Bipolar stepper motor: general information, the principle of the motor

Almost all electrical devices operate using drive mechanisms. They can have a different structure and principle of operation, as well as customization features. There are different types of such devices. One of the most popular and affordable is the bipolar stepper motor, thanks to which it is possible to provide the implementation of precise positioning systems.

General information

There are two types of device: unipolar stepper motor and bipolar. The device is a synchronous brushless electric motor with one or more windings. The current, which is supplied to the stator windings, causes the rotor to be fixed, due to which its discrete angular movements or steps are carried out.

The first models of such devices appeared in the 30s of the XIX century and were a kind of magnet that sets the ratchet wheel in motion. During switching on, it moved by the value of the toothed step.

Previously, the mechanism was used on ships of the British Navy. in order to move torpedoes in the right direction.

A few years later, the US Army adopted this device and began to actively use it in its warships and other mechanisms. In 1919, the Scotsman Walker received a patent for an engine with a rotor.

Currently, such mechanisms are in demand and are often used. The stepper motor is used to ensure the smooth functioning of the grinding and milling machines, various household appliances, production mechanisms and transport, as well as hard drives of personal computers. That is why it is so in demand. The device consists of several parts:

• a controller designed to regulate the operation of a stepper drive;
• special magnetic parts;
• windings;
• a panel that acts as a control unit;
• signaling devices and transmitters, thanks to which the operation of the device is debugged and uninterrupted.

Bipolar motors have only one winding in one phase, while unipolar ones contain two. The former are considered more difficult to control, but ensure smooth operation of the device.

Principle of operation

A stepper motor works according to simple principles. The first step is applying voltage to the terminals. Thanks to this, the brushes on the device itself begin to constantly move. The idle motor has the ability to convert incoming pulses.

These pulses have a rectangular direction and the transformation goes to a predetermined position of the drive shaft, which is attached to it. As a result, the shaft moves at a certain angle. Devices equipped with such a gearbox are quite effective and reliable, provided there are several electromagnets. They should be located around the central piece of iron, which has a toothed shape.

The external control circuit supplies a signal to the magnet. If it becomes necessary to turn the shaft in one direction or another, the electromagnet to which the impulse was sent begins to quickly attract the teeth of the wheel. They gradually align with this element, but move in relation to other magnetic parts of the fixture.

After turning off the first electromagnet, the second turns on and the continuous movement of the gear begins. This aligns the part with the previous wheel. This cycle is repeated as many times as necessary. Each of them is called a constant step. That is why the engine got its name. You can calculate the speed of its work by counting the steps that are necessary to ensure a complete cycle.

You can control the operation of the device using a special driver. This is usually necessary in the case of setting up a machine or wind turbine.

Basic modes

The product operates in several modes that are pre-configured depending on the needs of the person. The most common are the following:

• Wave mode involves the flow of electric current through only one winding. Today it is rarely used in order to reduce the load on the engine and the amount of electricity consumed.
• Full Step - This is used much more often and is considered the standard mode for this type of engine. The voltage on the winding during this operation is the same and the device requires the maximum voltage for correct operation.
• Half-step mode is one of the original ways to change the operation of the device without affecting the control unit. It consists in simultaneously energizing all pairs of windings, which leads to the rotation of the rotor by half its normal pitch. Using this method, it is possible to obtain a double power motor with minimal energy consumption. It will wear less and last longer than one that is constantly running in full step mode.
• Microstepping is the most commonly used stepper motor today. The principle of operation consists in applying to the winding not a pulse, but a signal resembling a sinusoid in shape. This mode makes the engine smoother, and the transition from one step to another is invisible. Thanks to this, jerks and jumps of the fixture are reduced, it can function as a normal DC motor.

The latter mode is advantageous as it is more of a method for feeding the motor rather than controlling the windings. That is why it can be used with a wave or full-step mode of operation of the device. If we consider the scheme of the device functioning in microstepping mode, it may seem that the steps become larger. In fact, this is not the case, but the process still becomes smooth and there are no jerks.

Varieties of devices

Several types of stepper motors are distinguished depending on certain parts. Each of them has some peculiarities of functioning.

