On 11/14/2012 8:09 PM, Keith Mc wrote:
> Michael S wrote:
>> Just throwing the thought out there
>> ...
http://detroit.craigslist.org/okl/tls/3310661186.html
>> (On it, it shows:)
>> ... Spare hydropneumatic counter balance
> Now THAT sounds interesting. Please tell us about that tech!
>
> Does the controller monitor the motors for residual unbalanced
> torque, and continuously pump water in & out of "counterweight
> shells" via air pressure to compensate for it, or what?
Nope, nothing so complex. The second axis (the "shoulder") has to
fight gravity going forward or back. If you look at the picture, the
second axis is standing almost straight up, and just to the left of that
axis is a hydraulic cylinder with a Tylenol-shaped air tank above it.
That cylinder and tank are linked to the second axis, and set to a
pressure (varies for different payload models) that exerts nearly zero
force on the arm when the 2nd axis is upright, and "pulls" that axis
towards upright from either direction. Basically, the cylinder helps
prevent the axis servomotor from over-speeding when it's moving "with"
gravity, and helps assist the servo when it's moving "against" gravity.
The dynamic model that drives the servo includes the force of the
counterbalance and adjusts the servo accordingly.
If you look past the cluster of three motors up on the "elbow" of
the arm, you'll see a large black block of cast iron -- that's a plain
old counterweight that serves a similar, though less dynamic, role for
the 3rd axis.
>
>> Yes but while Laser cutters are wonderful, they can't: [...]
>> [...] paint children's faces
> Well, just in Carbon Black, and Blood Red... But I'd imagine
> that would be pretty darn painful (and permanent, and tacky.... ;-)
I can imagine a scenario where I might be willing to let it paint
my face... with a high-compliance brush, and holding a deadman switch,
with the robot in strict speed-limited mode. But it wouldn't satisfy
RIA safety standards. There *are* ways to *make* it safe for that sort
of application under RIA standards, but it would require additional
expensive hardware.