All posts filed under “Poka-yoke

Getting someone to do things in a particular order (Part 3)

Continued from part 2

This series is looking at what design techniques/mechanisms are applicable to guiding a user to follow a process or path, performing actions in a specified sequence. The techniques fall roughly into three ‘approaches’. In this post, I’m going to examine the Poka-yoke approach. If you’ve been following the previous posts, you’ll probably have thought, “Well, all that’s pretty obvious.” And it is obvious – we encounter these kinds of design techniques in products and systems every day – but that’s part of the point of this bit of the research: understanding what’s out there already.

Poka-yoke approach

The mechanisms described in this approach are all based on technical (rather than explicitly human) factors, and involve designing the relationships between system elements.

Poka-yoke (Japanese: mistake-proofing) is an approach usually applied in manufacturing engineering, developed by Shigeo Shingo in the context of developing ‘zero defect’ assembly processes. The idea is to avoid slip-type errors by designing systems which prevent them occurring, prevent a user proceeding until the error condition has been rectified (control poka-yokes), or at the very least clearly warn the user of the error condition (warning poka-yokes).

Generally, when the design intent is for the user to follow a process or path in a specified sequence, a deviation from that sequence can be considered as an error, and thus the poka-yoke approach can be applicable outside its original field. Similar concepts, forcing functions, have been developed in interaction design, especially in the work of Donald Norman – the three main forcing function mechanisms, Interlock, Lock-in and Lock-out, broadly correspond to Shingo’s control poka-yoke category; all can help in assisting (or forcing) users to follow a process or sequence. In the warning poka-yoke category, the Arrangement detection mechanism is most relevant to this behaviour.


An Interlock combines elements of both lock-ins and lock-outs (see below), and is probably the most familiar forcing function mechanism: the ability to use one function is dependent on another running or being started, another component (such as a guard) being in place, or some other condition being fulfilled.

Toyota Verso clutch-ignition interlockToyota Verso clutch-ignition interlockToyota Verso clutch-ignition interlock
Example: This Toyota Verso requires the clutch pedal to be depressed before the starter button will operate, to reduce the risk of starting in gear.

Car ignitions which cannot be operated unless the driver’s seat belt is fastened – a system originally promoted as ‘Interlock’ in the US – microwave ovens not operating unless the door is closed, and airline or train toilets where the lighting does not operate until the user has locked the door, are some of the highest profile everyday examples, but the principle of the interlock is extremely common in engineering and manufacturing industry, often in the context of a machine tool which will not start until a guard is in place, or where opening the case automatically cuts the power.

Interlocks are often specified when it is imperative – rather than merely desirable – that a user follow a particular sequence, or at least two steps of a sequence, in exactly the right order, but their use need not be limited to critical safety design problems. Ecodesign applications might include (for example) a car’s air conditioning system requiring the windows to be fully closed before operating, or a sink requiring the plug to be in before the tap can be left in a ‘running’ position.

Microwave oven door interlockMicrowave oven door interlock
Example: The ubiquitous interlock on a microwave oven ensures that the door is closed before the oven will start.


The Lock-in mechanism in this context (rather than an economic one) refers to a system arranged such that a process, procedure or operation is kept active – the user can’t exit the operation until a certain condition is met, or the ‘correct’ next step is taken. This can be implemented using sensors, logic processing, physical architecture, or a number of other ways.

As Norman puts it, this prevents “someone from prematurely stopping” an operation – this could mean letting some ongoing process run its course to completion before starting the next, or denying the user access to another function which might interfere with the current process. It can also prevent accidental cancelling of an operation – inadvertent deviation from a specified sequence – by introducing an extra ‘confirmation’ step.

Confirmation dialogue
Example: The confirmation dialogue displayed by some software when a user attempts to exit can be seen as a lock-in to prevent inadvertent ending of the application.


Lock-out is closely related to Lock-in: in this case, the mechanism makes it difficult or impossible for the user to start certain operations, or denies or impedes access to particular areas or functions. In the context of encouraging or forcing a user to follow a path or process in a specified sequence, a lock-out helps prevent inadvertent or mistaken steps in that sequence. It can also help prevent an operation being started too early in the sequence, and may also be implemented as an extra ‘confirmation’ step.

