Engineering & Technology · Engineering Design Methods & Trade-offs

Ergonomics, accessibility and human-system interaction

A carrier fits its tools perfectly but asks a person to pinch two small catches while lifting the lid. Someone with limited finger movement cannot open it easily. Another person misreads the closed catch as an open one. These are design interactions to investigate, not evidence that the people need to become better users.

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.

Back to the chapter

After reading, you can

Examine physical and cognitive interaction across users, tasks and environments.

Fit the task to people’s capabilities

Ergonomics considers people’s interaction with tasks, equipment and environments. It includes physical factors such as reach, posture, grip, force and repetition, and cognitive factors such as noticing information, understanding a state and choosing an action. A design that reduces one demand can increase another: a lighter flexible wall may require a more awkward grip to stop it bending.

Accessibility asks whether people with different capabilities can use a system and obtain its intended outcome. Consider limited vision, hearing, movement or dexterity, as well as differences in experience and language. Temporary injury, gloves, glare or carrying another object can change the interaction too. These examples do not make everyone’s needs identical; they help identify conditions a single idealised user would miss.

Inspect the approach, action and feedback

A reachable control may still be unusable if a table blocks the approach or a lid requires an uncomfortable force. Draw the approach space, obstructions, needed body position and the motion of the device. Then observe representative use. Published accessibility dimensions apply within their own scope; a generic sketch cannot establish compliance or predict each person’s reach.

The figure compares two invented placements on the same top-view geometry. A target 450 mm from the near edge with a 200 mm intervening obstruction has a different approach problem from a target 250 mm from the edge in a clear lane. The numbers teach geometry only. They are not recommended reach limits or population measurements.

For a catch or display, check the sequence: can the person find it, understand what state it is in, act on it and recognise the result? Position a label near the thing it describes. Use more than colour alone for an important state, such as a visible position plus a word or shape. Make mistaken actions recoverable where the task permits.

Both top-view surfaces are 600 mm deep. A target is 450 mm from the near edge with a 200 mm-deep obstruction; B target is 250 mm from the edge with a clear lane. These are invented dimensions, not accessibility limits.

Evaluate outcomes and effort together

Invite people with relevant access needs into research and provide a usable research setting. Ask them to carry out a meaningful task without teaching the answer in the task wording. Record unsuccessful attempts, assistance, workarounds and comments alongside time. A rapid action that causes pain or a frequent wrong selection is not a successful interaction.

Do not average away an excluded group. If most participants complete a task but one cannot operate the catch, the barrier remains. Examine whether an alternative action, adjustment or different arrangement can preserve the intended outcome. User trials complement, rather than replace, applicable requirements and professional assessment for the actual context.

Compare use without hiding an accessibility barrier

In an invented mock-up trial, five of six participants open catch A without assistance and all six open catch B. A’s five successful times sum to 50 s, giving 10 s per successful attempt. B’s six times sum to 72 s, giving 12 s per successful attempt.

Calling A better because 10 is less than 12 ignores the person who could not open it and compares different sets of successful attempts. Keep completion counts and assistance separate from times, investigate the barrier, and compare representative tasks again. Six constructed cases cannot establish a population success rate.

Try the reasoning

Why can a control’s height alone be insufficient to assess access?
Show the answer and reasoning
Obstructions, approach space, action, force and the user’s capabilities also matter. A location is only part of the interaction.
Why show completion count beside average time?
Show the answer and reasoning
Timing only successes hides people who could not complete the task and can make an exclusionary option look faster.
Does an invented 250 mm target position establish a recommended accessible reach?
Show the answer and reasoning
No. It is geometry for this example. Reach suitability and applicable requirements need context-specific evidence.

What to carry forward

Evaluate approach, action and feedback with the people and conditions the design must serve.

References

Teaching resources and research supporting this lesson’s explanations and examples.