Positioning Method Type - Mitsubishi Electric MELSEC iQ-F Series User Manual

FX Series Programmable Controllers
Introduction to FX Positioning Control Systems
1.3

Positioning method type

In general, there are two methods to control the movement of a workpiece: speed control and position control.
For basic, more rudimentary positioning, speed control can be used with an inverter and general purpose
motor. For systems where precision is a must, servo systems are required for the advanced handling of pulse
commands.
Control method
Limit switch
method
Speed
control
Pulse count
method
Pulse
Position
command
control
method
*1. The stop precision shows a value in a case where the low speed is 10 to 100 mm/s.
Description
Two limit switches are provided in
places where a system's moving
part passes. At the first limit
switch, the motor speed
reduced. At the second limit
switch, the motor turns off and the
brake turns on to stop the moving
part.
In this method, because position
controllers are not required, the
system configuration can
realized at reasonable cost.
(Guideline of stopping precision:
Approximately ±1.0 to 5.0 mm)*
A position detector (such as a
pulse encoder) is set up in a
motor or rotation axis. The pulse
number generated from
position detector is counted by a
high-speed counter. When the
pulse number reaches the preset
value, the moving part stops.
In this method, because limit
switches are not used, the stop
position can be easily changed.
(Guideline of stopping precision:
Approximately ±0.1 to 0.5 mm)*
An AC servo motor which rotates
in proportion to the input pulse
number is used as the drive
motor.
When the pulse number
corresponding to the movement
distance is input to the servo
amplifier of the AC servo motor,
positioning can be performed at
high speed in proportion to the
pulse frequency.
(Guideline of stopping precision:
Approximately ±0.01 to
1
mm)*
1 The Basics of Positioning Control
Schematic drawing
Moving part
is
B IM
INV
be
High speed
DC0 to 10V
Movement
1 IM: Inductive motor
distance
B: Brake
INV: Inverter
Pulses are
fed back.
the
PLG IM
INV
DC0 to
10V
PLC
1
High-speed
Movement distance
counter unit
Pulses are
fed back.
PLG SM
Servo
amplifier
Command
pulse
PLC
0.05
Position controller
Movement distance
1.3 Positioning method type
Ball screw
Limit switch for
changeover to
low speed
Limit switch
for stop
Low speed
Moving part
Ball screw
IM: Inductive motor
PLG: Pulse generator
INV: Inverter
PLC: Programmable controller
High speed
Low speed
Moving part
Ball screw
SM: Servo motor
PLG: Pulse generator
PLC: Programmable
controller
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