Safety functions 67
Safe torque off (STO)
The STO function brings the machine safely into a no-torque state and/or prevents it
from starting accidentally. The STO function in the FSO module activates the drive
STO function, that is, opens the STO circuit in the drive. This prevents the drive from
generating the torque required to rotate the motor. If the motor is running when the
STO function is activated, it coasts to a stop.
You can configure the SBC function to be activated before, at the same time with, or
after the drive STO function. When you use an encoder, you can also configure the
SBC function to be activated at a user-defined speed limit.
This section describes the different versions of the STO function separately without
and with an encoder.
For more information on the STO function in the ACS880/DCS880 drives, see the
corresponding drive hardware manual.
WARNING! For the encoderless mode, you have to set parameters STO.14
and SBC.13 so that the motor has enough time to stop from full speed when
modulation is stopped.
Note: If the SSE is cascaded, STO activation also activates the SSE cascade
indication signal (output). See sections Safe stop emergency (SSE) on page 106 and
Cascade on page 62.
Note: Always set the parameters related to the STO function to have the correct
monitoring limit hit and fault reaction behavior. An internal monitoring of the FSO
module can trigger the STO function even if you have not defined an external request
signal. These internal monitorings trigger STO:
• SAR0, SAR1 or SSE/SS1 limit hit
• FSO module fail safe state.
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