What is servo motor and difference between DC servo motor and AC servo motor


  The term "servo" comes from the Greek "slave" means. "Servo motor" can be understood as a control signal to obey the command of the motor: before the control signal is issued, the rotor is stationary; when the control signal is issued, immediately turn the rotor; when the control signal disappears, the rotor can immediately stop.

  The servo motor is automatically controlled apparatus is used as a motor actuator, which is a function of an electric signal into an angular displacement or angular velocity of the shaft.

 Servo motor, AC servo and DC servo two categories

  AC servomotor basic structure of induction motor (induction motor) is similar. There are two phases in the stator field windings Wf and spatial displacement control winding WcoWf 90 ° electrical angle, then the constant AC voltage, AC voltage or phase-use change on the Wc applied to achieve the purpose of controlling the motor running. AC servo motor with a stable, controllable, fast response, high sensitivity and mechanical properties and regulation characteristics of the non-linearity index stringent (requirements were less than 10% to 15% and 15% to less than 25%) and other characteristics.   

  DC servo motor and the basic structure is similar to the general DC motor. Motor speed n = E / K1j = (Ua-IaRa) / K1j, where E is the armature counter electromotive force, K is a constant, j is the magnetic flux per pole, Ua, Ia is the armature voltage and the armature current, Ra is armature resistance, Ua change or alter φ, can control DC servo motor speed, but generally the method of controlling the armature voltage in permanent magnet DC servo motor, the field winding is replaced by permanent magnets, the magnetic flux φ constant . DC servo motor has a good linear regulation characteristics and fast response time.

Advantages and disadvantages of DC servo motor

  Advantages: accurate speed control, torque-speed characteristics hard, control principle is simple, easy to use and inexpensive.
  Disadvantages: brush commutation, speed limits, additional resistance, resulting in wear particles (dust explosive atmosphere should not)

Advantages and disadvantages of AC servo motors

  Advantages: speed control characteristics of a good, the whole region can achieve smooth control of speed, almost no shaking, more than 90% of high efficiency, low heat, high-speed control, high precision position control (depending on encoder resolution), rated operating region inside, it can realize constant torque, low inertia, low noise, no brush wear, maintenance-free (for clean, explosive atmospheres)
  Disadvantages: more complex control, drive parameters require on-site tuning PID parameters to determine the need for more connection.

DC servo motors are brush and brushless motors

  Brush motor low cost, simple structure, large starting torque, wide speed range, easy to control, the need to maintain, but easy to maintain (replace the brushes), electromagnetic interference, use of the environment is required, usually for cost-sensitive general industrial and civil applications.
  Brushless motor small size, light weight, large output, fast response, high speed small inertia, torque, smooth and stable rotation control complex, intelligent, flexible electronic commutation, can be square or sine wave commutation, motor maintenance-free, energy-efficient electromagnetic radiation is small, long life and low temperature, suitable for various environments.
  AC servo motor is a brushless motor is divided into synchronous and asynchronous motors, motion control is currently generally used synchronous motors, large power range, power can do big, inertia, the maximum speed is low, the speed increases with the power uniform drop suitable for low speed running smoothly case

  Servo motor is a permanent magnet inside the rotor, drive control U / V / W-phase electrical electromagnetic field is formed, the rotor under the effect of this magnetic field is rotated while the motor comes with encoder feedback signals to drive, with a target value for the feedback value, thereby adjusting the angle of rotation of the rotor, the accuracy of the servo motor is determined by the resolution of the encoder (lines)