Lock-out dialogue
Example: This file backup application prevents a user modifying the properties of a scheduled backup task while it is running – ensuring that the correct sequence is followed.

Arrangement detection

Arrangement detection is a ‘warning’ rather than ‘control’ poka-yoke mechanism, and may be considered as a ‘feedback’ analogue of interlocks, lock-ins and lock-outs – providing a warning (audible, visual, tactile) when system elements are incorrectly arranged (physically or procedurally).

Arrangement detection is about warning the user that the path or process is occurring in an incorrect sequence, rather than actually forcing the user to follow the correct sequence. While there are a number of possible warning poka-yoke mechanisms alerting users to incorrect behaviour, arrangement detection is most relevant to the specific issue of sequencing.

Seatbelt warning
Example: The seat belt warning on car dashboards (in this case a Fiat Punto) is an arrangement detection poka-yoke, providing a visual (and often also audible) alert that a belt is not buckled while the engine is running, or the car is moving.

In part 4, we’ll look at the Persuasive Interface approach to getting someone to do things in a particular order.

Home-made instant poka-yokes

Everyday poka-yoke

Update: Also known as Useful Landmines in the 43 Folders world – thanks Pantufla!

Mistake-proofing – poka-yoke – can be as simple as encouraging/forcing yourself to do things in a sequence, to avoid forgetting or avoiding intermediate steps. If you’re the sort of person who hangs a jacket or bag on the door handle, so it can’t be forgotten on the way out, puts things in front of the door so you can’t forget them when you’re going out, or at the top or bottom of the stairs so you’ll remember to carry them to their intended destination next time you’re using the stairs, you’re engaged in mistake-proofing. You’re introducing a behaviour-shaping constraint to assist your own effectiveness.

In the above photo, putting the mobile phone (on-charge) inside a shoe makes it more likely that it will be remembered when going out: the act of putting the shoes on requires the user to pick up the phone, which could otherwise be easily forgotten. Similarly, Mark Hurst (of Good Experience and ‘Broken’ fame) regularly features two very simple poka-yoke procedures in his Uncle Mark’s Gift Guide & Almanac:

How to remember if the batteries aren’t in your camera

Summary: If the batteries are dead, or aren’t in the camera, keep the battery compartment open.

Description: When you’re charging your camera batteries (in a wall charger, say), keep the camera’s battery compartment open. That way, if you pick up your camera to put it in your pocket or purse, you’ll see that the battery compartment is open and will remember that the batteries aren’t in it.

Leaving the camera battery door open

There’s also this:

How to make sure they see the papers you dropped off

Summary: Put the papers on their chair.

Description: Here’s a tip I learned years ago and have used ever since. If you want to make sure that someone sees the papers you dropped off at their desk, put the papers on their chair. The natural inclination is to drop the files on the keyboard, or beside the mousepad. What’s the first thing the person does when they get back to their desk? They shove the papers aside, onto a nearby pile. They want to check their e-mail immediately, and those papers are in the way!

But put the papers on their chair, and watch what happens: the person refuses to sit on them! They take a second to pick them up, and while they’re in-hand, the person takes a look at the files while they get comfortable in the chair. Bingo: you guarantee attention to your drop-off.

Papers on chair

Of course the papers-on-chair method can also be used to remind (or discipline) yourself about dealing with important papers.

This kind of very simple sequencing poka-yoke comes almost naturally in our everyday lives, at least with certain tasks. Sometimes it’s simply reminding ourselves to do something (e.g. putting a Post-It note somewhere we can see it); other times it’s trying to prevent us proceeding until some action has been taken (e.g. putting a Post-It note right in the middle of the computer screen so we can’t ignore it). Donald Norman’s Things That Make Us Smart has some interesting discussion of the power of Post-It notes and their importance as “information in the world”, disburdening some of our mental load – also part of the whole Getting Things Done phenomenon.

Sometimes we even (consciously or otherwise) try to ‘trick’ ourselves into behaving how we want to (or know we should) – the random offset alarm clock (patent; Halfbakery discussion) and Gauri Nanda’s “runaway success” Clocky being examples that spring to mind. (I once had a bedside clock radio where the button to set the minutes no longer worked, which meant that I could only set it either on-the-hour, or, because I forgot to do it at the right moment, set it maybe between 5 and 30 minutes fast. That meant that there was an uncertainty built into every time I glanced at the display, and indeed every time the alarm went off. I was rarely late, as a result.)

