The workers at the Ballard locks in Seattle used to use these because of some safety regs (for a short while). They all hated them because they jammed up all of the time.

Wish I knew the name of the mechanism they used, it looked interesting enough to get me talking to one of the workers about it.

Edit- the best I can find is either something called a 'starpass glider' mentioned on page 14 of http://s7d9.scene7.com/is/content/minesafetyappliances/Horiz...

or http://www.saferack.com/lifeline-cable-systems-fall-protecti...

The system I saw at the locks seemed like a better engineered system, from what I remember.

I wonder if that image is in public domain. Might be nice to add to the page.

Is it? I don't know how to look for whether a photo is in the public domain, but I did just Google with the image. https://encrypted.google.com/search?tbs=sbi:AMhZZisuyc26lmhJ...

I linked to it from here: http://www.drgoulu.com/2005/12/29/eviteur-daxe/ .

How is the top curved portion (that "cable to mine" connects to) affixed to the gear and thus the other half of the cable? I can't tell from the picture. If it is simply connected to the gear axle, won't that block the sweep wire from passing through?

The teeth of the wheel are holding on to it, and it looks like there are always two teeth inside the top.

Oh I see what you mean. The teeth slide through the curved channel, and are notched such that the channel is held in place. That is a clever design.

It's clever as long as you operate in a zero-friction environment :)

I'm wondering if the effects of friction could be mitigated by having ball bearings within the channel that the teeth pass through.

That's what I thought also. Wouldn't the amount of force pulling on the cable lead to some jamming as soon as the little spokes stopped spinning so freely?

No kidding:

"The device works by using a spoked, rimless wheel that allows cables to pass through as it rotates. The ends of the spokes are widened, and the cable is held together by a short curved sleeve through which these spoke ends slide."

I think the most interesting thing about that image is that the text seems to be written by hand. What excellent handwriting!