[time-nuts] pick and place problems/design (was: OT stuffing boards)
artgodwin at gmail.com
Sat Jun 25 04:12:41 EDT 2016
Many parts can't be recognised visually. Capacitors are the obvious example.
On Sat, Jun 25, 2016 at 6:11 AM, Chris Albertson <albertson.chris at gmail.com>
> The ideal hobby use pick and place machine would be very different
> from a commercial machine. Lets say I want one board made. What I
> want to minimize is my time. With a conventional machine by FAR most
> of my time is spent setting the machine up. In fact setup is so slow
> that for smaller PCBs I could do it with tweezers in a fifth of the
> time needed to set up the machine.
> So a hobby machine must be designed such that you could get it going
> in nearly zero time. In the ideal case you drop the parts all mixed
> up, (but right side up) in a small tray. They are mixed and in random
> orientation. then you give the machine your PCB design file (not a
> special pick and place file) and then a vision system IDs the parts.
> Today vision is dirt cheap.
> But the 3D printer needs one more degree of freedom. It must be able
> to rotate the part (or the PCB) as it is unlikely the part on the tape
> or tray only needs translation to the PCB, likely ration is required
> in almost all cases.
> I think a hobby machine would only be successful if it could reduce
> the setup time to nearly zero and for that it would need a really good
> vision system that could hunt down randomly placed parts. It would
> have to work pretty much like you or I would do the job manually. But
> we have software like openCV and good "board cams" with M7
> interchangeable lenses for $35. A vision system actually saves a ton
> of money because the machine need not be so precise as vision closes a
> feedback loop.
> Also how many hobbyists are going to have reels of parts? I might buy
> some parts by the dozen but most no more than about 4 or 6 at a time.
> I don't want a large machine. It should have a working surface, a
> white melamine table about 12 inches square and I place the PCB to be
> stuffed and all the parts on the same foot square table at any random
> location then press the "go" button. The camera scans the table.
> This kind of machine would be horrible for production work but a one
> foot cube machine that required zero setup is what most of us want.
> Going a little farther. I'd like this SAME machine to actually make
> the PCB too. A 3D printer could route the copper and drill holes and
> print the solder resist plastic too.
> On Fri, Jun 24, 2016 at 8:56 PM, Attila Kinali <attila at kinali.ch> wrote:
> > On Fri, 24 Jun 2016 13:59:58 -0500
> > "Graham / KE9H" <ke9h.graham at gmail.com> wrote:
> >> Lots of problems to be solved...
> > Most of these problems are easy:
> >> How do you take loose parts or cut tape or tape reels
> > You don't. No loose parts with any kind of pick&place machine.
> > As for cut tape, these can be taped on an empty reel to make
> > them compatible. Everything has to be in a tray, reel or similar.
> >> and get the right
> >> part out, and into the chuck, oriented in the right direction?
> > Orientation is defined by the reel/tray the parts come in.
> > This is also documented in the datasheet, usually.
> >> How many different kinds of parts, sizes, shapes, pin counts, IC
> >> footprints, can you handle at once?
> > As many as there is space around the machine :-)
> >> How do you know it is the correct part?
> > You put it manually in the right feeder and double check that it
> > fits the programming.
> >> How do you know where the "+" end, or "pin 1" is?
> > This comes with the orientation of the part in the reel/tray.
> >> How do you know that there actually is a part in the chuck?
> > Your trays are guaranteed to be non-empty by manually loading them.
> >> How do you know the part in the chuck is oriented the way you expected
> > The manufacturer guarantees that the reels/trays are loaded correctly.
> >> How do you know where the footprint on the circuit board is located?
> (to a
> >> few thousandths.)
> > This is provided by the pick&place file. Usually its 3-5 digits after the
> > decimal point, when using mm. But as I wrote before, you don't have to
> > place part hyper exact. Being within 0.1-0.3 of the pitch of the part
> > is usually enough. Surface tension does the rest.
> >> How do you know the part left the chuck and ended up where you intended
> >> to be?
> > You dont :-)
> > The way how this is checked is either a pre-solder and/or post-solder
> > inspection. This is either done manualy or using a camera system where
> > computer compares the PCB to the picture of a known-good PCB.
> > As this is ment for a small volume and hobbyist system, doing the visual
> > inspection manualy is good enough and more than fast enough.
> > Attila Kinali
> > --
> > Malek's Law:
> > Any simple idea will be worded in the most complicated way.
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> Chris Albertson
> Redondo Beach, California
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