Stepper motors are an important part of precision motion control systems. Their value lies in their ability to perform discrete controlled motions in steps. The operating performance of a stepper motor is closely related to its phase configuration, a fundamental concept that determines the number of steps per revolution, torque generation, and smoothness of operation.

What Does a Stepper Motor’s Phase Mean?

A phase in a stepper motor refers to an individual winding, or coil, in the stator. The stator is the stationary part of the motor, where electrical energy is converted into mechanical movement. Each phase is energized sequentially to create a rotating magnetic field, which pulls the rotor—a toothed permanent magnet or iron core—along with it. As the magnetic field moves step by step, so does the rotor, resulting in the characteristic stepping motion of the motor.

The number of phases in a stepper motor directly affects the motor’s behavior. For instance, common configurations include two-phase, three-phase, and five-phase stepper motors, each with its own performance characteristics.

Two-Phase Stepper Motors

Two-phase stepper motors are the most common type, particularly in low- to medium-performance applications. They are available in two main winding configurations: unipolar and bipolar.

Unipolar Stepper Motors

In unipolar stepper motors, each phase winding is split into two halves with a center tap. One coil can be efficiently charged at a time thanks to its design, which only permits current to pass through half of the winding at a time. The advantage of unipolar motors is that they simplify control circuitry because the direction of the current does not need to be reversed.

Characteristics of Unipolar Motors:

  • Simple Control: Unipolar stepper motors are easier to control since the current does not need to change direction.
  • Lower Torque: Because only half of the winding is energized at a time, unipolar motors tend to produce less torque compared to bipolar motors.
  • Common Applications: They are often used in low-power applications such as printers and CNC machines, where simplicity and cost-efficiency are prioritized.

Bipolar Stepper Motors

Bipolar stepper motors, on the other hand, utilize the entire winding for each phase, but they require the current to reverse direction. This means that bipolar motors need a more complex control system with H-bridge circuits to manage the direction of the current. However, because both halves of the winding are used, bipolar stepper motors produce more torque than their unipolar counterparts.

Characteristics of Bipolar Motors:

  • Higher Torque: The full winding is used, so the motor generates more torque than a unipolar motor of the same size.
  • More Complex Control: Requires H-bridge circuits to reverse current direction.
  • Common Applications: Bipolar stepper motors are used in higher-performance applications such as industrial automation, robotics, and high-end 3D printers.

Three-Phase Stepper Motors

Three-phase stepper motors are less common than two-phase motors but offer several advantages, particularly in terms of smoothness of operation and torque generation. The increased number of phases allows for a more continuous magnetic field rotation, which leads to smoother motion and less vibration.

Characteristics of Three-Phase Stepper Motors:

  • Smooth Operation: The more phases, the smoother the transition between steps, leading to less vibration.
  • Higher Efficiency: Three-phase stepper motors are more efficient and can generate more torque for a given power input compared to two-phase motors.
  • Complex Control Requirements: Although the motor performance improves with more phases, the control circuitry becomes more complex, requiring more sophisticated drivers.
  • Common Applications: These motors are often used in high-precision applications such as medical equipment, where smooth motion and high torque are critical.

Five-Phase Stepper Motors

Five-phase stepper motors offer an even finer level of control and are known for being the smoothest and most efficient of the stepper motor configurations. With more phases, the rotor can move in smaller increments, which increases resolution and reduces vibrations further.

Characteristics of Five-Phase Stepper Motors:

  • Very Smooth Motion: The large number of phases allows for extremely small step angles, resulting in very smooth operation.
  • Higher Resolution: Five-phase motors can achieve high-resolution steps, which is beneficial in applications requiring precise positioning.
  • More Expensive and Complex: Due to the additional phases, these motors are more expensive and require complex control systems.
  • Common Applications: When the utmost level of accuracy is required, they are employed in specialist machinery like semiconductor production machines.

How Phase Configuration Affects Performance

The number of phases in a stepper motor affects several key performance characteristics, including:

step angle of stepper motor

Step Angle

The angular distance the rotor travels in a single step is known as the step angle. Motors with more phases generally have smaller step angles, which allows for finer control over the motor’s position. A two-phase stepper motor, for instance, can have a step angle of 1.8 degrees, which means a full revolution requires 200 steps. In contrast, a five-phase motor could have a step angle as small as 0.72 degrees, allowing for 500 steps per revolution.

Torque

Torque generation is another critical factor influenced by phase configuration. Bipolar motors, which use both halves of each winding, produce more torque than unipolar motors of the same size. Similarly, three-phase and five-phase motors can produce higher torque due to the more continuous nature of their magnetic field.

Smoothness of Operation

More phases result in smoother transitions between steps, reducing vibration and improving performance in applications requiring precision. Five-phase motors are typically the smoothest, followed by three-phase, and then two-phase motors.

Control Complexity

The complexity of the control system rises with the number of stages. For instance, a two-phase unipolar motor is the simplest to control, whereas a five-phase motor requires more sophisticated circuitry to manage the energizing of the windings.

Conclusion

To learn more about phase configuration and how it affects motor behavior, ask a professional stepper motor manufacturer to ensure the optimal performance of precision control systems.