Outline Design Of Positioning Control System - Mitsubishi Electric MELSECQ Series User Manual

1 PRODUCT OUTLINE

1.1.3 Outline design of positioning control system

Programmable controller
CPU
Program
Intelligent
function module
parameter
GX Configurator-PT
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The outline of the positioning control system operation and design, using the QD70, is
shown below.
(1) Positioning control system using QD70
Positioning module
QD70
Read, write, etc.
Buffer
memories
/XY
device
Monitor date read
Initial setting /Auto rofresh setting/Monitor
Fig. 1.2 Outline of the operation of positioning control system using QD70
(a) Positioning operation by the QD70
1) The QD70 output is a pulse train.
The pulse train output by the QD70 is counted by and stored in the
deviation counter in the drive unit.
The D/A converter outputs an analog DC current proportionate to the
count maintained by the deviation counter (called "pulse droop"). The
analog DC current serves as the servomotor speed control signal.
2) The servomotor rotation is controlled by the speed control signal from
the drive unit.
As the servomotor rotates, the pulse encoder (PLG) attached to the
servomotor generates feedback pulses, the frequency of which is
proportionate to the rotation speed.
The feedback pulses are fed back to the drive unit and decrements the
pulse droop, the pulse count maintained by the deviation counter.
The motor keeps on rotating as the pulse droop is maintained at a
certain level.
3) When the QD70 terminates the output of a pulse train, the servomotor
decelerates as the pulse droop decreases and stops when the count
drops to zero.
Thus, the servomotor rotation speed is proportionate to the pulse
frequency, while the overall motor rotation angle is proportionate to the
total number of pulses output by the QD70.
Therefore, when a movement amount per pulse is given, the overall
movement amount can be determined by the number of pulses in the
pulse train.
The pulse frequency, on the other hand, determines the servomotor
rotation speed (feed speed).
search engine
Forward run
pulse train
D/A
Deviation
converter
counter
Reverse run
pulse train
MELSEC-Q
Drive unit
Speed
command
Servo
amplifiter
Interface
Feedback pulse
Servomotor
M
PLG
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