What Poka-Yoke Are And Are Not, And How To Sustain Them

Chet Marchwinski recently exhumed a 2011 discussion about Poka-Yoke that had been started by the following question:

I’m a manufacturing engineer and since I have started participating in kaizen workshops, I have noticed that production supervisors tend to disconnect some of the poka-yokes we’ve put in place in the machines. When I challenge them about this they argue that operators can’t run production and cope with the complexity of our machines. I am perplexed by this and wondered whether you’d have a comment.

In short, I can think of two reasons for production supervisors to disconnect Poka-Yoke:

  1. No production supervisor in his right mind would disconnect devices that make the work easier for operators. If they do disconnect them, the most likely explanation is that the devices described as “Poka-Yoke” actually add work for the operator. If you have to pick a part from one of ten open bins in front of you, you will spend precious seconds finding the right one; if all bins are covered with lids except the right one, not only are you physically prevented from picking the wrong one but you don’t have to look for it. It makes your job easier. On the other hand, if you have to scan a bar code on the part to validate the pick, it adds to your work load and your supervisor will pull the plug on the next production rush.
  2. The manufacturing process is not ready for Poka-Yoke. A production supervisor is quoted in the question as saying “operators can’t run production and cope with the complexity of our machines.” This suggests that the line has process capability issues that must be addressed before implementing Poka-Yoke.

The following paragraphs elaborate on these points.

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Beyond A3s: Options for Shopfloor and Management Communication

A3s are still being touted as nothing short of a management revolution, but few organizations actually use them for operator work instructions, problem-solving, or hoshin planning. This raises the question of whether the objectives pursued with a paper format may not be easier to achieve with more recent technology. In this post, we consider options for operator work instructions. The other applications of A3s deserve separate treatment.

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Ex-Toyota exec preaches production gospel to aspiring supplier | Automotive News

Paula Lillard is now the bright hope for nth/works. She has come to help instill the Toyota Production System — or TPS — for a supplier that urgently wants it.

Source: www.autonews.com

Michel Baudin‘s comments:

This article paints a picture of what implementing Lean is really all about. It starts from the business needs of a parts supplier to the household appliance industry that wants to move into auto parts, where tolerances are tighter.And implementation is centered around what Lillard calls giving the plant “a little TLC.”

According to the article, her first task was “to ask employees to write and create step-by-step instructions on how to do their jobs.”  This is a far cry from all the nonsense about starting with 5S. It does not require value-stream maps, and it cannot be done in so-called “Kaizen events.”

Instead, it is patient work that requires time and perseverance.There is a TPS twist on work instructions — using A3 sheets posted above workstations rather than 3-ring binders on shelves — but such instructions  have been recognized as essential since the 19th century, and have been part of the industrial engineering curriculum since its inception, decades before Toyota was started.

Yet,  the article implies that  a stamping parts manufacturer in the American Midwest survived for 70 years without them. Having seen many plants with non-existent or ineffective job instructions, I believe it, and it raises many questions.

Perspectives on Standard Work

In the TPS Principles and Practice group on LinkedIn, I started a discussion by asking “What do we mean by ‘Standard Work’?” At that point, I saw it as whatever you do to ensure that same work is done the same way every time, regardless of time of day, production line, or factory; 96 comments later, my perspective has changed somewhat.

Ensuring consistency is, of course, essential but the tool to do it is Job Instruction (JI) rather than Standard Work. An operator’s complete job often involves multiple tasks, each of which has its own instructions. Standard Work builds on these instructions by specifying how these tasks are sequenced and combined to make effective use of people and equipment.

The main contributors were Len CanootSid JoynsonPeter WintonCasey NgDavid Hayden, MBAAchyut VaidyaEmmanuel JALLASEdward M. WhartonStephen DuquetteErik HagerJoachim KnufPaul Perry,  Cid LiSalvador D. Sanchez, Richard KunstAnders PenkerAndrew Williamson, and Steve Milner. The discussion also cited publications by Mike Rother, Art Smalley, John Shook, and Taiichi Ohno. If you want to see the whole discussion, please check it out on LinkedIn. This post is a synthesis , organized by topic and with illustrations added.

