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What’s the difference between servo and closed loop stepper motors?

Servo and closed loop stepper motor have similar construction and share the same fundamental operating principle. Both motor types incorporate a rotor with permanent magnets and a stator with coiled windings … and both are operated by energizing or applying a dc voltage to the stator windings. That then causes the rotor to move. However, this is where the similarities between servo and stepper motors end.
Drive methods for stepper motors
Stepper motors have 50 to 100 poles and are two-phase devices.
In contrast, servo motors have between four and 12 poles and are three-phase devices.
What is more, stepper motor driver generate sine waves with a frequency that changes with speed … but with an amplitude that is constant.
What’s the difference between servo and closed loop stepper motors?
Servo drives, on the other hand, produce sine waves with variable frequency and amplitude — allowing them to control both speed and torque.
Control methods for stepper motors
Traditional stepper motors move when they receive a command to advance a certain number of pulses, which correlate to a distance. Steppers are considered open-loop systems because they lack a feedback mechanism to verify that the target position has been reached. Servo motors also move on receipt of a command signal from their controller. In contrast to the open-loop operation of stepper motor systems, servo motors are closed-loop systems, with built-in encoders that continuously communicate back to the controller, which makes any needed adjustments to ensure the target position is reached. Closed-loop stepper motors eliminate many of the disadvantages of traditional open-loop stepper systems, making them similar in performance to servo motors. But servo motors outperform even closed-loop steppers in applications that require high speed, high torque at high speed, or the ability to handle changing loads.
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