Question 1 of 7: Improving Product Functionality for a Specific User Group

Question 1: Improving Product Functionality for a Specific User Group (40 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

The product selected is the can opener, and the user group is adults with reduced hand function — principally osteoarthritis and rheumatoid arthritis of the hand, which affect roughly six million Canadians and reduce grip and pinch strength to between a quarter and a half of the healthy adult value. The can opener is a good vehicle for this question because it is one of the few remaining kitchen tasks that is genuinely gated by hand strength: a person who cannot open a can cannot feed themselves from the pantry, so a small mechanical change buys a large gain in independence. The design direction chosen and carried through every part below is shift the task from a strength-and-dexterity task to a low-force, low-precision, self-locating task, without changing the product category, its price point or its retail channel.

Part A — Three general ways to make a product more functional for a specific user group (9 marks)

The three levers below are deliberately general: they are the three ways any product can be made more usable by a group whose capabilities sit at the edge of the population the product was originally scaled for. They correspond to the low-physical-effort, simple-and-intuitive-use, and perceptible-information / tolerance-for-error clusters of the seven Principles of Universal Design, and they are ordered by how early in the design process they must be settled.

1. Reduce the physical demand — the peak force, the sustained force and the endurance the task requires. Every product embeds an implicit assumption about the strength of its user, usually the fiftieth-percentile healthy adult. Designing for a specific user group means re-deriving the force chain against that group’s capability distribution rather than the general one, and then changing the mechanics — lever ratios, gear ratios, spring rates, the working principle itself — until the demand falls below it. The important distinction is between peak force, which a user can often muster briefly, and sustained force, which fatigues quickly and is what actually defeats an arthritic user; a mechanism that latches, so that a clamping force is applied once rather than held for thirty seconds, removes the sustained demand entirely and is usually cheaper than doubling the lever ratio. This lever is a genuine engineering change, not a styling one, and it must be settled at the concept stage because it determines the architecture.

2. Reduce the precision, dexterity and coordination the task requires. Force is only half of hand function; the other half is fine motor control — the ability to pinch, to aim, to hold two things in a fixed relationship while doing a third. Reducing this demand means replacing fine motor actions with gross ones (a lateral pinch on a small key becomes a power grip on a large knob), making features self-locating so that the user does not have to achieve alignment (a V-groove that seats itself on the can rim rather than a wheel the user must position), enlarging the contact surfaces so that a weak grip does not have to be a precise grip, and eliminating steps that must be performed simultaneously. It also means designing for one-handed and either-handed use where the task allows, since many users in this group have one dominant unaffected hand.

3. Make the state of the product perceptible, and make errors benign and recoverable. A user who cannot see a small marking, feel a subtle detent or hear a quiet click cannot tell whether the product is set up correctly, and will discover the error only when the task fails — often in a way that costs them the workpiece or injures them. The design response is redundant, multi-modal feedback (a click that is both audible and tactile, a colour contrast that survives poor kitchen lighting, a shape that can be read by touch), and design of the failure mode so that getting it wrong is cheap: a mis-seated tool that simply refuses to advance is far better than one that skids off and cuts the user. This is the cluster in which most of the perceived “quality” of an accessible redesign actually resides, and it is also the cheapest to implement, because it is largely a matter of geometry, contrast and material rather than of mechanism.

Two remarks that matter for the marks. First, these three are not independent: reducing the force requirement usually costs size, and increasing size can degrade the perceptual clarity of a small tool, so they must be traded against one another explicitly rather than optimised one at a time. Second, all three exhibit the curb-cut effect — changes made for a group at the edge of the capability distribution almost always improve the product for the centre of it as well, which is what makes the business case for this kind of work.

Part B — Applying the three ways to the can opener (9 marks)

The baseline product is the conventional hand-held butterfly can opener: two plier-type handles pivoted near the head, a hardened cutting wheel on one jaw, a serrated feed wheel on the other, and a small winged key on the feed-wheel shaft that the user turns with a lateral pinch of the thumb and forefinger. The user must clamp the handles hard enough to keep the cutting wheel through the lid, hold that clamp for the whole circumference, and simultaneously turn the key with the other hand. This is precisely the wrong combination for the target group: a sustained high pinch, a fine lateral pinch, and a two-handed coordination task, all at once.

Given. The mechanics of the baseline and the redesign are quantified below. The jaw force required to keep a standard cutting wheel through a 0.22 mm tinplate lid is taken as the design load, and the accessible operating-force ceiling is taken from CSA B651, which caps the force to operate a control at 22.2 N (5 lbf).

Find. The hand force and turning force demanded by the baseline, the handle length that a pure lever change would require to reach the 22.2 N ceiling, and the demands of the redesign that actually reaches it.

Approach. Treat the handles as two first-class levers sharing the pivot, so that the jaw force and the hand force are related by the ratio of the lever arms; treat the turning control as a simple torque arm. Compute the baseline demand, compare it with the accessible ceiling, find the lever ratio that would be needed to close the gap by geometry alone, show that it is not achievable within a kitchen tool, and therefore attack the load as well as the ratio.

