Solutions Manual to Accompany Engineering Design Fourth Edition

George E. Dieter and Linda C. Schmidt

TABLE OF CONTENTS

Chapter 1 Engineering Design 2Chapter 2 Product Development Process 6Chapter 3 Product Definition and Need Identification 12Chapter 4 Team Behavior and Tools 18Chapter 5 Gathering Information 27Chapter 6 Concept Generation 31Chapter 7 Decision Making and Concept Selection 42Chapter 8 Embodiment Design 52Chapter 9 Detail Design 65Chapter 10 Modeling and Simulation 67Chapter 11 Materials Selection 76Chapter 12 Design with Materials 85Chapter 13 Design for Manufacturing 91Chapter 14 Risk, Reliability, and Safety 100Chapter 15 Quality, Robust Design, and Optimization 110Chapter 16 Cost Evaluation 120Chapter 17 Legal and Ethical Issues in Engineering Design 132Chapter 18 Economic Decision Making 138

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CHAPTER 1

ENGINEERING DESIGN

1.1. A company making snowmobiles should have the capability to design and build equipment that stands up in an aggressive service environment. Working in the snowmobile business should have resulted in expertise in small gasoline engines. The company probably sells to a network of distributors, so there is no experience in selling directly to the customer. Snowmobiles are part of the growing business market segment of recreational vehicles. An obvious business opportunity that would extend the sales year around is to develop water sport equipment like jet skies. The market is crowded with suppliers, but an innovative design with an attractive entry price, or novel technology or features, could find acceptance. Another market possibility is off-road vehicles like a small dune buggy or three-wheel motorcycles. The same conditions for a new product would apply as for jet skies. A related, but separate possibility for a new product would be specialized vehicles for business and industry. Some examples are: a safe vehicle for bicycle messengers in crowded city streets, a small logging vehicle, small construction machinery, a parts-picking vehicle for large warehouses. 1.2. This is an individualized exercise for each student. In general, to make it a design problem the student would remove specific data, like forces, material properties, and add constraints like safety, reliability, and conformance to standards. 1.3 Needs Analysis Must be capable of being constructed with local materials and labor. Total cost to be less than $300 (U.S.). Should be easily transportable to different locations. Must be powered with human labor since you cannot count on availability of electricity. Hydraulic components may be invalid solutions because of cost and/or maintenance (sand in seals, etc.). Musts Wants 1. Cost less than $300 1. Able to make tiles 2 x 6 x 12 in 2. Weight less than 130 lb. 2. Easily maintained 3. Human powered. 3. Easy and safe operation 4. Made from local materials 4. Adaptable to a variety of soil mixes. (mostly wood, plain carbon steel) 5. Easily manufactured in local garage shop 6. Produce 4 x6 x 12 in. blocks 7. Produce 600 blocks per day 8. Compressive strength at least 300 psi dry Problem Statement The objective of this project is the design and construction of a prototype model of a block making machine. The blocks are to be made of soil with a minimum of cement added, and are 4x6x12 inches. The machine must be human powered, weigh less than 130 lb., cost less than $300 to build, and be capable of producing 600 blocks per day with a 5 person crew. Blocks must have a compressive strength of 150 psi as formed and 300 psi when cured. The machine should be easily constructed of local materials with local labor ( assume a third world tropical

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location). The machine also should be adaptable to a variety of soil cement mixtures, and to making tiles 2 x 6 x 12 in. A crew of five persons should be capable of operating the machine to produce 600 blocks per day. Information Needed 1. Determination of the processing conditions for making blocks. What pressures must be generated? Curing temperature and time? Effect of different soil mixtures on pressure. 2. Mechanisms for generating pressure. 3. Human Factors Engineering Magnitude of force that can be produced by a human Human fatigue 4. Materials handling 5. Available construction materials and their properties. 1.4. This topic is covered in detail in a paper by M.R. Hanley, et.al, Trans. ASME, Jnl of Engr. Material , vol. 102, Jan. 1980, pp.26-31. 1.5. Some possible concepts are:

• Vapor deposition, in a vacuum on a continuous (as opposed to batch) basis. • Ion implantation. • Slurry coating with nickel powder; sinter and hot roll to form a bond with the base steel

metal. • Electroless nickel plating plus cold rolling.

1.6, This topic is treated in detail in a paper by W.G. Jaffrey and G.M. Boxal, Jnl. Iron and Steel Institute , May 1963, pp. 401-408. 1.7. This design problem is discussed in a paper by R. Davis and M.L. Hull, Trans. ASME, Jnl. of Mechanical Design, vol. 103, Oct. 1981, pp. 901-907. The need that an aluminum bicycle frame fulfills is decreased weight. While the section modulus will have to be greater for aluminum than steel because of its lower elastic modulus, 10 x 106 vs 30 x 106 psi, preliminary finite element analysis shows about a 20% weight reduction. A simple FEA using beam elements can establish the critically stressed joints. A more precise FEA can map out the stresses at these joints, and from this the stress concentration factors can be determined. The selection of the particular aluminum alloy will be based on cost and fatigue properties, using the methods discussed in Chap. 11. To give the problem a more current flavor, have the students find papers on the use of fiber-reinforced composites in bicycle construction. This will introduce the issue of material cost and difficulty in manufacturing the structural members. 1.8. (a) Societal impacts: supply of coal miners; accident rate of coal miners; long-term impact of respiratory diseases in miners; damage to environment from surface mining, especially in mountainous country; adequacy of railroads to transport coal; traffic interference, noise, dirt, accidents from coal transport; adequacy of engineering design talent to design plants since much of this expertise is now retired; control of greenhouse gases (CO2) in coal gasification process;

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impact of tightening federal regulations on cost of construction and operation, diversion of a large amount of nation’s investment dollars or tax dollars. But, since the U.S. coal reserves are so large compared to oil and gas reserves, is there any realistic alternative? (b). In the past there was a big difference between the way society views the impacts of energy generated from nuclear materials and coal. Nuclear is more difficult to consider on a rational unemotional basis due to fear of nuclear weapons and nuclear radiation leaks. Look how long it is taking to establish a national repository for spent fuel rods in the Nevada desert. On the other hand, some people remember when their homes were heated by coal. There is a romanticism associated with the coal miner. People are generally more comfortable with energy from coal than from nuclear sources. This is changing with the great concern about global warming from greenhouse gases, to which coal combustion is a major contributor. Nuclear energy does not contribute to global warming, and there has been no major nuclear incident in 30 years. Safe disposal of nuclear waste remains the main concern of many people, as is the possibility of terrorist acquisition of nuclear material. Alternative energy sources like wind, solar power, and biofuels will grow, but at this time they do not appear capable of reaching the magnitude needed for electric power generation by the nation. Thus, the path remains clear for resumption in building nuclear power plants. Perhaps, the greatest obstacle from this happening is the growing cost of construction of a nuclear generation plant. 1.9. The increased use of natural gas (NG) for generation of electricity has increased the price of NG such that it is economical to ship NG to the United States or Europe from Algeria, the Middle East, and the Caribbean. The natural gas is liquefied with refrigeration techniques to -260 F, which reduces its volume by a factor of 600. In the liquefaction process impurities such as water, hydrogen sulfide, and CO2 are removed to leave nearly 100 percent methane. The liquefied natural gas (LNG) is transported in special doubled-hulled tankers with insulated tanks to maintain the LNG at proper temperature. At the tanker terminal the LNG is transferred to double-walled storage tanks with insulation between the walls. The pressure must be regulated to minimize vaporization, for both economic and environmental reasons. The next step in the process is to pump the LNG to the vaporizer units, where it is heated under controlled conditions and introduced into the gas transmission pipeline. Technical Issues a. Design of the transfer piping system b. Design of the storage vessels c. Design of the vaporizer unit d. As discussed below, safety is a paramount issue, but so is cost. A LNG transfer terminal can easily cost $5B. There needs to be careful balance between these issues, with safety given top consideration. Societal Issues Safety is a major concern in working with LNG. Although LNG is not flammable or explosive, when exposed to 5 to 15 volume percent air it becomes highly flammable. If LNG hits

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water it vaporizes violently and rapidly, forming a gas cloud that can travel for several miles before dispersing to a safe level. If the gas cloud is ignited the flame can travel through the cloud back to the source of the vapor. Thus, the area covered by the fire can be extensive. A leak of LNG or a spill, if ignited, is called a pool fire. This is more localized than a cloud fire, but of longer duration. If LNG is accidently released from a pressurized containment the leak usually takes the form of a spray of liquid droplets and vapor. This is called a torch fire, and delivers greater radiant heating than a pool fire. If the LNG is confined when ignited, it can result in a violent explosion. When the transportation of LNG was first developed in the 1960s there were several major explosions and fires. Public concern arose over this new technology and as a result the U.S. government developed safety standards (49-CFR-193) and the National Fire Protection Association issued consensus standards ( NFPA-59A) which have been continually updated. Since most LNG transfer terminals have been sited in narrow harbors or waterways, there has been concern that a ship collision or grounding might cause a LNG release. More recently there is been concern that a terrorist attack could cause a fire or explosion. Accordingly, the U.S. Coast Guard has issued regulations dealing with the site selection and design of LNG terminals (33-CFR Part 127). Thus, the design of the LNG plant will be highly constrained by codes, regulations, and standards. One final societal concern deals with the emission of methane, which is a potent greenhouse gas. Clearly, the design must give high priority to preventing venting or escape of methane to the environment. We started this discussion with the statement that natural gas is a preferred fossil fuel from the standpoint of global warming. However there are some who claim that after all of the energy consuming processes of refrigeration and transportation are taken into account the net benefit of using LNG may not be beneficial to the environment. 1.10. Outsourcing manufacturing to a foreign country usually is done to take advantage of lower manufacturing wages. A secondary objective can be to increase sales in the country of manufacture. Most product development depends on fine-tuning the design once it gets into production to improve upon design features that make assembly difficult and some parts more expensive to manufacture than expected. Occasionally, customer usage uncovers functional issues that need correction. These follow-on design activities often involve the modification of tools and fixtures used in production, or even the design of a modified part. Often these design tasks are performed by a small design staff that is in residence at the manufacturing location. There are also issues with maintaining quality standards with a workforce where language and culture are much different from the home country. Therefore, moving the manufacturing plant offshore greatly increases the communication task of leader of the product development team. Early on he/she must visit the new plant and gain the confidence of the plant manager and the top engineer. It is also important to bring that engineer back to the home office to be trained in company values and procedures. Much communication will be done via the Internet, so effective communication protocols must be established.

