I work in a hotel and ride elevators upwards of 50 times a day. Never once has the bottom of the elevator been even a fraction of an inch above or below the floor where the elevator begins. Assuming there is a minimal amount of slippage in the cabling, how do the elevators move the exact same distance every single time? Is there some sort of cable/feet math going on where each floor is x amount of motor turns?
In: Engineering
There are a couple ways this can be achieved, here’s a common one:
The elevator knows that and which way it’s moving by an incremental counter that sends signals to the computer. Imagine basically the scroll wheel of a computer mouse pressed against the rim of the motor. As it moves, it “scrolls” along. It can be done a few ways, but this is the idea of it.
Now add magnets in the right positions at each door and a device on the cabin that looks for those magnets.
During initial setup, the cabin moves up and down the entite lenght slowly, remembering how much the scrollwheel moved from one set of magnets to the next. So it knows absolute positions (magnets) and also relative ones (scrollwheel).
When you then call it to a floor, it knows where it currently is, how many scrollwheel turns it needs to go, how many magnets it will pass along the way and so on.
Due do the scrollwheel it knows the distance between floors, so it can accelerate and slow down smoothly and knows where to stick the landing, while the magnets make sure it has confirmation it’s actually there.
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