CNC System Architecture
Comprehensive analysis of hardware and software components in modern nc cnc machine systems
A Computer Numerical Control (CNC) system serves as the core of modern manufacturing equipment, enabling precise control of machine tools through digital programming. The nc cnc machine integrates advanced hardware components with sophisticated software algorithms to deliver unparalleled accuracy and efficiency in production processes. This page explores the intricate relationship between hardware and software in CNC systems, their respective components, and how they work together to achieve high-precision manufacturing.
Understanding the architecture of a nc cnc machine is crucial for engineers, technicians, and manufacturers who seek to optimize performance, troubleshoot issues, or select the right equipment for specific applications. The following sections delve into the functional implementation, hardware composition, hardware architecture, and software structure of CNC systems.
1. Functional Implementation of CNC Systems
A CNC system consists of two major components: hardware and software. These two components work in harmony to implement all the functions of the numerical control system, including part program decoding, tool compensation, motion planning, interpolation and position control, PLC control, and human-machine interface (HMI) functions to realize part machining. In the nc cnc machine, this integration is critical for achieving the desired precision and efficiency.
In terms of information processing, software and hardware are logically equivalent. Some tasks performed by hardware (or software) can in principle be done by software (or hardware). However, hardware processing and software processing have different characteristics: hardware processing is fast but costly, has complex circuits, high failure rates, poor adaptability, and difficulty in implementing complex control functions. Software, on the other hand, is flexible and adaptable but relatively slow in processing. This balance is carefully managed in every modern nc cnc machine.
Therefore, in a CNC system, the rational division of functions between software and hardware—i.e., which functions are implemented by hardware and which by software—is an important task in the structural design of CNC systems. The principle of division between software and hardware is usually determined by the cost-performance ratio. Figure 3-51 shows several typical software and hardware division schemes for CNC systems.
Three Typical Hardware-Software Partitioning Schemes in nc cnc machine
Early NC Systems
- Most information processing by hardware
- Limited software functionality
- Less flexible, harder to upgrade
- Used in early nc cnc machine technology
Balanced Approach
- Hardware handles real-time operations
- Software manages complex algorithms
- Optimal performance-cost balance
- Common in modern nc cnc machine designs
Software-Centric
- Minimal hardware processing
- Most functions implemented in software
- Highly flexible and upgradable
- Latest trend in nc cnc machine technology
In early NC systems, most information processing functions were performed by hardware, as shown in Figure 3-51 (I). With the continuous enhancement of microprocessor computing power, more tasks are gradually being completed by software, while hardware assumes fewer tasks. Modern CNC systems commonly use schemes II and III in Figure 3-51, allowing for greater flexibility and more advanced features in the nc cnc machine.
2. Hardware Composition of CNC Systems
Regardless of the architecture of the CNC system, its hardware generally includes the following components. These components work together to ensure the proper functioning of the nc cnc machine, from receiving instructions to executing precise movements.
1. Computer Section
The computer is the core of the CNC system, mainly including the microprocessor (CPU) and bus, memory, peripheral logic circuits, etc. This part of the hardware is primarily responsible for arithmetic and logical operations on data, storing system programs, part programs, and intermediate variables of operations, as well as managing timing and interrupt signals. In the nc cnc machine, this section acts as the "brain" that processes all instructions and makes decisions.
1) Microprocessor (CPU)
The main work of the CPU is information processing, which includes both control and management tasks. Control tasks refer to performing corresponding arithmetic and logical operations on various data and information input to the CNC system (including part processing programs, various I/O information, etc.), including decoding, tool compensation, motion planning, interpolation, position control, and PLC control-related operations. Based on the operation results, control commands and data are sent to peripheral devices through various interfaces, enabling the user's instructions to be executed accurately in the nc cnc machine.
Management tasks include organizing and managing the entire CNC system, such as system initialization, interrupt management, bus arbitration, system error detection and handling, real-time task scheduling, and communication management. The performance of the CPU directly affects the processing speed and response time of the nc cnc machine, making it a critical component in determining overall system performance.
2) Memory
Memory in a CNC system is used to store various programs and data. It can be divided into read-only memory (ROM) and random access memory (RAM). ROM stores the system program, which is written during manufacturing and cannot be modified by the user. This program contains the basic control logic of the nc cnc machine.
RAM is used to store part programs, intermediate calculation results, setting parameters, and temporary data. This memory is volatile, meaning its contents are lost when the power is turned off, so important data is often saved to non-volatile storage devices in modern nc cnc machine systems.
3) Bus
The bus is the communication pathway between various components of the computer. It can be divided into three types: data bus, address bus, and control bus. The data bus is used to transmit data between components; the address bus is used to specify the memory unit or I/O port address to be accessed; and the control bus is used to transmit control signals and status signals. The bus structure directly affects the data transmission speed and overall performance of the nc cnc machine system.