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Chapter 2

PRODUCT DEVELOPMENT PROCESS 2.1 The following are some reasonable estimates. Power

screwdriver Desktop

inkjet printer Electric car

Annual units sold 100,000 4,000,000 300,000 Sales price $30 $150 $35,000 Development time 1 year 1.5 years 4.5 years Peak size of team 3 100 800 Development cost $250,000 $8 million $500 million 2.2 A toothpick, paperclip, a wooden baseball bat, a crowbar, a water glass, a tent peg are some examples of a product consisting of a single component. 2.3 In general terms, the need for advanced education decreases from research to technical sales in the spectrum of engineering functions. Many would say that research, development and design provide more intellectual satisfaction, but high job satisfaction can be found in any of the engineering functions depending on the individual and their circumstances. While R&D provides a high initial salary, the long-term financial rewards may be higher in production, sales, or management unless the researcher proves to be highly innovative. Opportunity for career advancement depends greatly on theindividual situation. Strong professional recognition can be provided by a lifetime in R&D. Career advancement within the corporation usually requires a broad exposure to most of the functions listed in Fig. 2.7. In general, the people-orientation increases in going from research to management. 2.4 • Show strong organizational skills: abilities to work with people, meet deadlines, coordinate

work, and administer paperwork. • Show leadership: capacity for organizing and directing people. • Strong communication skills: ability to write clearly and sell your ideas. • Attitude: willing to spend time on administrative details for the good of the group; willing to

delegate to and trust others; commitment to organizational goals. 2.5

The combination of an engineering degree plus a MBA provides the tools for broad corporate management. This will likely result in a career path that leaves technical work for marketing, finance, etc. MS in engineering is needed for higher level design work and is the minimum educational requirement for a career in R&D.

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2.6

Project Mgr. Functional Mgr.Takes lead in scoping project. Participates in development of project plans.

Takes responsibility for developing project needs for cost, schedule, and performance.

Participates in development of project resource needs for one specific specialty area.

Leads project team. Makes detailed estimate of specialty area

workloads. Integrates and communicates project information.

Assigns personnel to project.

Tracks and assesses progress against plan. Maintains technical excellence of specialty

area. Resolves conflicts. Recruits, trains, and manages people in

specialty area. Communicates. Communicates. 2.7 If the following questions can be answered affirmatively then the success of a new product would be likely. a. Is there an assured market for the product? Does the product satisfy a well documented societal need? Can the product be readily differentiated from its competition? Is the product free from governmental regulation? b. Do you have a proprietary position with the product? c. Do you have the technical expertise to design, produce, and service the product? d. Do you have sufficient financial controls in place to sell the product at a profit? 2.8 The word description of business portfolio strategy the Boston Consulting Group, discussed briefly in Sec.2.6.2 is shown pictorially on the nest page..

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This is shown chiefly because the words cash cow, star, and dog businesses are commonly used in the business literature. However, these strategies should not be taken too literally. In a mature technology area it may not make sense to just milk the cash cow and kill the dog because mature technology businesses tend to result in very large sales volume.. Therefore, it may make sense to do enough R&D to keep the cow healthy so that it can continue to provide the cash to start additional promising new tech businesses. Moreover, a moderate shift in a large market may turn a dog business into a cash cow. 2.9 Steps in technology transfer: a. Information must be prepared in a form suitable for transmittal. b. An appropriate audience to receive the information must be identified. c. Information must be transmitted to individuals who can act on it most quickly. These people must be able to understand the new information and have a position in the organization to allow them to act on it. Factors which make technology transfer a difficult process are: a. The quantity of scientific/technical information available. b. The need for feedback between user and originator. c. The need for multiplicity of communication channels. d. The need to provide for security of proprietary information. This is often difficult to achieve when outsourcing design and/or manufacturing functions. Information can be transmitted in the following forms: a. Technical reports and papers b. Newsletters c. Data sheets d. Workshops and seminars e. Internet f. Employees changing jobs g. Telephone “hot-line”. h. Service representatives, technical sales people, extension agents. 2.10 It is clear that John Jones is essential for the success of the team, so by both Jones and the team must compromise. Much work of the team is done outside of team meetings, so that Jones’

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unusual working hours will not be a hindrance to team progress provided some arrangement can be made for communicating with him. In a sense, this will be similar to the situation when part of a development project is off-shored to India which is separated from the U.S. by about 12 time zones. However, it is important for Jones to be at team meetings where the group expertise is used in making critical decisions. Here is where compromise is required. For example, it might be decided that every third meeting will be held from 4 to 6 pm, accommodating Jones’ schedule and requiring flexibility from the rest of the team. The team leader, and sponsor if needed, must obtain a firm pledge from Jones that he will faithfully honor this schedule. With realization of the accommodations the team members are making to utilize his special expertise, it is even possible that he will agree to come in early so that team meetings can be held in the early afternoon. 2.11 For any product development project there is a window of opportunity, or market window, in which customers are receptive to the product and no obvious competition exists. An experienced product development manager always lives in fear of the window being closed by the competition. Yet in the absence of any known competition it is often difficult to instill the needed urgency in the development team. When the market window closes the team must play “fast follower” and lose the advantages of being first to market. Another type of window of opportunity is found in the development of large technical systems, such as a military airplane. For strategic reasons the system must be developed over multiple years, and performance improvement achieved with new technology, has a high priority. As suggested by Fig.2.6b, there is a gap between what is currently achievable in some critical technology, and R&D currently underway. This gives promise of improving performance. But, the program can only keep the technology window open for a limited number of months. If the new technology is not proven capable in the time window the program must go with the next best alternative. The new, better technology might not get its chance until the next aircraft of its type is developed 20 years in the future. To better manage this problem many agencies or industries have developed technology roadmaps that attempt to give a time line for the advancement of a critical technology. 2.12 Prior to the adoption of the shipping container, consumer and industrial goods were shipped in crates, boxes, and barrels in the hold of a cargo ship (the break-bulk system). This freight was loaded and later hauled out of the bowels of the ship with cargo nets and winches and the hard labor of large gangs of stevedores. The process was very labor and time consuming. It often took 3 to 5 days to unload a cargo ship. The introduction of steel shipping containers in early 1960s resulted in major improvements in port handling effectiveness, significantly lowering shipping costs. This eventually made it cost effective to make products in China and ship them to the U.S. consumer. Malcom McLean is responsible for the concept and implementation of a complete containerized freight transportation system consisting of:

• standardized steel containers, 20 or 40 ft long x 10 high x 8 wide. • specialized container ships that carry stacked containers on deck as well as below in the

cargo hold.

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• special designed cranes portside to load containers directly on flatbed railcars or tractor-trailer trucks.

• computerized system for quickly identifying containers and their contents In addition to the technology of the new shipping system, several social and political innovations were necessary before containerized shipping became widely accepted. These were:

• Protracted negotiations with the longshoremen unions before they agreed to accept the early retirement buyout plan that reduced their ranks to the current smaller workforce.

• Major changes in th U.S. Interstate Commerce Commission regulations • International standardization for container dimensions, capacities, and corner fittings for

attachment to the crane. • Development of special dockside cranes along with specialized computer software for

deciding where to locate each container for optimum retrieval. Today, 90 percent of all non-bulk cargo worldwide moves in containers. References: Marc Levinson, The Box: How the Shipping Container Made the World Smaller and the World Economy Bigger, Princeton University Press, 2006 Wikipedia: see Containerization 2.13. Other technological developments, beside the shipping container, that have made the global marketplace a possibility are:

• Air freight - to delver critically needed parts overnight compared with the three week ship travel time from China

• Internet communication – for rapid communication with overseas suppliers, and for transmission of CAD drawings and other product development documents

• Electronic funds transfer – rapid settling of accounts is crucial for international trade. • Radio-frequency identification (RFID) tags that make it possible to quickly identify what

is inside each container. • Global positioning sensing (GPS) that makes it possible to track location of each

container.

2.14 Business Plan According to the National Marine Fisheries Service, 40 percent of the important species of fish are being taken from the sea at a rate faster than they can be replaced. Estimates by the U.S. Department of Agriculture are that the current fish harvest of 97 million metric tons per year will be far below the projected demand of 175 million metric tons in 2025. Aquaculture enterprises, in which fish are raised in enclosures close to shore or in ponds on land, cannot achieve the economy of scale needed to address this problem. The solution is fish farming in the open sea- mariculture- combining technology learned from deep sea drilling and aquaculture. Huge concrete and steel cages will radiate from a central column anchored to the floor of the Gulf of Mexico. The cages can be raised and lowered by buoyant tanks and rotated around a core support structure to aid in cleaning the cages. Pelletized food will be transmitted to the cages by pipes.

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Initially, high value species like red snapper, striped bass, and mahimahi will be raised. Depending on the species, one 10,000 sq.ft. unit can produce 3 to 5 million pounds per year of fish. It will take 20 pounds of feed@$0.35 per lb.to grow 10 pounds of fish, that will yield 3 pounds of fillets selling for $6 to $8 per lb. wholesale. Once the bugs are worked out of the technology, the return on investment, could approach 100 percent. Source : W.G. Flanagan, Forbes , Oct. 23, 1995, pp.328-329.

