WORKING OF SERVOMOTOR AND CONTROL
Working of servomotors :
We give command input according to the
position of shaft . If the feedback signal differs from the given input, an
error signal alerts the user. We amplify this error signal and apply as the
input to the motor, hence the motor rotates. And when the shaft reaches to the
require position , error signal become zero , and hence the motor stays
standstill holding the position.
The command input is in form of
electrical pulses . As the actual input to the motor is the difference between
feedback signal ( current position ) and required signal, hence speed of the
motor is proportional to the difference between the current position and
required position . The amount of power require by the motor is proportional to
the distance it needs to travel .
Controlling of servomotors :
Usually a servomotor turns 90 degree in
either direction hence maximum movement can be 180 degree . However a normal
servo motor cannot rotate any further to a build in mechanical stop.
We take three wires are out of a servo
: positive , ground and control wire. A servo motor is control by sending
a pulse width modulated(PWM) signal through the control wire . A pulse is sent
every 20 milliseconds. Width of the pulses determine the position of the shaft
.
for example ,
A pulse of 1ms will move the shaft
anticlockwise at -90 degree , a pulse of 1.5ms will move the shaft at the neutral
position that is 0 degree and a pulse of 2ms will move shaft clockwise at +90
degree.
variable pulse width control servo motor
When we command a servo motor to move
by applying pulse of appropriate width, the shaft moves to and holds the
require position of the shaft. However the motor resists to change . Pulses
need repetition for the motor to hold the position.
ABA ENGINEERING
MUHAMMAD NAEEM
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