ComputerAided_Design_Engineering_amp_Manufactur.pdf

cycle time and identifies bottlenecks. Because FMS operations may be distributed over a large area, it is
difficult to have a global view of the complete system. To simplify the design, debugging, and maintenance,
it is necessary to visualize the operations in a central location; there is an urgent need for the graphical
modeling and animation of FMS.
Our tool XPN-FMS4
integrates modeling, simulation, animation, analysis, and synthesis in one software
package. It can model and analyze the performance of an FMS cell based on Petri net theory. Using
X-window graphical interface and animation, this software allows modeling and analysis visualization
and is easy to understand and manipulate. It lets a user draw the factory layout of an arbitrary FMS cell
on screen using the tool. A corresponding Petri net model is deduced (not automatically) from the FMS
cell and can be displayed on the screen. It can also display the animated overall operating process of the
FMS corresponding to the Petri net model. By experimenting with different inputs and comparing the
output in a timed period, a user can quickly determine how to improve the efficiency, reduce the cost,
and pin down where the bottleneck is. This software is of practical value for industrial engineers and
manufacturing managers.
For the PN models of FMS that are decision-free, we exend the theory and algorithm of a unique
matrix-based method to search for subcritical loops and to support scheduling and dealing with transition
periods. This has been applied to find the optimal input sequence control. Recently, we have simplified
the tool to eliminate the codes for animation with slight modifications. A designer can design factory
layout using regular “graph” buttons and perform animation and simulations. This helps reduce the
effort necessary for the designer to learn to use the tool.
Various synthesis approaches1,2,6,8–16,18–22,27–32,34,36,40,41,47,48,50,51,54,55,58–64
have been proposed. According to
Jeng, 28 two dominant synthesis approaches are bottom-up and top-down. Bottom-up approaches start
with decomposition of systems into subsystems, then construct subnets for subsystems and merge these
subnets to reach a final PN by sharing places, 1,42 transitions, 29,31,52 and elementary paths31,32,51
or by linking
subnets. 19 Top-down approaches begin with a first-level PN and refine it to satisfy system specifications
until a certain level is reached. The stepwise refinement technique by Vallette51
is a top-town approach
where transitions are replaced by well-formed blocks. Suzuki and Murata50
generalized this technique,
but with the disadvantage of the need to analyze the blocks. Our knitting technique supplements this
approach by synthesizing the blocks without analysis.
To automate the synthesis, rules must be developed as in Esparza and Silva22
and Datta and Ghosh18,19
to synthesize free-choice (FC)
and extended FC (EFC). But they are unable to synthesize asymmetricchoice
nets (AC), and one needs to analyze whether the subnet is reducible. 19 Futhermore, they do not
have explicit algorithms and the associated complexity. Thus, most techniques do not deal with CAD
explicitly. We have devised some simple and yet effective rules to guide synthesis, e.g., for communication
protocols58
and automated manufacturing systems. 3,46,48,58 They required no analysis and the synthesized
nets constitute an new class of nets that are more general than FC, EFC, and AC.
6 This new class of nets
is referred to as the Synchronized-Choice (SC) nets.
SC nets possess some interesting properties as they satisfy the following two requirements:
1. If a circuit � has a PT-handle �,
� is bridged to � through a TP-bridge B.
2. If a circuit contains a TP-handle, then this TP-handle is bridged to the circuit through a PT-bridge.
The knitting technique by the author6,8–15
is a rule-based interactive approach. A net is expanded
to N by inserting new paths bearing some physical meaning such as increasing concurrency, alternatives,
etc. The generations are performed in such a fashion that all reachable markings in remain unaffected
in hence all transitions and places in stay live and bounded, respectively. is live and bounded
by making the new paths (NP) live and bounded. This notion is novel compared with other approaches
because it aims to find the fundamental constructions for building any PNs. There are two advantages:
(1) reduction of the complexity of synthesis as an interactive tool, and (2) providing the knowledge from
which the construction of the class of nets may be built. It therefore opens a novel avenue to PN analysis.
Due to the simplicity of the rules, it is easily adapted to computer implementation for allowing the
synthesis of PNs to be performed in a user-friendly fashion.
2
N 1
N 2 ; N 1
N 2
N 1