INTERNATIONAL CONFERENCE ON ENGINEERING DESIGNICED 01 GLASGOW, AUGUST 21-23, 2001

VERIFICATION OF A MODEL OF SYNTHESIS- THE METHODS FOR VERIFICATION AND RESULTS
Akira Tsumaya, Yutaka Nomaguchi, Masaharu Yoshioka,
Hideaki Takeda, Tamotsu Murakami, and Tetsuo Tomiyama
Keywords: protocol analysis, process modeling, synthesis, verification, reference model

1

Introduction

Engineering design consists of a variety of thought processes, but most of them can beclassified into two types, analysis and synthesis. There is a need to build an advanced CAD
system that can support not only analysis but also synthesis. However, traditionally, CAD
technologies have paid little attention to synthesis. Our project team, “Modeling of Synthesis”,
has focused on the synthesis thought process [1] and proposed a thought process model basedon knowledge level operations [2][3]. Following these results, this paper reports theverification phase of the project.
We verify the knowledge operation model with the following two methods. One is to test themodel against experimental data, and the other is to implement a system based on the model
to examine if the system behaves in accordance with the designers’ behavior. In this paper, we
use the former method and evaluate the applicability of the model by comparing it with otherexisting design process theories.
In this paper, first, we explain how to select a design case for verification. Second, we propose
a method to build a reference model of the design case. This reference model is framed in theknowledge operation model and other existing design process theories, viz., the cognitive
design process model of Takeda et al. [4] and German design methodology of Pahl and Beitz[5]. By doing so, we can compare the knowledge operation model with these existing theories.
From this comparison, we can evaluate and verify the knowledge operation model.

2

Selection of a design case for verification

Before verification, we need to set up a method to select a design case. Observing andrecording an actual industrial design case is difficult because of proprietary reasons and dataamount. Protocol analysis of design experiments such as Delft design protocol [6], provides
us with detailed data, but this approach often became a toy case, because of the limitation of
resources and laborious work for analysis.
For the verification of a design process model including synthesis process, design cases are
required to satisfy the following conditions:•

The design cases should be real design cases, but they should not be toy problems nor
created cases for verification.

•

The design cases must have “newness” which is the most important essence of synthesis.

•

Concrete data about the design process should be recorded.

•

The data of the design cases should be of a reasonable size for analysis. They should not
be too huge or complicated.

Considering these conditions, we selected a machine design conducted in a laboratory at the
University of Tokyo over four years. The design was the development of a high precisionstereo lithography machine for micro photoforming fabrication of micro flexible mechanisms[7]. This research contains “newness” that tries to increase manufacturing accuracy, and theamount and size of the data are reasonable. As the sources of information, we used threebachelor theses completed in 1995, 1996, and 1997, a PhD thesis in 1998, summary reports of
the research written occasionally, and weekly reports that usually consist of several lines
about what the student did in a week. We investigated these sources to analyze design
activities.
From this design case, we built a “reference model” of design process for verification of themodel of synthesis.

3

The method to build a reference model

3.1 Building a reference model using design activities
After selecting the design case, we built a reference model. To do so, we introduced theconcept of the frame cognition model that classifies design activities into some categories,
viz., “naming”, “framing”, “moving” and “reflecting” [8]. Figure 1 shows the relationships
among them. The subject that relates to the present design conditions is posed by “naming”.
The “framing” builds up a problem in a frame. The design proceeds to a solution categorized
to “moving”. The solution is evaluated by “reflecting”. Design protocols are analyzed andcategorized into these four activities. Using this classification, the design case was analyzed
into sequentially framed design processes and a reference model was obtained.

namingfra ming
movingreflect ing

Figure 1. Design Activities of the Frame Cognition Model [8].

The frame cognition model had some problems as well, because this model was originallyproposed as a result of the protocol analysis of the conceptual design of a simple component

[6]. Therefore, we had to modify the frame structure to accommodate our design case that wasmore complicated than the original design experiment. We needed to have, first, hierarchicalstructure of design processes and, second, consideration about information flow throughdesign activities. Adding these two modifications, design activities were picked out from thesources of the design case, and arranged sequentially. Figure 2 illustrates a part of thereference model displayed in the frame cognition model.
The device can't follow the minute change of the big atmospheric pressure. (1997.5.13)
There is a problem in making air p ressure a control object.
If the control of the thickness is done with the liquid resin?
Make a li qui d resin in a tank a control object. (1997.5.13)
Make air open system, and make a resin closed system.
Because a resin is incompressible, no influence of a change in atmospheric pressure is taken.
Because the heat expansion rate of a resin is small, influence of a change in temperature can beignored.
Think about the problem of “friction” and “seal” is necessary.
Design the device of the system that controls liquid resin. (1997.6.10)
Contrive the technique to adjust a liquid surface height by a stick for the adjustment that isfixed in the tank.
An adjustment stick is fixed on the tank and the hole which makes a hollow in the tank is made,and the experiment to confirm that it works is done.
The time when it takes it that a liquid surface height becomes stable is short and the vibrationof the liquid surface doesn't happen, either.
The method of liquid surface height control using an adjustment stick has possibility to use forthickness of the resin .

Figure 2. Part of the Reference Model.

Then, we began to verify our proposed design thought process model based on knowledge
operations (for further details, interested readers might refer to [2] and [3]). This model, called
theknowledge
operationmodel,
containssevenknowledge
operations:“knowledge/information acquisition”, “knowledge/information reorganization”, “information
confirmation”, “conflict resolution”, “knowledge/information revision”, “solution synthesis”,
and “object analysis”. For the verification of completeness of the knowledge operation model,
we checked the correspondence of the seven knowledge operations with design activities in
the reference model. Consequently, we could confirm that the seven knowledge operations
cover the reference model. Roughly speaking, three knowledge operations, “solution
synthesis”, object analysis”, and “conflict resolution”, are cycling in this order. “Information
confirmation” is usually observed when the focus of design changes from one component toanother, from the whole design object to components, and from a component design to thewhole. Another three knowledge operations appear randomly.

3.2

Using vocabulary about design

To evaluate the applicability of the knowledge operation model, we compared it that
represents the reference model with other design process models (such as [4] and [5], see
Section 4). This resulted in some problems, however, and the biggest problem was that one
design activity in the reference model sometimes corresponded to more than one stage ofthese design process models. This happened due to the difference in the concept granular sizes
between a design activity and a stage of the design process models. Because of this, we
introduced an intermediate abstract level between them, called design vocabulary andcomposed of standardized terms about design to represent each design activity at moregeneral and detailed level.

For example, we show the following design activities from the reference model.
-“Because of the moving mechanism of the table at the top, the upper contact side of thetank deviates and a hollow warps caused by the movement of the table.”-“Should I fix a table (X-Y table) at the top of the tank?”-“The X-Y table is relocated to the bottom of the tank, and the top of the tank is unified withthe tank.”

This series of design activities can be interpreted with the design vocabulary as follows.
-

The “estimation” of “Because of the moving mechanism …” and “knowledge acquisition”
were performed due to the contradiction in the experiment, and information is collected by
the “investigation” to solve the problem.

-

The “idea” of “Should I fix …” appeared in the process of the “arrangement of theinformation” of the collected information.

-

According to the idea, “knowledge acquisition” and “knowledge reorganization” arecarried out, and then “suggestion” of “The X-Y table is changed…” is made.

Using this interpretation, the three design activities in the example above are represented
more precisely and uniformly by eight terms. In the same way, each design activity can be
explained with the design vocabulary. The vocabulary included 112 standard terms that wereobtained through brainstorming of all members of the project. All design activities in thereference model were interpreted, and consequently, 102 design activities were converted into
223 terms correlated to 23 categories of the design vocabulary. We also analyzed thecorrespondences between the knowledge operation model and the design vocabulary. As aresult, we found out that each term in the design vocabulary is correlated to only one of theknowledge level operations. Table 1 shows the result of the analysis.
Table 1. The results of the analysis by using vocabulary about design.

