Kanban (or kamban in Hepburn romanization--kanji 看板, katakana カンバン, meaning "signboard" or "billboard") is a concept related to lean and just-in-time (JIT) production. According to Taiichi Ohno, the man credited with developing JIT, kanban is a means through which JIT is achieved.
Kanban is a signaling system to trigger action. As its name suggests, kanban historically uses cards to signal the need for an item. However, other devices such as plastic markers (kanban squares), balls (often golf balls), an empty part transport trolley, or simply a floor location can also be used to trigger the movement, production, or supply of a unit in a factory.
The need to maintain a high rate of improvements led Toyota to devise the kanban system. Kanban became an effective tool to support the running of the production system as a whole. In addition, it proved to be an excellent way for promoting improvements because reducing the number of kanban in circulation highlighted problem areas.
The term kamban describes an embellished wooden or metal sign often representing a trademark or seal. Kamban became an important part of the Japanese mercantile scene in the 17th century, much like the military banners had been to the samurai. Visual puns, calligraphy and ingenious shapes were employed to indicate a trade and class of business or tradesman.
In the late 1940s, Toyota began studying supermarkets with a view to applying store and shelf-stocking techniques to the factory floor, figuring, in a supermarket, customers get what they need, at the needed time, and in the needed amount. Furthermore, the supermarket only stocks what it believes it will sell, and customers only take what they need because future supply is assured. This led Toyota to view a process as a customer of preceding processes, and the preceding processes as a kind of store. The customer process goes to this store to get needed components, and the store restocks. As in supermarkets, originally, signboards were used to guide "shoppers" to specific restocking locations.
"Kanban" uses the rate of demand to control the rate of production, passing demand from the end customer up through the chain of customer-store processes. In 1953, Toyota applied this logic in their main plant machine shop.
An important determinant of the success of production scheduling based on "pushing" the demand is the quality of the demand forecast which can receive such "push". Kanban, by contrast, is part of an approach of receiving the "pull" from the demand. Therefore the supply, or production is determined according to the actual demand of the customers. In contexts where supply time is lengthy and demand is difficult to forecast, the best one can do is to respond quickly to observed demand. This is exactly what a kanban system can help: it is used as a demand signal which immediately propagates through the supply chain. This can be used to ensure that intermediate stocks held in the supply chain are better managed, usually smaller. Where the supply response cannot be quick enough to meet actual demand fluctuations, causing significant lost sales, then stock building may be deemed as appropriate which can be achieved by issuing more kanban. Taiichi Ohno states that in order to be effective kanban must follow strict rules of use (Toyota, for example, has six simple rules, below) and that close monitoring of these rules is a never-ending problem to ensure that kanban does what is required. Toyota's Six Rules are:
A simple example of the kanban system implementation might be a "three-bin system" for the supplied parts (where there is no in-house manufacturing) — one bin on the factory floor (demand point), one bin in the factory store and one bin at the suppliers' store. The bins usually have a removable card that contains the product details and other relevant information — the kanban card. When the bin on the factory floor becomes empty, i.e, there is demand for parts, the empty bin and kanban cards are returned to the factory store. The factory store then replaces the bin on the factory floor with a full bin, which also contains a kanban card. The factory store then contacts the supplier’s store and returns the now empty bin with its kanban card. The supplier's inbound product bin with its kanban card is then delivered into the factory store completing the final step to the system. Thus the process will never run out of product and could be described as a loop, providing the exact amount required, with only one spare so there will never be an issue of over-supply. This 'spare' bin allows for the uncertainty in supply, use and transport that are inherent in the system. The secret to a good kanban system is to calculate how many kanban cards are required for each product. Most factories using kanban use the coloured board system (Heijunka Box). This consists of a board created especially for holding the kanban cards.
Many manufacturers have implemented electronic kanban systems. Electronic kanban systems, or E-Kanban systems, help to eliminate common problems such as manual entry errors and lost cards. E-Kanban systems can be integrated into enterprise resource planning (ERP) systems. Integrating E-Kanban systems into ERP systems allows for real-time demand signaling across the supply chain and improved visibility. Data pulled from E-Kanban systems can be used to optimize inventory levels by better tracking supplier lead and replenishment times.