6. Conceptual Design

• The first creative stage of any design is to generate concepts such as the choice between gasoline or electric powered vehicles.

• The most important rule in conceptual design is generate a few concepts and then select the best.

6.1 Concept Generation

• This is the typically the hardest part of design.

• When talking about invention: this is the ‘inspiration’

6.1.1 Brain Storming

• Basically this method generates a large number of diverse concepts using a group.

• One approach might be,

1. Have a meeting individuals (6-12 is good) related to the design tasks.

2. Make it clear that criticism is not allowed and every idea is good.

3. Ask everyone to write ideas on separate pieces of paper.

4. Start going round the room one at a time, and ask for the ideas. (Don’t allow criticism or judgment!) After the idea is given, the paper is placed in the center of the table.

5. This continues until all ideas are exhausted. (Participants should generate new ideas based on what they have heard from others). Encourage participants to suggest ridiculous ideas.

6. Go through the ideas in the middle of the table, and vote for the best one(s). - Practice Problems

Problem 6.1 Use brain storming to develop concepts for putting on shoes.

6.1.2 Diagramming

• We can break functions down to subfunctions shown as black boxes

• Basically we draw functional blocks that show interfaced systems and indicating inputs and outputs of information, energy and materials.

• We can start by drawing one main box for a function (e.g., ‘a pen must draw a consistent line width)


• The rules of thumb when creating the main diagrams are,

pick reasonable function boundaries (not too much or too little)

conserve energy and material

indicate interfacing/involved parts of the system

add information flows to determine how well the system is performing

• (as with IDEF) we can break the main function into sub functions. To do this we,

make sub function boxes that show how

create as many boxes as possible

list alternates

make sure all applicable flows are included

consider sequences

use standard notations

use available documents, parts, etc to develop ideas

don’t be afraid to add new items not on the first diagram


• We can then combine the function blocks into a single diagram.


• Finally, we convert the diagram to a conceptual design. The functional diagram(s) are used to provide clues, and in many cases they will lead directly to a design. - Problems

1. Considering the example started in the notes,

a) develop more subfunction blocks for the pen

b) using the previous blocks, draw a detailed functional diagram

c) Develop a final pen design using the final diagram.

6.1.3 Patents

• Use patents as a source for ideas

• Using keywords patents can be searched on-line

• A patent is typically made of common parts. The most useful are,

an abstract


a long description

a set of specific claims

6.2 Concept Evaluation

• After design concepts have been developed they must be reviewed.

• When evaluating concepts, we are best to start with many concepts and then refine,



6.2.1 Decision Matrix

• Basically we set some criteria, give them a value, and then compare conceptual designs to it. The final results are numerical.

• For this method we,

1. list the conceptual designs as columns.

2. List the criteria as rows (these criteria are like those used in QFD).

3. A weight is given to each criteria.

4. A score is given to the concept for each criteria. The ranking is done relative to one of the design concepts, with the middle of the scale being the first concept. A scale of -3 to +3 is reasonable.

5. Using the criteria weights, the column values are multiplied and added to get a score for the design.

6. The design with the highest score is often judged the best candidate for detailed design (although other designs may be chosen).

6.3 References

6.1 Ullman, D.G., The Mechanical Design Process, McGraw-Hill, 1997.