Need help with unexpected/random stops on basic Parport/5 axis BOB setup

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18 Mar 2020 15:59 #160650 by tommylight

Lezard wrote: - same, enabled : readings between 110 and 440Vac (!!), from a multimeter set to 500Vac scale

That is not good, but at least now you have a route to follow :
Check the breaker boxes for loose ground wires,
Check all the sockets/plugs en route to the machine for proper ground wiring,
Check if you have a ground fault interrupter, if you do not, install one immediately, that is a must, not an option.
Then you have to check the equipment and find what is causing all that potential to run to the ground.
BTW, do not touch the machine while powered on and enabled and wear good isolating shoes, ruining shoes do just fine.

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18 Mar 2020 16:08 #160652 by Todd Zuercher
VFDs and servo drives can often send a lot of interference back up the main power lines. Sometimes it may be necessary to add an EMI filter before them.

That said, I am also having the exact same trouble with the same Chinese BOB. The input I am/was using for e-stop suddenly went intermittent. I've worked around it for now by connecting a 2nd unused input in parallel then to an or2 in hal. Mostly I think it is just a design defect or bad module on these cheap boards.

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18 Mar 2020 17:37 - 18 Mar 2020 17:39 #160664 by Lezard
Hi,

Todd Zuercher wrote: ... I've worked around it for now by connecting a 2nd unused input in parallel then to an or2 in hal. Mostly I think it is just a design defect or bad module on these cheap boards.


Thank you for your suggestion. I've done the same, it sort of improved things a bit, but I still had unexpected stops. I've read also about the debounce function, this might also help, haven't tried that yet. This cheap Bob was intended as a stepping stone towards a more robust solution, I stll plan to upgrade it as soon as cash allows...

tommylight wrote: Check the breaker boxes for loose ground wires,
Check all the sockets/plugs en route to the machine for proper ground wiring,
Check if you have a ground fault interrupter, if you do not, install one immediately, that is a must, not an option.


I appreciate your concern re. safety. I do have a 30mA ground fault interrupter installed at the main electrical panel in the workshop, if that is what you mean ( not sure about the correct translation here) It does work : I just triggered it when I inadvertently touched a phase wire with a ground connected wire... All parts of the machine are also connected (including gantry and Z-axis) and grounded at the CNC cabinet ground.

I've attached a thick copper wire from the CNC cabinet chassis, and pulled it near the electrical panel from where the CNC is wired. Resistance between the end of this cable and the GND on the electrical panel reads as 2 Ohms (control wire is 10mm diameter copper strand, +/-20m long). So I believe the cabinet is grounded, at least it's connected to the GND at the electrical panel.

Am I wrong ?

I have also pulled the same thick wire directly from the CNC cabinet chassis to the building ground stake, to bypass all the ground wiring : this has no effect on the ripples on the PC screen.

The friend who helped me with the wiring can"t join me, as we are under travel restrictions due to the COVID-19...
I'm a bit lost !
Last edit: 18 Mar 2020 17:39 by Lezard.

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18 Mar 2020 18:23 #160669 by tommylight
@ Todd,
Had the same problem with a cheap BOB, the optocouplers would weaken with time and needed more current to open properly. Adding some resistors parallel to the existing ones on the inputs did remedy that and luckily had no issues with it anymore.
@ Lezard,
Yes, that is the GFI in US or FID here in Europe. To test it's functionality just short the ground to the neutral, they are both located at the bottom of the socket and open to access, here in Europe.
If i remember correctly, whenever i measured between two grounds in my shop, i always get less than 1 Ohm.

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18 Mar 2020 19:07 #160670 by Lezard
OK, so if I try to summarize things, it seems to me that :
- the CNC cabinet GND _is_ connected to the building GND
- I may have un-expectedly high levels of EMI, some of these find their way to the PC, perturbating the PC screen and the reading of the inputs on the parport
- powering the PC from outside the CNC cabinet seems to alleviate the problem : no more ripples on the PC screen, and no more false readings of the e-stop
- EMI seem to come from the axis Delta vars : when I power only the spindle VFD, I see no ripples on the PC screen

Does this seem correct ?

When the PC is powered outside the cabinet, its GND connection is distinct (?) from the CNC GND. Is that why it seems to fix things ? If that were the case, this would mean that the perturbations come not from faulty isolation of the Bob, but rather from the common GND ?

@Todd : can you give some more details on how I could add an EMI before the vars ?

Thank you all for your help and time :-)
Laurent

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18 Mar 2020 19:56 #160672 by Todd Zuercher
Most of the servo drives I've installed have there own built in power supplies and are ran from mains power. The manuals for these drives specify an AC filter to be wired in the power supply line (preferably) as close to the drive as possible. For example the manual for one of the drive's I've used (a Teknic SSt-3100) specifies a "Shaffner model 350-12-29 filter". (Please don't ask me how these filters work or how to choose the right one for your drives, that is well beyond my knowledge.)

Here is a little reading.
support.automationdirect.com/docs/emi_mitigation.pdf

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18 Mar 2020 20:19 #160675 by Lezard
Thank you for the reading material.

I'll also check my vars doc (Delta ASD A2) and see what they tell me.
Meanwhile, I'll probably just run the CNC with the PC powered outside from outside the CNC cabinet, assuming it is safe enough ?

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18 Mar 2020 20:38 #160676 by Todd Zuercher

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20 Mar 2020 13:04 #160874 by andypugh
Two things I would suggest.

1) Fit a filter in the spindle drive power supply cable. Look on eBay for "RASMI" (one of the manufacturers) and pick one with the right number of phases and current capacity. (but be aware that these will often trigger a GFCI or RCD, so you need to look at their leakage current spec too)

2) Not a fix, but pragmatic, put a debounce HAL component between the e-stop input and LinuxCNC. 10mS extra delay before LinuxCNC knows about an e-stop won't matter, assuming that e-stop is also handled in hardware?

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25 Apr 2020 14:59 #165546 by Lezard
Hello,

Sorry, I've been so busy on an urgent (aka running late) project, that I didn't update this conversation.

I've tried several things with little success, and in the end, found that simply powering the PC _screen_ outside the CNC cabinet is enough to solve this problem...

So, I now have the PC unit powered from the CNC cabinet, the PC screen powered from an independent wall socket, and all is well in the world. Go figure !

I think I'll stop at this for the time being, as I still plan to replace the current office PC/parport/basic bob setup with a fanless PC mounted inside the cabinet, Mesa Ethernet card, and remote touch screen control.

Thank you all for your help and support, LinuxCNC world is the best :-)

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