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.