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There are three primary types of stepper motors available in the market today: Permanent Magnet (PM), Variable Reluctance (VR), and Hybrid. Each type has distinct features and applications, making the choice dependent on your specific needs.
**Permanent Magnet (PM) Stepper Motors**
PM stepper motors utilize permanent magnets in their rotors. This design allows them to deliver high torque at low to medium speeds. The rotor consists of two permanent magnet rotors that are slightly offset from each other and are axially magnetized. When current flows through the windings, the stator poles become magnetized, attracting the opposite poles of the rotor's permanent magnets.
A widely used PM stepper motor is the 2-phase claw type. The simplicity of its design makes it cost-effective to produce. However, PM stepper motors have limitations in high-speed performance due to significant energy losses during rotation. They are commonly used in applications requiring simple positioning, such as point-to-point movement, but often require microstepping for higher resolution. Microstepping demands precise current control from the driver, impacting the motor's positional accuracy. Additionally, PM stepper motors typically use constant voltage drivers, which can be more challenging to manage compared to constant current chopper drivers.
**Variable Reluctance (VR) Stepper Motors**
VR stepper motors feature a rotor and stator with teeth designed to concentrate magnetic forces. Among the three types, VR motors offer the simplest design. The rotor and stator teeth align when the stator poles are energized, causing the rotor to rotate. Unlike PM stepper motors, VR motors do not employ permanent magnets, which means they lack holding torque or detent torque when stationary.
One key advantage of VR stepper motors is their simpler drive circuitry since the polarity of the stator poles does not need to be changed. However, their torque control is less refined, as torque is proportional to the square of the current rather than the current itself. VR stepper motors perform better than PM stepper motors at higher speeds due to their lack of permanent magnets. To achieve finer resolutions, increasing the number of rotor teeth is beneficial, though this complicates manufacturing when stator slots are also increased.
**Hybrid Stepper Motors**
Hybrid stepper motors combine the best features of PM and VR stepper motors. They incorporate permanent magnets along with toothed rotors and stators, enabling them to focus magnetic flux more effectively. By stacking magnetic steel laminations, these motors achieve low losses while maintaining high torque and precision.
The hybrid stepper motor’s design includes two rotor cups (Rotor 1 and Rotor 2) and a strong rare earth permanent magnet magnetized axially. Ball bearings secure the rotor within the motor housing. Each rotor cup has either 50 or 100 teeth, with one cup magnetized as the north pole and the other as the south pole. Teeth on the rotor cups alternate between north and south poles due to their offset configuration.
Hybrid stepper motors rotate in increments of 1.8° per step with 50 teeth, or 0.9° per step with 100 teeth. The design ensures that the rotor moves a quarter of a tooth pitch per step, allowing for high-resolution movements. These motors offer excellent torque control and are easier to manage than VR stepper motors. They can achieve resolutions as fine as 0.72° per full step, with even higher resolutions possible through microstepping.
**Conclusion**
Among the three types, hybrid stepper motors are the most popular due to their superior performance, despite being more expensive. They are versatile and suitable for a wide range of applications, whereas PM and VR stepper motors are more limited in scope. Modern stepper motor drivers are increasingly sophisticated, offering advanced functions, distributed control, and easier programming. Adding gearheads and closed-loop feedback systems can further expand the motor's capabilities. Collaborating with a manufacturer that provides comprehensive support and training can greatly simplify implementation.
If you’re interested in exploring stepper motors further, consider reading our technical articles and white papers. We invite you to learn more about stepper motor fundamentals and discover how our high-torque hybrid stepper motors could enhance your projects.