Servo drive structure

Introduction to Servo Drive

Servo drives, also known as "servo controllers" or "servo amplifiers", are controllers used to control servo motors. They function similarly to frequency converters acting on ordinary AC motors. They are part of the servo system and are mainly used in high-precision positioning systems. Generally, servo motors are controlled in three ways: position, speed, and torque to achieve high-precision transmission system positioning. They are currently high-end products in transmission technology.

Figure 1 Principle block diagram of servo drive

Servo drive structure

Servo drives all use digital signal processors (DSP) as the control core, which can implement relatively complex control algorithms and realize digitalization, networking and intelligence. Power devices generally use drive circuits designed with intelligent power modules (IPM) as the core. The IPM integrates the drive circuit inside, and also has fault detection and protection circuits such as overvoltage, overcurrent, overheating, and undervoltage. A soft start circuit is also added to the main circuit to reduce the impact of the startup process on the drive.

Rectification section: The rectifier section converts the AC power into a DC power source, which is filtered by capacitors to generate a smooth and pulsating DC power source.

Inverter: The SPWM signal from the control unit drives the IGBT, converting the DC power supply into an SPWM waveform to drive the servo motor.

Control part: The servo unit adopts a fully digital structure, and realizes the software of closed-loop control through high-performance hardware support. Now all servos have adopted (DSP digital signal processing) chips, DSP, which can perform the functions of position, speed, torque and current controllers. Give PWM signal control signal to act on the power drive unit, and can receive and process position and current feedback, and has a communication interface.

Encoder: The servo motor is equipped with a high-performance angle measurement encoder that can accurately measure the position of the rotor and the speed of the motor.

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 (MOSFET) and insulated gate transistors (IGPT), etc. 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 especially 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 be directly interfaced with the output of the microprocessor. Its application significantly simplifies the design of the servo unit and realizes the miniaturization and micro-miniaturization of the servo system.

Structural composition

The structure of mechatronic servo control system has various types, but from the perspective of automatic control theory, servo control system generally includes five parts: controller, controlled object, execution link, detection link, and comparison link.

Comparison

The comparison link is a link that compares the input command signal with the system's feedback signal to obtain the deviation signal between the output and the input. It is usually implemented by a special circuit or computer.

Controller

The controller is usually a computer or a PID control circuit. Its main task is to transform and process the deviation signal output by the comparison element to control the actuator to act as required.

Execution

The function of the execution link is to convert various forms of input energy into mechanical energy according to the requirements of the control signal to drive the controlled object to work. The actuators in the mechatronics system generally refer to various motors or hydraulic and pneumatic servo mechanisms.

Accused

Mechanical parameters include displacement, velocity, acceleration, force, and torque for the controlled object.

Testing

The detection link refers to a device that can measure the output and convert it into the dimension required by the comparison link, generally including sensors and conversion circuits.