STO
–
Safe Torque OFF
Functional description
Operating Manual Rev. 1.3
www.engelantriebe.de
page 8
6
Functional description
The Safe Torque Off (STO) function is ensured by a redundant pulse inhibit. When the STO safety function is engaged,
the pulse inhibit disconnects the torque-determining pulse patterns (PWM) generated by the drive's microcontroller from
the power stage. Without suitable pulse patterns, the power stage is unable to develop a continuous torque in the motor
system, the motor is de-energised and torque-free.
6.1
Inputs of the STO channels
The safe pulse inhibit of the STO module has a dual-channel redundant design. Each channel has a digital input to control
its safety sub-function of the pulse inhibit.
When both STO channels are voltage-free (0
V), e.g. both inputs are open, the pulse inhibit is safely activated.
When both STO channels are supplied with voltage (24
V), the pulse inhibit is deactivated and the drive can be operated.
Activation of the STO function
➔
Channel STO1 = 0
V
AND
Channel STO2 = 0
V
Normal operation of the drive
➔
Channel STO1 = 24
V
AND
Channel STO2 = 24
V
Both STO channels must always be operated simultaneously and consistently, i.e. equivalently.
The STO inp
uts allow a direct connection to …
-
safe switching contacts such as electromechanical safety relays,
-
safe semiconductor outputs such as electronic safety relays,
-
passive safety sensors such as position switches with forcibly guided contacts
(see
Figure 6-1: STO function with emergency stop device
-
active safety sensors such as light grids with OSSD signals
(see
Figure 6-2: STO function with OSSD signals
).
Test pulses from OSSD switching devices type C with a pulse duration of
≤
1.0
ms and a period duration
≥
500
ms do not
affect the safety function. This means that the test pulses are safely blanked and that the STO function will not be activated.
Note!
No cross-circuit detection of STO channels 1 and 2 is performed, neither by the STO module
nor by the drive.
According to DIN EN 61800-5-2, a cyclical test must be carried out every 3 months at the
latest to ensure the specified PFH value (see chapter
Attention!
Note the following systematic behaviour of the drive:
In the event of a fault, a possible movement of the motor shaft of 60° (mech.)
cannot be ruled out, even if the STO safety function is activated!
When the safety function is activated and a defect occurs at the internal power stage on at
least two of the three motor phases, i.e. a total of two defects, motor phases can be energised.
In this case, a torque and a limited movement of the motor shaft may occur despite the
activated safety function, whereby the maximum angle of rotation of the motor shaft is limited
to 180° of the electrical period of the motor. For the 6-pole motor systems of the HFI series,
this corresponds to a mechanical angle of rotation of 60°.
