Feedback is when the output of a system is applied to the input.
Open-loop: Absence of feedback, no pathway from output to input.
- Simple but can be sub-optimal.
- Example: turning a car with your eyes closed by holding the steering wheel at a fixed angle for a specific amount of time does turn the car, but not safely or predictably.
Closed-loop negative feedback: Seeks to minimize the error between reference and measured signals.
- Example: A fridge door closes itself by applying a force proportional to how open the door is (the force decreases as the door closes).
- A driver turns a car with their eyes open until it is pointing in the desired direction (the driver reduces the steering wheel angle as the complete the turn.)
Closed-loop positive feedback: Causes the output to “stick” to one extreme and resist changing states.
- Example: Cabinet door with magnet keeps it stuck shut (magnet force increases as the door closes).