What Mechanical Engineers Should Know — Principles of Poka-Yoke Design

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Zero defects in quality is the ultimate goal that all industries strive to achieve. Companies such as Toyota in Japan managed to achieve zero defects in the car manufacturing process, where over 2,000 workers assembled 30,000 components, with not a single inspector on site. Poka Yoke, which serves to prevent mistakes and errors, naturally plays a crucial role in this regard. http://5b0988e595225.cdn.sohucs.com/images/20190508/d93f983977f44064b29ef143b8f66ba9.jpeg The role of foolproofing methods: During the execution of tasks, workers sometimes make mistakes due to carelessness or forgetfulness, and such mistakes account for a significant proportion of problems that arise. If foolproofing methods can be used to prevent such mistakes, then both the quality level and work efficiency will surely improve greatly. (1) The foolproof method means “getting things right the first time.” Poka-yoke employs a series of methods and/or tools to prevent mistakes from occurring, with the result being that things are done correctly from the very first attempt. (2) The foolproof method refers to the \"simplification\" of a process such that \"no mistakes will occur even due to human negligence or when handled by laypeople, requiring no special expertise or extra attention.\" Poka-yoke employs a series of methods and/or tools to prevent human errors, ensuring that things cannot be done wrong unless intentionally. (3) Improve product quality, reduce waste resulting from inspections, and eliminate rework and the waste it causes. Poka-yoke means “getting things done right the first time,” and the direct result is an improvement in product quality; poka-yoke eliminates the waste associated with inspections. Defects are eliminated, which leads to a reduction in the number of rework sessions; thus, the time and resources wasted due to rework are avoided. (4) Achieve automation to improve efficiency. Poka-yoke methods reduce reliance on human subjective judgment, aim to automate the manufacturing process as much as possible, minimize the likelihood of human errors, and improve work efficiency. (5) Ensure safety through foolproof methods: Make full use of various IE techniques to ensure that the mechanism can automatically detect the correctness of actions, even in the event of simple human errors, thereby guaranteeing safety between humans and machines. Poka-yoke Modes and Principles 1. Four Poka-yoke Modes: Poka-yoke employs different modes depending on the specific processes and types of errors; these are: (1) Physical Poka-yoke. The physical pokayoke mode is a hardware-based error prevention approach that takes into account the physical properties of products, equipment, tools, and operators. The sensor switch in a rice cooker is an example of a tangible POKA-YOKE error-proofing mechanism. If no water is added to the rice cooker, the heating switch cannot be set to the heating position; only by adding water can the heating switch be adjusted to that position. (2) Ordered Poka-Yoke: The ordered Poka-Yoke approach focuses on the sequence of process steps, by monitoring that order or by prioritizing the execution of those steps that are prone to errors or forgetting, and then carrying out the other steps. (3) Grouping and counting type foolproof mechanisms: The grouping and counting type foolproof mechanisms are error-prevention methods that prevent operational mistakes through grouping or coding. (4) Information-based poka-yoke: The information-based poka-yoke approach involves transmitting specific product information between different locations and different operators in order to enable tracking. 2. The levels of error prevention can be divided into 3 categories based on the effectiveness of the error-prevention mechanisms in use: http://5b0988e595225.cdn.sohucs.com/images/20190508/fedd4ceb87254adbb86ad431cb9e5f8d.jpeg http://5b0988e595225.cdn.sohucs.com/images/20190508/7472a0e92c6f4828bc5fc0fce9842056.jpeg 3. Principles for implementing error prevention methods Here are some basic principles for error prevention; by following these principles, operational errors can be effectively avoided. Simplicity principle: http://5b0988e595225.cdn.sohucs.com/images/20190508/47db575453054f3c928731c001b5beef.jpeg
Simple principle: http://5b0988e595225.cdn.sohucs.com/images/20190508/4a30325844fc4a79be30a3ed3ac38ecb.jpeg
Safety principle: http://5b0988e595225.cdn.sohucs.com/images/20190508/6e8ca568cd6e4b839895e33b7b1b4aca.jpeg
Automation principle: http://5b0988e595225.cdn.sohucs.com/images/20190508/f095107ffbee49bfb4cfcbdee4c7827f.jpeg
Examples: http://5b0988e595225.cdn.sohucs.com/images/20190508/9cc4aec967fe46dd82d0f003f80341ac.jpeg
