Poka Yoke

There is nothing like a real life story for demonstration.  This is a true story on product design, and a technique called Poka Yoke. In this case, the product is a complicated set of vehicle systems.  There are a number of pressure sensing elements, all the same type of sensor and distributed in a relatively common space.  Each of these sensors is connected electrically to other parts of the system and enables certain sets of features.  The wires are connected to each of these sensors discretely, that is, there are separate connectors and wires going to each of these sensors.

During the prototype development the entirety of the system is produced. The numerous subsystems are put together to make the functioning end product.  This system entirety will then be tested to assess the capability of the design. In the late phases of the project and product, these prototypes builds transition from engineering related to more manufacturing skills.  It is during this transfer that problems in the assembly are witnessed.  We have malfunctions on one of the end products that require engineers to investigate the cause of the problem.  This required numerous engineers of both pneumatic and electrical disciplines to find the source of the problem.  Waste of time and talent.

It turns out that each of the sensors did unique things in the system; all were similar looking and performed a similar but different function.  The pressure transducers convert pneumatic pressure to an electronic signal. This signal was routed to a variety of control units to make decisions based the state. These different functions required the connecting wires to be routed or connected to specific locations. There are six of these sensors, each with a discrete connector, and all six of the electrical connections likewise look alike.  To make the situation even more difficult, all of these sensors reside in a common area. It is very easy to put any of the electrical connections to any of the sensors.

Poka Yoke is often referred to as goof proofing but really means error proofing.  This technique is part of building in quality of the product and reduces inspection time and time to troubleshoot what should never have been a problem.  In this specific case, the sensors common appearance, the connection point common appearance made it easy to connect the incorrect wires to any of the given sensors.  The problem was found in a small build,  the system was not yet at full factory production, and that was fortunate. However, to find the root cause of why the system performed erratically required engineers climbing on the vehicle and disassembling various panels and parts to to determine the problem, and amounted to a waste of time and talent.

There are a number of ways this problem could have been avoided, for example, the sensors could have been color coded with corresponding color code applied to the connectors providing a readily visible correlation between the sensor and the connecting wires.  The connectors could have been “keyed” to only allow the appropriate harness to connect to the appropriate sensor.  We will not go into an exhaustive list of ways the accomplish (contact Value Transformation if you need help in this regard.  This sort of issue should have been identified in the Design for Manufacturing and Assembly (DFMA).  Doing this up front and deliberately can reduce these inefficiencies and time consuming activities that add no value.


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