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The QFD, TRIZ and Taguchi Connection: Customer-Driven Robust Innovation

| On 03, Jan 1998

John Terninko, Ph.D.
Responsible Management Inc. & Ideation International Inc.
The Ninth Symposium on Quality Function Deployment, June 10, 1997

Abstract

Taguchi’s approach to robust designs has been in North America since 1981. QFD arrived
in 1984, and TRIZ, the newcomer, arrived publicly in 1991. Each contributes to one aspect
of the design process. Together they become an unbeatable powerhouse of Customer Driven
Robust Innovations. QFD gathers and translates customer requirements (the voice of the
customer) into design requirements (the voice of the innovator/engineer). The
prioritization of desired improvements and the corporation’s performance measures in QFD
become, in TRIZ, the so-called “initial useful functions.” The output of the QFD
is used to rank the many innovative concepts generated by the TRIZ methodology. The TRIZ
methodology provides only the concepts of a design — not the design details.
Taguchi’s methodology determines the design specifications for a product to be insensitive
to uncontrolled influences. This paper discusses these and other linkages between these
powerful quality tools. The synergy formed becomes the ideal design process.

Key Words

A1 Matrix, Contradictions, Creativity, House of Quality, Ideality,
Innovation, Loss Function, QFD, Quality Function Deployment, Robust Design, Systematic
Innovation, Taguchi, Taguchi Methods, Theory of Inventive Problem Solving, TIPS, TRIZ,
Useful Function, Voice of Customer Table.

The Essence of QFD

The fundamental principle of QFD is to gather all relevant information
about the customer and use this information to drive the design of a product or service.
Several tools have been integrated into the QFD process to facilitate the deployment of
this information throughout the design and manufacturing processes, and to all relevant
organizational functions. The primary function of QFD is to identify important issues and
link priorities and target values back to the customer.

QFD started as a means to improve market share by reducing the gap
between the customer’s desires and the product’s performance.

Identification of the Customer Segments and using the Analytic
Hierarchy Process (AHP) to prioritize the customer is an effective first step. Gathering
the voice of the customer and the context of use is an important second step. Again AHP
can be used to prioritize the verbatim information. The context of use defines the
constraints in which the product must function or the service be performed. These
constraints often create design bottlenecks for which QFD provides no means for
resolution. For this reason the Theory of Inventive Problem Solving (TRIZ) is a welcome
improvement to past innovation tools.

The Essence of TRIZ

When Genrich Altshuller completed his research of the world patent base
he had identified four key learnings: 1. there are five levels of invention; 2. inventive
problems contain at least one contradiction; 3. there are standard patterns of evolution;
and 4. the same principles are used in many inventive designs and can therefore be
considered solution patterns.

Exhaustive study of the world’s patents reveals that the same
principles have been used in innovative solutions to problems in different industries,
sometimes with many years elapsing between applications. Access to this information is one
of the contributions of TRIZ. For example, the principle of separation by means of
increasing the pressure on some material and then suddenly returning it to one atmosphere
is the method by which artificial diamonds are cracked, sunflower seeds and cedar nuts are
shelled, the tops and insides are removed from peppers, powdered sugar is made, filters
are cleaned, and rust is removed from metal parts. All these applications use a sudden
pressure drop and all require engineering effort in order to determine the best system and
operating conditions. Splitting diamonds requires 2000 atmospheres where processing
peppers requires only five. Shelling cedar nuts uses high-pressure water where shelling
sunflower seeds uses air.

A visit to a museum of technology reveals that the same patterns of
evolution exist in very diverse products. One such pattern is the migration from exerting
no control over operating conditions to human control to automatic control. Another
pattern is the transition from a single-function product to one which has multiple
functions which may be either homogeneous or heterogeneous. The evolution of the
duplicating machine illustrates this pattern. Starting with simply coping one page, today
addition functions include digital storage of the master, printing on two sides,
collating, mixing feed stock and binding. TRIZ offers eight patterns of evolution
containing 280 lines of evolution from which tomorrow’s products can be designed today.

Using the TRIZ methodology, it is possible to generate concepts for
reducing negative effects and improving the performance of existing designs. TRIZ includes
four analytical tools used to structure the innovative problem and six knowledge-base
tools used to point in the direction of solution concepts.

Analytical Tools

Innovation Situation Questionnaire (ISQ)…………
Gathers all the relevant data for analysis.

Problem Formulator – Takes a single problem statement and, through
the use of linked cause-and-effect statements, generates an exhaustive list of more
explicit problems.

