Bad poka-yoke is worse than none

Last post, I talked about the lean concept of poka-yoke or “mistake proofing.” The idea of poka-yoke is that even the best worker can make costly or dangerous mistakes when their attention slips even just for a moment. This is certainly true in the world of childproofing, where any parent will tell you that toddlers can get into amazing dangers during the split second your back is turned.

That is why you need to have passive backups, to keep mistakes from happening when your attention is distracted for a second. A good example of this kind of backup is the cabinet lock, which keeps cabinet doors shut when the prying fingers of a toddler go to work on them when you aren’t looking. In theory, a cabinet lock should make it impossible for a toddler to open a cabinet they shouldn’t, whether you are aware of them doing it or not.

I say “in theory” because one of our cabinet locks, a very popular model (in fact, the only model available at any of our local stores), has a crucial flaw that makes its protection much less reliable than it should be. Here’s a picture of the offending lock:

It looks pretty good, right? You loop the U-shaped piece around your cabinet door handles, pass them through the ratcheting crosspiece, and push them together until the doors are secured. The tricky button-pressing motion required to open the lock keeps toddlers out.

Or at least, that’s how it’s supposed to work. In practice, there are four different ways the two pieces can come together, depending on their orientation. Unfortunately, only one of the four orientations will actually engage the ratchet and secure the lock. The other three orientations will not engage the ratchet and the lock can simply be pulled apart without resistance by the busy hands of a toddler.

Even worse, the three incorrect and unsafe orientations look exactly as secure as the correct orientation! You can’t tell just by looking whether you got the one right orientation or one of the three wrong orientations. Now, it is true that you can tell whether you got the right orientation by listening for the ratchet and testing the device carefully after you’ve engaged it. In other words, it’s just a training and experience issue, right?

Wrong. You can’t train mistakes out of existence.

My wife and I are both well aware of the issues, but when you have a hot pot on the stove and a timer beeping and toddlers pulling at your pant legs, it’s easy to forget to listen for a ratchet or give the lock device one more pull to doublecheck it. Even the best-trained, most-motivated workers can make mistakes when they are tired or distracted, even just for a moment. And a moment can be far too long when safety is at stake.

What this situation needs is not just training but effective poka-yoke. It needs to be physically impossible to put the lock pieces together the wrong way. To give credit where it is due, the manufacturers of the cabinet lock in question made an attempt at poka-yoke: The U-shaped piece has a small nub on one side, and the crosspiece has a small notch on one side. If the nub goes into the notch, the pieces are aligned correctly. Problem solved, or so it seems.

Unfortunately, the design of the lock made the holes in the crosspiece too big, and the diameter of the U-shaped piece too small, for the nub to be an effective poka-yoke device. With just a slight effort, the crosspiece can be pushed onto the U-shaped piece whether the nub is correctly oriented with the notch or not. (We know this because we’ve unwittingly done it ourselves many many times.) Which leads to my main point:

Ineffective poka-yoke is worse than no poka-yoke at all.

It should be obvious why: An ineffective safety measure gives you a false sense of security, and that may be even more dangerous than having no safety measures at all. A driver with no seatbelt will drive more carefully than a driver with a seatbelt that looks fine but will actually do nothing at all to protect him in an accident. Overconfidence can be dangerous.

So what can be done? With no other cabinet locks available, we are stuck with this one for now. So we made do. If you look at the photo again, you’ll see some red lines. We drew these on the lock with a marker to make it obvious to us when the device is in a correct orientation and when it is not. These visual reminders help, and qualify as a very weak poka-yoke aid, but a physical change in the device itself to make it impossible to engage it incorrectly would be much better.

As it is, we are still relying on our attention to always notice when the red dots are misaligned, and that means we are vulnerable. Hopefully a better solution will present itself.

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Poka-Yoke and Childproofing.