1. Why ask about Standard Work?

The House of Lean is a common metaphor. I use it sparingly, to make the point that the reason most Lean implementations in the US fail is that they are missing one of the two pillars:

House of Lean in Working with Machines

For this purpose, I don’t need to break down the details of what is in the Foundation or what the Goals are. Others provide many more details about the House of Lean, using it as a map of the whole system, with a prominent place given to something called “Standard Work” or “Standardized Work”:

As we can see, there is with variation in Standard Work  is supposed to mean. The Toyota description of Standard Work, for example, includes no reference to 5S or Visual Management, and explicitly excludes Job Instruction. The house on the right is from the Lean Enterprise Institute’s Lean Lexicon, and lists “Standard Work” and “Separating human work and machine work” as distinct entries but it is exactly what you accomplish with work combination charts, that are part of what Toyota calls Standard Work.

When you look it up on the Toyota Georgetown website or the LEI’s Lean Lexicon, it is about setting, for each operation, a takt time, work sequence, and required WIP, as expressed through a process capacity sheet, a work combination chart, and a work chart that is a layout diagram showing flows of parts and movements of operators between stations. (Click to see in full size.)

This is much more specific than what is meant by Standard Work is most discussions I have seen. I use capacity sheets, work combination charts and work station layout charts wherever you have to choreograph people working with machines, but I would not recommend them, for example, in manual assembly.

I have posted before about the work combination chart, as a powerful design tool for operator jobs, that also serves to communicate the sequence of tasks to operators, particularly new ones who are rotated into these positions. I see them as excellent tools, but it would not occur to me to label them “Standard Work,” because I don’t see any connection with the usual meaning of “standard.” I understand that “Standard Work” is an accurate translation of 標準作業 (Hyojun Sagyo), but I still don’t see a connection.

The following video clip, posted by JMA in Japan in 2009, shows what can be accomplished with work combination charts:

 

2. Standard Work and Process Stability

A process is stable if it can produce consistent output at a consistent pace. If it’s not stable, the first order of business is to stabilize it, but I don’t see standard work as the way to do it. You need to re-engineer the process to the point that its capability is no longer an issue and it is repeatable. Documentation and work instructions are an outcome of this effort, as needed to reduce the improved process to daily practice, but it is not the effort itself.

And the resulting documentation is not Standard Work. Standard Work, in the Toyota lexicon, is about takt time, work sequence, and required WIP, it doesn’t include process capability or even work instructions at the individual station level. It is only about the way you combine them in a line or a cell.

3. Is Standard Work the Best Known Way?

Most the Lean literature depicts Standard Work as an improvement backstop, a formalization of the improved process for the purpose of preventing backsliding. The following video is a quaint example of a PowerPoint animation used by a consultant to make that point. Note the yellow block preventing the wheel rolling back down:

Standard Work as “the best known way of doing the task” is the improvement backstop view, which I held without questioning it until I saw two articles disagreeing with it, and with each other, by Art Smalley .and Mike Rother. Mike Rother sees standard work as a target to shoot for rather than a backstop. Following is his rolling-wheel diagram:

Mike Rother's standard as a target condition

Mike Rother’s standard as a target condition

Yet another version was included in John Hunter’s review of Gemba Walkabout, and it shows standard work used to block progress instead of helping.

pdsa_blocked

These rolling-uphill diagrams remind me of the myth of Sisyphus, as described by Albert Camus. Sisyphus was a man condemned by the Gods to roll a boulder uphill everyday only to see it roll back down and start over, for eternity. See the following rendition by Marcell Jankovics:

Even if Sisyphus had had a backstop, it does not strike me as a particularly attractive metaphor for Kaizen.

