Apart from DC servomotors, other two commonly used electric-type actuator in the robots are AC servomotors and Stepper motors.

AC Servomotors:

The AC servomotors are incorporated with a large resistance and small-sized rotor, which is mostly used for obtaining a perfect and quick response.

The AC servomotors can be categorized into two different types such as:

• Synchronous
• Asynchronous

An AC servomotor is a reversible induction and two – phase motor, which is transformed for performing the servo process. When there is a possibility of rapid reversals, stops, and starts, this motor use to deliver a low inertia.

Most importantly, the performance of an AC servomotor can be increased similar to a DC motor with the help of an appropriate electronics package.

Advantages:

• When compared with DC motors, the manufacturing cost for AC servomotor is low.
• It is capable of providing high – power output.
• It does not include any sort of brushes.

Stepper motors:

The stepper motors are classified under the brushless DC servomotor category, and it is also known as stepping motors. This type of actuator is currently employed in the computer I/O devices.

The stepper motors are generally incorporated in the robots, which require a light – duty function. Moreover, it is mostly applied in the open – loop systems when compared with the closed – loop systems.

A sequence of discrete electrical pulses is used to power a stepper motor. The motor shaft is rotated to single step for each electrical impulse. As a result, it produces the discrete angular motion increments as the output.

Advantages:

• It can support both digital and analog feedback signals.
• It provides high dynamic torque with low pulse rates.

Disadvantages:

• Less efficient
• During high load inertia, it might require damping for avoiding oscillation.