Page 304 - Mechatronics for Safety, Security and Dependability in a New Era

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complicated problems into smaller and simpler sub-problems. Furthermore this reduces the influence
of uncontrolled elements in the latter stage of the production preparation. We also found that the
design standard can change the dependency relationship between the different tasks. The existing
study (Sato et ah, 2003) proposed the optimization technique for the oversea production preparation
process by considering the dependency relations between the different tasks, measuring the process
data and the design standard together. That approach uses the physical relations between the designed
variables, measured process data, and performance measures. By using the physical relations, the
dependency relations between tasks are generated in the Design Structure Matrix (Yassine et ah,
1999) and the process is optimized by considering the difference of the verification accuracy among
the different trial phases. But that approach has two major problems. One problem is the difficulty to
reveal the physical relations in the matrix expression when the number of the design variables,
measured process data, and performance measures is large. The other problem is the impossibility to
consider the essential constraint of the task order coming from the engineer's experience. The
proposed technique has been developed in order to overcome such problems.

With the new technique, the engineer writes the physical relation in the relation diagram expression as
shown in Figure 1, which is one of the seven new tools of the QC. The new optimization algorithm
considering the strong constraints on the task order is proposed based on the Genetic Algorithm
(Holland, 1975) with Partial Matched Crossover (Goldberg, 1989). The new technique is evaluated
using a hot forging trial process and the result showing at the end of this paper confirms the efficiency
of the proposed approach.

Cause—•Effect
Hardness Underfill |
of work
K ' \
Temperature of Friction
work as being \ of die
heated . /
/ \ \ / \
Heating Heating Quality of Diameter
voltage time material of row material

Figure 1: Relation diagram for physical relations between designed variables

APPROACH
We focus on the fact that different engineers perform the production preparation in different ways. We
think we should consider the relations behind the process, which are more general and don't depend
on the individual engineer. We have concluded that the physical cause-effect relations of the object to
be designed are the fundamental factors. Figure 2 shows the proposed hierarchical model of the
production preparation process. The proposed optimization technique is based on this model. The
lowest level is composed of the physical cause-effect relations of the object to be designed and the
company's design standards such as the standard design requirement and the standard design sequence.
The company's design standards are important factors to compete with rival companies. Tn the middle
level, the dependency relations between design and/or preparation tasks exist. The structure shows the
dependency relations between the tasks are constrained by the physical cause-effect relations and the
company's design standards. The product design and the production preparation process exist on the
dependency relations between the tasks and the essential constraints on the task order. The essential