Algorithm for Inventive Problem Solving (ARIZ)
An alternative way to structure problem definitions for more difficult problems.

Substance-Field Analysis (Su-Field) – Models a problem into three
components for breakthrough thinking with regard to system structure and energy sources.

Knowledge-Base Tools

Patterns/Lines of Evolution – Descriptions of the sequence of
designs possible for a current design. One line, for example, describes the evolution of a
system from a macro level to a micro level. Illustrating this is the system used to
support and transfer glass during the manufacturing process. Over time, smaller and
smaller rollers were used until eventually the use of molten tin (i.e., rollers at the
molecular level) was incorporated.

Inventive Principles & Contradiction Table
Design contradictions between two performance parameters (drawn from a total of 39) may be
resolved by using one or more from among 40 innovation principles. Successfully-used
principles for 1201 contradictions are presented in a matrix. As an example, if the design
effort to reduce the weight of a moving object is detrimental to force, the matrix
suggests using principles
8 Counterweight (i.e., a lifting force),
10 Prior Action (arrange items beforehand),
18 Mechanical Vibration (use resonant frequency), and 37 Thermal Expansion (change
dimensions using heat).

Separation Principles – The simultaneous occurrence of two
mutually exclusive conditions can be resolved using the separation principles. For
example, in a coating process which entails dipping parts in a bath of coating solution,
the throughput can be increased by increasing the solution temperature. Doing so, however,
reduces the usable lifetime of the solution bath. The principle of separation in space
suggests that the bath solution be cold but that the part be hot.

76 Standard Solutions – Generic system modifications for the model
developed using Su-Field Analysis. For example, if a system which employs a so-called
mechanical field is not effective enough, changing to the use of an electrical field — a
major paradigm shift — is suggested.

Effects – Physical, Chemical, Geometric, and other effects offer
“free” resources commonly forgotten and sometimes even incompatible with the
system as designed. The Seebeck Effect describes the phenomenon whereby an electrical flow
is created in the presence of two different materials at two different temperatures. This
effect can be used to generate electricity in remote locations such as on a space
satellite.

System of Operators – Universal operators are recommendations
which are potentially applicable to any situation, such as Excessive Action (e.g.,
painting can be accomplished by dipping the component and spinning off the excess paint).
General operators are recommendations applicable toward improving functionality and
eliminating undesired effects, such as Elimination of a Harmful Action (e.g.,
through isolation). Specialized operators are used to improve specific parameters or
features of a product/process, i.e., Improve Useful Actions (examples include those
for increasing reliability).

All off the TRIZ knowledge-base tools yield concepts which require
system design and engineering to satisfy the needs of the current innovative problem.
Taguchi’s approach to robust designs facilitates the engineering of the system.

The Essence of Taguchi

Classical Quality Control uses upper and lower specifications as
boundaries between acceptable and unacceptable performance. Performance between the
specifications is considered equally acceptable. Taguchi states that the customer’s
increased dissatisfaction with any deviation from the target value can be approximated by
a quadratic function. The limits are not the engineer’s specification but the customer’s
tolerance limits. The lower customer tolerance limit is shown as LCT in figure 1.

figure 1

Variation is now critical, as seen by the average loss (average
customer dissatisfaction) calculation. The average loss is the product of a constant times
the product of the variance and the square of the deviation from the target (T).

The basic building block of Genichi Taguchi’s philosophy is the idea of
reducing the effect of uncontrolled factors while assuring the performance is on target.
Which performance (A or B) is best is now dependent upon both the average and the
variation. Uncontrolled factors are the internal variations of the components or the
external variation of the environment. The concept of the loss function use the electrical
engineering signal-to-noise ratio used to, maximize the ratio of useful energy to wasted
energy.

Parameter investigations in the laboratory must be conducted in
controlled chaos. An example of this is to vary temperature, humidity and component
precision — parameters which are normally controlled — during data collection to
simulate the variance which would naturally occur. Design values are thus obtained which
result in close-to-target performances and which have little variation when artificially
generated variation is introduced. A system which incorporates these values will not be
sensitive to naturally-occurring sources of variation.

If a designed experiment is conducted using eight different
combinations of design variables the artificial sources of variations would be the result
of several combinations of noise factors. The noise factors could include different levels
of humidity, two different ages of materials and a variation in components.

