The applications and working principle of PM stepper motor

1.Definition

A permanent magnet stepper motor (PM stepper motor) is a type of stepper motor that uses a permanent magnet as the rotor instead of a traditional wound rotor. This allows for a simpler and more compact design, with high torque and precise motion control.

2.Worrking principle

The basic working principle of a PMSM involves the interaction between the magnetic fields of the stator and rotor. When a current is passed through the windings of the stator, it creates a magnetic field. This magnetic field interacts with the permanent magnetic field of the rotor, causing the rotor to turn, or “step”.

Single Phase Excitation: In this mode, only one phase winding is energized at a time. It results in the least amount of torque and power, but it conserves energy.

Two Phase Excitation: In this mode, two phase windings are energized simultaneously. It offers a higher level of torque and power compared to single-phase excitation.

3.Applications

(1)CNC Machines

CNC machines are highly advanced machines used for cutting, drilling, and shaping various types of materials. Permanent magnet stepper motor plays a crucial role in the operations of CNC machines.

Permanent magnet stepper motors move in small steps with high step resolution which results in precise positioning and allows to cutting of the materials in specific designs and shapes. These machines drill holes in materials with precision and repeatability. PM stepper motors offer high torque at low speeds, which helps the motor maintain its position and drill the material in repeated movement.

(2)3D Printers

A 3D printer is a highly advanced printer that has the ability to turn a digital design into physical objects by depositing layers of materials on each other.

The 3-phase stepper motor allows precise control over the movement of the 3D printer for depositing the materials layer by layer and is responsible for creating the intricate design with high accuracy. These motors can be programmed at different speeds and directions and allow printers to create intricate designs and patterns with multiple layers and different colors. 

(3)Medical Equipment

Permanent magnet stepper motors play an important role in various medical equipment such as MRI machines, robotic surgery machines, 

In MRI machines, these motors offer precision and accuracy, which help to position the patient correctly and obtain clear and accurate images of different parts of the body.

(4)Textiles Machines

Permanent magnet stepper motor plays an important in the functioning of textile machines. From spinning to weaving, dyeing, and finishing, these 3-phase stepper motors are used in every stage of manufacturing.

These motors use different stepping modes to move small steps in a controlled manner. This is crucial for textile machines, where even a small error will result in defective products. This ensures that each movement is accurate and results in high-quality products.

4.Advantages

It is compact and small in size, which makes it useful in many applications

Due to the absence of any external excitation, the losses are less and maintenance is less.

It can be connected to the external circuit, to control the speed of the motor

Sensors may be used to locate the rotor winding

Can be operated in a wide range of speed and torque.

Precise Control

The feature of planetary gearbox for stepper motors

Compared with ordinary gear drives, planetary gearbox for stepper motor have many characteristics. The main characteristics of planetary gear transmissions are as follows:

1. Small size, small mass, compact structure, and high load-bearing capacity. This is a common shaft due to the drive and power distribution of the planetary gearbox, as well as the transmission of the central wheel and the reasonable application of internal meshing gears.

2. Drive efficiency. This is because of the symmetry of the planetary gear drive structure. As is well known, there are many types of stepper motor planetary gearboxes. The reaction force of the minute wheel and the rotating arm can be balanced, which is beneficial for transmission efficiency. If the selected driver type is suitable and the structure is reasonable.

3. Comparison of large drives. The drive is larger than a planetary gearbox, and can still maintain the characteristics of compact structure, small volume, and small volume. It can also achieve synthetic decomposition motion and various complex movements. As long as the type of planetary gearbox and distribution scheme is appropriately selected, planetary gears can be achieved through synthesis and motion decomposition, and variables can be used to obtain a large number of gear ratios.

4. The planetary gearbox adopts the same planetary gears, with evenly distributed center wheels, allowing the planetary gears and force balancing arms to move simultaneously, ensuring the stability of the planetary gearbox. At the same time, with the addition of teeth, planetary gears move stably, with stronger impact resistance and vibration resistance, making their work more reliable.

The planetary gear set, also known as a planetary gearbox or planetary reducer, is mainly used to reduce input speed, output low speed, and increase torque to achieve ideal transmission effect.

Advantages:

1. High efficiency: The transmission efficiency of planetary gears can reach over 90%.

2. High precision: The compact structure of planetary gears can effectively ensure the stability of transmission accuracy.

Application: 

Planetary gearboxes are widely used, initially in conjunction with electric motors. In addition to being used for micro reduction motors, they are also used in the shading industry, office automation, smart home, production automation, medical equipment, financial machinery, game consoles, and other fields. For example, in industries such as automatic curtains, intelligent toilets, lifting systems, cash registers, advertising lightboxes, and so on.

Source: https://www.steppernews.com/2023/08/the-feature-of-planetary-gearbox-for_18.html

What is Best Choice Between Servo Motor and Stepper Motor？

 Servo Motor vs Stepper Motor: Which is right for your application?

It is an engineering truism that there is no perfect solution, just the best solution for the problem at hand. That holds particularly for servo motors and stepper motors. Both are broadly used in industry. Neither is a universal solution. When properly applied, however, both stepper motor and servo motor can provide effective, reliable power for a highly successful system. The decision tree for choosing between the two has many branches but the most important are speed, acceleration, and price target.

 

Stepper Motors
Stepper motors consist of a rotor with permanent magnets and a stationary stator that carries the windings. When current runs through the stator windings, it generates a magnetic flux distribution that interacts with the magnetic field distribution of the rotor to apply a turning force. Stepper motors feature very high pole counts, typically 50 or more. The stepper motor driver energizes each pole in sequence so that the rotor turns in a series of increments, or steps. Because of the very high pole count, the motion appears to be continuous.

Stepper motors have a number of positive attributes. Because they generate incremental motion, they are generally run open loop, eliminating the cost and complexity of an encoder or resolver. The high pole count allows them to generate very high torque at zero speed. They are compact and generally economical.

Stepper Motor
Figure 1: Stepper motors deliver good performance at an economical price point for applications requiring low speed, acceleration, and accuracy. (Courtesy of Kollmorgen)

On the downside, stepper motors have speed limitations. They generally run best at 1200 RPM or lower. Although they generate high torque at zero speed, torque falls off as speed increases (see figure 2). A motor that generates 100 ounce inches at zero speed might only deliver 50 ounce inches at 500 RPM, for example, and just 10 ounce inches at 1000 RPM. In theory, a gearbox could be used to increase torque, but this is where the low speed of stepper motors becomes a problem. Adding a 10:1 gear reducer to a 1200 RPM stepper motor might boost the torque by an order of magnitude but it will also drop the speed to 120 RPM. If the motor is being used to drive a ball-screw actuator or similar, it probably will not deliver sufficient speed to satisfy the needs of the application.

Stepper motors generally are not available in frame sizes larger than NEMA 34, with most applications falling in the NEMA 17 stepper motor or NEMA 23 stepper motor sizes. As a result, it is unusual to find stepper motors capable of producing more than 1000 to 2000 ounce inches of torque.

Stepper motors also have performance limitations. You can think of a stepper motor as a spring-mass system. The motor needs to break friction to begin turning and move the load, at which point the rotor is not fully controlled. As a result, a command to advance by five steps may only result in the motor turning four steps – or six. If the drive commands a motor to advance 200 steps, however, it will do so to within just a few steps, which at that point represents an error of a few percent. Although we command stepper motors with a resolution of typically between 25,000 and 50,000 counts per revolution, because the motor is a spring-mass system under load, our typical resolution is 2000 to 6000 counts per revolution. Still, at these resolutions, even a 200-step move corresponds to a fraction of a degree.