Quality Function Deployment Method (QFD)
Quality Function Deployment Method (QFD)
Concept Generation / Concept Selection
The quality function deployment method is defined as the strategic arrangement throughout all aspects of a product of appropriate characteristics according to customer demands. The QFD is essentially concerned with the translation of customer requirements into engineering characteristics. The QFD method involves identification of the customer requirements in terms of product attributes and then determining the level of importance of each one. Drawing a matrix of product attributes against engineering characteristics and rating the relationship between them will complete this area of the process. Engineering characteristics may have relationships between each other, this is called the house of quality. The table below illustrates the QFD for the yeast cultivator.
Quality Function Deployment
It is important to break up the design problem into several functions in order to gain a better understanding of the problem. Function analysis was used to decompose the cultivator problem into three main functions: environment, sampling, and structure. These were then broken down further into many individual sub-functions. A function tree was then used to display these functions and sub-functions because it was a clear way to identify the relationship/interdependency between each sub-function. This function tree is displayed in Figure 1.
Function Tree
Developing a design
requires that the design problem be increased into several different concepts
before the final design is narrowed to one solution. A method for
accomplishing this task is by forming a morphological chart. A morphological
chart is a list of means to achieve the function desired. As many methods as
possible for each function should be entered. Once finished, the
morphological chart contains the complete range of all theoretically
possible different concept forms for the product. This complete range of
concepts consists of the combinations made up by selecting one function at
a time. The morphological chart for the yeast cultivator is illustrated in
Appendix A. From the morphological chart different conceptual designs were
generated.
Morphological Chart
Concept Generation / Concept Selection
Concept Generation
Generating conceptual
designs is achieved by selecting a mean for each function and combining them
to form concepts. These combinations are existing solutions; some new
solutions, and some impossible solutions. During the process it is necessary
to identify potential solutions for further consideration. Using this method
three concepts for the cultivator were developed. A schematic drawing of
each concept was then created to visualize each
individual concept. These drawings are below.
Concept #1 Box Shaped Cultivator
Through further
analysis of the concept, several negative aspects were found to be inappropriate
for the design. Positive aspects from other concepts were incorporated in this
concept to produce the best possible design. Another reason for modification to
this concept was due to revisions made in the need statement and in the
specifications. There were several drawbacks in the selected design in which
altercations were needed. The Photon Multiplier (PM Tube) found in the bottom
of the system was discovered to be very sensitive to magnetic fields and was
subsequently removed from the bore of the magnet. By removing the PM Tube the
shutter was eliminated. This required that fiber optic cable be used to relay
the luminescence signal from the yeast to PM Tube. In order to magnify the
luminescence, a lens was attached to both ends of the fiber optics. Another
feature that was modified was in the sampling tube. A constraint on the amount
yeast being tested and the vertical magnetic field variation led to the redesign
of the tube. The new tube design consists of two concentric tubes in which one
is allowed to slide within the other. A small suction on the inner tube
allows a regulated sample to be taken; then the inner tube can be extracted
from the device in order to externally test the sample for contamination.
Insulation was added due to a large temperature gradient between the medium
and surface of the magnet bore. The insulation was installed on the outside
and inside surfaces of the water jacket as well as on the top and bottom of
the concept. Due to the added insulation the controlled water bath to the
medium was eliminated. A detailed drawing of this concept is below.
Final Concept
Last Revised: 2000-12-20