Controller losing communication!

[puffernutter]

A while ago I moved my CNC plasma set up It is now in quite a small block built room. It is a home built system using a small R-Tech plasma cutter and the controller is driven by PlanetCNC software. The controller, motor drivers, relay control of the plasma is in an earthed metal box, fixed to the wall about 500mm from the edge of the CNC cutting table. The R-Tech plasma cutter is on the floor on the same side. Cables to the steppers are 4 core screened. The PC is a HP desktop higher up on the same wall. The connection between the desktop and the controller is USB. I have fitted a ferrite at one end of the cable.

The problem I have is that if the arc fails to strike I get "Communication Lost with Controller" and everything freezes and I have to unplug and re-plug the USB lead to the controller and through the menus, reconnect the controller and all is good! This is happening quite often. Additionally, I have just changed two of the stepper drivers, that just stopped working.

My suspicion is that if it takes too long to strike, the high frequency used to ionise the air between tip and workpiece is affecting the USB signals. I should add that a lot of my career has been spent involved in railway signalling with EN50121 (all parts) which is interference between trains and signalling systems, so I am familiar with what interference can do (although this plasma cutter has nothing on the ringing you get when a DC train turns on, or a 25kV pantograph arcs!

Its not easy, but I could put the PC the other side of the wall, but there would still be some USB cable close to the plasma cutter head. I could possible move the controller, although that would involve extending the leads from the controller to the steppers and I am not sure if that would make things better or worse.

How do others have their set up and have you had this issue?

Cheers

Peter

 

[hotponyshoes]

Try wrapping the usb lead (and anything else that can pick up interference) in earthed tinfoil (as a test)

Or try and eliminate the failing starts in the first place. Why is it not firing properly every time?

 

[m_c]

Could be worth trying a USB isolator

 

[gaz1]

one other thing to check on is usb ports set to do not turn off in your power settings

 

[puffernutter]

Try wrapping the usb lead (and anything else that can pick up interference) in earthed tinfoil (as a test)

Or try and eliminate the failing starts in the first place. Why is it not firing properly every time?

After a long time of no use, I was setting it up and trying to find the sweet spot for distance from the workpiece. I was using some scrap plate that was quite thin and it was distorting which gave me the issues. It also seems at any time if it hiccoughs and has to re-strike that can cause the problem.

Peter

 

[Anguz]

Are all the screened cables earthed at only 1 end? And is that earth common

 

[puffernutter]

Are all the screened cables earthed at only 1 end? And is that earth common

Yes and yes.

Peter

 

[eddie49]

Have you always had a ferrite ring on the USB cable, or did you add it to try to solve the problem?
Since USB is digital, a ferrite bead will tend to slow the risetime the signals, which could cause timing problems.

 

[Erie Fred]

did this work properly in the old location ?

how is the main power ground from the plasma cutter (the output ground) connection
at the table slats ?

 

[puffernutter]

All,
Thanks for your suggestions, brilliant as usual.

In the new location, using the R-Tech etc., I did succeed in cutting through a 1mm plate without significant issues (distortion was a problem, but a fresh piece of metal and all was good). It was when I moved to a thicker piece of steel that the fun started and looking closely at the steel, it's not that clean, so that may be part of the issue.

So, a quick update. I looked at the USB isolators and one arrived yesterday. I was also in Bath yesterday and popped into Avery Knight & Bowlers and got some 3mm plate offcuts. The reason I was in Bath was to visit the Royal United Hospital and have a 24hr portable ECG fitted, so I have decided being in close proximity to a plasma with this device may not be one of my best ideas, so it will need to wait until tomorrow to play with the plasma!

I also got some aluminium bar as I have a larger plasma machine I'd like to try, but as this CNC table is a home made bodge, and the torch is different, I need to make a new mounting for it. I was wondering if a heavier current may be more stable? As an engineer, I am also aware of changing too much at once, so I will probably use the thicker plate and see if the R-Tech will cut (as it always used to) without affecting the USB before changing the plasma cutter! I will add in the isolator though. I'll need to look in the settings and find out about the USB ports turning off, I wasn't aware of that one!

Again, thanks for al the support and ideas, I'll keep you posted when I have finished my 24 hours and can play again!

Cheers

Peter

 

[Erie Fred]

did you change where the THC is sampling the plasma voltage ?

 

[puffernutter]

did you change where the THC is sampling the plasma voltage ?

Can you explain please?

 

[Erie Fred]

Can you explain please?

Are you running Torch height control ?

 

[gaz1]

with mine i have power settings set where stuff dosnt go into hiberation

but to get to it heres a pic

as long as you dont let certain stuff go into sleep or hibernate mode you dont need to change that usb setting, even a modem can go into sleep mode

but you can still use windows screen saver i dont but accept the screen can be screen burnt

just beaware screen saver takes up resources when it runs

 

[puffernutter]

Are you running Torch height control ?

Thanks, no I don't have one of those.

Cheers

Peter

 

[hotponyshoes]

Thanks, no I don't have one of those.

Cheers

Peter

Might be a worthwhile addition,
It should help with the starts and will certainly make things easier with thin or distorted sheet.

I think I've got a ballscrew assembly that should suit a thc if you want it?

 

[gerrymoore]

Hi Peter ..when I built my CNC many years ago I used an RTech plasma and no matter what I tried I could not get it to work all the time every time ..with many different issues. After tearing out what's left of my hair I bit the bullet and bought a Hypertherm 30 amp plasma cutter ..worked flawlessy with the original setup for the next 10 years!! I know they are expensive but it solved my problems completely. I was making a living with mine and you're not but it's just a thought??

 

[Red'n'Black]

I've never had much luck trying to get USB to work reliably with high levels of electrical interference. It was only really designed for an office/home environment, priority was cheapness and ease of use ('plug and play').

If the connection gets disturbed by electrical noise, it's supposed to recover automatically. But there are so many layers of software involved, some written by Microsoft, some by the PC chipset manufacturer, some by your controller manufacturer, that it only takes a bug in one of them for the connection to lock up and it has to be unplugged or powered off to recover.

Is there any way you can change the interface the controller uses? Ethernet is a lot more robust in a noisy environment IME even without shielded cables, being transformer coupled means you don't have to worry about ground loops etc. Plus the software protocols that sit on top of it, TCP/IP etc, were designed to cope with data randomly getting corrupted.

Failing that, try a USB isolator as suggested. And make sure the USB cables themselves are good quality, some of the cheap Chinese ones don't have a shield at all.

 

[puffernutter]

Now disconnected from my ECG, so I can play again. I do have another Plasma cutter, , but I will have to make a new mounting, so that may be the way forward. @hotponyshoes, thanks for the offer, but I do have a third axis and stepper on the height. I nearly bought a THC a while ago, so if anyone has one for sale, I may be tempted.

I'll keep you posted!

Cheers

Peter

 

[Erie Fred]

Is the failure upon initial firing ?
Or after the arc get's transferred ? (or attempts to xfer)