A major concern in any household with toddlers is safety. The little tykes just get into everything, especially if it’s dangerous or off-limits. As a result, making your home safe for children (despite their best efforts) could not be more important.

We’ve learned one simple lesson while childproofing our house:

Active safety measures are not enough. You MUST have passive safety measures as well.

The difference between active and passive measures is simple: Does the safety measure rely on your constant attention and participation to be effective? If so, it’s active. If not, it’s passive.

The reason why this distinction is important: It’s not enough to just “try really hard to keep an eye on the kids.” Sooner or later, you will be distracted or careless, just for a moment, and when that happens, all bets are off. To keep your kids safe, you have no choice but to have a backup method that doesn’t rely on your active attention.

For instance, until your kids are old enough to handle stairs without supervision, you really need to have baby gates. Your careful attention will eventually fail, if just for a second, and that’s more than enough time for a nasty tumble to take place. The metal of the safety gate, on the other hand, is passively solid and unyielding every moment of every day whether you are paying attention or not.

The idea that active safety measures must be backed up by more passive measures is common outside of child care as well. Most people acknowledge that even if you drive very carefully, wearing seatbelts and having a car with airbags are still pretty good ideas. And every carpenter knows that whatever your experience level, protective goggles are a great investment.


In lean production, these passive safety or defect-prevention methods are referred to by the term “poka-yoke.” Some observers translate poka-yoke as “idiot-proofing,” which seems unnecessarily pejorative. I prefer the alternate translation, “mistake-proofing.” Poka-yoke wants to make it impossible for people to make mistakes, whether through inattention, poor training, fatigue, or any other reason.

Industrial examples of poka-yoke are generally simple yet surprisingly effective physical “hacks.” Taping a piece of cardboard over a machine input can make it impossible to put a piece of raw material in the wrong way. Installing a “dead man’s switch” on a device can make it impossible for the operator to stick a vulnerable hand into a dangerous spinning mechanism while the machine is running (because the opening and the switch keeping the machine on are too far apart for the operator to simultaneously reach both). Using a simple torque-limiter on a screwdriver can make it impossible to overtighten screws. And so on. When a mistake becomes impossible, poka-yoke is happening.

Baby gates, outlet covers, doorknob spinners and cabinet locks are all poka-yoke measures that eliminate the kinds of household mistakes that can hurt a child. I’m going to start looking around my home for more ways to reduce mistakes by making them otherwise impossible to perform. Here’s a few I just thought up:

  • Make all of your outside door locks deadbolts that require a key to engage the lock. If you have to have a key on you to lock the door, it’s impossible to lock yourself out just because you left your keys inside.
  • Block your door with your briefcase to make sure you won’t forget it in the morning. It’s impossible to overlook something you have to move to get out of the house.
  • Take advantage of a built-in poka-yoke system and make sure your house outlets are polarized, making it impossible to put in a polarized plug the wrong way.

Next time I’ll talk about how a poorly-designed poka-yoke device in our home actually manages to make the situation worse rather than better.

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Falling down the chute.

It’s been a while since I posted to this blog. I wish I could say that part of the problem is that it’s hard to both DO lean things and WRITE ABOUT lean things at the same time. But that’s not really true. I haven’t been too busy pushing the state of the art of lean techniques to find time to write about them. I’ve actually been falling off the lean wagon a bit.

For example, one little trick I’ve used quite a lot recently is taking advantage of our house’s laundry chute for the easy movement of stuff to the basement. If a hammer needs to go back in the tool room or a lightbulb in the supply area, it’s easier just to drop it down the laundry chute onto the soft pile of clothes than it is to walk down all the way down to the basement to put away a single item.

It even seems like a lean technique: By avoiding multiple trips, I’m reducing transportation waste. But what I’m really doing is slipping from a lean production flow back into a conventional “batch-and-queue” system. When I go to gather laundry from the bottom of the chute, there’s all of these hammers and lightbulbs and other non-laundry things that have to be dealt with along with the clothes. So I put these weird pieces aside to put away later in one big batch.

