Positioning By Ac Servo System; Advantages For Using An Ac Servo System - Mitsubishi Electric MELSEC iQ-F Series User Manual

FX Series Programmable Controllers
Introduction to FX Positioning Control Systems
2.

Positioning by AC Servo System

2.1

Advantages for using an AC servo system

With an AC servo system, positioning can be performed by many diversified methods. Typically, a position
controller, servo amplifier and servo motor are required for positioning with an AC servo system. The
representative servo system configuration is shown below.
Commercial
power supply
Command
pulse
Positioning
controller
The positioning controller
generates a specified quantity
of forward rotation (or reverse
rotation) pulses at a specified
frequency.
In the latest AC servo systems, conventional weak points have been improved as follows:
• Although the latest systems are completely digital, they are equipped with parameters in conformance to
diversified mechanical specifications and electrical specifications so that simple set-up is possible.
• As frequent operation is enabled by a low inertia motor, the maximum torque is increased and the system
can be applied to a wide variety of machines.
• The latest systems are equipped with an auto tuning function, with which the servo amplifier automatically
detects the load inertia moment and adjusts the gain. This is possible even if the load inertia moment is
unknown.
• The command communication cycle from the controller to the servo amplifier is improved for
synchronization accuracy and better speed/positioning accuracy.
• The latest systems also allow for long-distance wiring, reduced noise resistance, and simplified wiring.
The top advantages to using an AC servo system are described below.
Compact and light servo
system
In the FA workplace, a
downsized AC servo
system occupying less
space is beneficial.
12
Servo amplifier
Smoothing
Converter
circuit
AC DC 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
motor is made from the
deviation (accumulated pulse
number).
When the accumulated pulse
number becomes 0, the servo
motor stops.
Robust servo system
In accordance with severe
operation conditions, a
tougher AC servo system is
often required.
2 Positioning by AC Servo System
2.1 Advantages for using an AC servo system
Inverter
DC AC
Feedback
current
PWM (pulse width
modulation) control
The servo motor is equipped
with a built-in encoder (pulse
generator), dedicated to high
speed response, and suitable
for positioning control.
Easy servo system
AC servo systems are
easier to handle than
hydraulic equipment. Easy
systems are also flexible for
new staff.
Servo
motor
SM
PLG
Encoder
Feedback
pulse
Good cost performance
servo system
An AC servo system with
good cost performance
saves a company in overall
engineering costs.