ServoMotor
What is Servo ?
The word Servo is from Latin Servus namely slave in English.
Let’s do
it Yes Sir
servo is one electronic slave which can follow the master order seriously and
precisely. And it can confirm whether the action it is making is accordant to
master.
Basics of Motion
Drive
Controller
Motor Result
Information Power
Controller Drive Motor
Overview – Different types of motors
Motors
brushed brushless
DC motors synchronous asynchronous
EC-Motor AC-Servo Stepper
Permanent Asynchronous
Permanent
magnet exited, Reluctance or motors with field
magnet exited,
closed loop, high hybrid, open oriented control
closed loop, Hall
resolution loop
commutation
commutation
Stepper motors
● Advantages
● Cost efficient solution for accurate positioning
● Very high torque density
● Very high stiffness in open loop
● Easy to install
● Very robust system
● Open loop mode
● Drawback
● Reduced power range
● Motor surface can be quite hot
● Resonances
● Noisy
Stepper motors – Working principle
Motor technologies Servo motors
• Advantages
– Very high overload capacity
– Very high torque density
– Easy to install
– Wide speed range
– High dynamic up to high speed
– High position accuracy
– Very robust system
– Closed loop mode for
• Torque
• Speed
• Position
• Drawback
– Feedback sensor required
– More expensive
Servo motors – Working principle
● Synchronous motor with permanent magnetic excitation operated in
closed loop with a changing frequency
AC Servo Motor Sectional view
Servo motors – Working principle
Rotor with Stator with
permanent winding
magnets
Servo motors – Torque-Speed curve
Peak Torque fixed Peak Torque
by Current Limitation limited
Peak Torque by maximum
300 % Voltage
200 % Intermittent
Operating Area
100 %
Continuous
Operating Area
r.p.m.
0 1000 2000 3000 4500
Servo motors – Feedback systems
● Feedback system necessary to close the loop
● Angle -> for commutation
● Position -> for position control
● Speed -> for velocity control
● Different technologies
● Incremental encoder
● Singleturn
● Multiturn
● Resolver
● Hiperface®
● EnDat®
● …
Servo motors - Incremental encoder
● Working principle Single turn encoder
● Optical system
● Turning disc
● 3 tracks: A, B, and Index
● A and B is shifted by 90°
Sensor
Index ¼ period
Sensor A Sensor B
Channel A
½ period
Channel B
period
Outside track Index
LED
Servo motors - Incremental encoder
● Working principle Multi turn encoder
● Basically same than Single turn
encoder
● Additional tracks to count the turns
● Provides a code that is an image of
the actual position
● On power-up the encoder provides
directly the position data, no homing
needed
● Absolute encoder
Servo motors - Resolver
● Measures the angle within
one revolution
● Cheap solution
● Robust
How to build one servo system
CN
C Gear
Box Device
Serv
o
PL Servo
C motor
Ball screw
arbor
Synchronous
Belt
Industrial
PC
Application Fields for Servo
Hoist
SMT
Food & Packaging
CNC
壓鑄 測量 印刷造紙
Printing
Casting
Position, Velocity and Torque Control of Servo Motor
