Engineering Design Methods: Clarifying Objectives

• Design Methods Lecture 2 focuses on clarifying objectives in design.
• Presenter: Badziili Nthubu, PhD, Lecturer in Mechanical, Energy, and Industrial Engineering.
• Date: Feb 19th, 2025.
• Venue: 125/005-006.

Project Assignment 1

• Need to read Chapter 5, page 61, of "Nigel Cross' Engineering Design Methods: Strategies for Product Design".
• It involves clarifying objectives in groups and creating an objective tree of functional objectives.
• Objectives should be formulated as [verb+noun] statements, as shown on page 73.
• Non-functional objectives such as reliability and safety will not earn marks.
• The assignment is due by 21/02/2025 at 1600 hours as a typed PDF document.
• Marks allocation: Submission on time (10 marks), presentation (20 marks), clarity of objectives (20 marks).

Clarifying Objectives

• Objectives are aims and conditions a designed object must meet, satisfy, or achieve.

Topic Outline

• Class activity : What are Design Methods?
• Objectives clarification is a design method.
• Focus on the position and context of 'OBJECTIVES CLARIFICATION' in the Design Process.
• Explore why objectives are clarified and how it differs from performance specs/product design specs.

Design Methods

• Engineering Design Models with DESCRIPTIVE & PRESCRIPTIVE flow diagrams, DO NOT answer the HOW in design.
• Design methods answer questions about DOING DESIGN and involve at least 4 steps from Nigel Cross.
• Design Methods are aids, tools, and support systems used to establish REQUIREMENTS and identify OPPORTUNITIES.
• These Methods are based on human needs which can transform into PERFORMANCE SPECIFICATION and FUNCTIONS
• They can be mapped and converted (under CONSTRAINTS) into DESIGN SOLUTIONS using creativity, scientific principles and technical knowledge, which can be economically manufactured and produced.

Position & Context

• Basic Design Model is a linear process: Exploration, Generation, Evaluation, Communication
• Design Methods help establish requirements and transforming them into performance specifications and functions
• Further maps them into Design Solutions

Clarifying Objectives

• It is one of the stages between CUSTOMER'S NEEDS and GENERATING DESIGN IDEAS.
• Can also can be referred to as: Engineering design specifications, Engineering requirements, Design requirements, Functional requirements, Objectives and constraints, Technical requirements, Technical specifications, Client requirements, User needs, PRODUCT DESIGN SPECIFICATIONS, problem definition.

Ulrich and Eppinger's Specifications

• A specification is a design parameter with a metric and a value/
• Example : Max Time to cut tile 60 seconds

Samuel & Weir's Specifications

• Goal: The overall intent in one sentence without reference to means.
• Objectives: Desired features of a design and major aspects of performance.
• Criteria: A scale for measuring success of a proposal in meeting a particular objective.
• Specification, as defined by Ulrich and Eppinger in the previous slide

Objectives / Constraints/ Requirements

• Constraints are required capabilities with mandatory limits. Such as meeting BOBS specifications and being able to support a 100kg load.
• Requirements are non-mandatory design limits or relaxable constraints.

Criteria & Guidelines

• Legally Imposed Requirements, Design Requirements, Standards, Discipline Requirements
• Not Legally Imposed : Guidelines
• Including Evolved Requirements on System, Subsystem Components : Eg Redundancy POGO, Accumulator Sensor Noise Requirements
• Product Design, Working on the boundaries, Philosophies and practices of the design process

Goals & Objectives

• They are elicited and generated before starting design.
• They represents "something" that the design must do
• Functional: Actions that the system must perform
• Nonfunctional: Places the bounds within which to perform the functions
• Demands: enhances the working of the system.
• Wishes: Not part of the functions or attributes of the system

Ullman's Classification

• Functional performance requirement
• Human factor requirement
• Physical requirement
• Reliability requirement
• Lifecycle concern requirement
• Resource concern requirement
• Manufacturing requirement

Use Of Checklists

• Design requirements checklists are lists of questions designers use to create design specifications.
• Designers create systematic approach to the creation of requirements.
• Checklists ensure no requirements are left out.
• Provides list of basic performance and physical characteristcs
• Includes standards, ratings, specifications, operating cycle
• Interfaces with requirements for materials
• Packaging handling and storage must also be accomodated
• There must be acceptance and transportation measures

Objectives Generation or Elicitation Tools

• Reuse of product design specifications,
• Whereby the new design work is based on a previous version
• Requirements Engineering [Karlsson & Rosenblad 1998],
• Design teams make their design choices accessible to users
• Users are invited to offer suggestions and input.
• Works when design team has easy access to users
• Voice of the customer,
• Quality Function Deployment

Software Engineering Tools

• Software Engineering Tools can be broken down to the following diagram
• Stakeholders, Requirements Elicitation, Prototype, Specifications and Rejection.

Requirement Elicitation

• Design problems are usually ill-defined and ill-structured.
• Formulation is not always definitive
• Some formulations emobody incosistencies

Objectives Interconnectedness

• Objectives Interconnectedness is broken down to the following
• Reliability
• Performance
• Manufacturing
• Geometry / Interface
• Cost
• Shedule
• Maintainability

Clarifying Design Objectives

• Clarifying Objectives is the FIRST STEP under Design Methods and comes immediately after any DESIGN BRIEF.
• It defines the set of objectives that the designed object must meet.
• Objectives are used to control and manage the design process.
• Designer has to do this step as customer needs are rare

Objectives Tree Method

• The Objectives Tree Method ensures that the client and designer must agree on the objectives.

Preparing A list Of Design Objectives

• Some objectives may be contained in the Design Brief.
• Other objectives come from questioning the client/ team
• Vagueness can be expanded, E.G machine tool must be safe
• Questions such as What, Why, and How are useful in clarifying objectives

Ordering Objectives

• Objectives tend to assume a means-end relationship.
• "automatic power cut off on overload" is a means of achieving "low risk of damage to the machine or work-piece".
• Must be ordered with the highest level objectives put into groups such as Safety, Reliability, Cost, etc.

Objectives Tree Method Example

• Machine must be safe
• Low risk of operator mistakes
• Low risk of injury to operator
• Low risk of damage to work-piece or tool
• Automatic cut-out on overload

Objectives Tree Widget Case Study

• Step 1: Problem Statement : Design a New Widget to supplement an existing part.
• Step 2 : Assumptions the part must compliment the existing part
• Justification students must be familiar with this existing part
• Step 3: Chart : Create and Objective Tree
  • Must measure four main groups -- Resources -- Economics -- Scope -- Technological
• Step 4 : Execute, test and iterate
• Ask for buy in to ensure a viable and satisfied customer results