Nowadays, with the continuous maturity of technology, AC servo motor technology has gradually replaced DC motor as the leading execution motor of servo system with its excellent cost performance. The maturity of AC servo system technology has also made the market show rapid diversification and become one of the supporting technologies of industrial automation.

main role

1. Control the high power load with a small power command signal;

2. In the absence of mechanical connection, the output shaft located at a distance is controlled by the input shaft to realize remote synchronous transmission;

3. Make the output mechanical displacement accurately track electrical signals, such as recording and indicating instruments.

Main classification

From the nature of the components of the system, there are electrical servo systems, hydraulic servo systems and electric-hydraulic servo systems and electrical-electrical servo systems;

From the physical properties of the system output, there are speed or acceleration servo systems and position servo systems;

From the characteristics of the components and signal characteristics contained in the system, there are analog servo systems and digital servo systems;

From the structural characteristics of the system, there are single-return servo system, multi-feed servo system, open-loop servo system, and closed-loop servo system.

The servo system is divided according to its driving components, and there are a step servo system, a DC motor (referred to as a DC motor) servo system, and an AC motor (referred to as an AC motor) servo system. According to the control method, there are open-loop servo system, closed-loop servo system and semi-closed-loop servo system. In fact, the numerical control system is also divided into three types: open loop, closed loop and semi-closed loop, which are related to the three methods of servo system.

1, open loop system

The open loop system is mainly composed of a drive circuit, an actuator and a machine tool. A commonly used actuator is a stepper motor. The open loop system, which is usually referred to as a stepper motor as an actuator, is a stepper servo system. In this system, if it is a high power drive, a stepper motor is used as the actuator. The main task of the drive circuit is to convert the command pulse into the signal required to drive the actuator.

2, closed loop system

The closed-loop system is mainly composed of an actuator, a detection unit, a comparison link, a drive circuit and a machine tool. Its block diagram is shown in Figure 2. In the closed loop system, the detecting component detects the actual position of the moving part of the machine tool and converts it into an electrical signal for feedback to the comparison link. Common detection components include resolvers, inductosyn, gratings, magnetic grids, and encoder discs. A servo system consisting of a detecting element mounted on a lead screw is generally referred to as a semi-closed loop system; a servo system composed of detecting elements mounted on a workbench is referred to as a closed loop system. Due to the transmission error between the lead screw and the table, the accuracy of the semi-closed loop servo system is lower than that of the closed loop servo system. The function of the comparison link is to compare the command signal with the feedback signal. The difference between the two is used as the following error of the servo system. After the drive circuit, the control actuator drives the table to continue moving until the following error is zero. According to the form of the signal entering the comparison link and the feedback detection mode, the closed-loop (semi-closed loop) system can be divided into three types: pulse comparison servo system, phase comparison servo system and amplitude comparison servo system.

Since the signal output from the comparison link is weak, it is not enough to drive the actuator, so it needs to be amplified, and the drive circuit is set for this purpose.

The function of the actuator is to convert the electrical signal representing the displacement into a mechanical displacement based on the control signal, ie the following error signal from the comparison. Commonly used actuators include DC wide speed motor and AC motor. The actuator is an integral part of the servo system, and the driver circuit varies from actuator to actuator.

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