Only block diagram of position control servo mechanism.

1. GOVERNMENT ENGG. COLLEGE, DAHOD
CONTROL ENGINEERING
BLOCKDIAGRAM OF POSITION CONTROL
MECHANISM

2. Introduction :
• The word servo means controlling mechanical position or
derivatives of position like velocity and acceleration.
• It is an automatic device that uses the error sensing negative
feedback to correction of performance of mechanism.
• Servo control mechanism uses negative feedback which is used to
control the mechanical position.
• Position control servo mechanism used in hydraulic and pneumatic
machines to control the position.
• It is also used in automatic machine tools, satellite tracking
antenna, Air craft system and navigation system.

3. Fig. Position controlled servo mechanism.

4. Various Components of the system :
• Drive motor dc armature controlled.
• Load is driven through a reduction gearing to amplify
torque for moving load.
• Load angular position is sensed by circular
potentiometer.
• Angle reference input sensed by an identical
potentiometer.
• Position error is fed to amplifier to feed the motor
armature at voltage Ea.

5. • For control system load reflected to motor shaft is
giving the effective inertia and friction at motor shaft
as,
J = JM + n2 JL
f = fM + n2 fL
• To begin with block diargam of linking wM motor
speed, armature voltage ea . It is given in figure of
block diagram.

6. • Reducing block diagram,

7. Various Components of the system :
• Drive motor dc armature controlled.
• Load is driven through a reduction gearing to amplify
torque for moving load.
• Load angular position is sensed by circular
potentiometer.
• Angle reference input sensed by an identical
potentiometer.
• Position error is fed to amplifier to feed the motor
armature at voltage Ea.

8. Complete Block diagram:
• Effective motor time constant including friction f and
equivalent friction effect cause by motor back emf
(Kb KT)/Ra.
• Symbol r is reversed for motor’s mechanical time
constant t = J/f.

9. Forward path transfer function :