2. Input/Output Devices
Input devices are used to input part programs, parameters, and commands into the CNC system. Common input devices include keyboards, MDI (Manual Data Input) panels, USB interfaces, network interfaces, and storage devices. Output devices display or print the status information, part programs, and processing data of the nc cnc machine. These include displays, printers, and plotters.
The human-machine interface (HMI) serves as the bridge between the operator and the nc cnc machine, allowing for interaction through input devices and providing visual feedback through output devices. Modern CNC systems often feature touch-screen interfaces for more intuitive operation.
3. Position Detection Devices
Position detection devices are crucial for ensuring the machining accuracy of the nc cnc machine. They detect the actual position, speed, and direction of the machine tool's moving parts and feed this information back to the CNC system for closed-loop control.
Rotary Encoders
Used to detect the rotation angle and speed of motors and spindles in the nc cnc machine. They can be incremental or absolute types.
Linear Scales
Directly measure linear displacement of machine tool slides, providing high-precision position feedback for the nc cnc machine.
Resolver
A type of electromagnetic sensor used for angle measurement, known for its robustness in harsh nc cnc machine environments.
Laser Interferometers
Provide extremely high-precision position measurement, often used for calibration and high-accuracy nc cnc machine applications.
The accuracy of position detection devices directly affects the machining precision of the nc cnc machine. Higher precision devices allow for tighter control loops and better part quality.
4. Servo Drive System
The servo drive system converts the control signals from the CNC system into mechanical motion of the machine tool. It consists of servo drives and servo motors, which work together to provide precise speed and position control for the nc cnc machine axes.
Servo drives receive command signals from the CNC system, amplify them, and send appropriate current to the servo motors. They also perform closed-loop control by comparing the feedback signal from the motor encoder with the command signal, making adjustments to minimize error in the nc cnc machine.
Servo motors are responsible for converting electrical energy into mechanical energy. Common types used in nc cnc machine systems include AC servo motors, DC servo motors, and stepping motors, with AC servo motors being the most prevalent in modern systems due to their high performance and reliability.
3. Hardware Architecture of CNC Systems
The hardware architecture of CNC systems can be classified according to different criteria. Understanding these classifications helps in selecting the appropriate nc cnc machine for specific applications and in troubleshooting system issues.
1. By Circuit Board Structure Characteristics
Large Board Structure
In this structure, the main functions of the nc cnc machine are concentrated on a single large circuit board. This design simplifies the system structure and reduces connection lines, improving reliability. However, it lacks flexibility and makes maintenance difficult, as a single fault may require replacing the entire board. This architecture was common in early nc cnc machine systems but is less prevalent today.
Modular Structure
The modular structure divides the nc cnc machine system into multiple functional modules, each implemented on a separate circuit board. These modules connect through a backplane or bus. This design offers high flexibility, easy maintenance, and convenient expansion. Most modern nc cnc machine systems adopt this architecture, allowing for customization and easier upgrades.
2. By Number of Microprocessors (CPUs)
Single Microprocessor Structure
This structure uses a single CPU to control all functions of the nc cnc machine. The CPU performs all data processing, including interpolation, position control, PLC functions, and HMI management, through time-sharing processing.
Advantages include simple structure, low cost, and easy software development. Limitations include limited processing capacity and potentially reduced performance when multiple tasks are running simultaneously in the nc cnc machine.
Multi-Microprocessor Structure
This architecture uses multiple CPUs to handle different tasks in the nc cnc machine, enabling parallel processing. Each CPU is responsible for specific functions such as interpolation, position control, PLC, and HMI.
Advantages include high processing efficiency, strong real-time performance, good reliability, and easy expansion. This structure is widely used in high-performance nc cnc machine systems where complex tasks need to be handled simultaneously.
3. By Type of Computer Used
Dedicated Computer-Based Structure
This structure uses a dedicated computer designed specifically for nc cnc machine control. The hardware and software are optimized for CNC applications, providing high reliability and real-time performance. Dedicated systems often offer better integration with machine tools but may have higher costs and limited flexibility in terms of software customization.
PC-Based Structure
This architecture utilizes a general-purpose personal computer as the core of the nc cnc machine system. It leverages the powerful processing capabilities and rich software resources of PC platforms while adding specialized hardware and software for CNC control.
Advantages include lower cost, easy software updates, good compatibility with modern software, and convenient networking. This has become a popular choice in many modern nc cnc machine systems.
4. By Communication Method with Servo Drives
Centralized (Parallel) Structure
In this structure, the CNC system communicates with servo drives through parallel interfaces. The control signals for all axes are transmitted simultaneously from the main controller to the respective drives. This approach offers high transmission speed but requires complex wiring and is less flexible for system expansion in the nc cnc machine.
Distributed (Serial) Structure
This architecture uses serial communication buses to connect the CNC controller with multiple servo drives in the nc cnc machine. A single communication line carries data for all axes, reducing wiring complexity and enabling easier system expansion.
