SERVOMOTORS | AC SERVOMOTORS | DC SERVOMOTORS | AC SERVOMOTORS ADVANTAGES-DISADVANTAGES | DC SERVOMOTORS ADVANTAGES-DISADVANTAGES | WHAT IS SERVOMOTOR | SERVOMOTOR SALIENT FEATURES
The motors that are used in automatic control systems are called servomotors. When the objective of the system is to control the position of an object then the system is called Servomechanism. The servomotors are used to convert an electric signal (control voltage) applied to them into an angular displacement of the shaft. They can either operate in a continuous duty or step duty depending on construction.
- Linear relationship between the speed and electric control signal.
- Steady state stability.
- Wide range of speed control.
- Linearity of mechanical characteristics throughout the entire speed range.
- Low mechanical and electrical inertia.
- Fast response.
Servomotors are classified as:
1.AC SERVO MOTORS 2. DC SERVO MOTORS
Advantages of DC servomotors are:
- Higher output than from a 50Hz motor of same size.
- Linearity of characteristics is achieved easily.
- Easier speed control from zero speed to full speed in both directions.
- Higher torque to inertia ratio that gives them quick response to control signals.
- DC servomotors have light weight, low inertia and low inductance armature that can respond quickly to commands for a change in position or speed.
- Low electrical time constants (0.1 to 6ms) and low mechanical time constants (2.3 to 40ms).
- DC motors are capable of delivering over 3 times their rated torque for a short time but AC motors will start at 2 to 2.5 times their rated torque.
The DC servomotors are generally used for large power applications such as in machine tools and robotics.
Advantages of AC servomotors are:
- Low cost.
- Higher efficiency and less maintenance (bcoz no commutator and brushes).
Disadvantages of AC servomotors are:
- Non-linear Characteristics.
- More difficult to control in positioning applications.
The AC servo motors are best suited for low power applications.