Mitsubishi Melsec-Q QD75D1, User Manual

Page: 806 / 858

Appendix - 120
MELSEC-Q
APPENDICES
DEVIATION COUNTER
Deviation counters have the following two
functions.
1) To count the command pulses issued from
the QD75, and transmit the count value to
the D/A converter.
2) To subtract the feedback pulses from the
command pulses, and run the motor by the
deviation value (droop pulse) of the
command pulses and feedback pulses until
the command pulses reaches 0.
PLG Encoder
Command
pulses
Deviation
counter D/A
convertor
Motor
Feedback pulses
DIFFERENTIAL OUTPUT TYPE
This is one type of encoder feedback pulse
output. When one signal is output with this
method, a companion signal having the
reverse polarity is simultaneously output. This
method enables high-frequency transfer, and
is resistant to noise, etc., so it is also used in
high-speed signal transfer such as inputting
and outputting of pulse trains. In general, the
transmission side is called the driver, the
reception side is called the receiver, and a
dedicated IC is used.
Command
device
Driver
Servo amplifier
Receiver
DIGITAL BUS CONNECTION
Commands are generally output from the
positioning module to the servo amplifier as a
pulse train. Recently, however, devices are
being digitalized. Accompanying that, a
connection method has appeared in which the
bus lines of both the positioning module and
the servo amplifier CPUs are connected. This
has enabled the construction of higher-
accuracy, higher-speed systems.
The MELSEC A70D, AD774M, A171SCPU,
A273UCPU etc., models employ this digital
bus connection.
DOG SIGNAL
The near-point dog of the OPR.
DRIVE UNIT
The commands output from the positioning
module are low-voltage, low-current
commands with insufficient energy to run the
motor.
The drive unit increases the width of these
commands so the motor can be run. It is an
accessory on servomotors and stepping
motors. Also called a servo amplifier.
Positioning
module Drive
unit
Motor
Power supply
DRIVE UNIT READY
This signal is output when the drive unit for the
motor is in a READY state.
This signal remains OFF when the drive unit
power is OFF, or during faults, etc.
DROOP PULSE
Because of inertia (GD
2
) in the machine, it will
lag behind and not be able to track if the
positioning module speed commands are
issued in their normal state.
Thus, for a servomotor, a method is used in
which the speed command pulses are delayed
by accumulation in a deviation counter. These
accumulated pulses are called the droop
pulse.
The deviation counter emits all pulses and
returns to 0 when the machine stops.
1,000
pulses
200 pulses
accumulate
in the
counter
800
pulses
Voltage D/A
DWELL TIME
This is the time taken immediately after the
positioning is completed to adjust for the droop
pulses in the deviation counter. The
positioning will not be accurate if this time is
too short.