How to pre-computer elevators work?

Question

If I press the "8" button on my elevator, how does it actually carry the elevator car up to the eighth floor and how does it "know" that I want to go to that floor? What is the mechanism?

It is a vintage 1920s building and the elevator is really old. It has a metal gate you have to pull shut for the thing to even move. There is NO computer controlling this. So what is controlling the movement and telling it which floors to go to?

Answer 1

The elevator in your building has been upgraded/modernized at some point in time. I know this because in the 1920's there were no automatic elevators. At this time there were people operating the cars since the technology required for automatic operation did not exist yet.

Since the car has obviously been modernized to work as an automatic elevator, it's hard to say what exactly is controlling the car. The key word here being 'controller'.

Back in the 1950's the technology allowed for automatic operation to be installed on new and old (modernization required) elevators. These were relay logic based controllers. No solid state devices, just relays, motor contactors, resistors and capacitors.

There are elevators out there that have been modernized multiple times and though they were initially installed in the 20's, they could end up with a high end solid state microprocessor based controller. I'm going to guess that yours hasn't been upgraded with a microprocessor controller since you have a collapseable gate. If your car was upgraded with a cpu based controller, fire code and ADA code would require the gate to be replaced with fire rated doors.

The mechanism that tells the car when you've reached your floor is the selector. On older automatic elevators the selector is a mechanical piece of equipment that worked off of the movement of the car. Otis used a 'pie plate' selector and Dover used cable attached to the top and bottom of the car that turned a drum attached to a moving carriage. It also has electrical components that work with the controller to give signals back and forth to tell the contoller when it's reached a certain floor.

It's really hard to describe how all of this stuff works since it's quite complicated and each manufacturer had a different way of achieving this goal. Ultimately, all of the old style elevators had to have a selector that was mechanically connected to the car with either a cable, steel tape, wire rope or chain.

Nowadays, we use tachometers, encoders and optical sensors (no moving parts) to get the cars to stop within a millimeter of perfect floor level.

Answer 2

moos is correct, it's relay logic that is used. I have a similar elevator in my condo building. You can hear the relays clicking.

If I had to design it, The 8 pushbuttons would go via cable to the control box, each to an individual latching relay. Also fed to the control box are contacts on each floor that close when the cab is at that floor. A relay AND logic decides if the cab has reached the proper floor and turns the motor off.

Other logic determines the motor's direction, and provides safety limit switches, etc.

Answer 3

Computers operate using microscopic switches, but they can all be paralleled at the macroscopic level with mechanical switches.  An elevator routine can be simple enough to run on a few mechanical switches, where connections between two wires are physically closed by pressing a button.  More mechanical switches are triggered when the elevator reaches a designated floor, turning off the drive motor.

Answer 4

The controller IS a computer, but it's electromechanical, not electronic.  The basic logic component is the electromagnetic relay.  It would be a good mental exercise for you to design such a control system using relays.