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Thread: CNC wiring: how to intregrate on/off, contactors, e stop etc

  1. #11
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    Industry says an Estop should kill power to the motor. I say OSHA can screw off, it blew up my $300 VFD doing that.
    My tabletop CNC mill uses a double pole switch that sends an Estop signal to both the G540 stepper driver and to the Acorn motion controller. Not getting any fancier than that!
    If the spindle was VFD driven, I believe the Acorn would trigger the Estop on the VFD. On my setup, the Acorn kills the motor power relay.

    Sent from my SM-G950U1 using Tapatalk
    Last edited by RB211; 07-30-2019 at 02:42 PM.

  2. #12
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    E-Stop means EMERGENCY STOP. That MEANS it is intended for EMERGENCY circumstances where stopping the machine right now is of paramount importance. And that means of stopping it should be as absolute as possible. To my way of thinking, that means that logic chips, logic circuits, or computer chips should NEVER be involved in that function.

    I am not a big fan of OSHA, but in this case, I think they are absolutely correct. An E-Stop circuit should be as simple as possible in terms of the components involved. It should interrupt power to the motors or other devices on the machine that can, in any way, cause damage. And it should require human action to reset it: it should NEVER have any facility for any software or other logic (non human) to reset it.

    For this I like:

    1. A lock-out style switch which, through it's own contacts, supplies power to all elements of the machine that can cause damage.

    2. A MECHANICAL relay/contactor which, through it's contacts, supplies power to all elements of the machine that can cause damage. It should be wired in a normally OPEN fashion so that any failure in it's switch circuit will result in the interruption power to all of those elements.

    In either case, these circuits SHOULD be either:

    1. On the primary power feed to the machine so that it interrupts everything. This is only acceptable if there are NO electronic controls with their associated motor control boards.

    2. On machines with electronic/computer controls and their associated motor control boards, on the wires leading directly to the motors. Why on the motor wires? Because some motor controllers, dare I say all of them, will have filter capacitors that can retain a charge and continue to supply current to the motors for a short time after power to them has been cut. Thus the machine can cut off a finger, you hit E-Stop, then it continues to run for enough time to cut off one or two more fingers.

    Also, in any E-Stop design I like the reset to require at least TWO distinct actions on the part of the human operator. Examples of this would be a reset switch with a covered lens or toggle arm. Or a E-Stop button that mechanically latches in the off position and has to be rotated in order to release that lock. Other designs would be possible, perhaps two push buttons that have to be activated IN SEQUENCE.

    I do not trust any E-Stop circuit that works through any electronic elements that are more complicated than a simple switch and/or a MECHANICAL relay/contactor. I specifically do not trust E-Stop function that works through any electronic logic: I have seen and had to repair far too many logic circuits. I do not trust solid state relays; solid state devices can fail in the ON state. Heaven only knows how much logic they build into those devices. Yes, mechanical relays can also fail, but the vast majority of those failures are in the OFF state.

    For reliable operation in an emergency situation, you do not want fancy. You want SIMPLE. As simple as possible.

    As for your $300 VFD being blown, I say that is a design DEFECT. You should state that to the manufacturer. I would not purchase a VFD that does not allow mechanical switching between it and the motors or other loads.

    A properly constructed E-Stop circuit, following my guidelines above, can also be used for normal operations. But using a stop function that is built into a logic or computer style control should only be used for normal operation and a completely separate E-Stop circuit should be added for actual emergencies.



    Quote Originally Posted by RB211 View Post
    Industry says an Estop should kill power to the motor. I say OSHA can screw off, it blew up my $300 VFD doing that.
    My tabletop CNC mill uses a double pole switch that sends an Estop signal to both the G540 stepper driver and to the Acorn motion controller. Not getting any fancier than that!
    If the spindle was VFD driven, I believe the Acorn would trigger the Estop on the VFD. On my setup, the Acorn kills the motor power relay.

    Sent from my SM-G950U1 using Tapatalk
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  3. #13
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    Quote Originally Posted by Mcgyver View Post
    I went quite as Milton your post caused me to think more on this and that my assumption was wrong....slap a cheapo BOB in, fire up some CAM software and away I go isn't going to cut it. in reading through the functionality centroid offers as well as an RJ45 connection, it or something similar would be the way to go.

    I've heard some service and software complaints on Centroid (going to look at installation soon to get more familiar) and I really dislike that the BOB/controller is married to the software. Mach 4 otoh, I really dislike that you have register some PC ID to make the software work (I wouldn't buy it if I was a crook, but don't bloody well load up my life with future complexity if I want to change computers. I probably wouldn't even buy the final computer until some future point and initially run it on a temp one). i suppose I could find something not to like about all them, but those are really irksome.

    Question for anyone up on this stuff, what are the current best choices of software and BOB/controller board (I already have the servos and servo controllers)? I'd like a slick piece of software, pendant and full function board (like the idea of controlling the VFD through it, fixing an encoder for rigid tapping, possibly a probe, etc). The machine as a bport series I with 750w Yaskawa servos
    I feel exactly opposite to you on the hardware/software all being from one source. With the Centroid controls you only need to get support from one source. The marriage of hardware/software from Centroid is one of the biggest pluses in my mind. Add in the fact that they have been around for a long time and their software is rock solid and quite simple to use for me it would be a no brainer to go the Centroid route. You just need to make sure your drives will accept step/direction input if you go the Acorn route. The Oak would be no problem I am thinking.
    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

  4. #14
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    Quote Originally Posted by Black Forest View Post
    With the Centroid controls you only need to get support from one source.
    such that it is . there's merit to your point, seems a bit like Apple or PC...pros and cons to each. I may well go for Centroid but am always leery of the lock in business strategy as can create a high switching cost, so for me its a con. Regardless, in deciding to up the budget to a quality control board w/ software, it behooves me to look all good options.
    Last edited by Mcgyver; 07-30-2019 at 05:00 PM.
    .

