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Author Topic: Is M4 supposed to save axes position on shutdown?  (Read 3231 times)

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Is M4 supposed to save axes position on shutdown?
« on: February 02, 2017, 06:41:14 AM »
Hello,

I'm not sure about the following feature: Is Mach4 supposed to save the axis position of all axes on shutdown and re-load them on start-up?
If not, is this a property of the motion plug-in?

Regards,
Paule
Re: Is M4 supposed to save axes position on shutdown?
« Reply #1 on: February 02, 2017, 02:03:25 PM »
FocusPaul,
What M4 does when you exit is save the last G54 coordinates.  Meaning if you have zero'd your machine prior to a job and set a new work coordinate (0,0) then that G54 setting is saved when you exit M4.  It asks you if you would like to save it when you exit.  If you never did anything but home your machine and used machine coordinates as your 0,0 it does nothing.

Russ
Re: Is M4 supposed to save axes position on shutdown?
« Reply #2 on: February 06, 2017, 05:05:47 AM »
Hello cncman172,

I feel like your answer lead me more close to the resoultion of my problem - still I'm missing something.

In some cases we do not use homing, because it does not allow our work piece to be positioned with precision of less than 10 ┬Ám. Instead, we do fine-grained jogging methods to get the exact position, then zero relevant axes and start the process.
I tried to reproduce the scenario like this:
Start M4. G54 offsets are all zero, machine coords are also zero, resulting in all axes being zero'ed.
Then I moved axes X and Y to 79 and 359 and zero'ed them to update G54 offset to 79 and 359. After this I moved both axis to 86 and 1086.
After closing and restarting M4, the axis positions have been set to -79 and -359, which is exactly negative values of G54 offsets. If I now _move_ them to zero positions, they will definitely not be at the position assumed.

I expected M4 to start up at positions 86 and 1086. Also it does not ask me to save G54 offsets (it does this by default).
Re: Is M4 supposed to save axes position on shutdown?
« Reply #3 on: February 06, 2017, 08:14:27 AM »
Very interesting.

When you home the machine do you have homing sensors?  If you don't the machine really never gets an official home location, only where you manually zero the location.  The homing sensor could be a micro switch, optical sensor, proximity switch, etc.  You can tell if it has been officially homed because the X,Y,Z dro indicator will have a GREEN ring around them indicating it was homed.

When you have set you G54 and jog somewhere on the table, and then issue a command
G1 X0 Y0 F50

The machine should go back to the G54 coordinates that you established.  If the home sensor indicators are GREEN and you setup a G54 location when you exit it should ask if you want to save your positions.  Try it.

Russ
Re: Is M4 supposed to save axes position on shutdown?
« Reply #4 on: February 06, 2017, 09:34:56 AM »
For machines that use stepper motors, the exact location of power down
cannot be reproduced upon power up unless the power down was done
with the stepper motor at the same phase condition that will be stepper
motor driver will establish when it is powered up again. The error involved
can be as much as 2 full steps of the motor due to the 4 quadrants of the
driving sequence of a standard 2 phase stepper motor. Some motor drivers
do provide an output signal to aid in this process, but I have not seen any
hobby grade systems that take advantage of it.


Steve Stallings
www.PMDX.com
For PMDX product support, please use PMDX forum or direct email for quickest response. We do not use this forum as our primary product support site.
Re: Is M4 supposed to save axes position on shutdown?
« Reply #5 on: February 06, 2017, 09:59:14 AM »
Steve,
Unless I misunderstood the exchange, I think there issue was the fact they never homed the machine.  They felt they could be more accurate jogging to the exact position they wanted for G54.

The issue with this approach is when you exit Mach it will not ask you to save your G54 coordinates.  Why?  Well as you know, since you never homed the machine, when Mach4 starts again it has no way of finding that location.  If the machine was homed it know it can index over from home to the old G54 location.

Never knew about the stepper issue, but I run servos.  Good to know. 

Russ
Re: Is M4 supposed to save axes position on shutdown?
« Reply #6 on: February 08, 2017, 09:10:29 AM »
Hello all,

the problem is still there. To eliminate misunderstandings, here's what I tried:

- Open M4.
- Machine coords and G54 offsets are all 0.
- Home X axis (yes, we have homing sensors). Machine coords and G54 does not change (as expected).
- Move X axis by 2.91 (or something). This changes machine coords accordingly.
- Disable -> close M4
- Restart M4
- And the machine starts with machine coords / G54 all zero, although X axis should somehow display 2.91 or something similar.

And no, it didn't ask about saving anything on shutdown.
Re: Is M4 supposed to save axes position on shutdown?
« Reply #7 on: February 08, 2017, 09:48:27 AM »
FocusPaul,

That is your issue.  Try things in this order.

- Open M4
- Home Machine this will reset the machine coordinates.  Make sure they turn GREEN and when machine coordinate button is pressed they should read X=0 Y=0
- now jog the machine to somewhere on the table where you would like the G54 coordinate.  Now zero X and Y on the DRO, you have now established your G54 location
- now if you press machine coordinates again you will see you are not at 0,0 but an offset distance on both X and Y.  Turn off machine coordinates
- now close M4
- since you have created a G54 location that is NOT the home location or machine coordinate 0,0 you should see M4 ask if you want to save this location right after you exit.   Say YES.
- now open M4
- now home M4, do not zero the DRO
- now issue the following command.   G0 X0 Y0
- the machine should move to the save G54 location and show 0,0 in the relative DRO.

Russ

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Re: Is M4 supposed to save axes position on shutdown?
« Reply #8 on: February 08, 2017, 09:52:53 AM »
Got to laugh Russ, ive just sat and typed basically the same with 1 finger on phone and press post to get

Quote
Warning - while you were typing a new reply has been posted. You may wish to review your post.

I must make my finger go faster.

DazTheGas
Theres always time for a choccy biccy
Re: Is M4 supposed to save axes position on shutdown?
« Reply #9 on: February 08, 2017, 10:06:31 AM »
DazTheGas,

Thanks for the laugh.  I needed it today.  You answer so many of these type questions figured I would give you a break.  LOL.  How are you doing, you making any more Mach4 videos.  I love watching your videos.  :)

Russ