The floor the elevator moves to, is controlled by the lift PLC with all the algorithms developed over the years, and that I understand well. What I am not able to understand is how does the lift stop at the exact landing position at a particular floor, neither too high nor too low, but on the same level as the elevator landing on the floor.
I understand that with modern Variable Frequency motor drive controllers and sensors this is not an unachievable task, but how did they do this in the olden days of relays? And even in today where the speed of the driving AC motor in many current elevator systems, is controlled through pole-switching? Do they use some special PID algorithm or some variant of that?