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Classification and characteristics of servo motors

September 05,2022

The word “servo” comes from the Greek meaning of “slave”. “ Servo motor ” can be understood as a motor that absolutely obeys the command of control signals: before the control signals are sent out, the rotor is stationary; When the control signal is sent out, the rotor rotates immediately; When the control signal disappears, the rotor can stop immediately.

Servo motor is a micro-special motor used as an executive component in automatic control devices, and its function is to convert electrical signals into angular displacement or angular velocity of the rotating shaft.

Servo motors are divided into AC servo and DC servo.

The basic structure of AC servo motor is similar to that of AC induction motor (asynchronous motor). On the stator, there are two excitation windings Wf and control windings WcoWf with phase space displacement of 90 electrical angle, which are connected with constant AC voltage. By using the AC voltage applied to Wc or the phase change, the motor operation is controlled. AC servo motor has the characteristics of stable operation, good controllability, fast response, high sensitivity, and strict nonlinearity index of mechanical characteristics and regulation characteristics (requirements are less than 10% ~ 15% and less than 15% ~ 25% respectively).

The basic structure of DC 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, Ia are armature voltage and armature current, and Ra is armature resistance. Changing Ua or changing Φ can control the speed of DC servo motor, but generally the armature voltage is controlled. In permanent magnet DC servo motor, the excitation winding is replaced by permanent magnet. DC servo motor has good linear regulation characteristics and fast time response.
Advantages and disadvantages of DC motor
Advantages: accurate speed control, hard torque and speed characteristics, simple control principle, convenient use and low price.
Disadvantages: brush commutation, speed limit, additional resistance, resulting in 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 range, almost no oscillation, over 90% high efficiency, less heat generation, high-speed control, high-precision position control (depending on the accuracy of encoder), constant torque, low inertia, low noise, no brush wear and maintenance-free (suitable for dust-free and explosive environments) in the rated operating range.
Disadvantages: the control is complicated, the driver parameters need to be adjusted on site to determine the PID parameters, and more wires are needed.

What is a servo motor? How many types are there? What are the job characteristics?

Servo motor, also known as executive motor, is used as executive element in automatic control system, which converts the received electrical signal into angular displacement or angular velocity output on the motor shaft.
Servo motors are divided into two categories: DC and AC servo motors. Their main characteristics are that when the signal voltage is zero, there is no self-rotation, and the rotation speed decreases with the increase of torque.

What is the difference between AC servo motor and brushless DC servo motor in performance?

The performance of AC servo motor is better, because AC servo is controlled by sine wave and torque ripple is small; Brushless DC servo is trapezoidal wave control. However, brushless DC servo control is relatively simple and cheap.
The rapid development of permanent magnet AC servo drive technology makes DC servo system face the crisis of being eliminated [/p] [p = 30,2,left] Since 1980s, with the development of integrated circuit, power electronics technology and AC variable speed drive technology, permanent magnet AC servo drive technology has made outstanding development, and famous electrical manufacturers in various countries have successively introduced new series of AC servo motors and servo drivers. AC servo system has become the main development direction of contemporary high-performance servo system, which makes DC servo system face the crisis of being eliminated.

Compared with DC servo motor, permanent magnet servo motor has the following main advantages:

1. No brush and commutator, more reliable operation and maintenance-free.
2.The stator winding heating is greatly reduced.
3. Small inertia and good system responsiveness.
4. High-speed and high-torque working condition is good.
5.Small size and light weight under the same power.