what isTHE diffrence between CNC and PLC

[ankush.neve]

i am intrested in getting functional difference between cnc and plc
where does a cnc is used
where is a plc used

 

[Terry Woods]

A CNC program is a step-by-step control of a tool, or tool-handler, to accomplish a particular task.

A CNC program usually, if not always, contains all of the steps necessary to accomplish the task.

A CNC program is always sequential. The code will not proceed from one step to the next until the previous step is completed. In a PLC, the code will constantly check all steps (rungs) to see if the necessary conditions have occurred before proceeding.

In general, a CNC program is a "One-Step-At-A-Time" sequence.

In general, a PLC program looks at all conditions, all of the time, to determine what to do next.

A CNC program is much easier to develop than a PLC Program.

A CNC Program is...
Do this...
Then this...
Then this...
Then this...
etc.

However, the better CNC Programming tools allow for fault handling, which includes over-travel, motor-fault, and etc.

 

[jstolaruk]

In addition to Terry's comments:

CNC: Computerized Numerical Control, mostly used as a control of machine tools and its primary purpose, using the programming as Terry pointed out, is to control servo motor controlled linear and rotary actuators and usually one or more spindles for the cutting tools. Often, the CNC controller will have a background task that takes instructions from the CNC program for auxiliary functions (coolant on/off, swarf coneyor on/off, etc) or may have a small PLC in the panel to assist in those auxiliary functions.

PLC: Programmable Logic Controller is more general purpose for automation control with field devices and runs one or more tasks of Ladder Logic. Included is the ability to control servo devices but does not feature the user-programmability of the CNC program. Servo driven axises will be gantries, linear slides, rotary actuators, etc. Special function machines primarily use PLCs and many applications in the process industries.

 

[mostafa65]

DEAR ALL

IT'S A GOOD MATTER TO OPEN THIS DISCUSSION .I WILL ASK A QUESTION
I HAVE A FUALTY CNC SYSTEM, CAN I USE PLC INSTEAD ?
THE PROBLEM I FACED WITH CNC IS I CAN,T READ THE PROGRAM TO UNDERSTAND WHAT IS GOOING ON ,CAN YOU TELL ME HOW I CAN DEBUG CNC PROGRAM?
ALSO ARE THERE ANY ONE HAS MANUAL FOR DELEM DE 59 CNC SYSTEM ?
REALY I NEED YOUR HELP ,WHY ?,I HAVE ONE PRESS BRAKE ,ONE OF THE AXIS DOES NOT TAKE IT'S REFERENCE POSITION .THE PROBLEM IS THERE IS NO ERROR MESSAGE TELLING ME WHAT IS WRONG .

HOPE TO BE CLEAR

WAITING FOR YOUR REPLYS

 

[jstolaruk]

mostafa65:

In general, the PLC is not a direct replacement. If you could marriage the PLC to the servo drives, you would still not have the flexibilty of the G-Code langauge available to you. If the G-Code programming capability is not important, it is possible that a PLC could do the job but then it would come down to the choice of PLC mfg and its hardware interface capabilities.

I'm 99% sure that the least path of resistance and cost in your situation will be to find a way to repair the one you have or if that is not an option, find a local integrator that can retrofit a new CNC control to your drives.

I'm sorry, I'm not familiar with the CNC equipment you said you were having trouble with. Someone else here may.

 

[mostafa65]

HI JSTOKURAK

your right i have one system consists os sinumerik 840d HMI + FMNC
numerik inerface +STEP7 300 PLC .and of course servo drives and motors .

so now i ask are you famliar with sinumerik system
bregards
mostafa

 

[jstolaruk]

No, I am sorry, I am not.

 

[CaseyK]

With some brands, there is often great similarities between the internal workings of cnc and plc products. sometimes output cards are identical, except for color and or part number. Same goes for some processors, sans programming logic.

Some plc's can be used for cnc.

Some cnc controls can operated machines like a plc.

But, they will not operate and interchange 100%.