A servo system mainly consists of a servo controller, a drive circuit, a servo motor, and corresponding feedback detection devices.
1. Servo System Principles
When a control signal is given manually and received by the servo control system, the actuator will perform a series of movements and actions according to the instructions of the control signal; if no signal is received, the controlled transmission device will stop moving until the control signal arrives.
2. Servo System Classification
(1) Based on the different objects they act on, they can be divided into two main categories: position servo systems and speed servo systems.
1) Position Servo System
A position servo system is a servo system capable of accurately tracking and locating a target command position. Based on the presence or absence of feedback, position servo systems are divided into two types: open-loop control and closed-loop control.
Open-loop position servo systems have the advantages of simple structure and low cost, but they do not have position and speed feedback functions. Their position control accuracy depends on the step angle of the stepper motor and the accuracy of the transmission mechanism.
Closed-loop control is divided into full closed-loop control and semi-closed-loop control. In full closed-loop control, the sensing element directly detects the displacement of the controlled object on the worktable and feeds this displacement back to the controller, thus forming a full closed-loop control. Because the controller can control based on the actual displacement of the controlled object, full closed-loop control has high positioning accuracy and can eliminate errors throughout the entire process from the motor to the mechanical transmission mechanism and then to the controlled object. However, closed-loop control structures are relatively complex, costly, and difficult to implement.
2) Speed servo system
The load torque of the driven machinery is usually constantly changing, as are the voltage and frequency of the power supply. Consequently, the running speed of the driven object is also typically variable. Therefore, the primary task of a speed servo system is to maintain the driven machinery (or load) at a stable operating speed (not just one specific speed) required.
(2) According to the different motors they use, they can be divided into DC servo systems and AC servo systems.
1) DC servo system
A DC servo system refers to a servo system in which the servo motor uses a DC motor.
2) AC servo system
An AC servo system mainly consists of an AC servo driver (or controller) and an AC servo motor. The system is centered around the driver, which controls the operation of the AC servo motor. Closed-loop control of torque, speed, or position ensures excellent dynamic and static performance. Industrial robots have four main components: the body, the servo motor, the reducer, and the controller. The typical structure of an industrial robot's electric servo system involves three closed-loop controls: a current loop, a speed loop, and a position loop. Generally, for AC servo drivers, multiple functions such as position control, speed control, and torque control can be achieved by manually setting their internal parameters.
A servo system, also known as a follow-up system, is a feedback control system used to accurately follow or reproduce a process. A servo system is an automatic control system that enables the output controlled variables, such as the position, orientation, and state of an object, to follow any changes in the input target (or given value).
Servo systems are products developed based on frequency conversion technology. They are automatic control systems that use mechanical position or angle as the controlled object. In addition to speed and torque control, servo systems can also perform precise, fast, and stable position control.
In a broad sense, a servo system is a control system that accurately tracks or reproduces a given process; it can also be called a follow-up system.
A narrow-sense servo system, also known as a position follow-up system, controls the linear or angular displacement of the load's mechanical spatial position as its controlled variable (output). When the position setpoint (input) changes arbitrarily, the system's main task is to make the output quickly and accurately reproduce the change of the setpoint.
