CDEDS (Constraint Driven Engineering Design Synthesis) Methodology

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
Introduction

•  Design is defined as creation of new things and
  Synthesis is the creative step itself in
  conceiving new solutions to solve a problem.
  Engineering is a subset of these design
  activities and it focuses more on the technical
  aspects of performance of designed systems.
  Engineering Design Synthesis is therefore key to
  defining effective methodologies and selection of
  appropriate software tools. 

 
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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
Different Stages of CDEDS Design Synthesis

• The methodology has recognized two stages of
  Design Synthesis, Namely

• Concept Phrasing  (non-detail)
• Concept Detailing

 
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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing

• During the creative stage of Concept Phrasing,
  an engineer is interested in answering the how
  of the problem.
• Multiple concepts are to be invented and
  evaluated.
• Conditions of acceptance typically relate to form
  and function and less to fit, physics or
  performance.

 
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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing

• Using a office cabinet door flap example, lets
  look into the functional requirements

Specification Requirement

• Design a door flap for a wall mounted office
  cabinet measuring Height 3 x Width 2 x Depth
  2.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing
Concept 1 Design a swing door flap that can
swing 90 degree for complete cabinet access.
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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing

• The large swing radius of Concept 1 is not
  convenient on cabinet doors that are taller than
  2.5 (or more than average arm length). 
• We need a door flap with smaller swing radius and
  yet provide full access to inside of cabinet.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing
Concepts 2A and Concepts 2B
Below images shows two candidate concepts. 
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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing
Concepts 2A and Concepts 2B
From the image we can conclude that,

• Concept 2A uses a sliding door flap.
• Concept 2B uses a split door flap that folds on
  itself.
• Both provide reduced swing radius but suffer from
  reduced access to the top shelf.
• We need clear passage to all the cabinet shelves
  in addition to reduced swing radius.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing
Concept 3
It Shows a shorter swing radius.
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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing
Concept 3

• The door flap is moved vertically up by a
  parallelogram mechanism. 
• It also provides clear passage to the all the
  shelves.
• Since the door flap is at least 3 tall and opens
  upwards.
• The installation of this mechanism demands a high
  roof clearance not usually available in offices
  with false roofing. 
• So we now need a design that has reduced swing
  radius.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing
Concept 4
Key take-away from Concept Phrasing example
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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing
Concept 4
Key take-away from Concept Phrasing example

• The first three concepts above, differ vastly
  from one another on how they approach the problem
  and so the mechanisms are also different. 
• The fourth one, is a variation of the
  parallelogram concept 3.
• It clearly shows that in the early stages of
  phrasing we need variety and also a bulk of
  ideas.
• Seeing the operational constraints early during
  ideation saves time and cost compared to seeing
  them later in the project life cycle.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
1. Concept Phrasing
Concept 4
Key take-away from Concept Phrasing example

• One can also notice that different working
  mechanisms result from different functional
  constraints being overlaid on the basic
  specification.
• These constraints, more so during Phrasing, can
  be translated to fundamental physical parameters
  like dimensional height, weight, area etc.
• The concepts can be sketched by hand or drawn
  using software but the key requirements are
  variety and bulk.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
2. Concept Detailing

• In Concept Detailing, one (or more) concepts
  from phrasing stage are typically subjected
  to Engineering rigor. 
• They are integral to making concepts practical
  beyond just dimensional requirements. 
• Depending on where you would want to stop, this
  step can actually end in well-conceived design
  solutions.

•  This are practical, meet engineering rigor and
  meet marketing specifications.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
2. Concept Detailing
Take Excavator example

• This example shows the selection of appropriate
  tools to address this stage of Engineering Design
  Synthesis.

Design Specification

• Design an excavator work group for a 23 ton
  tracked excavator that includes a boom, a dipper
  arm and a 1.2 cu.m bucket that delivers the range
  dimensions given.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
2. Concept Detailing
Take Excavator example
Design Specification

• The boom pivot point on the turntable should be
  at least 1200 mm from ground and at least 100 mm
  from slew centre to provide clearance for other
  machinery

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
2. Concept Detailing
Take Excavator example

• The Engineering Manager can be in three different
  situations relating to this requirement and he
  would react differently for each situation

• Situation 1 The specification is an extension of
  an existing design within the factory then the
  kinematic lengths of boom, dipper and bucket are
  almost known and the problem reduces to iterating
  the four-bar mechanism at the bucket end and
  arriving at the cylinder sizes.
• Situation 2 The specification is of a competing
  machine not within the factory  then the manager
  would conduct a competitive bench-mark exercise
  and arrive at starting lengths from the study.
• Situation 3 Specification is not a known
  configuration anywhere in the market If you
  address this last situation, then other
  situations are automatically addressed.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
2. Concept Detailing

• Concept Phrasing, have to be translated to
  boundary conditions or design constraints.
• Once the constraints are identified, solution to
  the problem can be found by applying the
  following methodology, described broadly below

• Each specification parameter, say maximum reach,
  is a configuration arising from two things.
• The kinematic lengths (of boom, dipper arm and
  bucket) and a particular orientation of the parts

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
2. Concept Detailing

• Since different configurations arise from just
  changes to orientation of the parts, we recognize
  that lengths between pivot points should remain
  same between the different configurations.
• We can model other specification parameters, max
  depth, cutting height etc., using the same
  variables for length between pivots.
• Other design criteria, can now be brought in as
  either more variables or more mathematical
  functions.
• Once we have equations for forces, section
  stresses can be described and consequently weight
  of parts can be estimated.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
2. Concept Detailing

• This methodology now suggest that the design
  synthesis problem can be solved numerically by
  applying multi-criteria optimization methods.
• The specification targets now described as
  Objective functions. 
• Simpler problems like those of door flap or
  Situations 1, 2 described above, can be solved
  using simpler numerical optimization methods.
• The seed/start/guess values for variables of
  lengths between pivots can always be generated
  from regression analysis of dimensions over
  weight of machine for different sizes. This is
  known to work.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
CDEDS Methodology Summary

• Attempt to get a variety and bulk of ideas in the
  Concept Phrasing stage.
• More concepts can be generated by adding/removing
  functional requirements arising from context of
  application.
• A tool that enables simplified modelling, should
  be used to distil the concepts to a handful of
  candidate solutions. 
• The software tool should have some simulation capa
  bility and should be able to handle dimensions. 

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
CDEDS Methodology Summary

• Once a concept is chosen, to bring engineering
  rigor, express all functional requirements
  as constraint variables.
• Dimension, weight, force or some physical
  parameter that enables further use of software
  tools.
• Ensure that the selected software can handle all
  forms of constraint expression. 
• A dead 2D drawing tool, 3D sketcher, spreadsheet,
  popular math and simulation tools 

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
CDEDS Methodology Summary

• Build a math model describing various operating
  conditions as configurations.
• The configurations are nothing but Objective
  functions for optimization.
• Key step Solve the math model numerically as
  multi-objective optimization problem.
• This guarantees that that ensuing solution is a
  consequence of the Simultaneous Action of all
  the Design constraints.
• Fine-tune the solution by defining bounding
  values for constraint variables.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology
Conclusion

• Whether such an interlinked mathematical
  description of geometry and constraints is
  possible would depend on the quality of the
  software tool(s) used for the purpose of Design
  Synthesis. And whether such a construct would
  result in a viable engineering solution would
  depend on the skill of the engineer. The ultimate
  measure however is the quality of the engineering
  solution delivered.

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CDEDS (Constraint Driven Engineering Design
Synthesis) Methodology