Servo driver, also known as "servo controller" or "servo amplifier", is a type of controller used to control servo motors. Its function is similar to that of a frequency converter acting on ordinary AC motors, and it is part of a servo system. Generally, servo motors are controlled through three methods: position, speed, and torque to achieve high-precision positioning of the transmission system.
1、 Classification of servo motors
Divided into two categories: DC and AC servo motors, AC servo motors are further divided into asynchronous servo motors and synchronous servo motors. Currently, AC systems are gradually replacing DC systems. Compared with DC systems, AC servo motors have advantages such as high reliability, good heat dissipation, small moment of inertia, and the ability to work under high voltage conditions. Due to the lack of brushes and steering gear, the AC private server system has also become a brushless servo system. The motors used in it are brushless cage asynchronous motors and permanent magnet synchronous motors.
1. DC servo motors are divided into brushed and brushless motors
① Brushless motors have low cost, simple structure, large starting torque, wide speed regulation range, easy control, and require maintenance. However, they are easy to maintain (replacing carbon brushes), generate electromagnetic interference, and have requirements for the operating environment. They are usually used in cost sensitive ordinary industrial and civil applications;
② Brushless motors have small size, light weight, large output, fast response, high speed, small inertia, stable torque and smooth rotation, complex control, intelligence, flexible electronic commutation methods, can be square wave or sine wave commutation, maintenance free, efficient and energy-saving, low electromagnetic radiation, low temperature rise, long service life, and are suitable for various environments.
2、 Characteristics of different types of servo motors
1. Advantages and disadvantages of DC servo motors
Advantages: Accurate speed control, strong torque speed characteristics, simple control principle, convenient use, and affordable price.
Disadvantages: Brush commutation, speed limitation, additional resistance, generation of wear particles (not suitable for dust-free and explosive environments)
2. Advantages and disadvantages of AC servo motors
Advantages: Good speed control characteristics, smooth control can be achieved throughout the entire speed range, almost no oscillation, high efficiency of over 90%, low heat generation, high-speed control, high-precision position control (depending on encoder accuracy), can achieve constant torque within the rated operating area, low inertia, low noise, no brush wear, maintenance free (suitable for dust-free and explosive environments).
Disadvantages: The control is complex, and the driver parameters need to be adjusted on-site to determine the PID parameters, requiring more wiring.
At present, mainstream servo drives use digital signal processors (DSP) as the control core, which can achieve complex control algorithms, digitization, networking, and intelligence. Power devices generally use driving circuits designed with intelligent power modules (IPM) as the core. IPM integrates driving circuits internally and also has fault detection and protection circuits for overvoltage, overcurrent, overheating, undervoltage, etc. Soft start circuits are also added to the main circuit to reduce the impact of the starting process on the driver. The power drive unit first rectifies the input three-phase or mains power through a three-phase full bridge rectifier circuit to obtain the corresponding DC power. After rectification, the three-phase or mains power is used to drive the three-phase permanent magnet synchronous AC servo motor through a three-phase sine PWM voltage source inverter for frequency conversion. The entire process of the power drive unit can be simply described as the AC-DC-AC process. The main topology circuit of the rectifier unit (AC-DC) is a three-phase full bridge uncontrolled rectifier circuit.
3、 Servo system wiring diagram
1. Driver wiring
The servo drive mainly includes control circuit power supply, main control circuit power supply, servo output power supply, controller input CN1, encoder interface CN2, and connected CN3. The control circuit power supply is a single-phase AC power supply, and the input power can be single-phase or three-phase, but it must be 220V. This means that when three-phase input is used, our three-phase power supply must be connected through a transformer transformer. For low-power drivers, it can be directly driven in single-phase, and the single-phase connection method must be connected to the R and S terminals. Remember not to connect the servo motor outputs U, V, and W to the main circuit power supply, as it may burn out the driver. The CN1 port is mainly used for connecting the upper computer controller, providing input, output, encoder ABZ three-phase output, and analog output of various monitoring signals.
2. Encoder wiring
From the above figure, it can be seen that we only used 5 of the nine terminals, including one shielding wire, two power wires, and two serial communication signals (+-), which are similar to the wiring of our ordinary encoder.
3. Communication port
The driver is connected to upper computers such as PLC and HMI through the CN3 port, and is controlled through MODBUS communication. RS232 and RS485 can be used for communication.
Post time: Dec-15-2023