Art Smalley sees Standard Work as a point of reference against which to measure future improvement. Taiichi Ohno does not say much about it in “Toyota Production System,”  but in Workplace Management,  he writes:

“There is something called ‘Standard Work,’ but standards should be changing constantly. lnstead, if you think of the standard as the best you can do, it’s all over. The standard is only a baseline for doing further kaizen. lt is kai-aku if things get worse than now, and it is kaizen if things get better than now. Standards are set arbitrarily by humans, so how can they not change?

When creating Standard Work, it will be difficult to establish a standard if you are trying to achieve “the best way.” This is a big mistake. Document exactly what you are doing now. lf you make it better than now, it is kaizen. lf not, and you establish the best possible way, the motivation for kaizen will be gone.

That is why one way of motivating people to do kaizen is to create a poor standard. But don’t make it too bad. Without some standard, you can’t say “We made it better” because there is nothing to compare it to, so you must create a standard for comparison. Take that standard, and if the work is not easy to perform, give many suggestions and do kaizen.”

4. John Shook on Standard Work

John Shook published three e-Letters on the subject of Standard Work in October 2009, called “Five missing pieces in your standardized work.”

In Part 1, he describes the goal of having the same work done the same way everywhere as distinct from Standard Work. He calls it “commonization” as a translation of 横伝(Yokoten). Literally, Yokoten means “lateral transfer,” but it is meant about know-how, not people. You invented a better way to do a job, and you propagate it to everybody else who does the same job.

When he discusses the distinction between Standard Work and Work Standards, Shook includes under Work Standards not just the time a task is supposed to take but all its technical parameters, such as critical dimensions, tolerances, etc.

He describes Kaizen and Standard Work as two sides of the same coin. You can’t have Kaizen unless you have Standard Work as the basis for improvement, and a Kaizen project is not finished until its outcome is incorporated in Standard Work. But Standard Work as he describes it —  with work combination charts — is used almost nowhere in American plants that claim to practice Kaizen. This means that some of the following must be true:

  1. The definition of Standard Work is too narrow. The need to specify takt times, work sequence and standard WIP is general, but different tools can be used to do it in different types of plants. A work combination chart, for example, is of limited value in a manual assembly process.
  2. Most plants that claim to practice Kaizen really don’t. In Japan, Kaizen designates small improvements to work methods, conceived and executed by the people who do the work, and US-style “Kaizen Events” are not Kaizen at all. A plant may run 50 Kaizen events per year and still not practice Kaizen. The means of implementing Kaizen include suggestion systems, that exist in many plants with varying success, and small-group, circle activities, that, in the US, are only found in Japanese transplants. As “Quality circles,” in the US, they were a fad in the 1980s; as Jon Miller pointed out in Quality Digest in 2011, circles are still going strong in Japan and in the rest of Asia.
  3. Some Kaizen activity is possible without Standard Work. What you really cannot do without is some metrics of before-and-after performance for the area that is improved, and these may be measured without Standard Work being in place.

The bulk of Part 2 is an example from Shook’s own experience on the Toyota assembly line in Takaoka in 1984. In Part 3, he describes Standard Work through the Purpose, Process and People framework, which he calls 3P. I had heard the “3P” acronym used before, by Shingijutsu people as the “Production Preparation Process,” which is something completely different.

5. Standard Work versus Work Standards

John Shook gives the following as examples of Work Standards:

  • Assembly – apply xx pounds of torque
  • Processing – heat treat at xxx degrees for x hours
  • Healthcare – provide xx medication at xx dose
  • Coffee – xx seconds for an espresso shot
  • Journalism – a weekly column of xxx words
Frederick Taylor quote

Frederick Taylor quote

Last month, the Institute of Industrial Engineers (IIE) had a conference in Chicago on “Managing Work Standards.” It was exclusively about how long it takes to do work, not about what the work is. It is a sensitive topic because it is associated in the minds of production operators with Taylor’s “scientific management” and his determination to prevent operators from colluding to curtail output, which he called “soldiering.” For all his great contributions, respect for humanity was not Taylor’s strong suit. He probably would have said that this man should have borrowed money from his parents to start a business…

What we are doing when analyzing video recordings of operations is more in line with what Frank and Lillian Gilbreth did: observing processes in order to improve them. The difference in thinking is obvious from just viewing the films the Gilbreths made about bricklaying operations.

