Servo system principles and classification

The servo system is mainly composed of a servo controller, a drive circuit, a servo motor and corresponding feedback detection devices.

1. Servo system principle

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 the signal no longer appears, the controlled transmission device will stop moving until the control signal arrives.

2. Servo system classification

(1) According to the different objects of its action, it can be divided into two categories: position servo system and speed servo system.

1) Position servo system

It refers to a servo system that can accurately track and locate the target command position. Depending on whether there is feedback, the position servo system is divided into open-loop control and closed-loop control.

The open-loop position servo system has the advantages of simple structure and low cost, but it does not have position and speed feedback functions, and its 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. Under full closed-loop control, the detection element directly detects the displacement of the controlled object on the workbench and feeds the displacement back to the controller to form full closed-loop control. Since the controller can control according to the actual displacement of the controlled object, the full closed-loop control has high positioning accuracy and can eliminate the error of the entire process from the motor to the mechanical transmission mechanism to the controlled object. However, the closed-loop control structure is relatively complex, the cost is high, and it is difficult to implement.

2) Speed ​​servo system

Usually the load torque of the driven machine changes frequently, and the voltage and frequency of the power supply also change frequently, so the running speed of the driven object also changes frequently. Therefore, the main task of the speed servo system is to keep the driven machine (or load) running stably at the required precise speed (not just one speed).

(2) According to the different actuator motors, it can be divided into DC servo system and AC servo system.

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

The AC servo system is mainly composed of an AC servo drive (or controller) and an AC servo motor. The system is centered on the drive to drive and control the operation of the AC servo motor. The closed-loop control of torque, speed or position makes the system have excellent dynamic and static performance. An industrial robot has four major components, namely the body, servo, reducer and controller. Among them, the general structure of the industrial robot electric servo system is three closed-loop controls, namely the current loop, speed loop and position loop. In general, for an AC servo drive, multiple functions such as position control, speed control, and torque control can be achieved by manually setting its internal function parameters.

The servo system (servomechanism), also known as the follow-up system, is a feedback control system used to accurately follow or reproduce a process. The servo system is an automatic control system that enables the output controlled quantity such as the position, orientation, and state of an object to follow any changes in the input target (or given value).

The servo system is a product developed based on frequency conversion technology. It is an automatic control system that uses mechanical position or angle as the control object. In addition to speed and torque control, the servo system 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, and can also be called a follow-up system.

In a narrow sense, the servo system is also called the position following system. Its controlled quantity (output) is the linear displacement or angular displacement of the load mechanical spatial position. When the position given quantity (input quantity) changes arbitrarily, the main task of the system is to make the output quantity quickly and accurately reproduce the change of the given quantity.