Stepper Motor Types and Winding Configurations Explained

Step by Step: Accurate Stepper Motor Movement

Stepper motors (PAP) are very accurate, able to move a step 'x' applied. They are capable of staying locked in one position or being completely free after each pulse. If one or more of its coils are energized, the motor coils are located in the corresponding position; otherwise, the motor would be free if no current passes through any of its coils. It is assumed that sliding motion can never achieve accurate speed and position control in open loop without using expensive real-time velocity measurement systems.

Permanent Magnet (PAP) Motors

These motors have a rotor with a series of permanent magnets and a stator with a certain number of coils that create the magnetic field. When applied in the proper sequence, the stator coils form magnetic fields that adjust the rotor's spin. They are low cost, operate at relatively low speeds, and offer higher torque compared to Variable Reluctance (VR) motors, with angular steps between 7.5 and 15 degrees. When one coil remains continuously energized, the rotor brake is engaged, which is known as the holding torque.

Variable Reluctance (PAP) Motors

These feature a rotor and stator with teeth. The rotor does not have permanent magnets, allowing it to rotate freely. Reluctance depends on achieving a phase rotor alignment. By energizing a phase, the rotor attempts to reach the position where reluctance is minimal. To achieve balance, the next phase is switched to achieve rotation.

Hybrid (PAP) Motors

These are more expensive than permanent magnet types but offer better features regarding step angle, torque, and speed. The rotor is toothed.

Stepper Motor Winding Configurations

Whatever the type of PAP motor, we can distinguish configurations based on how the stator windings are connected:

Unipolar Drive

• 5 or 6 cables accessible from the exterior.
• Each coil has a center tap connected to the power supply (Vcc), while the control circuit switches to ground.
• Excitation sequence can be performed in full step (energizing 1 coil at a time) or half-step (energizing 2 coils at a time).

Bipolar Drive

• Stator windings do not have a center tap, making this the simplest engine configuration.
• The external driver circuit must switch the polarity in each winding, requiring an H-bridge for each winding.
• It can follow an excitation sequence in full step or half-step (which results in smoother engine running but reduces holding torque).