Danfoss MCO 305 Design Manual page 41

MCO 305 Design Guide
__ Functions and Examples __
If the Sensor Distance is Larger than one Master Cycle Length
In many applications, the marker cannot be placed
within one master cycle length, for example in the
case of the following equipment for the production
of plastic bags:
Since no markers can be installed between the
slaves here, there is only a marker reader in this
application; the welding station is much farther
away than one master cycle length. Since the
distance of the sensor is larger than one master
cycle length, a buffer is provided for the marker
deviation. When the marker appears, the value is
entered in the buffer and read out upon the
appearance of the next marker: see figure.
In order to assess in what area corrections may be
made, you should subtract the master cycle length
as often as necessary until the value is < 1 master
cycle length. This is the maximum permitted
distance for making corrections. In this example, it
is 6375 – 4000 = 2375 and thus the same
correction range as in the previous example.
Problematic Situations in the Determination of the Marker Distance
If the marker is mounted so close to the processing
point that there is no time left to correct the syn-
chronization after the marker has been detected,
then you can remedy the problem only through
mechanical modification of the marker.
On the other hand, the same effect might also
occur if the marker distance is larger than the
master cycle length and if an insufficient distance
likewise remains after the subtraction of this value,
for example:
The value is entered into the buffer when the marker appears. The buffer is read out only when the next
marker is recognized. This means that the marker is only "recognized" at the master position 900 and that
there is little time left in our example to correct the error. It is the same effect as if the sensor had been
mounted at the value (distance – master cycle length) or (4100 – 4000), respectively, i.e. only 10 mm in
front of the processing point. See the effects (correction area) by means of the two screen shots.
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