Error proofing mistake proofing poka yoke leanteams

How to Reduce Errors and Increase Quality of Work

As many organisations progress in their lean journey, they start to look at how to can build quality into their process. In a traditional company, defects and errors are accepted as something that happens but can’t be prevented. It is quite common to see organisations adding inspection steps or asking people to be more careful when errors that cause issues for customers are discovered. These approaches are not only ineffective, even if they do protect the customer, they also add cost.   

Processing errors can quickly escalate into major defects that can negatively impact your company’s reputation and customer satisfaction levels. The good news? You can prevent this from happening through mistake proofing.

What is Mistake Proofing, Error Proofing or Poka-Yoke?

Mistake proofing, also known as poka-yoke, is a lean manufacturing concept aimed at preventing errors at the source. The goal of mistake proofing is to create processes and systems that make it impossible for a mistake to occur. In this way, errors are caught and corrected before they become defects that reach the customer.

Toyota Production System

Many Lean concepts are taken from the Toyota production system. We know Toyota mostly for making cars but when the company first started, it made textiles. The looms that Toyota made were imported to Japan.  However, one of the first adaptions that the company made to these machines was to cause the machine to automatically stop when it detected a broken thread. This had two impacts. First, it stopped any cloth being made with defects in the pattern. This saved on materials costs.  Secondly, it enabled one person to oversee several looms which resulted in a tremendous increase in productivity. The power of this “Jidoka” system went on to shape how the Toyota operated over the next century.

In many industries, it’s often more expensive to leave a simple error undetected than to spend time ensuring things are done correctly in the first place. This is particularly true in industries like construction. For example, consider an error in the design of a building like specifying the wrong size of a purchased door. Discovering this at the point of installation would incur material costs, procurement costs, plus delays to the overall building program. In addition, the whole activity of design and procurement and installation would have to be repeated.  The probable correction costs could be in the region of 100 times the cost of detecting the error at the time of design and specification.    

When working with our clients, we repeat the Lean Mantra –

Never pass defective production or information to the next stage

Errors and Mistake Proofing

For errors in health and care situations the costs can be much more than financial. These days, health professionals often work with “scripts” to check the condition of a patient before administering medicines. As I write this, my wife is being given an injection at home.  The nurse is asking her a series of questions on her current health condition and how the medicine has been stored. All these things will enable the medicine “to do what is should” and prevent any dangerous or adverse reactions to the drugs.

In more complex and risky interactions like surgery, the error and mistake proofing are stepped up. Many simple steps are now typical. For example, labelling and checking the identity of the patient stops the surgeon operating on the wrong person. In addition, the surgical team will mark the part of the body to undergo surgery.

Consequently, this prevents the surgeon from operating on a heathy body part. Another example is counting the number of “tools” the surgical team has at the beginning and end of the operation. This helps prevent leaving items inside the patient. Sadly, these types of simple processes are not always in place. 

How can you Implement Mistake Proofing?

First, we advise that you start by identifying the most critical steps in your processes where errors are most likely to occur. Then, create visual cues or physical devices that prevent mistakes from happening. For example, you could use colour-coded labels or shapes to ensure that parts are correctly assembled. In information processing, we see how organisations save time for themselves when you fill out online forms. For example, licence numbers must be in the correct format before you can submit a section of the form. 

Error Proofing

Employee Training & Development

Another way to prevent defects is by investing and dedicating time to employee training. Make sure that your team members understand the importance of quality in process.  Furthermore, you should give them the tools and resources they need to eliminate errors from their work.

Here are some practical steps you and your team can take to prevent errors and unsafe conditions in manufacturing and when handing physical processes:

  • Interlock switches which detect the position of a machine guard and switch off the machine when the guard is lifted. The machine will never operate when the guard has been lifted and this prevents accidents to the operator.
  • Light curtains in a factory detect when someone is near very dangerous machines and switches off the machine to prevent injuries. 
  • Safety mats near machine areas that pose a danger automatically trigger stoppage when someone steps on them. This prevents injury to personnel (such are technicians) who are trying to access dangerous sections of a machine.
  • Power guards on high inertia machines with moving parts prevent opening until the parts have stopped completely to prevent accidents.
  • Machines that must be controlled using both hands ensure that some distance is kept between the operator and dangerous machine parts.
  • In the food industry, gloves and other small pieces of personal protective equipment must be blue in colour for ease of detection in case they fall into food. This is because blue foods are rare in nature and the colour difference makes it easy to detect that a foreign object has fallen into the food.
  • Using standardised containers at the workstation enables workers to know exact quantities without having to weigh or count the contents.
  • Use of colour coded date labels to mark the production dates of products. In this way, the different batches are easily identifiable for the purpose of product rotation. The system is especially useful in the food industry where rotation of batches is very important because of hygiene considerations.

To prevent errors from becoming defects in office and transactional processes, you should aim for a specific hierarchy in the design and development of the process.

  1. Make it impossible to make the error.
  2. Make it harder to make the error.
  3. Make it obvious that that error has occurred.
  4. Make the system robust so that it tolerates the error.

Practical Examples for Error Prevention

  • Reduce the number of process steps required to complete a process as the inspection aspect is minimised or eliminated.                            
  • Set data validation so that a form can only contain certain information, like a phone number. Enter a value that doesn’t match the prescribed format and the system warns you, then forces you to correct the data before you can continue.
  • Templates and Checklists – commonly used, but not always successful especially if people fail to use the template or list. They can help detect errors before they become defects.                        
  • Information Omission Prevention – setting required fields in paper and electronic forms so that users are notified immediately when required information is not present.
  • Save doing manual data entry – using a reference Bar or QR code on the item to enter the data, can prevent manual data entry errors. This data can be used with other system interlocks to prevent errors.
  • Counter devices – these are useful in manual counting situations – count the number of items then check that that number has been input into the system.
  • Odd Part Out Devices – Visual coding systems that make it obvious that that a particular record is missing or out of place or missing e.g., Job Folder Organisers. Often part of the “set in order” stage of 5S.
  • Sequence Restriction Devices – used to ensure tasks are done in the correct order, many computer-based inputs are designed in this way.     
  • Standardise and Solve Devices – to identify non-standard conditions e.g., re-entering emails, number of digits in a phone number or credit card, if wrong or different users are promoted to re-enter data.

Conclusion

By implementing mistake proofing and investing in employee training, you can prevent processing errors from turning into costly defects that impact your bottom line. More importantly, you can ensure that your customers are receiving products that meet their expectations. As a result, this will make them more likely to return, recommend you to others, and grow your business over time.

Mistake proofing and many other Lean concepts are part of the training that we provide at LeanTeams. Our mission is to enable the people in your organisations to put these ideas into practice through our training and mentoring.

This blog post was written by Alex Gibbs, Lean Trainer and Mentor. If you are interested in working with us to empower your people to think and work better through training, coaching, and mentoring, please contact us

You may also be interested in reading our articles on How to Keep Up with Customer Demand using Lean Tools and Systems and How to Measure your Continuous Improvement Program.   Read all our blogs, news and insights.  Please connect with us on Linkedin  and Twitter   

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