【cnc machine】Difference among PLC,NC and CNC | en.ofweek.com

Could someone explain to me what are the differences between those three? Is one more advanced than another, or the controllers are used for different machinery, like one for welding and one for assembling (just giving an example, i know it's wrong).Now let en.ofweek.com editor Sherry to take you to understand their difference.


Manual machines are controlled by an arrangement of Cams and gear wheels. Simple linear trajectory of the part being machined or the tool being used can be controlled through hand operated or automated wheels that are connected to screws or rack and pinion arrangements. Complex paths are usually controlled by some kind of a cam follower device which follows a master template. Precision was realised by very high reduction ratio gear sets, which enabled movement of the resolution of microns by rotating a hand wheel by one turn or a fraction of a turn using marked dials or dial wheels. This arrangment requires great manual skills and hard stops to make precise features. It is analogous to an analog system.

Numerical controlled machines on the other hand use servo motors, encoders and ball screws. The servo motor can be instructed to rotate even as little as a fraction of a degree. Normally used ball screws have a pitch of around 10mm. Therefore one rotation of the ball screw moves the part or tool by 10 mm. By precisely controlling the rotation, even movement as small as nanometeric resolution can be obtained on modern machines. Most normal modern machine tools can make movements of 1 micron resolution quite reliably. The encoders provide a closed loop feedback to the servo motor driver, which makes for very precise positioning and thereby great accuracy of the machined part. These instructions can be numerical, and hence I suppose the name Numerical control.

Usually, the tool and the part are moved relative to each other by manipulating three servo motors on the x,y and z axes, which are linear axes. More complex movements can be achieved by incorporating rotary axes around the linar axes which are termed a,b and c axes. Very few machine tools have rotary axes, but that seems to be changing these days.

In a Numerically controlled machine, the trajectory (also known as tool path) and its velocity (also known as feed rate) is controlled by simultaneosly varying the speed and direction of the servo motors which control the linear and rotary axes. This involves complex trignometric and velocity calculations in real time based on real time feed back from the encoders. These calculations are carried out by the numerical controller in real time.

In the early days of Numerically controlled machines I suppose not much interaction was possible between the machine controller and humans. As has been pointed out, communication was rather limited through punch cards or tape. I suppose the machines only contained the Motion control kernel and not much else beyond that. Programs had to be manually written at the most basic level and fed into the machines.

Modern CNC machines however are much more advanced and have full fledged PCs which permit all kinds of interaction with the user. they can be networked throug ethernet, RS232, accept Compact flash cards, USB drives etc.

Personally, I dont see much difference between NC machines and CNC machines except in their ability. CNC machines accept programs in the form of G Codes which are instructions that provide the direction and speed for the tool trajectory. Many modern CNC permit high level programming of complex parts at the machine interface itself. Many common features are inbuilt as parametrized canned cycles
CNC (Computer Network Controller) is a computer application which particularly helps to to control a multi axis machine tool whereas PLC (Programmable Logic Controller) is a logic controller specifically designed to allow the user to create their own application and NC (Numerical Control) uses solid state logic and relays,timers etc to provide the application.

Plc stands for Programmale logic contoller and is mainly used for assembly line machines, but is not factory specific. You can have traffic lights controlled by a Plc, or an automatic parking system, or a home automation environement.
Cnc is a more specific programmable controller, and is used for precise operations in a factory, like drilling, cutting. Is used for low tolerance operations. Never heard until now about NC alone, but it might stand for Numeric Control.
When you need to movement of machinery on an assembly line, PLC(programmable logic controllers) is useful or capable for doing that. NC(Numerical Control) is identify as the form of programmable automation. You can use this technology for metal machine process. CNC is Computer Numerical Control. Now a day most of the NC is CNC(Computer Numerical Control).

See, there are differences between PLC and NC, CNC on controlling computer.
But, there is no major difference between NC ans CNC, in NC machine we not do not have CTR but in CNC you do have CTR.

There is also difference between two processor as well as in therms of advancement.
Generally speaking, NC - numerical control,CNC - computer numerical control ,CNC machines - Lathe,miling . the machine tool precisely controlled by computer and the program written in specific format.

CNC - computer numerical control
CNC machines - Lathe,miling . the machine tool precisely controlled by computer and the program written in specific format.
Hope can help you a lot!