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Engineering Design Notes III Conceptual Design
EE 498/499 Capstone Design ClassesKlipsch School of Electrical & Computer Engineering
Spring 2007 Design Notes III - Conceptual Design 2
Topics
Overview Definitions Conceptual Design Steps Activity Analysis Concept Generation Analysis and Feasibility Evaluation Methods Documentation
Spring 2007 Design Notes III - Conceptual Design 3
Overview
The Conceptual Design is the first part of the design process after the specifications have been determined.
This is to act as the intellectual exercise to generate ways accomplishing the actual design.
This step is successful if we have at least one feasible alternative to work with when we are done.
Specification
Establish functional requirementsDetermine design constraintsDetermine acceptance criteria
Generate Alternatives
Create alternative solutions to realize Specifications
Analyze Alternatives
How well do the alternative designs meet the Specifications
Evaluate Alternatives
Perform numeric comparison of the alternatives and the quality of their meeting Specifications
Fabrication specification for the best alternative
Redesign iteration
Feasible Alternatives
Design Process Version I
Spring 2007 Design Notes III - Conceptual Design 4
Definitions
What is the Conceptual Design process? It is the generation of design alternatives or Design Concepts and the supporting analysis to determine the feasibility of each alternative.
What is a Design Concept? It is a design alternative that includes at least one physical principle and one abstract embodiment.
Spring 2007 Design Notes III - Conceptual Design 5
Definitions
What is a physical principle? This is a natural law or effect that produces a useable method of modifying a signal or device to produce a functional output. For example, the photoelectric effect is a physical principle that produces a current in proportion to the intensity of the incident light.
An abstract embodiment is a diagram that shows the relative relationship between the actors in the design. It need not be to scale.
Spring 2007 Design Notes III - Conceptual Design 6
Definitions
Examples
BatteryChemical Storage
Energy Storage
Radio/modemLaser/detectorWiring harness
RFOpticalWire
Data Communications
Solar Cells
ReactorFurnace
Photoelectric EffectNuclear PowerCombustion
Energy Generation
Embodiment Method
Physical Principle
Design Element
Spring 2007 Design Notes III - Conceptual Design 7
Definitions
The Conceptual Design Diagram is A diagram with the Design Concept, Including the physical principles being used, and The abstract embodiment.
This is basically a block diagram or extended sketch with the necessary aspect labeled.
Note: systems usually need to have individual Conceptual Design Diagrams for the component subsystems rather than all-in-one diagrams.
Spring 2007 Design Notes III - Conceptual Design 8
Definitions
Example: Develop a Conceptual Design Diagram for a communications system composed of a modem, RF transmission unit, and antenna.
Note, actual components not specified at this level. Potential Physical Principles that can be considered:
RF, Optical, or Wire harness communications. Here, we consider the Conceptual Design Diagram
for the RF option. The RF embodiment is based on a RF unit and a modem. The following diagram shows the Concept.
Spring 2007 Design Notes III - Conceptual Design 9
Definitions
Communications Conceptual Design Diagram
Spring 2007 Design Notes III - Conceptual Design 10
Conceptual Design Steps
The proper Conceptual Design Process has the following stages: Activity Analysis: how will the design be used in
various stages such as normal use, battery recharging, disposal, start-up and shutdown, etc., as appropriate for the needs.
Generate Alternative Concepts: the design team uses various strategies to generate Concepts that should meet the design requirements.
Spring 2007 Design Notes III - Conceptual Design 11
Conceptual Design Steps
Conceptual Design Process (cont.) Analyze: use engineering analysis, simulation,
bench testing, etc. to verify that the design concept does work to meet the specifications.
Feasibility Test: does the design analysis indicate that the design concept will meet the specifications and actually can per executed.
Evaluate: determine which one or set of the feasible design concepts left are best (at least at the level we can tell at this time).
Spring 2007 Design Notes III - Conceptual Design 12
Activity Analysis
The Activity Analysis stage really is an exercise to determine how the design meeting the specifications is to be used in real life. This includes user activities and understanding the inputs and outputs (signals, power, etc.).
To do this activity, you will need to perform a functional decomposition and an I/O analysis.