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1. Designing out the causes of errors prevents mistakes from occurring in the first place. (1). Achieve it by elimination. Example: Removing a small plastic piece from one of the rewritable holes on the side of the floppy disk prevents rewriting. (2). Achieved through an “asymmetric shape”. (3) Using the “synchronization principle,” multiple actions must be carried out together to be completed. Example: The procedures for opening a bank vault. Example: Operating a punch press manually (using both hands to operate the switch) (4). Perform it using sequential actions. Example: Elevator door (5). Principle of limit positioning. Example: Hydraulic lifting limit contact stop switch (6). To be completed through interactive action. Example: Chain stores. 2. The separation principle – using partitions to divide different areas in order to protect certain zones and prevent any dangerous or erroneous situations from occurring. The isolation principle is also known as the protection principle. Example: A protective cover for electric circular saws to prevent cutting the hand. Use seat belts in cars, and wear helmets when riding a motorcycle. Add cardboard to reduce damage to the product during handling. Enter by swiping a card. 3. Process automation for error prevention utilizes various optical, electrical, mechanical, kinematic, and chemical principles to restrict the execution or non-execution of certain actions, thereby avoiding errors. Currently, these automatic switches are very common, and they represent a very simple form of automation application. (1) Controlled by means of “buoyancy”. Example: A toilet’s tank is equipped with a float; when the water rises to a certain level, the float pushes the switch rod, thereby cutting off the water supply. (2) It is completed using a “weight” control method. Example: When the elevator is overloaded, the doors cannot close, it cannot move up or down, and an alarm bell also sounds. (3) It is completed using a “light” control method. Example: In an automatic camera, the shutter cannot be pressed if there is not enough light. 4. Warning principle for error prevention: In the event of any abnormal conditions, various “warning” signals can be displayed through sound, light, or other means to prevent errors from occurring. Example: When the vehicle’s speed is too high, a warning light comes on. If the seat belt is not fastened properly or the door is not closed properly, the warning light comes on. When operating the computer, an incorrect key press triggers a warning sound. When there are errors in the English words in a Word document, the page is automatically marked with red lines as a reminder. How to effectively implement process foolproofing: 1. Regarding foolproofing, the following concepts should be adopted: ① Self-inspection and mutual inspection are the most basic, fundamental, yet highly effective error-prevention methods. ②Poka-yoke devices do not require significant resource investment or a high level of technology. ③Any job or transaction process can be protected against human error by incorporating error-proofing techniques during the initial design phase. ④Zero defects can be achieved through continuous process improvement and error prevention. ⑤Error prevention should be based on anticipation; error-proofing methods for various process operations should be considered from the very beginning of the design. ⑥Poka-yoke methods are considered in all locations where problems may arise. Applying the above concepts to process management enables the effective implementation of foolproofing methods. 2. General steps for implementing foolproofing methods: (1) Identify product/service defects and collect data ； (2) Trace the discovery process and generation process of the defect ； (3) Confirm the work instruction for the process where the defect occurs ； (4) Identify the differences between the actual operation process and the operation instructions ； (5) Check whether there are the following issues in the processing step: (6) Analyze the causes of the defects ； (7) Analyze the causes of operational errors ； (8) Design error-proofing devices or procedures to prevent or detect similar errors ； (9) Verify the error-prevention effectiveness and make process adjustments if necessary ； (10) Ongoing control and improvement. Application examples of process foolproofing – Example 1: Problem with the foolproofing device used for packaging power tools: Power tools, accessories, instruction manuals, and certificates of conformity are sent to customers as a single package, but cases of missing or incorrect items in the package still occur. Training and penalties for the employees responsible for packaging did not yield significant results. http://5b0988e595225.cdn.sohucs.com/images/20190508/fc55c734728f4e3f8b905fd4fabd48d1.jpeg Example 2: Improvements to prevent mistakes in the production of phone case molds http://5b0988e595225.cdn.sohucs.com/images/20190508/e0d9f1c3a54a40e8afe4ae410d8ee417.jpeg http://5b0988e595225.cdn.sohucs.com/images/20190508/20c9fca0ce634748b6f67350dcd12130.jpeg