Figure 1. Servo driver principle block diagram
Servo driver structure
Servo drives all use digital signal processors (DSPs) as the control core, enabling the implementation of relatively complex control algorithms and achieving digitalization, networking, and intelligence. Power devices generally adopt drive circuits designed around intelligent power modules (IPMs). The IPM integrates the drive circuit and also has fault detection and protection circuits for overvoltage, overcurrent, overheating, and undervoltage. A soft-start circuit is also added to the main circuit to reduce the impact on the driver during startup.
Rectifier section: The rectifier section converts AC power into DC power, and after capacitor filtering, it produces a stable and pulsation-free DC power supply.
Inverter: The SPWM signal from the control unit drives the IGBT to convert the DC power supply into an SPWM waveform to drive the servo motor.
Control Section: The servo unit adopts a fully digital structure, achieving software-based closed-loop control through high-performance hardware support. Currently, all servos utilize DSP (Digital Signal Processing) chips, capable of executing position, speed, torque, and current controller functions. It provides PWM control signals to the power drive unit and can receive and process position and current feedback, possessing a communication interface.
Encoder: The servo motor is equipped with a high-performance angle measurement encoder, which can accurately measure the rotor position and the motor speed.
Currently, servo control systems are increasingly using new power semiconductor devices with high switching frequencies, primarily high-power transistors (GTRs), power MOSFETs, and insulated-gate transistors (IGPTs). 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.
Of particular note 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). This device integrates input isolation, energy-saving braking, over-temperature, over-voltage, and over-current protection, as well as fault diagnosis, all within a small module. Its input logic levels are fully compatible with TTL signals and can directly interface with microprocessor outputs. Its application significantly simplifies servo unit design and enables the miniaturization and micro-miniaturization of servo systems.
Structural composition
The structure of mechatronic servo control systems varies greatly, but from the perspective of automatic control theory, a servo control system generally includes five parts: controller, controlled object, execution link, detection link, and comparison link.
Comparison phase
The comparison stage is a stage that compares the input command signal with the system feedback signal to obtain the deviation signal between the output and the input. It is usually implemented by a dedicated 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 comparator in order to control the actuator to act as required.
Execution phase
The function of the actuator is to convert various forms of energy into mechanical energy according to the requirements of the control signal, thereby driving the controlled object to work. In mechatronics systems, actuators generally refer to various motors or hydraulic/pneumatic servo mechanisms, etc.
Controlled object
Mechanical parameters, including displacement, velocity, acceleration, force, and torque, are the controlled objects.
Testing process
The detection stage refers to the device that can measure the output and convert it into the dimensions required by the comparison stage. It generally includes sensors and conversion circuits.
