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# Multiple Elevator Cars Per Shaft

Each elevator -- and counterweight! -- winches the one underneath.
 (+1) [vote for, against]

Synopsis: See Description underneath Title.

Details:
Imagine an ordinary elevator shaft, which has a powerful electric winch at the top, and a cable supporting the cab. Note that this is not the whole story; there is a second cable coming from the winch, that supports a counterweight. This counterweight is generally shaped like a thick rectangle, and slides up/down along one wall of the shaft (always missing the cab, of course); it also has somewhat more mass than the cab, such that when the cab holds an average number of people, THEN the masses balance. When either is lifted in the shaft, the other is let down. The electric winch has a comparatively easy time doing this, and only needs to be powerful enough to handle the maximum people-associated difference in mass between elevator cab and counterweight.

For this Idea, we require winches that are rather more powerful than normal. Also, each winch motor must actually be a motor/generator, as will be explained shortly. Finally, certain elevator cables also need to be quite a bit stronger than normal. Then all we need is some fancy computer software and control circuitry, along with standard elevator-safety equipment (if a cable breaks, certain levers that depend on cable tension are released, causing a cab to physically latch onto the walls of the shaft).

Let's consider a 40-floor building, and a single elevator shaft with five cabs in it. (This is not to imply that the building only has one elevator shaft; it is that I only need to describe one. :) The spacing between floors is such that a simple stack of the five cabs can simultaneously serve any five consecutive floors, depending on where the stack is located in the shaft. As you will see, there is reason to fill this building with such a variety of destinations that the people living and/or working in the building will not need to frequently leave the building.

Inside the shaft, starting at the top, we have two Primary Winches. Each controls one cable, one leading to the topmost cab in the shaft, and the other leading to the topmost counterweight in the shaft. As mentioned, the motors for these winches have to be extremely powerful, and they also need to be motor/generators. Finally, cables need to be extra thick and strong, and long enough to let the topmost cab reach down to the fifth floor (not counting any basement floors).

Next we have the topmost elevator cab and counterweight in the shaft. Embedded in the floor of the cab is another winch, with a very powerful motor/generator. Also, attached to the lower part of the counterweight is also another winch, again with a very powerful motor/generator. Only one cable leads from each of these two winches; they do not need to be quite as strong as the uppermost cable, but they are as long, able to reach across 35 floors of this building.

Next, lower down in the shaft, we have another elevator cab and another counterweight, supported by those just-described cables. These are also equipped with winches and motor/generators, although they do not need to be quite as powerful as the uppermost pair. Also, again the cables that descend from here don't need to be quite as strong as before -- but still 35 floors long.

Repeat for three more elevator cabs and counterweights, except of course the bottommost ones do not need any attached winches, cables, etc. And each motor/generator and cable that IS included can again be somewhat less powerful/strung than the one above it.

OK, now to describe this system in action!
40 counterweight5
39 counterweight4
38 counterweight3
37 counterweight2
36 counterweight1
...
5 cab5
4 cab4
3 cab3
2 cab2
1 cab1
Here we have all the cabs together at the lowest floors of the building, and their associated counterweights are at the highest floors.

40 cab5
39 cab4
38 cab3
37 cab2
36 cab1
...
5 counterweight5
4 counterweight4
3 counterweight3
2 counterweight2
1 counterweight1
Now ONLY the uppermost winches have been activated, lifing the entire stack of cabs 35 floors, and of course allowing the counterweights to descend 35 floors. This is as normal as if there was just one elevator in the shaft, although as explained below, independent motor/generators are still needed here.

40 cab5
39 cab4
...
28 counterweight5
27 counterweight4
26 counterweight3
...
15 cab3
14 cab2
13 cab1
...
2 counterweight2
1 counterweight1
This is where we start to see the need for sophisticated computer control. The lower three cabs have descended 23 floors, while the upper three counterweights have ascended 23 floors. Obviously the winch underneath Cab4 has lowered the other cabs, but to raise the counterweights, both the Topmost/Primary Cab Winch (which pulls) and the Counterweight3 winch (which unwinds) have to be activated synchronously. Because motor/generators are used, the descending cabs generate electricity during their controlled fall in the shaft; and that electricity is used to lift the counterweights. The NET effect is much like an ordinary counterwieght system, with only a small amount of additional electricity needed to run the system.

It should now be obvious that cabs and counterweights can be spread all through the elevator shaft, as long as appropriate motions occur synchronously.
40 cab5
39 cab4
...
33 cab3
...
28 counterweight5
27 counterweight4
...
14 cab2
13 cab1
...
8 counterweight3
...
2 counterweight2
1 counterweight1
Here the only difference from the last situation is that Cab3 has been lifted 18 floors, while Counterweight3 has been lowered 18 floors. The Cab4 and Counterweight3 winches wound up, while the the Cab3 and Counterweight4 winches unwound. All the other units remain stationary.

In full operation, every cab can more-or-less independently move up and down the shaft. The computer program in charge needs to be quite smart, of course, and may even need to be neural-net based, to be enabled to learn optimum performance. If someone wants to descend 25 floors, well, perhaps it will be OK (few others using elevators at the moment), and perhaps the computer will only take the cab down 15 floors, and request that people exit to catch the next cab going farther down (perhaps in adjacent elevator shaft!).

