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What is a motor? The role, types, history, working principles, and structure of motors

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1. What is a Motor? Understanding the Role of Motors

Motors are devices that convert electrical energy into mechanical energy. They are used in all kinds of devices that involve motion, ranging from home electronics such as washing machines, fans, and air conditioners to social infrastructure such as ATMs and automatic ticket gates.
It is probably safe to say that all people living today enjoy the benefits of motors in their daily lives. Besides motors, there are other sources of mechanical energy sources, such as combustion engines and steam engines.
However, motors have three advantages that other power sources do not have.

1. High energy conversion efficiency

For example, the thermal efficiency of engines ranges from 30 to 40%. This means that only 30 to 40% of the fuel's energy can be used to do useful work and the remaining 60 to 70% is dissipated as heat.
Compared to this, motors have a conversion efficiency of over 80%. This shows motors can turn energy into useful mechanical work much more efficiently than engines.

2. Simple structure for easy control

An engine consists of a number of components with each of them manufactured with high prevision. Also, electronic control of an engine is quite complicated and requires various sensors.
Motors, in contrast, have a much simpler structure. They are driven directly by electricity and therefore can be finely controlled by varying voltage.

3. Environmentally friendly

This point is in fact of great importance. Gasoline engines extract mechanical energy from fuel through combustion, inevitably emitting carbon dioxide (CO2). Motors, on the other hand, do not emit any gases themselves.
As the trend toward carbon neutrality accelerates, great expectations are being placed on motors.

Motors have such a significant advantage, and so they are used in countless types of machines as a driving force and control device. There will be more and more applications of motors in the future.

A related article "What is a stepping motor? The working, types, uses (drive circuits and control methods), advantages, and characteristics"
presents further on the working principles and features of stepping motors.

2. History of Electric Motors

Motors have been invented and evolved along with the wave of technological advance in society.
In the past, humans had used human and animal power to move things. It have always been and still is common for people to move things on their own. Horse-drawn carriages are said to have been invented as early as before BC, and as we know, the Heian aristocrats in Japan used ox-drawn wagons.
However, human and animal power, no matter the use of levers and pulleys, had limitations in terms of speed and power.

The Industrial Revolution from the late 1700s through the 1800s drastically changed this situation.
Steam engines, which had power far beyond that of humans and animals, appeared on the scene, and factory-based machine industry was established. The social structure was transformed from an agrarian society to an industrial society. The development of steam locomotives, steam automobiles, and steam ships also greatly changed the forms of transportation and logistics. However, steam engines had the disadvantage of being large and heavy.

Inventors and researchers began to search for alternatives to steam engines. Electric motors emerged in the midst of these changes.
The English scientist Michael Faraday discovered the principle behind the electric motor and generator in 1821. In 1831, he also discovered the principle of electromagnetic induction. This would be applied to motors, helping them evolve.
Following Faraday's discovery, a DC motor was developed by Thomas Davenport of the United States and others, but it didn't go far enough to be commercialized.

The first practical motor was probably the double-layer AC induction motor, which was invented by Nikola Tesla. In 1888, he developed a multi-phase induction generator to turn the motor he developed, which was patented in 1889. This led to the practical application of motors.

After that, motors have evolved continuously, not only as a driving force but also as a control device. It is said that about 50% of all electricity in Japan is currently consumed by motors. Motors are so closely connected to human life that they have become the backbone of civilization.

3. History of SANYO DENKI's Motors

The history of SANYO DENKI's motor manufacturing dates back to the first half of the 20th century.

First, in 1932, we developed a generator, whose structure is similar to that of motors, for use in radio communications equipment. In 1952, after the war, we modified the generator we had manufactured for military use before for civilian applications. In the following years, we had established ourselves a major manufacturer in the telecommunications and power supply fields.

Also in 1952, we received a request from the Electrotechnical Laboratory (now the National Institute of Advanced Industrial Science and Technology) to develop a servo motor, and began our research. Not long after, we successfully developed the first servo motor in Japan. It took some time before the servo motor saw the light of day due to unexpectedly low demand at the time, but it set the basis for the future, eventually becoming the current leading product of SANYO DENKI.

After the servo motor development, we also manufactured and launched the stepping motor and cooling fan, both for the first time in Japan. While developing these first products in Japan, we have also produced various motors on a global scale in response to the trends of office automation and factory automation.

4. Basic Theory, Structure, and Working Principles of Motors

A motor basically rotates by using the magnet's characteristics: "opposite poles attracting" and "like poles repelling."
For example, take a small motor used in radio-controlled cars. In a small motor, a coil is mounted on an axle and is placed between N and S poles of a permanent magnet.

When a current passes through the coil, it becomes an electromagnet. It is easier to understand if you consider that the coil turns into a magnet with N and S poles.

Then, the N pole of the permanent magnet repels the N pole of the coil, and the S pole of the permanent magnet repels the S pole of the coil. In other words, the N pole of the permanent magnet attracts the S pole of the coil, and the S pole of the permanent magnet attracts the N pole of the coil.
This causes the coil to rotate 180 degrees around the axis.

What most likely follows the 180 degree rotation, however, is the coil being at rest. This is because the N pole of the permanent magnet and the S pole of the coil attract each other, while the S pole of the permanent magnet and the N pole of the coil attract each other. What can be done to cause the coil to rotate another 180 degrees, a total of 360 degrees?

