12CONTROL SUB FUNCTIONS

12.7.8 Pre-reading start function

MELSEC-Q

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

 

 

 

 

 

 

 

 

t

 

 

Start time

 

 

Positioning start signal

ON

 

 

 

[Y10,Y11,Y12,Y13]

 

OFF

Positioning start timing

 

 

 

 

 

Execution prohibition flag

OFF

ON

 

 

[Y14,Y15,Y16,Y17]

 

 

Ta

3ms or less

BUSY signal

ON

 

 

 

 

[XC,XD,XE,XF]

 

OFF

 

 

 

 

Positioning data

Execution prohibition flag OFF waiting

 

 

analysis

Axis operation

During position

Standby

Analyzing

During position

status

control

control

 

 

 

 

 

 

Fig. 12.48 Operations of pre-reading start function

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Mitsubishi Electronics QD75D, QD75P user manual Pre-reading start function, Controls