Re: Stewart Platforms...

Hi Jason

>    From: "killthiskid" <jaskew@...>
> Subject: Stewart Platforms...
>
> I've been lurking for quite some time, and read many a back
> messages.  It is at this point that I'm ready to ask:  what about
> stewart platforms, or less specific, parallel style CNC?
>
> Here's the thing:  I've read wide and far about the subject.  I work
> at a university, and have gone deep into the many issues around
> paralell style machines, most specific the kinematics.  
>
> There are a few mentions of hexapod type machines, but no real
> discussion.  Having said that, I ask these questions:
>
> Is any one using or exploring parallel type machines?  If so, of what
> type?  3-3?  6-6?  And if you are, what type of software/hardware are
> you using?
>
> Thanks.  I am seriously impressed with the amount of knowledge shared
> on this forum.  I have already learned a great quanity about CNC.

There have been a number of these built over the years since Stewart
studied and published about the breed. Dave Anderson and I ran the NIST
cable hexapod at NAMES for a couple of years. There are a couple of
photos of larger cable versions on the NIST site. The latest is a 30'
triangular platform that moves around a couple of hundred foot work
envelope using winches.

I also visited a friend who works in a rather amazing lab in Stuttgart,
DE. There were a couple dozen Stewart platforms of various geometries.
One of them stood 16' tall, used fixed length struts, and at least a 2'
cube work envelope. A Swedish firm was installing an eight or nine axis
machine with some Stewart characteristics while I was there. You can see
just a bit of his work at

http://www.isw.uni-stuttgart.de/personen/t_franit/primodell/index.html

(There is a little English flag icon on the bottom of the left frame)
One of these is in a display cabnet and visitors can press the button to
see it run around and do it's thing.

The EMC has the ability to do the inverse kinematics required by stewart
platforms to take in xyzabc commands and turn them into motion splines
for each of the motors. There are sample matrix files in the repository
for at least two platforms. There is also the ability to do forward
kinematics and a sample matrix for one Puma robot.

Hope this helps.

Ray