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Figure 1 - Linear stepper motor
Modern motion controllers can include the ability to run stepper motors with encoder feedback, resulting in true closed-loop motion control. This mode of motor control is very similar to standard three-phase brushless servo motor control, where the three phases are offset 120 electrical degrees. With steppers, the motor has two phases offset by 90 electrical degrees. The benefits of closed-loop control with stepper motors include greatly improved velocity smoothness and reduced power consumption compared to open-loop steppers and much higher torque at low velocity compared with traditional three-phase brushless servo motors.