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
The elevator car is controlled by a computer that gets signals from sensors in fixed locations up the entire height of the shaft. They tell the computer where the elevator car is.
The computer can operate the motor and wind the cable up or down to position the car precisely at the correct level. It does not know exactly how many times to go around to achieve the desired result – it will simply wind up the cable until the sensors in the shaft tell it to slow down, and then stop entirely, at the right place.
If you pay attention, you can sometimes feel the car almost coming coming to a stop, and then slowly being moved a small amount more before the door opens. This is the fine movement that allows the level to match the floor perfectly.
Using sensors in fixed positions on the shaft means that it does not matter if the cable stretches over time – the motor will still move the car to the correct position.
You are overthinking the problem, when you tell an elevator to go up and down it’s not measuring cable length, there is simply a sensor at each floor. It only needs to know how many sensors up or down from its current position it needs to go
The sensors are built into the elevator shaft (either above the doors or the rails). You may have noticed that the cabin slows down when coming to the floor and then crawls for a couple of seconds before coming to the full stop. That’s done so it can stop the moment it hits the sensor and not over/undershoot the door.
Yes and Sensors. The whole elevator shaft is filled with Sensors, push buttons, etc. They are not very fancy but get the job done.
Example : Elevator is moving from 1st floor up towards 7th floor. The onboard computer calculates the time it will take, the speed, the acceleration/deceleration curve. It will also use simple push buttons to see where the elevator has reached and then make corrections if needed as well.
Modern elevators have even more complex set of sensors and circuitry involved and can do more complex calculations like the power it should use to optimize itself according to weight currently, making the ride more pleasant. When the companies install the elevator they will do calibrations to make it works perfectly for that building. It is also the reason elevators need frequent maintenances. Anything off will be dangerous, like when elevators sometime stop just a few millimeters above or below instead of being level.
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.
You are way overthinking this. It just counts floors. Floor height is standardised by building regulations, as are elevator shaft heights, car heights etc. No fancy maths is being done on the fly for this.
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