Zero Defects (無欠陥) – Part 3 of 3 Using Poka-Yoke (ポカヨケ) System

This is the third part of the article Zero Defects, and I have chosen the theme of pokayoke system, focused on the use of devices that are required to build a Pokayoke.

In my experience as a consultant, I have seen some Lean Engineers who lack practical experience in Pokayokes (they focus on philosophy but never built for themselves a system); so I hope that this post will provide information to help some people who need it, in next project.

Poka-yoke System Functions

A poka-yoke system processes two functions : It can carry out 100 percent inspection and, if abnormalities occur, it can carry out immediate feedback and action. The effects of poka-yoke methods in reducing defects will differ depending on the inspection systems with which they are combined: source inspections, self-checks, or successive checks.

Types of Poka-yoke

Poka-yoke systems fall in to regulatory function categories, depending on their purposes, and setting function categories, according to techniques they use.

Poka-yoke Regulatory Functions

Two regulatory functions are performed by poka-yoke systems.

1. Control methods

These are methods that, when abnormalities occur, shut down machines or lock clamps to halt operations, thereby preventing the occurrence of serial defects. Such methods have a more powerful regulatory function than do those of the “warning” type discussed below, and maximum efficacy in achieving zero defects is obtained by the use of these control type systems.

2. Warning methods

These methods call abnormalities to workers’ attention by activating a buzzer or a light. Since defect will continue to occur if workers do not notice these signals, this approach provides a less powerful regulatory function than control methods.

In cases where workers’ attention is captured by means of light, blinking lights can attract attention more powerfully than steady ones. Ultimately, this method is effective only when workers take notice, and the passive aspect of light signals makes it necessary to regulate placement, intensity and colour, etc.

Poka-yoke Setting Functions

The setting functions of poka-yoke systems can be divided in to three categories.

Setting Function Types and Examples

1.    Contact methods

Methods in which sensing devices detect abnormalities in product shape or dimensions by whether or not contact is made between the products and the sensing devises are called contact methods.

2. Fixed-value methods

With these methods, abnormalities are detected by checking for the specified number of motions in cases where operations must be repeated a predetermined number of times.

3. Motion-step methods

There are methods in which abnormalities are detected by checking for errors in standard motions in cases where operations must be carried out with pre determined motions. These extremely effective methods have a wide range of application, and the possibility of their use should by all means be examined when poka-yoke setting functions are considered.

Detection Measures for Poka-yoke Systems

Detection method Functions

Below are simple explanations of the functions of the various detection methods.

I hope this information help you in your next Kaizen Event.

Zero Defects (無欠陥)– Part 2 of 3- San-Gen-Shugi methodology (Genba ,Genbutsu & Genjitsu.)

I have considered to describe on this article the San-Gen-Shugi methodology, which underlies the breakthrough approach for Problem Solving.

San-Gen-Shugi – Genba ,Genbutsu & Genjitsu.

San (three), Gen (reality) what you actually see in front of you and Shugi (principle).

San-Gen-Shugi (Principle of three realities) has three elements as shown below.

·      Gen-ba means, "Real Place”: Go to the shop floor to understand the reality.

·      Gen-butsu means, "Real Part": Look at the real part or the real services provided and analyze it while focusing on the facts.

·      Gen-jitsu means, "Real Facts": Present conclusions using real data for a better understanding of what is actually happening in the field.

Fig

Principle of Genchi Genbutsu.

Taiichi Ohno ; always promoted the principle of Genchi Genbutsu which means “Go and see for yourself”

There is no substitute for direct observation.

In many Organizations the employees try to solve problems (for example, why a machine is unreliable) by thinking about the problem and devising hypotheses that haven’t checked on the field. Toyota gets their employees to recognize the importance of direct observation.

Fig.

Managers should coach, not fix.

Each worker looks for ways to improve the quality applying Problem Solving PDCA, and the manager’s role becomes one of involving the team in identifying the problems and not doing all the work himself.

