Siemens Simatic Manual page 45

Fail-safe function blocks for storage and retrieval machines
Note
The signal for RELEASE must be generated in a safety-related fashion, e.g. by
using a key-operated switch or similar device.
11. In order to permit retraction, X_POSITIVE_OK or X_NEGATIVE_OK is reset to 1 with a rising
edge at RELEASE; using a suitable user interconnection, a drive stop response should then
be deselected.
12. If, during retraction, SAFE_V exceeds the value of VMAX_RELEASE, then SLS_OK changes
to 0 and DIAG bit 2 is set.
13. A velocity error can always be acknowledged if the actual velocity SAFE_V again lies below
SLS_THRESHOLD.
14. As soon as SAFE_POS has returned to the parameterized, permitted range, after acknowl-
edgment, the axis can again travel at the full velocity; this means that the maximum velocity is
again set at SLS_THRESHOLD (maximum possible INTEGER value = 32767).
15. When retracting, if the axis is to travel to the opposite end stop, then the block behaves just
the same as for a corresponding end of range violation in normal operation. This means that
X_POSITIVE_OK or X_NEGATIVE_OK again changes to 0 and it is only possible to move in
the direction away from the end stop.
16. If V_VALID = 0 while SAFE_POS is outside the parameterized travel range, then the retrac-
tion velocity can no longer be monitored in a safety-related fashion. Therefore, selection using
RELEASE = 1 has no effect, and retraction motion is stopped.
17. To exit this state, V_VALID must be again set to a 1 signal using F_SAFE_POS by acknowl-
edging.
18. Retraction can then be continued. Alternatively, a jump can be made back to the initial state
by deselecting RELEASE with subsequent acknowledgment. If SAFE_POS is still outside the
parameterized travel range, then the response corresponds to Point 9.
Safety notes and instructions
Block F_SAFE_POS signals a 0 signal to V_VALID via output ERROR = 1. When
V_VALID goes to zero, a user interconnection must initiate a stop response in the
drive. All other blocks flag this state using an error code; to avoid a lot of messag-
es occurring at any one time, ERROR is not again set to a 1. The retraction veloci-
ty is no longer monitored. Active retraction monitoring errors can be immediately
acknowledged, SLS_OK is again set. Retraction via RELEASE can be exited
normally, MOVE_POSITIVE_OK and MOVE_NEGATIVE_OK are set again. If the
axis is not in a valid position range at this time, X_NEGATIVE_OK or
X_POSITIVE_OK is withdrawn and ERROR set.
If a 1 signal is again available at V_VALID, then the associated DIAG bits 6 is
reset, and retraction that may be presently active is again monitored.
Safety notes and instructions
The parameterization of input V_MAX_RELEASE must be adapted to the permis-
sible safely reduced velocity according to the application-specific risk assess-
ment.
Safety notes and instructions
The interconnection of output MOVE_POSITIVE_OK must match the selection of
the SDI drive function for the positive direction. For MOVE_POSITIVE_OK = 0,
motion must no longer be possible in the positive direction.
The same applies when interconnecting the MOVE_NEGATIVE_OK output – and
inhibiting the negative direction of motion.
It is absolutely essential that the block outputs are connected with the correct
signals for controlling the drive.
Otherwise, an impermissible motion toward the end stops is possible, which can-
not be identified internally by the block.
S7-Distributed Safety/SIMATIC Safety - fail-safe function blocks for storage and retrieval machines
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