The relationship between CNC (Computer Numerical Control) machine tools and PLC (Programmable Logic Controller) is fundamental to the operation and automation of modern manufacturing processes. Both CNC machine tools and PLCs are essential components in industrial automation, working together to ensure precision, efficiency, and reliability in various manufacturing applications.
Basic Concepts Of CNC Machine And PLC
CNC machine tools are automated systems used for machining workpieces with high precision and repeatability. They are equipped with computer-controlled mechanisms that enable precise control of the cutting tools’ movements, as well as other auxiliary functions, such as tool changes and coolant flow. The CNC system reads a series of numerical codes (G-codes and M-codes) from a part program and converts them into specific movements and actions to produce the desired component.
PLC is a specialized digital computer used to control and automate industrial processes, such as manufacturing, assembly lines, and equipment operation. PLCs are designed to withstand harsh industrial environments and can process inputs and outputs (I/O) from sensors, switches, and other devices. They are programmable, meaning their behavior can be customized by writing a program that dictates how they respond to different input conditions.
Key features of CNC machine tools include
- High accuracy and repeatability: CNC machines can execute complex machining operations with exceptional accuracy and consistency.
- Flexibility: They can be reprogrammed easily to produce different components, allowing for quick changeovers and customization.
- Multi-axis control: Many CNC machines have multiple axes (e.g., X, Y, Z, A, B, C) that enable simultaneous movement and machining in multiple directions.
- Wide range of applications: CNC machine tools are used in various industries, including aerospace, automotive, medical, electronics, and more.
Key features of PLCs include:
- Reliable and rugged: PLCs are designed to operate reliably in industrial settings with high levels of resistance to temperature, humidity, and mechanical stress.
- Digital and analog I/O: PLCs can handle both digital inputs (ON/OFF signals) and analog inputs (continuous signals), making them suitable for a wide range of applications.
- Real-time control: PLCs provide real-time control and response, ensuring precise timing and coordination of industrial processes.
- Programmable flexibility: PLC programs can be easily modified or updated to accommodate changes in the manufacturing process or new production requirements.
CNC Machine Tools, Digital Control
The CNC machine tool is mainly composed of three parts, namely the machine body, the numerical control device that commands and controls the CNC machine tool, and the servo system that drives the machine tool actuator to implement movement. Its core part is the numerical control device. Its internal system is called numerical control system (NumeficM Control system), which is the application of digital control method. Numerical control, referred to as NC (Numefied Contr01): refers to the use of discrete digital information to control the operation of machinery and other devices, which can only be programmed by the operator. CNC is the abbreviation of Computerized Numerical Control (Computerized Numerical Con-tml). Parts processing program storage. Most of the numerical control systems we use now refer to CNC, but some books still use the term NC, which actually refers to CNC (Computerized Numefial Contr01).
Programmable controller (PROGRAMMABLE CONTROuJER, referred to as PC). Different from the PC of the personal computer, it is represented by PLC. PLC is a new generation of industrial control devices formed by introducing microelectronic technology, computer technology, automatic control technology and communication technology on the basis of traditional sequential controllers. Sequence control function to establish a flexible program control system. PLG is used for automatic control of general equipment. PIE is used for the control of peripheral auxiliary electrical of CNC machine tools, which is called programmable machine tool controller. Therefore, it is called PMC (programmabhmachine tool controller) in many CNC systems.
The Relationship Between PLC And NC
The numerical control system has two parts, one is NC, the other is PLC, the role of the two in the numerical control machine tool is different. The scope of action of NC and PLc can be divided as follows:
- Realize the digital control of the geometrical motion law of the tool relative to each coordinate axis of the workpiece. This task is done by NC;
- The control of machine tool auxiliary equipment is completed by PLC. During the operation of the CNC machine tool, according to the internal signs of the CNC and the status of the control switches, detection components, and running parts of the machine tool, according to the control logic set by the program, such as the movement of the tool magazine, the tool changing mechanism, the operation of the coolant, etc. Control. In CNC machine tools, these two control tasks are inseparable, they are divided according to the above principles, and they are also connected in a certain way. The interface between NC and PLC follows the international standard “IssO 4336-1981
(E) Numerical control of machine tools – Specifications for the interface between the numerical control device and the electrical equipment of the numerical control machine tool”, the lathe, the interface is divided into four types:
- The connection circuit related to the drive command;
- The connection circuit between the numerical control device, the multiplication measuring system and the measuring sensor;
- Power supply and protection circuit;
- On-off signal and code signal connection circuit;
From the interface classification standard, the first and second types of connection circuits transmit the control information between the numerical control device and the servo unit, servo motor, position detection and data detection device.
The third category is composed of the power control circuit in the strong current circuit of the CNC machine tool. Usually composed of power transformers, control transformers, various circuit breakers, protection switches, relays, contactors, etc. Power supply for other motors, solenoid valves, electromagnets and other actuators. Compared with the numerical control system, these belong to the strong electric circuit.
These strong current circuits cannot be directly connected with the weak current circuits of the control system. They can only be converted into switching signals that work under DC low voltage through electronic components such as intermediate relays, so as to become acceptable for PLC or relay logic control circuits. the electrical signal.
On the contrary, the control signal from PLC or relay logic control must also pass through the intermediate relay or conversion circuit into a signal that can be connected to the strong current circuit, and then the strong current circuit drives the actuator to work. The fourth type of signal is the input and output control signal transmitted by the numerical control device to the outside.
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