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Chapter 3

PROBLEM DEFINITION AND NEED IDENTIFICATION

3.1 This exercise requires students to select 10 products from online catalogs and consider the motivation a purchaser has when they acquire the product. Students must identify which of Maslow’s hierarchy of needs (Section 3.3) are satisfied by the acquisition of the product and the features of the product that make it attractive to the purchaser. Finally, for each product students are asked to place the needs the product satisfies into the four Kano categories (Section 3.3.2). The goal of this exercise is for students to examine the needs for which products are designed. Instructors can provide additional instructions in the form of specific online catalogs or a required mix of products to direct students to a variety of product types or some that are outside students’ everyday experience. So, students should not choose computer technology equipment, software or clothing. 3.2 The transistor evolved into the microprocessor, integrated circuits, and very large-scale integrated (VLSI) circuits Their chief effect was in reducing the size and cost of digital computers and greatly increasing their reliability. The spin-off of the computer has affected many industries.

• Automotive—much improved fuel and emission control • Business—better inventory control and payroll processing • Consumer appliances—“smart” washers and dryers • Defense—cruise missiles, smart weapons • Finance and banking—electronic funds transfer (EFT) and online banking • Manufacturing—computer-aided design and manufacturing (CAD/CAM), process

control • Medical—CAT scan, MRI, improved medical diagnosis • Telecommunications—satellite TV, digital switching • Transportation—computer scheduling, global positioning, traffic control

3.3 This exercise requires students to list products with which they are familiar but, nevertheless do not completely satisfy the user. This exercise leads students to identify unmet needs in products that they currently use. Students must be encouraged to generate a list of at least 15 items. The second part of the exercise directs students to compare lists with team members. This is an exercise that can be done in advance of a group brainstorming session on possible product improvements. We often use this process for student teams to identify topics for their term project. 3.4 Creating a survey to elicit customer requirements for a microwave oven can be accomplished by following the steps in Section 3.2.2.

• Instructors should have students clearly identify their target customer because a student end-user will have different needs than another user, for example, the developer of an

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upscale condominium community. It would be interesting to have students work with different target customers.

• Developing an entire survey is a good team exercise. 3.5 Cross-country skis that ski on dirt or grass A list of requirements to provide a new, relatively inexpensive recreational product for devotees of cross-country skiing includes the following:

1. Provide for speeds up to 20 miles per hour 2. Be strong enough to absorb shock while riding over uneven terrain and rocks 3. Provide enough stability in use to minimize the number of times a user will fall while

riding them. 4. Work with conventional shoe bindings 5. Have a retail price under $300 a pair.

The “musts” requirements include those describing safety-related issues, numbers 2 and 3. The “wants” requirements are those that the product would satisfy if the design can be developed to deliver attributes like speediness, convenience, and moderate price (numbers 1, 4, and 5). 3.6 The functional characteristics of a helicopter are: rises vertically without need for taxiing; can hover in flight; can lift at least 2000 lbs.; creates noise and wind turbulence from rotating blades. These characteristics suggest that the helicopter would satisfy the following societal needs: flying ambulance, a fire engine that doesn’t need roads (fighting forest fires); flying crane. The noise, high cost, and safety considerations suggest that the helicopter is not the answer to highway congestion. 3.7 Thumb drive This exercise requires that students create a list of engineering characteristics that would be suitable for the design of a thumb drive. Four customer requirements are given. The engineering characteristics listed in the right column must be linked to the customer requirements in the left column to determine if the set of ECs are adequate to fulfill the set of CRs.

Customer Requirements (CRs)

Engineering Characteristics (ECs)

Enough memory for engineering student (1, 2)

1. Memory capacity

Interface with any computer a student may need to use (3, 5)

2. Size of case

Near 100% reliability (2, 3, 4) 3. Operating system

4. Exterior covering to protect connector 5. Interface port Signal when it is in use (6)

6. External operating light

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Students can be asked to add additional customer requirements based on their own experience with this type of portable memory device. The list below includes a couple of requirements that are not available in the drives on the market at the time of this writing (the last two). These final requirements would be “delighters”. When considering these new requirements it is necessary to review the list of engineering characteristics to see if they are adequate to satisfy each added requirement. If the existing set of engineering characteristics will not fulfill these requirements, new ECs must be identified to serve that purpose.

1. Survive being carried in a pocket or backpack 2. Be easy to find in a full backpack or other bag 3. Allow for personal identification 4. Indicate unused capacity when not active

3.8 Heating and air conditioning design problem This exercise requires that students create a House of Quality with rooms 1, 2, 4 and 5 as shown in Fig. 3.8. Customer requirements and engineering characteristics are given.

Engineering Characteristics Improvement

Direction ↑ ↓ ↓

Units % n/a n/a Yrs hrs

Customer Requirements

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Low operating costs 4 9 3

Improved cash flow 5 9 9 3

Managed energy use 4 3 9

Increase occupant comfort 3 9 3 3

Easy to maintain 4 1 9

Raw score 85 51 45 45 60 286 Relative Weight % 30 18 16 16 21

Rank Order 1 3 4 4 2

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3.9 Flip-lid Trash Can This exercise requires that students create a House of Quality with (at least) rooms 1, 2, 4 and 5 as shown in Fig. 3.8. Instructors should let students know which rooms are required for this exercise. Students begin with the customer requirements. The list is comprehensive. A list of engineering requirements and their definitions is required for the HOQ.

1. Material—the can and lid will need to be fabricated out of some type of material. 2. Trash capacity—Trash can capacity impacts the number of times that the trash must be

moved out of the can. Since there is a requirement that the trash can fit standard trash bags, some assumptions can be made. As this is to be a kitchen trash can, the standard 13 gallon kitchen trash bag will be the standard size that the can must accommodate. This engineering characteristic must be the same for all designs; therefore, it is a constraint and could be left out of the HOQ.

3. Mechanism for lid control—There are a variety of mechanisms that could be used to design the top. The name of “flip-lid” implies a lever mechanism that will raise the lid from horizontal to vertical.

4. Power supply—Nothing in the problem statement specifies the degree of automation desired in this trash can. There are cans with a foot pedal that are manually activated. There are also cans that have a visual sensor powered when activated by a hand signal.

5. Lid activation signal—This engineering characteristic covers both automatic and manual operation.

6. Seal type—A simple seal is needed to prevent the escape of odors. 7. Can cross-section geometry—Trash cans are designed in a variety of shapes: circles,

squares, rectangles, to name the most common ones. Standard garbage bags can be used with many can geometries. Geometry plays a larger role in design when it comes to adding a mechanism to control the raising and lowering of the lid. There are also differences in aligning a lid of different shapes (i.e., a round lid should fit a round can easily because there are no corners to align)

8. Center of Gravity (empty)—Some of the engineering characteristics listed above will contribute to reducing the risk of tipping over the can while it is in use (e.g., cross-sectional geometry and material type). However, the center of gravity is a more direct measure of likelihood of tipping when comparing designs. All things being equal, the most vulnerable configuration for tipping will probably occur when the can is empty and the lid is in the raised position. It is easy to estimate the height of the COG and the distance from the vertical axis of the can once a conceptual design is developed.

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Engineering Characteristics

Improvement Direction ↑

Units n/a. Gals. n/a n/a

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n/a n/a in

Customer Requirements

Impo

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Easy to open when holding trash 5 9 9 1

Closes correctly (never stays open) 4 9 3 3

Lasts at least one year 3 3 9 3

Light weight 2 9 9 3 3

Will not tip over in use 4 1 3 9

Prevent odors from escaping 4 3 9

Use standard tall kitchen trash bags 5 9 1 3

Safe for elderly, children and pets 4 9 3 3

Raw score 39 63 154 29 66 63 23 36 Relative Weight % 8 13 33 6 14 13 5 8

Rank Order 4 3 1 6 2 3 7 5

The QFD shows that each of the CRs is strongly related to at least one EC except power supply. It clearly indicates that the mechanism for opening and closing the lid is the most important aspect of the design be needed. It is also important for the closing mechanism to give a signal that the lid is closed securely. Also, the design of the seal for the lid needs to be carefully integrated with the closing mechanism. The can geometry is not a critical parameter, and the low ranking for the power supply indicates that first emphasis should be given to a human powered design..

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3.10 Product design specification for the flip-lid trash can. This is based on a product selling for $40 that is a plastic cylinder, with a lid opened by a manually operated foot pedal. The PDS is formatted after Table 3.3 in the text.

Product Design Specification Product Identification • Quick Flip Trash Can • Flip-Lid kitchen trash can for use with standard 13-

gallon tall kitchen bags • Odor minimizing due to tight seal on can • Allows for opening w/o use of hands

Market Identification • Medium-income families • Anticipated market demand (100,000 units /yr) • Competing products • Branding strategy (Trademark, logo, brand name) What is the need for a new (or redesigned) product? How much competition exists for the new product? What are the relationships to existing products?

KEY Project Deadlines -- Accept any reasonable answer Physical Description What is known (or has already been decided) about the physical requirements for the new product? • Design variable values that are known or fixed prior to the conceptual design process (e.g., external dimensions) • Constraints that determine known boundaries on some design variables (e.g., upper limit on acceptable weight) Financial Requirements What are the assumptions of the firm about the economics of the product and its development? What are the corporate criteria on profitability? • Pricing policy over life cycle (target manufacturing cost, price, estimated retail price, discounts) • Warranty policy --- Company will replace defective items in the first 90 days of use • Expected financial performance or rate of return on investment. Life Cycle Targets • No installation required. • Maintenance schedule and location (non expected) • Reliability (mean time to failure) Identify critical parts and special reliability targets for them • End-of-life strategy—the can and lid will be formed from recyclable aluminum; the pedal will be recyclable plastic;

the flip mechanism will be easily detachable Social, Political, and Legal Requirements Are there government agencies, societies or regulation boards that control the markets in which this product is to be launched? Are there opportunities to patent the product or some of its subsystems? • Safety and environmental regulations. Look these up • Standards. Pertinent product standards that may be applicable ( Underwriters Laboratories, OSHA) • Safety and product liability. Predictable unintended uses for the product, Safety label guidelines, applicable

company safety standards, • Intellectual property. Patents related to product. Licensing strategy for critical pieces of technology. Manufacturing Specifications Which parts or systems will be manufactured in-house? • Manufacturing requirements. Processes and capacity necessary to manufacture final product. • Suppliers. Identify key suppliers and procurement strategy for purchased parts