I have a hunch that almost trivially simple sequencing poka-yokes (in particular) could be important in designing for sustainable behaviour, such as reducing energy use and waste generation. For example, if your rubbish bin had a recycling box built into the top, so that you had to lift it out of the way (hinged, perhaps, to make it hassle to remove entirely) before putting anything into the main bin, it would be difficult to ignore the recycling box. Hence, learning as much as possible about different methods people use to mistake-proof themselves, or shape their own everyday behaviour, is likely to be useful in exapnding this line of research.

So, what are the everyday home-spun (or otherwise) tricks you use to help mistake-proof yourself?

Spear’s Spellmaster: Poka-yoke in the classroom

Back in September we looked at Mentor Teaching Machines, a clever type of non-linear textbook from the early 1970s which guides/constrains the user’s progression, in the process diagnosing some common types of misunderstanding and ‘remedying’ them. The comments were enlightening, too: there’s a lot more history to programmed teaching texts and programmed instruction than I realised, and I will certainly be covering some of this, and what useful design principles and inspiration can be drawn from it, at some point.

Now, this is not in the same league, but interesting nonetheless: a ‘game’ to teach children (4 years onwards) spelling using a poka-yoke technique. The Spellmaster, from J W Spear & Sons – the example here is from 1980 (the Enfield factory was closed after a Mattel takeover in 1994) featured eighty plastic letter tiles, Scrabble-like but larger, with raised pegs underneath, a different pattern for each letter.

Spear's Spellmaster

Spear's Spellmaster

Spear's Spellmaster

Spear's SpellmasterSpear's Spellmaster

The letter tiles are used to spell the names of objects and concepts (colours, numbers) illustrated on punched cards which fit onto a backing board, the tiles only fitting in their spaces correctly if the pegs pattern aligns perfectly with the punched holes. If the wrong letter is used, the tile doesn’t fit properly and sits at an angle rather than snapping neatly into place. The ‘snap’ of a correctly positioned letter is actually pretty satisfying – surprisingly so, given the combination of plastic (urea formaldehyde, I think) and 30-year old cardboard.

Spear's Spellmaster

Spear's Spellmaster

Spear's SpellmasterSpear's Spellmaster
Left: The wrong tile – the pegs do not align with the punched holes. Right: The correct tile – everything lines up. Below: The wrong tile here – note the extra peg on the left-hand edge of the tile, which doesn’t match up with the punched hole, and leads to the tile not sitting down properly.
Spear's Spellmaster

Spear's Spellmaster

Letters which could work either way up, such as ‘o’ and ‘s’ have – as would be hoped – symmetrical peg patterns. It’s a simple system, but it’s clever and while not offering any ‘remedial’ function to the child, I would think it’s not too likely that many children would try all 25 other letters assuming the first one didn’t fit. Hence, there is some bias against pure trial-and-error. It’s interesting to think how immediately we might consider a computer-based solution to this kind of design brief today, where a purely physical one would work very well and give a different kind of tactile satisfaction.

Spear's Spellmaster

Spear's Spellmaster

Full, tilt

Balancing bowls. Image from Royal VKB websiteJan Hoekstra’s Balancing Bowls for Royal VKB (via Boing Boing) are an interesting ‘portion control/guidance’ solution – as Cory Doctorow puts it:

The tilt is tiny, all of 3 degrees, and the net effect is very satisfying — you gradually add snacks to the “light” side until it makes a soft and very definite *click* as it falls.

This kind of ‘very mild persuasion’ example is a great demonstration of how a simple physical property can be used to inform the user – the conventional modern solution in this area might be to monitor users’ behaviour, e.g. by weighing the amount of food put into the bowl, and then display it electronically, with an indication of whether a pre-set portion size has been exceeded. But these bowls simply tilt, with no electronics or moving parts (other than the bowl itself) necessary. It’s an elegant poka-yoke style solution.

Portion perception (and unit bias) is a fascinating area – we’ve looked briefly at it a few times – but I hope to explore it in more detail in due course, along with a review of Dr Brian Wansink‘s Mindless Eating – in a post about how cognitive biases could be used in designing behavioural change.

