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.
- Geometry – Dimensions, space requirements, etc.
- Kinematics – Type and direction of motion, velocity, etc.
- Forces – Direction and magnitude, frequency, load imposed by, energy type, efficiency, capacity, conversion, temperature
- Material – Properties of the final product, flow of materials, design for manufacture (DFM)
- Signals – Input, output and display
- Safety – Protection issues
- Ergonomics – Comfort issues, human interface issues
- Production – Factory limitations, tolerances, wastage
- Assembly – Set by DFMA or special regulation or needs
- Transport – Packaging requirements
- Maintenance – Servicing intervals, repair
- Costs – Manufacturing costs, material costs, tooling costs
- 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.
Applying are two generic questions te each input yields some interesting possibilities for specifications. The possible specification topics are shown in the table below.
Input |
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 |
Output |
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
Category
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Sample Context Factors
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HOWApplication Context |
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WHEREEnvironment Context |
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WHOCustomer Context |
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MARKETThe Competition |
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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 |
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WHEREEnvironment Context |
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WHOCustomer Context |
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MARKETThe Competition |
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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.