Servo motor control

A servomotor is a motor combined with a feedback device and a control system so that its shaft can be commanded to a precise position, speed or torque. The defining feature is closed-loop control: a sensor continuously measures the actual output, the controller compares this with the desired value, and it adjusts the drive to reduce the difference. This feedback distinguishes a servo from an ordinary motor run open-loop, and it is what allows accurate, repeatable motion in robotics, machine tools and automation.

Servos are built around several motor types. Small hobby and industrial DC servomotors use brushed or brushless DC motors, while higher-performance systems often use brushless AC servo motors for smoothness and reliability. The motor is paired with a position or velocity sensor such as an encoder or potentiometer, and a controller that closes the loop. The familiar small radio-control servo, for instance, contains a DC motor, gears, a potentiometer and a circuit that drives the motor until the measured position matches the command.

Command and power delivery commonly rely on pulse-width modulation (PWM). In hobby servos a pulse whose width encodes the target position is sent repeatedly, and the internal electronics move the output to match. In industrial drives PWM switches the supply rapidly to regulate the average voltage and current fed to the motor, controlling torque and speed efficiently. The controller's design determines how quickly and accurately the servo settles on its target without overshoot.

Frequently asked questions

What makes a servomotor different from a normal motor?

A servomotor uses closed-loop feedback: a sensor measures the actual position or speed and the controller continually corrects the drive so the output matches the commanded value.

How does a hobby servo interpret a PWM signal?

A repeating pulse whose width represents the desired position is sent to the servo, and its internal circuit drives the motor until the measured position corresponds to that pulse width.

Why are brushless AC servo motors used in industry?

They offer smooth, reliable, high-performance operation without brush wear, which suits the demanding accuracy and duty cycles of industrial automation.