Welcome W 7.1 Introduction to Engineering Design II (IE 202) Chapter 4: Design Requirements 1 1

Today’s Learning Outcomes By the completion of today's meeting, students should be able to: Specify functions. Express attributes and functions. Practice Functions and Requirements. 2 2

Preview What have we covered so far? Overall design process Project management Problem definition 3 3

2nd Task in the Design Process 4 4

Design Requirements Specifying functions, behavior and attributes: Attaching numbers to design requirements (utility function) Setting performance levels (threshold, saturation plateau) Interface performance requirements 5 5

Objectives vs. Functions Objectives specify the qualities or attributes of a “good” design, and are usually expressed in the language of the client or users. Functions express the actions that the designed artifact must perform to accomplish the designer’s intention successfully . Functions are often expressed in the language of engineers or scientists, in the form of verb-object pairs. 6 6

Requirements/Specifications Prescriptive requirements answer questions of “how well” an artifact must do a function (values - the thickness of a ladder step will be > 10 cm) Procedural Requirements: procedures for calculating the behaviour (it will be made of disposable materials). Performance requirements: performance levels that must be met (by testing) for successful behavior (shall carry 50 kg loads). 7 7

Performance Specifications Metrics and performance specifications are similar. Metrics apply to objectives. Performance specifications are usually applied to functions and physical characteristics. Metric values are usually based on judgements. Performance specifications are compared with test results of the artifact. 8 8

Setting Performance Levels Setting prescriptive performance specifications usually depends on having done a good job of determining all the functions. For each function, the designer asks questions such as “how much” or “what range is of interest”, etc. 9 9

Can you think of answers? An example The textbook presents the guitar as a design problem, what would be the requirements and design specifications? Can you think of answers? 10 10

Answers Support strings in proper location. Vary tension of individual strings. Accept user input to vary effective length of strings. Convert mechanical vibration into electrical output. Process electrical signal (e.g., tone and volume control). 11 11

Interface Performance Specs Particularly important for systems that must work with other systems This is very common, and requires a good deal of attention Black box functional specification tools are often quite useful in this area 12 12

Can you think of answers? The example (Cont’d) Think of the guitar again, and try to explore the interfaces. Can you think of answers? 13 13

Answers guitar - amplifier interface for getting the louder sound (usually a plug) guitar - player’s hand (strumming). guitar - player’s other hand (fret board). guitar - player’s body (affects shape of guitar, use of strap, or both). guitar controls - player (some guitars use knobs or slider bars). 14 14

Team Practice Suppose that the university decided to build a train system to transfer students from one place to another in the campus. What would be the requirements and performance specifications the train system must have? Can you come up with possible interfaces? Work as teams. 15 15

Exercise # 4 This is an exercise to be solved as a team. The answer should be submitted electronically. The file name for your work when submitted should be: Exercise # 4 – Z?? e.g. Exercise # 4 – ZX9 16 16