Ideas sought for arresting the fall of a large mass
Ideas sought for arresting the fall of a large mass
(OP)
Hi
We are developing a machine that involves a mass of the order of 300-400 tonnes suspended on cables. The mass will be lowered at a constant acceleration of about 0.5g to a maximum velocity of 12m/s. We need to have a secondary system that is able to trim the velocity of the mass should it exceed the maximum velocity, or to arrest its fall should the acceleration exceed the design value (i.e. if one of the suspension cables fail).
Does anyone have any ideas about how this could be done? We are thinking about secondary ropes that reel from drums at the top of the shaft and which are monitored and braked if neccessary, or maybe using caliper brakes just like a lift. Is there anything else that might be suitable, or has this situation been solved somewhere else already?
Any help is greatly appreciated.
We are developing a machine that involves a mass of the order of 300-400 tonnes suspended on cables. The mass will be lowered at a constant acceleration of about 0.5g to a maximum velocity of 12m/s. We need to have a secondary system that is able to trim the velocity of the mass should it exceed the maximum velocity, or to arrest its fall should the acceleration exceed the design value (i.e. if one of the suspension cables fail).
Does anyone have any ideas about how this could be done? We are thinking about secondary ropes that reel from drums at the top of the shaft and which are monitored and braked if neccessary, or maybe using caliper brakes just like a lift. Is there anything else that might be suitable, or has this situation been solved somewhere else already?
Any help is greatly appreciated.





RE: Ideas sought for arresting the fall of a large mass
RE: Ideas sought for arresting the fall of a large mass
I do not know what exactly the device is, or exactly how it works, but it is something you can checkl into.
Crude idea - if this involves a true potential emergency, one crude back-up might be a parachute.. probably a dumb idea, but it never hurts to think WAY outside the box just to get a new direction.
RE: Ideas sought for arresting the fall of a large mass
<nbucska@pcperipherals.com>
RE: Ideas sought for arresting the fall of a large mass
If a guiding system is present, then you could consider the elevator parachutes suggested by others, or a kind of shock absorber (if the falling height is not excessive) or an eddy current brake with permanent magnets: this is used in the free fall towers in amusement parks and its main characteristic is the very high reliability, as it requires no power nor mechanical actuation to perform its action.
prex
http://www.xcalcs.com
Online tools for structural design
RE: Ideas sought for arresting the fall of a large mass
I think that in the event of the mass accelerating outside the design range (either because of a suspension rope failure or as part of normal operation) the mass does not need to be brought to a halt, but it certainly must be prevented from accelerating any further so that it becomes a controlled descent. Caliper brakes do seem to be a obvious choice (which could be triggered by an external monitoring system) and provided that they can generate a total reaction equal to the mass times 1g then it should prevent the mass from accelerating further.
However, this machine will operate every 80 seconds and there is a possibility of the weight accelerating outside the design range every time. I would be worried about heat build up/premature wear that a normal caliper brake would have to endure and so I am wondering if there is any other system/material that might be able to generate such high reactions quickly and repeatedly without problems.
RE: Ideas sought for arresting the fall of a large mass
RE: Ideas sought for arresting the fall of a large mass
To limit the velocity reliably I'd look at Hush's idea.
Probably we'd all be a bit less vague if we had some idea of what you were trying to do.
Cheers
Greg Locock
RE: Ideas sought for arresting the fall of a large mass
This sistem must be mounted on separated bases and joined
to heavy weight(Cables) with two degree of fredom.
RE: Ideas sought for arresting the fall of a large mass
RE: Ideas sought for arresting the fall of a large mass
Think of a column, of suitable mass, free to rotate about its base and somehow connected to the falling mass. I'll leave the somehow part to you. Now you have the kinetic energy of a rotating mass, controlling the rate of decent of a falling one.
BTW, if you aren't aware, O-O-B is the latest buzz word in "Problem Solving!" I added the 'T' and 'S' bits!
RE: Ideas sought for arresting the fall of a large mass
RE: Ideas sought for arresting the fall of a large mass
I meant to say a column pivoted, not rotated, at its base, like a felled tree, only it can be initially positioned anywhere in its 360 deg range of motion, i.e., +Y, -Y +X, or -X, and 0,0 is the pivot point!
Now, go out and amuse!
RE: Ideas sought for arresting the fall of a large mass
RE: Ideas sought for arresting the fall of a large mass
After two weeks, I would like to add an idea,
What about using a motor and a regenerative variable frecuency drive to absorbe the energy in the system. In that way, you can give back to the electrical circuit the energy to be disipated, and you can control the amount of torque to be used and thus the tension on the steel rope. I have not done the numbers on the economical meaning of the electricity, but it sounds like an interesting idea. Another posibility is to use the energy to move a big blower, since the blower will have a cubic law against speed, it will achieve equilibrium with your falling system at some point (with some calculations, not so fast, I expect)
sancat
RE: Ideas sought for arresting the fall of a large mass
Think of the spreading opposing rails used on other amusement park rides such as roller coasters used to retard car movemement as an example.
RE: Ideas sought for arresting the fall of a large mass
RE: Ideas sought for arresting the fall of a large mass
Is there a relation between your project and the new thrill ride "the Sky Swatter" in Utah, mentioned in the April issue of "Popular Mechanics?"
RE: Ideas sought for arresting the fall of a large mass
RE: Ideas sought for arresting the fall of a large mass
Cheers
Speedy
"Tell a man there are 300 billion stars in the universe and he'll believe you. Tell him a bench has wet paint on it and he'll have to touch to be sure."
RE: Ideas sought for arresting the fall of a large mass
I just came upon this thread in searching for something else. I have worked with a few different water brakes in the distant past. Basically these are a paddle wheel or tubine wheel arrangement immersed in a tub of water of glycol and connected to a cable or tape reel. Very repeatable, very reliable and fairly low maintenance. I've seen them used in oil rigs for exactly your application and also military applications (which is my experience). These might be adaptable to your project. If you are still looking for ideas, I might have some for you. Write back if you do.
TC7
RE: Ideas sought for arresting the fall of a large mass
To control speed descent, take a look at the lifeboat lowering systems which use a centrifugal brake pad arrangement to control lowering speed, the disadvantage here would be the high heat loads generated.
RE: Ideas sought for arresting the fall of a large mass
RE: Ideas sought for arresting the fall of a large mass
if there is an opportunity in it for them, they'll be more than glad to assist you..
RE: Ideas sought for arresting the fall of a large mass
RE: Ideas sought for arresting the fall of a large mass
RE: Ideas sought for arresting the fall of a large mass
You could even have some fun with the exhausted air from the air bag. i.e. blow up a big balloon
Or a water bag that would drive a big fountain and shoot a jet of water into the air?
Rick Kitson MBA P.Eng
Construction Project Management
From conception to completion
www.kitsonengineering.com