With electronic protection devices there are safety functions integrated in the drive control in order to
minimize or eliminate danger by malfunctions in machines. The integrated safety functions replace
the complex installation of external safety components. The safety functions can be requested or
released by an error.
Warning
Regular checks
In order to ensure permanent security, the functions must be checked in
regular intervals according to the results of the risk analysis.
3.2 Safe torque off (Safe Torque Off - STO)
Installation work or troubleshooting can be necessary in hazard areas, whereby protective devices
such as line- or motor contactors shall not be activated. The safety function STO can be used there.
Depending on the application the use of line or motor contactors can be void by using STO.
In case of error or request, the power semiconductor of the drive module are switched off and the
drive is not supplied, which causes a rotation or torque (in case of a linear drive movement or force).
The unit can be safe switched off and/or remain if an error occurs.
Danger
Electric Shock
Continue mains voltage with active STO function.
Compared to the disconnection by line contactors or motor contactors the integrated safety function
enables a simple integration of drives to functional groups of a system. Thereby safe torque off can
be limited to certain systems. Another advantage is that the recharge and discharge time of the
COMBIVERT DC link must not be considered. Thus the unit is faster again ready for operation after
an interruption.
Regular electromechanical equipment are liable to abrasion. Loss of these equipment occurs by us-
ing the STO function and the maintenance costs are reduced.
Characteristic data for „Safe torque off“
• Power supply for the rotation direction of the motor is interrupted (free-wheeling motor)
• Used when monitoring of standstill is not necessary
• Unintentional starting of the motor is prevented
• No galvanic isolation of the motor from the drive module DC link
What is realized by the STO function related to EN 60204 -1 ?
• Emergency stop can be realized by the STO function, since the mains voltage may remain ef-
fective.
• Emergency stop can be realized only in connection with a line contactor, which disconnects the
mains voltage !
17
SAFETY FUNCTIONS
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