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CHAPTER 4

TEAM BEHAVIOR AND TOOLS

4.1 Generally, teams composed of engineering students are not very interested in “playing games” as icebreakers. One reason is that by the time they get to be juniors or seniors they are used to forming and working in teams. However, in the initial team meeting they should take the time to introduce themselves in some detail and to exchange complete contact information. If the situation calls for more of a warm-up or icebreaker, there are many websites that sell materials for team warm-up sessions. One useful site with free information is: http://www.teampedia.net/wiki/index.php?title 4.2 Some starter ideas: wrap fish; line the parrot’s cage; print a book; insulate a house, make more paper (recycling); fly swatter; rain hat; logs for fireplace; confetti; book mark; protect floor 4.3 The following is a typical format for a Team Charter. In an industrial setting the draft of the Team Charter is developed between the sponsor and the team leader, with the help of the facilitator. The draft of the charter is presented to the team at an early meeting. The modified charter is reviewed by the sponsor, and if acceptable, transmitted back to the team. In the college situation the instructor usually is the sponsor. Often there is not a designated team leader, so the team develops the Charter in conjunction with the instructor. Project Title: A brief 3 -4 word title for the project Problem Statement: A one or two sentence description of the stimulus for creating the team. The problem statement should not focus on a particular solution and should attempt to describe the problem from the customer’s perspective. Need to Address the Problem: Cite survey data. operational data, cost statistics, anecdotal evidence, etc. that justify the need to organize this team. Project Scope: List open-ended questions which frame the dilemmas faced by the current process owners and service providers in attempting to deal with the problem. Describe the boundaries of the problem. List the issues that are outside of the bounds of this project. Final Report Expected By: Interim Milestones Required of the Team: List any preliminary products required of the team prior to its completion. Resource Issues: Describe any resources set aside to assist the team in its work. Describe any limits on resources that should affect team recommendations.

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Project Sponsor: Team Leader: Team Membership: Team Facilitator: Others Influenced by the Problem: List interested individuals, offices, projects, committees, who might act as a resource to the team. Also list individuals who will be kept informed of the team’s progress and recommendations. Implementation Plan: This is to remind the team and the sponsor that an implementation plan is required, in addition to recommendations for solving the problem. The sponsor should indicate the degree of specificity expected in this implementation plan. Students often have difficulty differentiating between the Team Charter and the Team Guidelines (see Table 4.3). The Team Charter is an agreement between the team and team sponsor (usually the instructor or some other faculty advisor). It serves chiefly to make sure that the team and sponsor are in agreement with the problem definition and scope, and the required deadlines and project deliverables. It also forces the team to think about its organization. The Team Guidelines describe the details of the process by which the team will work to be successful. Of particular importance is an honest description of what the team agrees to do about a team member who misses team meetings or who does not follow through on assignment made at team meetings. In the case of a “problem member” of a team, a signed Team Guideline is a good first step toward arriving at a resolution. 4.4 Typical problems that attract student interest are:

• Improving the curriculum • Making study aids more available to students • Increasing the hands on aspects of the curriculum

The TQM tools that are most often involved in technical design decisions are:

• Brainstorming for problem definition and concept generation. • Affinity diagram for bringing clarity to a multidimensional problem and breaking it down

into more manageable chunks. • Cause and effect diagram for laying out the factors involved in a problem. See diagram

below for factors in selecting a manufacturing process to make a part. • How-how diagram for stimulating and organizing solutions to design issues

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4.5 The nominal group technique (NGT) is a method for group idea generation and ranking the ideas for consensus. Often it starts with silent brainstorming (brainwriting) to generate the ideas. The use of the term “nominal” in this method comes from the fact that it often starts out with a nominal, i.e., silent and independent idea generation, group activity, and, independent evaluation by each team member. Next the ideas or topics are written on a blackboard. If the number of choices generated by brainstorming is large, it may be useful to employ some list reduction method. Start with the entire list of ideas displayed so that everyone can see them. For each item ask the question, “Should this item continue to be considered?” A simple majority vote keeps the item on the list; otherwise it is marked with brackets. At the end of voting, any item marked with brackets can be put back on the list by a single team member. Next, each idea is compared with all others, in a pairwise fashion, to decide whether they are different ideas. If all team members feel they are essentially the same, then the ideas are combined with a new wording. The last step of the NGT involves decision making, with the members of the team acting independently and anonymously. If the number of choices is relatively small, then each person can rank order the choices. For example, if there are five choices, A, B, C, D, E, each person would associate a value of 1 to 5 to each choice, where 5 is best. The values for all members of the team would be combined, and the choice with the highest score would be the team’s first choice. When the number of choices is large, e.g., 20, it becomes difficult to rank order so many items. Here, the “one-half plus one” approach is often used. The team is asked to pick the top 11 items (20/2)+1 in rank order. Again, the ranking of each team member is combined to arrive at the overall team decision. A variation on decision making by ranking is rating by multivoting. Each team member receives a number of votes, usually about one-third of the total number of choices. You can distribute these votes among as many or as few choices as you wish. Often the voting is done

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by giving each team member the appropriate number of colored sticky dots, and the voting is done by going to the chart of options and pasting them beside your choice(s). Multivoting usually proceeds in stages. In the first round those choices with only a few votes are eliminated. The number of votes per member is adjusted, and a second round of voting is held. The process is repeated until a clear favorite emerges. The advantage of the NGT is that team members with differing styles of providing input are treated equally because the process imposes the same format requirement on each member. Strong personalities do not unduly influence the outcome. The volume of the loudmouth is turned down while the soft-spoken voice is more clearly heard. While the method reduces the pressure to perform, because of the lack of group interaction during idea generation, it has a lower chance of generating truly unique ideas. Also, note that NGT combines idea generation and evaluation into a single session. Thus, it often is used in instances where time is very short and a solution with consensus must be found quickly. 4.6 A possible force field diagram for Example 4.2 is given below.

4.7 Suggested issues to consider when evaluating team performance:

• Does the team understand what they are to accomplish at the meeting? Do they follow an agenda?

• Is there effective leadership? • Is there a feeling of collegiality and easy give and take between members? • Do all team members appear to contribute? • Does the team reach decisions efficiently? Do these appear to be mainly consensus

decisions? • Does the meeting end with well defined tasks for each member to complete before the

next meeting (action items)? 4.8 A useful team evaluation form is shown on the next page. In order to be effective we find that this survey should be administered three times during the semester: (1) after an early project deadline; (2) at the midpoint of the class, and (3) at the end of the project. In the initial evaluation, emphasize that the peer evaluation is aimed at identifying areas for growth of the team members. Generally, students will initially give each other strong positive

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ratings, often giving each member an identical high rating. Emphasize that giving realistic ratings is expected in professional practice. As the use of the peer evaluation instrument continues students gain better understanding of their team and what is expected in peer evaluation. An important way to give credibility to peer evaluation is by insisting that students who receive low peer ratings in the first evaluation request feedback and develop a plan for improvement. As a first step, ask the student to meet with their team to discuss the perceived weakness and develop a plan for improvement. If this is not possible, then the instructor should discuss the problem with the student. 4.9 Include the following categories: class time; personal time (eating, sleeping, personal hygiene), commuting time; fitness time (exercise); study time, class project time, working time; extracurricular activities time; socializing. .10 (a) The scheduling network is incorrect as shown in the text, because B precedes both D and E, while according to the problem it should only precede E. The correct network is obtained by introducing the dummy activity connecting events 3 and 4. Note that a dummy activity has zero duration.

(b) The network in 4.10(b) is incorrect because as drawn A precedes D,E, and F while the problem states that A precedes only D and E. The correct network is

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4.11 (1) Draw the network diagram for the problem. The network is started by locating the start event (1). Activities that do not require any preceding activities (A,B, and C) are drawn from the first event. Note that activities are represented by line segments with arrows pointing in the direction of progress, not vectors, so their length and orientation is not important just so long as all the activities form a connected network.

Check to see that precedential relationships are satisfied. (2) Calculate the earliest start time (ES). This is the earliest possible starting time for each activity after the first activity has been started. ES is found by taking a forward pass through the network (following the direction of the arrows) starting at the first event and ending with the last event. By convention, ES for event 1 is zero, i.e. ES1=0. ES for the next event is also the earliest finish time (EF) for activity A. EF1 = ES2 = ES1+D, where D is the duration of the next activity. Rule 1 This relationship holds so long as only one activity leads to the event, as is the case with activity I leading to event 7 in the above network. However, when several activities lead to an event, as is common in the above network, the ES for the event is equal to the maximum of all the EFs leading to this event. Rule 2

Starting with event (1): ES2 = ES1+D = 0+4 = 4. But there is a second activity leading to (2). Thus, we need to find ES2 = ES3+D = ES3+2. Before we can move forward we need to find ES3. ES3 = ES1 +B = 0+3 = 3 and ES2 = ES3+2 = 3+2 = 5. Applying Rule 2 we find that ES2=5. Applying rule 2 at events 4,5,6, and 8 and rule 1 at event 7, we arrive at the following table for earliest start time (ES). The activities leaving each event are also listed, since these will be needed later for determining the critical path.

Event Activity leaving event Earliest start time ES 1 A, B, C 0 2 H, G 5 3 D, E, F 3 4 I 4 5 J, L 8 6 M 10 7 K 8 8 ---- 13

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(3) Calculate the latest start time (LS). This is the latest possible time an activity can be started if the project is to be completed on schedule. LS is found by taking a backward pass through the network (against the direction of the arrows) starting at the last event and ending with the first event. LS for the next event is the LS for the event at the arrow head minus the duration of the activity (D). For example going from the last event to the next to last, 8 to 7 is LS7 = LS8 –D = 13 – 2 = 11.

