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An elevator is a car that travels between floors, stopping at precise heights. There are certain logical constraints used for safety and convenience. The points below emphasize different types of control problems in the elevator.

Logical:

1. The elevator must move towards a floor when a button is pushed.
2. The elevator must open a door when it is at a floor.
3. It must have the door closed before it moves.

etc. Linear:

1. If the desired position changes to a new value, accelerate quickly towards the new position.
2. As the elevator approaches the correct position, slow down.

Non-linear: 1 Accelerate slowly to start.

1. Decelerate as you approach the final position.
2. Allow faster motion while moving.
3. Compensate for cable stretch, and changing spring constant, etc.

Logical and sequential control is preferred for system design. These systems are more stable, and often lower cost. Most continuous systems can be controlled logically. But, some times we will encounter a system that must be controlled continuously. When this occurs the control system design becomes more demanding. When improperly controlled, continuous systems may be unstable and become dangerous.

When a system is well behaved we say it is self regulating. These systems don’t need to be closely monitored, and we use open loop control.

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