Mitsubishi Electric MELSECQ Series User Manual page 19

1 PRODUCT OUTLINE
Positioning
module
Speed=Pulses frequency
Movement amount=No. of puleses
Feedback pulses=
Pulses generated by detector
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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
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 QD70 to the drive unit, control to move
the designated distance can be executed.
The machine side movement amount when one pulse is issued to the drive unit is
called the "movement amount per pulse". This value is the min. value for the workpiece
to move, and is also the electrical positioning control precision.
Speed control
Though the above "total No. of pulses" is an element needed to control the
movement amount, speed must be controlled to perform equal-speed operation.
This "speed" is controlled by the "pulse frequency" output from the QD70 to the drive
unit.
Servo
amplifiter
Feedback pulses
Fig. 1.1 Relationship between position control and speed control
POINT
• The "movement amount per pulse" is the value determined on the machine side.
(Refer to Section 1.1.3.)
• The QD70 uses the "total No. of pulses" to control the position, and uses the
"pulse frequency" to control the speed.
search engine
Designated distance
=
Movement amount of machine (load)
side when motor rotates once
Pulse frequency
[pps]
Servo
motor
A
Detector
Pulse
encoder
0.4
MELSEC-Q
No. of pulses
required for motor to
rotate once
This area is hte total
No. of commanded
pulses.
ta td (s)
1.2 0.4
Movement amount t = 2
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