Information Technology Reference
In-Depth Information
6
Case Studies
What we have discussed in the previous sections has been implemented and integrated
in the supervisory control tool Supremica [19] which uses JavaBDD [20] as BDD pack-
age. In this section, the implemented program will be applied to a set of relatively
complicated examples
1
.
6.1
Benchmark Examples
A set of benchmark examples is briefly described as follows.
Automated Guided Vehicles.
An AGV system, described in [21], is a simple manu-
facturing system where five automated guided vehicles transport material between sta-
tions. As the routes of the vehicles cross each other, single-access zones are introduced
to avoid collisions.
Parallel Manufacturing Example.
The Parallel Manufacturing Example, introduced
in [22], consists of three manufacturing units running in parallel. The system is modeled
in three layers in a hierarchical interface-based manner.
TheTransferLine.
The Transfer Line TL
(
n,m
)
, introduced as a tutorial example
in [23], defines a very simple factory consisting of a series of identical cells. Each
cell contains two machines and two buffers, one between the machines and one before
a testing unit which decides whether the work piece should be sent back to the first
machine for further processing, or if it should be passed to the next cell. The capacity
of each buffer is
m
, which is usually chosen to be either
1
or
3
.
The Extended Cat and Mouse.
An extended cat and mouse problem [8], which is
more complicated than the transfer line model, generalizes the classic one presented in
[1]. The extended version makes it possible to generate problem instances of arbitrary
size, where
n
and
k
denote the number of levels and cats respectively.
6.2
Approach Evaluation
In this section, we evaluate the approach from two aspects. First, a comparison between
two partitioning techniques is made by analyzing the statistical data from Fig. 1. In
addition, the extended cat and mouse example with multiple instances is utilized to
investigate how the choice of heuristics in the workset algorithm influences the time
efficiency.
Conjunctive vs. Disjunctive.
Figure 1 shows the result of applying two partitioning
techniques for the examples explained above. The supervisors synthesized for these
examples are both non-blocking and controllable and the safe states are reachable. It
is observed that both of the partitioning based algorithms can handle the AGV and the
Parallel Manufacturing example, for which the number of reachable states is up to
10
7
.
1
The experiment was carried out on a standard Laptop (Core 2 Duo processor, 2.4 GHz, 2GB
RAM) running Ubuntu 10.04.