How this research will be moving forward

A new course for the research

UPDATE: This 2-page PDF (produced summer 2008) introduces the research

I’ve taken the plunge, and will be starting a PhD in September at Brunel University, Uxbridge, in the School of Engineering & Design.

The chosen subject incorporates both a formal investigation and review of certain architectures of control in design, and practical application of them for what I see as a worthwhile purpose: reducing the environmental impact of consumer products. This is an area which has come up quite a few times on the blog and in my previous research, and which I feel is both timely and worthy of a detailed treatment. The initial official title of the research is Reducing the environmental impact of products by using design to change user behaviour, and I’ve quoted a slightly shortened version of my brief tentative proposal below:


Much research has concentrated on reducing the environmental impact of consumer products through improving manufacturing methods, efficiency of operation, and end-of-life processes. Attention is also being turned to changing consumers’ behaviour to the same end, through public education, policy and taxation emphasis – and product design methods, on which this study will focus.

Various techniques allow the characteristics of a product’s use phase to be influenced in favour of increased sustainability or reduced environmental impact. In purely technological terms, increased efficiency of operation is clearly a major goal, yet it may also be equally – and independently – important to reduce or otherwise to alter the period or manner of the product’s use, and that means changing users’ behaviour. Methods of achieving this, by using design techniques, range from ‘hard’ coercive constraints (technology which ‘refuses’ to be operated in a certain manner) to ‘softer’ psychological constraints which encourage or guide the consumer to use the product in a different way. The field lies at the intersection of technology and human factors, with the limits of any approach’s impact being determined by both technological and interaction design issues.

The study

This study will, in the first phase, review and characterise existing and novel design- and technology-led approaches to changing users’ behaviour to reduce the environmental impact of products. Donald Norman’s concepts of forcing functions and behaviour-shaping constraints, Shigeo Shingo’s poka-yoke methods, and B.J. Fogg’s ‘captology’ research at Stanford are pertinent here as starting points, since while these have been developed in the contexts of interaction design, manufacturing engineering and computer science respectively, there is significant potential to apply similar thinking with environmental considerations in mind; as far as the author is aware, this has not previously been done systematically.

A few specific technological approaches include: use of interlocks to ensure users make decisions or perform actions in the ‘right’ order when the ‘wrong’ order can be detrimental environmentally; sensors to shut down functionality when a product is not being used (e.g. motion-detection for lighting); sensors which prevent unnecessary energy use (e.g. a vehicle throttle which prevents over-revving when stationary); and the use of designed-in obsolescence to produce ‘optimum environmental lifetime’ products which expire at predetermined lifetimes, perhaps even using active disassembly techniques.

The second phase will involve testing-out of selected approaches through user trials and simulated trials of a number of functional product prototypes incorporating the behaviour constraints to determine levels of actual environmental benefit, and establish the technological and human factors affecting the ‘real-world’ applicability of these. Comparing life-cycle analyses of existing products’ use phases with those of the prototypes will allow a quantitative assessment of the benefits of different techniques in these contexts.

For example (illustrative only): A lot of electricity is wasted due to over-filling of electric kettles – a trial might compare prototypes ranging from the ‘soft’ constraint of a kettle with clearer visual/audio indications of fill level (prominent ‘x cups of water’ display) or financial implications of the energy use (‘Boiling this amount of water will cost you x pence’), through a kettle with a requirement to pre-select the water fill-level before filling (hence forcing the user to think about what he or she is doing), to a more extreme constraint of a kettle which will only boil one cup of water at a time – rapidly, but ensuring there can be no over-filling. Analysing the results of user trials of a range of prototypes such as these, and comparing with the energy usage of a conventional kettle, would allow actual energy savings to be quantified, and the limits of efficacy due to human factors (e.g. user frustration or misunderstanding) to be established. (The kettle examples described here are simplistic but this is the sort of approach intended.)

Another aim is to develop a ‘toolkit’ of tested design approaches, with relative efficacies and pertinent issues specified, to be of use to designers and engineers looking to create more environmentally friendly products. The outcome here would be an accessible publication (a short book, eBook and/or presentation, separate from the thesis) illustrating and detailing the techniques, made available to companies and students. It is hoped that government eco-design initiatives may also be interested in the practical implications of the work.