  5. #15
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    Quote Originally Posted by Paul Alciatore View Post
    E-Stop means EMERGENCY STOP. That MEANS it is intended for EMERGENCY circumstances where stopping the machine right now is of paramount importance. And that means of stopping it should be as absolute as possible. To my way of thinking, that means that logic chips, logic circuits, or computer chips should NEVER be involved in that function.

    I am not a big fan of OSHA, but in this case, I think they are absolutely correct. An E-Stop circuit should be as simple as possible in terms of the components involved. It should interrupt power to the motors or other devices on the machine that can, in any way, cause damage. And it should require human action to reset it: it should NEVER have any facility for any software or other logic (non human) to reset it.

    For this I like:

    1. A lock-out style switch which, through it's own contacts, supplies power to all elements of the machine that can cause damage.

    2. A MECHANICAL relay/contactor which, through it's contacts, supplies power to all elements of the machine that can cause damage. It should be wired in a normally OPEN fashion so that any failure in it's switch circuit will result in the interruption power to all of those elements.

    In either case, these circuits SHOULD be either:

    1. On the primary power feed to the machine so that it interrupts everything. This is only acceptable if there are NO electronic controls with their associated motor control boards.

    2. On machines with electronic/computer controls and their associated motor control boards, on the wires leading directly to the motors. Why on the motor wires? Because some motor controllers, dare I say all of them, will have filter capacitors that can retain a charge and continue to supply current to the motors for a short time after power to them has been cut. Thus the machine can cut off a finger, you hit E-Stop, then it continues to run for enough time to cut off one or two more fingers.

    Also, in any E-Stop design I like the reset to require at least TWO distinct actions on the part of the human operator. Examples of this would be a reset switch with a covered lens or toggle arm. Or a E-Stop button that mechanically latches in the off position and has to be rotated in order to release that lock. Other designs would be possible, perhaps two push buttons that have to be activated IN SEQUENCE.

    I do not trust any E-Stop circuit that works through any electronic elements that are more complicated than a simple switch and/or a MECHANICAL relay/contactor. I specifically do not trust E-Stop function that works through any electronic logic: I have seen and had to repair far too many logic circuits. I do not trust solid state relays; solid state devices can fail in the ON state. Heaven only knows how much logic they build into those devices. Yes, mechanical relays can also fail, but the vast majority of those failures are in the OFF state.

    For reliable operation in an emergency situation, you do not want fancy. You want SIMPLE. As simple as possible.

    As for your $300 VFD being blown, I say that is a design DEFECT. You should state that to the manufacturer. I would not purchase a VFD that does not allow mechanical switching between it and the motors or other loads.

    A properly constructed E-Stop circuit, following my guidelines above, can also be used for normal operations. But using a stop function that is built into a logic or computer style control should only be used for normal operation and a completely separate E-Stop circuit should be added for actual emergencies.
    I disagree as well, in that the E-Stop is also a safety device to disable the machine when you are working on the machine, changing tools, removing parts, etc. It isn't just for emergencies.

    Sent from my SM-G950U1 using Tapatalk

  6. #16
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    Documentation for linuxcnc
    http://linuxcnc.org/docs/2.7/html/

    Great forum
    https://forum.linuxcnc.org/

    An industrial quality ethernet interface solution for step/dir (5 step/dir outputs, 48 i/0, +/-10v output + ttl/diff spindle encoder input and expandable) $199
    https://mesaus.com/index.php?route=p...&product_id=66

    Mesa has analog control interface boards too..

    You need a computer that plays well with real time. From my experience this is pretty easy to find. (Don't need a $Window$ license..)

    sam

  7. #17
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    Quote Originally Posted by RB211 View Post
    I disagree as well, in that the E-Stop is also a safety device to disable the machine when you are working on the machine, changing tools, removing parts, etc. It isn't just for emergencies.
    By definition, an e-stop is for emergencies. That's why it is called an emergency stop as opposed to a lockout or a shutoff switch.

    As an addendum to the the e-stop suggestions, it should not be normally open (ordinarily anyway), as I and others here have seen done.

  8. #18
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    Quote Originally Posted by Joel View Post
    By definition, an e-stop is for emergencies. That's why it is called an emergency stop as opposed to a lockout or a shutoff switch.

    As an addendum to the the e-stop suggestions, it should not be normally open (ordinarily anyway), as I and others here have seen done.
    With VFD drives, at least the ones I've used, you have to use a NO switch. NC would be ideal so fault detection is employed.

  9. #19
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    Also the N.A. electrical code allows for a controlled stop, where the controlled stopping of a VFD can be done according to code using a Safety Relay, these can be obtained with all kinds of features such as issuing a stop input to the VFD PLC input followed by a disconnect via the supply contactor.
    The have been in use on European machines for some years, they are slowly becoming more popular and eventually mandatory for N.A.
    Max,

  10. #20
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    I, at least partially, agree that working on the machine is a possible legitimate use for an E-Stop circuit. However, I suspect that OSHA and any other safety oriented authority would tend to go for a complete power lock-out device for at least some of those activities. Things like power disconnects and lock-outs are common in both industrial and even home situations. I even said that using the E-Stop for normal operations was, at least in my mind, an acceptable, secondary use. My main point was that a circuit that relies on logic circuits or computer control is not a proper Emergency Stop circuit as it is not dependable enough.

    Just saying, not trying to argue the point.



    Quote Originally Posted by RB211 View Post
    I disagree as well, in that the E-Stop is also a safety device to disable the machine when you are working on the machine, changing tools, removing parts, etc. It isn't just for emergencies.

    Sent from my SM-G950U1 using Tapatalk
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

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