Fiducials for non-squareness compensation

[Erich Styger]

Related to the non-squareness compensation:

currently with OpenPnP I can use a fiducial for visual homing which is great. Any thoughts on extending this to use three fiducials on the work platform to do automatic non-squareness calculation?

With this, the machine would do visual homing and then at least two other fiducials on the ground plate/platform.

The fiducials on a PCB are great to increase the accuracy of the machine for the PCB itself, but if it is about accurate bottom camera location or nozzle changer position, fiducials for the machine itself would be a great help.

Thoughts?

Thanks,

Erich

[Mark]

Hi Erich

 

> currently with OpenPnP I can use a fiducial for visual homing which is great. Any thoughts on extending this to use three fiducials on the work platform to do automatic non-squareness calculation?

> With this, the machine would do visual homing and then at least two other fiducials on the ground plate/platform.

 

The problem is: how would you know the true geometric location of these fiducials? Unless you have a machine table with drilling holes made by a precision CNC that you can trust, this is a Münchhausen-Trilemma.

 

Millimeter paper seems the cheapest way out of it.

https://github.com/openpnp/openpnp/wiki/GcodeDriver#non-squareness-compensation

 

Usually you just want to do that once, so adding computer vision for that seems a bit overkill.

 

Note that you do not want to do this repeatedly. Once you’ve set the compensation, all your stored feeder locations, nozzle tip changer locations etc. would be broken, if you change it again.

 

Personally I think it would be a more useful addition to add fiducials to the feeders* and nozzle tip changers etc. so the machine could recalibrate these coordinates. This would also address imprecision that comes from a modular machine, where you can slot-in feeders etc.

 

*) Of course this already takes place with feeders that use sprocket holes as a calibration reference.

 

 

> The fiducials on a PCB are great to increase the accuracy of the machine for the PCB itself, but if it is about accurate bottom camera location or nozzle changer position, fiducials for the machine itself would be a great help.

Thoughts?

 

My thoughts:

https://groups.google.com/d/msg/openpnp/bMcTCErszQc/CwnazPW2BAAJ

https://groups.google.com/d/msg/openpnp/bMcTCErszQc/xTMkuHDHBAAJ

 

Grüessli,

_Mark

 

[Erich Styger]

Hi Mark,

many thanks for your thoughts!

I was thinking to have a permanent millimeter paper with fiducials on it, so to have accurate position information (as accurate it can be).

But you are correct: the better solution would be to have fiducials for the nozzle change position(s) and the (auto)feeders.

I'll have a look how I could add that to system.

Au es Grüessli,

Erich

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