Lean Six Sigma 100%

Yellow Belt · Control phase

Lesson 9: Holding the gain - Kanban, Poka-Yoke, and the control plan

IASSC Body of Knowledge 5.1, Lean Controls, and 5.3, Six Sigma Control Plans · 14 practice questions

0:00 / --:--

Reading

An improvement that erodes back to the old, broken state within a few months was never really finished. This lesson covers the Control phase material in the Yellow Belt Body of Knowledge: the Lean tools used to hold a gain in place day to day, and the formal control plan document that makes holding it everyone's explicit, assigned job rather than a hope.

The control loop a control plan and a response plan run together The process runs, is monitored against the control plan, and if it stays in control the process simply continues. If it goes out of control, the response plan defines the corrective action to take before the process resumes. Run the Process Normal operation Monitor Control chart vs. the control plan In control? Yes: continue as normal No Response Plan Defined corrective action, owner, and timing Corrective action taken, process resumes
The control plan and response plan work as a loop: monitor the process, and when it goes out of control, the response plan's pre-defined corrective action brings it back before returning to normal operation.

Control methods for 5S

5S, covered in Lesson 4, decays without deliberate upkeep; a workspace that was Sorted, Straightened, and Shined once will drift back toward clutter within weeks unless something actively sustains it. The standard control method is a recurring 5S audit, a short, scheduled walkthrough against a checklist, scored and tracked over time, often visually posted so everyone can see the current state and the trend. The audit is what turns Sustain, the fifth S, from a vague aspiration into an actual, repeatable practice with accountability attached.

Kanban

Kanban is a visual signaling system, originally a physical card in Toyota's system, used to control inventory and work in process by triggering replenishment or production only when it is actually needed, rather than on a fixed schedule or forecast. This is a pull system: downstream demand pulls work forward, as opposed to a push system, where each step produces according to a schedule regardless of whether the next step is ready for it. Kanban directly attacks the overproduction and excess inventory wastes covered in Lesson 4, since nothing gets made or moved until a real signal calls for it, which keeps work in process visible and bounded rather than silently piling up between steps.

A Kanban signal pulls work forwardDemand: Downstream work, needs replenishment. Signal: A visible request, calls for work. Replenish: Produce or move, when it is needed DemandDownstream workneeds replenishmentSignalA visible requestcalls for workReplenishProduce or movewhen it is needed
Read this sequence as a pull signal: downstream demand calls for replenishment. The lesson contrasts this with production based only on a schedule or forecast.

Poka-Yoke, mistake-proofing

Poka-Yoke, a Japanese term usually translated as mistake-proofing, credited to Shigeo Shingo, is the practice of designing a process so that errors are either physically impossible to make or are caught immediately if they occur, rather than relying on an inspector or an operator's attention and memory to prevent them. Poka-Yoke devices split into two broad types: prevention, where the error cannot physically occur at all, such as a part designed so it can only be assembled in the one correct orientation, and detection, where the error can still occur but is caught and signaled immediately, such as a sensor that stops a machine the instant a required step is skipped. Prevention is generally preferred over detection whenever it is achievable, since a prevented error never happens at all, while a detected error still occurred and still has to be corrected, just sooner rather than later.

Cost-benefit analysis for control

Not every control method is worth its ongoing cost. Before a control is built into a process permanently, it is weighed against the cost and frequency of the problem it prevents. A control that costs more to run, year over year, than the defect it prevents would have cost the organization is not a good design choice, and this is exactly the same logic used earlier, in Lesson 3, to build a project's financial case in the first place: a control plan is itself a small, ongoing investment decision and deserves the same scrutiny.

Elements of the control plan

A control plan is the formal document that hands a finished project off to the Process Owner named in the original charter, in Lesson 3, so that the gain survives after the project team disbands. At minimum, a control plan specifies: which CTQ or process characteristic is being controlled, how it is measured and how often, what the acceptable range or specification is, who is responsible for checking it, and where the data or results are recorded. A control plan with no named owner, or no defined checking frequency, is not really a control plan, just a description of a good idea that nobody is specifically accountable for maintaining.

Elements of the response plan

A response plan is the part of the control plan that answers a different question: what happens the moment a control point signals a problem. It specifies who is notified, what immediate action they take, and what corrective or containment steps follow, so that the reaction to an out-of-control signal is decided in advance, calmly, rather than improvised under pressure in the moment the problem actually appears. A control plan that only says what to measure, with no response plan for what to do when the measurement goes wrong, leaves the process exposed exactly when it matters most.

