Page 288 - Mechatronics for Safety, Security and Dependability in a New Era

Ch55-I044963.fm Page 272 Tuesday, August 1, 2006 9:39 PM
Ch55-I044963.fm
272
272 Page 272 Tuesday, August 1, 2006 9:39 PM
2 APPROACH

In this implementation, we aimed to confirm that the system integrity on the whole. In order to
make its information processing simple, the process management engine uses only typical durations
to process each step in the manufacturing materials or installing them, and the bills of materials.

In order to trace WIPs (Work In Processes), we installed several checkpoints representing bound-
aries of logical activities, which we named "gates", in the process through material-manufacturing
and building-construction. On WIPs passing these gates, RFIDs are read and progress reports are
collected.As the WIP's due time for passing the final inspection process gate is deduced from the
overall schedule of the construction, the due time for passing each gates can be calculated from
the given final due time and the typical durations from one gate to the next. On the other hand,
when WIPs pass each gates, the estimated time for passing following gates can be calculated.

In these way, for each building materials types, we can obtain both due time for all demands and
for all gates, and actual or estimated time for all WIPs. By associating each demands and each
WIPs in the order of time passing a certain gate for each materials type, we carry out the allocation
of demands and WIPs. In the case of due time of allocated demands is earlier than estimated time
of associated WIP passing by, we assume that tardiness is expected and some action is required.

3 THE IMPLEMENTATION
3.1 Gates
In order to trace WIPs, we have set up nine gates within both material-manufacturing and building-
construction processes, as follows; (I) Design approved, (2) Ordering raw material, (3) Start pro-
cessing, (4) Assembling, (5) Shipping out from the manufacturing plant, (6) Carrying into the
construction site, (7) Distributing within the construction site, (8) Installing building material in
the building, (9) Final inspection. It is easy for the system to change the number of gates, to
change typical durations from gate to the next.

When the WIPs pass gates, following processes are took place. (1) Reading RFID on the WIP, (2)
Converting to the WIP identifier, (3) Logging the time passing the gate, (4) Logging the physical
position of WIP, (5) Logging the result of the post-process testing. These data are accumulated
within an actual achievement database resides in the shared data space, described later.

3.2 Tracking Works with RFIDs

At each gate, the system gathers actual achievement information by means of RFIDs. In this
implementation, we used read-only type RFIDs with 128 bit length identifiers. Generally speaking,
as each building materials consists of multiple parts which are manufactured independently in the
manufacturing line, single building material may contain multiple RFIDs in it. On reading RFIDs
of a building material, some RFIDs may respond and some may not, but the tracking engine should
handle these information properly. In some cases, an assembled WIP may be dis-assembled and
re-assembled find much more matching combination.

So, the tracking engine should have following features.
1. Identifying the WIP from partial RFIDs information.
2. Keeping RFID identifiers of all parts consisting the WIP.
3. Keeping tree-structured information including assembling order and part structure, for the case
of dis-assembling and re-assembling.