Event Activity LS Event Activity LS 8 ---- 13 5 -2 G 5 8-7 K 11 5-3 E 6 8-6 M 10 2-3 D 3 8-5 L 9 4-3 F 6 7-4 I 7 4-1 C 4 6-5 J 8 2-1 A 1 6-2 H 5 3-1 B 0

Now consider event (5) of the backward pass. The tails of two activity arrows merge at event (5). This is similar to what happened with activity E and G at event (5) during the forward pass. In that case, in finding ES at event (5) the value of ES at (5) was the largest of the values (Rule 2). Now in a backward pass we do the opposite, and select the smallest of the LS values (Rule 3). The above table shows that LS in going from (8) to (5) is 9, while going from (6) to (5) LS is 8, Therefore, applying rule 3, LS5 = 8. We use this result to find LS2. At this event the tails of activity arrows G and H converge. Arrow D is not part of the decision since its tail is at (3) and the head at (2). On going from (5) to (2), LS5 = 8-3 = 5. Since LS5 on going from (6) to (2) is also 5, we have LS5 established. The tails of three activities converge at (3): 5-3 LS3 = 8-2 = 6 2-3 LS3 = 5-2 = 3 4-3 LS3 = 7-1 = 6 Applying Rule 3 we find that LS3 = 3 The next three backward paths of the network are straightforward. We note than one of the passes ending at event (1) is zero, as is required to close the network. (4) Calculate the total float. The total float (TF) for an activity indicates how much the activity can be delayed while still allowing the entire project to be completed on time. TF = LS – ES By going back to the tables of earliest starts and latest starts, we construct the following table for each activity.

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Activity Duration ES LS TF A 4 0 1 1 B 3 0 0 0 C 3 0 4 4 D 2 3 3 0 E 2 3 6 3 F 1 3 6 3 G 3 5 5 0 H 5 5 5 0 I 4 4 7 3 J 2 8 8 0 K 2 8 11 3 L 4 8 9 1 M 3 10 10 0

Activities for which the total float is zero lie on the critical path because there is no tolerance for any delay else the total project would be delayed. On the other hand, activity C could be delayed by 4 weeks without jeopardizing the schedule for the project. The critical path is B-D-H-G-J-M. Note that the critical path branches at event (2), one branch being H and the other G+J.

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CHAPTER 5

GATHERING INFORMATION

5.1 Students should review Sec.5.1.1. A good personal plan for combating technological obsolescence will discuss the following points:

• Plans for further formal education • Plan for achieving professional registration as an engineer • Topics they want to learn more about by taking a short course or from personal study • Names of periodicals or technical journals they plan to read to keep up in their field • How much money they are expecting to spend annually from their own pocket in pursuit

of continuing education (society memberships, subscriptions, books and software, attendance at meetings)

• Plans for developing a professional network • Professional or technical societies they expect to join

5.2 The instructor should indicate which of these assignments can be found on-line and which should involve actual physical journeys to the library. It might be a good idea to require each student to interview a reference librarian and bring back their autograph. 5.3 Students should record their search plan and discuss which indexing/abstracting services were most useful in finding references. The report should state what key words were used initially in the search and show how these were refined as the search progressed. It is important for the students to learn how to properly list references in a technical paper or report. 5.4 (a) To find U.S. government publications that deal with disposal of nuclear waste, go to www.gboaccess.gov/index. Click on Catalog of Government Publications (CGP). Enter “nuclear waste” in Quick Search box This returns about 50 records. (b) To find government reports dealing with research on Metal Matrix Composites, go to the National Technical Information Service (NTIS) at www.ntis.gov. Click on Search Library. Enter metal matrix composites and receive more than 100 records. Note, if nuclear waste disposal is entered it will return many records. 5.5 The following are some easy responses to these questions. (a) Look in the Yellow Pages of your telephone directory. A quick look gave me seven practitioners located within 30 miles of my home. One was 20 minutes away. Entering Yellow Pages Directory in Google was less helpful. It gave me two results, one that I had found in the phone book and the other was in Texas. Presumably the other taxidermists did not subscribe to this internet directory.

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(b) Check the current technical periodical literature for the authors of current papers. Call the local engineering school and ask if they have anyone on staff with that expertise, or alternatively, check their website. Some technical societies, when contacted at their national headquarters will give a list of possible technical experts. Use your personal network: contact former professors, former class mates, or local engineers who you know from attending technical meetings. (c) Look in Thomas Register for names of suppliers and contact them, or ask your purchasing agent to get the information for you. (d) Osmium is a rare precious metal. Section 5.6.2 refers the reader to Chapter 11 for information on materials. In that chapter, Sec.11.4.1 lists Metals Handbook, Desk Edition, 2d ed. as a good reference for properties of metals and alloys. On page 626 in Table 1 the melting point of osmium is given as 3046 degrees Celsius. If you did not know that osmium is a metal, it would be logical to look in Google. Entering osmium gives an article in Wikipedia that gives the melting point as 3033 degrees Celsius. The article links to the website www.webelements.com which gives the melting point as 3036 degrees Celsius. These differences could be due to slight differences in impurity levels, or most likely the difficulty of precisely measuring such high temperatures. (e) This information deals with the heat treatment for a specific alloy. Once again, Section 5.6.2 refers the reader to Chapter 13 for information on manufacturing processes, of which heat treatment is a major category. Chapter 13, Table 13.1 on p.566 gives a comprehensive list of texts and reference books. ASM Handbook, Vol. 4, Heat Treating, is an authoritative source that is available in nearly all engineering libraries. 5.6 American Society for Testing and Materials (ASTM) Standard F558-03 gives Standard Test Method for Measuring Air Performance Characteristics of Vacuum Cleaners. This was found by first using the Index to ASTM Standard to determine which of the many volumes of standards should be examined. This standard is found in Volume 15.08, which besides vacuum cleaners covers sensory evaluation, security systems, detention facilities, and food service equipment ( a really eclectic collection). Besides F558, there are 26 other standards pertaining to vacuum cleaners, including such issues as noise level, bag integrity, dirt removal effectiveness, performance characteristics of motors and fans, and testing vacuum cleaner hose. 5.8 To establish priority of invention you must prove to the U.S. Patent Office that you were the first to conceive the invention and the first to reduce the invention to practice. You must show that you were diligent after conception in reducing the invention to practice. Long delays from conception to reduction to practice can jeopardize your patent position. The party who is first to conceive of an invention and who is diligent in reducing it to practice will prevail in an interference action over another party who conceived the invention second in time but who was first to reduce it to practice. However, if one party is first to think of the invention but inexcusably delays reducing it to practice, he or she will lose to a party who conceived the invention second in time but acted diligently to first reduce it to practice.

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In establishing the dates of conception and reduction to practice the word of the inventor alone is insufficient. Thus, it is extremely important to maintain witnessed and dated records of these events. in bound laboratory notebooks. The United States is the only major country that uses first to invent as the main criterion for establishing priority in invention. The other countries use first to file with the Patent Office in determining priority among claimants for a patent. This is easier to substantiate and avoids what are often long and expensive legal cases. Legislation currently before Congress would change the U.S. system to first to file to bring it into agreement with the rest of the world. Those who oppose this change feel that it would give unfair advantage to large corporations with large legal staffs over small companies or the individual inventor. 5.9 A provisional patent has been available in the U.S. patent system since 1995. Advantages

• Simple to prepare and file. Does not require legal assistance. Does not contain formal claims as in standard patent application.

• Inexpensive. No legal fees and filing fee is about one-third of standard patent. • Used mainly as a way of establishing an early filing date, to “lock in” potential patent

rights while seeking funding for further development. Often used by universities. • Provisional patent is not published for the general public, so existence of patent, while

not secret, is not widely known. • Submitting a provisional patent allows use of term Patent Pending in connection with the

invention Disadvantages

• Provisional patent is for a term of 12 months from the date of filing. Application for a non-provisional patent must be done within this time period if a standard patent is to be obtained.

• Because of the quick turn around by the USPTO there is no evaluation of the patentability of the invention in terms of prior art. Thus the patent has not be tested in the way that a standard patent is examined by the Patent office.

Reference: www.uspto.gov/web/offices/pac/provapp.htm 5.10 Jerome H. Lemelson was the second most prolific U.S. inventor next to Thomas Edison. he was both lauded for his support of the individual inventor and reviled by some for what are felt to be paper patents without substantive reduction to practice. http://en.wikipedia.org/wiki/Jerome_H._Lemelson 5.11 Originally computer programs were protected by copyright, and many still are. Copyright prohibits the users of a software program from making copies of it without the permission of the company that owns the program. It prevents one company from taking another company’s work and selling as its own. But, the existence of a copyright does not prevent other programmers from using algorithms contained in the program in their own programs - based on the doctrine of “fair use.”

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Historically, copyrights and patents have been thought to apply to different kinds of things. Copyrights pertained to protection of the expression of ideas, not to the ideas themselves. Patents pertain to processes, materials, and machines. Starting in the late 1980s the Patent Office began to issue more patents for computer software. At question is whether much software can legitimately meet the novelty requirement for patenting and whether the patent involves a practical implementation, not just a mathematical algorithm. By 2004 149,000 patents for software had been issued in the United States, but there still is not a universally accepted way of defining what is or is not a software patent. Most software companies are applying for patents and cross licensing with other companies to avoid patent infringement. http://en.wikipedia.org/wiki/Software_patenthttp://en.wikipedia.org/wiki/Software_patent_debate

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CHAPTER 6

CONCEPT GENERATION

6.1 This exercise encourages students to discover some unusual combinations of functions by asking them to randomly select two personal devices from an online catalog and combine them into something new. This will require discipline on the part of the students to actually randomly select devices. Instructors may wish to take a print catalog (e.g. stores include Brookstone or Sharper Image) and cut out pictures of devices from which students randomly draw two. The goal of the exercise is to have students focus on the key functionality of devices. Imagination is necessary and students should be encouraged to develop innovative combined uses that are practical for realistic situations.