Stage of the knowledge level
operation (times of appearance)
Knowledge/informationacquisition (61)Knowledge/information
reorganization (33)Information confirmation (10)Conflict resolution (8)Knowledge/information revision(9)
Solution synthesis (44)Object analysis (58)

Vocabulary about design (times of appearance)

investigation (26), knowledge/information acquisition(19), problem indication (16)arrangement of the knowledge/information (13),knowledge/information reorganization (10), making
concrete (7), drafting (3)confirmation (10)conflict resolution (8)strengthening of the constraint (6),knowledge/information revision (3)suggestion (24), idea (8), selection (7), improvement (3),decision (1), association (1)evaluation (27), trial manufacture (14), experiment (9),estimation (4), numerical analysis (3), derivation (1)4Comparison of the knowledge operation model with existing
design theories

In this section, we verify the knowledge operation model by comparing the model with otherexisting design theories. The method for comparison between the knowledge operation modeland the existing design process theories is shown as follows.
1. Analyze the knowledge operation model that frames the reference model with the design
vocabulary, and check the correspondences of the knowledge operations and the terms inthe design vocabulary.
2. In the same way, analyze and check correlation between stages of an existing design
process theory and terms that represent the reference model.
3. Obtain the relationship among the design process models using the terms in the reference
model as a mediator.

4.1 Comparison with the cognitive design process modelFirst, we compared the knowledge operation model with the cognitive design process modelof Takeda et al. [4] using the reference model as a mediator. The cognitive design model has
the following five sub-processes, viz., “awareness of the problem”, “suggestion of candidate
solution”, “development”, “evaluation”, and “decision”. Table 2 illustrates the comparison
result between the two models that shows good correspondences between them. For instance,“Suggestion of candidate solution” corresponds to “solution synthesis”, “Development” to“object analysis”, and “Evaluation” to “object analysis”. “Decision” corresponds to“information confirmation” and “conflict resolution”. In the former, the designer madepositive judgment to a solution whereas the designer found some problems about a solution in
the latter. “Awareness of the problem” corresponds to “knowledge/information acquisition”,“knowledge/information reorganization”, and “knowledge/information revision”, but
often implicitly.
We also found that the cognitive design process model cannot classify some terms of theknowledge operation model. This is because the cognitive model treats nothing about
information from outside, whereas the knowledge operation model has consideration aboutthat.

4.2 Comparison with German design methodology
In German design methodology (e.g., [5]), the designer begins design with analysis anddecomposition of functional requirements, followed by embodiment of function into structure.
Because our design case is conceptual, we focused on two parts of the design process inGerman design methodology, viz., “clarification of the task” and “conceptual design”.
“Clarification of the task” contains two stages, i.e., “clarify the task” and “elaborate thespecification”. “Conceptual design” consists of “identify essential problems”, “establish
function structure”, “search for solution principles”, “combine solution principle and selectsuitable combination”, “firm up into concept variants”, and “evaluate against technical andeconomic data”.
Next, we compared the knowledge operation model with German design methodology. Table
3 exhibits the result of the comparison, “Identify essential problems” corresponds to“knowledge/information acquisition”, and “Establish function structure” to“knowledge/information reorganization”. “Search for solution principles” and “combine
solution principles and select suitable combinations” correspond to “solution synthesis”.
“Firm up into concept variants” corresponds to “object analysis”. “Evaluate against
technical and economic criteria” corresponds to “object analysis”, “information
confirmation”, and “conflict resolution”. In this stage, first, “evaluation” of a design
solution is performed, followed by “confirmation” or “conflict resolution”. “Clarify the task”
corresponds to “knowledge/information acquisition”, and “elaborate the specification” to“knowledge/information revision”. These two mainly follow “conflict resolution”. This
result shows similarity of the two models. However, our proposed model has advantage tointerpret functional design in that our model can not only acquire and refer to functional
information but also treat other types of information, such as physical entities which
traditional functional decomposition method cannot handle.
Table 2. Comparison the knowledge level operation model with the cognitive design process model.

