In this section, we go through an example of a team using the design process. This section provides more detail about the steps of the sequential design process.
Define the ProblemEdit
Problem definition is one of the most critical steps in the design process. Since the design team trying to solve this problem will expend a significant effort, it is very important that the problem being addressed is actually the problem that is important to potential customers. It is also important that the problem be clearly defined and understood by the design team.
Many techniques can be used to clearly define and understand the problem. These techniques include:
- gathering information from customers and other stakeholders,
- finding expert information (either in person or through books or other sources),
- doing a root cause analysis to identify what the real problem is.
The SCV design team began by gathering information about the issues associated with vehicular commuting and traffic congestion. They found and read several government reports. They interviewed various stakeholders in the commuting problem; these included people who commute to and from work in their car each day, officials from state and local departments of transportation, and representatives of environmental groups. They also used their own experience as commuters.
Identify Criteria and ConstraintsEdit
The problem statement is used as a starting point to develop an understanding of the characteristics of a good solution. These characteristics are described in terms of constraints and criteria. A constraint is a limitation or condition that must be satisfied by a design. A criterion is a standard or attribute of a design that can be measured. The constraints and criteria are used in subsequent steps of the design process to determine which of many possible designs should be implemented.
With criteria and constraints identified, the design team begins to generate concepts for the design. This is the step in which creativity plays a very important role—good designs are often very different from existing solutions to a problem. In addition to creativity, the design team must use discipline to ensure that they explore enough options and potential solutions to guarantee a good design. Therefore, it is important to use a structured process to generate concepts for a design. Many different processes could be used. The one presented here is adapted and simplified from Product Design and Development by Eppinger and Ulrich. It includes the steps of problem decomposition, searching externally and internally for ideas, and systematically exploring possibilities.
Decompose the Problem into SubproblemsEdit
When a design problem is complex, it can be very beneficial to decompose the problem into subproblems. Subproblems are smaller problems that must be solved in order to solve the overall problem.
Search Externally for IdeasEdit
Once the problem is decomposed into subproblems, the design team can begin to search for ideas to solve each subproblem. One source of ideas is to look at existing products and ideas to see whether there are already solutions to the overall problem or the identified subproblems. Sources of external information include interviews with potential customers or experts in the subproblem areas, patent and other technical databases, and existing products. Much of this information is now available on the World Wide Web.
Search Internally for IdeasEdit
Searching internally for ideas is often called brainstorming. The goal of brainstorming is to develop as many ideas as possible without worrying whether they are feasible. Sketches are often good tools to capture ideas and to generate new ideas.
Searching externally and internally will generate many possible solutions for each of the subproblems. To ensure that good solutions are not left out of the set of possible designs, it is important to use a structured process to examine possible combinations of subproblem solutions. A tool for systematic exploration is the concept combination table. In this table, solutions for each of the subproblems are combined; Figure 7 shows a concept combination table for the commuter vehicle.
To use the table, a solution for each subproblem is combined, and then a sketch or description of the resulting concept is created. For example, if the concepts are combined as shown in Figure 8, then the possible design in Figure 9 results. This design could be very similar to a standard bicycle with an added solar cell canopy that shades the driver. The pedals of the bicycle would be removed and replaced by an electric motor that drives the vehicle forward.
Note that the combination of design elements often does not provide a complete design concept; decisions must be made to fill in the gaps. For example, if solar cells are included as part of a design, they could be placed on the vehicle or they could be part of a fixed charging station that charges a battery on the vehicle; the design team must decide which configuration would make the most sense.
Explore Possibilities and Select a DesignEdit
The design concepts are explored to understand their characteristics. For example, exploring Concept 1, the solar-powered bicycle in Figure 9, leads to the following conclusions:
- The design would use only renewable energy.
- The design would be relatively inexpensive to manufacture and would cost nothing to operate.
