8-1
8-1 Safe Torque OFF Function
OMNUC G5-series AC Servomotors and Servo Drives User’s Manual (with Built-in EtherCAT Communications)
8
Safety Function
8-1 Safe Torque OFF Function
The safe torque OFF function (hereinafter referred to as STO according to IEC 61800-5-2) is
used to cut off the motor current and stop the motor through the input signals from a safety
device, such as a safety controller or safety sensor, that is connected to the safety connector
(CN8).
When the STO function is operating, the
Servo Drive turns OFF the servo ready completed
output (READY) to go into the safety status.
 The PFH value is 2.30 × 10
−8
.
Precautions for Safe Use
 When using the STO function, be sure to execute a risk assessment of the equipment to confirm
that the system safety requirements are met.
 There are the following risks even when the STO function is operating. Be sure to take safety into
account as part of the risk assessment.
• The motor runs if an external force is present (e.g., force of gravity on a vertical axis). If holding
is required, implement appropriate measures, such as providing external brakes. The brakes
for a
Servo Drive with brakes are used for holding only, and cannot be used for control.
• Even if there is no external force, when the Fault reaction option code (605E hex) is set to free-
run with the dynamic brake disabled, the motor uses free-run stopping and the stop distance
is long.
• In case of internal failure of components, the motor may operate in the range of up to 180
degrees of electrical angle.
• The power supply to the motor is cut off by the STO function, but the power supply to the
Servo
Drive
will not be cut off nor electrically isolated. For Servo Drive maintenance, cut off the power
supply to the
Servo Drive through another means.
 Do not use the EDM output for any purpose other than the failure monitoring function. The EDM
output signal is not a safety output.
 Be sure to check the wiring when installing. Especially check the following:
• The wiring is not short-circuit or disconnected.
• The polarity of EDM circuit is not reversed.
• SF1, SF2 and EDS operate properly.
 The system with incorrect wiring may damage the safety function.
 The dynamic brake and external brake release signal outputs are not safety-related parts. Make
sure to design the equipment not to be dangerous even if the external brake release fails during
the STO status.
 When using the STO function, connect equipment that meets the safety standards.
 The OMNUC G5-series AC Servo Drives fulfill the requirements of the following certifications
(application pending):
• CAT-3 (EN 954-1)
• Performance level d (EN/ISO 13849-1)
• SIL 2 (IEC/EN 62061)
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