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Author Topic: How to recover from power interuption?  (Read 11729 times)

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How to recover from power interuption?
« on: September 09, 2010, 11:24:09 PM »
I have moved to Africa for my old age and would like to do some CNC milling and MACH3 seem the answer.

Problem. -- In this part of the world we often get power outages.
To get over this I could use a UPS to keep things going for a very short time.
It seem to me that I would need an input to MACH3 that would lift the cutter to a safe height and send x & y to zero, (so that when power is restored I can start over without losing registration) then power everything down.
I could do it all, except, the "getting MACH3 to do what is needed when given an external input.
My intention would be to do work that may take many hours to run, so the machine will be un-attended.

Anyone know if this can be done?
Dennis

I think that I posted this in the wrong place at first; sorry!

Offline Hood

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Re: How to recover from power interuption?
« Reply #1 on: September 10, 2010, 02:16:51 AM »
If you have accurate home switches then all you need to do is re-home then start from the position you got to when the power went off.
Hood

Offline stirling

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Re: How to recover from power interuption?
« Reply #2 on: September 10, 2010, 05:52:32 AM »
Off the top of my head - how about something like this: In any job (ok - some jobs) there are places that are "ok" and "not so ok" to stop maching if you have to. How about putting a custom macro into your code at all the places where a stop would be "ok". That macro would check if the power is on/off. If "on" then just carry on else do the controlled stop thing whilst you still have UPS. Typically the macro might just turn off the spindle, mill and controller, do a feedhold and store the current line for later. Mach could be left running in power saving mode and subsequently shut down by the UPS if neccessary.

Ian
Re: How to recover from power interuption?
« Reply #3 on: September 10, 2010, 12:58:13 PM »
Thanks for the ideas.

What type of home switch is available that can hold to 0.0005 or better?

How would Mach3 know that the power is off? Would I have to use one of the inputs that are in short supply? Maybe a second parallel port!
Is it possible to have the keyboard monitored by Mach3 for some combination of keys? I could fix a solenoid to operate on mains failure?

Dennis

Offline Hood

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Re: How to recover from power interuption?
« Reply #4 on: September 10, 2010, 01:29:41 PM »
Optical switches can be very accurate but if used on a machine where dust or coolant is present you really need to shield them in some way. That can be done by housing them in a small box and having a rod protruding from the box at either side. The rod has a flag which interrupts the light in the opto and is held central by two springs.

Hood

Offline stirling

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Re: How to recover from power interuption?
« Reply #5 on: September 11, 2010, 05:53:13 AM »
What type of home switch is available that can hold to 0.0005 or better?
Note that my scheme above doesn't require the use of the home switches.

How would Mach3 know that the power is off? Would I have to use one of the inputs that are in short supply? Maybe a second parallel port!
That would be my choice.

Is it possible to have the keyboard monitored by Mach3 for some combination of keys? I could fix a solenoid to operate on mains failure?
Not the route I'd personally take.
Re: How to recover from power interuption?
« Reply #6 on: September 11, 2010, 12:32:49 PM »
Thanks for the comments.

How is this problem solved in other places in the world that have unreliable power? Even if they don't use Mach3 they must have a workaround.
Next week I will start looking a the limit switch idea. To write a macro that checks an input from time to time sounds attractive, but, is there any information on how to do this kind of thing available on the net, or, is it something for programmers only?

I should like to hear from any member who live with the problem at their work.

Dennis

Offline BR549

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Re: How to recover from power interuption?
« Reply #7 on: September 11, 2010, 04:50:08 PM »
It will ALL depend on the tolerance you work with. Hood has the correct and most common method. It is FAR easier to restart an ACURATE machine than try and recover after an outage. It will also depend on when you loose power. During a rough cut no problem, during a finish cut?? BIG problem if you have low tolerance finishes say sub .001"

Unless you have a UPS big enough to run the entire CNCmachine you have a very limited time to react AFTER the power shuts down. Usually about 1 sec or less before the energy stored in the CAPS have been used up. This does NOT give you enought time to react and finish a stored position solution before the machine looses position.

NOW even if you have UPS capacity to run the machine during this time as soon as it does shut down and the drives loose power the axis's can DRIFT and loose position unless you have axis brakes to hold it on position(now we really get complicated)

With Hoods method all you have to do is re home and restart somewhere near where you left off.

I would try and only machine during the times that are LEAST likey to have a power outage maybe at night????

Just a thought, (;-) TP
Re: How to recover from power interuption?
« Reply #8 on: September 11, 2010, 05:56:50 PM »
Challanging problem.

I would break it in two:

1. If you do job shop work, homing again (with an accurate homing scheme) is the best solution.

2. Suppose serial production is being run unattended at night and you cannot afford to loose production when there is power. Then ................ maybe program the machine to home automatically  after power is recovered and restart the program. Certainly more complicated.

Re: How to recover from power interuption?
« Reply #9 on: September 12, 2010, 04:05:59 AM »
The kind of work that I have in mind is based on a machine that I have with a 0.01 resolution on three axis and involves 3D carving by scanning across the image to give very fine detail.   The UPS can keep the steppers in place under low power for hours; so that's no problem. I will need the line number that the programme was at when the power failed, and that I can get by recording the monitor screen. Question:- If I fit an extra parallel port; is there a way to detect one of the inputs and do a macro/jump to a given line in the programme code/change the way Mach3 continues? (Continues - Not stop)

For the sake of interest; there have been 42 power faults sense I started the request for information. Some just for a few seconds, but long enough to wreck the kind of work I wish to do.

Dennis