Monday, August 8, 2016

Seven Best Poka-Yoke Devices


Generally the most effective way to achieve quality is to avoid having defects in the first place. It is much less costly to prevent a problem from ever happening than it is to find and correct the problem after it has occurred. Focusing on prevention activities whose purpose is to reduce the number of defects is better. The idea is to have processes and procedures in place that reduce or eliminate mistakes.

Mistake Proofing is about adding controls to prevent defects, reduce their severity, and detect them if they can occur. The concept was first put to widespread use by Shigeo Shingo within the Toyota Production System (TPS).

The main aim of mistake proofing is:

PREVENT a defect from occurring and when this is not possible, DETECT the defect every time one occurs.

Defects found in later operations or steps of a process have more costs associated with them. There are more materials, labor, overhead, previously reworked product that are at risk. Ultimately if the product gets to the customer as a defect, the intangibles, such as reputation, can exceed the tangible cost.

Poka-yoke devices could be characterized by effectiveness:

GOOD: Detect defect before proceeding to next step.
BETTER: Detects defects while in process at an operation.
BEST: Prevent defects from occurring at all.

The 7 best poka-yoke devices are:

1. Guide Pins

Guide pins of different sizes and/or shapes and placed in the proper locations ensure that parts are being assembled correctly by providing the operator feedback when a mistake has been made. Guide pins can also be used to ensure proper positioning of the part.

Applications
  • Proper alignment of a work piece
  • Proper orientation of a work piece
Features
  • Easy to develop & implement
  • May be the result of DFA and DFM activities
Human Error Prevention
  • Wrong order, incorrect selection, incorrect positioning, incorrect orientation

2. Error Detection & Alarms

In general, an error detection device can provide a visual alarm such as a flashing light or an audible alarm such as a horn or siren.

These devices signal that a problem is either about to occur or has just happened. With a warning effect, the response is not automatic; someone has to take action.

Application
  • The signal must be triggered by something in the process, usually a sensor.

Features
  • For audible warnings, there are sirens, horns, bells, and even voice synthesizers.
  • For visual alarms, there are lights that flash, rotate, strobe, or just light up.

Warning: If you do use these warnings, the audible or visual signal must stand out from background noise and lights. If audible alarms are used, be careful not to exceed noise standards.

Be careful of “alarm silence buttons.” It is easy to silence the alarm and then forget to take action. Operators need thorough training on how to react to warnings.

3. Limit Switches

Limit switches are electro-mechanical devices that are activated or deactivated when an object comes in contact with them. They are used to detect the presence or absence of an object.

Applications
  • Proper positioning of safety devices
  • Detection presence or absence of an object
  • Positioning of a work piece

Features
  • Requires physical contact

Human Error Prevention
  • Omission, excessive/insufficient repetition, incorrect selection, incorrect counting, incorrect positioning, incorrect orientation

4. Sensors

A. Proximity Sensors
Proximity sensors emit a high-frequency magnetic field and detect an upset in the field when an object enters it. They can be used to detect the presence or absence of an object.

Applications
  • Sensing of tank or bin level
  • Confirmation of part or object passes by
  • Detection presence or absence of object
  • Positioning of work piece

Features
  • Non-contact
  • Work in harsh environments
  • Small sensors are available for installation in tight areas
  • Fast response speed

Human Error Prevention
  • Omission, excessive/insufficient repetition, incorrect selection, incorrect counting, incorrect positioning, incorrect orientation

B. Laser Displacement Sensors

Laser displacement sensors focus a semiconductor laser beam on a target and use the reflectance of the beam off the target to determine the presence of a target and distance to it.

Applications
  • Measuring distance
  • Detection of presence or absence of a feature
  • Confirmation of part or object passes by
  • Positioning of work piece

Features
  • Non-contact
  • Works in harsh environments
  • Some devices can achieve measurement precision down to 0.004 mils (0.1 um)

Human Error Prevention
  • Omission, incorrect selection, incorrect counting, failing to sense danger.

5. Vision Systems

Vision systems use cameras to look at a surface and then compare the surface viewed to a “standard” or reference surface stored in the computer. They can be used to detect the presence or absence of an object, the presence of defects, or to make distance measurements.

Applications
  • Missing of incorrect parts in an automated assembly line
  • Poor quality surfaces or components
  • Correct orientation of parts or labels
  • Ensure correct relative position
  • Color detection

Features
  • Non-contact
  • Need to have sufficient light
  • Flexible (can be reprogrammed for a variety of applications)
  • Compact systems are now available

Human Error Prevention
  • Omission, incorrect selection, incorrect positioning, incorrect orientation, misrecognition

6. Counters & Timers

Counters (optical or electro-mechanical) look at the occurrence of events. They are usually triggered by some type of sensor. Counters can be programmed to shut down the process if a set number of events do not occur or if too many events occur. Timers can shut down the process if processing time or activity time does not meet or exceeds a preset level.

Applications
  • Ensuring the proper number of events occurred
  • Preventing failure of equipment or a component usage

Features
  • Flexible
  • Easy to use
  • Easy for people to understand

Human Error Prevention
  • Excessive/insufficient repetition, incorrect counting, incorrect positioning, incorrect orientation

7. Checklists

A checklist is a type of informational job aid used to reduce failure by compensating or potential limits of human memory and attention. It helps to ensure consistency and completeness in carrying out a task.

Applications
  • Shift Start-up
  • Product Changeover
  • Equipment Set-up

Features
  • Easy to develop
  • Easy to use
  • Easy for people to understand

Human Error Prevention
  • Omission, early/late execution, wrong order, misrecognition
Ideally, poka-yoke ensures that proper conditions exist before actually executing a process step, preventing defects from occurring in the first place. Where this is not possible, poka-yoke performs a detective function, eliminating defects in the process as early as possible. Don't allow defects to occur in your processes by neglecting to prevent mistakes in your work. Use poka-yoke to make the work easier and mistake proof your process.

Post Courtesy of QualityTrainingPortal.com


Subscribe to my feed Subscribe via Email LinkedIn Group Facebook Page @TimALeanJourney YouTube Channel SlideShare

No comments:

Post a Comment