1. Establish the baseline mechanical advantage and the hand force it demands. For a lever pivoted between the load and the effort, moment equilibrium about the pivot gives the mechanical advantage as the ratio of the two arms, $MA = L_h / L_j$, and hence $F_h = F_j / MA$. Substituting the baseline geometry, $MA = 80/20 = 4$ and $$F_h = \frac{F_j}{MA} = \frac{240}{4} = \boxed{60\ \text{N}}$$ which is a sustained pinch held for the several seconds it takes to travel the rim. Healthy adult pinch strength is comfortably above this, but a hand with moderate rheumatoid arthritis typically manages 15 to 25 N, so the baseline product is not merely inconvenient for the target group — it is unusable, by a factor of about three.
2. Establish the baseline turning demand. The tangential force a user must apply at the winged key follows from the torque arm, $F_t = T / r$. With the baseline key, $$F_t = \frac{0.30}{0.010} = 30\ \text{N}$$ applied as a lateral pinch on a wing about 5 mm wide. Lateral pinch is the weakest of the standard grips and the one arthritis degrades first, and the narrow wing concentrates that force onto a small area of a painful joint. This is the second independent barrier, and it is a dexterity barrier as much as a strength one.
3. Test whether a lever change alone can reach the accessible ceiling. Setting the hand force to the CSA B651 limit and solving the same lever relation for the arm gives the required geometry directly: $$L_h = \frac{F_j}{F_{max}}\,L_j = \frac{240}{22.2}\times 20 = 10.8 \times 20 \approx 216\ \text{mm}$$ A 216 mm pivot-to-grip arm makes a tool about a quarter of a metre long overall — a bolt cutter, not a can opener. It would not fit a kitchen drawer, it would be unwieldy at the rim of a small can, and the wide handle spread would itself defeat an arthritic hand, whose functional span is small. Pure parameter scaling therefore cannot reach the target, which is exactly the finding that forces the design back up to the concept level rather than leaving it in detail design.
4. Attack the load as well as the ratio: design change 1 (physical demand). The required jaw force is not a constant of nature; it is set by the geometry of the cutting wheel. Halving the included angle of the cutting edge from about 60° to about 30° and reducing the wheel diameter concentrates the same penetration into a smaller contact patch, roughly halving the normal force needed to keep the wheel through the lid, so the design load falls to $F_j = 120\ \text{N}$. Combining that with a modest handle extension to 120 mm, well within a kitchen tool, gives $MA = 120/20 = 6$ and $$F_h = \frac{120}{6} = \boxed{20\ \text{N}} \; < \; 22.2\ \text{N}$$ so the demand now sits under the accessible ceiling with a small margin. A sprung over-centre latch on the handles converts even this to a momentary rather than a sustained force: the user squeezes once, the latch holds the clamp, and the hand is then free. The cost is a sharper wheel that dulls faster, which is taken up in the specification as a replaceable-wheel requirement rather than pretended away.
5. Design change 2 (precision and dexterity). Replace the winged key with a 40 mm diameter knurled knob turned by a whole-hand power grip. The same torque relation now gives $$F_t = \frac{0.30}{0.020} = 15\ \text{N}$$ spread across the whole palm instead of two finger pads — a halving of the force and a change of grip class, which is the larger gain. Alongside it, a moulded V-groove in the head seats itself on the can rim so the user no longer has to aim the cutting wheel, and the latch of change 1 removes the requirement to clamp and turn simultaneously, making the tool genuinely one-handed once it is latched.
6. Design change 3 (perceptibility and error tolerance). Give the latch an audible and tactile click at the seated position, so that “the tool is on the can correctly” is signalled in two modalities rather than inferred. Change the working principle of the cut from a top-cut through the lid to a side cut through the seam: the lid comes away with a rolled, blunt edge instead of a sheared, sharp one, and the jaws retain the lid when the tool is lifted so it cannot drop into the food. The failure mode becomes benign — a mis-seated tool simply will not advance, rather than skidding across the lid — and the residual hazard of a sharp edge is designed out rather than warned about.

Part C — Impact on society, and three improvements to that impact (4 marks)

The direct societal effect of the change is on independence in the activities of daily living. Roughly one Canadian in five is now over 65 and the proportion is rising, and arthritis is the single commonest cause of activity limitation in that group; a pantry that cannot be opened is one of the small failures that accumulate into a loss of independent living. A can opener that a person with moderate arthritis can use unaided therefore has a health-system value out of all proportion to its retail price, because it defers or reduces the need for assistance with meal preparation. The change also propagates: the curb-cut effect means the lower forces, the self-locating head and the blunt-edged cut are strictly better for every user, including children and the merely tired, so the improvement is not confined to the group it was designed for. The negative side of the ledger must be stated honestly — a sharper wheel wears faster, a latch adds parts, and if the product is positioned as an assistive device it will carry an assistive-device price premium and reach far fewer of the people who need it.

