Other Methods to Generate Specifications

List Generation: Categories of Specifications

A list of specifications can be generated by studying a list of general categories of specifications.  The list below was proposed by Franke in 1975.

  1. Geometry – Dimensions, space requirements, etc.
  2. Kinematics – Type and direction of motion, velocity, etc.
  3. Forces – Direction and magnitude, frequency, load imposed by, energy type, efficiency, capacity, conversion, temperature
  4. Material – Properties of the final product, flow of materials, design for manufacture (DFM)
  5. Signals – Input, output and display
  6. Safety – Protection issues
  7. Ergonomics – Comfort issues, human interface issues
  8. Production – Factory limitations, tolerances, wastage
  9. Assembly – Set by DFMA or special regulation or needs
  10. Transport – Packaging requirements
  11. Maintenance – Servicing intervals, repair
  12. Costs – Manufacturing costs, material costs, tooling costs
  13. Schedule – Time constraints

Using FSD”s to Generate Specifications

Function Structure Diagrams (FSD) can be used to help a design team generate specifications.  The first step is to look at the inputs and outputs and ask the following questions:

  • How much of an input or an output is required?
  • What conditions should the inputs or outputs meeet?

To illustrate this method, consider the function structure diagram for a coffee bean roaster shown below.  The inputs are start signal, roast level, beans and electricity.

Function structure diagram of a coffee been roaster.

Applying are two generic questions te each input yields some interesting possibilities for specifications.  The possible specification topics are shown in the table below.

Specification topics
Roast Level The number of roast levels available.
Beans Quantity of beans the machine can process.
Electricity The maximum number of Volts and amps the machine will draw

Specification topics
Heat The highest allowable temperature of air escaping the machine.
Noise Maximum permissible noise.
Roasted Beans The maximum temperature of the roasted beans.Maximum time required to roast the beans.


Consider the Context of the Product

Context is the set of circumstances or setting in which an product is used, maintained and discarded.  A customer’s satisfaction with a product depends on the context of the product’s use.  Context factors can be diveded into four categories shown in the table below.


Sample Context Factors

HOWApplication Context
  • Application task
  • Usage frequency
  • Transportation mode
  • . . .
WHEREEnvironment Context
  • Infrastructure (e.g. energy & cost)
  • Weather and climate
  • Maintenance and parts availability
  • . . .
WHOCustomer Context
  • Physical Abilities
  • Skills and education
  • Cost expectations
  • . . .
MARKETThe Competition
  • Features of available products
  • Performance and quality of available products
  • Cost of available products

Consider each context factor,  what topics for specifications does the context factor trigger in your mind?  Applying this technique to our coffeee bean roaster example yields some interesting possibilities for specifications.  The possible specification targets are show in the table below.

Context Factor

Specification topics
HOWApplication Context
  • Volume of beans the device can roast
  • The number of roasting cycles in the product expected life.
  • Cycle time for the device.
  • Time to clean the device.
WHEREEnvironment Context
  • Volts and amps available in a kitchen.
  • Resistance to chemical cleaners.
  • Mean time between failures.
  • Volume required for storage.
WHOCustomer Context
  • Maximum production cost.
  • maximum weight.
  • Number of roast options.
MARKETThe Competition
  • Drop test specification.

Do You Have a Complete List of Specifications?

Were all stake holders consulted?

Does your list of specifications describe exactly what the product must do to satisfy the customer?  Remember the finished design will be tested to meet the specification.

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