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  1. #21
    Quote Originally Posted by birchy View Post
    It's a PCPPS V3.0 board. Doesn't appear to have any E-Stop contacts on it. My thinking is that if I kill all the AC devices, then the 50V supply to the steppers will also be killed which should be as safe as it can get?
    It does but it's not shown has E-stop and is just an input. Any input can be used for E-stop and just setup in control software to watch this pin.

    Quote Originally Posted by Web Goblin View Post
    It would stop the machine but you would lose position and not be able to restart the job from the same position easily. I dont have any experience with this pcb but I would think that one of the inputs would be able to be configured as a estop sense so that the software can recognise an estop signal.
    After any E-stop It should be Assumed that your out of position due to inertia pushing.!! That's why home switchs make it easy to get back in position.

    Quote Originally Posted by birchy View Post
    Must admit I hadn't really considered maintaining position in order to restart as I assumed that an E-Stop would be in emergencies only because something had gone drastically wrong. Would it not be more accurate to re-zero the tool because it would most likely overrun slightly when the E-Stop is activated? Plus a tool breakage would probably require manual movement of the Z-axis in order to replace it.
    Yes exactly what should be done after any E-stop which has occurred at anything other than very low feeds.

    What you should really be doing is Mechanicly killing either signals or Electrical connections to devices and not relying on software to do it.

    So thru relay contacts either kill the Enabel signal to drives or the power.? If you just kill the enable signal then the drives will stop but remain powered so keep there holding Torque. (Position will still have been lost.!) Personaly I kill the power to the transformer has I want the power shut down just to be extra safe.
    Then at the same this happens the control software should be informed thru the input used for E-stop telling it to stop the code.

    The BOB and PC should be left powered and out side the e-stop circuit.

    Any other Powered Devices like spindle, Coolant pump or Vacuum should be shut down thru killing power Via Relay contacts. Again signalling to control software thru inputs.
    Any device powered by VFD should be left powered but stopped by breaking Run signal thru a relay contact.

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


  3. #22
    I would much prefer to kill the power and re-zero rather than rely on software. At the end of the day, it's a safety circuit. I'm not going to add spindle speed control at this stage, however I may add it in the future if I need to replace the motor and/or upgrade to an inverter drive. Latest drawing is attached. Please let me know if you see any mistakes or can suggest improvements!


    Click image for larger version. 

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  4. #23
    Quote Originally Posted by JAZZCNC View Post
    I didn't think anybody would be that Stupid Andy and also like GOBY presumed it incomplete.!! . . But suppose I should know better Esp after Seeing first hand the Strike time Bomb.!!
    I didnt think I had said anything that required being called "Goby" but never mind.

    Birchy the estop input is not relying on the software to stop the machine but rather informing it that an estop has occurred but I think youve got that now.
    I would still leave the pc on a seperate supply though but thats a personal opinion. I would not like a fault on the machine control side to trip the mcb and dump the pc at the same time.

  5. #24
    Quote Originally Posted by Web Goblin View Post
    I didnt think I had said anything that required being called "Goby" but never mind.
    Didn't say anything wrong and No offence ment Mr was just being lazy.!!

  6. #25
    Don't see any limit switch's. . . Are you not using them.?

    If you do plan to use wire them in series with E-stop. Which then you'll need a limit override momentary button to back off.!

  7. #26
    Quote Originally Posted by Web Goblin View Post
    I would not like a fault on the machine control side to trip the mcb and dump the pc at the same time.
    Fair point and easy to change.

    Quote Originally Posted by JAZZCNC View Post
    Don't see any limit switch's. . . Are you not using them.?
    Ermmmm...good question! I presume you mean limit switches to prevent the X, Y, Z from trying to drive beyond their physical stops? Although I've considered them, I was thinking that the stops can be set within the software, and if something went wrong, the drives would trip on overcurrent protection? Should limit switches REALLY be wired into the Safety Circuit? It seems wrong to me as they should be part of the machine functionality rather than an Emergency or Safety device?

  8. #27
    Quote Originally Posted by birchy View Post
    Ermmmm...good question! I presume you mean limit switches to prevent the X, Y, Z from trying to drive beyond their physical stops? Although I've considered them, I was thinking that the stops can be set within the software, and if something went wrong, the drives would trip on overcurrent protection? Should limit switches REALLY be wired into the Safety Circuit? It seems wrong to me as they should be part of the machine functionality rather than an Emergency or Safety device?
    Not wrong very correct and right.!! . . . They are safety limits so should be part of the E-stop system and again the software should just be informed not left in charge.!!

    Edit:

    The other beauty of running 24v thru limit switch's(And E-stop) is better noise immunity which can affect the standard 5V signal from Parallel port. The 5v signal is just used to inform software so the wire run is tiny just coming from BOB (+) input passing thru relay contact and back to (-) input so far less chance of picking up noise.!
    Last edited by JAZZCNC; 16-12-2012 at 09:02 PM.

  9. #28
    I maintain and repair industrial machines daily (production machines...not CNC) and have never (yet) seen a safety circuit that protects anything other than the end user. Things like E-Stops, gate switches, door interlocks, break-beams, pressure mats, etc are always there to protect the operator and must be activated manually. Things like position sensors, limit switches, etc are always kept separate. I understand the need for limit and homing switches (and not relying on the software), however I disagree that they should be part of the Safety circuit. Run off 24V DC....YES. As part of the machine logic...YES. As part of the Safety circuit...NO.

    My reasoning is that if a drive goes to the end of its travel and activates a limit switch, we don't want it to kill everything and have to carry out a manual reset. It's not an emergency or a safety issue. Even if the drive keeps going, the physical stops will prevent it going any further. It might be an inconvenience to the operator but not a safety hazard...unless the machine is badly designed mechanically. So my idea of a limit switch is that it should stop the drive and inform the software but NOT kill the whole machine. Would you not agree?

  10. #29
    Jazz,
    Sorry just checking. I thought maybe I had upset you and not realised it. Thanks for clearing it up.
    Birchy I would seperate the supplies for the cooling fans and fit a seperate fuse or mcb for them. The amount of times I have seen fans sieze up and take out control circuits isnt real. What rating is MCB1 going to be? Just wondering about the descrimination between it and the fuse for the WM16, a fault here might bypass the fuse and take out the mcb.

  11. #30
    We have collision switches (proximity switches)mounted on our cnc machines at work at the cutting head and printer head mounts. These switches are connected to the emergency stop circuits to protect the machine and not the user.

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