Only half kidding; the power room of a Titan I missile site would just
about do. 55 F year around. IIRC the measuring system needs about 4X the
resolution of the tolerance you need to hold. Concrete and steel have
approx the same thermal coeff of expansion.
I like the idea of access to a major waterway. I really could not
believe it when the contractor for the new sections of the Narrows bridge
opted to ship by truck. ( I90 Chicago to Tacoma) Got held up for quite
a while at the WA border while everyone fought of regs and paperwork.
My thought was the they had decent waterway all the way and basically
could have lifted them off the ship ... or off a barge into place.
But then what do I know. Politics and logic are rarely in the same room. ;-)
Most interesting project.
Dave
On 08/23/2017 09:59 AM, Dave Cole wrote:
Sounds like you have a budget and if you are willing to put up a tilt
up building and temperature control it, you have some money to spend.
There was money to spend on the system I was quoting about 9 years ago
until the DOD budget was slashed, then it all went away. I got
Siemens involved and they had no issues tying a laser tracker into
their CNC system. The router was a 5 axis design. We were using
standard Siemens servo drives connected via Ethernet/Profinet on Fiber
optic cable. The actual control system will not be the big cost for
your system. The drives and mechanical system/gantry and building
will be much more costly. The laser tracker was some serious cash as
well, but not much compared to the building and gantry and framework.
Siemens had all of the CAM software required as well.
It can be done. All of the technology existed 9 years ago. But
there is nothing cheap about it.
If you are really going to do this, you might want to make sure you
have flexibility designed into the system so you can do multiple
processes with your system. Welding, cutting, routing, etc. Being
close to a waterway might be a good idea as well. Huge things don't
fit on semi trailers very well.
Dave
On 8/23/2017 12:19 PM, Rick Gresham wrote:
The building will likely typical concrete tilt-up or something
similar. The system will have to track/control position in real
time. Collisions will be very expensive so redundant systems are
easily justified. It may need some sort of collision avoidance
system as a back up, too. If the crosses some boundary, everything
stops. Stoppages are not a big problem, bumps in the dark are.
I've wondered about redundant control systems but haven't come across
any information yet. Anyone remember the triple Tandem non-stop
systems NASA used? Three fault-tolerant systems running in
parallel. If they came up with different results, it was
odd-man-out. Probably don't need to go that far for this
application unless something available off the shelf affordably.
On Aug 23, 2017, at 8:56 AM, Chris Albertson
<albertson.ch...@gmail.com> wrote:
There are many ways to measure position. With something this big and
expensive I would suggest some redundancy. The cost of measuring is
tiny
computer t the cost of a 100f gantry.
One of the bigger problems I see is flex in the system and thermal
expansion. If the goal is 1/8th inch over a 100 foot run then
their needs
to be some design margin so you'd be designing for something like
1/16th
inches.
I doubt that simply measuring how for you are along a steel bed will
work.
Yes you could try but the beam itself will bend and change it's length.
You would have to measure absolute position relative to fixed
locations on
the floor.
I don't think I've ever seen a building made to close tolerances
either.
The sports are not going to be square to each other or level or
vertical.
I't not hard to compensate for the not-perfect mechanics. You can also
continuously calibrate the sensors from know references inthewtork
space
On Wed, Aug 23, 2017 at 2:21 AM, andy pugh <bodge...@gmail.com> wrote:
On 23 August 2017 at 05:17, Dave Cole <linuxcncro...@gmail.com>
wrote:
A 3D laser tracker was part of the control scheme to track the actual
tool
head location.
That way standard rack could be used for the positioning mechanism
and
the
position could be corrected on the fly via the laser tracker.
That might still be a good idea, because it seems that such a machine
might need to be modular, so units that are friction-drive on standard
rolled steel sections seems like a likely solution.
There will be some tyre-creep, but the laser (or acoustic) feedback
could correct it.
I heard of a system where you have a microphone in each corner of the
room and a "clicker" that is localised in space by clever acoustic
processing.
The application was measuring accelerometer positions when
instrumenting a car or van body. If you have ever "walked" a Faro arm
round a van body you would know why the system seemed attractive.
--
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916
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