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Stepper Motor Basics: Types, Purpose and How They Work

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In this article, we'll cover the basics of stepper motors. You will learn about the working principle, control method, usage and types of stepper motors.

Introduction of stepper motor

Stepper Motor Basics

A stepper motor is an electric motor whose main feature is that its shaft rotates by performing steps, that is, by moving by a fixed amount of degrees. This feature is obtained thanks to the internal structure of the motor, and allows to know the exact angular position of the shaft by simply counting how may steps have been performed, with no need for a sensor. This feature also makes it fit for a wide range of applications.

Stepper Motor Working Principles

As all with electric motors, stepper motors have a stationary part (the stator) and a moving part (the rotor). On the stator, there are teeth on which coils are wired, while the rotor is either a permanent magnet or a variable reluctance iron core. We will dive deeper into the different rotor structures later. The basic working principle of the stepper motor is the following: By energizing one or more of the stator phases, a magnetic field is generated by the current flowing in the coil and the rotor aligns with this field. By supplying different phases in sequence, the rotor can be rotated by a specific amount to reach the desired final position.

Stepper Motor Driver Types

There are different stepper motor drivers available on the market, which showcase different features for specific applications. The most important charactreristics include the input interface. The most common options are:

  • Step/Direction – By sending a pulse on the Step pin, the driver changes its output such that the motor will perform a step, the direction of which is determined by the level on the Direction pin.

  • Phase/Enable – For each stator winding phase, Phase determines the current direction and triggers Enable if the phase is energized.

  • PWM – Directly controls the gate signals of the low-side and high-side FETs.

Another important feature of a stepper motor driver is if it is only able to control the voltage across the winding, or also the current flowing through it:

  • With voltage control, the driver only regulates the voltage across the winding. The torque developed and the speed with which the steps are executed only depend on motor and load characteristics.

  • Current control drivers are more advanced, as they regulate the current flowing through the active coil in order to have better control over the torque produced, and thus the dynamic behavior of the whole system.

Stepper Motor Types

1. Reactive stepper motor 

The stator of the reactive stepper motor is made of silicon steel sheets, and the opposite two magnetic poles are wound with the same winding with different winding directions. When energized, a pair of N and S poles are formed, and there is no winding in the motor rotor. The rotor of the motor is made of soft magnetic material. There are many small teeth with the same size and the same spacing on the outer surface of the rotor pole and the inner surface of the stator pole. Electromagnetic force is the driving force for the reactive stepper motor to move. Under the action of electromagnetic force, the rotor will move to the position of maximum magnetic permeability (or minimum magnetic resistance) and be in a balanced state.

2. Permanent magnet stepping motor

The material of the rotor of the permanent magnet stepper motor is permanent magnetism, the number of poles of the rotor and the stator is the same, the output torque of the motor is large, and the step angle is relatively large, but the working performance is good.

3. Hybrid stepper motor

The structure of the hybrid stepper motor stator is the same as that of the reactive stepper motor. The rotor is divided into two sections in the axial direction. The same number and size of small teeth are evenly distributed in the circumferential direction of the iron core of the two sections, but they are misplaced by half the tooth pitch. A permanent magnet is embedded in the middle of the two iron cores, so that the iron core at one end of the rotor is N pole and the iron core at the other end is S pole, as shown in Figure 1.1. The N and S polarities of the rotor remain unchanged, and the sequential change of the N and S polarities of the stator magnetic poles is realized by controlling the stator winding current, and a corresponding force is generated on the N and S poles of the rotor to push the rotor to rotate as required. Because the permanent magnetic field of the rotor of the hybrid stepper motor also generates part of the torque, it is larger than the torque generated by the stator magnetic field of the reactive stepper motor.

Picking a stepper motor for CNC is about understanding your torque and RPM (speed) requirements.

The best stepper motor will be capable of delivering your required torque while also being fast enough.I tell you my best picks depending on the category of the stepper motor:

Stepper Motors Advantages

Now that we understand the working principles of the stepper motors, it is useful to summarize their pros and cons compared to other motor types.

Stepper motors are electric motors that convert electrical pulses into precise mechanical movements, making them an ideal solution for many medical applications. Medical devices and equipment often require high-precision positioning, low noise, and high torque capabilities, all of which can be achieved with stepper motors.
One of the primary benefits of stepper motors is their ability to provide precise and accurate movements. This makes them an excellent choice for medical applications such as surgical robots, infusion pumps, and CT scanners, where even small deviations from the intended path or position can have serious consequences. Stepper motors can also be programmed to provide smooth, controlled movement, which is essential in surgical procedures and medical imaging. The percentage step error does not accumulate as the motor rotates.
1. It is able to run at wide range of speeds, including very slow speeds without reduction gearing.
2. Stepper motor provide excellent response during start, stop and reverse mode.
3. It is highly reliable since no brushes or commutator are used. Its life time depend on life of the bearing.
4. Stepper motor control circuit is simple and low cost. It is mainly used for low power applications.The number of phases of the stepper motor: refers to the number of coil groups inside the motor. Currently, two-phase and three-phase are commonly used.
1. Step angle: corresponding to a pulse signal, the angular displacement of the motor rotor.
Electrical parameters: current, resistance, inductance.
Holding torque: refers to the moment when the stepper motor is energized but not rotating, the stator locks the rotor.
2. Positioning torque: The locking torque of the motor rotor itself when the motor is not powered.
3. Running torque-frequency characteristics: The curve of the relationship between the output torque and frequency during the operation of the motor measured under certain test conditions.

Stepper Motors Applications

First, the stepping motor is mainly used in some occasions with positioning requirements, such as: wire cutting table dragging, tufting machine table (pore positioning), packaging machine (fixed length), basically all occasions involving positioning Use it.

Second, it is widely used in 3D printers, monitoring equipment, smart locks, blood analyzers, smart microscopes, vision testers and other fields, especially suitable for applications requiring stable operation, low noise, fast response, long service life, and high output torque.

Third, stepping motors are widely used in textile machinery and equipment such as computerized embroidery machines. The characteristics of this type of stepping motors are that the torque is not high, the frequent start-up response speed is fast, the running noise is low, the operation is stable, and the control performance is good. , The cost of the whole machine is low.

Stepper motor application precautions:
  1. The stepping motor is used in low-speed occasions---the speed does not exceed 1000 revolutions per minute (6666PPS at 0.9 degrees), preferably between 1000-3000PPS (0.9 degrees), and it can be used here by a decelerating device. At this time, the motor has high working efficiency and low noise.
   2. The stepping motor is best not to use the full-step state, the vibration is large in the full-step state.

   3. For loads with large moment of inertia, a large frame size motor should be selected.
4. When the motor is at a higher speed or a large inertia load, it is gene.

Stepper Motor Application - HOLRY

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