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MELSEC-Q
12 CONTROL SUB FUNCTIONS
12.7.8 Pre-reading start function
The "pre-reading start function" does not output pulses while the execution prohibition
flag is ON if a positioning start request is given with the execution prohibition flag ON,
and starts outputting pulses within 3m after OFF of the execution prohibition flag is
detected. The positioning start request is given when the axis is in a standby status,
and the execution prohibition flag is turned OFF at the axis operating timing. This
shortens the virtual start time. The QD75 normally takes 6 to 7ms from when it
receives a positioning start request until it starts pulse output (start time). Some
systems often need the start time to be shortened. This "pre-reading start function" can
improve the tact time of the system.
The "pre-reading start function" will be explained below.
[1] Controls
[2] Controlling instructions
[3] Program examples
[1] Controls
The pre-reading start function is performed by turning ON the positioning start
signal [Y10, Y11, Y12, Y13] with the execution prohibition flag [Y14, Y15, Y16,
Y17] ON, or by executing the dedicated instruction (PSTRT1, PSTRT2, PSTRT3,
PSTRT4). However, if positioning is started with the execution prohibition flag
ON, the positioning data is analyzed but pulse output is not provided. While the
execution prohibition flag is ON, "
Md.26
Axis operation status" remains
unchanged from "5: Analyzing". Pulse output starts within 3ms after the execution
prohibition flag [Y14, Y15, Y16, Y17] has turned OFF, and "
Md.26
Axis
operation status" changes to the status (e.g. during position control, during speed
control) that matches the control system. (Refer to Fig. 12.48)
V
Positioning start signal
[Y10,Y11,Y12,Y13]
Execution prohibition flag
[Y14,Y15,Y16,Y17]
BUSY signal
[XC,XD,XE,XF]
OFF
OFF
ON
t
Ta
OFF
ON
ON
Md. 26 Axis operation
status
Start time
Positioning start timing
3ms or less
Positioning data
analysis
Execution prohibition flag OFF waiting
Standby Analyzing
During position
control
During position
control
Fig. 12.48 Operations of pre-reading start function