Kanban is an agile technique to maximize throughput in complicated processes.
Originating in the mid-20th century at Toyota, Kanban has been adapted to a variety of processes that require coordination across multiple work centers. It is a "pull system"; that is, downstream work centers "pull" work from upstream work centers when they have the capacity to do so. This approach is driven by demand, ultimately by the customer. And, it allows teams to identify bottlenecks in the process and work to improve throughput.
Kanban means "signboard" in Japanese. In manufacturing, signs (or cards) were literally used to identify when additional upstream work-in-process should be pulled into a work center.
Kanban only requires two things:
- Make the work flow visible to everyone, and
- Establish work-in-process (WIP) limits for each work center.
The visible work flow (also known as "information radiators" or just "big visible signs") is often posted as a chart of work flow, each work center shown left-to-right in the sequence of work. Modern Kanban systems often use computer software tools to maintain the Kanban information.
WIP limits are a critical attribute of Kanban. First, they help avoid multi-tasking; having workers work on too many things at once. Ideally, team members should work on one item to completion before starting another. This minimizes the waste and inefficiency of context switching between work items.
But WIP limits also help identify bottlenecks. Work centers may not pull work if they are currently at their WIP limit. The WIP limit counts all work items in the work center, even if they're "done" and ready for the next work center in the process. If the next work center is unable to pull the completed work, there is a bottleneck somewhere in the system. All team members should break through the bottleneck and find ways to remove it from limiting throughput in the future.
In addition to the two required attributes of Kanban listed above, many teams add additional features to enhance the value they get from it. A partial list of optional techniques in Kanban:
- Prioritize incoming work so that the most important work is done first.
- An "urgent lane" to expedite critical work.
- Working in fixed-time iterations to drive evaluation of product and process.
While this is an incredibly simplified description of Kanban, it provides the essential elements in any successful Kanban implementation.