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Servo Motors

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Mohamed Gaber Nassar

on 26 May 2016

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Transcript of Servo Motors

Contents :
Servo Motors construction
How Servo Motors work ?
Encoder Types
Servo Motors Types
Servo Motor Advantages and Disadvantages
How to select servo motors in a project
Servo Motor Advantages and Disadvantages :
Servo Motors
Presented By :

Servo motors have been around for a long time and are utilized in many applications.
They are small in size and are very energy-efficient. These features allow them to be used to operate remote-controlled or radio-controlled toy cars, robots and airplanes.
Servo motors are also used in industrial applications, robotics, in-line manufacturing.
Servo Motors
How to select servo motors in a project
By determine the torque which will effect on the motor in the joint
Some Applications
Servo motors are also used in industrial applications, robotics, in-line manufacturing.
Servo Motors Construction
How Servo Motors work ?
Mohamed Gaber Nassar
Servo Motors Construction
A servo system mainly consists of three basic components :
- a controlled device
- an output sensor
- a feedback system.
This is an automatic closed loop control system.
Servo Motors Construction
Servo Motors Construction
Inside there is a pretty simple set-up:
- a small DC motor,
- potentiometer,
- a control circuit.
How Servo Motors work ?
A servo motor is a closed-loop servo mechanism that uses position feedback to control its motion and final position.
The input to its control is some signal, either analog or digital, representing the position commanded for the output shaft.

The motor is paired with some type of encoder to provide position and speed feedback.
In the simplest case, only the position is measured.
The measured position of the output is compared to the command position, the external input to the controller.
If the output position differs from that required, an error signal is generated which then causes the motor to rotate in either direction, as needed to bring the output shaft to the appropriate position.
As the positions approach, the error signal reduces to zero and the motor stops.
How Servo Motors work ?
Servos are controlled by sending an electrical pulse of variable width, or pulse width modulation (PWM), through the control wire.
There is a minimum pulse, a maximum pulse, and a repetition rate.
A servo motor can usually only turn 90 degrees in either direction for a total of 180 degree movement. The motor's neutral position is defined as the position where the servo has the same amount of potential rotation in the both the clockwise or counter-clockwise direction.
How Servo Motors work ?
The PWM sent to the motor determines position of the shaft, and based on the duration of the pulse sent via the control wire; the rotor will turn to the desired position.
The servo motor expects to see a pulse every 20 milliseconds (ms) and the length of the pulse will determine how far the motor turns.
How Servo Motors work ?
For example, a 1.5ms pulse will make the motor turn to the 90-degree position. Shorter than 1.5ms moves it to 0 degrees, and any longer than 1.5ms will turn the servo to 180 degrees. as shown :
Types of Encoders
Simple servo motors may use resistive potentiometers as their position encoder
Absolute rotary encoder
Absolute encoders can determine their position at power-on, but are more complicated and expensive.
Incremental rotary encoder
Incremental encoders are simpler, cheaper and work at faster speeds.
Servo Motors Types
DC Servo Motor
Stator : permanent magnet
Rotor : Coil
Speed : up to 3000 r/min
Power : up to 5 KW
AC Servo Motor
Stator : Coil
Rotor : permanent magnet
Speed : 1000 to 5000 r/min
Power : up to 22 KW
AC Servo Motor
Stator : Coil
Rotor : Coil
Speed : up to 20000 r/min
Power : 2.2 to 55 KW
high performance,
higher speeds,
accurate positioning (because of feedback)
Disadvantages :
higher cost ,
requires setup/tuning
T = F * L
Full transcript