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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.
(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.
In terms of the entire system's safety, a boundary limit switch should be provided,
and an external circuit that turns the motor's power OFF when the limit switch
turns ON should be provided.
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