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Thread: Connecting a PLC to a CNC

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    Default Connecting a PLC to a CNC

    Hello everyone,

    I am working on a project which is automating a CNC machine using a robotic hand. this is a university project. Naw ofcourse this will be dne by using a PLC.

    so what i want to do is to send a signal from the PLC to the CNC in order to start the machining process, and a signal bck from the CNC to the PLC when its done. CAN THIS BE DONE!!! AND if someone can walk me through the steps.

    Thanks.

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    Default Re: Connecting a PLC to a CNC

    Ali,

    There are several different methods of interfacing a PLC to a CNC. However, with safety in mind you'll want to consider a couple more signals to monitor on both ends.
    Power-status
    E-Stop status
    Ready to receive/send
    Clear to receive/send ...etc.


    What kind of PLC and what kind of CNC are you looking at?

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    Default Re: Connecting a PLC to a CNC

    yes it can be done, ie, connecting an external plc to cnc. you could take an output signal from plc and give it as an input to cnc and visa versa . you could also configure m codes on the cnc to send or accept your intended functions.pls do take care of the safety interlocks.

    regards,
    bernieboy

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    Default Re: Connecting a PLC to a CNC

    I am taking safety into consideration actually its one of the major aspects when dealing with such a project, but all of these are gna be taken care of through sensors connected to the PLC, but am really clueless when it comes to the CNC. Because the only thing i did on a CNC was generate G codes to do something, never got into its system and how to control it. so if u can elaborate more it'll be appriciated.

    thanks.

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    Default Re: Connecting a PLC to a CNC

    It sounds like what you are doing is the same type of interface as a magazine barfeed interface. The barfeeds are nothing more then an expernal PLC connected to a lathe. The process usually sees the CNC as the main control and the PLC as the slave. That way most of the safety concerns are already handled by the CNC. The question becomes what brand of CNC and the age of the CNC are you attaching this to? The older ones are more limited on interfacing, but it can still be done. Do you have the wiring diagrams to the CNC? I spend a lot of my time talking people through interfacing barfeeds to lathe. If this sounds like what you are doing, you may call me during business hours in CA, you can find my web site on Google search with the key word "Autobar 400".

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    Default Re: Connecting a PLC to a CNC

    Quote Originally Posted by Ali jamal Eddine View Post
    I am taking safety into consideration actually its one of the major aspects when dealing with such a project, but all of these are gna be taken care of through sensors connected to the PLC, but am really clueless when it comes to the CNC. Because the only thing i did on a CNC was generate G codes to do something, never got into its system and how to control it. so if u can elaborate more it'll be appriciated.

    thanks.
    With regards to how the Emergency Stop is handled, its state is monitored by the PLC only for the purpose of halting the PLC in a civilised manner. The E Stop circuite should be made independent of the control and that it works in a way to remove power from all drive components of the machine.

    When you have peripheral device, its E Stop circuite and that of the Host machine, should be intertwined. That is, actuating the E Stop of the Peripheral Device should have the same effect on the Host machine as if the Host machine's E Stop was actated, and visa versa.

    Regards,

    Bill

  7. The Following User Says Thank You to angelw For This Useful Post:

    Ali jamal Eddine (05-22-12)

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    Default Re: Connecting a PLC to a CNC

    Quote Originally Posted by CNC Enhancements Tech View Post
    It sounds like what you are doing is the same type of interface as a magazine barfeed interface. The barfeeds are nothing more then an expernal PLC connected to a lathe. The process usually sees the CNC as the main control and the PLC as the slave. That way most of the safety concerns are already handled by the CNC. The question becomes what brand of CNC and the age of the CNC are you attaching this to? The older ones are more limited on interfacing, but it can still be done. Do you have the wiring diagrams to the CNC? I spend a lot of my time talking people through interfacing barfeeds to lathe. If this sounds like what you are doing, you may call me during business hours in CA, you can find my web site on Google search with the key word "Autobar 400".
    CNC Enhancements Tech can i make the PLC as the main control and the CNC as the slave, because i kind of want the PLC to deligate the work to the other components.
    but in any case the CNC we have is an XL-leader, model BM-1250 with a fagor controller.
    does the wiring come with the CNC? if so i could ask the technitian to pull them out for me.

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    Default Re: Connecting a PLC to a CNC

    Quote Originally Posted by angelw View Post
    With regards to how the Emergency Stop is handled, its state is monitored by the PLC only for the purpose of halting the PLC in a civilised manner. The E Stop circuite should be made independent of the control and that it works in a way to remove power from all drive components of the machine.

    When you have peripheral device, its E Stop circuite and that of the Host machine, should be intertwined. That is, actuating the E Stop of the Peripheral Device should have the same effect on the Host machine as if the Host machine's E Stop was actated, and visa versa.

    Regards,

    Bill
    thanks for the eye opener.

