Types of Stepper Motors: What You Need to Know

Types of Stepper Motors

What is a stepper motor? What are the types of stepper motors? And why is it essential in precise motion control? Stepper motors, also known as pulse motors, convert electrical pulse signals into precise angular or linear movements. These motors are widely used in open-loop control systems for applications requiring accurate positioning without feedback systems.

Stepper motors come in different types. Generally, they can be classified according to the number of stator phases (divided into single-phase, two-phase, three-phase, and multi-phase forms), rotor structure classification (including permanent magnet stepper motors, reactive stepper motors, hybrid stepper motors), and drive mode classification (bipolar drive/unipolar drive).

Next, let’s learn about types of stepper motors.

The Basic Principle Of Stepper Motor

A stepper motor is controlled by electrical pulses, converting these pulses (digital signals) into angular displacement.

Basic Principle Of Stepper Motor

The rotor of a typical stepper motor is a permanent magnet. When current flows through the stator windings, a magnetic field is generated. This magnetic field causes the rotor to rotate to align with the stator’s magnetic field.

When the stator’s vector magnetic field rotates at an Angle. The rotor is also rotated at an Angle with the magnetic field. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed Angle (called the “step Angle “) in the set direction, and its rotation is run step by step at a fixed Angle.

1. Classified by number of stator phases

Stepper motors can be classified based on the number of stator phases. The “x” phase indicates the motor has “x” number of windings.

Single-Phase Stepper Motors

Single-phase stepper motors generate electromagnetic torque only when the stator current changes. Their average torque is much lower than that of motors with two or more phases, and they operate at a low pulse frequency of less than 100 pulses per second (pps). Due to this, their use is limited to light-load applications with low pulse frequency requirements, such as clocks, vehicle timers, and water meter counters.

Two-Phase Stepper Motors

Two-phase stepper motors are among the most commonly used stepper motors. They balance simplicity and performance, making them suitable for a wide range of applications.

two phase stepper motor structure

Three-Phase Stepper Motors

Three-phase stepper motors have a stator coil configuration where the number of poles is a multiple of three, such as 3, 6, 9, or 12. This design increases smoothness and torque, making them ideal for more demanding applications.

Four-Phase Stepper Motors

Four-phase stepper motors have more complex driver structures and higher costs. They are generally reserved for specialized applications that require specific performance.

four phase stepper motor structure

Five-Phase Stepper Motors

Five-phase stepper motors offer smoother operation and higher precision than their counterparts but come with more complex setups and are typically used in advanced or industrial applications.

2. Classification by Rotor Structure

Stepper motors can also be classified based on the structure of their rotor. The rotor plays a key role in determining the motor’s performance and characteristics.

Permanent Magnet Stepper Motor (PM)

The rotor of a permanent magnet stepper motor is made from magnetic material. The PM rotor is typically an inner-rotor type, with the outer surface of the cylindrical rotor arranged with alternating N and S poles, but without teeth on the surface.

Permanent Magnet Stepper Motor (PM)

Characteristics: PM stepper motors offer higher torque and better dynamic performance. However, they have larger step angles, meaning they may lack fine precision compared to other types.

Variable Reluctance Stepper Motor (VR)

variable reluctance stepper motor is also called reluctance stepper motor, its rotor is a non-magnetic, soft iron, toothed structure; The stator is composed of an exciting coil; Since the rotor is a non-magnetic structure, there is no magnetic interaction between the stator and the rotor until the stator is not energized. Therefore, the reactive stepper motor has no detent torque.

variable reluctance stepper motor

The rotor of a variable reluctance stepper motor is made from ferromagnetic materials, such as silicon steel or pure iron. The rotor has a toothed surface, and as the rotor moves, the magnetic reluctance changes due to the varying magnetic resistance, hence the name “variable reluctance motor.”

When the stator coil is energized, the stator poles become magnetized and attract the rotor teeth, creating torque that moves the rotor one step. Unlike permanent magnet motors, which generate both attractive and repulsive forces, VR stepper motors only produce attractive torque.

In the example of a VR motor, the stator may have 12 evenly spaced poles, each 30° apart, and four coils forming one phase winding. The rotor has 8 teeth, and when a phase winding is energized, the stator poles attract the rotor teeth, minimizing magnetic reluctance and holding the rotor in place.

Hybrid Stepping Motors (HS)

The hybrid stepper motor has two phase, three phase and five phase. This section describes the two-phase hybrid stepper motor.

Hybrid stepper motor

The name of the hybrid stepper motor is derived from its rotor structure, which is a complex of the PM rotor and the VR rotor.

The rotor structure of the hybrid stepping motor consists of two magnetic discs sandwiching a permanent magnet cylinder in axial string. The outer circular tooth pitch of the two magnetic discs is the same as that of the aforementioned VR rotor structure. The teeth of the two discs are staggered by 1/2 tooth spacing and the rotor cylinder is axially magnetized, with a section of N and the other end of S.

Hybrid stepper motor rotor structure

From the structure point of view, the N pole and S pole of the PM-type rotor are distributed on the outer surface of the rotor, to improve the resolution, it is necessary to increase the number of poles, usually the rotor of 20mm diameter can be configured with 24 poles, such as increasing the number of poles, it will increase the magnetic leakage and reduce the electromagnetic torque.

The rotor N pole and S pole of the hybrid stepping motor are distributed on two different soft magnetic disks. so the number of rotor poles can be increased, thereby improving the resolution, the rotor with a diameter of 20mm can be configured with 100 poles. and the magnetic pole magnetization direction is axial, the N pole and the S pole are magnetized after assembly, and the magnetization is simple.

The stator pole corresponding to the rotor teeth has a small tooth with the same pitch as the rotor teeth in the inner diameter of the main pole, which interacts with the magnetic flux of the rotor teeth in the air gap and can generate electromagnetic torque.

3. Classification by drive mode (bipolar drive/single-pole drive)

The motor is also divided into unipolar stepper motor and bipolar stepper motor according to the driving mode.

In simple terms, if the coil of the stepper motor can be bidirectional conduction, then the stepper motor is bipolar, on the contrary, if the coil of the stepper motor is only allowed to conduct unipolarity, then the stepper motor is unipolar.

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Types of Stepper Motors

Types of Stepper Motors: What You Need to Know

What is a stepper motor, and why is it essential in precise motion control? Stepper motors, also known as pulse motors, convert electrical pulse signals into precise angular or linear movements. These motors are widely used in open-loop control systems for applications requiring accurate positioning without feedback systems.

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