Automated sorting of tree trunks

Logs of different lengths are randomly placed over one belt in queued system. These tree trunks must be sorted into two boxes by length. After release, the logs are transported to the measuring and sorting station. The length measurement by photocells B1, B2 and B3 takes place as follows:

B1 interrupted → Short tree trunk.
B1 and B2 interrupted → Half-length tree trunk.
B1 and B2 and B3 interrupted → Long tree trunk.

If there is a short tree trunk on the belt, the operation carrier B7 of the tree trunk can be pushed into box 1 by the ejector 1.
If there is a half-length tree trunk on the belt, the operation carrier B8 of the tree trunk can be pushed into box 2 by the ejector 2.
Long logs pass through for further processing. The pneumatic ejectors B7 and B8 are delayed for 5 seconds and then reverse back to their resting position.

Only after the sorting has been done (that is, B4 or B5 or B6 is interrupted) a new tree trunk may be supplied. This is the enable signal. 

Operation can be done in three different ways:
 - Automatic operation.
 - Semi-automatic operation.
 - Manual operation.
The selection is made with switch S3.

AUTOMATICALLY
The sorting of short and medium tree trunks and the operation of the ejecting happens automatically, as well as releasing a next one tree trunk.

SEMI-AUTOMATIC
The ejection of the logs is done manually by operation of buttons S1 and S2, when B7 or B8 given a signal (a pulse is sufficient). The request for the next tree trunk is done automatically.

MANUAL
Ejection is done manually via the push buttons. Also the release for the next tree trunk is done manually, via the release button. Long tree trunks cannot be sorted.

The inputs of the PLC are connected to the panel as follows:
Inputs Meaning Additional information
I4.0 Automatic operation Switch S3
I4.1 Semi-automatic operation Switch S3
I4.2 Manual operation Switch S3
I4.3 Driver B7 NO
I4.4 Driver B8 NO
I4.5 Push button ejector 1 NO
I4.6 Push button ejector 2 NO
I4.7 Photocell B1 “1” on interruption
I5.0 Photocell B2 “1” on interruption
I5.1 Photocell B3 “1” on interruption
I5.2 Photocell B4 “1” on interruption
I5.3 Photocell B5 “1” on interruption
I5.4 Photocell B6 “1” on interruption
I5.5 Push button “release” NO

The outputs of the PLC are connected to the panel as follows:
Outputs Meaning
Q8.0 Ejector 1 “ON”
Q8.1 Ejector 2 “ON”
Q8.2 Enable signal
Q8.3 Release indication

In this design a didactic panel ET708 is connected via the input and output connectors to the
PLC. We programmed an automated solution to this problem in FC1 of the S7 program “Tree Trunk” and tested it out using a didactic panel ET708.