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Servo & Motion

How Does a Servo Drive Work?

The closed-loop structure of a servo system: drive, motor and feedback (encoder) for precise speed/position/torque control.

5 min readUpdated: 2026-07-05

A servo system is a closed-loop control system of drive + motor + feedback (encoder). The drive continuously compares the command with the encoder feedback and corrects the error.

Three nested loops

  • Torque (current) loop — fastest
  • Speed loop
  • Position loop — outermost
Poorly tuned loop gains cause oscillation, noise and position error. An encoder fault breaks control entirely.

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