The Gilbreths were working to make the bricklayers’ job easier, not to make them exert more effort, but Taylor’s name is better known, and his legacy is a challenge to live down.

I think we need to improve the terminology. Having two different concepts called “Standard Work” and “Work Standards” is confusing, especially when Toyota uses “Work Standards” to mean something other than the IIE. Incidentally, it is confusing in Japanese too.

How about using “Work Instructions” for what Shook calls “Work Standards”?

6. What is the Scope of Standard Work?

What is the scope of Standard Work? I have seen described, I don’t remember where, as the process as seen through the eyes of a first-line manager — also currently known as production supervisor, group leader, or area coordinator, and formerly as foreman. This is a member of management, with direct responsibility for quality, cost, and delivery by a few teams of operators.

This person sees the work as a sequence of tasks to which operators are assigned and among which they rotate as needed. The technical and human unit processes at each station are the foundation on top of which the supervisor works. This would be why Standard Work is focused on takt time, work sequence and work combinations, as opposed to tolerances and job instruction (JI).

7. Standard Work, Yokoten, and Revision Management

Also, Standard Work comes in the form of documents that are seen on the shop floor and that people are expected to follow. This makes them official, with revision numbers and approval stamps by stakeholders. Revision management on Standard Work is a whole other topic that I have not seen discussed anywhere.

8. Is Standard Work a Proper Focus for a Project?

Standard Work is a 2nd tier tool, like Visual Management, meaning that it is part of every project but never the focus of a project in its own right. In a brownfield situation, making “Standard Work” a project would lead you to attempt the precise documentation of work methods that need to be changed anyway, which would not be terribly useful and could bog you down for so long that you never get to do anything else.

On the other hand, if you identify specific dysfunctions in a process and organize a project to fix them, then you want the new and better way to be documented in such a way that it can be propagated across shifts and to other shops that do the same work.

9. Is Every Problem a Deviation from a Standard?

Peter Winton feels strongly that it is. And this is about standards in general, not just Standard Work. If every problem is a deviation from standards, however, we have an easy way of solving all our problems: let us just scrap the standards… But it would not solve all our problems, would it?

It would solve some problems, because there are futile standards. As David Meier pointed out, when you set a standard, you create an opportunity for deviation, and the need to respond to these deviations. So don’t standardize what you don’t need to.

The absence of a standard can be a problem. I remember a 2-in binder of specs on how to inspect an aerospace part that did not actually contain objective criteria for rejecting a part.

More generally, Standard Work, Job Instructions, Acceptance Specs, etc. are documents that are necessary to ensure a consistent output but not sufficient to guarantee that products will work for customers.

Products that are perfect on our terms may still displease customers, because they are using them in ways we didn’t anticipate. That is a problem, but it is neither the lack of a standard nor a deviation from any standard.

From what you write, I assume that you consider a standard to be an explicit statement of what should be, whether it is expressed as “this bolt should be tightened to x foot-pounds of torque,” or “this bolt should be tightened until the nutrunner’s light goes green.”

There are problems that cannot be expressed as a deviation from standard. As we all know, the proof of a cake is in the eating, which means that it cannot be tested before leaving the pastry shop. You serve this untested cake to your guests and it’s awful. The taste of the cake, in Juran’s terms, is a true characteristic. It is really what you are after but, more often than not, it is something you don’t know how to measure, and you can’t set a standard for.

You can measure some substitute characteristics of the cake, like its diameter, sugar content, or fat content. For these substitute characteristics, you can have specs to deviate from, and, if a cake is out of spec, you know it’s bad. It is, however, possible for a cake to meet all the specs you have defined and still taste awful. Whatever standards you define work as a one-way filter. What they allow you to reject is defective, but you don’t know that what they let through is not.