Common serial bus protocols used in modern nc cnc machine systems include Profibus, Ethernet/IP, SERCOS, and EtherCAT, each offering different advantages in terms of speed, determinism, and flexibility.
The purpose of studying the architecture of CNC systems is to enable system designers to master solid system design theories and methods, establish their own development platforms based on existing material foundations, and carry out system design for a series of machines. Understanding these architectural differences is crucial for selecting the right nc cnc machine for specific manufacturing requirements and for optimizing system performance.
4. Software Structure of CNC Systems
Many control tasks of CNC systems, such as part program input and decoding, tool radius compensation, interpolation calculation, position control, and accuracy compensation, are implemented by software. Logically, there are coupling relationships between these tasks; in terms of time, there are timing coordination issues between these tasks. When designing the software (system software) of a CNC system, the main consideration is how to organize and coordinate these tasks so that they meet certain timing and logical relationships, ensuring the smooth operation of the nc cnc machine.
Key Software Tasks in nc cnc machine
Part Program Input & Decoding
This module receives and stores part programs, then converts them into a format understandable by the nc cnc machine. It checks for syntax errors and prepares the data for subsequent processing steps.
Placeholder
Placeholder text
Tool Compensation
This function adjusts the tool path based on the actual tool dimensions, ensuring accurate part dimensions. Both tool length compensation and tool radius compensation are critical for precision machining in the nc cnc machine.
Motion Planning
This module determines the optimal path and speed for the tool movement, considering acceleration, deceleration, and jerk limits to ensure smooth operation and minimize cycle time in the nc cnc machine.
Placeholder
Placeholder text
Interpolation
Interpolation calculates intermediate points between specified coordinates to generate smooth tool paths. Common interpolation methods in nc cnc machine systems include linear, circular, and spline interpolation, enabling complex part geometries to be machined accurately.
Position Control
This function compares the commanded position with the actual position feedback from sensors, generating control signals to drive the servo motors and minimize position errors in the nc cnc machine.
Placeholder
Placeholder text
PLC Control
The Programmable Logic Controller handles auxiliary functions such as spindle control, coolant on/off, tool changes, and safety interlocks, coordinating the various components of the nc cnc machine during the machining process.
Characteristics of nc cnc machine Control Software
Multitasking Nature
The control software of a nc cnc machine must handle multiple tasks simultaneously. These tasks can be categorized into:
- Real-time tasks (interpolation, position control)
- Non-real-time tasks (program editing, parameter setting)
- Periodic tasks (status checking, display updates)
- Event-driven tasks (error handling, user input)
Real-time Performance
Real-time performance is critical for nc cnc machine software, as it must respond to events within strict time constraints:
- Hard real-time tasks (interpolation, servo control) must meet deadlines
- Soft real-time tasks (display updates) have more flexible timing
- Task scheduling algorithms prioritize critical operations
- Deterministic response times ensure consistent machine behavior
Common Software Structures in nc cnc machine
1. Foreground-Background Structure
This structure consists of two parts: foreground (interrupt service programs) and background (main program). The foreground program handles real-time tasks with high priority, such as interpolation and position control, through interrupts. The background program executes in a loop, handling non-real-time tasks like program editing and parameter management when no interrupts are occurring.
This structure is simple and easy to implement, making it suitable for small nc cnc machine systems with relatively simple tasks and low real-time requirements.
2. Modular Structure with Preemptive Scheduling
In this structure, the nc cnc machine software is divided into independent functional modules, each responsible for a specific task. A real-time operating system (RTOS) manages these modules, using a preemptive scheduling algorithm to ensure that high-priority tasks can interrupt lower-priority ones when necessary.
This approach offers better real-time performance and flexibility, allowing for more complex task handling in modern nc cnc machine systems. It simplifies software development and maintenance by encapsulating specific functions within modules.
3. Hierarchical Structure
The hierarchical structure organizes the nc cnc machine software into multiple layers, each with distinct responsibilities. Typical layers include:
- User interface layer (HMI)
- Task management layer
- Core algorithm layer (interpolation, compensation)
- Hardware abstraction layer
This structure promotes modularity and separation of concerns, making the software easier to develop, test, and maintain. It also facilitates portability across different hardware platforms in nc cnc machine systems.
The hardware and software architecture of CNC systems represents a sophisticated integration of mechanical, electrical, and computational technologies. The continuous evolution of nc cnc machine technology has led to increasingly powerful and flexible systems that can handle complex manufacturing tasks with unprecedented precision and efficiency.
By understanding the intricate relationship between hardware components and software algorithms, engineers and manufacturers can make informed decisions about nc cnc machine selection, optimization, and maintenance. As technology continues to advance, we can expect further innovations in CNC system architecture, enabling even more capable and intelligent manufacturing solutions.