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MELSEC-Q
1 PRODUCT OUTLINE
The principle of "position control" and "speed control" operation is shown below.
Position control
The total No. of pulses required to move the designated distance is obtained in the
following manner.
Total No. of pulses
required to move
designated distance
=
Designated distance
Movement amount of machine (load)
side when motor rotates once
No. of pulses
required for motor to
rotate once
The No. of pulses required for the motor to rotate once is the "encoder resolution"
described in the motor catalog specification list.
When this total No. of pulses is issued from the QD75 to the servo amplifier, control to
move the designated distance can be executed.
The machine side movement amount when one pulse is issued to the servo amplifier is
called the "movement amount per pulse". This value is the min. value for the workpiece
to move, and is also the electrical positioning precision.
Speed control
The "Total No. of pulses" mentioned above is invariably required for controlling the
distance. For positioning or speed control, the speed must be controlled as well.
The speed is determined by the frequency of pulses sent from the QD75 to the drive
unit.
Positioning
module
Servo
amplifier
Servo
motor
Detector
(Pulse
encoder)
Feedback pulses
Speed = Pulses frequency
Movement amount = No.of pulses
Feedback pulses =
Pulses generated by detector
Movement amount t = 2
0.4 1.2 0.4
ta td (s)
Pulse frequency
[pps]
A
This area is the total
No. of commanded
pulses.
Fig. 1.1 Relationship between position control and speed control
POINT
The QD75 controls the position with the "total No. of pulses", and the speed with
the "pulse frequency".