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    Default Re: Connecting a PLC to a CNC

    Quote Originally Posted by MMMMM View Post
    Ali,

    There are several different methods of interfacing a PLC to a CNC. However, with safety in mind you'll want to consider a couple more signals to monitor on both ends.
    Power-status
    E-Stop status
    Ready to receive/send
    Clear to receive/send ...etc.


    What kind of PLC and what kind of CNC are you looking at?
    the CNC am Using is an XL-Leader vertical machinig center, and the PLC is a Delta SS.

    what do u mean by
    Ready to receive/send
    Clear to receive/send

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    Default Re: Connecting a PLC to a CNC

    Quote Originally Posted by bernieboy View Post
    yes it can be done, ie, connecting an external plc to cnc. you could take an output signal from plc and give it as an input to cnc and visa versa . you could also configure m codes on the cnc to send or accept your intended functions.pls do take care of the safety interlocks.

    regards,
    bernieboy

    but how do u connect the PLC to the CNC?

    thanks

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    Default Re: Connecting a PLC to a CNC

    Quote Originally Posted by Ali jamal Eddine View Post
    the CNC am Using is an XL-Leader vertical machinig center, and the PLC is a Delta SS.

    what do u mean by
    Ready to receive/send
    Clear to receive/send
    OK - interface signals that should be used when interfacing equipment;
    "Ready to send or receive"; should be a signal from the CNC to the PLC that it is in an "OK and Safe" position to begin loading to (or unloading).
    This is typically provided as a TRUE statement or ON signal when ALL of the following signals are true on the machine: Power ON, No alarms, E-Stop OK, In "load/unload Position", etc. (additionally maybe, IN-CYCLE or M-Code xxx active - I'm not sure how you're planning to do this)

    The machine should be in a "HALTED STATE" until the PLC tells the machine to continue. This would be considered a "Send Completion" or acknowledgement signal to the machine to continue its operation. (That the PLC function is complete)

    Basically, there should be a constant hand-shaking of signals from the CNC to and from the PLC. This ensures that the equipment is ONLY doing what its suppose to do when it is commanded to. Also, to eliminate the potential that the machine can do something that it shouldn't.

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    Default Re: Connecting a PLC to a CNC

    Quote Originally Posted by Ali jamal Eddine View Post
    but how do u connect the PLC to the CNC?

    thanks
    Typically there are two different connections that need to be made;
    Hardware interlocks
    Software interlocks

    The Hardware interlock, at minimum should include a wire in series from the E-Stop string through a double-contact E-Stop switch on the new equipment. (So that when either E-stop is triggered, it stops both equipment)
    Some other Hardware interlocks may include, Fence gates, guarding, Power, equipment positions, part confirmations, etc.)
    The Software interlocks can be accomplished many different ways. The easiest (without getting into the CNC's logic) would be to use isolated relays and discrete power supplies on both ends.
    Using the CNC's (user) M-Code inputs and outputs, you can basically run a parallel circuit off of the relays in the cabinet to your PLC to monitor status and change states.

    By all means, use negative logic with serial positive conditions on your PLC ladder so that a broken wire doesn't give you a false negative. (or false positive condition)

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    Default Re: Connecting a PLC to a CNC

    Ali,

    Which university are you performing this project at?
    Perhaps there is someone local that might be able to provide you better assistance since, as easy as it may seem, there are many things to consider when connecting one piece of equipment to another.
    Without knowing more specifics, we can only offer generalized advice and would advise you to seek assistance from someone with experience.

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    Default Re: Connecting a PLC to a CNC

    The Fagor control is very different from most CNC controls.

    As to can the PLC controlling the CNC; yes it could as the Fagor control does offer a cycle start and feed hold to interface too. However, using these can be very dangerous, as there is no hand shaking from the CNC before the PLC tells it to run. If something goes wrong and the PLC starts sending a cycle start to the CNC when someone is changing tools or positioning a part better, the CNC would take off very fast, and could cause a lot of personal damage. In safely signals you not only have to consider how it should work, but how the village idiot will try to make it work, and how it might work if a sensor or signal fails.

    If the CNC is controlling the PLC, then the hand shaking is done by the operator observing that it is ok to run the CNC, and then pressing the Cycle Start button. Then the CNC tells the PLC it is ok to load / unload a part, and when the PLC is done it tells the CNC it is ok to continue.

    As to actual signals; the Fagorís M-codes are addressable to whichever output you may want, so getting a wiring diagram of the CNC is very important. Also, the safety signals like E-stop need to be found in the wiring diagram. You may also want to talk to Fagor or the XL-Leader manufacturer about the programming in the CNC, as from what I have seen it is not that hard to modify the programming on site in a Fagor control.

    Do you have and can you post the electrical diagram for the CNC? I think to really help much farther we would need to see that.

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