Brake Pad options

A few thoughts - If this is done like the drawing involving load rollers and chains against that column, there's going to be greases and oils about... Running any sort of a friction brake acting on that steel tubing column directly is simply not going to happen.

You could use a vertical toothed gear rack and a triggered pawl, just like the original Elisha Grey Otis "Safety Elevator" patent - but that was meant for slow freight elevators...

You'll have to design in some sort of a buffer to absorb the energy of hauling your lift to a stop when the pawl is engaged. Or it'll just strip all the teeth off the stop pawl and Pshhooom! down it goes.

If you can come up with a place or way to mount it that is relatively shielded from grease (Good Luck...) you could use a vertical brake fin on the device, and a clamp-style brake mounted on the structure, like on roller coasters. (Intamin design on California Screamin' at DCA would work great for this.)

The brake is a Linear 'Disc Brake' with two pads clamping together onto the fin mounted on the car, activated using standard Class 8 Truck spring brake air chambers.

How about a huge Acme screw and half-nuts setup? Or steal one from a Saginaw Gear steering box, a big ballscrew and a recirculating-ball nut on the lift arm? Like a worm-gear drive, you stop the motor spinning the screw shaft with a small motor clutch-brake and your load isn't moving anywhere barring mechanical failure. And it gets rid of the chain or cables, except perhaps to a counterweight...

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That's a term I'll have to remember.

"The expensive bit was broken by uncommanded motion into the workholding vise."

Ned, You should consider existing brakes first. Reinventing the wheel rarely makes economic sense. Check out Kobelt Manufacturing...they are excellent. Steve

How about a safety latch system. Real simple design. First weld a stop rack to the column. Only needs to be 1/2" thick or so. Then for the stop a simple rocker that is spring loaded. On the rocker you place two sprockets that will engage the chain. The chain running between the two sprockets holds the latch off the track. If the weight drops on the chain the weight of the latch drops it into place.

I OI I IO I

I is your chain, The Os are the sprockets. With weight on the chain the sprockets stay in this position.

I O/ / /O I

Chain fails and the sprocket and mount rock down and the latch drops into the track.

Wouldn't need to use sprockets if the space is tight. Simple nylon or UHMW plastic could be used as rubbing blocks.

Simple, Safe and easy.

Great description of those safeties. I think the cable grippers you are referring to are these:

Which are now regularly installed both in the Canada (where code required it first) the US and world-wide to prevent "unintended motion". I think these can accurately be described as "Safety brakes" because they actually use brake pads to slow the car to a stop over a controlled distance, as opposed to as fast as possible.

Interesting how terminology changes, I never heard of "uncommanded motion". I like the term "uncommanded motion".

Simple, higher pump output.

Exactly, in the new application you'd replace the basic hydraulic power pack normally mounted on the column, with a "real" industrial hydraulic power unit with a large tank and probably 10HP+ motor rated for continuous duty.

Thanks to everyone who responded. I still have to do some tweaking and check proportions and strengths of the various components, but this should be pretty close.

If the chain goes slack: the stack of Belleville washers (magenta) pulls the chain rod (gray) down; as the collar on the rod (gray) falls the arm (green) rotates CW; allowing the torsion spring to rotate the collar (gray) CCW; the pawl (green) rotates along with the collar and engages the slotted track (orange).

There was something very similar in one of the patents I looked at. Unfortunately, I have about .050" between the attachment points for the chain and the column.

I'd be surpised if it was that simple. At 1+ ft/sec an appropriately sized cylinder would be borderline for oil velocity with standard ports and full-size plumbing to match. Considering that the lift business is very competive, I doubt that the mfrs run 3/4" lines if

3/8" will do. On top of that, there's some sort of flow divider to keep the two columns in sync, which I'm sure is also sized for the actual flow, not 5x as big as required.

economic sense. Check out Kobelt

Thanks, Steve, I looked and didn't see anything I could use now. Quite likely there's something there that would have worked if the safety was designed in from the start, but as I mentioned elsewhere, this was a supposed to be a prototype and only to be run to prove out a concept. Not so anymore.

Take a look at an actual lift. There is no flow divider, there is a "T" connecting the two cylinders. Synchronization is provided by steel cables and pulleys much like on a drafting table.

Looks good. Not sure where the chains are attaching, but you may want to look at the lower spring loaded one and see if it should be a rigid mount, i.e. not spring loaded with different types of springs at each connection point.

Looks like a good solution. You might think of making the lower portion of the threaded rod as smooth as it can be. If the chain breaks it is likely to fly away and pull the threaded rod into a bind. A smooth, lubricated rod would probably not bind if pulled sideways.

Paul

There's a considerable amount of difference between locking the load in place once it has come to a stop and having the lifting gear fail (cable or chain break) if this load is already descending at a pretty good clip.

The chain runs in a loop, with the drive sprocket overhead and an idler at the bottom. The bottom spring protects the drive if the car overtravels in the down direction as a result of operator error or a control malfunction. The normal down position is about 1/2" over the floor. The spring allows the chain drive a couple extra inches of travel before the frame starts to lift if the car bottoms out on the floor.

And thanks for aiming me at the garage lifts.

>

That one of the required tweaks -- the originals are made from alloy threaded rod, and I just lengthened one for the layout. The new ones will need to have only enough thread on the lower end to adjust the chains.

Tim, having spent a lot of time living in or around the maintenance world, I'd say your suspicion is very well founded. The quality of maint techs and the safety ethos of management varies widely.

Wes

Does the number of belleville washers provide the travel you need? I'm used to seeing a large number of those things in drawbars to provide a small amount of travel.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller