SIEMENS
SINAMICS S150 NEMA
Engineering Information
3
Siemens D21.7
(Part 2) – 2015
3/21
Safe Stop 2 (SS2)
The SS2 function brings the motor to a standstill quickly and
safely and then activates the standstill position once the
motor has stopped.
Effect
The Safe Stop 2 function can safely stop the drive in
accordance with EN 60204-1, Stop Category 2. When the
SS2 function is selected, the drive brakes autonomously
along a quick-stop ramp. In contrast to SS1, the drive
control remains operational afterwards, i.e. the motor can
supply the full torque required to maintain zero speed. The
standstill is safely monitored by the Safe Operating Stop
(SOS) function.
Application
As with SS1, the SS2 function ensures the quickest possible
deceleration of the motor. However, the motor power is not
switched off. Instead, a control system prevents it from
leaving the standstill position – even if it is affected by
external forces.
Customer benefits
The SS2 function ensures a rapid axis stop. Since the control
remains active, productive operation can immediately
continue without referencing after the safety function is
deselected. This ensures short setup and standstill times and
high productivity.
Safe Stop 2 (SS2)
Safe Operating Stop (SOS)
With the SOS function, the stopped motor is held in position
and monitored by drive control.
Effect
The SOS function constitutes 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
autonomously by the drive.
Application
SOS is the ideal function for all those applications for which
the machine or parts of the machine must be at a safe
standstill for certain machining steps, but where the drive
must also supply a holding torque. It is ensured that despite
counter torque the drive remains in its current position.
When SOS is selected, the drive does not influence the speed
setpoint autonomously (in contrast to SS1 and SS2). Instead,
the drive expects the higher level control system to initiate
coordinated power-down of the axes as a group within an
adjustable wait time. This can be used to prevent any
damage to the machine or product. Typical applications
for SOS include 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 may occur. Due to the
short switching times and the fact that the drive control
always remains active, setup and downtimes are reduced.
Re-referencing of the axis after exit from the SOS function is
not necessary. The axis can traverse again immediately after
deactivation of the SOS function.
Safe Operating Stop (SOS)
Safety Integrated – Description of functions
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