AKD Installation | 6 Technical description and data
6.16 Safe Torque Off (STO)
An additional digital input (STO) releases the power output stage of the drive as long as a 24
V signal is applied to this input. If the STO input goes open-circuit, then power will no longer
be supplied to the motor, and the drive will lose all torque and coast to a stop.
Input STO (X1/3)
l Floating, reference ground is GND
l 24 V ±10%, 20 mA
This input is not compatible with IEC 61131-2.
You can thus achieve a category 0 stop (➜ p. 50) by using the STO input without switching a
mains contactor.
Advantages of the STO function:
l The DC bus link remains charged, since the mains supply line remains active.
l Only low voltages are switched, so there is no contact wear.
l Very little wiring is required.
The STO safety implemenation on the AKD is certified. The safety circuit implementation
used for the safety function "Safe Torque Off" in the drive is suited for SIL 2 according to IEC
61508-2 and PLd / CAT3 according to ISO 13849-1.
6.16.1 Safety characteristic data
The subsystems (AKD) are described with the following characteristic data:
Device Operation Mode ISO 13849-1 IEC 61508-2 PFH [1/h] SFF[%]
STO STO single channel PL d, CAT 3 SIL 2 0 20
6.16.2 Use as directed
The STO function is exclusively intended to provide a functional safe stop of the motion sys-
tem. To achieve this functional safety, the wiring of the safety circuits must meet the safety
requirements of IEC 60204, ISO 12100 and ISO 13849.
6.16.3 Prohibited Use
The STO function must not be used if the drive is to be made inactive for the following rea-
sons:
l Cleaning, maintenance and repair operations, long inoperative periods. In such cases, the
entire system should be disconnected from the supply and secured (main switch).
l Emergency-Off situations. In an Emergency-Off situation, the main contactor is switched
off (by the Emergency-Off button).
52 Kollmorgen™ | May 2013
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