Vision for Strips and Head Offsets

[Justin Rajewski]

I followed the OpenPnP machine design pretty much verbatim. I got everything setup and assembled my first few batches of boards last week. However, I've run into a few issues I feel should be common so there are probably existing solutions.

First, I'm currently using cut tape and the "ReferenceStripFeeder" with some custom tape holders. This works pretty well except the parts I have are pretty loose in the tape so they shift and rotate around. This causes them to be placed poorly with manual fixing almost always necessary. The ReferenceTapeFeeder seems to has a vision system already setup to handle this issue, but it looks like this is for a an actual feeder. Is it possible to set this up for cut tape or use vision on the parts (not the tape holes) with the strip feeder?

Second, I'm having trouble setting up the dual nozzles. I can setup one so that it picks up parts and places them really well. The problem is when I try to get the second one running. I set the Z offset so that both nozzles touch the PCBs at the same value. However, when it comes to picking up parts (which have a different height than the PCBs) the nozzles don't match up anymore. I assume this is because of how the head works with the stepper rotating to push the nozzles down. When I zero it, it is offset quite a bit. I feel like if I could offset the "zero" point so that the stepper bar is horizontal the offsets should be symmetric and everything should be happy. Is there a way to do this or did I setup the offsets wrong? 

Also, not sure if this is an issue or not but I get an endless stream of errors similar to "Corrupt JPEG data: 44 extraneous bytes before marker 0x1c". I'm using the camera from the BOM (http://www.ebay.com/itm/221448995232).

One problem I ran into when build my PnP was that the 5mm to 5mm couplers linked in the BOM had set screws that were 180 degrees from each other. This allowed some play in one direction and make it nearly impossible to get the nozzles attached perfectly inline with the motor. I bought some new ones with 90 degree offset set screws and it's a lot better. I updated the BOM with the new coupler and added a note about it.

This project is awesome! Thanks to everyone who has worked on it.

[Jason von Nieda]

Hi Justin, I am out of town for a few days but I will try to answer your questions in the next couple hours when I am near my computer again. 

The short answers are:

Bottom vision, coming very soon

Nozzle problem sounds like an offset error, will need to get some more data from you

Corrupt jpeg, annoying but not a problem. Just ignore it.

Sent from my BeOS enabled toaster.

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[Justin Rajewski]

Hey Jason,

Thanks for the quick response. I actually bought a second camera (and LED ring and 3D printed holder) with the hopes of adding it for bottom vision.

Is there a procedure I should use for setting up the offsets?

Also I made a universal cut-tape holder if anyone wants the design. Here's a picture of it holding various sized parts.

[Jason von Nieda]

Hey Justin,

I don't actually remember how I got all the offsets set up for the Z axis and since I am out of town I can't find it out. I'll be home Wednesday and will let you know then. I believe I had to set an offset in the Smoothie config that might be different for your setup. I'll let you know as soon as I can. Sorry for the delay.

Jason

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[Jason von Nieda]

Ah ha! Found it: https://github.com/openpnp/openpnp-openbuilds/blob/develop/Smoothie/config#L108

That number is the offset from home to horizontal. So, home Z and then jog it so the bar is horizontal and then use the different in your Smoothie config.

Jason

[Justin Rajewski]

That did the trick! I got both heads going now. I ended up changing to something like -23, but the offset I measured by jogging it was -6 so it doesn't seem like these use the same units.

Do you have any idea when bottom vision will be implemented? I know these kinds of thinks rarely have an ETA but I was just curious if it's on a days, weeks, or months time scale?

[Jason von Nieda]

I'm hoping to have something basic working for bottom vision in the next two weeks or so. I'm in the process of recovering from 3 months in China so I have some catchup to do, but bottom vision is priority #1 right now.

Jason

To view this discussion on the web visit https://groups.google.com/d/msgid/openpnp/380d023f-38ad-4ea0-99f6-8c9464a77255%40googlegroups.com.