Engineering & Technology · Engineering Design Methods & Trade-offs
Functional decomposition and generating alternative concepts
A tool carrier must contain tools, support their weight, permit movement and tell someone where each tool belongs. Calling every function “make a box” would hide these separate jobs. Functional decomposition opens them up so that different concepts can be assembled and questioned.
Use the opening design, measurement, sketching and everyday-materials ideas as support. This chapter introduces its own comparison tools and explains the simple weighted sums and cost equations when needed. All users, observations, test results, prices, dimensions and energy values are constructed teaching cases. None is a product specification, legal compliance assessment, real study or population capability limit.
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Separate what a solution must do from the mechanisms that might do it.
Describe a function with an action and an object
A function describes an action: contain tools, transmit a carrying load, restrain movement or show tool positions. A component is one proposed means: wall, handle, strap or label. Beginning with functions helps avoid assuming a particular component before alternatives have been explored.
Decomposition divides a broad function into smaller related functions. “Return tools” can involve identify the destination, hold the set together, move it, place it near storage and release each tool. Some steps are performed by a person; others may be supported by an object or information. The system includes those interfaces, not only the carrier’s material.
Generate different means, then test their compatibility
For each function, sketch several mechanisms. Containment might use a shallow rim, separated pockets or a closing cover. Movement might use two side grips, a central handle or a wheeled base. Identification might use printed outlines, shaped locations or a separate inventory card. A table of functions and alternative means is sometimes called a morphological chart.
Choosing one means for each of three functions can generate many combinations, but not every combination works. A central handle might obstruct tool removal; a cover might hide the identification marks; a wheeled base needs a suitable route and storage space. Interfaces are where separately reasonable ideas can conflict. Note compatibility before spending effort scoring complete concepts.
The diagram shows three functions with two alternatives each. The count 2 × 2 × 2 = 8 describes the possible combinations before compatibility checks. It does not claim eight useful designs or eight completely independent ideas.
Compare complete concepts at a similar level of detail
Write each candidate as a short description plus a sketch: how it is held, how tools are retained, how they are removed, and where identification appears. Include how the carrier is cleaned and stored. Comparing a carefully detailed favourite with a vague alternative makes the favourite look better partly because of presentation.
Look for a concept that changes the task itself. Moving the return shelf closer to the work area might reduce the need to carry tools far. Keeping the existing system with clearer markings can be a genuine alternative. The team still needs to check that such changes satisfy the same underlying need and do not shift the difficulty to someone else.
Keep discarded concepts with brief reasons. An idea rejected because a route is too narrow could become useful if the route changes. A decision record should distinguish a demonstrated incompatibility from an untested concern or a preference.
Prune a concept without closing the search too early
An invented chart offers two containment methods, two carrying methods and two identification methods: eight nominal combinations. Two combinations place a fixed handle directly over a required removal path. If those are the only demonstrated conflicts, six combinations remain for further examination.
Record the conflict as an interface problem, not as “handles are bad”. A removable or offset handle might change it. The function still needs a means of transmitting the carrying load, so deleting the handle without supplying another means would leave the concept incomplete.
Select a few structurally different candidates for inexpensive mock-ups. The count of remaining combinations guides exploration; evidence about the actual task guides selection.
Try the reasoning
Is “plastic lid” a function?
Show the answer and reasoning
It is a proposed component and material. “Retain tools during movement” is a function that a lid or another mechanism might serve.
Why can eight chart combinations yield fewer than eight feasible concepts?
Show the answer and reasoning
Some mechanisms conflict at interfaces, duplicate a job, or fail a constraint when combined.
Why retain an alternative that uses the existing carrier?
Show the answer and reasoning
It may meet the need with less change. It deserves the same explicit task and requirement checks as a new object.
What to carry forward
Generate means for functions, then examine their interfaces. A list of components is not yet a complete working concept.
References
Teaching resources and research supporting this lesson’s explanations and examples.