A stepper motor is a type of electric motor that converts electrical pulse signals into corresponding angular or linear displacement. For each input pulse signal, the rotor rotates by an angle or moves forward one step. The output angular or linear displacement is proportional to the number of input pulses, and the rotational speed is proportional to the pulse frequency. Therefore, a stepper motor is also called a pulse motor.
Stepper motors can be classified into various types based on their structure, including variable reluctance (VR) stepper motors, permanent magnet (PM) stepper motors, hybrid stepper motors (HS) stepper motors, single-phase stepper motors, and planar stepper motors. In my country, variable reluctance stepper motors are the most commonly used type.
The operating performance of a stepper motor is closely related to its control method. From the perspective of control method, stepper motor control systems can be divided into three categories: open-loop control systems, closed-loop control systems, and semi-closed-loop control systems. In practical applications, semi-closed-loop control systems are generally classified as either open-loop or closed-loop systems.
Reactive stepper motors: The working principle of reactive stepper motors is relatively simple. The rotor has many small teeth evenly distributed, and the stator teeth have three excitation windings, whose geometric axes are sequentially offset from the rotor tooth axes. The motor's position and speed are directly related to the number of conduction cycles (pulse count) and frequency. The direction is determined by the conduction sequence. Two-, three-, four-, and five-phase reactive stepper motors are most common in the market. The characteristics of reactive stepper motors are that the stator has windings and the rotor is made of soft magnetic material. They have a simple structure, low cost, and small step angle (down to 1.2°), but poor dynamic performance, low efficiency, high heat generation, and unreliable reliability.
Permanent magnet type: Permanent magnet stepper motors, also called PM stepper motors, use permanent magnets for the rotor. The stator of this type of stepper motor is machined into claw-shaped poles by stamping, and the rotor uses radially multi-pole magnetized permanent magnets. This type of motor is inexpensive. Its characteristics include good dynamic performance and high output torque, but it has poor precision and a large step angle (typically 7.5° or 15°).
Hybrid type: Hybrid stepper motors are stepper motors designed by combining the advantages of permanent magnet and reactive types. They are further divided into two-phase, three-phase, and five-phase types. The step angle of a two-phase stepper motor is generally 1.8 degrees, that of a three-phase stepper motor is generally 1.2 degrees, and that of a five-phase stepper motor is generally 0.72 degrees.
Hybrid stepper motors have magnetic rotors, resulting in higher torque output from the rotor compared to reluctance stepper motors under the same stator current. Their step angle is also typically smaller. Therefore, economical CNC machine tools generally require hybrid stepper motors for drive. However, hybrid rotors have a more complex structure and higher rotor inertia, leading to lower speed performance compared to reluctance stepper motors.
Hybrid stepper motors have magnetic rotors, resulting in higher torque output from the rotor compared to reluctance stepper motors under the same stator current. Their step angle is also typically smaller. Therefore, economical CNC machine tools generally require hybrid stepper motors for driving. However, hybrid rotors have a more complex structure and higher rotor inertia, leading to lower speed performance compared to reluctance stepper motors.
Hybrid stepper motors combine the advantages of reactive and permanent magnet motors. Their stator has multi-phase windings, and the rotor uses permanent magnet materials. Both the rotor and stator have multiple small teeth to improve step accuracy. They are characterized by high output torque, good dynamic performance, and small step angle, but their structure is complex and their cost is relatively high.
Based on the stator windings, stepper motors are classified into two-phase, three-phase, and five-phase series. The most popular is the two-phase hybrid stepper motor, accounting for over 97% of the market share, due to its high cost-effectiveness and excellent performance when paired with microstepping drivers. This type of motor has a basic step angle of 1.8°/step; with a half-step driver, the step angle is reduced to 0.9°, and with microstepping drivers, the step angle can be subdivided up to 256 times (0.007°/microstep). Due to friction and manufacturing precision limitations, the actual control accuracy is slightly lower. The same stepper motor can be equipped with drivers of different microstepping levels to change the accuracy and performance. The rotor position changes are small, making it easy to achieve optimal operation control; the axial magnetization circuit uses new permanent magnet materials with high magnetic energy product, which is beneficial to motor performance; the rotor magnets provide excitation; and there is no significant oscillation throughout the entire operating range.
