Mark-referenced positioning
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11.1.3 Mark-referenced positioning
Application:
Pieces with lengths of between 100 mm and 500 mm should be cut from a plate roller. The cut-off positions
are specified by marks on the plate. If two marks are separated by more than 500 mm, the plate should be
pulled back to the last cut-off position.
Assignments:
label
light
barrier
shears
A
50mm
P38 = +650
P39 = +680
label window: range within which labels are detected
initial position
B
P37 = +50
P39
P38
P37: minimum distance to label.
: maximum distance to label.
: maximum feed if no label appears
within the window.
A :
POSR
50mm
POSR
position if label
appears at 50mm.
B : position if label
appears at 650mm.
The plate is fed by a roller feed controlled by COMPAX. A reflex light barrier detects the marks on the plate
and reports this to COMPAX. The distance between the light barrier and the shears is 50 mm. The shears
are controlled and monitored by COMPAX.
Wiring up the digital inputs and outputs:
I5
I6
+24V
start
stop
O7
I7
COMPAX
O15
massage
1 = label missing
0 = label detected
I15
O16
shears
0 = block
1 = activate
shears
0 = block
1 = open
O14
I14
I16
label input
0 = no label
1 = label
shears
light
barrier
Function:
The first event after COMPAX has been started is a rest of the control outputs. Once assurance has been
received that the blades of the shears are open, COMPAX is ready for the initial cutting to length.
The cutting to length process is triggered by a start pulse. COMPAX firstly activates the mark reference (I14)
using O14. After a waiting time of 10 ms (which is used to compensate for any possible COMPAX timing
offset), the mark-referenced positioning process is started using the "POSR 50 mm" command. The mark
input (I16) is approved after a travel distance of 50 mm (P37). If the light barrier now detects a mark,
COMPAX pushes the plate another 50 mm. This distance corresponds to the distance between the light
barrier and the shears and is programmed using "POSR 50 mm". If no mark has been detected after a travel
distance of 650 mm (P38), COMPAX stops the feed movement after a total of 680 mm (P39).
At the end of the positioning process, output O16 indicates whether a mark has been detected within the
mark window or not. This output is queried using I15.
If I15 is at 1 (i.e. mark found), COMPAX sets the message output O15 to 0 and activates the shears. Once
the blades have opened, COMPAX waits for the next start pulse. If I15 is 0 (i.e. no mark found), COMPAX
sets the message output O15 to 1, blocks the mark reference (I14) via O14, pulls the plate back by 680 mm
to the last cut-off position and waits for the next start pulse.
