A servo system is a feedback control system that precisely follows or reproduces a process
Servo system, also known as follow-up system, is an automatic control system used to accurately control the position, orientation, status and other output controlled quantities of objects. It enables the output (such as mechanical displacement, velocity, or acceleration) to accurately follow the change of the input target (or given value), and is widely used in industrial automation, national defense and military industry.

The basic requirements for the servo system are stability, precision and fast response.
Good stability: after the disturbance acting on the system disappears, the system can return to the original stable state or under the action of input command signals, the system can reach a new stable state of operation, and under the given input or external interference, it can reach a new or return to the original equilibrium state after a short adjustment process;
High accuracy: The accuracy of the servo system refers to the accuracy of the output following the input. As a CNC machine tool for precision machining, the required positioning accuracy or contour machining accuracy is usually relatively high, and the allowable deviation is generally between 0.01~0.00lmm;
Good fast response: There are two meanings, one refers to the rapid change of the output with the input command signal in the dynamic response process, and the other refers to the rapid degree of the end of the dynamic response process. Fast response is one of the signs of the dynamic quality of the servo system, that is, the response of the tracking instruction signal is required to be fast, on the one hand, the transition process time is short, generally within 200ms, or even less than tens of milliseconds; On the other hand, in order to meet the overshoot requirements, the leading edge of the transition process is required to be steep, i.e., the rate of rise should be large.
High energy saving: Due to the rapid response of the servo system, the injection molding machine can quickly adjust the supply according to its own needs, which can effectively improve the utilization rate of the electric energy of the injection molding machine, so as to achieve high efficiency and energy saving.

The role and composition of servo system in CNC machining
In the automatic control system, the system in which the output can change with a certain degree of accuracy with the change of the input quantity is called the follow-up system, also known as the servo system. The servo system of CNC machine tool refers to the automatic control system with the position and speed of the moving parts of the machine tool as the control quantity, also known as the follow-up system.
The servo system is composed of a servo drive device and a driving element (or actuator servo motor), and the high-performance servo system also has a detection device to feedback the actual output state.
The function of the CNC machine tool servo system is to accept the command signal from the numerical control device, drive the moving parts of the machine tool to follow the command pulse movement, and ensure the fast and accurate action, which requires high-quality speed and position servo. The above refers to the main feed servo control, in addition to the servo control of the main movement, but the control requirements are not as high as the former. Technical indicators such as accuracy and speed of CNC machine tools often depend mainly on the servo system.
Application Trends
Automatic control systems are not only developing rapidly in theory, but also in their application devices. Modular, digital, high-precision, long-life devices are updated every 3~5 years. The traditional AC servo motor is soft, and its output characteristics are not single-valued; The stepper motor is generally open-loop control and can not be accurately positioned, the motor itself has a speed resonance zone, the PWM speed regulation system has poor performance on position tracking, the frequency conversion speed regulation is simple but the accuracy is sometimes not enough, the DC motor servo system is widely used in the position follow-up system with its excellent performance, but it also has shortcomings, such as complex structure, the contradiction of the dead zone is prominent at ultra-low speed, and the reversing brush will bring noise and maintenance problems. The new permanent magnet AC servo motor has developed rapidly, especially after the development from square wave control to sine wave control, the system performance is better, it has a wide range of speed regulation, especially the low speed performance is superior.