Open-loop control
Elementary
Think of a machine that is trying to reach a goal, like a toaster making toast. In open-loop control, the machine acts without checking the result.
High school
Consider a controller that chooses the input to a system. In open-loop control, the controller chooses the input without measuring the result.
Undergraduate
Consider a control system $\dot x = f(x, u)$. In open-loop control, the input $u$ is computed in advance, or from the reference alone, and does not depend on measurements of the system’s output.
Examples
Examples
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A toaster that runs for a fixed time
Elementary
A toaster that runs for a fixed time is open-loop control because it does not measure how brown the toast is.
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A precomputed optimal input $u(t)$, applied without measurements
High school
A precomputed input is open-loop control because it uses no measurements.
Non-examples
Things that may be mistaken for examples.
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A thermostat
Elementary
A thermostat is not open loop because it reacts to measurements of the temperature.
Distinctions involving this term
- Types of control: A controller can decide its input with or without measuring what the system is doing. Open-loop control computes the input without measuring the output, and closed-loop (feedback) control uses the measured output to correct errors. Feedforward acts on a measured disturbance or a known reference before it affects the output, and is usually combined with feedback.