SERVOMOTORS

BY R.PRABHU

• A Servo is a small device that has an output shaft.

• This shaft can be positioned to specific angular positions

by sending the servo a coded signal.

• As long as the coded signal exists on the input line, the

servo will maintain the angular position of the shaft.

• As the coded signal changes, the angular position of the

shaft changes.

Definition

What makes a Servo?

Servo motors and are constructed out of basic DC

motors, by adding:

• some gear reduction

• a position sensor for the motor shaft

• an electronic circuit that controls the motor's

operation

Inside a Servo

1) D.C. Servomotor:-

Shunt wound d.c. motor Series wound d.c. motor Compound wound d.c. motor

Types of servo

2) A.C. Servomotors:-

Induction motor a.c. motorSynchronous a.c. motor

DC servo motors are controlled by DC command signals applied directly to coils

The magnetic fields that are formed interact with permanent magnets and cause the rotating member to turn

One type of PM uses a wound armature and brushes like a conventional DC motor, but uses magnets as pole pieces

Another type uses wound field coils and a permanent magnet rotor

DC Servo Motors

Controlled by AC command signals applied to the coils

AC Brushless Servo Motor◦ Operates on the same principle as single-phase induction

motor

AC Servo Motors

AC Servomotors

• It is a two phase a.c. induction motor. There are two

winding, one fixed or reference winding is supplied

with a fixed voltage and frequency from a constant

voltage source. Second winding is called control

winding, with variable supply voltage of same

frequency.

• The stator has two distributed windings displaced 90

electrical degree apart.

• One winding is the reference phase and is connected

to a constant voltage source.

• The other winding is the control phase and is

supplied with a variable voltage of the same

frequency as the reference phase but is phase-

displaced by 90 electrical degree.

The two major advantages of using a SERVO

MOTOR in sewing machines and other machines in

the sewing operation are that, one can always control

the speed of the motor and that they are completely

silent when the pedal is not engaged.

ADVANTAGES OF SERVO MOTOR

The other advantages include:

They consume up to 90% less energy than clutch motors.

1/3 times lighter than clutch motors Reverse motor rotation with the flick of a

switch Adjusted speed remains the same no matter

how hard the pedal is pressed.

Position control

Uses

• Speed control