Chapter and acceleration. These devices are seldom seen but



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This Chapter is about literature review of our project. DC motors are widely used in many applications that we use in our
daily life. They can be found everywhere, from house appliances to our
vehicles, desktops and laptops, and industrial applications such as production
lines, remote control airplanes, automatic navigation systems and many other

There are two types of positional rotation servo motor which are DC
servo motor that is controlled by DC, and Alternating Current (AC) servo motor
which is controlled by AC. The servo motor “internal” positional feedback
consists of either encoder feedback or voltage feedback.

The built-in encoder inside the servo motor provides a pulse signal that
is processed by the servo controller to get the position feedback. The voltage feedback
consists of a built-in potentiometer which is coupled with the servo motor axis
to get the relative angular position depending on the value of the
potentiometer. In particular, the DC servo motor is mostly utilized in the
field of electronic, robotics and automation system, especially for special
types of applications where the rotation of the motor only requires a certain
angular movement such as for robot arm, robot gripper, and etc.


2.1    Historical


motors came to fruition due to the invention of the battery (A. Volta, 1800),
the electro magnet (W. Sturgeon, 1825) and the discovery of a magnetic field
from electric current (H. C. Oersted, 1820). The first working rotating
electric motor was introduced in May 1834 by Moritz Jacobi. In 1838, Jacobi
reintroduced an improved and more powerful motor. However, these electric
motors were large and weak compared those we use today. Servo motors
were designed to work within a closed-loop control system. Servo motors provide
precise control of position (angular or linear), velocity, and acceleration.
These devices are seldom seen but are used by an average person daily: The
sliding doors at the supermarket; the power windows in a car; the elevator at
the office, and the ice delivery system on a refrigerator. Servo motors are so
sophisticated that they are used in robotic manufacturing, such as those used
to assemble automobiles. 3


2.2    Types of Servo

motors are classified into different types based on their application like
Brushless DC, AC, continuous rotation, linear and positional rotation, etc. 4

2.2.1  DC Servo Motor  


Generally, this
motor has a distinct DC source in the winding and the armature winding field.
The control can be archived either by adjusting the armature current or field
current. Field control includes some profits over armature control. Similarly,
armature control comprises some benefits over field control. Based on the uses
the control should be practical to the DC servo motor.



2.2.2  Synchronous DC


This motor includes encoder which is used with controllers for giving closed loop control and
also response. This motor can be working to high accuracy and also controlled
exactly as required for the uses. Often these motors have advanced designs of patience
or better bearings and some simple designs also use higher voltages in order to
achieve greater torque. Positional Rotation Servo

This is a most common type of motor and the
o/p of the shaft rotates in about 180. It encompasses physical stops situated
in the gear device to stop rotating outside limits to defend the rotation
sensor. Continuous Rotation Servo

This motor is quite linked to the common
positional rotation servo motor, but it can move in any direction indefinitely.
As per the speed & direction of rotation, the control signal rather than
set the stationary position of the servo is expected.


2.3    Limitations


Since the servomotor tries to
rotate according to the command pulses, but lags behind, it is not appropriate
for accuracy control of rotation.

Higher cost.

When stopped, the motor’s rotor
continues to move back and onward one pulse, so that it is not appropriate if
you need to prevent vibration.


2.4    Summary


This chapter presented the literature review of
servo motor Controller, and the project and research that are related to
Controller have been reviewed. The limitations of servo motors controllers have
been outlined.