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Many people are very confused about the definition of the term servo motor. I have seen so many of the following.
The idea that a servo motor is actually a DC brushless motor.
The idea that a servo motor is actually an AC motor.
Think that a servo motor is any brushless motor.
that a servo motor is synonymous with a motor.
In fact, a servo motor is such a motor, which is mainly used for more precise position, speed or torque output. To be precise, a servo motor is not so much a motor as it is a system. So just one motor can't even be considered a servo motor, because they don't have the functions of a servo motor. A servo motor is a motor system which contains a motor, a sensor and a controller. A DC brushless motor can be part of a servo motor, as can an AC motor, but they are not servo motors. As a system, it can have reduction gears or not.
So what is a servo? A servo is a common name, given by people who play with model airplanes and boats. This is because this type of motor is more commonly used for rudder steering. A rudder is actually a low-end servo motor system, and it is also the most common servo motor system. It compares the PWM signal with the voltage of a sliding resistor and achieves position control with a fixed control gain by means of a hardware circuit. In other words, it contains the motor, sensor and controller and is a complete servo motor (system). Inexpensive and compact, but with very low accuracy and poor position calming capability, it is able to meet many low-end requirements. (Of course there are also smaller servo motors with metal gears for higher precision in the industry, those motors are not covered here)
Stepper motors rely primarily on a sequence of stator coils energised to form a magnetic field at different angles in sequence, pushing and pulling the stator to rotate. The advantage of stepper motors is that you can dispense with the sensors used to measure the angle of rotation of the motor. It therefore has certain advantages in terms of construction and price. And it is relatively simple to control position and speed. The disadvantages are, firstly, that the loads are relatively small compared to motors of the same power and that you cannot output large torques without an angle sensor. Secondly, the power consumption is relatively high and it is either fully on or fully off. So either it is close to full power consumption or it cannot produce power. (The specific reasons and structure of the relevant information can be consulted, the Internet is everywhere, it is not difficult to understand, I will not be redundant here) Therefore, stepper motors are generally only used for small and very certain load, position accuracy requirements are not very high, sensitive to the volume or in the lower price want to do a higher reliability of the occasion.
The most common are optical drives, scanners, photocopiers and so on. Of course, like the servo, it is also popular with hobbyists who cannot afford to build their own servo motor system and is used in some hobby projects as a replacement for a complete servo motor system.
So to give a simple example. Scanners (including those inside business printers these days) often have a movement where the scanner has to move quickly from one end of the slide to the other before it can actually scan. That is actually the system finding the zero point of position. What is used there is a stepper motor which drives the movement of the scanner. But when it starts the scanning task, the system doesn't know the exact position of that scanner (because there is no position sensor), so it has to drive the scanner towards the other side of the slide first. At that end of the slide, there is a touch switch that generates an electrical signal once the scanner touches it. This way the system knows that the scanner has gone to the end, at which point the position of the scanner is determined so that it can start scanning. This stepper motor is switched off when it has finished its task (because the power consumption is not low), so the scanner can easily be shifted if there is a vibration or something. So the next time the stepper motor is powered up, you have to perform the same action as described earlier to determine the position of the scanner again.
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