Design Requirement/Constraints

Ref: Voland, G., Engineering by Design. Addison Wesley, 1999

& Larry Hand, Peavey Electronics, 2000

So you have figured out what you are going to do (Problem Statement), what next?

So you have figured out what you are going to do (Problem Statement), what next?

Create the technical formulation of the problem!

A technical formulation takes an idea and translates it to an engineering context, complete with relevant objective technical and practical design constraints and appropriate theory and design methodologies needed to address the design. 

It translates a design idea into a set of related, feasible engineering specific problems.

A technical formulation takes an idea and translates it to an engineering context, complete with relevant objective technical and practical design constraints and appropriate theory and design methodologies needed to address the design. 

It translates a design idea into a set of related, feasible engineering specific problems.

Constraints are a “Good Thing”

• Define the boundaries within which the search for solutions must be conducted

• Enhance the effectiveness of the design

• Avoid designs that are illegal or hazardous

• Make designs economically viable

Types of Constraints or Specifications

• Can be broken down several waysExample: Bus specification

Physical (dimensions, connectors, pins)Functional (arbitration protocol, read cycle)Electrical (impedance, max/min signal levels)

• We will use– Technical Design Constraints– Practical Design Constraints

Technical ConstraintsRequirements on which technical aspects of the

design hinges• Signal tolerances (> 30% duty cycle clock at 1MHz +/-1%)

• Supply current range (.5 mA min to 100 mA max)

• Power efficiency (83% supply efficiency at rated load)

• Speed (interrupt service latency < 1 S)

• Conversion rate (12-bit conversion at 500Ksamples/sec)

• Transmission distance (100 M with unobstructed view)

• Quantization error (+,- 5mV)

• Frequency response (20 Hz to 20 KHz, +/- 3 dB)

• Signal-to-noise ratio (50 dB min)

Practical Design ConstraintsBroader issues affecting design’s success

• Economic

• Environmental

• Sustainability

• Manufacturability

• Ethical

• Health and Safety

• Social and Political

Economic

• Limits on Production Cost

• Depreciation of Equipment

• Operating Cost

• Service or Maintenance Requirements

• Existence of Competitive Solutions in the Marketplace

How is Cost Determined(Note that cost is NOT price)

How is Cost Determined(Note that cost is NOT price)

• Material Cost

• Labor Cost

• Manufacturing Burden

• Selling, General, and Administrative Expense (SG&A)

Example Case:How Much does it Cost

Example Case:How Much does it Cost

• Material Cost --- 52% of Total Cost– Unit Price * Quantity for all (Bill of Materials)

BOM items

• Labor Cost --- 8% of Total Cost– Direct labor or value added labor required to

manufacture the product

How Much Does it CostHow Much Does it Cost

• Manufacturing Burden --- 17% of Cost– Indirect Labor – Utilities– Facilities– Employee Benefits– Depreciation, rent, etc..

How Much Does it CostHow Much Does it Cost

• Sales/General and Administrative -- 23% – Cost of Selling the Product– Sales commission– Advertising– Service and Warranty– Corporate Management– Research and Development– Bad Debt, etc..

Environmental

• Temperature Ranges

• Moisture Limits

• Dust Level

• Intensity of Light

• Noise Limits

• Potential Effects Upon People or Other Systems

SustainabilitySustainability

• If you birth it, It’s always your baby

• Customer complaints

• Obsolete & sole-source Parts

• Warranty claims and field failures

• Specification changes in standard components

ManufacturabilityManufacturability

• Programs for Automated Assembly Equipment– Axial Sequencer and Insertion– Radial Insertion– DIP Socket and IC insertion– Surface Mount Chips, IC’s, Odd Shaped

Components– Automated Test

More things to considerMore things to consider

• Mechanical Design and Packaging– Space Allocation or Dimensional Requirements– Weight– Material Characteristics– Power Requirements

• Protect Unit During Shipment• Attractive at Point of Sale• Advertising• OEM or Consumer packaging

Legal

• Governmental Safety Requirements

• Environmental or Pollution Control Codes

• Production Standards

Health and SafetyHuman Factors/Ergonomics

• Users Characteristics– Strength– Intelligence– Anatomical Dimensions– Visual Acuity– Hearing Discrimination– Reaction Time– Reading Skills

Social and PoliticalAgency Approvals

Social and PoliticalAgency Approvals

• UL• CSA• FCC• NOM• CE• NEMKO• DEMKO

• VDE• IRAM• SASO• SANZ• SAA• JIS• and more.....

Sources of Engineering Standards

• Companies

• Engineering Societies

• Governments (U. S., others)

• Special Interest Groups

• Federations of Private and Public Interests (American and International)

• Independent Laboratories

ExamplesSee http://www.dma.org/~rohrers/subject/standorg.htm for extensive list of links

• ACM (Association of Computing Machinery)

• AES (Audio Engineering Society)

• ANSI (American National Standards Institute)

• EIA (Electronic Industries Association)

• ESD (Electrostatic Discharge Association)

• IEEE (Institute of Electrical and Electronics Engineers)

• ISO (International Standards Organization)

• ITU (International Telecommunications Union)

• OSHA (Occupational Safety & Health Administration)

• PCI SIG (PCI Bus Special Interest Group)

• UL (Underwriters Laboratories)

• USB Developers (Universal Serial Bus Developers Forum)