5.5 Safety Function STO
The Safe-Torque-Off (STO) feature protects personnel against unintended restarting of drives. See chap-
ter 7.6 for connector description.
5.5.1 Typical use
A typical use case of the STO function is the integration in the safety concept of a CNC machine. The
door of the critical area contains a safety switch attached to a safety device. If the door is opened, the
safety device opens two relay contacts. These are wired to the STO function of the drive. With the con-
tacts open, the two channels of the STO cut the energy to the motor leaving the drive in a safe state.
5.5.2 Commissioning
Before using the STO safety features:
Execute a risk assessment of the equipment to confirm that the system safety conditions are met.
The following actions need to be taken during installation before using the STO safety features.
Make sure the STO channels are connected to the external safety switch as defined during parent
system design.
Setup the drives and start communication. Enable the axis. Make sure there is no error message.
Disconnect one STO channel from the Safety switch and check the drive state. The state must show
the error "STO inconsistent".
Connect both channels as standard, clear the error from above and Enable the axis again.
Disconnect both channels simultaneously. The state must show ”STO Active Error”.
TwinCat users: Be aware that the system level designer might have chosen to disable direct error
event reporting from the triamec module to the user. It is at the system level designers responsibil-
ity to propagate the plc-axis errors during commissioning in this case.
Some internal tests (flash and RAM-tests) are only done during 24V start-up and after resetting an STO
fault. Make sure any one of the following procedures is done minimum once a year:
Turn off 24V for at least 10s or
Generate an STO error, e.g., STO-Inconsistent (a STO-Active warning is not sufficient) or
Software activation of this error is also possible, ask Triamec Motion AG for details.
5.5.3 Functional Description
The drives main semiconductors may be activated only, if both STO channels are enabled, i.e., their
voltage is high enough. These channels engage the power supply of the semiconductor drivers.
Cutting any of these two channels below
U
Safe
STO
will deactivate the drivers and the motors do not re-
ceive any energy after a maximum time of
t
Safe
STO
(process safety time). This feature has priority over
software and may not be disabled by software. For external diagnostic purposes, the channels may be
pulsed with 0V pulses of maximum duration
t
Ignore
STO
at a maximum rate of
f
Ignore
STO
.
Standard case
: If STO is activated simultaneously on both channels as intended, the drive will enter a
safe state:
The warning state "
Not-ReadyToSwitchOn/STO-Active
" is entered
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