Spring 2007 Design Notes III - Conceptual Design 13
Activity Analysis
The functional decomposition takes the design functional requirements and refines them respective subfunctions and sub-subfunctions.
The functions are not broken down by expected embodiments but by similar functions.
Spring 2007 Design Notes III - Conceptual Design 14
Activity Analysis
The I/O analysis looks at the control, data, and power signals coming into and out of a function.
This will become a basis for the designs Interface Control Document that specifies and documents all interface details.
Spring 2007 Design Notes III - Conceptual Design 15
Activity Analysis
Comms Example Functional Decomposition Antenna
Transmit Frequency Receive Frequency
RF unit Transmit Electronics Receive Electronics Computer Control
Set Frequencies Set Power
Modem unit Waveform Processing Computer Control
Set Baud rate Set comms parameters
Buffer data
Comms Example I/O Analysis Antenna
RF signal in RF signal out
RF Unit Computer interface RF signal in RF signal out Signal from modem in Signal to modem out Power
Modem unit Signal from RF in Signal to RF out Computer interface Power
Spring 2007 Design Notes III - Conceptual Design 16
Activity Analysis
Activity Analysis results: An assessment of which functions can be
combined A check-off to ensure that all required functions
are addressed An understanding of the required interfaces A possibility that the design requirements may
need to be reviewed and iterated upon to update them.
Spring 2007 Design Notes III - Conceptual Design 17
Concept Generation
The design team uses various strategies to generate Concepts that should meet the design requirements.
This is also sometimes called synthesis. Use brainstorming, past experience, similar
designs, Google searches, WAGs, sleeping on it, etc.
This process may take some time!
Spring 2007 Design Notes III - Conceptual Design 18
Analysis and Feasibility
Analyze: use engineering analysis, simulation, bench testing, etc. to verify that the design concept does work to meet the specifications.
Feasibility Test: does the design analysis indicate that the design concept will meet the specifications and actually can per executed.
From the analysis and testing, we should also eliminate those designs that cant be built, would cost too much, etc.
Spring 2007 Design Notes III - Conceptual Design 19
Evaluation Methods
Once the design concepts are generated and evaluated for feasibility, the surviving design concepts need to be evaluated to determine which one is best.
How does one define best? One common method is to use the criteria for the
design and weight the relative importance to determine best.
Note: the designers must be careful not to rig the weighting to make a favorite come out best.
Spring 2007 Design Notes III - Conceptual Design 20
Evaluation Methods
Weighted Evaluation Method: Select the evaluation criteria and place in column 1 of a
matrix. Importance weights are assigned to each criterion and
placed in column 2 of the matrix. The concepts to be evaluated are placed in subsequent
columns of the matrix. Each concept is rates against the criteria and a score of 0
to 4 is given. A 0 implies unsatisfactory performance while a 4 is implies very good performance.
Each score is multiplied by the weighting factor and the scores are summed. Highest weighted score wins.
Spring 2007 Design Notes III - Conceptual Design 21
Evaluation Methods
Example evaluation matrix. Notice, functional requirements are not included because it is
assumed that all design concepts meet the testable requirements. This is for the intangibles or more subjective criteria. Testable requirements with varying degrees of performance can also be included.
2.802.953.50100
0.3030.4040.20210Buffer Capacity
0.4530.6040.30215Cost
0.4020.6030.80420Mass
0.7530.7531.00425Physical Size
0.9030.6021.20430Operating current
Weighted RatingRating
Weighted RatingRating
Weighted RatingRating
Importance Weight (%)Criteria
Internal ModemDSP ModemExternal COTS Modem
Concept Alternatives
Spring 2007 Design Notes III - Conceptual Design 22
Documentation
At the end of the Conceptual Design stage, the following documents should be part of the design documentation, at a minimum: Operations Concept document Conceptual Design Diagram Function Decomposition I/O Analysis Design Analysis showing that Conceptual Design
meets requirements Design Evaluation matrix
Spring 2007 Design Notes III - Conceptual Design 23
Documentation
Additional documents that can be started at this stage include: Budgets: mass, size, link analysis, power, etc. Start considering how the various components will
be integrated and tested. Integration and test plans can be started.
Note, in some cases, these will be no more than outlines with placeholder sections to be developed further.