wrote:
On Mar 15, 9:33 am, Ned Simmons wrote:
On Mon, 15 Mar 2010 10:05:04 -0600, "Pete C."
wrote:





"Pete C." wrote:
Ned Simmons wrote:
On Mon, 15 Mar 2010 09:34:07 -0500, Ned Simmons
wrote:
I'm working on a fail safe brake along the lines of an elevator safety
brake -- it will prevent a heavy load from falling if the supporting
roller chain breaks. I need brake pads that can be attached to the
device that will bear on a large rectangular tube column when
activated, 4 pads near the corners of the column. I found some rough
dimensions online of performance auto disc brake pads that are about
2" square, which seems appropriate. The four pads will be required to
support about 3000 pounds total.
Potential problems with automotive pads? Any suggestions other than
auto pads? McMaster has lining material, but I'd rather not design and
fabricate something that can be more easily purchased.
A picture of the device. The purple plates are 15x22x3/4 and there's
5/8" clearance between the plates and the gray column. No clearance
between the column and the yellow chain brackets.
http://www.suscom-maine.net/~nsimmon...Car100315a.jpg
--
Ned Simmons
The ratchet plate I mentioned in my other post could readily fit in that
5/8" clearance you have. Indeed, you could do one on either side, double
ratcheted, providing four ratchet surfaces and you could make the pawl
plates engage several teeth, so you should be able to handle any
possible load.
Looking further at your drawing, I'd take a close look at the two column
auto lifts and see if one of those might provide a good starting point
to modify for your application and save some work. These lifts are
remarkably inexpensive these days, ~$3k for a basic one.
Thanks, Pete. I knew I had seen those ratcheting safeties, but
couldn't remember where. I started looking at patents for auto lift
safeties and see that some use a slotted bar, which hadn't occurred to
me and looks promising.

For example:http://www.google.com/patents/about?...BAJ&dq=4331219

Re the auto lift as a whole, the most restrictive factor in the design
of this device was the available space. It also travels at a much
higher speed than an auto lift and supports very asymmetrical overhung
loads in some orientatiions. It was supposed to be a quick and dirty
prototype, but is morphing into a permanent solution, if all the
safety issues can be addressed. I wish I could say more -- the
manufacturing operation is pretty wild and metal related.

--
Ned Simmons

Ned, can we explore this a little further. Will the safety be such
that once activated, it will never be released? Or will the safety be
required to operate on a regular basis? The answer will point you in
the direction of the simplest device to solve the problem.

Knowing whether a failed safety will result in loss of life & limb or
just a bunch of product to be scrapped may help guide your thinking, as
well.

Any time I start thinking "life safety" I start getting suspicious of
hypothetical future maintenance folks, and the managers who approve
their time.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com