Focal plane, lighting and homing questions

[Sahiru Hettiarachchi]

Hi I have several things I don't quite understand with configuring openPnP.

Focal plane for up looking camera.

Let's say it is picking 1mm and 10mm parts in height. So for the up-looking camera should we set the focal plane at a level where the tallest component can be in the focal plane? So when it moves to check with the up looking camera, the nozzle tip is 10mm away form the focal plane, and the part pads are perfectly on the focal plane. When we pick a 1mm part the nozzle has to travel down to get it to the focal plane?

Or can openPNP work with something out of focus too and this really does not matter?

Lighting

What is the best lighting LEDs that has worked for you. I am thinking of using addressable LEDs, but I feel like it is not needed. So I thought to go with regular SMD white LEDs. Then I saw a build that uses side emitting LEDs. 😂  Please share your suggestions.

Homing

When you press the HOME icon on the OpenPNP UI. It is going to actually move to the end-stops and home or is it going to set the current positions to 0 and consider it as home? As I type these I realize these can sound really stupid. Sorry for the trouble.

Thanks

[Sahiru Hettiarachchi]

I will share real images of my machine tomorrow. Here is a picture from the CAD.

[Michael Anton]

Ideally, you want the bottom camera focal plane to be the same as the PCB plane.  Achieving this will eliminate any errors that would occur from the nozzle not travelling perpendicular to the plane.

[mark maker]

Michael is right, choose the focal plane so it is the same as the PCB surface. That's the ideal setting. It will physically cancel out any tilt errors in the nozzle Z axes.

OpenPnP will hold the part above the camera, so its underside aligns with the focal plane, i.e. it adds the part height to the Z.

> Or can openPNP work with something out of focus too and this really does not matter?

Yes it can, if you enable nozzle tip calibration. Then any tilt errors in the nozzle Z axes are compensated by the software. Whether the software compensation is any worse than using the same Z, I don't actually know.

https://github.com/openpnp/openpnp/wiki/Nozzle-Tip-Calibration-Setup#what-is-the-bottom-camera-location-and-how-can-it-vary-between-nozzles

Generally, it is more important to make absolutely sure the homing fiducial is at PCB Z. I also strongly recommend to have the primary calibration fiducial at PCB Z.

https://github.com/openpnp/openpnp/wiki/Vision-Solutions#calibration-rig

In addition, it is favorable to have the feeders also roughly at PCB Z. One could argue that the part underside should align with PCB Z, because that is what we will be relevant when doing bottom vision and when the part is placed on its pads. However, don't panic if that is not the case. It is only relevant for tall parts and tall parts usually have clunky contacts, so placement need not be super accurate (self-alignment in reflow).

_Mark

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