[time-nuts] pick and place problems/design (was: OT stuffing boards)

[Chris Albertson]

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 it?
>
> 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 it
>> to be?
>
> You dont :-)
>
> The way how this is checked is either a pre-solder and/or post-solder visual
> 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