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  1. #51
    Quote Originally Posted by Jonathan View Post
    Looks like we're all largely saying the same things now.
    Didn't see your post until after I'd posted that.


    Quote Originally Posted by Jonathan View Post
    For the non-emergency stop button, you could just wire it to an input set to activate the feed hold, so the machine does in a controlled manner. It's still likely to leave a mark on the work, but prevent something worse.
    Erm.!! . . . Well that would just be a Feed hold so why not Call it Feed Hold.??

  2. #52
    Quote Originally Posted by Jonathan View Post
    What's your point? The timed switch off mentioned twice (now three times) in this thread would have turned it off. Also you can't judge how likely something is with such a small sample size.
    Point is that it does happen and equally you can't say it's unlikely because it has happened.!! . . . . . Agree thou it's irrelevant has it will be safe eventually if power cutoff is just delayed. ( I was more meaning it's unsafe if just relying on Signals.)

  3. E-stop systems are always a good cause for debate.
    Ultimately they should stop movement likely to cause personal injury, and how that can be acheived depends on the machine.

    We've got some quite expensive lorries at work with external equipment where some will kill everything including the lorry engine when an E-stop is pressed, whereas others will only kill the external equipment. There are pros and cons to both.
    The key requirement is they should be fail safe, and periodically checked.

    One question for everybody is, when did you last check all your limits and E-stop buttons worked?

  4. #54
    Quote Originally Posted by m_c View Post
    One question for everybody is, when did you last check all your limits and E-stop buttons worked?
    Don't have limits but I must hit the Oh shite button at least ounce per day. . .Lol

  5. #55
    Quote Originally Posted by EddyCurrent View Post
    .....
    The main aim of this is to get a good emergency stop system using the gear we've got.

    It would be useful if we could define some scenarios and strategies for stopping a cnc machine, your input is valuable here.

    I've listed some ways to stop the machine and the strategy to adopt, I'm not saying it's comprehensive so please add or amend as you think.
    .....
    This is a great idea Eddy, great for noobs like me. Might be nice to add example circuits for each strategy (might be getting carried away now...)?
    I have made some changes based on some of the feedback and tried to make clear which things should be done in hardware and software, hope that's ok. Maybe it could make a good sticky?

    List of scenarios and possible strategies for dealing with them.

    Scenarios

    • Emergency stop button pressed - Strategy 1, 2 or 2.5
    • Limit switch activated (not home limits) - Strategy 2 or 2.5
    • Spindle over temperature switch activated - Strategy 3 or 3.5
    • Stepper driver alarm relay activated (e.g. AM882) - Strategy 3 or 3.5
    • 'Stop' button pressed - Strategy 4
    • Charge Pump error - Strategy 1, 2 or 2.5


    Strategy 1

    • remove power to all devices immediately (Hardware)
    • Inform control software of Estop condition (Software)


    Strategy 2

    • remove power to stepper drives immediately (Hardware)
    • remove power to ancillary devices immediately e.g. air, water, dust extraction (Hardware)
    • issue stop command to VFD then after delay remove power to VFD (Hardware)
    • Inform control software of Estop condition (Software)


    Strategy 2.5

    • Issue stop to stepper drives then after delay remove power to stepper drives (Hardware)
    • issue stop command to VFD then after delay remove power to VFD (Hardware)
    • remove power to ancillary devices immediately e.g. air, water, dust extraction (Hardware)
    • Inform control software of Estop condition (Software)


    Strategy 3

    • issue audio visual alarm before taking action (with time delay) (Hardware/Software)
      After delay:-
    • Stopping of all machine actuators and ancillary devices (Software - "Stop" Command)
    • leave power supply on to VFD


    Strategy 3.5

    • issue audio visual alarm before taking action (with time delay) (Hardware/Software)
      After delay:-
    • inform control software to activate Feedhold (Software)
    • Move to safe Z (Software)
    • Issue stop command to spindle (Software)
    • leave power supply on to everything


    Strategy 4

    • Stopping of all machine actuators and ancillary devices (Software - "Stop" Command)
    • leave power supply on to VFD
    Last edited by cncJim; 15-11-2013 at 11:36 AM.

  6. #56
    Thanks to all who contributed it's been very rewarding I think and thanks to Dean and Jim for pointing out the FeedHold function of Mach3. With all of this each individual will have to make their own judgement, this is just mine.
    After going through the available information I decided to list the 'stopping methods' for each of the major components, i.e. VFD, stepper motors, Mach3, ancillary equipment.
    I decided that cutting power directly to the VFD was not for me so will implemented method 1 below.
    Also I decided that control of the ancillary equipment was currently outside the scope of my control cabinet but if later on it does fall within the scope changes will have to made.