The TPS lends itself to Deming’s writings about Leadership who understood that traditional supervisory activities are reactive rather than proactive. Many managers to pay a great deal of attention to reports and data which tell them what happened yesterday, last week, last month, or last year. Often such reports highlight the things that have gone wrong. Deming has compared this to attempting to drive a car by looking only in the rear-view mirror. Because of this, he observed that, “A supervisor is an auditor of failure, while a leader listens and learns, studies and understands and works to improve the system.” He also noted that “One important characteristic of a leader is that he will forgive a mistake – there will be mistakes.”

Fig

On real Manufacturing world; the Engineers Team Support and Managers should work more like Dr. Gregory House rather than Dr. G , the difference is obvious Dr. House is fighting to save his patients , identifying how to solve pathological enigmas and in other hand Dr. G is analyzing why the patient has already dead.

If the organization wants solve problems and reach Zero Defect, the reaction time should be immediate ASAP.

For that purpose the Manufacturing Lines must be adapted with: Andons lights to call for assistance, Jidoka for Auto stops can be added, Defects Tables (Genbutsu Tables) and Defects Red Bins to avoid mix the Defects parts and Good parts, and also avoid the Defects Parts been Reworked.

The Standard Work for Problem Solving includes a clear Escalation path for problems assistance, next to the line and very visible, the Problem Solving template to use etc.

Fig.

Do not rework is critical for problem solving, to establish this rule is basic for a Zero Defect implementation, actually this is an important behavior that you may take in your account, if the Management have a real support for Lean Manufacturing they must be agree on this, otherwise the Management are just looking for Lean Fake and don’t have real intention to fix the problems.

The Team members must be conscious about the Defects; the Lean Managers should look for different ways to make them understand what a Defects means.

Fig.

The Management Roll in Problem Solving.

The management has the main roll on Problem Solving; maybe this is the most critical difference between Toyota and other Organizations, unfortunately in most of the organization the Management delegates this responsibility to lower levels.

•       Quality management method

1. Do you understand the defect condition?
2. If yes, did you define the correct method – to set up Defects Table to control the condition?
3. If yes, did you fully utilized Defects Table?
4. How to fully utilize the Defects Table? – Any defect must display in Defects Table managers and engineers shall check Defect Table every one hour, engineer must use 5why to analyze and resolve the problem immediately
5. Check if defects reduced
6. If defect number close to 0
7. If the same defect code happen again, the machine should be able to stop automatically until the leader or technician resolve the problem, operator not allow to reset the machine, which is PoKa-Yoke method to prevent the defect happen again.

•       If you want to become a Problem Solving Master - Do not assume or talk only or if not, you become a fortune teller:

1. Do you understand the problem?
2. If yes, do you understand the method to change or correct?
3. If yes, did you follow the method to do?
4. If yes, did you confirm the achievement? 
5. If yes, did you monitor if the abnormal still there?
6. If the abnormal confirmed does not exist anymore, did you Yokoten the method to other lines?
7. If you did Yokoten, did you monitor if the good condition maintain?
8. Until you do till the item 7, you become an honest person a Real Problem Solving Master, or if not, you are assuming the situation can be better, then you will become a fortune teller.

Metrics to Zero Defects.

•       MTBF : Mean Time Between Failure

•       MTBR: Mean Time Between Response

•       MTBRC: Mean Time Between Rood Cause

•       MTBPS: Mean Time Between Permanent Solution (Pokayoke)

•       Top Defects – Solve one per day

•       Time to attend Red Light – 10 sec max.

•       Time to implement Quality Alert:

•       Customer defects finding  - 1 day

•       Internal defects top finding – 1 hr

•       Zero Defects per line – No ppm´s  No % yield

ΠChange ATTITUDE : San Gen Shugi

. . .Applying “Genjitsu” means being realistic, not idealistic.  “Genba” means going out on the shopfloor to discover the real root causes of problems.  And “Genbutsu” refers to real parts, and the way of dealing with non-conformance. 

We must use non-conformance parts to learn how to improve and achieve Total Quality.    

I have only two methodologies:  my eyes and my legs.  These are all I need to see, to judge, to consider, to decide.  This is the basis of “SanGenShugi”. . .

(Kazuo Kawashima, June, 2002)

We should follow the advice of Sensei Taiichi Ohno and look on "facts"..... 

I hope this help you in your next Problem Solving Event…..