Duerkopp Adler 550-12-12 Service Instructions Manual page 49

13.4 Tape Pull-Off Unit (5)
It is an independently working unit only requiring a 24V current supply
for operation.
Function:
With cl. 550-12-12 the edge binding should have no pre-tension during
feed. This is only possible if the edge binding is drawn off of a loosely
hanging loop when being sewn on.
The controls of the tape pull-off unit must thus effect that there is a
sufficient loose tape reserve available at all times.
For this the tape loop must be scanned. Because of the thin and
narrow tape an indirect scanning had to be chosen.
When falling below a pre-determined remaining length the tape being
run off raises a light metal roller. This lift is registered by a sensor. This
switches on the advancing motor of the tape pull-off unit for a certain
period.
(
Tape advance)
Gearing motor
Number of
revolutins
Controls
Scanning
Tape Reserve
Adaptions:
As soon as the sensor registers the raised roller the advancing motor
is switched on for an adjustable period with an adjustable rpm.
The speed is set at the factory for about 90% of the maximum rpm. The
period for the tape advance is set at the unit.
With maximum rpm (via parameter 117 on the Efka drive limited to
3000 rpm) and greatest desired stitch length a check is made if for this
greatest tape pull-off speed the tape loop is still large enough. If not
the time must be increased.
Problem area
The advancing length has (see above) been firmly set. By chance the
advancing motor can be switched on just at the end of the tape being
sewn, that is, during cutting. Because the advancing length is set for
maximum tape pull-off there would now be a much too large tape
reserve, that is, a loop hanging too low. The signal "Tape Cut" is sent
from the tape feed unit to the electronics as a control signal. This
reduces the time for a running advancing motor by about 50%. For this
the 3rd (green) wire is required.
Time
white/+20-40V
brown/ov
green/tape advance small
49