Henry Liu wrote:
> What's a good pneumatic dispenser? If it has an electronic on/off
> switch, I hook it up to my cnc with a relay + M code switch.
>
Positive displacement pumps are the most accurate, time/pressure would
probably be good enough. Epoxy is often dispensed with a stamp, that
might work for you.
> I think if I do it a lot then I'll just program my cnc machine to do
> it like this guy: http://www.youtube.com/watch?v=HdqVt0jCBHk
>
> I think it's pretty easy, just move X,Y,Z down activate dispenser,
> move up Z and move to next XY in a loop.
>
That's how I drill my boards. I use a commercial XY table, and a home
built Z stage with a Dremel attached. A PIC receives NC drill data from
a laptop and drives steppers with Allegro A3955 chips. After it mills
out the board, I transfer toner and etch.
> If I can source a good vacuum pump lift I can place the part too. I'm thinking:
>
The Laurier machines I worked on (HA225, HA250, DS3000) used a venturi
when house vacuum wasn't available.
> Pick and place machine
> 1) put components randomly on flat white background on top of rotary
> table (http://www.sherline.com/8700inst.htm)
> 2) mount camera on CNC spindle
> 3) segment image
> 4) detect lines using hough transform
> 5) rotate plate using rotary table to align lines either 90 degrees or 0
> 6) resegment image to find centroids of objects
> 7) move spindle over and pick it up with vacuum chuck
> 5) drop it on centroid of pcb
>
> I write image recognition software all day long at work so the
> software is no problem but not so sure about the lift/drop.
>
The lift and drop are easy, but unless vision software has made amazing
strides in the last 10 years, you need parts to be at least close to
correctly oriented. With the Acumen system we used, +/-15° was about
all you could expect. And watch out for vibration. Parts can slide
while the rotary table moves if they aren't in a Gel-pack.
On the HA225, we offered a manual procedure. A Lazy Susan centered
under the camera with a pedestal with parts on it sitting on that. Find
the part, rotate, step on footswitch. Worked great.
Kerry
> I think I'm getting ahead of myself though as I probably will only
> make a few boards a year lol.
>
> Too many projects, too little time...
>
> Cheers,
> Henry
>
>
>> I tried a stencil when the board house offered it free with the PCB,
>> one board turned out quite good but for the second the stencil didn't
>> lie flat and it was a mess. I'll stick to the syringe in the pneumatic
>> dispenser for now. If you do more than ones and twos the stencil
>> probably pays off.
>>
>> ST
>>