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MELSEC-Q
6 SEQUENCE PROGRAM USED FOR POSITIONING CONTROL
6.1 Precautions for creating program
The common precautions to be taken when writing data from the PLC CPU to the
QD75 buffer memory are described below.
When diverting any of the program examples introduced in this manual to the actual
system, fully verify that there are no problems in the controllability of the target system.
(1) Reading/writing the data
Setting the data explained in this chapter (various parameters, positioning data,
block start data) should be set using GX Configurator-QP.
When set with the sequence program, many sequence programs and devices
must be used. This will not only complicate the program, but will also increase
the scan time.
When rewriting the positioning data during continuous path control or continuous
positioning control, rewrite the data four positioning data items before the actual
execution. If the positioning data is not rewritten before the positioning data four
items earlier is executed, the process will be carried out as if the data was not
rewritten.
(2) Restrictions to speed change execution interval
Provide an interval of 100ms or more when changing the speed with the QD75.
(3) Process during overrun
Overrun is prevented by the setting of the upper and lower stroke limits with the
detail parameter 1.
However, this applies only when the QD75 is operating correctly.
It is recommended to create an external circuit including a boundary limit switch
to ensure the whole system safety as follows: the external circuit powers OFF the
motor when the boundary limit switch operates.