What is CNC System & Components, Types and Classification of CNC System

2019/10/10 11:47:13

CNC system is computer numerical control system working for CNC process. It does not just represent the CNC technology, processing machinery or the program. In this article, we'll introduce the basic components, types, classifications of CNC system and what is CNC system. 

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What is CNC System?

CNC is a technology to control some objects by a program composed of digital information. The whole set of devices and equipment that use numerical control technology to realize digital control is called the CNC (computer numerical control) system. CNC system generally consists of a CNC processing program, input/output device, CNC device, servo drive control device and electrical logic control device of the machine tool. The core part is the CNC device.

Components of CNC System - Basic Configuration of the CNC system

A CNC system generally includes the following elements or parts:

1. CNC control unit (numerical controller part)

2. Servo drive unit and feed servo motor

3. Spindle drive unit and spindle motor

4. PMC (PLC) controller

5. The input/output (I/O) unit of the control signal of the machine's power cabinet (including the magazine)

6. The position measurement and feedback unit of the machine (usually included in the servo drive unit)

7. External shaft (mechanical) control unit, such as the drive shaft of the tool magazine, exchange workbench, loading and unloading robot

8. Information input/output device, such as computers, disk drives, memory cards, keyboards, special information devices, etc.

9. The internet, such as Ethernet, HSSB (high-speed data transmission port), RS-232C port and other processing local area network.

The hardware of the CNC unit (controller part) is actually a dedicated microcomputer. It is the core of CNC machine control designed and manufactured by the CNC equipment manufacturer. 

Types and Classification of CNC System

1. According to the moving trail, the CNC system can be divided into point, line and contouring control system.

  • Point control system refers to only control precise positioning of the moving parts of CNC machines from one point to another without machining in the process of moving.

  • Linear control system is to control the moving speed and trajectory between two related points besides the accurate positioning of the moving parts of CNC machines from one point to another.

  • Contouring control system controls the coordinated motion of several feed shafts at the same time, so that the workpiece moves in accordance with the programmed trajectory and speed relative to the cutter, and the continuous cutting process is carried out during the movement.

2. Classified by the servo system, it can be divided into open-loop control system, semi-closed loop control system and closed-loop control system.

  • Open-loop control system means that there is no detection and feedback device. After power amplification by the driving circuit, the instruction signal from CNC device drives the machine table to move through the stepping motor, and the signal transmission is unidirectional.

  • Semi-closed loop control system adopts the angular displacement detection device, which is directly installed at the end of the servo motor shaft or ball screw to detect the rotation angle of the servo motor or screw, calculate the actual displacement of the worktable, and then feed back to the comparator of the NC device, compare with the original instruction displacement value, and control with the difference value after comparison. Fill up the displacement until the difference is eliminated.

  • Closed-loop control system adopts a linear displacement detection device, which is installed on the moving parts or workbench of the machine tool. The actual displacement detected is fed back to the comparator of the CNC device, and is compared with the program instruction value. Control with the difference value until the difference value is zero.

3. Classified by the manufacturing method, it can be divided into Universal CNC system and Dedicated CNC system.

  • Universal CNC system uses PC as the support platform of CNC device. According to the user's needs, the manufacturers of CNC machine tools have developed CNC software and control cards, which constitute the corresponding CNC device.

  • Dedicated CNC system is developed by the manufacturer of the NC system. It has strong specificity. After a long period of use, the quality and performance of the system are stable and reliable.

4. Classified by the functional level, it can be divided into Economic CNC system, Popular CNC system and Advanced CNC system. 

  • Economical CNC system is controlled by 8-bit CPU or single chip computer with resolution of 0.001 mm and feed speed of 6-8 m/min. It adopts step motor and linkage under 3 axes. It has simple CRT character reality or digital tube display function.

  • Popular CNC system uses 16 bits or higher CPU with a resolution of less than 0.001 mm and feed speed up to 10 m/min. It uses AC or DC motors with linkage less than 5 axes and has CRT character display or planar graphic display function.

  • Advanced CNC system uses 32 bit CPU or higher performance, resolution is 0.0001 mm, feed speed can reach 24 m/min, using digital AC servo motor, with networking function, linkage above 5 axes, with three-dimensional dynamic graphics display function.

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