Philip Crosby

Philip Crosby

Joseph M. Juran

Joseph M. Juran

This was the old debate between Philip Crosby, for whom quality was “compliance to requirements,” and Juran, for whom it was “the agreement of reality with expectancy.” These are different philosophies, leading to different practices. For engineering students, for example, the Crosby approach would equate scoring As on exams with being a good engineer; in the Juran approach, there is more to it.

10. Is it “Standard Work” or “Standardized Work”?

It is “Standardized Work” that is the questionable translation. The Japanese term is 標準作業 (Hyojun Sagyo). 標準 (Hyojun) means Standard and 作業 (Sagyo) means work. Google translates 標準作業 to Standard Work and Standard Work to 標準作業. If you translate “Standardized Work” into Japanese, you get 標準化された作業 (Hyojunka sareta sagyo) and more syllables on both sides. I prefer the shorter version.

The same concept is called “Standard Work” by Ohno, “Standard Operations” in the JMA’s ‘Kanban, Just-in-Time at Toyota” and in Monden’s “Toyota Production System,” and “Standardized Work” in the LEI Lean Lexicon and on the Toyota Georgetown website.

If the terms were intended to designate different things, they should be more distinctive. I actually don’t think either one makes much sense because they are too generic and not descriptive. If you hear “page scanner” for the first time, you guess accurately what it does; for “Standard Work” or “Standardized Work,” good luck! Everybody thinks they know what it means, but all interpret it differently, which does not help communication.

11. Standard Work for Leaders and Managers

David Hayden brought up the subject of Standard Work for leaders, managers, and engineers. I see all jobs as routinely involving a mix of the following:

  • Repetitive tasks
  • Planned responses to events
  • Decision making in the face of unplanned events.

For production operators, it is mostly repetitive taks; for CEOs, mostly decision making. Standard Work, if defined as the combination of takt time, work sequence and standard inventory, is only applicable to production operators. In a broader sense, it can be applied to all repetitive activities.

A team leader in a cell, for example, does production work for about 50% of the takt time, and, in addition, is responsible for

  1. Maintaining the pace.
  2. Relieving other team members as needed.
  3. Supplying materials and tools to other team members.
  4. Keeping records.
  5. Coordinating changeovers.
  6. Coordinating 5S at the end of the shift.

Planned responses are not Standard Work in the strict sense. As far as I know, within Toyota in the US, they are organized under “Change Point Management” (CPM). In Japanese, as Casey Ng pointed out, it is called 変化点管理 (Henkatenkanri). About the scope of CPM, he wrote:

“For change point management such as a change in takt time , the introduction of new members to a  line, preparation to shut down, startup after week-end, resuming production after a power failure, introducing a new product, changing of new version of parts etc. There are all sort of standards which may generally call Standard Work.”

12. Standard Work and Project Management

Len Canoot asked whether the elements of Standard Work were translatable to project management.

The time it takes to do the work is the process time or the cycle time, not the takt time. In a line that works at a steady pace, the takt time is the interval between consecutive unit completions in order to meet the schedule within the work time available.

Does it translate to projects? It depends what kind of projects. If all your projects are “Kaizen events,” each one takes 11 weeks: 6 weeks of preparation, 1 week of focused activity, and 5 weeks of follow-up. It is a standard process, and you can to run them at fixed intervals in different areas of your plant. Most projects, however, are not reducible to this kind of cookie-cutter approach.

In a more general setting, there are tools you can use to manage a flow of projects, like capping the number in progress, so that participants’ attention is not spread too thin. At the very least, all your projects are either waiting to start, in progress, or finished. Often, however, they all go through a more detailed, common sequence of phases through which you can track them, even though the work required for a project through a given phase may vary.

Does that add up to standard work for projects?

13. Standard Work versus Standards in general

About the usual meaning of standard, this is what Wikipedia says about technical standards:

“A technical standard is an established norm or requirement in regard to technical systems. It is usually a formal document that establishes uniform engineering or technical criteria, methods, processes and practices.”

