In conjunction with the increase in production volume, awareness of the importance of production control increased, and in 1954, the 'supermarket method' was introduced.

The production method used until then (in the case of the machining plant) was to attach one voucher to each part to be machined and for the transport team to transport the parts to the machinery assembly plant. This is the method of transporting parts from the prior process to the subsequent process and parts are delivered regardless of whether they are needed by the subsequent process or not. This causes processed parts to accumulate at the machine assembly plant in volumes greater than needed, requiring an expensive storage area to such an extent that the plant could be more properly referred to as a parts storage area then an assembly worksite.

Machine assembly processes were performed by checking which assembly part models were to be installed while monitoring the inventory of parts. When all the necessary parts were not available, just the delivered parts were assembled and the leftover parts were temporarily removed from the line until the needed parts arrived. In the early part of each month, when it was difficult to gather all of the necessary parts, assembly was roughly half the planned volume.

The completed assembly parts were then transported to the production line in the general assembly plant, the next process. No matter what model was being assembled, it could only be assembled in the quantity for which parts were available, and as a result, it was nearly impossible to assemble components to produce models in the planned necessary amounts. As a result, it was extremely difficult to proceed according to the daily plans until about the middle of the month when parts steadily accumulated.

At the end of the month, when all of the parts were available, so-called 'end of month catch-up production' was conducted. Using the same number of workers as at the beginning of the month, the conveyor speed was increased at the end of the month in an effort to catch up. This signifies at the beginning of the month there were an excess number of workers simply waiting for parts. This was because of the lack of uniform production throughout the month by the machining, machine assembly, and the general assembly processes. In the end, it was not possible to produce the planned volume each day.

Even with this situation, thanks to low production volumes and the excess personnel, little issue was made and responses to the inadequate control were made based on the discretion of individuals. In conjunction with rising production volumes, however, developing production control systems became an urgent issue and the following measures were implemented:

1. 1.Machining processes were regulated and standardized by type and machines were located based on the standards.
2. 2.Standard worksheets for each part on the production line were prepared and workers were instructed to perform basic work based on the worksheets.
3. 3.Machines were inspected daily and preventive maintenance was performed.
4. 4.Waste, inconsistencies, and unreasonable requirements were eliminated to improve work.

As a result of these measures, systematic and efficient production was achieved in the machining processes, and it became necessary to reconsider the work of transporting parts from those processes to the machine assembly processes. Introduction of the supermarket method was considered for this purpose.

The supermarket method was introduced based on hints obtained from a report on a Lockheed aircraft plant in the United States in an industry publication in the spring of 1954. According to the article, by using the supermarket method to assemble jet bombers, expenses were reduced by $250,000 annually and 60,000 square feet of storage space could be used for other purposes.

At that time, supermarkets were not common in Japan, and no one had personal experience with supermarkets to help in their understanding of the system. Toyota Motor Co., Ltd. inferred from the article that the subsequent process is the 'customer' and the prior process is the 'supermarket'. The method of the customer retrieving necessary items from the supermarket shelves was understood to mean that the subsequent process retrieves parts from the prior process.

By applying this concept to assembly processes, it was possible to assemble the required vehicle models according to plan by attaching assembly parts in advance and having the general assembly plant retrieve them. The same method was adopted at the machine assembly plant, which retrieved the parts it needed from the machining plant. This was the creation of Toyota Motor Co., Ltd.'s supermarket method.1

The supermarket method evolved into the Kanban System with the addition of a production instruction sheet known as the Kanban (card or board indicating the product name, product number, and quantity). The system further developed into the Just-in-Time system, a method of producing only what is needed, when it is needed, and in the amount needed, creating an innovative system that was widely adopted even by suppliers.