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Home Offset
« on: December 14, 2017, 10:41:27 PM »
Set up system today,

All Axis home to switch then to encoder marker. Z, X ,Y - All works as expected.

Then I programmed a Home Offset for the X Axis.

When run the Homing again, the X Axis move negative to the home switch backs off until the encoder marker, then lurches and trips on following error.

The same thing happens with Y and Z.

If I set the offsets to back to Zero all home and no errors.
Re: Home Offset
« Reply #1 on: December 18, 2017, 10:50:23 PM »
sounds to me like when you program an offset the effective machine coordinate goes from zero (no offset) to
a number, your home offset in an instant. That would require infinite acceleration, its not going to happen.

'I enjoy sex at 73.....I live at 71 so its not too far to walk.'

Offline Davek0974

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Re: Home Offset
« Reply #2 on: December 24, 2017, 06:25:13 AM »
Is this on a CSMIO controller?

I have home offsets on my mill and it works ok, what version Mach are you running?
Re: Home Offset
« Reply #3 on: December 24, 2017, 08:10:09 AM »
I am running the latest version of Mach 4 Hobby
The controller is a Vital Systems DSPMC/IP

Offline Davek0974

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Re: Home Offset
« Reply #4 on: December 24, 2017, 08:15:55 AM »
Ok, thanks, it just similar to issues i had on CSMIO, I also know nothing on Mach4 i'm afraid.
Re: Home Offset
« Reply #5 on: December 26, 2017, 10:16:22 PM »
did you ever get this sorted?

I'm interested in how you got on.

My guess is that as the home switch activates Mach backs off until the switch returns to in-active, from your description you have index homing in action, the servo
drives until the index signal is active and sets the machine coordinate to 1) zero, if no home offset is active or 2) home offset for that axis when active.

If for whatever reason the position accumulator in your servo drive was at 34567 say at the instant that the machine coordinate was reset. If however Mach sets
the machine coordinate to your home offset, say 20mm, with steps per of 500 say, then the position accumulator would suddenly be presented with a position
change of 20 x 500 =1000, ie the accumulator would jump to 34567 + 1000 =35567. That would constitute an instaneous jump of 1000 counts. If your following
error is set less than that, almost certain, then it would attempt to accelerate to the new position but fault 'following error' almost immediately.

What intrigues me is that my understanding of home offset is that it sets the machine coordinates to the required offset but does not issue a command to go to
that location. Therefore I would not expect the position accumulator to experience the suuden jump in position. Whats going on?

One experiment I would like to suggest is to temporarily mount one home switch somewhere in the middle of travel of one axis. Disable the index homing for that axis
and try it again. If my understanding is correct index homing is enacted by the motion controller not Mach. I do not use index homing nor even home offsets but such
experimenting I have done with home offsets suggests that Mach is performing as I expected. This experiment would allow you to rule the motion controller
in or out.

I think also that if the Machine Diagnostics page were open when you homed that axis you might see the machine coordinate entry change which may in turn give you some
insight as to whats going on.


'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: Home Offset
« Reply #6 on: January 03, 2018, 09:20:11 AM »
I have tried numerous variations with the home switch placement and the disabling of the index homing. Nothing changes other then if the Home Offset is set to Zero. Ant other value causes the axis to be have as described and cause a following error.

This happens with any axis that is not set to Zero for a Home Offset

Here is a list of the hardware I am using

Mach 4 Hobby - 2.0.3481

DSPMC/IP motion controller - Plugin -2.01.72

Yaskawa servo drive - SGDV-7R6A01A

Yaskawa motor - SGMGV-09ADC61

I have also attached a copy of the error log file and a copy of Mach 4 project file,

Any help with a review to see what I may have missed would be great.

Re: Home Offset
« Reply #7 on: January 04, 2018, 05:14:32 AM »
You might want to try posting in the DSPMC section where the Vital system guys will see this and jump in.
If I remember I will try this on my machine tonight. I don't use a home  offset so I have never seen this problem.

We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.