As previously mentioned, a building that has this kind of elevator system is a building that should NOT be especially sectionalized. Some shops should be on every floor. Some business offices should be on every floor. Some apartments should be on every floor. An so on. People living in the building will probably be able to usually enter/leave with but a single cab-transfer, and sometimes none or two. But having a variety of needs met by close-by facilities, it could be that most of the time they won't want to go so far up or down as to need to change cabs at all. And thus the first miniature arcologies will come into being....

 — Vernon, May 18 2004

sorry. (-)
 — neilp, May 18 2004

 Vernon that picture 1000 word thing again.

What if you are on the ground floor and want to get to the top floor? if i understand your description you would have to change lifts.
 — engineer1, May 18 2004

 The idea is workable. The length of the post isn't :p

Create adjoining "up" and "down" shafts such that many lifts could occupy the two shafts. Really old lifts do this, with a continuous stream of cars going up one way and down the other. Maybe it'd be worth updating this idea to meet modern safety standards.
 — david_scothern, May 18 2004

This has been developed by an elevator company. I'll see if I can come up with a link.
 — Laughs Last, May 18 2004

I needed a elevator just to get to the bottom of this idea,and one just to get back up here again.
 — skinflaps, May 18 2004

 [engineer1], yes, the main text does state that changing cabs is a likely event in many cases. One possible modification to this idea is to have a 35-floor building with a 5-floor underground parking gararage. Then you park at the appropriate level and you CAN catch a single cab to take you to your desired floor. Still, in any really tall skyscraper, it is not feasible for a single elevator to cover all the floors, so certain floors are designated a places where people must change cabs, when accessing sections of the building-height. Here almost any floor can be a place to change cabs, especially if there are two adjacent shafts running multiple cabs.

 I might also mention that my description of 5 cabs in a 40-floor building may be a bit much, because the same cable stresses that prevent single cabs in a 100-floor shaft could be expected to prevent that many cabs in a smaller shaft. However, I did want to make it clear that the multiple-cab idea can work for more than two.

 [david scothern], dedicated adjacent UP and DOWN shafts is another idea I've played with over the years, and I do know of a safe way to implement it, even as a no-cable elevator system. I was about to start writing it down for the HalfBakery when THIS notion occurred to me.

[Laughs Last], that link does indeed lead to a similar notion, but since details are missing there, that one is rather WIBNI-like. You can be sure that when I write down that other scheme just mentioned above, it will be as detailed as this. And if some outfit has really implemented the trick desribed here, fine; I'll delete this as being baked and insufficiently original (but it IS independently original).
 — Vernon, May 18 2004

 Dont forget though, that while any given cab has stopped, loading/unloading passengers, it effectively limits all the ones above it to the floors above it, and all the ones below it to the floors below it. Thus if you get on cab5 at floor 40 intending to descend to say floor 20, you might have to wait at floor 38 because cab 2 is loading on floor 37 etc etc. Basically you have created a queuing mechanism for elevators. The saving on the number of shafts required would probably be more than outweighed by the departure of all of the tennents when they get sick of waiting in the queues for ages.

Why not create a computer/mathematical model of this system using real data about the number of people entering/exiting at each floor and their intended destinations. Using this I suspect you could demonstrate by what (huge) factor the average waiting + journey time would rise.
 — dobtabulous, May 18 2004

[dobtabulous], your argument regarding delays seems to be based on the faulty assumpton that there is only one multi-cab elevator shaft in the building. Next, On The Average, I would expect that with 5 elevators for 40 floors, each would spend most of its time going up and down among about a dozen floors, with occasional longer journeys. Also note that it could well be that a shaft with 5 cabs is too many for a 40-floor building (the main description was mostly to show that that part of the Idea was workable, not that it was optimal).
 — Vernon, May 18 2004

 vernon this just looks like a great way to build a disaster movie...

Cable snaps lift plummets hitting next lift in shaft. Fire breaks out the lift shaft becomes a chimney.
 — engineer1, May 18 2004

ONLY in a movie, [engineer1]; ONLY in a movie. In real life elevators do indeed have mechanical means of automatically becoming immobile in the shaft, if the cable that support it breaks. This safety gadget was what got people to finally trust elevators --which existed and were quite dangerous for years before Mr. Otis patented that gadget.
 — Vernon, May 18 2004

So [Vernon], if the advantage isn't in saving on shafts, what on earth is it?
 — dobtabulous, May 18 2004

[dobtabulous], a big building presently may have half a dozen or more elevator shafts. Count the cabs! Now cut the number of shafts in half, and triple the number of cabs. There WILL be advantage to that! Also, consider that the computer program that controls this elevator system should have control over at least two shafts. It can then ensure that if passengers must move to another cab, then both cabs arrive at the same time, at some appropriate transference-floor.
 — Vernon, May 18 2004

[+] ... the Summary helped; I imagine you'd want a small coffeeshop on the changeover floor.
 — FlyingToaster, Nov 12 2010

Personally, I like my "Multiple Cab Elevator Loop" Idea better (it's at upper right of this page). It still allows multiple cabs per shaft, but is rather simpler (NO winches, cables, or counterweights!).
 — Vernon, Nov 12 2010

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