Dynamic applications of Taguchi’s thinking are useful for future models
of a product. The Ideal Function of a design represents the theoretically-perfect
relationship between performance and a signal input to a device. In the case of a spring,
the ideal design would provide a linear relationship between applied force and the length
of the spring, and ignore the effects of fatigue, temperature, etc. (as we so often did in
school). Dynamic applications look for design parameters which increase the linearity of
the relationship by making the response independent of the sources of variation. These
applications are particularly important for measurement devices and control of
manufacturing processes.

Taguchi methodology assumes that both the ideal function and the system
design are known.

The QFD, TRIZ and Taguchi Synergy

QFD, TRIZ and Taguchi’s methods fit together like a three piece jigsaw
puzzle (figure 2) to form a complete picture of the design process. Missing from QFD is
bottleneck engineering and optimization. Bottleneck engineering can be overcome with the
solution concepts generated via TRIZ. TRIZ is weak, however, in the areas of
customer-driven requirements and optimization. QFD provides the customer input and Taguchi
provides the process for determining the best parameter values for a

figure 2

robust design. Taguchi’s methods lack the customer-driven priorities
and the tools required for system definition. These are provided by QFD and TRIZ,
respectively.

The linkage is rather elaborate and can recycle through the sequence of
QFD, TRIZ, Taguchi several times. Using the five-step model presented in
“Step-by-Step QFD: Customer-Driven Product Design,” the process starts with
customer analysis. The voice of the customer is prioritized and sorted into Functions,
Demanded Quality, Performance Measures, Failure Modes, Concepts, and Manufacturing.

The gathering of data for the customer context table should be
attentive to the needs of both TRIZ and Taguchi. TRIZ cultivates a thorough understanding
of the constraints, resources, historical solutions, and harmful and useful functions of a
system. The visit to the gemba is the best source for this information. Taguchi’s
method requires an understanding of the sources of variation and freedom to change design
parameters. Gathering this information at the gemba is the ideal source.

If QFD is applied to an existing design, and the organization chooses
to first use the House of Quality, then the TRIZ methodology reduces the constraints
identified in the roof of the house. Often an existing design contains conflicts between
performance measures used to evaluate the design. These same performance measures are used
during technical benchmarking. Taguchi suggests that sources of variation should be
included to obtain realistic data. The TRIZ methodology can be used to protect a company’s
design by providing for a patent fence around a competitor’s design.

How QFD is helped by TRIZ and Taguchi

The five-step model of QFD will be used with additional comments for
comprehensive QFD. A count for the number of impacts TRIZ and Taguchi have on the QFD are
recorded after each example.

Step 1

The first step is the identification of customer segments, selecting
criteria for ranking the segments, and ranking the segments. Recognizing the power of TRIZ
to improve designs never considered becomes possible, and the new demands are possible to
satisfy.

TRIZ (1) allows a more aggressive attitude because of the possibilities
offered by the technical lines of evolution.

Step 2

The second step is to understand the customer’s needs and
environment by going to the gemba. The customer’s needs are sorted into demanded
qualities, functions, reliability issues, solutions, safety and failure modes. Because
“ideality” utilizes resources, the voice of the customer context table should
add the system and environment resources to the “who,” “what,”
“where,” “when” and “how” information.

The experienced practitioner of TRIZ (2) would look for the resources
available to provide for a more ideal design, as well as consider historic constraints,
and useful and harmful functions.

With Taguchi (1), identifying the sources of variation and the ideal function offer
another perspective.

Step 3

The third step maps the subjective demanded quality information of the
customer into the objective measures of performance used by the engineer. The matrix used
is often called the House of Quality. If a product is a model upgrade, it is important to
identify conflicts between different performance measures. These conflicts influence the
compromises in target values set after doing a technical benchmarking.

There are several aspects of TRIZ which can help these activities. The
most profound is to ignore the conflict because, with TRIZ, the degree of conflict is
often reduced.

With TRIZ (3), the conflict is not used to establish compromises in
performance, but to start the TRIZ analysis for physical and technical contradictions.

Taguchi (2) can take advantage of the positive interactions.

Part of the thought process for selecting target values is the relative
performance of the existing design against the competition, and the anticipated direction
of the competition. The lines of evolution used to create new designs by TRIZ can be used
to forecast the competition’s future designs.

TRIZ (4) can be used to resolve conflicts — both technical
contradictions and physical contradictions — and thus the setting of target values
need not be compromised.

This allows for the application of patent fences to stop the
competition and/or protect the existing and future designs.

Taguchi (3) offers the loss function as a more effective measure for
technical benchmarking.

