Zero quality control through Poka-Yoke

 

Monark Bag

Lecturer, Indian Institute of Information Technology, Allahabad

 

Introduction

 

Customers in general expect a certain quality when they are spending money. A company will never do well if the customers are unsatisfied. This is why various quality control systems have been created. One of them is the Poka-Yoke Japanese zero quality control management. Poka-yoke is a combination of two Japanese words, ‘Poka’ meanings ‘inadvertent errors’ and ‘Yoke’ (derived from Japanese word Yokerie) meaning ‘to avoid’ and together they translate as ‘error / mistake proofing’ or ‘fool proofing’ or ‘Faisafing’ a work process system to eliminate inadvertent errors. It pronounced as POH-kah YOH-kay. It is discrimination between mistake and defects. Poka-Yoke is a powerful and comprehensive tool for identification, measurement and analysis of mistakes / defects at the Gemba (real place of work) and implementation of measures that prevent the activity from being incorrectly performed, thereby ensuring production of quality goods and services. Poka yoke has two statuses: The fault will happen or the fault is happened and has three functions: stop, check and alarm.

 

Shigeo Shingo introduced Poka-Yoke method in 1961, when he was one of engineers Toyota Motor Corporation. This method, in other words, is to prevent defects and errors originating in the mistake. In age of 50, Shigeo Shingo being an advocate of statistical process control systems in Japanese companies realizes that such a solution would never improve the manufacturing process. It is therefore started in Japanese organizations to implement a Zero Quality Control (ZQC). One of its elements implementing the principle ZQC is just Poka- Yoke method. The name poka-yoke Shigeo Shingo established in 1963, it is translated as "resistance to errors" [avoid (yoker) errors resulting from inattention (poka)]. The philosophy, which is the core for Poka-Yoke method, is respect for human rights, and above all his intelligence. In the course of repetitive operations, which depend on vigilance or memory, poka-yoke, may save time, release the mind of worker for operations more creative, and increase their value. At each stage of the product life cycle, in each process and its operations there is a possibility of errors. In the consequence of errors, the final product has defects and customer is discontented and disappointed. The method Poka-Yoke is based on convenience that it is not acceptable to produce even very small quantities of defective products. For the companies, production of products in 100% without any defects is not only challenge, but also necessity. Poka-Yoke method is a simple technique which allows you to reach just such a production.

 

Technical aspect of Poka-Yoke method

Poka-Yoke technique can be applied both to prevent causes, which will result in subsequent occurrences of errors and to carry out inexpensive control determining whether to adopt or reject the product. It is not always 100% probability elimination of all errors, in such cases it is the task of Poka-Yoke methods is detection as soon as possible. Analyze the process of product defects formation noted that between a mistakes resulting from the defect is yet one, the potential possibility: The observation mistake and its correct. It is therefore the proposal-method for reducing defective is planning conditions in which error may not happen, or will be immediately visible and captured. Take into account the above Shigeo Shingo developed a achieving "zero defects" in industrial conditions, i.e. in such a way as simple and cheap. Was itself at the matter, that it is not possible to reduce the defects using random checks. It is necessary to the total control - 100% control. Shigeo Shingo adopted following assumptions:

i) in the case of confusion applying the statistical process control is ineffective,

ii) monitoring and control the poka-yoke should be:  a) autonomous, i.e. operations carried out by the contractor without intervention from the outside, b) 100% - the total, c) cheap.

 

Shigeo Shingo has analysed in detail the process formation of defects and errors from the source to effect. He said that mistake from the producer becomes defect for the user in this moment when the customer unnoticed this defect. It should be therefore a maximum reduced and speed up action coupling back, and so on

1. As soon as possible –and simplest should be detect errors (inspection of information, "after the fact", typical for statistical control),

2. At the earliest as soon as possible signal error before it become the defect (in the inspection of information is amended to self-control 'upwards' means checking prior operations and material obtained),

3. Eliminate possibility of the occurrence error (inspection at source, verify the conditions under which runs the operation in order to eliminate the possibility formation error).

The Poka-Yoke is a technique for avoiding human error at work. A defect exists in either of two states; the defect either has already occurred, calling for defect detection, or is about to occur, calling for defect prediction. Poka-yoke has three basic functions to prevent or reduce defects: shutdown, control, and warning. The technique starts by analyzing the process for potential problems, identifying parts by the characteristics of dimension, shape, and weight, detecting process deviation from nominal procedures and norms. There are two approaches to implementation of Poka-Yoke method: control method and warning method.

