Question

Explain construction and working of AC servomotor.

Answer 1

### AC Servomotor: Construction and Working

An AC servomotor is a type of electric motor used in automatic control systems to control the position, speed, and acceleration of a system with high accuracy. It operates on alternating current (AC) and is mainly used in applications like robotics, CNC machines, and automation.

Construction of AC Servomotor:

1. Stator:
   

   - The stator is the stationary part of the motor. It consists of laminated cores and is wound with coils that are connected to the AC supply.
   - The stator produces a rotating magnetic field when current passes through the windings. This rotating magnetic field interacts with the rotor to produce motion.

1. Rotor:
   

   - The rotor is the rotating part of the motor, which is placed inside the stator. The rotor can be of two types:
     - Squirrel cage rotor: Commonly used in AC motors, it consists of a laminated core with short-circuited conductors.
     - Wound rotor: It consists of windings that are connected to external circuits via slip rings.
   - The rotor rotates when the rotating magnetic field of the stator induces current in it, causing a torque that drives the mechanical load.

1. Feedback Device:
   

   - AC servomotors use an encoder or resolver as a feedback device. It provides information about the rotor’s position, speed, and direction to the control system, ensuring the motor performs accurately.

1. Control Circuit:
   

   - An electronic controller (like a PWM controller) governs the input to the motor, adjusting the voltage and current to control speed and position.
   - This is done by comparing the feedback signal from the encoder or resolver to the desired position or speed.

1. Bearings:
   

   - Bearings are used to support the rotor and ensure smooth rotation within the stator.

Working of AC Servomotor:

1. Power Supply:
   

   - The AC power supply is fed to the stator windings. The stator generates a rotating magnetic field when current flows through these windings.

1. Magnetic Field Interaction:
   

   - The rotating magnetic field of the stator induces a current in the rotor (through electromagnetic induction), which causes the rotor to rotate.
   

1. Torque Generation:
   

   - The interaction between the magnetic fields of the stator and rotor generates torque. This torque causes the rotor to rotate, driving the mechanical load.

1. Feedback Mechanism:
   

   - A feedback system (encoder or resolver) constantly monitors the position and speed of the rotor.
   - The controller compares the actual position of the rotor with the desired position or speed set by the user.
   

1. Control Signal Adjustment:
   

   - Based on the feedback, the controller adjusts the current or voltage supplied to the stator to either speed up, slow down, or stop the motor at the desired position.

1. Closed-loop Control:
   

   - This process is part of a closed-loop control system where the motor's performance is continuously adjusted to match the control input.

Key Features of AC Servomotors:

1. Precision and Accuracy: AC servomotors are designed for precise control, especially in terms of speed and position.
   

1. Feedback System: The feedback mechanism (encoder or resolver) allows for real-time adjustments, ensuring high performance.
   

1. High Torque at Low Speeds: AC servomotors provide high torque even at low speeds, making them suitable for applications requiring precision and controlled motion.
   

1. Efficiency: These motors are designed to be energy-efficient, offering minimal losses during operation.
   

Applications of AC Servomotors:

1. Robotics: For precise movement control.
   

1. CNC Machines: To control the position of machine tools.
   

1. Automation Systems: Used in conveyor belts, packaging machines, etc.
   

1. Aerospace and Defense: For controlling the movement of various parts of the aircraft and defense systems.
   

In summary, an AC servomotor is an essential component in high-precision systems, using a combination of a rotating magnetic field, rotor movement, and feedback control to provide accurate and reliable motion control.