What is a servo motor?

by:V&T Technologies     2020-01-25
Servo motor, also known as Executive Motor, is used as executive element in automatic control system to convert received electrical signal into angular displacement or angular velocity output on motor shaft. The rotor inside the servo motor is a permanent magnet. The U/V/W three-phase electricity controlled by the driver forms an electromagnetic field. The rotor rotates under the action of this magnetic field. At the same time, the encoder provided by the motor feeds back signals to the driver, the driver adjusts the rotation angle of the rotor by comparing the feedback value with the target value. The accuracy of the servo motor depends on the accuracy of the encoder (Number of lines) That is to say, the servo motor itself has the function of sending out pulses. Every time it rotates at an angle, it will send out a corresponding number of pulses, thus the pulses of the servo driver and the encoder of the servo motor echo each other, so it is closed-loop control and stepping motor is open-loop control. Servo'The word comes from Greek. 'Slave'Meaning. 'Servo Motor' It can be understood as a motor that absolutely obeys the command of the control signal: the rotor is still before the control signal is sent out; When the control signal is sent out, the rotor rotates immediately; When the control signal disappears, the rotor can stop rotating immediately. Servo motor is a micro-special motor used as an executive element in automatic control device. Its function is to convert electrical signals into angular displacement or angular velocity of rotating shaft. Servo motors are divided into AC servo and DC Servo. The basic structure of AC servo motors and AC induction motors (Asynchronous motor)Similar. There are two phase space displacements of 90 on the stator. The excitation winding Wf and the control winding WcoWf of the electrical angle are connected with a constant AC voltage, and the change of AC voltage or phase applied to Wc is used to control the operation of the motor. AC servo motor has strict nonlinearity indexes of stable operation, good controllability, fast response, high sensitivity and mechanical characteristics and adjustment characteristics ( Requirements are less than 10% ~ 15% and below 15% ~ 25%)And other characteristics. The basic structure of DC servo motor is similar to that of general DC motor. Motor speed n = E/K1j = (Ua-IaRa) /K1j, where e is armature back electromotive force, K is constant, j is magnetic flux per pole, Ua and Ia are armature voltage and armature current, Ra is armature resistance, change Ua or change & phi; , Can control the speed of DC servo motor, but generally adopts the method of controlling armature voltage. In permanent magnet DC servo motor, the excitation winding is replaced by permanent magnet, magnetic flux & phi; Constant. DC servo motor has good linear regulation characteristics and fast time response. Advantages and disadvantages of DC servo motor: accurate speed control, hard torque and speed characteristics, simple control principle, convenient use and low price. Disadvantages: brush commutation, speed limit, additional resistance, wear particles (Dust-free and explosive environment is not suitable) Advantages and disadvantages of AC servo motor, advantages: good speed control characteristics, smooth control in the whole speed zone, almost no oscillation, high efficiency over 90%, less heat, high speed control, high precision position control (Depends on encoder accuracy) In the rated operation area, constant torque, low inertia, low noise, no brush wear, maintenance-free (Suitable for dust-free and explosive environments) Disadvantages: The control is complicated, the driver parameters need to be adjusted on site to determine PID parameters, and more connections are needed. Related reading: 42 stepper motor, how does the motor work, TAG motor, servo, what?
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