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Author Topic: Variable offset in Mach4  (Read 447 times)

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Re: Variable offset in Mach4
« Reply #10 on: January 13, 2019, 11:01:02 PM »
Hi Steve,
best wishes for the coming year. Sounds like it has started with a bit of a rush what with the forum serach issues etc.
I am delighted you have been able to fix it all, please pass on my compliments to all those who worked up the solution.

This 'Table Mapping' idea sounds great. How does it work?

As I replied earlier in this post I use Autoleveller, a software utility that probes a PCB blank and THEN re-writes the
Gcode to include subtle variations in Z (due to the machine or the PCB warp/bow). When the modified code runs instead
of a Z cut depth of -0.06mm (60um nominal) the Z DRO will show a cut depth of -0.07mm say when the PCB blank is low
or -0.05 mm when the PCB blank bows upward by 0.01mm.

The variations in Z (from nominal) are explicitly programmed by Autoleveller re-writing the code.

I wondered about having an 'over-ride axis'. Thus the Z DRO would continue to show a cut depth of -0.06mm
but a secondary Z axis stepper or actuator would vary this up and down slightly. I cannot conceive however that the
Z DRO would track the combination of the programmed Z height (-0.06mm) plus a correction of 0.01mm say for a total
Z height of -0.05mm.

I remember Steve Stallings saying something towards the end of last year about using an override axis to enact THC.
It would avoid the motion controller having to make real-time corrections to the Z axis which would have to be reflected
BACK to Mach or risk losing accurate Z reference.

Craig
My wife left with my best friend...
     and I miss him!

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Re: Variable offset in Mach4
« Reply #11 on: January 13, 2019, 11:30:06 PM »
Well...  It is pretty much doing the same thing as the Autoleveler program is doing.  Only it is compensating for the table error at the output (motors), not the input (G code).

The map file can be created manually.  But what a pain in the rear!  So Brett wrote a Wizard that generates a G code probing routine to automate the mapping.  Of course this requires the use of a touch probe though.  You can specify the resolution required and the area of the table you wish to map.  For the base table map, one would obviously do the whole table area.  As for the resolution, you need to make is fine enough for your application.  The error map is interpolated between the map points.  This is what I would call the base table map. 

After you have the base table map (or your table is flat and you don't need base table map compensation), you can just load a map for a particular part.  This is almost exactly as you describe with the Autoleveler process with the exception that the G code is not modified and instead, the produced map file is loaded. 

For warped/bowed PCBs, one would necessarily have to "map" the board each time a new board is done.  But for getting rid of table error, the base table map only needs to be done once.  So this will work perfect for the OP's issue. 

This table mapping isn't using the override axes.  However, the THC control does indeed use that.  THC control will also be front and center in the next release. 

Steve

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Re: Variable offset in Mach4
« Reply #12 on: January 13, 2019, 11:40:44 PM »
I forgot to mention that this stuff is in our current development version, build 4026.  The mapping wizard is mcMapSurface.mcc in the wizards directory.  Right now, the only way to load a map is with the surface map plugin configuration dialog.  In the future, there is a way to load maps via the register interface making it possible to totally automate mapping a warped/bowed PBC scenario without having to load files manually, etc...

Steve
Re: Variable offset in Mach4
« Reply #13 on: January 14, 2019, 11:26:15 AM »
That sounds too good to be true! Now Mach4 is not worth considering to buy, with "Table Mapping" buying is a must. (At least for me).

Frank