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Posted by Sadia Waseem
Poka-Yoke is a Japanese term that literally means “mistake-proofing” or “error prevention”. Poka means ‘inadvertent errors’, and Yoka translates to ‘avoiding’. It simply refers to a system or a device that helps an operator or equipment to prevent mistakes during a process.
Although the concept of Poka-Yoke in manufacturing was introduced a long time ago, it was Japanese Engineer, Shigeo Shingo who developed the mistake-proofing idea into a commendable tool. Initially, the tool was called “Fool Proofing”. However, Shingo recognized that this title could offend workers so he came up with the term “Poka-Yoke”.
Poka-yoke is based on the principle that it is not acceptable to produce even a single defect— a necessity to sustain in this competitive manufacturing world. While zero-defects might still not be a possibility, it is important for manufacturers to adopt a philosophy of producing zero-defects, and poka-yoke methods can help with that.
In this article, we will discuss the principle of Poka- yoke and how you can digitize it with the help of computer vision and AI.
Modern manufacturing is complex and faced by numerous challenges such as labor shortages, irregular demand and supply chain issues, which makes it difficult to maintain high-quality. On top of it, operators also introduce variability in a process due to fatigue, training levels, and experience that lead to mistakes. According to research, operator errors can add up to 14% waste in total manufacturing costs.
Poke-yoke or mistake-proofing is a proactive approach to address the issues faced by modern manufacturing. Implementing Poka-yoke directly into a manufacturing process significantly reduces the probability of error.
The effectiveness of poka yoke can be judged from a case study, where a poke-yoke system is implemented in a small company and it reduced assembly time by 7% and error rate by 35%.
Modern manufacturing is shifting towards the implementation of Industry 4.0 in their process. Every manufacturer is striving to shift from traditional way of manufacturing to smart manufacturing. Poka-yoke aligns seamlessly with this transformation. By integrating mistake-proofing into smart manufacturing systems, you can leverage data analytics and automation to identify potential errors and implement preventive measures proactively. This not only enhances productivity but also improves product quality and overall operational efficiency.
The core principles of poka-yoke are based on error prevention and mistake-proofing. Here are the core principles of poka-yoke:
Elimination: This principle includes designing a manufacturing process in such a way as to eliminate errors from products or process. For example, using a fixture that holds a part only in the certain position for drilling to ensure accurate drilling.
Prevention: The prevention principle focuses on modifying an existing process in such a way that it is impossible to make a mistake. Example include using a plug that only fits into its corresponding socket in one direction to prevent incorrect assembly.
Replacement: In the replacement principle, there is no new design or modification. Instead, this principle replaces a complex process with a simpler one to minimize the probability of errors. For example, replacing a manual system with an automated one.
Facilitation: Facilitation means leveraging guiding materials and tools in such a way that they help an operator throughout a process. Guidance makes a process seamless and reduces chances of errors. For example, using color-coded tools for different types of assembly.
Detection: Detection is focused on catching errors before they move ahead in the assembly line. It emphasizes, alerting operators about a mistake in time so that the error can be fixed immediately. Some examples include using sensor, color-coded lights, or visuals.
Mitigation: The principle of mitigation focuses on minimizing the effect of error once it has occurred. It means reworking product defects in such a way, so they are tolerable, and don’t increase scrap costs.
How Poka-Yoke address Human Errors: Poka-Yoke system focuses on preventing or reducing the probability of human error through:
How Poka-Yoke address Mechanical Errors: Poka-yoke can detect when a machine is not operating as per its normal parameters. A few examples of poka-yoke solutions for mechanical errors include:
How Poka-Yoke address Process Errors: Poka-yoke focuses on designing process in such a way that it prevents errors from occurring in the first place. Poka-yoke solutions for these errors include:
Control Poka-Yoke systems are designed to prevent errors from occurring in the first place. In case there is an error in the system, the process stops then and there until the error is corrected.
Examples of Control Poka-Yoke
Examples of control poka-yoke system are:
Limit Switches: Limit switches are used to detect presence or absence of objects in a machine. They control machinery and stop it if a component is not placed in the correct position, which prevents further processing until the issue is resolved and quality is ensured.
Interlocks: An interlock stops a machine from operating until certain conditions are met. It ensures that the process only happens in the correct operational sequence. Interlocks can be of various types such as a safety interlock that prevents a process from starting until the guard is in the right place.
Torque Limiting Wrench: They are used in automotive assembly to ensure bolts are tightened in correct specifications, preventing over-tightening or under-tightening.
Warning poka-yoke system sends alerts to operators when a machine is not operating in its normal condition. These devices do not prevent errors by themselves but send a signal when an error is about to happen so that an operator can take corrective action.