- The design may not be convenient for the commuter, since the motor will only run when sunlight falls on the solar array. This means that it is impossible to commute at night or on cloudy days.
- The design will not be particularly comfortable for the commuter, since they will be exposed to hot, cold, and rainy weather, and the seat appears to be uncomfortable.
Develop a Detailed DesignEdit
After concept selection, the team has a general design concept; they have decided how each subproblem will be addressed and have an overall understanding of the design. Before the design can be manufactured, the team needs to develop the details of the design. A detailed design includes:
- The shapes and dimension of all physical components.
- An understanding of which components will be acquired from external vendors and which will be fabricated within the company and, if fabricated within the company, the materials and fabrication processes to be used.
- A detailed schematic diagram of any electrical subsystems and computer code for any embedded processors.
- Assembly processes.
The development of a detailed design from a design concept may occupy the majority of time allocated to a new product design project. This step will also have a significant impact on the success of the project; a poor detailed design can ruin a good design concept.
In the process of developing a detailed design, the team may use many or all of the subsequent design steps of prototyping, testing, and refinement. This process may require many iterations as the testing of prototypes reveals previously unknown characteristics of the design.
A major step in the process of going from a design concept to a detailed design is the development of the design architecture. The design architecture is "the assignment of the functional elements of the product to the physical building blocks of the product" (Eppinger and Ulrich, 2003).
For example, one architectural decision for the SCV design is how to incorporate the solar array into the design. Should the array be a separate physical block of the vehicle, for example creating the canopy structure in Figure 9, or should the array be created as an integral part of the frame? The first option represents a modular architecture, while the second option represents an integrated architecture.
Prototype, Test, and RefineEdit
A prototype or model is a representation of some aspect of the design. The purpose of models and prototypes is to provide additional understanding of the design and its performance. A prototype may implement only a small portion of design or may be comprehensive and implement the whole design. For example, while developing a detailed design for Concept 1, the design team may initially wish to develop a prototype only of the electrical system (the solar cell array and the electric motor). Once the electrical system design is verified, they may implement a comprehensive prototype of the whole vehicle.
Prototypes may be physical or virtual. A physical prototype may be implemented out of materials that are very similar to those that will be used to manufacture the final design, or, to reduce cost or save time, the prototype may be implemented out of other materials. A virtual prototype may be created using a computer-aided design and drafting (CADD) program. Modern programs can simulate many aspects of a physical system, revealing flaws or promoting understanding of the design without the need to implement it physically.
One important function of a prototype is to test whether the design will work as expected. Understanding of the design and confidence that it will work is gained as prototypes are tested and evaluated relative to the constraints and criteria for the design. Testing procedures should be carefully planned to ensure that questions about the design are answered without requiring too much time and resources. The test results should be evaluated relative to specifications that reflect the constraints and criteria.
Testing and evaluation of the prototype may reveal weaknesses in the design or may provide information that can be used to improve the design. In this case, the design will often be refined, particularly if it does poorly with respect to some of the criteria or constraints. Sometimes, the chosen design concepts do not meet the criteria or constraints, and the design team must go back and perform more concept generation and then select another concept. This is an integral part of a spiral design process.
Communication and ImplementationEdit
As the design team has gone through the design process, they have kept records of the different processes that they used and results of these processes. Often, this information is used to create user manuals and maintenance manuals for the product. This information is important for team members who will be required to update or modify the design in the future. Lessons are learned in the design process that should be conveyed to other teams in the company or perhaps to external stakeholders in government or academia. An important part of the design process is to document these issues and communicate the results to the appropriate stakeholders.
As the design is completed, the effort to implement the design increases. If the design is of a product that is manufactured, a manufacturing system must be developed. For example, in the alternate commuter vehicle design, suppliers for components such as motors and solar cells must be located; facilities for manufacturing the frame are created; and a sales and marketing staff are identified.
- An object made by a human being for a particular purpose.
