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Servo Driver Working Principles

Shenzhen ECON Technology Co.,Ltd | Updated: Nov 15, 2017

 Servo Driver Working Principles


Servo driver simply saying:one kind of controller that is used to control a servo motor,its role is similar to the role of the inverter to AC motor,is part of the servo system,mainly use in high-precision positioning system.Generally through the position,speed and torque control mode control the servo motor,then achieve high-precision positioning of transmission system,is the high-end products of transmission technology at current.Here introduce the working principle of servo drives.


The servo drives all adopt the digital signal processor (DSP) as the control core,which can realize more complicated control

algorithms and achieve digitalization,networking and intelligence.The power devices generally adopt the drive circuit designed

with intelligent power module (IPM) as the core,IPM integrated drive circuit,and over-voltage,over-current,overheating,under-voltage and so on fault detection and circuit protection,the main circuit also join the soft-start circuit to reduce the impact of the startup process on the drive.

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Servo driver working principle diagram


First,the power drive unit rectifies the input three-phase power or AC power by the three-phase full-bridge rectifier circuit to obtain the corresponding direct current.After the rectification of three-phase electricity or AC electricity,and then through the three-phase sinusoidal PWM voltage inverter convert frequency to drive AC servo motor.The whole process of power drive unit can be simply referred to as AC-DC-AC process.The main topology circuit of rectifier unit (AC-DC) is a three-phase full-bridge uncontrolled rectifier circuit.Servo drives generally have three control mode:position control,torque control,speed control.Position control mode generally determines the rotation speed by the frequency of an external input pulse.The rotation angle is determined by the number of pulses.Some servos can directly assign the velocity and displacement through communication.Since the position mode have a very strict control of speed and position,so general application is positioning device.


Torque control mode is to set the output torque of the motor shaft through external analog input or direct address value.The set torque can be changed by changing the setting analog value in real time,also through communication to change the value of the corresponding address to achieve.Mainly use on which material force has strict requirements winding and unwinding devices,such as winding devices or fiber-optic devices,the torque setting according to winding radius change to change to ensure the material force will not change as the winding radius changes at any time.


Speed mode can control operation speed by the analog input or pulse frequency.When the upper control device has outer PID 

control,the speed mode can also position.However,the position signal of the motor or the direct load position signal send to the upper to do computing.The position mode also supports the direct loading of the outer ring to detect the position signal.In this case,the motor shaft end encoder only detects motor speed and the position signal is provided by the direct final load end detection device.This has the advantage of reducing the intermediate transmission error,increases the positioning accuracy of the entire system.


■ If have no requirements on motor speed and position,as long as the output of a constant torque,use torque mode.

■ If there is a certain accuracy requirement for the position and speed,but not for the real-time torque,the torque mode is not convenient,and the speed or position mode is better.

■ If the host controller has a good closed-loop control function,the speed control effect will be better;if its own requirement is not very high,or basically no real-time requirements,the use of position control is better. 


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