10.6.3 STO (Safe Torque Off)
Safe Torque Off description for drive option Functional Safety 1.
10.6.3.1 Description
STO is suited for SIL 2 according to IEC 62061 and PLd / Cat.3 according to ISO 13849-1.
STO is a type A subsystem according to IEC 61508.
STO turns off the drive output stage that powers the motor. STO function corresponds to a
not controlled braking according to IEC 60204-1, category 0.
10.6.3.1.1 Important Notes
The safety properties given in this documentation refers to the device AKD2G with func-
tional safety option 1. The user has to determine the safety properties of the safety chain.
No Brake Power!
Serious injury could result when a suspended load is not properly blocked. The drive cannot
hold a vertical load when STO is active.
Add a safe mechanical blocking (for instance, a motor-holding brake).
10.6.3.1.2 Precondition before activation
None.
10.6.3.1.3 Activation
The digital STO inputs (channel A and B) must be connected to the output of a safety control
or a safety relay, which at least meets the requirements of PLd, Cat.3 according to
ISO13849. Technical data of the safe inputs (➜ # 127).
If one of the STO inputs goes open-circuit or 0V, then power supply to the motor stops within
3.5ms. The motor will lose all torque and coast to a stop.
If the drive detects that the two STO inputs are in a different state for longer than 100 ms,
then a simultaneity fault F9005 occurs (➜ # 132).
Review the enclosure and wiring instructions (➜ # 126).
Wiring example STO single axis, SIL2/PLd, Emergency Stop
Note: AXIS1.SAFE.STO.REPORTFAULT should be set to 1 if STO is activated by a
switch.
AKD2G-S Installation, Safety 1 | 10 Functional Safety
Kollmorgen | kdn.kollmorgen.com | S101, December 2018 129
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