Many organizations stop after completing the House of Quality and
continue with their existing design process.

TRIZ (5) improves manufacturing equipment by looking at problems and
conflicts.

TRIZ (6) improves the manufacturing process by looking at process
evolution.

TRIZ (7) reduces cost via ideality, which looks at system and
environmental resources.

Step 4

The fourth step is concept generation. This is one of the most powerful
aspects of TRIZ. The inputs for this analysis are the target values for the performance
measures, priorities and conflicts. The reliability, manufacturability, cost, and
environmental impact can be added to these.

TRIZ (8) would generate many alternatives as defined by the performance
measures.

In TRIZ (9), different lines of evolution identify possibilities for
designing tomorrow’s product today, and thus bypass the competition’s existing patents,
and excite the customer in the
Kano sense.

Taguchi (4) will determine the best design values for a robust design
for each considered concept.

Step 5

Step five looks at an organization’s knowledge base of their
manufacturing process. They have concerns with the process, the equipment and the
capability of their current technology. Each of these can be significantly improved by
TRIZ and Taguchi.

TRIZ (10) provides for a search for technologies which can improve the
products made from one manufacturing process, thereby increasing the breadth of the
product base.

TRIZ (11) addresses the work flow of the manufacturing process in terms
of useful and harmful functions, then applies ARIZ to improve the process.

With TRIZ (12), the design of the equipment used to make a product can
be enhanced by looking at the evolution of the equipment. This often results in a quantum
jump in equipment design, thereby improving product quality and profitability.

Using Taguchi’s (5) robust operating conditions for the important
operating conditions is only a beginning.

Taguchi (6) provides for finding the appropriate signal to select the
exact desired output for the production process.

With Taguchi (7), developing a database upon designed experiments for
important operating conditions is preferable to depending on a soon-to-retire employee.

A total of twelve TRIZ hooks and seven Taguchi hooks are identified for
five-step QFD.

Comprehensive QFD has more depth in the analysis. The flowchart looks
very much like Bob King’s matrix of matrices, but is a true flowchart. King’s
matrices are just a listing of possible analyses. The TRIZ and Taguchi hooks in the
five-step QFD are also present in the comprehensive QFD. The additional hooks in the
comprehensive QFD were mentioned previously as activities to be continued in an
organization’s design process.

Comprehensive QFD expands the beginning and the end of the process by
using the Seven Process Tools in the beginning and including delivery and service at the
end. The middle analysis is increased by a factor of four.

The Ideation Methodology has taken all the pieces of so-called
“classical” TRIZ and integrated them into a unified whole. The analytical and
knowledge-base tools have been expanded and modified to eliminate the weaknesses of
classical TRIZ. Ideation has developed additional tools for comprehensive and directed
product evolution, for eliminating future failures, and for formulating problems
associated with products, processes, services and interpersonal issues.

Comprehensive QFD includes all the other information identified and
sorted from the customer. Functional analysis links the demanded quality of the customer
to system functions and rearranges the priorities accordingly.

Using TRIZ (13) and Ideation’s Problem Formulator, normal function
analysis is extended by identifying harmful effects and defining related problem
statements.

Designing a world-class, customer-driven product is possible by using:

TRIZ (14) — as incorporated in Ideation’s directed product
evolution — in the concept generation stage.

Rather than belabor the point that there are many instances in which
TRIZ can complement QFD, it can simply be noted that anyone who has been involved in a QFD
project recognizes that there are many times that the project team is searching for
direction. TRIZ with the formulation process and the structured way of searching through
the 400 system operators with 1,600 links forming associative chains guide the design team
toward increasing a system’s ideality.

Dr. John Terninko

John has taught QFD and Taguchi philosophy to corporations in North
America, Central America and Europe for 12 years. He is a recipient of the 1985 Taguchi
Award for promotion and application. He has integrated his diverse experience base
(electrical engineering, operations research, organizational development, teaching, and
management consultation) to develop an approach to the problem-solving required for QFD
and utilizing the synergy with Taguchi’s philosophy. In 1995 he began integrating TRIZ
into QFD.

John has applied QFD to health care, the automotive industry, consumer
products, service industries, and durable products. He adapts the QFD process to suit the
unique needs of each project.

John has provided TRIZ training and consultation in North America and
Europe for both manufacturing and design audiences.

John is a principal with Responsible Management Inc., cofounder and
director of the QFD Institute, cofounder and director of the QFD Network, and director of
education, training and publications for Ideation International Inc. John is also a TRIZ
specialist.