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

bownes bownes at gmail.com
Sat Jun 25 13:16:41 UTC 2016


And try to tell transistor A from transistor B from diode C when they are all upside down. 

A moving head design can be made to pick up parts off of reels on all four sides. But it takes more table space. Which is money. 

As someone else said, you need Z rotation, which isn't as easy as it sounds when using pneumatics to pick up the part. 

Moving table design sounds like a recipe for shaking the parts off the solder pads. I've not had good luck with solder paste staying tacky for long. In which case you are dispensing paste then sticking part. Not a deal breaker but slow. 

> On Jun 25, 2016, at 04:12, Adrian Godwin <artgodwin at gmail.com> wrote:
> 
> 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>
> wrote:
> 
>> 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
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