SERVO

1. SERVO SYSTEM
BY
NITISH SINHA
M.TECH(CAD-CAM)

2. DEFINITION
 Servo is an automatic device that uses error-sensing
feedback to correct the performance of a mechanism.

3. HISTORY
 In 1886 used feedback device by SS Great Eastern.
 In 1888 Electrical Servomechanism in Elisha Gray’s
Telautograph.
 In 1909 Ragonnet power reverse mechanism was steam
powered servo amplifier for linear.
 In 1930 using PRC to control searchlight.

4. Classification of servo system
• Closed loop system
• Open loop system
a) Automatic washing machine
b) traffic signal system
c) home heating system

5. Closed loop system
 System where out
put has an effect
upon the input
quantity in such a
manner as to
maintain the
desired output
value.

6. Open loop system

7. Closed loop system
Advantage Disadvantage
 Accuracy: They are more
accurate than open loop
system due to their complex
construction.
 Noise reduction ability:
they are composed of a
feedback mechanism, so they
clear out the errors between
input and output signals.
 Construction: They are
relatively more complex in
construction and hence it
adds up to the cost making.
 Stability: It is less stable than
open loop system .
 it also reduces the overall gain
of the system.

8. Open loop system
Advantage Disadvantage
Simplicity and stability:
they are economical and stable
too due to their simplicity.
 Construction: Since these
are having a simple layout so
are easier to construct.
 Accuracy and
Reliability:they are very
inaccurate in terms of result
output and hence they are
unreliable too.
 Due to the absence of a
feedback mechanism, they
are unable to remove the
disturbances occurring from
external sources.

9. FUNCTIONAL SERVO LOOPS
 Position Servo Loop
 Velocity Servo Loop
 Acceleration Servo

10. Position Servo Loop
 Control the position of the load it is driving.
 . Position a great number of devices.
 For ac position servo system, amplitude and phase of
the ac error signal determine amount & direction the
load will be driven.

11. Velocity Servo Loop
 VELOCITY of the output is sensed.
 When the velocity loop is at null position, an error signal is
still present and the load is moving.
 speed is governed by the level of the error.

12. SERVO CHARACTERISTICS
 Time lag.
 Over damped : This is an excessive time requirement for the
system to reach synchronization.
 Under damped : The unfavourable trait is an erratic operation
around the point of synchronization.

13. Servo feed control system in micro- EDM
 To Keep The Gap Distance Constant, Adaptive Servo
Feed Control Is Used In Conventional EDM.
 The gap distance in micro-EDM is much shorter than
that in conventional EDM due to the small pulse
energy.
 In conventional EDM, to realize servo feed control, it is
necessary to connect a pair of electric wires to monitor
the average working voltage.
 Servo feed control systems were therefore developed
for the RC pulse generator and transistor type isopulse
generator.

14. Servo feed control system for RC pulse generator
 It consists of an average working voltage detection
circuit, comparator, servo feed control circuit to
calculate the feed rate, and machine drive system.
 The average working voltage is monitored as a
feedback signal to control the feeding speed.
 The average working voltage is monitored as a
feedback signal to control the feeding speed.
 Two large resistors of 47 kΩ are inserted between one
wire and the tool electrode, and the other wire and the
work piece.

17. Machined surface in micro-EDM
 Machined surface was
smoother use transistor
type isopulse generator.
 Discharge energy from
the transistor type
isopulse generator is
constant for each
discharge.

18. Removal rate in Semifinishing
 Three times higher than
that of the RC pulse
generator with servo feed
control.
 Improve removal rate by
about 24 times higher
than that of the
conventional RC pulse
generator with constant
feed rate control.

19. Removal rate in finishing
 Removal rate of RC(SFC)
was about 15 times higher
than that of RC (CFRC).
 Removal rateof the
transistor type iso pulse
generator with the servo
feed control was about 1.8
times higher than that of
the RC pulse generator
with servo feed control.

20. Effects of servo feed control Machined surface
 Effects of servo feed control in finishing are greater
compared to semifinishing.
I. the pulse energy in finishing is smaller.
II. short circuiting occurs more easily.
III. unstable machining during finishing.