Example Solution: Devices are selected from the online site of the Container Store (http://www.containerstore.com/)

Fig. 6. 1 See & Store Containers & Strip Pkg/5

(Product 10023527 from website)

Fig. 6. 2 Mini-Mantle Bedpost Shelf

(Product 10034276 from website)

The functions of providing small containers for storing needed items in a desk area via a

magnetic strip can be combined with the function of providing a shelf mounted on a bed post to create a vitamin or medication storage and reminder unit. The storage containers can be filled with daily vitamins or medications and attached to the bedpost shelf. The shelf’s glass holder allows the user to stage the vitamins or medication for easy dosing. 6.2 This exercise requires students to apply the Key Questions Technique (Section 6.3.2) to the problem of eliminating puddles from forming on pedestrian walkways. The starting point for creating new solutions is the existing solution: waiting for puddles to evaporate.

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Example Solution: The following table summarizes notes that might be generated from the application of the first two of the Key Questions to the problem. As with all concept generation exercises students should be asked to sketch one or more of their concepts and explain concept functionality. Table 6.1 Application of Key Questions “Who” and “What” to puddle evaporation

Question Answer Implication for Solution

New Concept

Who uses it? Who wants it? Who will benefit by it?

• Pedestrians • City Officials who hear

complaints

Pedestrians or city officials might pay for solution improvement

Nothing

• What happens if we wait for puddles to evaporate? What is successful about it?

• What is a shortcoming or failing of this solution?

• It takes time because evaporation is the result of the air conditions outside.

• The success is that nature takes care of the problem.

• The failing is that there is no control over the evaporation.

• Don’t put walkways outside.

• Can we help nature along with the conditions for evaporation?

• Can we eliminate the dependence on nature?

• Create covered pedestrian walkways

• Heat the walkways to increase evaporation.

• Use porous asphalt as sidewalk material.

Where questions Why questions How questions

6.3 This assignment is written to be given in conjunction with a group brainstorming exercise. Students could be asked to brainstorm ideas for a new personal transportation device (as mentioned in an upcoming exercise of this chapter. One student in a group would be designated to record ideas during the exercise in a concept map format like the one shown in Fig. 6.1. It is likely to be difficult for one person to accurately record every idea and how it fits with the previous ones in a brainstorming session. It is possible to have multiple students record ideas during the session and compare diagrams afterwards. The assignment can also be given as an individual homework prior to a group brainstorming exercise. Each student can be asked to create their own concept map on ideas for a new personal transportation device and turn it in, prior to participating in a group brainstorming session. This will help students prepare for the group exercise and allow them to reflect on associations they did not see when comparing their concept maps to those of others in the same group. 6.4 A team of mechanical engineering students developed the following ideas in a 40-minute brainstorming session. 1. Slurry pipeline- water medium 2. Slurry pipeline- oil medium 3. Slurry pipeline- air medium 4 . Slurry pipeline-vacuum medium

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5. Underground storage 6. Truck convoy 7. Underground storage- coal in pipes laid in the ground 8. Unit train 9. Deliver via subway - at night 10. Conveyor belt 11. Dirigibles 12. Barges 13. Pipeline along existing right-of-way 14. Storage bunkers 1 5 Aerial cable cars 16. Airplanes 17. Kites 18. Balloons 19. Big birds 20. Skids-tractor or cable-powered 2 1 Skids-powered by linear motor 22. Canals and barges 23. Underground pipeline 24. Pressure vessel storage 25. Extend plant by filling in river or lake 26. Screw conveyor 27. Piston-ram pipeline 28. Slingshot 29. Mobile power plant 30. Transport steam instead of coal 31. Many small coal piles in backyards of surrounding homes. 32. Close off streets for storage 33. Make storage areas by purchasing surrounding homes 6.5 Students are asked to dissect a small appliance, create a physical decomposition diagram for it and an accompanying narrative to articulate how it operates. Product dissection is such a popular activity in courses that there are many online resources students may turn to. There is a short YouTube video of the dissection of a Toastmaster Hand Mixer (http://www.youtube.com/watch?v=fAQfl6ww1-c accessed 6/8/08). The figures of the mixer are taken from that site. Labels have been added. Instructors may wish to show a portion of the video (or other online source material) to students in class.

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Explanation of Mixer Operation: To operate the hand mixer, the user must first connect the beaters (4) to the internal beater housing (10) through openings in the lower housing of the mixer. This should be done only if the mixer is turned off and the cord set (3) is unplugged. Once the beaters are seated in the mixer the user grips the mixer by the handle built into the upper housing (1) and directs the beaters into a container holding solids and liquids to be mixed. At this time the mixer can be plugged into an electrical socket with the controls set to the “off” position. Once the beaters are immersed in the material to be mixed the user activates the operating button (6) that turns on the motor (12) set in the lower housing (2). The mixer has a number of power settings that are indicated on the control faceplate (7) set into the mixer handle portion of the upper housing (1). These controls interface with the operating electronics (8) housed in the handle portion of the upper housing (1) and send control signals the motor control electronics (9) that are set in the lower housing near the motor assembly (12). Once the mixing is complete, the user can remove the beaters from the mixer for cleaning by pressing the beater release trigger (5) extending out from the upper housing (1).

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Physical Decomposition Diagram of Hand Mixer

6.6 Students are asked to create the function structure for the hand mixer of the previous problem.

Black Box Representation of Mixer

Fig. 6.3 Function structure of mixer

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Function structures are not unique. Fig. 6.7 holds one version of a valid function structure for the hand mixer. More details that could be included in a different function structure include a function block for steering the beaters through the ingredients to be mixed using human energy and a “guide” function block. The electrical cord could be represented by a “channel” function block that would direct the flow of energy from a wall socket source to the device. 6.7 Students are asked to create a function structure for a dishwasher. One must create a black box representation of the device. The inputs and outputs are defined as is the overall function of the device itself. Fig. 6.8 is a black box description of a dishwasher

Fig. 6.8 Black Box Representation of Dishwasher

Once the inputs and outputs have been determined, it is useful to recognize the different functions that the device must fulfill in the course of washing the dishes. A partial list includes: contain dishes, apply a mixture of soap and water with some force, apply clean water only to rinse the dishes, and schedule and monitor all these operations so that they occur in the appropriate order. Fig. 6.9 displays a possible function structure for a dishwasher. Another option would include a drying cycle for the clean, wet dishes. It is clear to see that the function structures can become very complex, depending on the amount individual functions used to describe the combined functioning of the device and the degree of automated control that is depicted. Functions such as “sense” can be added to the function structure to create more accurate control loops. These control loops would need to be powered, requiring energy flows as well.

Fig. 6.9 Function Structure for Dishwasher

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Students should be given a sense of how detailed their function structures should be when given this type of assignment. 6.8

Fig. 6.4 Morphological design “cube” for personal transportation device concepts

6.9 This exercise requires students to repeat the process of creating a function structure for a mechanical pencil that has been done in Section 6.5. Students can find a mechanical pencil that is very similar to the one used to create the function structure in Figure 6.8 in the text. Differences may include a combined grip and support function for a pencil that has an ergonomic grip surrounding the barrel. Key characteristics of a good submission for this exercise include:

• A clear sketch of a mechanical pencil with a view of the lead advancement mechanism. The advancement mechanism is the subsystem in which differences can be expected.

• A function structure that differs from Figure 6.8 in a meaningful way. • Students may seek to expand on a function like “Advance Lead” and use different

mechanisms to distinguish their example from that presented in the text. 6.10 This is a request for students to repeat the process used to develop the two syringe design concepts described in Section 6.6.2. Sketches of the student designs are required in addition to stating which function embodiments are chosen from Table 6.7. Students may find they need to add minor parts (e.g., sleeve, valve, joint) to make their selected embodiment work. The goal of the exercise is to make the embodiment work even if it is not the most efficient or streamlined design. 6.11 The creation of a morphological chart requires a valid function structure that is general enough to accommodate different embodiments of the functions. The embodiments listed in the table should be feasible for the application. In the case of the mechanical pencil, for example, there is

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not a practical way to load lead except by hand. Therefore, we are not including “Import” as a function with optional embodiments in the chart.

Table 6.2 Morphological Chart for Mechanical Pencil

Functions for Handling Lead in a Mechanical Pencil Store Isolate Advance Position

Single cylinder (large

diameter)

Narrowing channel Friction roller Fixed channel

Long single channel (single lead diameter)

Pistol-style individual chambers

Gravity Feeder Adjustible chuck-like

device Cone shape

with narrowing diameter

Stopper with single-lead

diameter hole

Ratchet mechanism

Caliper grippers

Students could choose different combinations of solutions for each function to create sketches of new mechanical pencils. 6.12 Students are required to do research on the life of Genrich Altshuller and provide some details in a short report. This is a simple exercise for students and Altshuller’s life includes colorful events. A few are as follows:

• Inventor of device to create oxygen from hydrogen peroxide (when he was 14) • Joined Soviet Army in WWII • Post WWII became an inspector of inventing in the Soviet Navy • Turned to psychology for ways to assist others in becoming creative - but was not

impressed with results • 1946 determined to create a new science for theory of invention and began by studying

“author certificates”, the Soviet Union’s equivalent of patents. • Altshuller and Shapiro (his friend) wrote a letter to Stalin suggesting that they had a way

to improve the invention process to benefit the Soviet Union o The letter about TRIZ ideas was not received well o The pair were sentenced to 25 years in a prison camp within the Arctic Circle o Altshuller released in 1954 (one year after Stalin’s death)

The text contains many references that will lead students to these and other facts about Altshuller and TRIZ. 6.13 Students are asked to rework the powder metal transport problem by determining how to improve the energy spent (parameter 19) by the moving powder particles moving through a pipe with a 90-degree bend, without degrading the other parameters of the system. To recap, the objective is to increase the energy of the particles (19) without increasing the force (10) on the elbow, decreasing the durability (15) of the elbow, or requiring increased wall thickness (substance - 26). For each of the parameters, the table lists the suggested inventive solutions.

38

This discussion illustrates the type of reasoning student will use to propose solution. Insights students should gain from this exercise are that not all inventive principles are easily interpreted to a given design scenario and some may not lead to any feasible solutions. This discussion illustrates the type of reasoning student will use to propose solution. Insights students should gain from this exercise are that not all inventive principles are easily interpreted to a given design scenario and some may not lead to any feasible solutions.