- CADD stands for computer-aided design and drafting. It is the practice of using computer software to represent the geometry of designed objects.
- carbon dioxide emissions
- Carbon dioxide is a gas that results from burning fuels that contain carbon (e.g., coal and gasoline). Because carbon dioxide is a greenhouse gas that traps solar radiation, release of large amounts of carbon dioxide into the atmosphere by burning fossil fuels is believed to contribute to global warming.
- Something is characterized by discovering its distinctive features.
- concept generation
- The process of developing ideas that may be used to create a design.
- An arrangement of the elements of a design in a particular form.
- A constraint is a limitation or condition that must be satisfied by a design. Constraints are either satisfied or they are not.
- A criterion is a measurable standard or attribute of a design; for example, weight and size are both criteria. Criteria are used to compare different possible designs and determine which better solve the design problem.
- A person or organization that pays for the design either directly or through the purchase of a product.
- Decompose means to break down into simpler parts.
- design architecture
- The design architecture is the assignment of the functions that the design performs to the physical building blocks of the design.
- A specification of height, width, depth, or length.
- greenhouse gas
- A greenhouse gas is a gas in the atmosphere that traps solar radiation and re-radiates it as heat, leading to warming of the environment.
- incremental design
- The incremental design process begins with an existing design that is modified.
- Infrastructure is the basic structures and organization needed for the operation of a society. For example, the automotive transportation infrastructure is the roads, bridges, traffic signals, traffic signs, etc. necessary to drive cars.
- An iterative process is one that may be repeated.
- A model is a purposeful abstract representation of some aspect of a design. Types of models include equations, physical representations, computer representations, and other representations.
- Photovoltaic means that light energy is converted into electrical energy (see also solar cell).
- problem statement
- A problem statement is a concise description of the problem or need a design will address.
- A prototype is a first or a preliminary model of the design or some aspect of the design. Prototypes are often physical models, but increasingly computer models are used as prototypes. Prototypes are used to evaluate designs and discover flaws and weaknesses.
- regenerative brakes
- Brakes that slow a vehicle by converting its energy of motion into electrical energy that can be stored in a battery.
- renewable energy
- Renewable energy is energy that comes from sources that are not permanently depleted by use. For example, solar and wind energy are renewable, while coal and oil are nonrenewable.
- root cause analysis
- An analysis of a problem or situation to find the real cause (root cause) of the problem and deal with it; in the absence of a root cause analysis, people often deal only with the symptoms of the problem.
- solar cell
- A solar cell is a device typically made of metal and semiconductors that converts light energy into electrical energy.
- A stakeholder is a person or organization who has a stake in (e.g. an interest in or one who may be affected by) a design project. Stakeholders often include users and customers, the design team, and the company that employs the design team.
- A sustainable solution is one that can be continued without using up nonrenewable resources.
- A design is unfeasible if it does not meet the constraints.
- Viable means able to work successfully.
- ABET, Inc. "Criteria for Accrediting Engineering Programs 2007–2008". Downloaded March 17, 2007. Available on the web at http://www.abet.org/Linked%20Documents-UPDATE/Criteria%08%20EAC%20Criteria%2011-15-06.pdf
- Gerhard Pahl and Wolfgang Beitz. Engineering Design: A Systematic Approach. Springer, 1999.
- H. Scott Fogler and Steven E. LeBlanc. Strategies for Creative Problem Solving. Prentice-Hall, Upper Saddle River, NJ, 1995.
- Joseph W. Walton. Engineering Design: From Art to Practice. West Publishing, St. Paul, MN, 1991.
- Karl Ulrich and Steven Eppinger. Product Design and Development. McGraw-Hill/Irwin, 3rd edition, 2003.
- US Department of Transportation. "BCW: About the Program—Facts and Figures". Downloaded October 2006. Available on the web at http://www.bwc.gov/about/facts.htm
- Yousef Haik. Engineering Design Process. Thomson-Engineering, 2002.