Maintaining the insertion of cars to the warehouse

1. Handling entries to the warehouse

1.1. Starting a read operation

The entire operation is started by the PLC, which detects an approaching car by means of limit switches of the conveyor system. An appropriate command is sent to the PC via channel 0 of the PLC-PC interface. The PC starts the scanner for reading the PKN number. This is done with a serial message containing the start character STX.

1.1.1. Operations after good read

When the scanner has read the PKN number it is transferred to the PC. The PC uses this number for retrieving a record from its database.

When the record was found, the data that is contained in this record will be used for selecting one out of the five stacks.
If the record was not found, a fast request message for the PKN number is sent to FIS. FIS performs a lookup in its database and sends the requested data back to PY.
If no connection to FIS is available or FIS does not respond to the fast request a message is sent from the PC of system PY to the PC of system NZ with a similar fast request functionality, except that no PKN number is contained in this request. System NZ sets a flag in the database, which is monitored by the MMI system in the control room. The MMI system will generate an audible alarm, alerting the operation personal. Since the required data is visible on the barcode label, the operation personal may now read the type of the car body plus the color code from the video monitor and enter this data into the MMI system. The entry is sent to system NZ, which in turn passes it with a special message to system PY.
The car body will not become released until the type of the car body and the color code has been collected either from the internal database, a fast request to FIS or manual entry in the control room! Since there is no visible information concerning this process available at the location of the car body, maintenance people could easily make the false judgment of a system malfunction and override this operation by manual intervention to the control of the conveyor system. If this happens, the image of the warehouse is corrupted and does not reflect the actual situation in the warehouse!
The data that PY is looking for is mainly the type of the car body and the color code.
When the data has been found either in the internal database or by receiving a fast response from FIS, the operation continues with the selection of a stack.

1.1.2. Operations after bad or no read

When the car body has reached the barrier of the conveyor system an appropriate command is sent from the PLC on channel 1 to the PC indicating that the reading window of the scanner has come to an end. The PC now stops the scanner by transmitting a serial message with the stop character ETX. Concurrently an EDE-message is sent to the FIS-Video system. This system will generate an audible alarm and alerts the operation personal in the control room.
The car body was halted exactly in a position where the PKN number can be seen by means of a video camera. The operation personal in the control room has to enter the PKN number, which is sent back to the waiting system PY.
The car body will not become released until the PKN number has been collected either from the scanner or from manual input operations! Since there is no visible information about this process available at the location of the car body, maintenance people could easily make the false judgment of a system malfunction and override this operation by manual intervention to the control of the conveyor system. If this happens, the image of the warehouse is corrupted and does not reflect the actual situation in the warehouse!
When the PKN number was found either by a good read of the scanner of by manual input, the operation continues with the insertion process.

1.2. Selecting a stack

Now that the required data for the current car body was found, the following operations are performed:

1.2.1. Checking for SPECIAL CAR criteria

Due to a definition in the list of duties the data that was retrieved either from the internal database or from a fast response from FIS contains a character ‘0’ or ‘1’ that declares this car to be a SPECIAL CAR. If this flag was set to ‘1’ all further stack-select operation are disabled and the car is sent to stack number 4, regardless of its color and the actual contents of stack 4. If stack number 4 is completely filled at this moment, the conveyor system will not be released and the car body will wait at the barrier until space in stack 4 is available.
Since there is no visible information about this process available at the location of the car body, maintenance people could easily make the false judgment of a system malfunction and override this operation by manual intervention to the control of the conveyor system. If this happens, the image of the warehouse is corrupted and does not reflect the actual situation in the warehouse!

1.2.2. Searching the stacks for the same color code

If the check for the SPECIAL CAR failed all stacks, which have at least one space available AND are not blocked, are checked for a match in the color code. The color code of the last position of each stack is compared with the color code of the current car body. If a match was found, the number of this stack is sent to the PLC by acknowledging the scanner start command previously given on channel.

1.2.3. Searching the stacks after color search failed

If the comparison of the color codes failed, all stacks, which have at least space for one car AND are not blocked, are searched. If such a stack was found, the number of this stack is sent to the PLC by acknowledging the scanner start command previously given on channel 0.

1.2.4. No stack found

If none of the operations described above have found a target for the waiting car body, the stack selection process will not terminate and is repeated continuously. The conveyor system will not become released!