When An Ac Servo System Is Introduced - Mitsubishi MELSEC-F Training Manual

Positioning Control
2. Positioning by AC Servo System
2.1

When an AC servo system is introduced

• Positioning can be performed by many diversified methods. Recently, AC servo methods
which offer many advantages are often introduced.
• In the positioning system of an AC servo method, a position controller, servo amplifier and
servo motor are generally required. The representative system configuration is shown
below.
Commercial
power supply
Command
pulse
Position
controller
T h e p o s i t i o n c o n t r o l l e r
g e n e r a t e s a s p e c i f i e d
quantity of forward rotation
(or reverse rotation) pulses at
a specified frequency.
The AC servo system satisfies the needs for
multi-model small-lot production through only
simple changes in the program.
Servo amplifier
Smoothing
Converter


AC DC
Speed
command
Deviation
counter
Current
control
The command pulse number
is subtracted by the feedback
pulse number, and the speed
command to drive the servo
m o t o r i s m a d e f r o m t h e
deviation (accumulated pulse
number).
When the accumulated pulse
number becomes 0, the servo
motor stops.
Why is the AC servo system attracting attention?
Inverter
circuit


DC DC
PWM (pulse width
modulation) control
AC servo systems are easier to handle than
hydraulic equipment.
As an AC servo system can generate large
torque, it can satisfy the needs for down sizing
and high power.
- Release from oil management
Robots in conjunction with an AC servo system
can satisfy the needs for labor saving and
automation.
- Release from dangerous, hard and dirty
working environments
Positioning by AC Servo System 2
Servo
motor
AC SM
PLG
Feedback
current
Feedback
pulse
The servo motor is equipped
with a built-in encoder (pulse
generator), dedicated to high
speed response, and suitable
to positioning control.
2-1
Encoder