252 Rockwell Automation Publication MOTION-UM003K-EN-P - January 2019
Chapter 11 Commission an Axis
Understanding STO Bypass When Using Motion Direct Commands
For complete information about Motion Direct Commands in motion control
systems including the Safe Torque Off feature, see the publications that are
listed in the Additional Resources on page 9
.
The drive does not allow motion while the safety controller is in Program
mode by default. This condition applies only if a safety connection between
the GuardLogix safety controller and the drive was established at least once
after the drive was received from the factory.
The drive does not allow motion because the Safety Task is not executed while
the GuardLogix® safety controller is in Program mode. This condition applies
to applications that run in a single-safety controller (with Motion and Safety
connections). The standard controller can transition to Program mode while
the safety controller stays in Run mode and continues to execute the Safety
Task. This transition occurs when an integrated safety drive has a Motion
connection to a standard controller and a separate Safety connection to a dual-
safety controller.
However, applicable drive systems are designed with a bypass feature for the
STO function in single-safety controller configurations. You can use the
Motion Direct Command (MDC) feature to allow motion while following all
necessary and prescribed steps per machine safety operating procedures.
ATTENTION: Consider the consequences of allowing motion by using MDC
when the controller is in Program mode. You must acknowledge warning
messages in the Logix Designer application that warn of the drive bypassing
the STO function and unintended motion can occur. The integrated safety
drive does not respond to the request of STO function if MDC mode is
entered.
ATTENTION: It is your responsibility to maintain machine safety integrity
while executing Motion Direct Commands. One alternative is to provide
Ladder Logic for Machine Maintenance mode that leaves the controller in
Run mode with safety functions executing.
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