Mitsubishi Electric RD77GF8 User Manual page 4

[Design Precautions]
WARNING
● When connecting an external device with a CPU module or intelligent function module to modify data
of a running programmable controller, configure an interlock circuit in the program to ensure that the
entire system will always operate safely. For other forms of control (such as program modification,
parameter change, forced output, or operating status change) of a running programmable controller,
read the relevant manuals carefully and ensure that the operation is safe before proceeding. Improper
operation may damage machines or cause accidents.
● Especially, when a remote programmable controller is controlled by an external device, immediate
action cannot be taken if a problem occurs in the programmable controller due to a communication
failure. To prevent this, configure an interlock circuit in the program, and determine corrective actions
to be taken between the external device and CPU module in case of a communication failure.
● Do not write any data to the "system area" and "write-protect area" of the buffer memory in the
module. Also, do not use any "use prohibited" signals as an output signal from the CPU module to
each module. Doing so may cause malfunction of the programmable controller system. For the
"system area", "write-protect area", and the "use prohibited" signals, refer to the user's manual for the
module used.
● If a communication cable is disconnected, the network may be unstable, resulting in a communication
failure of multiple stations. Configure an interlock circuit in the program to ensure that the entire
system will always operate safely even if communications fail. Failure to do so may result in an
accident due to an incorrect output or malfunction.
● To maintain the safety of the programmable controller system against unauthorized access from
external devices via the network, take appropriate measures. To maintain the safety against
unauthorized access via the Internet, take measures such as installing a firewall.
● Configure safety circuits external to the programmable controller to ensure that the entire system
operates safely even when a fault occurs in the external power supply or the programmable controller.
Failure to do so may result in an accident due to an incorrect output or malfunction.
(1) Machine home position return is controlled by two kinds of data: a home position return direction
and a home position return speed. Deceleration starts when the proximity dog signal turns on. If
an incorrect home position return direction is set, motion control may continue without
deceleration. To prevent machine damage caused by this, configure an interlock circuit external to
the programmable controller.
(2) When the module detects an error, the motion slows down and stops or the motion rapidly stops,
depending on the stop group setting in parameter. Set the parameter to meet the specifications of
a positioning control system. In addition, set the home position return parameter and positioning
data within the specified setting range.
(3) Outputs may remain on or off, or become undefined due to a failure of a component such as an
insulation element and transistor in an output circuit, where the module cannot detect any error. In
a system that the incorrect output could cause a serious accident, configure an external circuit for
monitoring output signals.
● If safety standards (ex., robot safety rules, etc.,) apply to the system using the module, servo amplifier
and servomotor, make sure that the safety standards are satisfied.
● Construct a safety circuit externally of the module or servo amplifier if the abnormal operation of the
module or servo amplifier differs from the safety directive operation in the system.
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