What are the components of a servo system?

1、 Servo system
A servo system refers to an automatic control system that utilizes the action of a component (such as a control rod) to reach or approach a predetermined state, and can compare the desired state (desired value) with the actual state, adjusting the control components according to their differences (sometimes the rate of change of this difference). Looking back at the development history of servo systems, from the earliest hydraulic and pneumatic to the current electrification, servo systems composed of servo motors, feedback devices, and controllers have gone through nearly 50 years.

Nowadays, with the continuous maturity of technology, AC servo motor technology has gradually replaced DC motors as the dominant executive motor in servo systems due to its excellent cost-effectiveness. The maturity of communication servo system technology has also led to rapid and diversified development in the market, and has become one of the supporting technologies for industrial automation.

2、 Servo system composition
The servo drive mainly consists of a servo control unit, a power drive unit, and a communication interface unit. The servo control unit includes position controller, speed controller, torque and current controller, etc.

The servo drive can be roughly divided into two modules: power board and control board. The power board is a strong electrical component (a power component with high power, high current, and low frequency), which includes two units: a power drive unit IPM for motor drive, and a switching power supply unit that provides digital and analog power for the entire system. The control board is the weak current part, the control core of the motor, and the operating carrier of the servo drive technology core control algorithm. The control board outputs pulse width modulation (PWM) or pulse frequency modulation (PFM) signals through corresponding algorithms as driving signals for the drive circuit, to change the output power of the inverter and achieve the purpose of controlling the AC servo motor. Among them, the inverter is a converter that converts direct current energy (batteries, storage batteries) into fixed frequency and voltage or frequency and voltage regulated alternating current (usually 220V, 50Hz sine wave).

Among the main material costs of servo drives, IGBT and DSP chips account for over 50% of the total material costs. IGBT, also known as insulated gate bipolar transistor, is a composite fully controlled voltage driven power semiconductor device composed of bipolar transistor and insulated gate field-effect transistor. It combines the advantages of high input impedance of MOSFET and low conduction voltage drop of power transistor. When used in power driving units, it can assist in the conversion of DC to AC.

3、 The development trend of servo systems
（1） Communicationalization
Servo technology will continue to rapidly shift from DC servo systems to AC servo systems. From the current international market situation, almost all new products are AC servo systems. In industrialized countries, the market share of AC servo motors has exceeded 80%. In China, there are more and more manufacturers producing AC servo motors, gradually surpassing those producing DC servo motors. It can be foreseen that in the near future, apart from certain micro motor fields, AC servo motors will completely replace DC servo motors.

（2）Fully digitized
The servo control unit using new high-speed microprocessors and dedicated digital signal processors (DSPs) will comprehensively replace the servo control unit mainly composed of analog electronic devices, thus achieving a completely digital servo system. The implementation of full digitization has transformed the original hardware servo control into software servo control, making it possible to apply advanced algorithms of modern control theory in servo systems, such as optimal control, artificial intelligence, fuzzy control, neural networks, etc.

（3）Adopting new power electronic semiconductor devices
At present, the output devices of servo control systems are increasingly using new power semiconductor devices with high switching frequencies, mainly including high-power transistors (GTR), power field-effect transistors (MOSFETs), and insulated gate transistors (IGBTs). The application of these advanced devices significantly reduces the power consumption of the servo unit output circuit, improves the system's response speed, and reduces operating noise. It is worth mentioning that the latest servo control systems have begun to use a new type of module that integrates control circuit functions and high-power electronic switching devices, called Intelligent Power Modules (IPM). This device integrates input isolation, energy consumption braking, over temperature, over voltage, over current protection, and fault diagnosis functions into a small module. Its input logic level is fully compatible with TTL signals and can directly interface with the output of the microprocessor. Its application significantly simplifies the design of servo units and achieves miniaturization and miniaturization of servo systems.

Source: 21ic Electronic Network