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MELSEC-Q
12 CONTROL SUB FUNCTIONS
V
t
Ts
Tw
t
Ts
Ts
1
Feed shaft
Cutter shaft
Feed shaft
start request
Cutter shaft
start request
Start
time
Start
time
Start
time
Stop time
2
Fig. 12.50 Operation timings of system example
The cutter shaft starts from the moment the feed shaft has completed feeding the
stock "
1
", and the feed shaft starts from the moment the cutter shaft has
returned to the standby position "
2
". Actually, however, there is a delay of start
time Ts (6 to 7ms) from when the QD75 receives a start request until it outputs
pulses. The system's tact time can be reduced by the shortening of this delay
with the Pre-reading start function.
In Fig. 12.50, the feed shaft stands by during the stop time Tw.
Hence, pre-reading of the next data starts during the stop time Tw. If Tw is a
certain period of time, the analysis of the next data is completed during that
period, and the system is placed in an execution prohibition flag OFF waiting
status. Therefore, replacing the positioning start timing at
2
with the execution
prohibition flag OFF allows the time from when the axis operation request turns
ON until pulse output starts to be reduced to within 3ms in the sequence
program. (Refer to Fig. 12.48)