Table 6.3 Inventive Principles for Transporting Metal Powder in Example 6.1 of the text

Inventive Principle to Apply to Avoid Degradation of Parameters Listed in Columns

Para

met

er

to Im

prov

e

Force (10) Durability (15) Amount of substance (26)

Ener

gy sp

ent b

y a

mov

ing

obje

ct –

the

parti

cles

(19

)

16. Partial or excessive actions using 'slightly less' or 'slightly more' of the same method 26. Copying Instead of an unavailable, expensive, fragile object, use simpler and inexpensive copies. 21. Skipping 2. Taking out Separate an interfering part or property from an object,

28 Mechanics substitution Replace a mechanical means 35. Parameter changes Change the degree of flexibility. 6. Universality Make a part or object perform multiple functions; eliminate the need for other parts. 18. Mechanical vibration Cause an object to oscillate or vibrate.

34. Discarding and recovering Make portions of an object that have fulfilled their functions go away Conversely, restore consumable parts of an object directly in operation. 23. Feedback 16. Partial or excessive actions Using 'slightly less' or 'slightly more' of the same method. 18. Mechanical vibration

It is logical to begin solution generations with the principles to solve the contradiction involving force and then checking for compatibility with the other contradictions. Inventive Principle 16 – suggests replacing the 90 degree-bend with a series of bends of smaller angles (e.g., six 15-degree bends in series). With smaller angles, fewer particles would hit the bends so less force would be imparted to the pipe wall. This solution will require a redesign of the pipe. Durability should be preserved because the number of particles hitting the bend will be reduced so the material will not be eroded away as quickly. Some increase in material may be required as the series of bends may increase the pipe length required to change the particle direction by 90-degree but the increase will not be as costly as thickening the pipe walls throughout the system. Inventive Principle 26, Copying, does not have ready application to this problem. Nor does Principle 21, Skipping steps in the system or process. However, using Principal 2, Taking out, does lead to a good solution. Taking out a part of the system leads to the idea of using an electromagnetic field to change particle direction.

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6.14 Students are required to repeat the application of TRIZ Inventive Principles to solve a technical contradiction in the design of the mechanical pencil they chose for Exercise 6.9. One problem common to all mechanical pencils is the need to store more lead in the pencil without increasing the size of the barrel of the pencil beyond a comfortable diameter. This is contradiction can be expressed in TRIZ terms as improving the amount of pencil lead (26) without degrading the weight of the pencil (1), the volume of the pencil (7) or the convenience of use of the pencil (33). Students will need to look up appropriate inventive principles and apply them to the design task. 6.15 Students are asked to write out the Design Matrix, [A], and identifiy the function requirements (FRs) and design paramaters (DPs) as defined by Axiomatic Design for the second portable syringe design described in Section 6.6.2. In the design equation below, the term HE stands for human energy and KE for kinetic energy

⎪⎪⎪

⎭

⎪⎪⎪

⎬

⎫

⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

=====

⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢

⎣

⎡

=

⎪⎪⎪

⎭

⎪⎪⎪

⎬

⎫

⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

=====

cuff & Strap tubing Flexible tool Shearing

cylinder and Piston Liquid

muscle into flow liquid Guide muscle Pierce

muscle near liquid Position liquid to KE Transfer KE to HE Convert

5

4

3

2

1

5

4

3

2

1

DPDPDPDPDP

XX00000X00000XX000XX000X0

FRFRFRFRFR

Recall that the design equation is defined as follows:

. DPADPADPADP A FR

DPAFR

nin1n)1n(i22i11ii

n

1j jiji

++++=

=

−−

=∑L

that so,

.DPFRA

j

iij ∂

∂=

For this syringe design, the matrix tells us that

5554545

3434

2321313

2221212

2121

DPADP A FRDP A FR

DPADP A FRDPADP A FR

DPAFR

+==

+=+=

=

In the language of Axiomatic Design the design matrix [A] is coupled. As shown by the equations, you can not fulfill all the function requirements by setting the value of an individual design parameter independent of the impact on other function requirements. For example, FR1 can fulfilled by setting the value of DP2, but the value of DP2 also influences the fulfillment of FR2 and FR3. The current design is such that FR4 is the only function that can be fulfilled by an independent decision about DP3. For example, FR1 relies on a single DP but 2 1DP links not only to FR

40

2 3but to both FR and FR , making all three DPs interdependent. So that the design process can proceed separately from the rest of the systems design. FR5 can be fulfilled by setting two other parameters at the same time, giving it a kind of separation from the system. However, since two design parameters affect the same function requirement it does not strictly follow the form of functional independence. 6.16 Students are asked to apply the design generation tools demonstrated in other exercises to the design of a garlic press. The typical garlic press uses the same physical parts to fulfill multiple functions so it tends to be a functionally coupled design. It will be difficult for students to justify redesigning a commercially available garlic press to satisfy the Axiom of Functional Independence. This result focuses on a weakness of Axiomatic Design as a general method. Namely, not all good designs display strict functional independence.

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CHAPTER 7

DECISION MAKING AND CONCEPT SELECTION

7.1

7.2 (a). Assume that you will know which competing products will be in the market. Choose the model you will launch under each of the three possible conditions. The strategy to use is decision-making under certainty. You will have three different answers; each one applies to the three possible market competition scenarios.

1. Acme launches their product: Launch Model a3 to earn 50% market share. 2. Luxur launches their product: Launch Model a1 to earn 60% market share. 3. Acme & Luxur launch their products: Launch Model a2 to earn 30% market share.

(b) In this scenario you are given insider information on the likelihood that the competitors will enter the market place.

The strategy to use is decision-making under uncertainty. This strategy applies because there are multiple scenarios and you know the probability of each. You choose the product that has the highest expected value of market share, E(ai), under the likelihoods you are given for the future scenarios.

%4.34)a(E%),20(20.0%)30(48.%)50(32.0)a(E%4.36)a(E%),30(20.0%)40(48.%)35(32.0)a(E%2.48)a(E%),25(20.0%)60(48.%)45(32.0)a(E

33

22

11

=++==++==++=

so so so

You choose to Launch Model a1.

(c) In this scenario you have no information on the behavior of competitors and you are told to act in a very conservative way. You interpret this to mean that you want to achieve the best possible outcome in scenarios in which the worst events occur.

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The strategy to use is Maximin. Under this strategy you maximize your minimum payoff. So, you assume that both competitors go into the market place. Your market share under those conditions can be read from the last column in table given in the exercise description. The products earn the following market shares: a1 earns 25% of the market; a2 earns 30% of the market; and, a3 earns 20% of the market. You want to maximize the outcome to you under these, the worst possible scenarios, so you choose to Launch Model a2. 7.3

Decision Criteria 1 . Maximize the net expected value. payoffs are +; costs are - High-tech: NEVht = -4M + 0.8(16M) + 0.2(10M) = $10.8M Low-tech: NEVlt = -1.5M + 0.3(12M) + 0.7[-3.2M + 0.8(10M) + 0.2(3M)] = 5.88M Therefore, the high technology alternative looks better. 2. Minimize the opportunity loss. Since the high technology option has the greatest payoff, any other strategy would represent an opportunity loss. We can determine the net opportunity loss by subtracting the low-tech option from the appropriate high-tech option.

This analysis shows that if the chance of the market accepting the technology is risky, then a low tech approach followed by an upgrade is a good strategy.

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7.4 Pugh concept selection for a fast-food coffee cup. We have substituted a paper cup with a cardboard sleeve for concept (e) in the problem statement, since it is a more current concept. DESIGN CONCEPTS Design requirements

Regular paper cup

Styro- foam cup

Rigid injection molded with handle

Double-wall biodegradable plastic

Paper cup with fold- out handle

Paper cup with cardboard sleeve

Temperature in the hand

+ + + + +

Material environ- mental impact

D _ _ + S S

Indenting force of cup wall

A + + + S S

Porosity of cup wall T + + + S S Manufacturing complexity

U + _ _ _ S

Ease of stacking the cups

M + _ S _ S

Ease of use by customer

S + S _ +

Temperature loss of coffee over time

+ _ + S S

Overall cost S - - - - +∑ 6 4 5 1 2

−∑ 1 5 2 4 1

S∑ 2 0 2 4 6

This problem illustrates that the Pugh chart is an excellent tool for quick comparison of alternative concepts, but that numerical values should be used with caution. A rigid summation of pluses and minuses should never be done. An analysis of this type would show that the Styrofoam coffee cup is superior to the paper cup (DATUM) and to all other proposed concepts. However, its one negative outweighs all other considerations. Since Styrofoam does not degrade in a landfill it is banned in many jurisdictions and strongly frowned upon in others. All concepts are superior to a paper cup in providing better thermal insulation so that the cup is not too hot in the hand. However, they are all more expensive than either a paper or Styrofoam cup. The biodegradable plastic cup would be a superior solution but it is the most expensive concept. The most widely adopted solution appears to be a paper cup with a cardboard sleeve. While it does not provide as much thermal protection as the two designs with handles, it is cost effective and acceptable to most people. Students often run through the Pugh chart without giving much thought to the task. It is important to emphasize to them that the chief benefit to using the Pugh Chart is the insight to the problem to be gained from deep group discussion. Often concepts with many minuses have the kernel of a winning idea when combined with other concepts.

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7.5 Hierarchical objective tree for determining weight factors The human mind has difficulty grasping more than five or seven factors at a time. Thus, if we focus on the four main factors, and break these down with a hierarchical objective tree or a relevance tree, the individual weighting factors are more readily determined.

For example, the weighting factor for workmanship = (1 /8) x (1/2) = 0.062. The complete list of weight factors is given in the table. Weight factor Weight factorBody (1/8) Reliability (3/8) 0.375

Interior (1/4) 0.031 Exterior (1/4) 0.031 Performance (1/4)

Workmanship (1/2) 0.060 Handling (1/3) 0.083 Cost (1/4) Brakes (1/3) 0.083

Purchase cost (2/3) 0.167 Ride (1/6) 0.042 Fuel economy (1/3) 0.083 Comfort (1/6) 0.042

Total 0.997 7.6 The weighting factors come from the following objective tree.