That covers the metric system and the internet protocols. Wikipedia also says the following about Standard Operating Procedures (SOP):

“In clinical research, the International Conference on Harmonisation (ICH) defines SOPs as ‘detailed, written instructions to achieve uniformity of the performance of a specific function’.”

When I see “detailed, written instructions,” it makes me think of the victorian-novel sized instruction binders that sit on shelves in many plants, unread, dusty, and full of obsolete information. Standard is also used in many other ways.

14. Standard Work and Changes in Takt Time

Anders Penker brought up the issue of the effect of changes in pace on Standard Work. One key reason you set up U-shaped cells, with the operator work area inside, is staffing flexibility. If it takes, say, 5 operators to operate at capacity, you can operate with 3, 2 or 1 operator at reduced rates, as seen below:

Takt time change in cells

Of course, your work chart and work combination chart for 6 operators are not applicable when you only have 4 or 3. But operating at a reduce pace with fewer people is something you can anticipate and plan for. You should have Standard Work ready for these circumstances, and post it as needed.

And there are circumstances where these charts are not applicable, for example when you apply the bucket-brigade method to make custom-configured products. But that is a different topic.

Standard Work in Low-Volume/High-Mix Manufacturing

In the TPS Principles and Practices discussion group on LinkedIn, Brian Miller initiated a discussion on “How do you create standard work for a customized product that has over a billion combinations?” It has had 31 comments so far, and I would like to share here a few that I made.

Even in a plant that is perceived to be focused on low-volume/high-mix production, you usually have an uneven demand pattern, calling for different approaches to standard work by product category.

You start with a Runner/Repeater/Stranger analysis to determine what it is we do often and what not. Without this analysis, we commingle in the same lines products made every day with other products made sporadically (See Lean Assembly). In Japan, this is called P-Q, or Product-Quantity analysis, with the categories called A, B and C. The more vivid Runner/Repeater/Stranger terminology comes from Lucas Industries in the UK. You then use a dedicated, integrated production line for each Runners, a flexible line for each family of Repeaters, and a job-shop with functional groupings of equipment for Strangers.

Then, obviously, you face different challenges for developing standard work in each category:

  1. In a runner line, you can post A3 sheets above each workstations with instructions for the purpose of allowing supervisors to monitor how the work is being done. This is the normal situation of high-volume production.The operators themselves do not need to read the instructions for every workpiece; as soon as they are proficient in the job, they work from memory.Operator instructions in auto parts assembly
  2. A repeater line is for a family of products with variants but with a high commonality of materials and processes. The instructions that can be posted on A3 sheets are then limited to the common processes, but the operator needs to read what is specific to each workpiece. For final assembly of cars, Toyota has provided “build manifests” printed on larger sheets mounted on car bodies and bearing all the option information. The kitting of workpiece-specific components also helps. In computer assembly, workpiece specifics are shown on electronic displays, with component picks validated by auto-ID technology, including bar codes, QR-codes, or RFID chips.Toyota build manifest Valenciennes cropped
    Kit-trays-with-instructions-web

    Kit trays with instructions for repeaters in electronics assembly

  3. Strangers are the odds and ends with sporadic demand, one-of-a-kind systems, or new product prototypes. For strangers, you cannot rely on operator memory or habit. For one-of-a-kind systems or prototypes, you cannot even assume you have the knowledge needed to produce workable detailed instructions. Each stranger is a job in a job shop and requires instructions on a traveller that moves with the workpiece. The traveller may be hardcopy or electronic. An electronic traveller may either be a device containing all the instructions or an ID that triggers the download of appropriate instructions at each station. Strangers are usually built by skilled craftsmen able to work directly from engineering drawings. Given the nature of strangers, however, the time required cannot be precisely known and sequencing mistakes will happen, making rework inevitable.
Stranger assembly in Yatai at Omron

Stranger assembly in Yatai at Omron