 

 

 

 

The Relationship between Poka-Yoke and Inspection

 

Shingo differentiated between three different types of inspection—judgment, informative and source. Judgment Inspections discover defects by sorting the defective pieces out from finished products. Judgment inspections gave rise to the term “inspecting quality into a product”. Shingo agreed with the consensus in modern quality management that “inspecting in quality” is not an effective approach to realizing quality and he advocated against its use. Informative inspection, on the other hand, uses data gained from inspection as feedback to control and improve the process and reduce the occurrence of defects during production. Traditional statistical process control (SPC) is a type of informative inspection. In Shingo’s Zero Quality Control (ZQC) system, both successive checks and self-checks are also types of informative inspection. Successive checks were Shingo’s response to the insight that the speed of improvements is a direct function of the timeliness with which quality feedback is obtained. Typically, work-in-process undergoes many processing steps as it is moved through a manufacturing facility, but inspections are often not conducted until the intermediate stages. Shingo’s concern was that inspections might not occur soon enough after a production process to give the timely information necessary to determine the cause of the quality problem and to prevent its recurrence in the future. His solution was to have each operation inspect the work of the prior operation, so that quality feedback can be provided back upstream almost immediately. Implementing successive checks involves having the nearest downstream operation check the work of the operation that feeds it. Under this approach, each operation in the flow performs a quality inspection. Effective poka-yoke devices make such an inspection system possible by reducing the time and cost of inspection to near zero. Because these inspections entail minimal cost, every item may be inspected. If work-in-process inventories are low, quality feedback used to improve production processes can be obtained very rapidly by the upstream operation that needs to make an improvement. While successive checks give rapid feedback, carrying out self-checks by having each worker use poka-yoke devices that allow him/her to assess the quality of his/her own work provides even faster feedback. Because operators check every unit produced, they are able to recognize what process conditions have changed when a defect is produced. This insight can then be used to prevent further defects (i.e., root-cause analysis). Because of the immediate feedback capability, self-checks are preferred to successive checks whenever possible.

 

Shingo believed that, while informative inspections and self-checks each had their place in quality management, the most significant form of inspection was source inspection. Source inspections attempt to eliminate defects by determining that the conditions necessary for defect-free production exist prior to the commencement of actual production. Under a source-inspection system, poka-yoke devices are employed to ensure that the optimal conditions for error-free production exist and, in fact, prevent the production process from beginning until such a state has been realized. You may be thinking that pokayoke really represents corrective actions that involve root cause analysis. However, what a poka-yoke strategy really does is add preventive actions to an organization that will result in the earlier detection or prevention of product and process nonconformities, permitting corrective actions to be taken instantaneously if they are needed at all. There is still some overlap between being corrective vs. preventive actions, but poka-yoke represents a continual improvement strategy where the need for corrective actions is reduced or eliminated by improving the QMS’s processes. In summary, poka-yoke is an improvement method whereby Shingo’s ZQC can be realized. The aim of ZQC is zero defects in production. As Shingo has written, “The most effective strategies for reaching zero defects are using source inspections to move through management cycles at the level of causes, and using source inspections in combination with 100 percent inspections and poka-yoke devices to speed up feedback and action.”

 

Example of Poka yoke devices

 

Poka yoke may be designed either to help the operator to recognize the defect before it is about to occur called ‘prevention type Poka-Yoke’ or to help the operator to know immediately on occurrence of the defect called ‘detection type Poka-Yoke’.

Some of the Poka-Yoke devices, which can help to avoid defects, are –

1. Guided pins / Locators

2. Errors detection buzzers / alarms and blinking lights

3. Limit switches / indicators

4. Counters

5. Colour coding

6. Check list etc.

Characteristics of Poka Yoke devices

 

a) Simple and cheap

b) Part of the process, permitting 100% inspection

c) Placed closer to where the mistakes occur, providing quick feedback

d) Designed to stop a particular mistake

e) A detection device cannot provide a complete error proof solution

f) Necessary and not a sufficient solution

 

Conclusion

 

The aim of Poka-Yoke method is to eliminate or minimize human errors in manufacturing processes and management as a result of mental and physical human imperfections. For the main part is to eliminate errors independent (so-called problem resistance to stupidity while-en. fool proof). The main idea of this method is preventing causes, which may result in errors and use relatively cheap control system for determining compliance of the product. Use of Poka-Yoke requires strong basis in the overall quality management. Necessary are clear indications to distinguish between a defective and correct product and therefore company regularly carry out training crew. It should not be forgotten that the method Poka-Yoke requires an immediate reaction and the correction as well as a result in the operation. Errors arise from various reasons, but most of them can be prevented if only people are be able to identify the problem at the time of formation, define the causes and make appropriate corrective steps. Prevention of defects in the process before their appearance is the best way of defects reduction and thus minimizes the costs.

 

References

 

1.      Shigeo, S., (1986). Zero Quality Control: Source Inspection and the Poka Yoke System, Massachusetts and Norwalk: Productivity Press Cambridge.

2.       Shigeo, S., (1988). Poka Yoke: Improving Product Quality by Preventing Defects, Massachusetts and Norwalk: Productivity Press Cambridge.

3.      Shingo, S. (1988). Non-Stock Production: the Shingo system for continuous improvement. Productivity Press.

4.      Shingo, S. (1989).  A study of the Toyota production system from an industrial point of view. Productivity Press, Cambridge, MA.