Machsupport Forum

General CNC Chat => Show"N"Tell ( Your Machines) => Topic started by: Mogal on December 26, 2015, 10:18:53 PM

Title: I messed up with my new bench: EMF
Post by: Mogal on December 26, 2015, 10:18:53 PM
:-[

My CNC is now losing steps, and think its due to EMF

I built a new cabinet and installed a new computer system for the CNC.

Now i'm losing steps. I'm thinking of pulling everything and lining the back with tinfoil
and installing some sort of a divider plate between the CPU and CNC electronics.

I had no issues with the old setup.

Thoughts?
Title: Re: I messed up with my new bench: EMF
Post by: RICH on December 27, 2015, 07:35:48 AM
EMF can be tricky to resolve "if that is truly the culprit", but in general, the trick is to find the cause, reduce / contain / eliminate it.
I would suggest simply  boxing the pc & the complete  controller which can be simply a cardboard box lined with Al foil. No need to take things all
apart and then try.

One can "sniff" to find the culprit using a small battery operated radio and just scanning around using the antenna as the noise will create
interference on the radio when near the field. DO NOT actually touch  anything with the antenna ( place some electrical tape over the end of the antenna).

Above is  about as simple as I could explain things and better understanding of EMF  would be a book.

If you truly had no noise  problem before then effectively duplicate what you had before on the new cabinet!

RICH



Title: Re: I messed up with my new bench: EMF
Post by: Ya-Nvr-No on December 27, 2015, 10:17:38 AM
Most typical noise issues are on the E-stop or limit switches lines. Based on the photo I suspect the E-stop wire that is looped around the back of the monitor, (inherently emits high emf & generated voltage of over 300 volts to drive the screen). Or If you have a separate monitor try to unplug the one in the cabinet and use one off to the side to see if that monitor is an issue. But id suspect it is something simple. Not like you changed anything in the computer connections. Just rearranged things.
Title: Re: I messed up with my new bench: EMF
Post by: Mogal on December 27, 2015, 01:05:09 PM
Thanks for the ideas.
I'll test out a couple of things (I'll have to find an old radio)
Being as xmas just past, I have a few spare boxes now ;)
Title: Re: I messed up with my new bench: EMF
Post by: Mogal on December 27, 2015, 01:05:57 PM
Oh, I already have small caps on the stop and limit switches now, can't remember the size though.
Title: Re: I messed up with my new bench: EMF
Post by: Tweakie.CNC on December 28, 2015, 02:03:59 AM
Oh, I already have small caps on the stop and limit switches now, can't remember the size though.


They need to be 0.1uF

Tweakie.
Title: Re: I messed up with my new bench: EMF
Post by: garyhlucas on December 28, 2015, 07:49:17 AM
Mogal,
I hate to say it but you have pretty much broken all the rules regarding electrical noise. First is non-metallic backplane, that doesn't provide a good ground plane. Second the signal cables should all be shielded cables. Third all components should be oriented so that signal and power wires can be routed away from each other. Mounting all 3 drives vertical would have helped routing, and then the heat sinks would work properly. Vertical heatsinks generate a flow of cooling air as warmed air rises. Experience will let you recognize a mistake, when you make it again.
Title: Re: I messed up with my new bench: EMF
Post by: Mogal on December 30, 2015, 03:56:39 PM
Sigh, newbie errors I know  :'(

The CNC electronics are on an aluminium backplate, and the computer MoBo and components are still mounted on the 'case'
If I can't soon find and fix the issue, I will completely redo the system (after learning more on EMF)

But! I think I found my issue.
I went to load in a test file, so moused up to 'File' and noticed the very top corner of the screen was 'vibrating'
I didn't notice that before. I uncoiled the power cable and wrapped it around the monitor instead.

The screen isn't vibrating any more, and my test file was within 0.0005 on all axis after a verifying.
I'm currently running a new program and will report back on what happens.

Thanks,
Chris
Title: Re: I messed up with my new bench: EMF
Post by: Mogal on December 30, 2015, 04:03:41 PM
Okay, delay last, I'm still losing steps.
After a 30 minute run, the X and Y axis are within 0.001" and Z was 0.020" out from a verify.

K, back to the drawing board.
Title: Re: I messed up with my new bench: EMF
Post by: Mogal on January 03, 2016, 06:28:07 PM
Well, here's a weird one.

