foundation for future PLC development.
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