POKA YOKE

• POKA YOKE:

                     Poka-Yoke is a method of using the processes or design features in order to prevent errors, defects and their negative impact on the productivity. Poka-Yoke means mistake proofing, and it is a Japanese slang for avoiding inadvertent errors, which was formulated by the well-known statistician Shigeo Shingo. Poka-Yoke is the inexpensive and very effective technique for mistake proofing based on simplicity & ingenuity. It does not rely on operators for catching mistakes. It is inexpensive at the point of inspection and gives quick feedback over 100% of the time.

Importance of Poka Yoke:
              Statistical Process Control (SPC) is the good strategy for detecting shift or irregularity in the process mean or variance. By applying the Poka-Yoke changes in the process can be readily detected.
             As human errors tend to be rare or intermittent events, they can not be readily detected by control charts. So that most of the indusries prefer Poka-Yoke, and not SPC to reduce defects caused by human errors the most of the time. It helps to reduce inspection time and more value added activities can be introduced in the lead time. It helps to save cost for scrap, rework, inspection and logistic losses. Our  customers rightfully expect defect-free products, but always mind that 100% inspection by the traditional way won't provide 100% defect-free products. So that it must have a common approach for eliminating human & mechanical errors by common sense ideas and methods, to make it impossible to make mistakes.

Main Causes Of The Defects:
1) Poor procedures and standards
2) Abnormalities in machines and equipment
3) Defective or out of specification material
4) Worn tooling
5) Human errors

          Except for human errors, other causes of the defect can be predicted and corrective actions can be taken to eliminate causes of the defect. Mistakes for operation are the conditions, which are not implemented, or may be wrong or absent for successful manufacturing of the product. Apart from that errors, responsible for the defects are mostly depend on chosen workplace, the operator approach and workplace culture ( environment) 

Top 10 Human Mistakes/ Errors That Cause Defects:

1) Processing omissions ( The step was forgotten)
2) Processing errors ( Something was done incorrectly)
3) Errors in setting up the workpiece
4) Assembly omissions ( The part/ component was forgotten)
5) The wrong part/ item/ component was included
6) The wrong workpiece processed
7) The operational errors ( Incomplete information/ SOP not followed)
8) Adjustment, measurement, dimensional, parallax errors
9) Equipment maintenance errors
10) Errors in the preparation of tools, fixtures, blades & jigs etc. for the operation

Other Causes Of The Defects:

a) Forgetfullness
b) Language barriers
c) Misunderstanding in instructions/ SOP
d) Error in part identification and placement recognition
e) Errors due to lack of experience
f) Pace ( The speed is the extremely high or too less)
g) Lack of the standards, instructions, SOP, 
h) Incomplete information
i) Incorrect or incomplete processing
j) The tools, fixtures & jigs, are out of tolerance and hence errors in adjustment & placement
k) The foreign material in procedures, the assembly or the system
l) Damaged, loose, reversed, misaligned or wrong parts in manufacturing process

The Methods for Using Poka-Yoke:

               The Poka-Yoke system consists of three primary methods and each method can be used in the control systems, the warning systems or the shutdown systems. Each method uses the different process prevention approach for dealing with the irregularities.

1) Contact Method:
               The passive devices are sometime the best method for the Poka-Yoke. This method uses simple devices and design features and physical phenomena like uneven shape, weight or dimensions for arresting defects and abnormalities.

2) Counting Method:
               Counting method uses fixed number of operator activities or operations required within the process. In which sensors or counters are used as mistake-proofing device. The fixed number or range of numbers  are specified, and then change in desired value of quantities like pressure, current, voltage, temperature and time etc. can be detected.

3) Motion-Sequence Method:
               In thi method process sequence should be as design, otherwiswe system takes corrective actions that has been feed to it. It has two subtypes; the first subtype is by the 'process sequence method', that controls the operations in proess. And another one is, by 'in-process sequence method', that controls the standards of the process, if not followed or missed.

Mistake-Proofing Devices:

               For mistake-proofing, some devices are also used. Traditionally used Poka-Yoke devices are divided into three categories:
1) Physical contact devices
2) Energy sensing devices
3) Warning sensors
               Each category of these devices includes a broad range of devices that can be used depending on the process.
E.g. a) Guide/ reference/ interference rods, pins, stopper or gate
b) Limit switches/ micro switches
c) Electronic sensors like the proximity sensors, photo-electric sensors
d) Counters and critical condition indicators
e) Templates

Guideline To Poka-Yoke Attainment:

1) Quality process:
              Design robust quality processes to achieve zero defects.
2) Utilise the team environment:
               Leverage the knowledge, experiences shared by the team members to enhance process.
3) Elimination of errors:
                Utilise the robust problem solving methodology to drive defects towards zero.
4) Eliminate the root cause:
                Make the use of '6W2H' technique to eliminate the root cause of any problem.
5) Eliminate non-value added (NVA) activities:
                 Don't Make excuses, just eliminate the non-value added activities present in current work.
6) Do it right from the first time:
                 Utilising resources to perform functions correctly right from the first time i.e. 100% RFT.
7) Implement the continuous improvement' approach:
                 Implement the improvement actions immediately and focus on continuous improvement in your workplace everytime and do smartwork whenever necessory.

Hints For Good Poka-Yoke:

1) Think about the product characteristics, because they vary with every product.  
2) Think about the process sequence.
3) Detect and study the deviations from fixed value.
4) Eliminate, Simplify, Reduce or Combine the operations.

Never forget these '3 Rules of Poka-Yoke':

1) Don't wait for the perfect Poka-Yoke. Do it now!
2) If your Poka-Yoke idea has better than 50% chance to succeed. Do it now!
3) Improve later. Do it now!

         The last but not the least, Poka-Yoke is the part of continuous inprovement approach and there is always chance to improve. I hope you have better understand about the Poka-Yoke system. If you like this article, don't forget to follow me on Google+