What do stepper motors do

In this article, we will cover the basics of stepper motors. You will learn about the working principles, construction, control methods, uses, and types of stepper motors, as well as its advantages and disadvantages. 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. 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. Figure 1 shows a drawing representing the section of the motor is shown, where the rotor is a variable-reluctance iron core.

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. Figure 2 shows a representation of the working principle.

At the beginning, coil A is energized and the rotor is aligned with the magnetic field it produces. The same happens when coil C is energized.

In the pictures, the colors of the stator teeth indicate the direction of the magnetic field generated by the stator winding. The performance of a stepper motor — both in terms of resolution or step size , speed, and torque — is influenced by construction details, which at the same time may also affect how the motor can be controlled.

As a matter of fact, not all stepper motors have the same internal structure or construction , as there are different rotor and stator configurations.

For a stepper motor, there are basically three types of rotors:. The stator is the part of the motor responsible for creating the magnetic field with which the rotor is going to align. The main characteristics of the stator circuit include its number of phases and pole pairs, as well as the wire configuration. The number of phases is the number of independent coils, while the number of pole pairs indicates how main pairs of teeth are occupied by each phase.

Two-phase stepper motors are the most commonly used, while three-phase and five-phase motors are less common see Figure 5 and Figure 6. We have seen previously that the motor coils need to be energized, in a specific sequence, to generate the magnetic field with which the rotor is going to align.

Several devices are used to supply the necessary voltage to the coils, and thus allow the motor to function properly. Starting from the devices that are closer to the motor we have:. Figure 7 shows a simple representation of a stepper motor control scheme.

Terms and conditions apply. Stepper motors are often misconceived as the lesser of servo motors, but as a matter of fact, they are highly reliable just like servo motors. The motor operates by accurately synchronizing with the pulse signal output from the controller to the driver, achieving highly accurate positioning and speed control.

Stepper motors feature high torque and low vibration at low-speeds, ideal for applications requiring quick positioning in short distance. Servo motors must have better performance. Obviously there is a major misconception about stepper motors. In fact, stepper motors have been used in various types of applications such as advanced equipment and accessible automated instruments.

The reasons why stepper motors have been continuously chosen are explained in this article. Some readers may say that they have never seen a stepper motor before. Stepper motors have been used in many applications and industries as the motor solution for drive systems requiring high accuracy control, such as factory automation FA , manufacturing equipment for semiconductor, FPD and solar panel, medical devices, analytical instruments, precision stage, financial systems, food packaging machines, and aperture diaphragm adjustments for cameras.

According to the survey of stepper motors users, many favor stepper motors for their "ease-of-use," "simple operations", and "low cost" derived from the structure and system configuration. It makes sense that many users find such positive aspects in stepper motors, thanks to the simple structure and system configuration.

However, some readers may be skeptical about the actual performance of the motor in terms of its accuracy and torque. It is not easy to fully grasp the whole idea unless there are comparison examples against other control motors such as servo motors. By knowing the characteristics and taking on different approaches based on required operations, stepper motors certainly can reduce the cost of the equipment.

The characteristics and technical information of stepper motors are explained below:. Stepper motors have remarkable stopping accuracy, and accurate control with open-loop is possible.

Because stopping position errors do not accumulate between steps, high accuracy positioning is possible. The structure of the stepper motor, which requires no encoder, allows for the simple drive system and low cost.

One of the main features of servo motors is to generate flat torque from mid to high speed ranges. Servo motors are suitable for long-stroke operations many rotations. On the other hand, torque characteristics of stepper motors are not flat. Besides the stable rotations in the low speed range, which servo motors struggle with, stepper motors can offer high torque within the required speed range for short-stroke operations less rotations , thus they are suitable for selecting the desired step angle for multiple rotation tables and inching applications.

This is due to the short positioning time for the short-stroke operation, thus the motor decelerates and stops before reaching the maximum speed. In other words, high-speed characteristics are usually not required. The third remarkable feature of stepper motors is responsiveness. The open-loop control, which sends one-way commands to the motor, has a high followup mechanism toward commands.

While servo motors, which wait for feedback from the encoder, tend to have "delays" with commands, stepper motors operate synchronously with a pulse. Therefore, there are very few "delays," resulting in excellent response. For this reason, stepper motors are suitable for applications that require synchronous operations of multiple motors. One example is a board transferring application that requires two conveyors, with one motor mounted respectively, to transfer boards in between the two conveyors.

Torque in an even lower speed range can be up to 5 times higher. Other than an inching application with frequent starting and stopping, stepper motors are suitable for positioning of image check processors that dislike vibrations, cam drives that would be difficult to adjust with servo motors, and low rigidity mechanisms such as a belt drive.

Furthermore, cost is reduced significantly by replacing a ball screw drive to a belt drive. Besides cost reduction, stepper motors have many advantages in terms of performance.

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