    VFD stopping methods
    ---------------------------------
    1. immediately issue 'emergency stop' command and after delay remove power to input ('e/stop' command can be set to stop drive faster than 'stop')
    2. immediately issue 'stop' command and leave power to input
    3. use STO function if available to prevent restart (this is not a stopping function)

    Stepper Drivers stopping methods
    -----------------------------------------------
    4. immediately remove power to stepper drivers
    5. immediately activate 'enable' signal (breakout board also uses charge pump signal to disable outputs to stepper drivers (not using 'enable' signal)

    Ancillary equipment stopping methods
    -----------------------------------------------------
    6. immediately issue stop command (varies according to equipment)

    Mach3 stopping methods
    -----------------------------------
    8. immediately issue Feed Hold command to Mach3
    9. immediately issue Stop command to Mach3

    Other stopping methods
    ---------------------------------
    7. immediately issue audio visual signal

    Next I looked at the stopping scenarios, developed strategies and assigned 'stopping methods' to them, I felt it was important to minimise the number of strategies so carried out some mental boolean algebra and Karnough mapping.

    Only strategy 1 will be considered Safety related, it also aligns with the suggested drawing in Mach3 documentation.
    Emergency stop is obvious, for me limit switch activation may lead to a dangerous situation, charge pump activation means Mach3 has lost control so anything could happen.

    *emergency stop button pressed - strategy 1
    *limit switch activated (NOT home limits) - strategy 1
    *Charge Pump error - strategy 1
    *'Stop' button pressed - strategy 2
    *spindle over temperature switch activated - strategy 5 (assumes someone is in attendance otherwise use strategy 4)
    *Stepper driver alarm relay activated (e.g. AM882) - strategy 3

    Strategy 1 ( 1,4,9 )
    Strategy 2 ( 2,5,9 )
    Strategy 3 ( 2,4,9 )
    Strategy 4 ( 2,5,8 )
    Strategy 5 ( 7 )

    Next up will be some updated drawings to implement this.
    Last edited by EddyCurrent; 15-11-2013 at 05:24 PM.

  7. #57
    In the interest of practicality I'm proposing these changes

    *emergency stop button pressed - strategy 1
    *limit switch activated (NOT home limits) - strategy 1
    *Charge Pump error - strategy 1
    *'Stop' button pressed - strategy 2 or strategy 4
    *spindle over temperature switch activated - strategy 5
    *Stepper driver alarm relay activated (e.g. AM882) - strategy 2

    The reasons being,
    * If the spindle is overtemp then sound an alarm and let the operator take action at the Mach3 screen or otherwise.
    * If the stepper driver alarm relay operates then it should be sufficient to issue the 'enable' signal, if not then the emergency stop can be operated.

    finding a suitable off delay for the VFD contactor AT THE RIGHT PRICE is proving a challenge right now. There are some cheap ON delays which could be used but would not be fail safe.
    Last edited by EddyCurrent; 15-11-2013 at 10:33 PM.

  8. #58
    This seems to be the document required, have not read it yet but the title is "Application Note
    Interfacing AC Drives with Safety Relays"

    http://www.ab.com/support/abdrives/p...lays_Rev04.pdf


    Also a section in this

    http://www.bara.org.uk/info/safety/A...pplication.pdf
    Last edited by EddyCurrent; 16-11-2013 at 06:09 PM.

  9. The Following 2 Users Say Thank You to EddyCurrent For This Useful Post:


  10. #59
    Kill all power, no doubt.

    Here is how i have my CNC working:

    -the PC id surge protected and connected to a 1500w UPS. Also the CNC is conected there
    -the VFD enables the BOB
    -the charge pump enables the BOB and the VFD

    Typical everyday scenarios:

    Power interruption from outside of the house. It happens a lot here in Spain. Or a fuse trip. I have a lot of stuff at that fuse :-)
    -the VFD stops and stops Mach3. I go and see which line the process is. I write it down on a piece of paper. If power comes for the next half hour , i just continue from there. If not, i stop the PC and when i have power again, simp[ly continue from the line.

    My mistake
    -Spindle digs, VFD trips, Mach3 stops, Usually reset, lift the Spindle, check Z0, usually that is the mistake, Z0 and voilaaa

    Mach3 goes down and decides some crazy movement. Happens rarely but happens.
    -the bit digs, spindle stops and trip signal stops the process. if nothing is damaged, i check the xyz0 and if ok i continue from there, if not, i throw in the garbage and do it again

    PC stops, restarts alone or whatever similar.
    -VFD stops

    I hit the EStop
    -no power to the drives, no power to the BOB, VFD stops

    I greatly recommend a pause button also on the machine. Sometimes when not sure what is happening if nothing crashes is better to just pause the process and contemplate. Though an extra second is lost meanwhile
    Last edited by Boyan Silyavski; 16-11-2013 at 05:44 PM.

  11. #60
    Quote Originally Posted by silyavski View Post
    I greatly recommend a pause button also on the machine. Sometimes when not sure what is happening if nothing crashes is better to just pause the process and contemplate. Though an extra second is lost meanwhile
    What would you have it do ?

    Stop the VFD
    Send a FeedHold signal to Mach3 and let it control the stepper motors


    Is it not just as easy to do it from the PC ?
    Last edited by EddyCurrent; 16-11-2013 at 06:56 PM.

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