UPS for CNC

[BanduraMaker]

So, I'd like to head down to the shop to make a few fretboards for a customer but, we've got thunderstorms with plenty of lightning and wind coming through - conditions which have lead to brownouts and short blackouts in the past.

What I'm wondering is if anyone has any ideas on how to integrate a UPS into a CNC system.

My spindle is run from a VFD which runs for about 15 to 20 seconds after you un-plug it so I imagine it might run for a second or so under load.

When power is removed from the driver, the Z axis usually drops a bit. In case of a black out or an e-stop, the part is typically ruined due to the Z-drop.

So, I think the solution to protection from brown/black outs would be to run the system from a UPS. Upon power failure, or perhaps 500ms of total power failure, the system would immediately feed hold, retract to safe Z and shut off the spindle and then sit until the juice runs out.

If power returns before the computer shuts off, it would just be a matter of hitting stop, re-starting the spindle and doing a "run from here" to finish the piece.

Does anyone know how hard it would be to get the message to Mach 3 that there is a power failure and for that message to run a macro that would perform those tasks?

UPS's with USB connections are pretty common these days, I just bought one for my computer for I think about $65 or something like that. I haven't written a lick of code in about 15 years so I have no idea how one would go about writing a plug in for Mach to read the UPS status over USB.

Thoughts?

[jckstrthmghty]

UPS's with USB connections are pretty common these days, I just bought one for my computer for I think about $65 or something like that. I haven't written a lick of code in about 15 years so I have no idea how one would go about writing a plug in for Mach to read the UPS status over USB.

Thoughts?

I guess it would be a matter of figuring out what pin on the USB is the output and whether it was within the volt range of your controllers input the using a similar code to what the auto zero tool does.

Never done it myself but it should be possible.

[keebler303]

I'd think you could hack into the indicator ligths on the UPS if nothing else. Many have an LED to show normal and UPS operation. If you could tap into the LED which shows it is running on battery power, you could feed that signal into your BOB to halt mach.

Matt

[BanduraMaker]

It's not so simple unfortunately. USB uses a serial protocol to communicate with the PC using some sort of standardized messaging for UPS devices. If it was a simple logic level output, you'd be right but, it's not.

p.s. didn't read about the LED hack idea - that's an interesting one and might just work.

[DonFrambach]

Rather than hack into the UPS, you could use a 120 v relay (to detect power loss {link: http://www.mouser.com/ProductDetail/...EXNyXZ1uAQsEWG } ) and feed in either the NC or NO output (as you feel is appropriate) to your BOB.

[vid1900]

Finding your way back from the lost steps is the hard part.

If you were using a 1/4" bit, you could make a 1/4" plunge hole somewhere in the waste, and that could be your reference starting point should you have to run your code again.

If you added some extra deep cycle lead acid batteries to your UPS, you might be able to add enough reserve to finish a medium size job. You see solar guys using 500 amp hour batteries chained together.

The trade off would be: are the ruined pieces worth the price of the battery bank over a year's time?

[BanduraMaker]

I use home switches so that's actually the easy part.

I really like the idea of using some sort of sensor to trip an input on the G540 and run a macro rather than using the USB output from the UPS. A cap on the output line could put a little delay in there to keep from tripping on a very small brownout event. I might have to do some testing to see how long my spindle runs when power is dropped.

I'm not really interested in spending a ton of money on this and besides that, my spindle runs off 220 so I'd need a 220 inverter which would be ridiculously expensive.

The brownouts and blackouts are somewhat rare but we do probably get about a half dozen per year.

Now how do I get an input to run a macro?

[vid1900]

I use home switches so that's actually the easy part.

We all do, but have you ever tried to restart a part? Was it EXACTLY on?


Usually (and mind you my table is 60x120" ) it is off by a mm or so. Acceptable for some jobs, but not all.

[BanduraMaker]

I typically use fixtures with a dowel pin hole that I use as the origin set to a particular offset. e.g. for my fretboards, the fixture is G59P7. So far, every time I've re-mounted the fixture, it's been within .001" of where it's supposed to be. That is, when I check it with a 1/4" pin in the spindle, it goes right in the hole. I can hear a change in tone from the stepper maybe 50% of the time which means it's off by a little bit.

I do have one fixture that's totally off by about .040" all the time. I think it has to do that the fence I used to cut it originally was off by about that much but I can't be sure.

I have done a few "run from here's" e.g. after breaking a .024" bit during fret slot cutting and it was dead nuts on.

[vid1900]

.

I'm not really interested in spending a ton of money on this and besides that, my spindle runs off 220 so I'd need a 220 inverter which would be ridiculously expensive.

220-240v UPS are standard throughout most of the world. But you are right, they, and the batteries would cost you money.

[vid1900]

I typically use fixtures with a dowel pin hole that I use as the origin set to a particular offset. e.g. for my fretboards, the fixture is G59P7. So far, every time I've re-mounted the fixture, it's been within .001" of where it's supposed to be. That is, when I check it with a 1/4" pin in the spindle, it goes right in the hole. I can hear a change in tone from the stepper maybe 50% of the time which means it's off by a little bit.

I do have one fixture that's totally off by about .040" all the time. I think it has to do that the fence I used to cut it originally was off by about that much but I can't be sure.

I have done a few "run from here's" e.g. after breaking a .024" bit during fret slot cutting and it was dead nuts on.

Cool, then you have a great system in place already!

[lgalla]

Andy are you thinking of a UPS for the whole machine?
The Z axis may drop with power off if you have a ballscrew as the weight of the spindle will allow it to drop without a brake.
On a brown or blackout,what happens when the power comes back on
Larry