I. Servo Motor System
Its main task is to amplify, transform, and regulate power according to control commands, making the torque, speed, and position control of the drive device highly flexible and convenient. In many cases, a servo motor system specifically refers to a feedback control system where the controlled variable (the system's output) is mechanical displacement or displacement velocity/acceleration. Its function is to ensure that the output mechanical displacement (or rotation angle) accurately tracks the input displacement (or rotation angle). Its structural composition is not fundamentally different from other forms of feedback control systems. Servo motor systems were initially used in national defense and military industries, such as artillery control, ship and aircraft autopilot, and missile launches. Later, they were gradually extended to many sectors of the national economy, such as automatic machine tools and wireless tracking control.
Servo is short for ServoMechanism, derived from the Greek word meaning "slave." As the name suggests, it refers to a system that follows external commands to perform desired movements, including physical quantities such as position, velocity, and torque. Looking back at the development of servo motor systems, from the earliest hydraulic and pneumatic systems to today's electrified systems, servo motor systems, composed of servo motors, feedback devices, and controllers, have been around for nearly 50 years.
Today, with the continuous maturation of technology, AC servo motor technology, with its excellent cost performance, is gradually replacing DC motors as the dominant actuator in servo motor systems. The maturity of AC servo motor system technology has also led to rapid and diversified market development, making it one of the supporting technologies for industrial automation.
The continuous upgrading of my country's manufacturing industry has provided a huge market for the development of my country's servo industry. In recent years, with the continued good development of industries such as CNC machine tools, packaging machinery, and electronic special equipment, as well as the increasing maturity of AC servo technology, the application of servo technology in emerging industries such as wind power in the new energy industry has led to the rapid development of my country's servo market. In 2010, my country's servo market grew by 39.7% year-on-year, with a market size of 3.99 billion yuan.
Many forward-thinking domestic manufacturers are increasing their R&D efforts to improve product performance, thereby expanding their brand appeal. It is expected that domestic servo manufacturers will soon break the import monopoly. Based on this, it is predicted that in the next five years, my country's servo motor system industry will benefit from industrial upgrading and maintain a growth rate of over 20%. By 2015, the market size of my country's servo motor system industry is expected to exceed 10 billion yuan, with domestically produced servo products accounting for approximately 40% of the market share.
II. Main Applications of Servo Motor Systems
In automatic control systems, a system whose output can follow changes in the input with a certain degree of accuracy is called a servo system, also known as a follow-up system. The servo motor system of a CNC machine tool refers to an automatic control system that uses the position and speed of the machine tool's moving parts as control quantities; it is also called a follow-up system.
A servo motor system consists of a servo drive unit and a drive element (or actuator servo motor). High-performance servo motor systems also have a detection device to provide feedback on the actual output status.
The function of the servo motor system in a CNC machine tool is to receive command signals from the CNC device, drive the moving parts of the machine tool to follow the command pulses, and ensure the speed and accuracy of the movements. This requires high-quality speed and position servo control. The above mainly refers to feed servo control; there is also servo control for the main motion, but the control requirements are not as high as the former. The accuracy and speed of a CNC machine tool often depend primarily on the servo motor system.
III. Development Trends of Servo Motor Systems
As the preceding discussion has shown, the application of digital AC servo motor systems is becoming increasingly widespread, and users are placing increasingly higher demands on servo drive technology. In general, the development trends of servo motor systems can be summarized in the following aspects:
1. Communication
Servo technology will continue its rapid shift from DC servo motor systems to AC servo motor systems. Currently, almost all new products in the international market are AC servo motor systems. In industrialized countries, the market share of AC servo motors has exceeded 80%. The number of domestic manufacturers producing AC servo motors is also increasing, gradually surpassing the number of manufacturers producing DC servo motors. It is foreseeable that in the near future, except in certain micro-motor applications, AC servo motors will completely replace DC servo motors.
2. Fully digital
Servo control units employing new high-speed microprocessors and dedicated digital signal processors (DSPs) will completely replace those based primarily on analog electronic devices, thus realizing a fully digital servo motor system. This full digitalization transforms traditional hardware servo control into software servo control, making it possible to apply advanced algorithms from modern control theory (such as optimal control, artificial intelligence, fuzzy control, and neural networks) within the servo motor system.
3. Employing novel power electronic semiconductor devices
Currently, servo control systems increasingly utilize high-frequency power semiconductor devices for their output circuitry, primarily high-power transistors (GTRs), power MOSFETs, and insulated-gate transistors (IGBTs). The application of these advanced devices significantly reduces power consumption in the servo unit's output circuit, improves system response speed, and reduces operating noise. Particularly noteworthy is the emergence of a new type of module in servo control systems that integrates control circuit functions with high-power electronic switching devices, called Intelligent Power Modules (IPMs). These devices integrate input isolation, regenerative braking, over-temperature, over-voltage, and over-current protection, as well as fault diagnosis, all within a small module. Their input logic levels are fully compatible with TTL signals and can directly interface with microprocessor outputs. Their application significantly simplifies servo unit design and enables the miniaturization and micro-miniaturization of servo motor systems.
