question to DC42 about H parameter in auto-leveling deltas.
Posted by shadowphile
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question to DC42 about H parameter in auto-leveling deltas. September 09, 2017 12:47AM |
Registered: 9 years ago Posts: 280 |
Hi David, you said at one point in the past that the auto-probe results printed to the console of the web interface do not reflect the impact of the H parameter offsets, which means it can report worse than it actually is.
If that is true, is there a reason why that can't be different? It's awfully misleading.
thanks
If that is true, is there a reason why that can't be different? It's awfully misleading.
thanks
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Re: question to DC42 about H parameter in auto-leveling deltas. September 09, 2017 03:35AM |
Registered: 10 years ago Posts: 14,672 |
I don't understand the question.
The purpose of H parameter offsets is solely to compensate for variations in the trigger height of the Z probe. Nothing else. On delta printers in which the Z probe is separate from the nozzle, variations in trigger height are common, because even a small geometrical error will cause the effector to tilt slightly as it moves in the XY plane, and tilt in one direction changes the relative heights of the nozzle and the Z probe. If the probe is 30mm to the side of the nozzle, a change in tilt of just one degree will change the relative trigger height (that is, the height of the nozzle above the bed when the probe triggers) by about 0.5mm.
The best solution is to design and build the printer so that there are minimal geometrical errors, and to use the nozzle itself as the probe so that trigger height is not affected by any small amount of tilt that there might be. That is why we developed the smart effector - to make it easier to get good geometry and to integrate the nozzle contact probe.
But if you have a separate Z probe, mount it as close to the nozzle as you can get it, and adjust the printer to minimise effector tilt - a round spirit level on the effector helps a lot. Then measure the trigger height at each probe point (which is tedious, but necessary) and use the H parameters to correct for the differences. H parameters should never be chosen on the basis of anything other than measured trigger heights.
HTH David
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
The purpose of H parameter offsets is solely to compensate for variations in the trigger height of the Z probe. Nothing else. On delta printers in which the Z probe is separate from the nozzle, variations in trigger height are common, because even a small geometrical error will cause the effector to tilt slightly as it moves in the XY plane, and tilt in one direction changes the relative heights of the nozzle and the Z probe. If the probe is 30mm to the side of the nozzle, a change in tilt of just one degree will change the relative trigger height (that is, the height of the nozzle above the bed when the probe triggers) by about 0.5mm.
The best solution is to design and build the printer so that there are minimal geometrical errors, and to use the nozzle itself as the probe so that trigger height is not affected by any small amount of tilt that there might be. That is why we developed the smart effector - to make it easier to get good geometry and to integrate the nozzle contact probe.
But if you have a separate Z probe, mount it as close to the nozzle as you can get it, and adjust the printer to minimise effector tilt - a round spirit level on the effector helps a lot. Then measure the trigger height at each probe point (which is tedious, but necessary) and use the H parameters to correct for the differences. H parameters should never be chosen on the basis of anything other than measured trigger heights.
HTH David
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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Re: question to DC42 about H parameter in auto-leveling deltas. September 11, 2017 07:37PM |
Registered: 9 years ago Posts: 280 |
thanks David, I agree with everything you said!
Maybe I don't quite understand HOW those corrections are used.
I'm just trying to make sure that when I probe a point (G30 S-1) after an auto-cal and it reports a height that it matches the physical height I would get if I measured manually.
thanks
Maybe I don't quite understand HOW those corrections are used.
I'm just trying to make sure that when I probe a point (G30 S-1) after an auto-cal and it reports a height that it matches the physical height I would get if I measured manually.
thanks
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Re: question to DC42 about H parameter in auto-leveling deltas. September 12, 2017 03:34AM |
Registered: 10 years ago Posts: 14,672 |
When a probing move is made, the head is moved towards the bed until the probe triggers, at which point it stops. The firmware then assumes that the height of the nozzle above the bed is the Z parameter in the G31 command, except for a G30 S-1 report-only command. However, if the G31 bed probing command has an H parameter, that will be added to the G31 Z parameter, and the firmware assume that the nozzle height above the bed is that sum.
IOW the trigger height is taken to be the G31 Z parameter plus any H parameter that was provided.
HTH David
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
IOW the trigger height is taken to be the G31 Z parameter plus any H parameter that was provided.
HTH David
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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