The document describes the components and block diagram of a position control mechanism. It contains: 1) A DC motor that drives a load through a gearing to amplify torque. The load position is sensed by a potentiometer and compared to a reference input from an identical potentiometer to determine position error. 2) This error signal is fed to an amplifier to control the motor armature voltage. The effective inertia and friction at the motor shaft is calculated. 3) A block diagram shows the relationship between motor speed, armature voltage, and other components in the closed loop position control system.

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 :