7.15.9 Functional description
There is one STO-Enable input and one STO-Status output for each string. The string STO-
Enable input releases the power output stage of all AKD-N (without option "DS" or "DT") con-
nected to the string as long as a 24 VDC signal is applied to this input. When STO function is
engaged during operation by separating STO-Enable from 24 V, the drives (without option
DS/DT) connected to the string slow down without control.
When the global STO function (Safe Torque Off) is not needed, then the inputs STO-
Enable 1/2 must be connected directly to +24 VDC. The function is then bypassed and can-
not be used in the machinery safety concept.
In case of using an AKD-N with option "DS" or "DT" (local STO input) in the string, then the
string STO-Enable signal will have no influence to this specific drive. The local STO-Status
of this drive nevertheless is monitored in the string STO-Status.
The string STO-Status output at the AKD-C is a logical OR of all STO-Status of the drives
connected to that respective string. STO-Status is high:
- during system boot (power up), or
- if the string STO-Enable input is 0V, or
- if the communication with one of the connected drives is lost, or
- if no drive is connected to the string, or
- if the local fieldbus doesn't work.
Possible states of the drives connected to the string referring to the global STO function:
String
STO-Enable
String
HW Enable
String
STO-Status
Safety acc. to
SIL2
AKD-N on String can
produce Torque
0 V
no
high
yes
no
0 V
yes
high
yes
no
+24 V
no
low
no
no
+24 V
yes
low
no
yes
Use the following functional sequence when the STO function is used:
1. Brake the drives in a controlled manner (speed setpoint = 0 V).
2. When drives speed = 0 rpm, disable the string (enable = 0 V).
3. If a suspended load is present, block the drive mechanically.
4. Activate the STO function.
It is not possible to perform a controlled brake if the STO-Enable is off. If controlled braking
prior to the use of the STO function is necessary, the drive must be braked first and the input
STO must be separated from +24 V time-delayed.
When wiring the input STO within one enclosure, the cables and the enclosure must meet
the requirements of IEC 60204-1. If you are wiring leads outside the specified enclos-
ure,then the cables must be laid durably and protected from outside damage.
AKD-C Installation | 7 Technical description and data
Kollmorgen | kdn.kollmorgen.com | February 2018
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