Design Process 중앙대학교 전자전기공학부
2. Design Process • Engineering • : Problem solving through specialized scientific and mathematical knowledge • Engineer • : People who solves a variety of problem as a routine part of their job • Engineering problem • : So complex, the engineer cannot instantly see the solution. therefore, the methodological approach becomes more important In chapter 2, we will focus on the methodological engineering design process to tackle a complex problem
2.1 General engineering process Customer needs Engineer’s translation of needs including desired outcomes Synthesis : Putting together of parts or elements so as to form a whole, typically associated with a new system Analysis: A separating or breaking up of any whole into its part, especially with an examination of these parts to find out their nature, proportion, function, inter relationship, etc REPEAT (Find Solutions) Decision: Best solution being among the solution found increase number of solution generated, how many solution needed to explored? TRADE - OFF
Let’s cast a die!!! (Example 2.1) Each face of the die has one of six possible solutions! We don’t know the value of six possible solution until casting The cost of obtaining a solution is 1 M$. How much money is required for the first solution? How much money is required for the 6th solution? • Probability problem >> 6 M$ - Only one casting needed : 1M$ Engineer does not know the worth of any solution that has not been obtained, the only way the engineer can be sure to obtain the best solution is to obtain all six, however, the cost of all solution is relatively high. And the most expensive is likely to obtain 6th solution Decision making whether further solutions are developed is very important
2.2 Applying the general engineering process • 1. Symptom, Problem: • AC outlet circuit to power block heater get overloaded time to time, the unsuspecting user plug their block heaters into dead outlets • Block heaters burn out and go open circuit • 3. Customer has to know if things were not working properly when they plugged in their block heaters. Oops, Engine block heater is out of order 2. Problem definition Design a device to be integrated with an extension cord that will detect the difference 0.5 A (not working) and 3 A (working). The device must not consume more than 5 Watt and its manufactured cost including the cost integration must be less than 6 dollars Block heater: preventing engine oil from getting viscous on the cold winter days 3. Synthesis First attempt using LED 4. Analysis High current LED is too expensive 3A (working) 0.5A (Out of order)
Repeat synthesis/analysis again! 3.1 Synthesis 1st solution using current transformer 3.2 Synthesis 2st solution using Light bulb with momentary switch 4.1 Analysis - Transformer equation - Cost : 4.5$ 4.2 Analysis - User has to push the switch when he or she uses - Cost : 4.0 $ Ask to the Customer Which one is better?
2.3 Evaluation of alternative solutions • General engineering process has been described in terms of arriving at a “best” or “optimum” solution. • In most practical situations, true optimum solutions are impossible • to derive. The best that can be achieved is near optimum, or the best among several alternative. • How we decide which of several solution is the best alternative? The problem definition is the yardstick for judgment and therefore it becomes a critical step in the design process. Main factor judging the design performance cost Reliability maintainability If a decision is difficult to make, it is probably because there is not much difference in the worth of the alternatives. Do not waste time agonizing over these decisions. Simply flip the coin!!!
2.4 Design methodologies Given 10,000 4-digit numbers. Add the numbers with a hand-held calculator and submit their answers. Contestants whose answer is correct are ranked in the order of submission. Contestants submitting incorrect answer disqualified. The object is to finish with a high rank. Methodology A Methodology B - Focusing on getting correct answer - Focusing on minimizing key strokes - Add all numbers and do it again until two sums are the equal - Partitions numbers to 100 pieces - Same tactics for 100 number - Same tactics for 100 pieces If both contestants make no errors A is more faster than B If both contestants make the same number of errors B is more faster than B
2.4 Design methodologies Methodology A Methodology B - Considers only one possible solution - Considers a number of solution at a time - Completes the detailed design, implement the solution and evaluates according to design criteria - Does not carry them to the detailed design and implementation stage instead, only completes initial or block-level design - Repeat until satisfactory solution is obtained • Evaluate the block-level design and discard some solution not satisfying the criteria • Select some promising solution for further investigation - More effort and thought is devoted to unused solution - Less expensive, Fast development time Design methodology affects both the efficiency and effectiveness of engineer.
Design methodologies • A subjective comparison of design methodologies is an onerous task for the primary reason that engineering problems have multidimensional evaluation criteria. Design Criteria Consumer product Industrial product Sensitive to Cost Sensitive to Performance • A good design methodology must determine early in the process whether or not the problem can be solved
2.5 A methodology for high quality documentation Design criteria - Consumer product: Cost - Industrial product: Quality Ideal design methodology (does not allow for correction of mistakes) Practical design methodology
2.5 A methodology for high quality • Action item 1 • Action item 2 • Action item 3 Requirement specification • Action item 1 • Action item 2 • Action item 3 Documentation System specification • Action item 1 • Action item 2 • Action item 3 Functioning module • Action item 1 • Action item 2 • Action item 3 This chapter provides us an overview of a design methodology, In next chapter, the associated concept will be explained Ideal design methodology (does not allow for correction of mistakes) Practical design methodology