Stepper Motors Jason Wells

Background Brushless, synchronous electric motor Brushless, synchronous electric motor No feedback necessary (open loop) No feedback necessary (open loop) Divides the full rotation into multiple steps Divides the full rotation into multiple steps Precise, repeatable steps Precise, repeatable steps

Types Variable-Reluctance Variable-Reluctance Rotor teeth are attracted to the energized stator Rotor teeth are attracted to the energized stator

Types Permanent Magnet Permanent Magnet Alternating N to S poles Alternating N to S poles degree steps degree steps steps/rev steps/rev

Types Hybrid Hybrid Combination of the two previous Combination of the two previous.9 to 3.6 degree steps.9 to 3.6 degree steps 100 to 400 steps/rev 100 to 400 steps/rev

Two Phase Steppers Unipolar Unipolar Requires 1 power supply Requires 1 power supply Two windings per phase Two windings per phase Ends of windings alternately grounded to reverse direction Ends of windings alternately grounded to reverse direction Driver circuit simple Driver circuit simple Bipolar Requires 2 power supplies One winding per phase Current must be reversed to change direction Driver circuit more complicated (H-bridge)

Drive Options Full Step Full Step Both phases on Both phases on Wave Wave One phase activated at a time One phase activated at a time Half Step Half Step Alternates between one phase and two phases on Alternates between one phase and two phases on Micro step Micro step Sine/cosine wave input to each phase Sine/cosine wave input to each phase

Drive Sequence Example

Torque vs. Speed

Stepper vs. DC Stepper Motor Stepper Motor High precision applications High precision applications No feed back necessary No feed back necessary More costly than an equivalent DC motor More costly than an equivalent DC motor Not easily operated at high speeds Not easily operated at high speeds DC Motor Feed back circuit needed to know the motors position Less costly than an equivalent Stepper motor No problem with high speeds

Additional References motorbas.pdf motorbas.pdf motorbas.pdf motorbas.pdf sign_ref/actuators/stepper_intro.html sign_ref/actuators/stepper_intro.html sign_ref/actuators/stepper_intro.html sign_ref/actuators/stepper_intro.html

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