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Free fall brake?

Question asked by Tom Hickerson on Apr 5, 2017
Latest reply on Aug 17, 2018 by Dwight Livingston

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I have a machine that travels vertically up and down. Id like to have some sort of brake to stop the moving portion from going into a free fall if things break when we have some type of failure. The machine is closed its not a safety issue, but it might damage itself if this happens. I want the design to be as simple as possible. Id like something similar to a fall arrest device used for people, but I don't know how well that would hold up going up and down all day every day. Fully loaded this mechanism will weigh about 1200 lb.

Any ideas?

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Dennis Dohogne Apr 5, 2017 1:08 PM
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Look up energy absorbers or shock absorbers. I think you might like what you find. They are compact, reliable, adjustable and often the most affordable solution.
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- Tom Hickerson @ Dennis Dohogne on Apr 5, 2017 1:23 PM
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  The energy absorbing devices are a good idea, but as the device is loaded the location where the free fall would damage the machine changes. I could use them at the bottom of the stroke, but by the time it gets there the damage would already be done.
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Christian Chu Apr 5, 2017 1:14 PM
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1200 lb - it's heavy - Have you thought of a lock cam
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- Tom Hickerson @ Christian Chu on Apr 5, 2017 1:25 PM
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  I just googled lock cams, and from what I found I am not sure what you had in mind. Could you elaborate?
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  - Christian Chu @ Tom Hickerson on Apr 5, 2017 1:34 PM
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    I assumed you use cam/follower or to move the machine up/down. if something happens, the cam shaft will be locked which stops the follower
    or leadscrew is a better choice for positive stop
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John Pesaturo Apr 5, 2017 1:43 PM
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Tom, we use these for our kiln covers ... Failure mode on them is locked. Any number of electric winches are setup the same way where the failure mode locks the motor but it's done through a series of pawls. Not to confuse this with a braking system which actually assists in raising/lowering by keeping tension on the line at all times but is not a failure mode system. Depending on the severity of what your looking to support, you could also look into elevators as they have by far the most redundant failure mode related systems on the market.
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- Tom Hickerson @ John Pesaturo on Apr 5, 2017 6:32 PM
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  I looked into elevators but I didn't see anything that translated over to my design.
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Dan Pihlaja Apr 5, 2017 1:49 PM
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What is the source that moves your machine up and down? A cable? Like an elevator? Or is it a slide mechanism driven by hydraulics?

If it is a cable, you might be able to rig something up like an elevator uses, in which a spring loaded mechanism is held in check by the cable pressure (i.e., the weight of the machine), but once that pressure is released, spring drive brakes out the side into the wall, which has arresters in it to stop movement.

If hydraulics, then can you set something up that senses a pressure drop and throws a brake in a similar manner?
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- Tom Hickerson @ Dan Pihlaja on Apr 5, 2017 6:33 PM
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  The device you describe for the cable is what I tried to find. I have no idea what its called, and my google skills didn't lead me to find it.
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  - Dan Pihlaja @ Tom Hickerson on Apr 6, 2017 8:56 AM
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    Well, here's the patent on it. LOL Ye Olde English!
    
    Edit: forgot to add the link:
    https://www.google.com/patents/US31128
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    - Tom Hickerson @ Dan Pihlaja on Apr 6, 2017 9:22 AM
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      Awesome Thanks. I wonder how they drew the sprocket in 1861!
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Mike Pogue Apr 5, 2017 2:00 PM
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A centrifugal brake would drop the machine gently in the event of a failure.
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Rick McDonald Apr 5, 2017 5:33 PM
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What is the range of the lift?
Can you show a picture?
As Dan asked - what is the drive source.
Are there guides or a framework that can be clamped on to?
How far would it fall before you would want to break it? (if you are moving 5 feet it's one thing, if your are moving 30 feet is something else).
What would cause it to drop (power loss, cable breaking ...?)
For a power loss, you could have a solenoid that would have a spring loaded plunger, that if the power was lost the plunger would push out and activate a pin or bar or some other breaking mechanism (we have done this on a smaller scale and it works well). When power is on it pulls in the plunger to allow the lift to move.
More information would be helpful.
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- Tom Hickerson @ Rick McDonald on Apr 5, 2017 6:29 PM
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  Its lifted by a servo motor , gearbox , belt drive, and finally the lifting belt wrapped around a spool.
  Its guided by hevi rail bearings (very similar to a single stage forklift mast)
  Maximum fall would be about 8 feet
  The fall could be caused by a failure of the servo internal brake, gearbox failure, drive belt failure. There are two lifting belts.
  The servo motor should kick in its own brake on a power loss so the most likely failure would be the drive belt or gearbox failure.
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  - Ben Stutzman @ Tom Hickerson on Aug 16, 2018 10:41 AM
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    I have been searching for answers to this same question. From this description it sounds like I have the same type of drive system. Did you come up with a solution to the problem?
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Dwight Livingston Aug 17, 2018 11:13 AM
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Tom

I suggest a counterweight. If the live load doesn't vary much, you can simply balance the load and let friction stop the system if you loose power. You also get savings for both power requirements and wear.

Dwight
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Free fall brake?

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