26
19
16
13
2

8

7
3

confirmation10

conflict resolution

8

strengthening of the constraint

6

knowledge/information revision3

suggestionidea
selection
improvement
decisionassociation
evaluation
trial manufacture
experimentestimation
numerical analysis
derivation

cannot beclassified

object analysis

decisionsolution synthesis

evaluation

information
confirmation
conflict
resolution
knowledge /information
revisiondevelopment

knowledge /information
reorganization

investigation
knowledge/information acquisition
problem indication
arrangement of theknowledge/information
knowledge/information
reorganization
making concrete
draftingsuggestionawareness ofthe problem

knowledge /informationacquisition

24
8
7
3
1
1
27
14
9
4
3
1

Table 3. Comparison the knowledge level operation model with German design methodology.

26
1

5

13

16
13

9

1

7
3

confirmation7

conflict resolution

8

strengthening of
the constraint
knowledge /information
revisionsuggestionidea
selection
improvement
decisionassociation
evaluation
trial manufacture
experimentestimation
numerical
analysis
derivation

cannot be classified

evaluate against technical andeconomic criteria

firm up into concept variants

objectanalysiscombine solution principle
and select suitablecombination

solutionsynthesis

search for solution principles

knowledge /information
revisionestablish function structuresinformation
confirmation
conflict
resolution

identify essential problems

knowledge /information
reorganizationelaborate the specification

clarify the taskknowledge /informationacquisition

investigation
knowledge /informationacquisition
problemindication
arrangement of
the knowledge /information
knowledge /information
reorganization
making concrete
drafting

6
3
24
8
7
3
1
1
27
14
9
4
3
1

3

5

Conclusions

We proposed a new method, called a reference model, to verify the knowledge operation
model of synthesis. To do so, we investigated how to select a suitable design case. A reference
model was built from an actual design case and design activities were identified. Furthermore,
we introduced abstract standard terms, called design vocabulary, to build a reference model.
By using the reference model described with the design vocabulary, we confirmed that theknowledge operation model could cover the reference model with good correspondence. Thisjustifies the completeness of the knowledge operation model. We also compared it with otherdesign process theories and found that the knowledge operation model is compatible withthem.
This research was supported by the Modeling of Synthesis Project (JSPS-RFTE 96P00701)
under the Research for the Future Program of the Japan Society for the Promotion of Science.
References[1]

Tomiyama, T., Murakami, T., Washio, T., Kubota, A., Takeda, H., Kiriyama, T., Umeda,
Y., and Yoshioka, M., “The Modeling of Synthesis – From the Viewpoint of Design
Knowledge”, Proc. ICED ’97, Tampere, 1997, pp.97-100.

[2]

Yoshioka, M. and Tomiyama, T., “Toward a Reasoning Framework of Design as
Synthesis”, Proc. 1999 ASME International Design Engineering Technical Conferences
and Computers and Information in Engineering Conference, The American Society of
Mechanical Engineers (ASME), Las Vegas, 1999, DETC99/DTM-8743 (CD-ROM).

[3]

Takeda, H., Yoshioka, M., and Tomiyama, T., “A General Framework for Modeling ofSynthesis Integration of Theories of Synthesis”, Proc. ICED 2001, (submitted)[4]

Takeda, H., Veerkamp, T., Tomiyama, T., and Yoshikawa, H., “Modeling Design
Processes”, AI Magazine, 11, 1990, pp.37-48.

[5]Pahl, G. and Beitz, W., “Engineering Design: Systematic Approach”, Springer-Verlag,
Berlin, 1988.

[6]

Cross, N., Christiaans, H., and Dorst, K. (eds.), “Analysing Design Activities”, John
Wiley & Sons, 1996.

[7]

Xie, T., Murakami, T., and Nakajima, N., “Micro Photoforming Fabrication Using a
Liquid Hollow Shaped by Pressure Difference and Surface Tension”, International
Journal of the Japan Society for Precision Engineering, 33, 1999, pp.253-258.

[8]

Valkenburg, R.C. and Dorst, K., “The Reflective Practice of Design Teams”, Design
Studies, 19, 1998, pp.249-271.

TSUMAYA, Akira
Collaborative Research Center for Advanced Science and Technology, Osaka University,
Yamadaoka 2-1, Suita, Osaka 565-0871, Japan, +81-6-6879-4191, +81-6-6879-4191,
tsumaya@crcast.osaka-u.ac.jp, http://www.crcast.osaka-u.ac.jp/crcast23/index-e.html