Here’s what that looks like in practice:

Pile of stuff

Yep, lots of junk, mostly tools, piled up on a board balanced on the edge of a laundry sink. I never quite get around to putting away this big batch of stuff all at once, so the pile grows larger and more precarious. What I’ve done is reduce transportation waste at the cost of increasing inventory waste:

  • The stuff is taking up space I could be using for something else. The sink is totally unusable as a sink right now.
  • The stuff makes it impossible to know where anything is. I couldn’t find my hammer the other day because is it in the workshop, or in the pile next to the laundry chute, or in the laundry chute…?
  • The stuff is hiding other problems. Since I don’t know where anything is, I also don’t know when anything is missing. It’s a big issue when you have toddlers roaming around whom would find a sharp awl, for instance, very interesting.

It’s amazing how easy it is to fall into these kinds of traps when you stop thinking carefully about wastes in your processes. That’s presumably why lean thinking is a continuous battle, not a one-time event, and as such it depends highly on the controls you put in place to maintain your improvements over the long term.

So I’m back on the wagon. And no more dumping stuff down the chute to get them out of the way (except for clothes, of course). Everything has a proper place, and it’s my job to get it back there, every time.

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Kitchens are already Lean

I’ve been reading Jay Arthur’s Lean Six Sigma Demystified, which makes an interesting point: Most kitchens are already arranged around some lean principles:

  • Small batches. People don’t make hundreds of meals at a time and only eat the first meal after the final meal has finished production. They make one meal at a time and eat it immediately.
  • Work Cells. In kitchens with a good work flow, the food flows from one station to the next (fridge, counter, stove, table) in a smooth progression. The tools are arranged by where they are needed in the flow of cooking rather than by their function. For example, the microwave and the stove aren’t always next to each other just because they are both “ovens,” they are placed wherever they might be used in the process.
  • Small inventories. With the exception of people buying in bulk, it is not traditional for families to purchase a full year’s groceries at a time and then store it. They buy what they need for a week or two at most, then use it up quickly. There’s no need (and usually not much room) for huge inventories.
  • No wasted motion or transportation. A well-arranged kitchen will have the appliances arranged in a convenient triangle pattern so there’s only a step or two needed to get a plate anywhere in the kitchen.
  • Right-sized equipment. The stove or blender is big enough for the family’s needs, but small enough that maintenance and upkeep are minimized.

Unfortunately, these observations are only true for “well-arranged kitchens.” Many kitchens are poorly arranged, with wasted space, counter-productive layouts and little difficult-to-reach storage areas where items can go hiding.

Our kitchen, for instance, is not laid out in the most functional pattern possible simply because the architecture won’t allow it. (This is true for most people who don’t design their own kitchens as Arthur did.) There are five doors and two windows, which severely limit arrangement options along the limited wall space.

Even when you can design your own kitchen with lean production in mind, it’s easy to veer off track as impressing people can be almost as important as getting things done. Modern dream kitchens, with their huge floorplans, massive central islands and huge rows of cabinetry, will inevitably be cursed with large amounts of wasted motion, an over-accumulation of inventory, and an over-sizing of common tools (e.g., using a massive professional stove for a small family’s cooking needs).

So are most kitchens lean by nature? No. In fact, I’d guess that very few of them are, even in the best of circumstances. But they can all get leaner, even in the worst of circumstances. Our kitchen is proof of that.

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New dishwasher and root causes.

I’m need to talk, once again, about our dish washing process. One of the problems remaining as we’ve tried to make our dish washing process leaner is that the dishwasher itself is in poor health. Cups and dishes on the top shelf always end up coated with a small amount of gross-looking baked-on crud, requiring me to re-wash many of them as I unload the dishwasher.

