[time-nuts] OT stuffing boards: was GPS interface/prototyping board

[Bob Camp]

Hi

The vision stuff comes in a few ways:

1) Your board needs to be aligned to the machine. There may or may not be accurate holes in the board to do this. 
Doing it with holes still leaves you with the need to get the board location “into” the machine’s coordinate system.

2) Tapes come in fairly fixed widths. The pockets on them likewise are not as custom as you might think. An open loop 
system may or may not grab a part accurately as a result. With lead free solder, surface tension may not be as big a
help as it once was. 

3) For large / fine pitch IC’s the orientation and location process becomes even more difficult. Trays are not very accurate. 
Surface tension compared to the weight of the part does not have the “pull” it does on an 0402 resistor. 

Do you *need* vision in all cases? Of course not. That’s why they sell machines without vision. Doing stuff at 0.5 mm pitch
and below fully open loop can be a major pain without vision. 


> On Jun 25, 2016, at 12:28 AM, Mark Sims <holrum at hotmail.com> wrote:
> 
> I have seen pick and place systems built around  CNC machines (same applies to 3D printers).  The reel strips are fed through a slotted guide.  The pickup head has a finger (or some use the pickup nozzle... a flat tipped hypodermic needle) that is used to advance the reel.  It drops down into the component pocket on the reel (or the index holes) and pulls the strip forward one pocket length.  This movement also peels back the tape cover strip.  The nozzle moves to the center of the pocket,  sucks up the component,  rotates it,  moves to the position on the PCB, and places the component.
> 
> Translating the design files into gcode commands for the required head movements is a fairly trivial bit of code (says the man (me) who wrote a 90,000+ line C program that can translate between the dialects of over 100 different CNC machines, 3D printers, and CAD programs).

Good of you to volunteer for the next re-write of OpenPnP …:)

Bob

> 
> Vision system is nice,  but a decent CNC is more than accurate enough for 0402 sized parts.  Again, surface tension is your friend.
> 
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