Siemens SIMATIC FM 351 - Encoders

9
9-17
FM 351 Positioning Function Module
EWA 4NEB 720 6001-02
9.8 Single Setting Loop Traverse
With the single setting Loop traverse you define the direction in which a
target is approached.
A target which is approached against the specified direction is first passed by.
Then the FM 351 carries out a reversal of direction and approaches the target
in the specified direction.
With this single setting you can ensure that a target is always approached
with force contact.
The loop traverse can be simultaneously called with the following single set-
tings:
 Do not evaluate enable input.
You can use the loop traverse when force contact between the motor and the
axis can only be ensured in one direction.
Make sure that you select the correct loop traverse for the force contact.
Specifying the wrong loop traverse may mean that the drive does not reach
the target.
When you start positioning to a target, which is located against the direction
of the parameterized loop traverse, the FM 351 determines a fictitious target
for this target. At the fictitious target it executes a change of direction and
then approaches the real target in the correct direction.
This fictitious target must be located within the permissible range for incre-
mental dimensions.
The distance of the fictitious target from the parameterized target is found
depending on the direction:
Table 9-8 Calculation of the Position of the Fictitious Target during a Loop Traverse
Specified Values Position of the Fictitious Target
Parameterization: Loop + and
traverse in negative direction.
The distance of the fictitious target is calculated from:
 The positive switch-off difference and
 The negative switch-over difference.
The fictitious target (Target
f
) has the value:
Target
f
= Target - Positive switch-off difference - Negative switchover differ-
ence
Parameterization: Loop - and tra-
verse in positive direction.
The distance of the fictitious target is calculated from:
The negative switch-off difference,
 The positive switch-over difference.
The fictitious target (Target
f
) has the value:
Target
f
= Target + Negative switch-off difference + Positive switchover dif-
ference
Definition
Use of the Loop
Traverse
Fictitious Target
Operating Modes and Settings