This re-washing of the same dishes that were JUST WASHED in the dishwasher is classic Overprocessing, one of the big seven wastes of lean production. We’ve tried to get rid of this waste (as I mentioned in my discussion of defects) by running various cleansers through the machine and having a dishwasher repair person out to look at it several times. It was no use. The dishwasher gets better for a few days, then gets bad again.

So, finally, we gave in and yesterday placed an order for a new dishwasher. It’s a shame that we have to lay down the not-insubstantial sum for a new piece of equipment, but we don’t have much choice. Either we get a dishwasher that works the first time, every time, or we’ll continue spending way too much of our time washing and rewashing dishes, piling up defects and overprocessing waste as we go along. That’s not the way to create a lean process!

I’ll have more to say on “root causes” some other time; for now I’ll just point at our new dishwasher (arriving in three weeks) as an example of the basic point: Until you go back through your process and find the real reason for the waste you are seeing, you will never be truly rid of it.

It’ll just keep happening, generating more waste (and more waste, since even in this simple dishwasher situation one kind of waste [Defects] quickly lead to another [Overprocessing]). It’s usually worth the extra time and expense to fix the root cause now rather than deal with its downstream effects indefinitely.

This idea of stopping everything until you solve the underlying waste-creating problem is called jidoka, and is one of the two pillars of lean production (“just-in-time” being the other one). And yes, there will be more to say about that in later posts. Right now I’m going to go fantasize about sparkling clean dishes that can go right in the cabinet. Bliss.

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5S in the kitchen #5: “Kaizen” versus “Kaizen blitzes.”

It’s been a while since I wrote an update on my applying the “5S” organization process to our kitchen. The reason for this delay is related to something I mentioned once before: We have VERY little time to do anything but childcare, and definitely don’t have BIG BLOCKS of time to get anything major done without interruption.

I didn’t realize this would affect the 5S process, but I should have. All of the narratives I’ve read where companies applied the 5S process to their workspaces took place during big lean rollout workshops. That is, the workers had hours or days totally unobstructed in which to do the full 5 S process to its conclusion.

In our household, there is no time for a hiatus or seminar or workshop to get these big changes made. The toddlers are almost always here, and if they aren’t here, we aren’t either. If something can’t be rolled into the daily routine of keeping things going, it can’t happen.

So after I Sorted and Straightened the kitchen, the 5S process ground to a halt. There simply isn’t the time to do the Sorting and Straightening that needs to be done to get it “right.” We don’t have time to totally go through the cabinets and fridge and freezer and get everything sorted out properly. Despairing of this reality, I got stuck.

There’s a bigger issue here: At the center of lean production is the concept of kaizen, meaning “continuous incremental improvement.” The idea is that the lean worker is always looking for ways to improve the process, even in tiny ways, in a cycle that never really ends.

This is an inspiring idea in many ways, but from what I’ve seen, American business wasn’t very responsive to it when lean ideas began to proliferate in the 1980’s and 1990’s. Gradual incremental improvement just sounded too slow. They needed things to get better now, not wait around for thousands of tiny fixes to gradually accumulate in the system.

So American organizations popularized the idea of the “kaizen blitz,” a short period of highly-focused lean transformation where you’d drop everything else and radically transform your business to a leaner, better form. In theory, this blitz would take many of those tiny little improvements and jam them into one frenzied weekend or week or month or quarter, then blast off the operation into a different stratosphere when work resumed.

It’s an exciting idea, but has some issues:

  • It takes time to reprogram people with traditional mass-production mindsets into leaner ways of thinking, and a brief blitz may not be long enough to accomplish this. People end up just going through the motions for a while and then sliding back into systems they understand better.
  • Kaizen blitzes have a marketing aspect to them, with a lot of lean experts offering to come transform your organization in just few days or weeks for a low-low consultation bill. Some of these experts may be able to do what they claim, but many others have a fly-by-night feel reminiscent of the cheesy “investment seminars” and “body detox weekends” run by charlatans in airport hotel conference rooms. Like anything else, it probably sounds too good to be true for a reason.
  • Lean production is a method for learning about your organization so that you can improve it. The results of that organizational leaning process may take considerably longer to develop than it takes to simply learn the basics of lean production. I’m not saying that lean transformations cannot have immediate results; they can and often do. It’s just important to distinguish the way you think about your process from the results of that thinking. After all, even Toyota is still learning new things about how to make cars.