Practice questions

1. What does a recurring 5S audit accomplish?

  1. It replaces the need for the Sustain step entirely, since a scored checklist makes the fifth S redundant
  2. It turns Sustain from a vague aspiration into a repeatable practice with accountability
  3. It calculates a Risk Priority Number
  4. It is only used during the Define phase

2. Kanban is best described as which kind of system?

  1. A pull system, where downstream demand triggers replenishment or production
  2. A synonym for a control plan
  3. A push system, where each step produces on a fixed schedule regardless of downstream readiness
  4. A random sampling system for inspection

3. Which two of the seven wastes from Lesson 4 does Kanban most directly attack?

  1. Overproduction and excess inventory
  2. Motion and transportation only, the two wastes involved in moving people and material
  3. Defects and overprocessing
  4. Waiting and motion only

4. What is Poka-Yoke?

  1. A synonym for Kanban, the card-based visual signaling system used to trigger replenishment of parts and production
  2. Designing a process so errors are either physically impossible to make or are caught immediately
  3. A statistical test for hypothesis testing
  4. A type of value stream map

5. A part is designed so it can only be assembled in the one correct orientation. Which type of Poka-Yoke is this?

  1. Detection
  2. Prevention
  3. Reproducibility
  4. Response

6. Why is prevention generally preferred over detection in Poka-Yoke design, when both are achievable?

  1. Detection devices are always cheaper to build
  2. Prevention only works for attribute data
  3. There is no meaningful difference between the two in practice
  4. A prevented error never happens at all, while a detected error still occurred and still has to be corrected

7. What determines whether a control method is a good design choice, according to cost-benefit analysis for control?

  1. Whether it uses a physical device rather than a written checklist, since devices are always more reliable
  2. Whether leadership personally likes the idea
  3. Whether its ongoing cost is less than the cost and frequency of the problem it prevents
  4. Whether it was included in the original project charter

8. Which of the following is NOT typically specified in a control plan?

  1. The acceptable range or specification for the characteristic being controlled
  2. Who is responsible for checking the measurement
  3. The original members of the executive leadership team from a decade ago
  4. How often the characteristic is measured

9. A control plan names a CTQ, a measurement frequency, and a specification range, but has no named owner. What is missing?

  1. Accountability; without a named owner, it is a description of a good idea, not a real control plan
  2. Nothing; this control plan is complete as described, since the CTQ, frequency, and range are all present
  3. A Risk Priority Number
  4. A Gage R&R study

10. What does a response plan specifically add beyond the rest of the control plan?

  1. The original business case for the project
  2. A repeat of the measurement frequency already stated elsewhere
  3. The project's financial savings calculation
  4. What happens the moment a control point signals a problem: who is notified and what corrective action follows

11. As contrasted with Kanban in this lesson, which of the following describes a push system?

  1. A synonym for a control plan's response plan
  2. Downstream demand pulls work forward only when it is actually needed
  3. Work in process is kept visible and bounded by a visual signal
  4. Each step produces according to a fixed schedule regardless of whether the next step is ready for it

12. GCHS's rehab crew currently orders replacement HVAC filters on a fixed monthly schedule regardless of how many are actually used on site, leaving a growing stockpile in the supply closet. Which control concept from this lesson would most directly address the excess inventory this creates?

  1. Calculating the Risk Priority Number for the filters by scoring severity, occurrence, and detection
  2. Kanban, triggering reorders only when a real downstream signal calls for them
  3. A response plan naming who is notified of a stockout
  4. A 5S audit of the supply closet

13. A sensor on GCHS's drywall lift detects that a safety strap was left loose and immediately stops the lift and sounds an alarm, after the strap had already been left unsecured. Which type of Poka-Yoke is this?

  1. Reproducibility
  2. A response plan
  3. Detection, since the error already occurred but is caught and signaled immediately
  4. Prevention, since the strap can be fastened in only one position and the lift cannot start unsecured

14. GCHS's control plan for its window-repair CTQ names the characteristic being controlled, the measurement frequency, and the acceptable range, but does not say who should be notified or what immediate action to take if a measurement falls outside range. What is missing?

  1. A response plan
  2. A control chart
  3. A capability study
  4. A Gage R&R study

Glossary

Kanban
A visual pull system that triggers replenishment or production only when downstream demand calls for it.
Pull system
A system in which downstream demand pulls work forward, as opposed to a push system's fixed schedule.
Poka-Yoke
Mistake-proofing: designing a process so errors are either physically impossible or are caught immediately.
Prevention (Poka-Yoke)
A mistake-proofing design in which the error cannot physically occur at all.
Detection (Poka-Yoke)
A mistake-proofing design in which the error can still occur but is caught and signaled immediately.
Control plan
The formal document specifying the CTQ controlled, how and how often it is measured, the acceptable range, and who is responsible.
Response plan
The part of a control plan specifying who is notified and what corrective action follows when a control point signals a problem.
5S audit
A recurring, scheduled walkthrough against a checklist that sustains a 5S workspace over time.
Back to course Next lesson