konnect Issue-Date:30-08-18

Importance of Automation for POKA – YOKE

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Anil Kumar HP (Hon. Secretary ISAB)
Director Agraj Automation
Bangalore

Automation: The dictionary defines automation as “the technique of making an apparatus, a process, or a system operate automatically.”

International Society of Automation, ISA Define Automation as "The creation and application of technology to monitor and control the production and delivery of products and services.”

Quality: The most important aspect of any manufacturing unit is to produce Quality product. Productivity is next.

Quality is no more an inspection. It is to be built in the product during manufacturing. In this regard Automation plays an important role.


Poka-yoke is a Japanese term, meaning "mistake-proof" or “Fools proof manufacturing” Or “Avoiding errors/ Fault/ mistake in manufacturing”.

Simple example of POKA-YOKE:

poke

Left side picture shows 3 pin plug and socket, in which Line voltage is on Right, Neutral is on Left and the earth pin on top.

Phase and neutral supply is connected through the particular wires.

Earth wiring is there to prevent shock and the phase or the line voltage will be connected to Left side pin (Right side of socket) only, and Right side pin will be connected to Neutral.

Whereas in the second picture it is a 2 pin plug without earth connection (no safety) and there is no guarantee for which pin phase or Line voltage is connected and for which pin neutral connection is given. In this case there may be voltage near equipment even when the equipment switch is off.

We can say even though two wire is sufficient for giving power to Light, Fan etc, 3 Pin plugs are manufactured for safety and mistake proof in connecting power to equipment. This method of improvement for safety, Quality in manufacturing is called Poka – yoke.

2 pin with out poka-yoke and 3pin connection with Poka- yoke.


Poka - Yoke for Quality:

The main application of Poka Yoke is for manufacturing Quality products.


Importance of Poka – Yoke system:

Almost all kind of manufacturing industry must think of adopting appropriate Poka yoke system in the manufacturing or process plant. Recently you might have heard the case of a noodle manufacturing company. The company lost business and image because of not adhering to norms and deviated from quality. The company assumes, however, that during packing or processing due to human mistake one pack quality deviated and unfortunately the same pack was picked for inspection from external agency. Think of the inconvenience caused.

You might have heard of several products(Vehicles of some company) pulled back from market due to mistake in manufacturing, rejected from customers, penalty from government agencies, etc.

Also Death of a person due wrong medicine, wrong date printed food products, Accidents due to mistake in new vehicles, Accident due to failure of new lift, and so on. By all these above examples we can understand how important the poka yoke system can be in manufacturing units. In almost all Japanese associated companies Kaizen and Poka- Yoke is given utmost importance. Often the best suggestion will be rewarded.

For example, Few years back in one automobile manufacturing unit more than 200 poka yoke systems were executed by Automation companies. Some of them are small with only sensors and actuators and some other projects are using PLC and some with SCADA.


Case studies of Poka-Yoke in Automobile Industries:

Case study 1

Missing washer or parts in an Automobile Engine:

The previous method: They had already taken some precaution and the washers were kept in different trays which are painted with different colors to identify and also serial number was given for each tray. Part number of particular model to use the washer was written on the tray. The operators used to select the proper washer from particular tray as per instruction given and were assembling.

In spite of that, extra washer or missing washer, and sometimes change in size of washer was noticed during quality inspection or testing of the engine. Due to some reason, if the defect escaped the quality inspection a fatal accident may happen on the road causing huge damage. They cannot take a chance.

The changes made: Several ideas came from the company executives. One concept was finalized and as per that new trays were made, the tray shape changed. The trays were longish and with a small opening. The opening is of the size of a hand, just enough to put hand inside and take washer. Each tray was equipped with a sensor to detect the entry of hand. The system is made in such a way that once he picks a washer it is recognized and signal given to PLC.

Each tray was equipped with a sensor to detect the entry of hand. The system is made in such a way that once he picks a washer it is recognized and signal given to PLC.

We can select a particular model in the PLC/ HMI. The PLC is programmed with the number of washer, sequence of particular washer, based on the model selected. When the technician takes a washer the system gets the signal through a photo sensor provided at the opening of the container. It records and checks the sequence and all necessary signals. On any deviation from the sequence it gives an audio alarm with indication of fault. If the operator do not reset, the system does not allow the conveyer to move the assembly to next position. Therefore the operator must be extra careful and check the alarm. Otherwise he cannot proceed to next operation. In addition to this, finally the whole assembly is moved on a platform where weighing system was introduced. The PLC is programmed in such a way that if it weighs 10 gram more it shows one washer is missing. If it weighs 10 grams more it shows one washer is extra. The system tells the missing part based on weight of the part.
The complete engine is now assembled without any missing or extra parts.


Case study 2

POKA - YOKE System in an automotive industry:

Mr. Ram (Say) purchased a new car and scheduled to take delivery in the evening after his office hours. As he was busy he arrived at the show room little late to collect his new car. He checked all accessories and left the show room by driving his new car, It was rainy season and on the way back home he was caught in the heavy traffic and it started to rain, as it was getting dark he switched on the head lights but it was not turning on.
Imagine the Panicky situation.

What has happened?
Consultation with Automation expert:

The subcontract manufacturer called Automation professional and asked for a solution. He checked the process. Found that each part was checked and sent for assembly. The cover assembly was made using electric screw drivers. Once the quality of headlight assembly and wire harness is checked it is given for bulb fixing and testing. Then light assembly front glass is fixed and dispatched.

He suggested them to change the process and adopt simple Poka – yoke.

Simple solution:

The process flow was changed. Before assembling doom the bulb must be fixed and then top cover to be assembled (using Electric screw driver). Next day he brought some photo relays and visited with a technician. He Fitted the photo relay below the light assembly and asked them to give power supply to switch on the light before assembling. (This is new Light testing area.) Interlock was made in such a way that the electric screw driver will not work if the photo relay is not on, and the bulb cannot be assembled.

Advantage:

There is no separate area for bulb/ light testing. It is combined with doom assembling area. No chances of missing or faulty light. Company saved its image and continued to be a subcontractor.

Like this we can make a system to avoid missed or wrong operation or any kind of deviation in quality.

“Let us determine to produce quality products for MAKE IN INDIA”