Chapter 1 Overview - Mitsubishi Electric MELSEC Q Series User Manual

CHAPTER 1
The QD73A1 possesses a deviation counter and D/A converter inside as in the following figure.
CPU module Positioning module QD73A1
Sequence Setting
program data
Current
value
Data writing/reading
Parameter data
Positioning data
OPR parameters
A system with the QD73A1 operates as follows.
Once a command pulse train for positioning is output, pulses are accumulated in the deviation counter. The
Start integrated value of pulses (accumulated pulses) is converted into DC analog voltage by a D/A converter, then
turns into a speed command to a servomotor. The speed command from a drive unit starts servomotor rotation.
Once the servomotor starts rotating, feedback pulses that are proportional to the number of rotations are
generated by a pulse generator (PLG) attached to the servomotor. The generated feedback pulses are
Operation
subtracted from the accumulated pulses in the deviation counter. The deviation counter continues to rotate the
servomotor, maintaining a constant amount of accumulated pulse.
Once the command pulse output from the QD73A1 stops, the accumulated pulses in the deviation counter
Stop
decrease, so does the speed. When there is no more accumulated pulse, the servomotor stops.
The rotation speed of a servomotor is proportional to command pulse frequency, while the rotation degree of the
servomotor is proportional to the output command pulse amount. By setting feed per pulse beforehand, analog voltage
that is proportional to the number of pulses in a pulse train is output, and a workpiece can be moved to the set position.
Note that pulse frequency defines the rotation speed of the servomotor (feedrate).
OVERVIEW
Command
pulses
Electronic Deviation
gear counter
Feedback pulse
addition/
subtraction setting
Multiplication
Feedback pulses from the pulse generator (PLG) may be input to the QD73A1
via the drive unit
Check which method applies in the manual for the servomotor or drive unit to
be used.
Drive unit
Speed
Analog
command
voltage
D/A
converter
Interface
Feedback pulses
*1
Feedback pulses
*1 *2
or directly depending on the servomotor to be used.

CHAPTER 1 OVERVIEW

Servomotor
Servo
M
amplifier
*1
PLG
*2
17
1