This Too is a Kanban

The orthodox description of a kanban is a rectangular card in a plastic sleeve used to reorder materials from a supplier or an upstream process, or a triangular metal plate used to signal production for a process that requires changeovers for lot production. However, orthopraxy (correct practice) is more important than orthodoxy (correct teaching), a point Taiichi Ohno drummed into his students without needing to use Greek words.
The tile of section 3 of chapter 4 from the first textbook on the Toyota Production System is titled “This Too (is a kanban)”. The author (possibly dictated by Ohno, possibly written by Fujio Cho, it’s not clear) states that as long as the item acts as a visual display and performs certain functions, it can be a kanban. Three examples are given, as summarized below:
Carts can be kanban. When a set number of carts containing a set quantity of parts of a set item is moved between set locations based on set rules, this can be kanban. Simply, when there are a certain number of empty kanban carts, the upstream process takes these and brings them back full. The upstream process cannot produce more than has been pulled, because there is no place to put the extra materials, if not on an empty kanban cart.
Reserved seating can be kanban. These reserved seats are locations on the conveyor lines specifying which parts go where. This keeps control not only of quantity but of sequence also in mixed model production. For example a paint line where particular hooks are reserved for particular parts is an example of this reserved seating kanban.
The third example involved balance weights used for propeller shafts. There were five types of weights depending on how out of balance the propeller shaft was, so production planning was a constant changing of plans and a lot paperwork. Although the production was not repetitive (one of the requirements for using kanban), Toyota was able to use kanban to maintain quantity and sequence even to this process which they initially thought kanban could not be applied.
The section ends with two lessons. First, that by being creative, kanban can be used to improve the level of shop floor management and that the level of use of kanban reflects the level of shop floor management. Second, kanban systems must be constantly developed and advanced.
Even if it is working, a static kanban system optimized for the current situation must not be left alone but constantly challenged. We can’t leave good enough alone. A kanban system is a visual control calling out to us “I am inventory, reduce me”. This too is a kanban.