Three improvements that would increase the social benefit:

1. Price and channel it as mainstream, not assistive. Design the redesign to be mass-manufacturable at parity with the conventional product and sell it in ordinary grocery and hardware channels rather than through medical suppliers. Accessibility that is only available at a premium, from a specialist retailer, with a stigma attached, reaches a small fraction of its potential users; volume in the mainstream channel is what converts a good design into a public-health outcome.
2. Design for durability and repair rather than replacement. The sharper wheel is a consumable, so make it a user-replaceable part with a standard interface, use mono-material handles that can be recycled without disassembly, and specify a corrosion-resistant wheel material so the tool lasts a decade. This prevents the accessibility gain from being paid for with a shorter life and more waste, which would simply move the social cost downstream.
3. Publish the ergonomic basis and push it into a standard. Release the force and anthropometric data behind the design and take it to a standards committee so that an operating-force ceiling for hand-held kitchen tools becomes a published requirement rather than one manufacturer’s choice. A single accessible product helps its buyers; a standard changes the whole category, and it is the difference between a marketing feature and a durable social improvement.

Part D — Engineering specifications to implement the three changes (9 marks)

The design changes of Part B are intentions; they become engineering work only when they are expressed as metrics with units, a marginally acceptable value and an ideal value, in the target-specification form of Ulrich and Eppinger. Each row below is measurable by a defined test, and each traces to one of the three changes so that the specification can be audited against the design intent rather than being a wish list. Values are given as marginal (the product is not shippable below this) and ideal (the value the design is aiming at).

Two features of this table are worth naming because they are what distinguish an engineering specification from a marketing brief. First, every row is a number with a test beside it, so a prototype either passes or it does not, and disputes are settled by measurement. Second, rows 15 and 16 are the two that couple everything else: the usability rate is the only whole-product measure and is the one the design actually exists to achieve, while the cost target is the constraint that will drive the trade-offs of Part E. Specifications 5 and 12 are in direct tension with specification 1 — a sharper, smaller wheel lowers the force but wears faster and leaves a keener edge — and that tension is deliberately exposed here rather than discovered in testing.

Part E — Three things to do when not all specifications can be met (9 marks)

It is normal, not exceptional, for a first prototype to miss part of its target specification; Ulrich and Eppinger treat the setting of final specifications as a distinct step precisely because the target specification is written before anything has been built. What must never happen is that a specification is quietly abandoned. The three responses below are ordered by cost, and the correct discipline is to try them in that order.

1. Trade off within the specification, using the needs–metrics relationship to decide what gives. Not all specifications are equally load-bearing. Return to the needs–metrics matrix and identify which metrics are strongly coupled to the critical customer needs and which are proxies that can be relaxed from their ideal towards their marginal value with little loss. For this product, if the cost target of row 16 cannot be met at the ideal wheel life of row 5, the right move is to relax the wheel life towards its marginal value and lean on the user-replaceable wheel of row 6 — because the need behind row 5 is “the tool keeps working”, and a replaceable consumable satisfies that need by a different route. The tool for this is a trade-off curve plotted from the model rather than an argument: hand force against handle length is a hyperbola, so the last two newtons cost far more length than the first ten, and the curve shows where the knee is. Relaxations are recorded against the affected need, benchmarked against the competition so that the product is not relaxed below the market, and signed off, so that the final specification is an explicit document and not an erosion of the target one.

2. Change the concept rather than the parameters — go back up the design process. If the shortfall survives the trade-off analysis, it is usually a sign that the chosen working principle cannot reach the target, and no amount of dimensional tuning will rescue it. That is exactly the situation Step 3 of Part B uncovered: scaling the lever to reach 22.2 N demanded a 216 mm handle, which fails specification 3, so the parameter route is closed and the answer had to come from a different working principle — a sharper wheel geometry and a latch. The systematic form of this response is to decompose the offending function, re-enter concept generation for that sub-function only (internal and external search, then a concept classification tree), and re-select with a Pugh screening matrix against the incumbent as datum. It is more expensive than a parameter change and much cheaper than discovering the same shortfall after tooling; the general rule is that roughly three-quarters of a product’s lifetime cost is committed by the end of concept development while only a few per cent has been spent, so a concept change made now is the cheapest it will ever be.

3. Re-negotiate and re-baseline the specification with the stakeholders, explicitly and in writing. When neither trade-off nor a new concept closes the gap, the specification itself must change, and that is a decision for the people who own the requirement — marketing, the regulatory group, the customer — not for the design team alone. The options are to re-scope the target user segment so that the shortfall no longer matters, to stage the release so that the ideal value becomes a second-generation target while the marginal value ships now, or to accept the shortfall with a documented mitigation and a re-validation plan. Three disciplines make this legitimate rather than an excuse. The deviation is recorded formally, with the measured value, the reason, and the risk to the affected customer need. Anything with a safety or regulatory dimension — here, the cut-edge radius of row 12 — is treated as non-negotiable and is never traded, no matter what the schedule pressure. And the changed specification is re-validated with the target-group panel of row 15, because the whole-product usability measure is the only one that tells you whether the relaxations have collectively destroyed the design intent even though each looked survivable on its own.