The author studied Industrial Design Engineering at Brunel from 2000-4, and did a (taught) Cambridge-MIT Institute Master’s in Technology Policy from 2004-5. He has since worked in freelance design engineering and product design for a number of clients including, currently, Sir Clive Sinclair. His Master’s dissertation (and ongoing independent research in this area) investigated ‘architectures of control’: intentionally controlling user behaviour, mainly for political and commercial reasons, in a variety of fields, especially the built environment and digital rights. This forms a useful background to the proposed study.

Contribution to knowledge

The aim of the study will be to address these questions, reformulated as appropriate: How can users’ behaviour be changed, through redesign of products, to reduce environmental impact? Which methods are most suitable for specific situations? How significant are the impact reductions, and what technology and human factors issues affect the implementations? It is hoped that the process of investigating and answering these questions, together with an outcome synthesising the practical applications (the ‘toolkit’ described above), in addition to the thesis, will constitute an original, distinct and useful contribution to knowledge.

I’m excited: this gives me a fantastic opportunity to develop and extend the architectures of control research into what I consider to be a positive area (rather than the generally distasteful social engineering/’security’/designed-in-compliance/economic lock-in), which was otherwise going to be very difficult. I’m very lucky, thanks to the efforts of my supervisor, to have a studentship, which effectively means that this PhD is a job in environmentally sensitive design research, at one of the best technological design institutions in the UK.

I’ll continue to chart and examine all architectures of control via this blog, of course, but will now have the backing of some academic credibility – and resources – which should allow a more rigorous level of analysis, and exposure to expertise, precedents and inspirations.

The decision to go for a PhD wasn’t taken lightly; deciding how to progress professionally is something which has been taxing me for some time, alongside the challenges of freelance work (one reason why this blog has suffered over the last few months). I’m aware that it is not going to be easy, by any means (Tom Coates’ article – and the appended comments – and Rich Watts’ blog, for example, were very helpful in this regard), but it’s a long time since a project has excited me as much as this one, and I take that as a very positive sign.

Why Brunel? It’s where I did my undergraduate degree (although at the Runnymede campus, very different to Uxbridge), and many of the same staff, research strengths and commercial partnerships remain or have further developed. The university has greatly expanded the promotion of engineering and design and, as a future part of the University of London, seems a lot more confident about itself. While I very much enjoyed my time at Cambridge doing my Master’s, and it sparked my academic interest in architectures of control (specifically, in Frank Field’s lectures, both in person and via MIT videolink), I want (using my background) to develop the subject in a design context, which Cambridge does not offer in the same way.

The success of this blog in attracting some amazing, insightful comments (from what I can assume are amazing, insightful readers) has also given me a lot more confidence that taking this research further is not just worthwhile, but something I really must do, and I’m very grateful to all who’ve helped along the way so far.

The next post will review some of the ‘environmental architectures of control’ examples (both real and suggested) which I already have on my list, from this blog and elsewhere. Other than that, my girlfriend and I are off to Dublin for a few days’ break, and I’ve pledged not to take any work with me, physically or mentally, so let’s hope the spam filter can take care of the blog until next week!

Tidying up the /cig-bin

Cigarette receptacle with sloping top
Cigarette receptacle with sloping top
Two types of cigarette receptacle with sloping tops to prevent cigarettes (and other litter) being put on top. Images from the New Pig catalogue pigalog.

These smokers’ bins from New Pig employ a very simple architecture of control – simply, sloping tops which prevent litter (including cigarette butts) accumulating. Compared with more conventional flat-topped cigarette receptacles this is presumably effective, although it does mean that anything placed on top will end up on the floor.

As with cone cups and wire-mesh bins, the success of the design in reducing the ‘undesirable’ behaviour must be down to people’s (conscious or otherwise) antipathy to an immediate ‘messy’ consequence of their actions. If you throw a cigarette butt on the ground straight-off, you can immediately forget about it. If you put it on top of a flat-topped bin, you can also immediately forget about it. But putting it on a sloping bin top and seeing it (or imagining it) falling off onto the ground somehow draws attention to your actions, just as leaving a paper cone cup with some liquid spilling out onto the table is rarely done, but leaving a conventional flat-bottomed paper cup is very common.

Incidentally, New Pig seems quite an interesting company with a playful approach to building its brand.