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Vishwadeep Khatri

Visual Control vs Mistake Proofing

Visual Control is any communication device used in the work environment that tells us at a glance how work should be done or how the mistakes have to be avoided

 

Mistake Proofing or Poka Yoke - is a technique for eliminating errors by making it impossible to make mistakes in the process. It is often considered the best approach to process control.

It works on the principle - "It is good to do it right the first time. It is even better to make it impossible to do it wrong the first time".

Mistake Proofing can be preventive (prevent the error from occurring) or detective (detect the error if it happens) in nature and is usually implemented in one of the following ways

1. Warning: audio and/or visual warning either before the error occurs or after it has occurred

2. Control: errors are not possible or even if an error occurs, it is not allowed to move to the next step

3. Shutdown: machine or process shutdown when an error is about to happen or as soon as an error occurs

 

An application-oriented question on the topic along with responses can be seen below. The best answer was provided by Shashikant Adlakha and Ram Rajagopalan

 

Applause for all the respondents - Shashikant Adlakha, Ram Rajagopalan, Sunder Khatri

Question

Q 245. Fuel indicator in a car is not a mistake proofing device. Rather it is a visual control. How do you differentiate between the two? Under what circumstances will you prefer to use a visual control rather than mistake proofing?

 

 

Note for website visitors - Two questions are asked every week on this platform. One on Tuesday and the other on Friday.

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Mistake proofing (Poka Yoke) is based on detecting and solving the problems, as close to the source as possible, rather than identifying and solving when the product  or service has already been through the customers. So the products are designed in ways such  that auto detection happens at different stages and without manual or auto correction the production or the process gets halted, thereby ensuring that there are no flaws or defects.   

 

Mistake proofing is based on these six principles, based on order of priority in addressing issues

Elimination:  Eliminating the  errors by redesigning of  part of the product or process.

Replacement: Use of automation or robotics in place of manual process to prevent errors

Prevention: Using features, that prevent  wrong processes, e.g- connectors to avoid misconnecting wire or cables in electrical assembly.

Facilitation: Specific methods such as visual controls, that includes use of color coding, labelling on parts to facilitate execution of right process.  

Detection:  Using sensors or detection alarms, whenever wrong parts have been assembled or wrong processe has been executed.

Mitigation:  Reducing the impact of  errors, when they are discovered e.g- Fuses to prevent overloading in short circuits.

 

 

Mistake-proofing opportunities and their potential control actions  can be prioritized by failure modes and effects analysis (FMEA) of process and design. Mistake-proofing techniques need to be  developed for every  step in  both manufacturing and  service industry.

 

Visual control  methods can be used as a part of mistake proofing in facilitation methods. But the basic difference lies in the fact that visual control mechanisms do not  make the process completely mistake free, rather by providing visual inputs of critical processes and statistics, there  is   marked increase in  efficiency and improvement  of the process and chances of mistakes is diminished.  Where as mistake proof methods by definition should make the product or service process mistake free.

 

Common uses of visual controls, where they are preferred over complete mistake proofing methods are: 

-Commonly  Used with 5S methods to create overall standardization and a part of continuous improvement process.

- Kanban boards for inventory controls and Heijunka boxes for production scheduling.

-Large scale communication boards for easy display of quality indicators, so that any possible deviation is  met with serious contemplation and prompt corrective actions.

-Easy display of shop floor  schedules, performance measurements, communication and feedbacks mechanisms involving supervisor and workers. Daily work flow in a car service station is a good example of this.

-Visual display of prescription pills, so that it is difficult to  miss any dosage and mistakenly take wrong pills.

-For the safety and warning signs, e.g- stop signs, handicap parking signs, no smoking signs, color coding of bins for collecting different categories of biological wastes etc

-Control  and maintenance of tools and equipments, displaying their maintenance status and the  service dates, calibration dates etc.

-Quality management in various organizations by display of quality charts, cause and effect diagrams etc.

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Visual control: Management technique where information is communicated through display board.

 

Error proofing: Preventive technique which gives a alert message if there is input of unwanted information.

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Visual control is broadly a practice of monitoring performance, predicting abnormality and alerting when required.

 

Mistake proofing is in a way a subset of/ derives a lot from Visual management, with primary intention being to avoid any mistakes/ deviations.

 

Visual management is widely used. In Operations this included cases incoming, completed, pending and potentially missing SLAs. A contact center dashboard has details on calls incoming, handled and metrics like abandoned, service level etc. Alerts are for managers to look into long calls. In Manufacturing, it provides a visibility into the production floor, in Retail its about sales & stock. Project management has also moved to more visual approach using Kanban cards.

Business Intelligence technologies are widely used in Business to provide visibity into operations.

 

Outside the business world, visual management include Road signs that provide directions, warnings etc.

 

Mistake proofing is intended to avoid defect and subsequent financial, time and resource wastes. In airports you notice clearly demarcated lines for planes and other vehicles to ensure there are no personal injury or loss. Countries are laying out dedicated lanes for bicylces, buses etc. In warehouses, you tend to notice a lot of clearly demarcated zones.

 

In Business operations, typically checklists are used to ensure compliance to processes.

 

Visual management is more of standardization to observe and control process deviations, while mistake proofing is about eliminating deviations beyond threshold. Visual management is designed for self explaining, self controlling and self improving. Anyone should be able to tell whats happening based on the visual management. Each process should have error-proofing to ensure defects are not passed on to the next step and that each operation has mistake proofing in place to ensure only defect free parts are accepted in.

 

Mistake Proofing

The website https://www.six-sigma-material.com/Mistake-Proofing.html had good examples of Mistake proofing

  • Spell check on work editor
  • UPC codes and scanners (reduces data entry errors)
  • Snooze
  • Circuit breaker
  • Operator training
  • Low fuel alarm and visual indicator on vehicle
  • Instructions on assembling furniture or light fixture
  • Automatic save features on software
  • Pull down menus for consistent data entry
  • Inspection
  • The hole in the upper portion of a sink to prevent overflow
  • Pressure relief valve on hot water heater
  • Coffee maker shut off feature when pot is removed
  • Tinting of contact lenses to assist in locating them
  • L or R on the contact lens case to indicate left or right eye
  • Kill switch of jet-ski attached to life jacket
  • Limit switches 
  • "Are you sure you want to DELETE?" reminder
  • Sorting of suspect material
  • Force or sound detection monitors on machines
  • Fire and Carbon Monoxide alarms
  • Infrared imaging surveys to detect hot spots
  • Kill switch on a forklift seat
  • Rubble strips on shoulders of roads
  • Oven Timer
  • Traffic lights
  • Rubble strips on road shoulders
  • Various lane stripes and colors on roadways
  • GFCI outlets
  • Double hand jog systems
  • Almost any type of sensor or alarm is a poka-yoke device
  • Wall stud finder
  • Car beeping if lights are left on
  • Automatic shut-off for car lights accidentally left on

 

 

Visual Control

Example from https://www.sixleansigma.com/index.php/wiki/lean/lean-visual-management-visual-control/

A. Seeing as a Group

  1. • Production status
  2. • Inventory levels
  3. • Machine availability

B. Knowing as a Group

  1. • Delivery commitments
  2. • Goals and schedules
  3. Management rule

C. Acting as a Group

  1. • Consensus on rules & objectives
  2. • Involvement in improvement activities

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