I had my pulse freq set at 35,000. I'm loosing steps
I switch to 25,000 and I'm not losing steps (Verify shows approx 0.0005" - acceptable margin of error?)

BUT!

I have my steppers set at a speed of 140ipm.
The DRO reads out 152ipm when I rapid move.

Turns out the frequency is actually 27,300 pulses (Not 25,000)

So my question is, is there any way to fix this?
I'f I'm not losing steps, and my accuracy remains, can I assume all is well?

I think I've also narrowed down my interference to the relay controlling the router.
I also sucked it up and bought some higher end shielded wires and power cable for the router.
Title: Re: I messed up with my new bench: EMF
Post by: danilom on January 26, 2016, 06:37:46 PM
You should try another PC, this one seems to have bad latency issue or use some motion controller for generating pulses if you need more than 25khz for step lines.
Title: Re: I messed up with my new bench: EMF
Post by: Mogal on February 14, 2016, 09:55:49 PM
I have my steppers set at a speed of 140ipm.
The DRO reads out 152ipm when I rapid move.
Any ideas to this one?
Got me completely stumped :(
Title: Re: I messed up with my new bench: EMF
Post by: garyhlucas on February 15, 2016, 07:31:52 AM
Two things, if the rapid is two axis moving at the same time then the combined velocity will be higher than either axis alone. Its a rapid, be happy that it goes as fast as possible when not doing any cutting. As long as position is correct you are good to go.
Title: Re: I messed up with my new bench: EMF
Post by: stirling on February 15, 2016, 08:47:27 AM
BUT!

I have my steppers set at a speed of 140ipm.
The DRO reads out 152ipm when I rapid move.

Turns out the frequency is actually 27,300 pulses (Not 25,000)

There's your answer right there in the numbers.

27300 / 25000 = 1.092

1.092 * 140 = 152.88

Unless your PC shows a rock steady exact 25000 pulse frequency (which I'd be surprised if anyone's does) then this is what happens.

Perhaps more curiously, when I FIRST start Mach, the actual pulse frequency is a rock steady 25,324. However if I close and restart, this drops to a rock steady 24,397. If I close and restart again it's rock steady at 23,674. Closing/re-starting from then on has no further effect and it remains at 23,674. If I re-boot then the whole (3) cycle will repeat exactly. Just one of those Mach3 things I suppose.
Title: Re: I messed up with my new bench: EMF
Post by: Tweakie.CNC on February 15, 2016, 08:53:15 AM
Quote
Perhaps more curiously, when I FIRST start Mach, the actual pulse frequency is a rock steady 25,324. However if I close and restart, this drops to a rock steady 24,397. If I close and restart again it's rock steady at 23,674. Closing/re-starting from then on has no further effect and it remains at 23,674. If I re-boot then the whole (3) cycle will repeat exactly. Just one of those Mach3 things I suppose.

How on earth you discovered that beats me - it appears that the more I learn, the less I know about Mach3.  :'(

Tweakie.
Title: Re: I messed up with my new bench: EMF
Post by: stirling on February 15, 2016, 11:15:29 AM
I'd be very happy to tell you exactly how I discovered it - if only I could remember  ;D
Title: Re: I messed up with my new bench: EMF
Post by: Mogal on February 15, 2016, 03:17:18 PM
BUT!

I have my steppers set at a speed of 140ipm.
The DRO reads out 152ipm when I rapid move.

Turns out the frequency is actually 27,300 pulses (Not 25,000)

There's your answer right there in the numbers.

27300 / 25000 = 1.092

1.092 * 140 = 152.88

Unless your PC shows a rock steady exact 25000 pulse frequency (which I'd be surprised if anyone's does) then this is what happens.

Perhaps more curiously, when I FIRST start Mach, the actual pulse frequency is a rock steady 25,324. However if I close and restart, this drops to a rock steady 24,397. If I close and restart again it's rock steady at 23,674. Closing/re-starting from then on has no further effect and it remains at 23,674. If I re-boot then the whole (3) cycle will repeat exactly. Just one of those Mach3 things I suppose.

Okay, thanks for verifying that for me...
Know that I "know" its okay I can continue with the next step.

So...

@ 25k pulse, everything 'seems' to be good, but at 35k pulse, I'm losing steps...