Examples of Warning Poka-Yoke
Some examples of warning poka-yoke system include:
Warning Lights: Some of the machines in manufacturing industries are equipped with warning lights. Usually, the red light denotes when there is a problem with the part or machine.
Display Screens: Display screens on an assembly line show warning messages if there is a problem in the line like when the part is missing or one of the machines stopped working.
Detection poka-yoke devices identify errors that have already occurred, allowing for immediate corrective action. It allows rectification of mistakes before they reach customers. These devices are frequently used during inspection and testing phase of production.
Examples of Detection Poka-Yoke
Examples of detection poka-yoke include:
Sensors: Sensors inspect parts for defects or variations. They sometimes use a camera to check products for their parameters.
Visual Inspection Systems: Automated systems that use cameras to inspect products for defects, ensuring that any faulty items are identified and removed from a production line.
Weighing Systems: Weighing systems check the weight of the final product to ensure it meets specifications. Sometimes, the weight of a product ensures that all required components are present in the part.
Poka-yoke is widely used in many industries to prevent errors and ensure production of high-quality products. Here are a few examples of manufacturing sectors where poka-yoke is used in different ways:
Various studies indicate successful implementation of poka-yoke in the manufacturing sector. A research was conducted regarding the application of poka-yoke in the automotive industry. The decision to run poka-yoke was proven to be successful as it reduced the amount of dimension defects material on the rotor component delivered to the production process up to zero the following month and improved the cycle time to 79.77 seconds. The research highlights that when used correctly, poka-yoke method can prevent defective material from entering into a production process.
Another research was conducted on a punching machine regarding the application of poka-yoke. The punching machine was used to make holes in the car parts. These car parts needed small metal pieces before punching the hole. In some of the lots, the hole was being punched without the metal pieces. To fix this problem, poka-yoke was implemented to make sure that no hole was punched until all the metal pieces were in place. After the successful implementation of poka-yoke, rework time was eliminated and the company was able to achieve 0 defects.
Poka-yoke has also proven effective in assembly lines. One of the studies showed that before poka yoke, there were a lot of issues such as the usage of additional manpower, delay in delivery and rework. After implementing Poka-yoke, the number of rejections gradually reduced to zero.
These examples demonstrate the effectiveness of poka-yoke and how it can increase productivity, reduce rework time, and ultimately reduce defects to zero.
Poka-yoke is a proactive approach to error prevention that significantly reduces defects. By intercepting errors early in the production process, it helps companies avoid the time-consuming and costly consequences of producing defective products. Poka-yoke ensures product consistency by maintaining standardized specifications across all units, which ultimately contributes to overall process stability and consistent quality.
Poka-yoke significantly reduces costs associated with scrap, rework, and warranty claims by preventing errors and defects before they occur. It eliminates the root causes of these issues and minimizes material waste and enhances overall process efficiency.
While it is essential to implement the error-proofing system, it can be sometimes complex and lead to confusion. There must be a balance between implementing effective poka-yoke devices and ensuring that they are simple and easy to use. The poka-yoke system itself requires regular maintenance and updates to ensure its effectiveness. As processes change or evolve, Poka-Yoke solutions may need to be adjusted or redesigned.
Traditional poka-yoke methods, while effective in preventing errors, come with several limitations. Implementing physical devices can be costly and time-consuming, and they often restrict process flexibility. Moreover, these methods primarily target known error points, leaving potential issues unaddressed. Collecting data for performance evaluation is also challenging, and their applicability is limited to simpler processes. As a result, traditional poka yoke methods are not really effective for the complex manufacturing processes today.
Retrocausal’s Assembly Copilot offers a modern approach to poka yoke. The software combines the power of computer vision and advanced AI algorithms to prevent operators from making mistakes.
The system keeps a track of the process and gives operators audible and visual alerts if they make mistakes, allowing them to correct errors immediately before they propagate further down the line. The software also collects data automatically on every step performed on the assembly line, making it easier to conduct analysis later.
The best part about Assembly Copilot is that it can be seamlessly integrated with existing manufacturing execution systems (MES) and common tools like barcode scanners and torque wrenches. This plug-and-play capability simplifies the implementation process and enhances the overall efficiency of the assembly operation.
Poka-Yoke is a powerful methodology for mistake-proofing processes in manufacturing. It helps organizations minimize errors, reduce costs, and create a continuous improvement culture. Like manufacturing processes, poka yoke has also evolved and become digitized.
Retrocausal’s Assembly Copilot exemplifies the future of error prevention. The cutting-edge solution leverages provides real-time feedback, data-driven insights, and seamless integration with existing systems, making it a ideal for modern manufacturing environments.
Want to digitize your Poka-Yoke system? Book a free demo now.
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