RE: [CAD_CAM_EDM_DRO] Robotic Arm

I haven't built one, but I have just bought one for smt pick n place.

Perhaps a description might help some of you.

It has four axes and lots of fiddly bit.

On the right hand side of the machine is a long linear carousel that holds
all the parts on reels. The carousel moves along the Y direction of a mill.
As each part is moved past the pickup point, a pneumatic plunger can be
raised to advance that part. The reels have tapes holding the parts, the
sides of the tape are punched like photographic film, and an adjustable
ratchet mechanism advances each part if it actuation lever is hit by the
plunger.

The PCB table sites to the left of the parts carousel, it also only moves in
the Y direction. It is independent of the carousel so both can be
positioning themselves at the same time, but for a slower machine they could
be allowed to move together.

The pickup head moves in the X, and Z direction. It holds the part with
vacuum, on a nozzle, a bank of nozzles are mounted on the back of the PCB
table, and it can automatically select the correct nozzle for the component.
Two pairs of tweezers at 90 degrees to each other also meet with the part to
position it. The tweezers are cut with steps in them and can be moved in the
Z direction to decide what part they are going to grip with.

For all parts the vacuum pressure is adjustable, the pressure the head
places down on the part to pick it up, the pressure it presses it down onto
the PCB.

There are also syringes for glue and solder paste that are operated by a
controlled plunger on the head.

Theres are also cameras, and error checking software that checks the place
part matches with the picture in memory.

The pickup vacuum has a sensor to check whether it has actually grabbed a
part.

IC chip parts holders have the chips in alloy channels with vibrators to
rattle them down to position.



I think that about it. My machine is a 90's model so not new, but low
mileage and came at a good price. The manufacturer claims 4000 to 4500 parts
per hour, but 3000 is more like it.

It's quite quick, though positional accuracy is about a thou, now where near
as accurate as a mill, and if you get it that close, the part will normally
float to position by the surface tension of the solder paste when molten in
the oven

Newer machines will to 15000 plus parts per hour, many have multiple heads
to achieve this so they put several parts down at the same time. They also
have much better photographic recognition.



Now I have one, I realise it is quite a task to build one, not difficult,
but there's one hell of a lot of work for a one off. Just the parts holders
are complex enough.

Anyhow that should give you something to think about.



Dr. Mark Vaughan Ph'D. B.Eng. M0VAU

Managing Director

Vaughan Industries Ltd, reg in UK no 2561068

Water Care Technology Ltd, reg in UK no 4129351

Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH, UK.
Phone/Fax 44 1872 561288

RSGB DRM111(Cornwall)

_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of roboticscnc
Sent: 25 March 2007 21:38
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Robotic Arm



Hi Group,
Has anyone built a robotic arm for pick & place ?
Is it possible to teach ( digitize ? ) Mach 3 to control one ?
Could a conversion ( Macro ? ) be used to generate X,Y,Z positions
from X,Y,Z co-ordinates in G Code ?
I've looked around for different software ( EMC, etc. ) but can't find
much info for home built machines. I've been using Mach 3 for a while
so this helps with the learning curve but eventually it will be asked
to do a routine from a PLC, in which case linux may be a better choice ?
Thanks,
Glen.





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