Jidoka - Quality At Source

Jidoka was first introduced by Dr Taichi Ohno into the Toyota Motor Company in the early 1960s. In the process of producing an efficient material flow system, he realised that quality must be excellent and that problems must be dealt with on the spot rather than set aside for others to sort out. He believed in the Henry Ford principle of handling 'one at a time' but needed some way to synchronise all operations as well as dealing with deviations in quality. To accomplish this, he installed a set of lights at each work station. The lights were called Andon lights and their purpose was to identify problems and synchronise operations.

There are three lights - green signifies normal production; yellow means that the operation has slowed, possibly due to problems with the material, the speed of the line or the process itself. A red light means - stop everything! The word Jidoka means 'stop everything if there is a problem'. Any worker may stop the line if there is a problem, eg a defective part, possibly scrapped or supplied in a defective condition. Contrast this with other systems. How long might it take to determine what to do with the defective part or to find someone to discuss the problem with who has the authority to make a decision? Also, how long will it take before the effect of the defect is known? Meanwhile, all other operations are busy producing parts, oblivious to the problems being encountered. The net effect might mean disruption or stoppage of the line later and systems with too much work-in-progress. By synchronising operations and dealing with problems on the spot, Ohno produced the most material flow efficient car plant in the world. The principles of zero inventory and Jidoka were intended to reveal problems that must be overcome in order to improve material flow efficiency. In high inventory systems, should there be a problem, eg a defective part, then the worker always has another batch to work on.

Managers are happy because their people are busy and the system appears efficient. Defects are seen as an every day occurrence. The Japanese river analogy explains their perspective. If the water level in the river is high (this equates to a large inventory holding). It hides problems from view. When we reduce the level of the water (inventory), it falls until we only have enough inventory to work on. In order to reduce inventory levels to a minimum we must encounter problems (the rocks) which are usually hidden from view when inventory levels are high. Therefore reducing inventory levels forces management to address problems which usually encourage bad practices. To continue our journey, the problems must be removed. There is an important point here for operations managers. In companies, we are always searching for techniques to improve efficiency and raise productivity. This may include the installation of a management information system and/or new equipment. In the Japanese system, by reducing inventory, they have devised a means of highlighting the areas that must be improved. Simply, push down the level of inventory and our attention is brought to bear on the area that should receive our attention. This focuses investment and ensures that it achieves the desired improvement in productivity. This approach provides Japanese managers with a fly-wheel effect on productivity improvements, with an ever-increasing rate of inertia being generated. This table compares conventional and Japanese wisdom.