What is a servo motor? Essentially, a servo motor is a motor and the driver that controls it. The motor is called a servo motor, and the driver is called a servo driver. The word 'servo' originates from control, and is synonymous with precise control. Clearly, a system like the "servo" was specifically developed to control motors, and precisely control them. At this point, many people might wonder: why create such a complex system to control a motor? This necessitates introducing some information about motor applications, principles, and development.
An electric motor is an electronic product that uses electromagnetic principles; a current-carrying coil rotates under the influence of a magnetic field. Based on application development, electric motors are classified as DC motors and AC motors. DC motors are further divided into brushed and brushless motors, primarily because brushed motors require periodic replacement of carbon brushes, making maintenance cumbersome; AC motors are further divided into single-phase, three-phase, synchronous, and asynchronous motors. Electric motors are essential for generating motion in steam engines and internal combustion engines. Therefore, based on various applications and operational requirements, early humans designed numerous types and categories of electric motors, each with its own strengths and advantages, and they existed for a considerable period. However, their inherent shortcomings and characteristics gradually became unable to meet human needs. For example, the speed of all electric motors is difficult to control. Even DC motors, known for their speed control, still find it very difficult to maintain a precise and constant speed. Furthermore, based on electromagnetic principles, we know that motor coils are typically composed of low-resistance materials such as copper, meaning the instantaneous current can be extremely large. The force of the magnetic field on the coil is closely related to this current. Only when the motor's speed and inductive reactance are constant can the current flowing through the motor remain constant. Experience shows that the starting current of a motor is 5 to 10 times its normal operating current, and below 3 times the normal operating current, the motor struggles to start. These are inherent characteristics and shortcomings of electric motors to this day. Therefore, it's easy to understand that if a motor stalls (completely stops moving), the current flowing through it can be catastrophic. At the same time, it is not difficult to understand that, compared to the transmission system, the torque of the motor at the moment of startup can be very destructive, because the difference between the torque and the torque under normal working conditions is too great.
Therefore, people have been focusing on the speed and torque control of motors for a long time. Later, breakthroughs were made in frequency conversion technology, leading to the development of variable frequency drives (VFDs). These drives can control the speed of three-phase motors to a certain extent and also alleviate the torque and acceleration problems during motor startup. The variable speed elevators and escalators we use daily are basically based on VFD technology. VFD technology uses inverter technology to control the frequency and current of the three-phase power supply to the motor, thereby achieving a certain degree of control over the motor to maintain a constant speed. The key to this technology lies in the algorithm within the programmable chip (commonly known as the CPU) of the VFD. Therefore, the VFD itself has many parameters that users can adjust to suit different application scenarios.
Servo motors are a further development of frequency conversion technology. They use an encoder mounted on the motor to provide feedback. The CPU inside the driver then combines this feedback to generate pulses that control the three-phase current output, thus achieving precise control of the servo motor. Enabling a servo driver essentially involves starting a pre-designed pulse from the three-phase motor power supply, causing the motor to hover between stopping and starting. This solves the problem of the initial instability of the motor's start-up and allows the servo driver to quickly rotate the motor upon receiving an external "motor rotate" command. The numerous parameters within a servo motor are simply categorized and adjusted according to the various applications, working in conjunction with a host computer, machine tools, and specific transient and force-related adjustments.
I think that laymen can't understand highly technical terms, while insiders seem to understand all the terms but can't imagine how they are actually expressed.
So, we can understand a servo system through the lens of a company's finance department. The boss typically only tells the finance staff, "I need this kind of report," "I need this kind of income and expenditure statement," "I need this kind of business trip arrangement," and so on. The finance department then uses all the information and methods available within the company to calculate and arrive at the answer the boss needs. A servo system is exactly that kind of system.
