Safe Operating Stop (SOS)

With the SOS function, the stopped motor is brought into position and monitored by a drive control.


The Safe Operating Stop function represents safe standstill monitoring. The drive control remains in operation. The motor can therefore deliver the full torque to hold the current position. The actual position is reliably monitored. In contrast to safety functions SS1 and SS2, the speed setpoint is not influenced automatically. After SOS has been activated, the higher-level control must bring the drive to a standstill within a parameterized time and then hold the position setpoint.


SOS is an ideal solution for all applications in which the machine or parts of the machine must be safely at standstill for certain machining steps, but in which the drive must also provide a holding torque. It is ensured that the drive remains in its current position despite the load torque. In contrast to SS1 and SS2, the drive does not brake automatically in this case. It expects the higher-level controller to coast down the relevant axes as a coordinated group within an adjustable delay time. This can be used to prevent any damage to the machine or product. SOS is widely used, for example, in winders, converting and packaging machines, and machine tools.

Customer benefits

No mechanical components are necessary to keep the axis in position despite any counterforce that might appear. Because switching times are short and the position control always remains active, setup and downtimes are reduced. Recalibration of the axis after exiting the SOS function is not necessary. The axis can immediately be moved again after deactivation of the SOS function.