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Concurrent Engineering
Eng. K.C Wickramasinghe
BSc(Hon’s), AMIESL
Dept. of Mechanical & Manufacturing
Engineering,
Faculty of Engineering,
University of Ruhuna.
Lecture Session 02
01
Rule Based Methods :- Axiomatic Design
Axiomatic design is a general methodology that helps designers
to structure and understand design problems, thereby facilitating
the synthesis and analysis of suitable design requirements,
solutions, and processes.
Axiomatic design was developed by Nam Suh.(1990)
Axiomatic Design
02
Steps in design process
03
Establish design objectives to satisfy a given set of customer
attributes
Generate ideas to create solutions
Analyze the solution alternatives that best satisfies the design
objectives
Implement the selected design
Decisions are made at each of these steps To facilitate
Axiomatic Design Theory
Key Concepts
04
Exists four domains in the design world
The whole design process involves the continuous processing of
information between and within four distinct domains.
05
Key Concepts
{CN}
Solution alternatives are created by mapping the requirements specified in one domain
to a set of characteristic parameters in an adjacent domain.
The mapping process can be mathematically expressed in terms of the
characteristic vectors that define the design goals and design solution.
Key Concepts
06
The output of each domain expressed in a top-down or
hierarchical manner
Hierarchical decomposition in one domain cannot be performed
independently of the other domains, i.e., decomposition follows
zigzagging mapping between adjacent domains.
Key Concepts
07
An example : for a parachute
FR1: The parachute will slow down a descent to prevent injury
FR2: When not in use it will be easily carried by a user
FR3: Reliability will be greater than 1 failure in 20000 users
FR4: The user will be able to redirect the descent vector
DP1: Material chosen for chute- weight and strength
DP2: Length of cords between rider and chute
DP3: Number of cords between rider and chute
DP4: Area of chute
DP5: Vents in chute
DP6: Packing and release methodology
08
Key Concepts
Two design axioms provide a rational basis for evaluation of
proposed solution alternatives and the subsequence selection of the
best alternative.
It focus on the nature of the mapping between “what is required”
(FRs) and “how to achieve it” (DPs).
A good design maintains the independence of the functional
requirements.
In the physical domain - Mapping between FRs and DPs (Needed
minimum set of independent Functional Requirements - two or more
dependent FRs should be replaced by one equivalent FR)
09
Axiom 1 (independence axiom): maintain the independence of the FRs.
Key Concepts
10
Establishes information content as a relative measure for evaluating and
comparing alternative solutions that satisfy the independence axiom.
The mapping between functional, physical domains and process domains
To satisfy the Independence Axiom, matrix [A] and [B] must be either
diagonal or triangular
Diagonal :- each of the FR can be satisfied independently by means of one
DP : Uncoupled design
Triangular :- independence of FRs can guarantee if the DPs are changed in a
proper sequence : Decoupled design
Axiom 2 (information axiom): minimize the information content of the design.
PVBDP
DPAFR
Key Concepts
11
A design’s information content is calculated according to the following
logarithmic expression.
PI
1log2
Key Concepts
12
If there are n functional requirements
The second axiom says that when two or more alternative
designs satisfy the first axiom, the best design is the one with
the least information.
RangeCommon
RangeSystemI 2log
n
i
itotal II1
13
Example
Designs which do not satisfy the Independence Axiom are called
coupled. An everyday example is a typical water faucet. The two FRs
are "control the temperature" and "control the flow rate." The two DPs
are the hot- and cold-water handles. This design is coupled because it
is impossible to adjust either DP without affecting the other FR: Each
handle affects both temperature and flow rate.
Example
14
In the above example, the two FRs- "control the temperature" and
"control the flow rate" are independent. One DP does not effect the
other so this design is uncoupled.