Reply with QuoteNFPA requires power disconnected during e stop, so yes its correct.
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E-Stop on axis motor wiring.
The wiring diagram shows the cables from the AC/DC 30 drivers, to the motors, going through contacts of the E-stop contactor. This does not seem correct, as in an E-stop situation, the axis motors should be stopped instantly. If the wires to the motor are broken, then they are free to coast to a stop.
What is correct?
Regards, Colin
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NFPA requires power disconnected during e stop, so yes its correct.
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Google brought up National Fire protection association, but that makes no sense, so I'm lost. It would seem that the E-stop is for operator safety, and motors that stop instantly must be the safest for the operator?
Colin
The instructions for the Inverter control, for the main spindle motor, says under no circumstances wire through, fuses, or overloads, or any other means of breaking the power supply, as the inverter is designed to take care of stoping quickly, handling overloads, and any other event that might occur.
There are of course, the main, ampage controled, circuit breakers, for the overall supply to the machine.
Colin
NFPA develops and publishes the NFPA 70, aka NEC (National Electrical Code) and also NFPA 79 (Electrical Standard for Industrial Machinery), which are both applicable to this subject area.
However, I am not familiar with any explicit requirement that motors be disconnected from drives in case of E-stop. The far more common implementation is to either remove power from the drives (on the supply side), or to disable the drives (if the drives provide an inhibiting means which is certified to be reliable (e.g. the Safe Disable function on CN8 of Yaskawa Sigma V drives).
underthetire: do you have a reference for this?
The NFPA79 is Electrical Standard for Industrial Machinery, (I also have a copy in PDF).
The requirements for E-stop is that power will be removed from all motors and motive power.
In cases where the control is left powered, there can also be a E-stop signal to the controller to disable the command signal.
An exception can be made where a controlled shut down is carried out when damage to equipment and/or personnel can occur, and in this case a Safety Relay is used with the appropriate features.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
Agreed. But I don't think that precludes the common practice of cutting the servo drive off from its power supply, and not cutting the motor off from the servo drive.
As the OP indicated, the former is preferable because it gives the servo drive the opportunity to apply dynamic braking.
I would like someone from Ajax to reply, with the logic they use, when making up their circuit diagrams, for people like me to follow. North American rules do not apply to me, I would have to look up what the equivalent NZ reg's are. But I always think that common sense should prevail, so will use, what ever I think is the best for my situation.
If someone said I should disconnect the brakes and steering on my car, in an emergency, I think that I would not. This is a similar analogy to removing the the control voltage from the motor controlers, is it not?
Colin
Like I said, if your are concerned about the power supply decay etc causing run-on (very rare), then the E-stop circuit/device/relay would input an E-stop to the controller, this allows the controller to shut the drives off, or instantly remove the move command.
This is normal industrial practice.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
You started this discussion by stating that the schematic shows the wires from the AC/DC drive to the motors routed through the E--stop contactor. I believe if you take another look, you will see that it is in fact the VM+ and VM- supply wires to the AC/DC which are routed through the contactor, so that in an E-stop condition, it is the supply voltage that is disconnected from the drive and not the motors.
My drawing is at the factory, so I will look closely tomorrow. That makes more sense, as the control power supply is still connected to the AC/DC drive, so it is still in control. Sorry if I have caused a stir, but I for one, have learnt from the discussion.
Thanks, Colin
Might want to look at the new standard, soft inhibit is no longer OK. Must be a power disconnect now. Contactor's are fine between the vfd and motors, all double wound spindles etc use them. You just don't want to use them for start and stop if the vfd is running. I typically inhibit the drive and drop power to the drive myself. The problem lies if your drive holds a charge, motion stop during an emergency has to occur within a set time( no codes with me) and its quite small.Originally Posted by Al_The_Man
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I intended the power removal to be used in tandem with the processor shut off.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
Thought if anyone would know, it would be you.
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