That last point is key for me as I ponder why I the 5S process bogged down in my kitchen. Figuring out how to keep a kitchen organized properly for cooking is an ongoing process, one that I simply can’t blast through completely in one week. I definitely can’t blast through it in a week when I get so little uninterrupted time to pursue it.

So I’m going to scale back and see this as just the first pass in a series of ongoing 5S procedures. I don’t have the unobstructed time I need to properly organize the cabinets and fridge and freezer right now, so I won’t. I will keep working on the countertops, a manageable goal, and return to the rest of it on the next pass.

So I’m now on to the Third S in this more-focused 5S process, “Sanitizing.” More on that next post.

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5S in the kitchen #4: On to Straightening

As a first step towards “lean” cooking, I am working through the 5S workplace-organization process that begins many lean tranformations. I have now completed the First S – “Sorting”, in which you toss all the unnecessary stuff and keep only the things you really need at hand to get the task done.

In the course of doing this sorting, I’ve learned a few things:

  • You have to be clear on your focus for the space. In the case of the kitchen, the main focus is “preparing meals.” There are many other secondary activities that people do in the kitchen, such as socializing, doing odd household jobs, etc., but allowing too much vagueness about what the room was for is what made it cluttered. When it’s decision time, I decided that the room was for cooking, period.
  • You also have to be realistic. Even though our kitchen is for cooking, it’s where our back door is, so there needs to be a place to put coats and shoes. By the same token, ours is a nice kitchen, but it does not have dozens of extra cabinets and acres of extra counter space. Some things that we’d rather move out have to stay, and some things we’d rather stay have to move out. It’s a shame, but it’s also one of the ways that everyday life is different from a factory: We don’t have the luxury of building custom spaces for every task we do.
  • You may surprise yourself. As I mentioned before, once we moved items from our counters to the staging area on the dining room table, we suddenly realized how unnecessary some previously-critical items were. Now that the counters are wide open and clear, we are reluctant to put things back on them again. So the popcorn popper that just had to be out all the time is finally making the move to a closet after two years on the stove.

Now that the necessary has been separated from the unnecessary, we move on to the next S in the ‘Five S’s’: “Straightening.” This step is also sometimes called “Stabilizing” or “Setting Up” or something like that. (Again, these multiple variations are the consequence of trying to capture the meaning of a Japanese word beginning with S (seiton) with an English word ALSO beginning with S.)

The basic idea of “Straightening” is to put the items in your workspace (which are by now only the truly necessary items for your task) in order. The goal is for the location of items to be efficient, tidy, and easily-understood. Among the commonly mentioned methods:

  • Let the worker who does the job organize their tools rather than some supervisor. Only the worker knows the right placement for their actual workflow.
  • Use ample labeling so that anybody attempting to perform the task, even if it’s not usually their workspace, can easily find what they need.
  • Use visual inventory methods, like drawing an outline around the spot where the tool is kept, so it will immediately be clear where something goes (and more important, when something is missing or out of place).
  • Keep the focus on the work flow. It’s more important that a tool be where it needs to be when it is required than making sure it is grouped with similar tools. For instance, wooden spoons need to be near the stove so they be easily used to stir something in a cooking pot. Sure, wooden spoons could be kept with the dining and serving spoons (since they are all spoons) in a drawer over by the dining room, but that would be valuing “similarity” over “making it easier to cook.” Don’t worry about external categories, worry about keeping the work flowing.

Enough talk, I’m off to do some Straightening.

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