In this blog post, we’ll explore the principles of motor control, the roles of encoders and PWM—key technologies in this field—and why motor control is so important in modern engineering.

Why is motor control important?

Since the dawn of the 21st century, the scope of engineering has expanded significantly, and technological standards have become increasingly sophisticated. In particular, the rapid advancement of computer technology has become the key driving force behind the development of cutting-edge engineering, and many people immediately think of computers when they hear the term “cutting-edge engineering.” However, there is a field whose importance is relatively less well known, even though it involves devices just as crucial as computers: motors. When people hear the word “motor,” they often think of small DC motors found in miniature race cars or the motors in electric fans. At first glance, these motors seem far removed from cutting-edge engineering, so why are they considered a technology as important as computers?
Let’s take a look at some representative engineering technologies that are attracting a lot of attention today. 3D printers, drones, humanoid robots, and rocket attitude control systems are prime examples. These devices all share the common feature of using motors to control movement. However, an even more important commonality is the need to achieve extremely precise motion. 3D printers must deposit material at the desired location without any error, while drones must control the rotational speed of each motor in real time to maintain a stable flight attitude. Humanoid robots and rocket attitude control systems also require extremely precise control of a motor’s rotation direction, speed, and output to maintain balance. The reason motors are as important as computers lies not simply in the fact that they are rotating devices, but in the “motor control” technology that enables such precise movements.
The simple DC motor we commonly think of is a device that starts rotating immediately when connected to a battery. So how is it possible to achieve precise position or speed control with such a simple device?
Simply put, motor control is the technology that allows us to control exactly how fast, in which direction, and how much a motor rotates.
To understand this more easily, let’s imagine a motor as a person spinning in place. If a person decides in advance how many revolutions to make and how fast to spin before starting, they would count the number of revolutions each time they complete a full circle until they reach the target number. They could also adjust the force in their legs to change the rotation speed. In other words, to control rotation, you need, first, a way to determine how much rotation has occurred, and second, a way to adjust the rotation speed.
Motors also utilize these two elements. An encoder is used to detect the amount and direction of rotation, while a control method called PWM (Pulse Width Modulation) is used to control the rotational speed and output. So, how do encoders and PWM perform these functions, respectively?

Encoder

The basic principle of an encoder is relatively simple. To put it simply, it consists of two switches arranged at regular intervals, with each switch generating a signal as the motor rotates. The key is that by analyzing the order in which these two signals are generated, the direction and amount of rotation can be determined.
For example, let’s assume that Switch A is on the left and Switch B is on the right of a reference line. If we label the signal generated by A as [A] and the signal generated by B as [B], then when the motor rotates clockwise, the signals are generated in the following order:

[B][A][B][A][B]________[A][B]_______

Conversely, when rotating counterclockwise, the order is as follows:

[A][B][A][B][A]________[B][A]_______

As shown, the amount of rotation can be calculated based on the number of repetitions of [A][B] or [B][A], and the direction of rotation can be determined by the order in which the two signals are generated.
In fact, encoders used in industrial settings offer much higher resolution than this. Products that generate hundreds to thousands or more pulses are widely used, allowing for precise measurement of even very small angular changes. These high-resolution encoders play a key role in fields requiring precise control, such as industrial robots, CNC machine tools, and semiconductor equipment.

PWM (Pulse Width Modulation)

Now, let’s consider a DC motor used in a mini race car. It’s easy to see that even with the same motor, supplying a higher voltage causes it to rotate faster and with greater force. In other words, the motor’s rotational speed and output are closely related to the average voltage supplied.
However, in actual electronic devices, generating and supplying the desired voltage freely is not as easy as one might think. This is because most standard power adapters only output a fixed voltage. So, how can we achieve a variety of speeds?
The method used here is PWM.
PWM does not continuously vary the voltage itself but instead switches the power on and off at a very high speed. In digital circuits, only two states can generally be output: 0V as 0 and 5V as 1. The key to PWM is controlling how long the 5V output is maintained during a fixed signal period.
The proportion of the signal period during which voltage is output is called the duty cycle. By adjusting the duty cycle, the motor is effectively supplied with different average voltages.
For example, if the duty cycle is 10%, the average voltage applied to the motor is approximately 0.5V; if it is 50%, the average voltage is approximately 2.5V. In this way, PWM enables very precise control of a motor’s speed and output by switching the power supply extremely rapidly, and it is one of the most widely used methods in modern motor control systems.
Even today, the general public still tends to view motors as devices of little particular importance. Consequently, people often fail to fully appreciate the significance of motor control technology. However, as computer technology, communications technology, control technology, and semiconductor technology have advanced, cutting-edge engineering fields now demand even higher precision and stability; consequently, motor control has become an essential technology rather than an optional one.
Even today, motor control technology is utilized as a core foundational technology in various cutting-edge industries, including industrial robots, electric vehicles, drones, autonomous driving systems, smart factories, and medical robots. In this article, I have introduced representative motor control methods using encoders and PWM, along with examples of their application. I hope readers will gain an understanding of the principles behind motor control and be able to answer for themselves the question posed in the first paragraph: “Why is motor control a technology as important as computers?”