1. Poka-Yoke (Mistake Proofing)
5/22/05 Fixed repeated note on slides
Added slide 2 with quotation from Douglas Adams
Added Sean’s Law to slide 4
Slide 24, added instructor note, “May be performed as a group or in break-out groups of 4-5 ea.”

2. “A common mistake of people who try to make things completely fool-proof is to underestimate the ingenuity of complete fools.”
-- Douglas Adams

3. Module Outline Background Introduction First poka-yoke device
Categories of poka-yoke
Examples
Tips and techniques
Summary
Practical exercises
References

4. Background The real world
People make mistakes
People are human
Mistakes are inevitable
Murphy’s Law: “If something can go wrong it will”
Sean’s Law: “Murphy was an optimist”

5. Background The old way to prevent mistakes Reprimand worker
Retrain worker
Motivational talks
Tell them to “be more careful”
Tell them to “pay attention”

6. Background A better way to prevent mistakes
Remove the opportunity for error
Improve the process
Make wrong actions more difficult
If you can’t remove the opportunity for error
Make it easier to discover the errors that do occur

7. Introduction
Shigeo Shingo invented the Japanese concept called Poka-Yoke (pronounced POH-kah YOH-kay)
Poka-Yoke means to mistake proof the process
The essential idea of poka-yoke is to design your process so that mistakes are impossible or at least easily detected and corrected

8. First Poka-Yoke Device
Shingo suggested a solution that became the first Poka-Yoke device
In the old method, a worker began by taking two springs out of a large parts box and then assembled a switch
Problem: Sometimes the worker failed to put both springs in the switch

9. First Poka-Yoke Device
In the new approach, a small plate is placed in front of the parts box and the worker's first task is to take two springs out of the box and place them on the plate
Then the worker assembles the switch. If any spring remains on the plate, then the worker knows that he or she has forgotten to insert it
The new procedure completely eliminated the problem of the missing springs
Empty plate

10. Categories of Poka-Yoke
Poka-yoke devices fall into two major categories:
Prevention
Detection
A prevention device engineers the process so that it is impossible to make a mistake at all

11. Prevention Example
A classic example of a prevention device is the design of a inch computer diskette
Impossible to put in upside down

12. Categories of Poka-Yoke
A detection device signals the user when a mistake has been made, so that the user can quickly correct the problem

13. My car beeps if I leave the key in the ignition
Detection Example
My car beeps if I leave the key in the ignition

14. Other Poka-Yoke Examples
Locking devices on filing cabinet prevents opening multiple drawers which would lead to tipping

15. Other Poka-Yoke Examples
Gas pumps are equipped with hose couplings that break-away and quickly shut-off the flow of gasoline

16. Other Poka-Yoke Examples
This rental truck has a door latch which will not allow the loading ramp to slide out while the latch is in the closed position

17. Other Poka-Yoke Examples
The Saf-T-Smart valve kit detects when the washing machine is operating and opens the valves allowing water to flow freely.
When the washing machine is off the valves are closed, reducing pressure on the hoses and avoiding serious water damage (and returning to a flooded house).

18. Other Poka-Yoke Examples
The U.S. Consumer Product Safety Commission has recorded 105 deaths that were caused by wheelchairs rolling away from the person.
The response? A mistake- proofing device that locks the wheelchair when no one is sitting in it. An unlocking lever on the handle allows the wheelchair to be moved when empty.

19. Other Poka-Yoke Examples
When pipes are likely to freeze, the common practice is to open faucets slightly and let them drip.
This device automatically opens a valve that discharges just enough water to avoid pipes freezing.

20. Other Poka-Yoke Examples
Limit switches
Interlocks
Jigs
Alignment marks
Go/no-go devices
Electronic eyes
Checklists

21. Tips and Techniques Eliminate unnecessary or duplicate steps
Use flow charts to visualize the process
Keep it simple
You don’t have to spend a lot of money
Use many Poka-Yoke devices in a process
There isn’t a quota on how many you can use

22. Summary Poka-Yoke means to mistake proof the process
Remove the opportunity for error
Improve the process
Make wrong actions more difficult
If you can’t remove the opportunity for error
Make it easier to discover the errors that do occur

23. Each table or group is to list other examples of
Class Exercise
Each table or group is to list other examples of
Poka-Yoke (mistake proofing) devices
Brainstorming!!
Examples:
Treadmill with safety kill switch on a string
Iron with automatic cut-off
Lawnmower will cut-off if you get off
Bathroom sink with overflow hole
Circuit breaker will trip before overheating
Garage door opener
Door-a-jar light on car
Fluid indicator on car
Window on envelope prevents letter from going to the wrong person

24. Class Exercise Mistake-Proof This:
I always end up putting slides into the carousel projector up-side-down, backwards, or sideways.
Propose a change that will ensure the correct orientation or make incorrect orientation obvious.
Suggested answer: Mark the top left or right corner with a bright marker. May be performed as a group or in break-out groups of 4-5 ea.

25. Class Exercise Mistake-Proof This:
A local countertop company makes and then loads the countertop pieces on to a truck and goes to the customer’s home and installs the countertop.
More than 15% of all installation jobs have to be done with more than one trip to the customer’s home because one or more pieces of the countertop was not loaded on the truck.
Propose a change that will ensure all the material is loaded on the installation truck.

26. Class Exercise Mistake-Proof This:
Mechanics in the instrument lab have to calibrate instruments in accordance with a procedure that has several steps. They sometimes inadvertently skip a step in the procedure.
Propose a change that will ensure no steps are skipped.

27. Class Exercise Mistake-Proof This:
The far-sighted instructor in a rush to get to work on time often forgot and left his glasses at home.
Propose a change that will ensure the instructor does not forget his glasses.

28. References John Grout Other authors www.campbell.berry.edu/pokayoke
"Mistake-Proofing Production." Production and Inventory Management Journal Vol. 38, No. 3, pp
"Failsafing and Measurement Control Charts" with Brian T. Downs. Quality Management Journal. Vol. 5, No.2, pp
Other authors
Services: Make your service fail-safe. Chase, R. B., and D. M. Stewart Sloan Management Review (Spring):
Links to design:The role of variation, mistakes, and complexity in producing nonconformities. Hinckley, C.M. and Barkan, P Journal of Quality Technology 27(3):
The design of everyday things: Norman, D.A New York: Doubleday. (“poka-yoke” not discussed, still applies, very cool.).
IMPROVE Poka Yoke rwk.ppt Module - Knight 05/07/02.

29. QUESTIONS