Tracking
High school
Tracking is making a quantity follow a changing target, as a driver steers a car to follow a road.
Undergraduate
In control theory, tracking is a control problem with the goal of making the output $y(t)$ follow a time-varying reference $r(t)$, so that the tracking error
\[e(t) = r(t) - y(t)\]converges to zero (or stays small).
Examples
Examples
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A robot arm following a moving conveyor belt
Elementary
Following the conveyor belt is tracking because the reference position changes over time.
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A spacecraft following a planned trajectory
Elementary
Following a planned trajectory is tracking because the reference is a time-varying path.
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An aircraft approaching a tanker aircraft and then holding position behind the tanker to refuel in flight
High school
An aircraft refueling in flight solves a tracking problem while refueling, because the aircraft must hold its position relative to the moving tanker at every time.
Non-examples
Things that may be mistaken for examples.
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Cruise control holding 100 km/h on hilly roads
Elementary
Holding $100$ km/h is not tracking, because the reference does not change.
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Balancing an inverted pendulum upright
High school
Balancing an inverted pendulum upright is not tracking, because the reference does not change over time.
Properties
- Tracking a reference can be posed as stabilizing the origin of the error dynamics.
Distinctions involving this term
- Types of control objectives: A feedback controller is designed to meet a goal, and the goals have different names. Stabilization makes an equilibrium asymptotically stable. Regulation holds an output at a constant set point despite disturbances. Tracking makes an output follow a reference that changes over time.