Switch the direction of the electric current flow in reverse. This will switch the positions of the coil's N and S poles.
Recall that now the N pole of the permanent magnet and the S pole of the coil attract each other, while the S pole of the permanent magnet and the N pole of the coil attract each other. By reversing the current flow through the coil using a rectifier and a brush, the N and S poles of the coil can be switched.
Then, this causes the N pole of the permanent magnet to repel the N pole of the coil and the S pole of the permanent magnet to repel the S pole of the coil. At the same time, the N pole of the permanent magnet and the S pole of the coil attract each other, while the S pole of the permanent magnet and the N pole of the coil attract each other. This causes the coil to rotate another 180 degrees. The coil has now rotated 360 degrees.

Motors rotate continuously by repeating this cycle.
In the following sections, we'll look at the types of motors as a driving force and the types of motors as a control device.

5. Types of Motors as a Driving Force

Types of Motors as a Driving Force

When you think of motors as a driving force in machines, they can be classified into two groups depending on the power supply: DC motors and AC motors.

What Is a DC (Direct Current) Motor?

DC motors are an electric motor that runs on DC power.
They are used in a wide variety of products, from electrical appliances commonly used in daily life to equipment used in factories.
DC motors are divided into two types: brushed DC motors and brushless DC motors. A brush is a component for conducting electricity to the motor coils.

A brushed DC motor has an inner rotor with coils and an outer permanent magnet, and the rotor rotates with a DC current passing through a brush. This is the motor with a simple mechanism introduced above, and it is used in radio-controlled cars and models.

This motor has a basic characteristic that its rotational speed increases in proportion to the voltage.
For example, when a DC brush motor is powered by dry cell batteries, it rotates faster when two batteries are connected than when one is connected. However, the commutator and carbon brush, which change the direction of electricity flowing to the coil, are always in contact, wear out after prolonged operation, requiring periodic maintenance.

On the other hand, a brushless DC (BLDC) motor has an inner permanent magnet and outer coils. This motor runs by having the inner permanent magnets rotated with a current passing through the coils via a current control circuit, Since there are no brushes, the maintenance frequency can be reduced. Also, brushless DC motors do not produce carbon dust coming from a brush, thus the operating environment can be kept clean. However, they require a circuit outside the motor to control the direction of the current, making them more expensive than brushed DC motors.

Motor types
Advantages Disadvantages
Brushed DC motor Low cost Prone to wear
Brushless DC motor Long life High cost

What Is an AC (Alternating Current) Motor?

An AC motor is an electric motor that is powered by alternating current. It consists of an outside stator having coils and an inside rotor.
A significant advantage of AC motors is that a rectifier, brush, or control circuit is required. Since they have a simple structure and can be manufactured with low cost, they are used in a variety of applications, including home electronics such as electric fans and vacuum cleaners, electric water pumps, and conveyors.

6. Types of Motors as a Control Device

For motor use as a control device for precisely controlling the motion of machines, there are two major categories: stepping motors and servo motors.

Stepping Motor

Stepping Motor

Stepping (stepper) motors rotate precisely at a constant angle.

Imagine an analog clock with the second hand rotating every second. Stepping motors can be controlled so that they rotate only at a set angle at a time. Aside from analog clocks, they can be found in applications such as printers, the airflow direction louver in air conditioners, ATMs, ticket machines, and automatic ticket gates.

The working of rotating a motor precisely at a constant angle is quite simple. The rotor in a stepping motor has a number of teeth. First, pass a current through the motor; wait until the rotor rotates by the amount you desire, and then stop the current. That's it. The motor stops after rotating precisely the desired amount.

For example, typical 2-phase stepping motors have 200 rotor teeth. These motors have 200 steps to complete a 360 degree rotation, so they rotate 1.8 degrees per step. If you want the motor to rotate by 18 degrees, you need to pass a current through it and stop the current after the motor rotates by 10 teeth.

By the way, controlling a stepping motor requires a driver, a control device. With a driver, you can designate the amount of motor rotation you want and send a command pulse to the motor. A pulse is an electrical signal produced when a power supply is turned on and off. When the driver sends a pulse signal to the stepping motor, the motor rotates by one-tooth and comes to a stop.

As in the earlier example, suppose you want to rotate a typical 2-phase stepping motor with 200 teeth by 18 degrees. In this case, you need to send 10 pulse signals from a driver. Then, the stepping motor will receive and follow the pulse signals, rotating by 10 teeth—18 degrees—and then coming to a stop.

As you see, a driver is essential for controlling a stepping motor.

Servo Motor

Servo Motor

Like stepping motors, servo motors are designed to rotate by the amount you want. However, there is a clear difference between servo motors and stepping motors.

Servo motors, unlike stepping motors, do not have teeth on the rotor. Therefore, there are no limitations such as rotating the rotor in 1.8-degree increments, so if a high-resolution encoder is used, it is even possible to stop the rotor precisely after much smaller rotations, such as one-millionth of a degree.

This precise control requires an encoder. With an encoder accurately tracking the angular position of the rotor, servo motors can be precisely positioned at the intended angular position. Even after the motor is positioned, the encoder continues to monitor the motor position; as soon as a positional deviation from the target position is detected, the encoder automatically sends a feedback, ensuring correction.

7. Conclusion

This training article has provided the "role, types, history, working principles, and structure of motors."
Knowing and understanding motors better will help you select the best motor for your equipment, which will boost its performance.
SANYO DENKI offers a wide variety of motors available. Feel free to contact us if you have any questions on selection of motors.

Date of publication: August 5, 2022

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