For example, the weighting factor for gas mileage is 0.25 x 0.7 = 0.175. Other objective trees can be constructed to be consistent with the weighting factors given in the problem.

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The scores in the decision matrix are taken from Table 7.4 and their value is based on the data given in the problem. The Rating in the weighted decision matrix is weight factor x score.

The decision matrix indicates that concepts B and C should be pursued further. Note that the results are strongly leveraged by the heavy weighting given to ride comfort. Is this justified in a sport-utility vehicle? Some students will be tempted to take a very literal approach to setting the scores where they interpolate fine differences between the values given in Table 7.4. They get confused between ranking (arranging in order) and rating (assessing against a scale). They may rate the alternatives as if they represent an entire population of values where half rate below average. This is usually inappropriate for set of feasible designs. 7.7 Each student is required to use AHP to solve the vehicle selection problem of 7.6 according to the student’s own personal preferences on the given set of vehicle performance criteria. The vehicle design options and the vehicle performance data from the problem remain the same. The method detailed in Section 7.3.5 can be used to complete the exercise. It is strongly suggested that students use an Excel spreadsheet to perform the calculations and matrix manipulations required by AHP. There is no single correct answer to this exercise. Each student will have unique preferences to guide the setting of weighting factors for the selection criteria. One possible solution is given in partial detail. 1. Complete the criteria comparison matrix [C] following the AHP methodology and using the AHP ratings for pair wise comparison of selection criteria in Table 7.6 in the text. 2. Normalize the matrix [C] by dividing each column cell by the column sum. The resulting matrix, Norm[C] is shown below with [C]. Please note that this solution was created when the price of gasoline was under $2/gallon. As a result, the preference for gas mileage compared to other vehicle selection criteria is not as high as it might be for an informed gasoline consumer today.

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[C]               

Criteria Gas 

Mileage Range 

Ride Comfort

Ease to 4WD 

Load Capacity

Cost of Repair 

 

Gas Mileage  1      3       1/3  5       1/3   1/7   Range   1/3  1       1/7  3       1/5   1/7   

Ride Comfort  3      7      1      9      5      3       Ease to 4WD   1/5   1/3   1/9  1       1/7   1/9   Load Capacity  3      5       1/5  7      1       1/3   Cost of Repair  7      7       1/3  9  3      1       

   14.533  23.333  2.121  34.000  9.676  4.730                  

Norm[C]               

Criteria Gas 

Mileage Range 

Ride Comfort

Ease to 4WD 

Load Capacity

Cost of Repair  {W} 

Gas Mileage  0.0688  0.1286  0.1572  0.1471  0.0344  0.0302  0.0944 Range  0.0229  0.0429  0.0674  0.0882  0.0207  0.0302  0.0454 

Ride Comfort  0.2064  0.3000  0.4716  0.2647  0.5167  0.6342  0.3989 Ease to 4WD  0.0138  0.0143  0.0524  0.0294  0.0148  0.0235  0.0247 Load Capacity  0.2064  0.2143  0.0943  0.2059  0.1033  0.0705  0.1491 Cost of Repair  0.4817  0.3000  0.1572  0.2647  0.3100  0.2114  0.2875 

   1.000  1.000  1.000  1.000  1.000  1.000  1 

3. The average of each row in Norm[C] is a provisional weight factor (e.g., 0.944 for gas mileage, 0.3989 for ride comfort). It remains provisional until the consistency of the pair wise comparisons is demonstrated. Maintaining consistency when the number of comparisons exceeds 9 is very difficult. The widely adopted benchmark for consistency in AHP matrices is that a precisely calculated consistency ratio (CR) must be less than 0.10. The CR calculations are based on the [C] and Norm[C] matrices values. If the CR exceeds 0.10, the decision maker must adjust the [C] comparison ratings to achieve an acceptable value. Much iteration may be necessary, supporting the use of an Excel spreadsheet for AHP exercises. The consistency checking process for the matrix values given above is shown below. The CR value is adequate at 0.097.

47

 

 

       Criteria  {Ws}=[C]  {W}  {W}   {Cons} =   {Ws}/{W} 

Gas Mileage  0.5777  0.0944  6.1210 Range  0.2788  0.0454  6.1435 

Ride Comfort  2.8300  0.3989  7.0937 Ease to 4WD  0.1563  0.0247  6.3303 Load Capacity  1.0076  0.1491  6.7567 Cost of Repair  2.0683  0.2875  7.1941 Average of {Cons} approximates lambda  6.607 

              n    6          RI    1.2500  function of n   CI    0.1213  (lambda‐n)/(n‐1)   CR    0.0970  CI/RI      

4. As the next step in AHP, each of the vehicle performance criteria must be used to compare and rate the four given design alternatives. Once that is finished, we can use the results and the consistent set of weighting factors to create the final step in AHP, a weighted decision matrix. Thus, we need to repeat the AHP process used to find weighting factors that represent the relative performance of the design options with respect to each of the six selection criterion. That means the process described in the prior three steps needs to be followed for each criterion. We will develop the pair wise comparison ratings between design concepts using the performance data given in the problem statement and the rating values in Table 7.9. The rating value definitions are changed to better reflect the reasoning used when comparing design option performance with respect to a criterion. The results for the gas mileage criterion are as follows.

[C]            

Miles Per Gallon  Gas Mileage  Design A Design B Design 

C Design 

D 

20  Design A  1  3  5  1 16  Design B  1/3  1  3  1/3 15  Design C  1/5  1/3  1  1/5 20  Design D  1  3  5  1 

    2.533  7.333  14.000  2.533 

Norm[C]              

Gas Mileage  Design A  Design B  Design C Design 

D  {W} Design A  0.395  0.409  0.357  0.395  0.389 Design B  0.132  0.136  0.214  0.132  0.153 

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Design C  0.079  0.045  0.071  0.079  0.069 Design D  0.395  0.409  0.357  0.395  0.389 

   1.000  1.000  1.000  1.000  1.000            {Ws}=[C]*{W}  {W}  {Cons} =   {Ws}/{W}     

1.5817  0.3889     4.0668    0.6188  0.1535     4.0327    0.2754  0.0687     4.0093    1.5817  0.3889     4.0668    

Average of {Cons} approximates lambda   4.0439                    

n  4           RI  0.89  function of n     CI  0.0146  (lambda‐n)/(n‐1)     CR  0.0164  CI/RI        

The results show that Designs A and D are equal in terms of performance on gas mileage with values of 0.389 out of 1. It is not difficult to achieve consistency when you have such clear information on performance as gas mileage values. The results for the cost of repair criterion are given below.

[C]           

Value ($) Repair Cost 

Design A  Design B  Design C  Design D 

700  Design A  1  1/3  1/5  1/9 

625  Design B  3  1  1/3  1/7 

600  Design C  5  3  1  1/5 

500  Design D  9  7  5  1 

    18.000  11.333  6.533  1.454 

Norm[C]              

Repair Cost  Design A  Design B  Design C  Design D  {W} Design A  0.056  0.029  0.031  0.076  0.048 Design B  0.167  0.088  0.051  0.098  0.101 Design C  0.278  0.265  0.153  0.138  0.208 Design D  0.500  0.618  0.765  0.688  0.643 

   1.000  1.000  1.000  1.000  1.000            {Ws}=[C]*{W}  {W}  {Cons} =   {Ws}/{W}     

0.1947  0.0480     4.0572    0.4063  0.1010     4.0208    0.8799  0.2083     4.2249    2.8234  0.6427     4.3931    

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Average of {Cons} approximates lambda  4.1740                    

n  4           RI  0.89  function of n     CI  0.0580  (lambda‐n)/(n‐1)     CR  0.0652  CI/RI        

Is it important to remember the direction of improvement desired in a criterion. In the case of gas mileage, higher is better. In the case of repair cost, lower is better. Therefore the best design option is Design D with a relative weight of 0.643 and the worst is Design A with a weight of 0.048. 5. The last step in the AHP process is to create the final decision matrix. Following is that matrix.

Final Decision Matrix 

Criteria Criteria Weights

Design A 

Design B 

Design C 

Design D    

Gas Mileage  0.094  0.3889  0.1535  0.0687  0.3889  1.0000 Range  0.045  0.2083  0.0480  0.1010  0.6427  1.0000 

Ride Comfort  0.399  0.0569  0.5579  0.2633  0.1219  1.0000 Ease to 4WD  0.025  0.6470  0.1481  0.1481  0.0567  1.0000 Load Capacity  0.149  0.4236  0.1007  0.4236  0.0521  1.0000 Cost of Repair  0.287  0.0480  0.1010  0.2083  0.6427  1.0000 

   1.000  0.1618  0.2869  0.2428  0.3084  1.0000  AHP’s decision matrix indicates that the best solution alternative is Design D, with Design B coming in as a close second choice. This is different from the solution for Exercise 7.6 for two reasons: different performance criteria preferences were chosen and a more structured decision-making process was used. Additional Material Once the AHP problem is set up, it is easy to reflect changes in preferences for criteria. The individual design performance vectors, {W}, remain the same. Only the criteria weighting factors need to be changed. The following is a new decision matrix created in a consumer market where gasoline has risen to $4/gallon and there is no assurance that it will stay at this level.

Final Decision Matrix with High Gasoline Prices 

Criteria Criteria Weights

Design A 

Design B 

Design C 

Design D    

Gas Mileage  0.235  0.3889  0.1535  0.0687  0.3889  1.0000 Range  0.087  0.2083  0.0480  0.1010  0.6427  1.0000 

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Ride Comfort  0.446  0.0569  0.5579  0.2633  0.1219  1.0000 Ease to 4WD  0.029  0.6470  0.1481  0.1481  0.0567  1.0000 Load Capacity  0.088  0.4236  0.1007  0.4236  0.0521  1.0000 Cost of Repair  0.114  0.0480  0.1010  0.2083  0.6427  1.0000 

   1.000  0.1966  0.3138  0.2079  0.2817  1.0000  The increased emphasis on gas mileage as a decision making criterion results in the recommendation of Design B as the clear favorite.

51