1. Synchro and servomotors
content
Synchros
Servomotors
Prepared By
Mr.K.Jawahar, M.E.,
Assistant Professor
Department of EEE
Kongunadunadu College of Engineering and Technology Depar tment of EEE
Synchro and Servomotors
2. Synchros
• The term synchro is a generic name for a family of inductive
devices which works on the principle of a rotating transformer
(Induction motor).
• The trade names for synchros are selsyn, Autosyn and
Telesyn.
• Basically they are electro-mechanical devices or
electromagnetic transducers which produces an output voltage
depending upon angular position of the rotor.
• A synchro system is formed by interconnection of the devices
called the synchro transmitter and synchro control transformer.
They are also called as Synchro Pair.
• The synchro pair measures and compares two angular
displacements and its output voltage is approximately linear
with angular difference of the axis of both the shafts.
Kongunadunadu College of Engineering and Technology Depar tment of EEE
Synchro and Servomotors
3. Synchro pair used in the following two ways
1. To control the angular position of load from a remote
place/long distance.
2. For automatic correction of changes due to disturbance in
the angular position of the load.
Synchro transmitter
Synchro control transformer
Synchro as error detector
Kongunadunadu College of Engineering and Technology Depar tment of EEE
Synchro and Servomotors
4. SERVOMOTORS
• 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.
• It is used to convert an electrical signal (Control voltage)
applied to them into an angular displacement of the shaft.
Featuresof servo motors
1. Linear relationship between the speed and electric control
signal.
2. steady state stability.
3. Wide range of speed control
4. Linearity of mechanical characteristics throughout the
entire speed range.
5. Low mechanical and electrical inertia.
6. Fast response.
Kongunadunadu College of Engineering and Technology Depar tment of EEE
Synchro and Servomotors
5. • Depending on the supply required to run the motor, they
are broadly classified as DC servomotors and AC
servomotors.
• The DC motors are expensive than AC motors. But, the
DC servomotors have linear characteristics and so it is
easier to control.
The advantages of DC servomotors
• Higher output than from a 50hz motor of same size
• Linearity of characteristics are achieved easily
• Easier speed control from zero speed to full speed in both
directions.
• High torque to inertia ratio that gives them quick
response to control signals.
Kongunadunadu College of Engineering and Technology Depar tment of EEE
Synchro and Servomotors
6. • The DC servomotors are generally used for large power
applications such as in machine tools and robotics.
Advantage of AC motors
• Lower cost
• Higher efficiency
• Less maintenance since there is no commutator and brushes.
Disadvantage of AC motors
• Its characteristics are quite nonlinear and this motor are
more difficult to control especially for positioning
applications.
Applications
• Low power applications such as instrument servo(eg.
Control of pen in X-Y recorders) and computer related
equipment( eg. Disk drives, tape drives, printers, etc.,)
Kongunadunadu College of Engineering and Technology Depar tment of EEE
Synchro and Servomotors
7. Reference:
• A.Nagoor Kani, “ Control Systems”, RBA Publications, June
2012.
Synchro and Servomotors
Kongunadunadu College of Engineering and Technology Depar tment of EEE
