12.2010 Configuration and Connection Examples
Siemens AG 6SE7087-6QX70 (Version AM)
SIMOVERT MASTERDRIVES Compendium Motion Control 2-19
2.4.2 Overview
2.4.2.1 Safety function STO – Safe Torque Off
The purpose of the STO safety function (Safe Torque Off) is to prevent
a drive from starting up unexpectedly. This function prevents
unexpected starting of the motor (from standstill) that is connected to
the drive control unit. The motor shaft is in a no-torque condition when
the "Safe Torque Off" function is active. This is the reason that this
safety function may be activated only after the drive actually comes to a
standstill. Otherwise, it will not be able to brake. An external machine
control must be employed to reliably bring the drive to a standstill and
activate the function "Safe Torque Off". If the drive is at a standstill and
the function "Safe Torque Off" is active, additional brakes may be
required in cases where there is a risk of external forces acting on the
drive axes.
The "Safe Torque Off" function on SIMOVERT MASTERDRIVES is a
"mechanism for shutting down a drive and preventing it from restarting
unexpectedly" in accordance with EN 60204-1, Section 5.4.
This behavior is identical to Stop Category 0 in accordance with
EN 60204-1:2006 /R9/.
The "Safe Torque Off" function does not isolate the drive from the
supply system. It does not therefore provide any protection against
"electric shocks".
2.4.2.2 Safety function SS1 – Safe Stop 1 (time controlled)
Trip
s motor deceleration and activates the STO function after an
application-specific time delay.
This behavior is identical to Stop Category 1 in accordance with
EN 60204-1:2006 /R9/.
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