The permanent magnet motor is considered the most popular, is easy to set up and operate. The device carries a round magnet that resembles a disk and has different poles. When the device is turned on, the stator windings attract and repel the magnet on the rotor, which ensures the torsion of the mechanism.

When using this type of motor, the step size is measured, and the indicator fluctuates between 45-90 degrees. The ease of use of the device makes it in demand, and its long service life allows you not to think about frequent replacement.

Variable magnet instrument

Such devices do not have a special magnet on the rotor. This part is made of magnetic, soft metal, in the form of a toothed disk that resembles a gear. There are more than four different windings on the stator. They are powered in opposite pairs and attract the rotor.

It should be noted that the amount of torque is somewhat reduced, since the device does not have a permanent magnet. This is considered a disadvantage, but there is also an advantage, since there is no stopping moment during the operation of the device.

The stopping moment consists in rotationcreated by permanent magnets located on the rotor. They are attracted to the stator, namely to its armature, in the absence of electric current in the windings. It is easy to fix this moment - you need to try to turn the engine by hand in the disconnected state. In this case, clicks are usually heard at each step. The step range in such an engine ranges from 5-15 degrees.

Hybrid models

This type of device got its name because of the peculiarity of work, which involves a combination of the principles of a stepper motor with permanent and variable magnets. Provides good holding and dynamic torque. The advantage of the device is the minimum step size, which does not exceed 5 degrees. This ensures maximum accuracy.

The mechanical parts of the fixture rotate much faster than in other models with a similar operating principle. Often used in manufacturing machines. The main disadvantage of such an engine is its high cost.

It is known that a conventional motor with 8 windings will have 50 positive and negative poles, but such a magnet cannot be produced. That is why the device of the hybrid motor includes 2 magnetic disks, each with 50 teeth, as well as a cylindrical permanent magnet.

In the process of manufacturing the device, the disks are welded to different poles of this cylindrical magnet and it turns out that one of them on each of its teeth has a positive pole, and the other - negative. When viewed from above, the structure looks like a single disc with 100 teeth.

There are 75 steps per revolution of such an engine, each of which has an indicator of no more than 1.5 degrees.

Two-phase motors

The two-phase stepper motor is very easy to use, it can be installed and adjusted even by a person without experience and relevant skills. The device has two types of coil winding:

1. Unipolar consists in installing one winding, as well as a special magnetic tap in the center, affecting any phase. Each section is switched on to provide the required direction of the magnetic field. The advantage of this design is the ability to function without special switching. One transistor is needed for each winding, so the installation of the device is easier. There are three wires per phase, and six wires are required for the output signal. The windings can also be connected by connecting wires with permanent magnets. It is worth remembering that it will not be easy to turn the shaft when you touch the terminals. This is due to the fact that the common wire is slightly longer in length than the part that is used to connect the coils.
2. Bipolar motor types have only one winding. Electric current enters it by a special breaking method through a pole provided by a magnet. Each phase has two different wires. The device is somewhat more complicated than in unipolar models, but the efficiency is higher.

There are also three-phase motors that have a narrow area of ​​use: disk drives, various milling machines, printers and some cars where an unusual damper is used.

Other types of devices

The main feature of reactive devices is a small step, which reaches no more than 1 degree, as well as the location of the teeth located on the stator poles. The disadvantage of such a motor is the lack of a synchronizing torque in the event of a power outage of the windings.

To manufacture such a device, you will need a special switch, so its cost is high. Self-creation is also excluded due to the complexity of the design.

Synchronous linear stepper motors are used when it is necessary to automate the production process. To do this, you should ensure the movement of objects in the plane. For this purpose, a special transducer is used, which changes the rotary motion to translational. This can be achieved by using kinematics.

It is for this purpose that a linear motor is used, which converts impulses into movement along one line. In addition to automating the process, the device will simplify the kinematic diagram of the wires. In such a device, the stator is made of a soft magnetic metal, and there is also a permanent magnet. Stable operation of the motor is carried out under the condition of constant supply of pulses to the windings.

Stepper motors are versatile devices that ensure the smooth operation of a variety of electrical appliances and production equipment.