Taiichi Ohno, Toyota manager considered one of the fathers of the Toyota Production System, says:
"All we do is look at the timeline from customer order to payment [...] and we constantly reduce this time by removing all waste that does not add value."
This statement encapsulates a fundamental concept: the organization of activities must constitute a "continuous flow," whose flow time is minimized through the elimination or reduction of "non-value-adding" activities. Generating an efficient continuous flow means eliminating all obstacles that, by not adding value from the customer's point of view, prevent its seamless flow from order receipt to payment, with the goal of ensuring the customer's Quality, Cost and Time (QCT) requirements.
In the lean system, in order to achieve continuous flow, all steps are integrated directly into the process, including the control step. All operators can check its status in real time and stop the flow immediately when a variation from the standard occurs.
For this to be possible, some preconditions are needed:
1. The use of SMART indicators and visual management tools for the control phase
2. Widespread empowerment to delegate responsibility to the appropriate level
3. The presence of standards in processes to immediately highlight the appearance of an anomaly
4. The use of problem solving tools to promptly resolve problems encountered
This integrated approach makes it possible not only to quickly identify and correct nonconformities, but also to prevent them, thus constantly improving the quality and efficiency of the entire production process.
In the lean system there are key concepts that represent widespread practices and techniques useful in achieving continuous flow: jidoka, poka-yoke and andon.
Jidoka (autonomation) is a concept coined by Sakichi Toyoda--founder of Toyota Industries Corporations--that expresses the ability of machines and operators to immediately stop the process when an abnormality occurs. Its first application dates back to the creation of the Type G, an automatic textile loom that could autonomously stop processing as soon as a warp thread broke, thus preventing the generation of defects in the fabric.
In day-to-day activities, errors are a possible source of anomalies and can result in nonconformity to specifications or customer expectations. A seemingly small defect, if not corrected in a timely manner, can propagate within the process exponentially amplifying its economic impact. Intensifying the quality control phase is not an efficient solution to this issue: the correct approach is to prevent the occurrence of defects as much as possible.
In this context, a key methodology supporting Jidoka is Poka-Yoke.
The term Poka-Yoke (error-proof) refers to a process, equipment and machinery design technique aimed at preventing errors. This technique aims to create products and processes that place limits on the way an operation can be performed, forcing the operator to perform correctly and thus ensuring "quality first time".
In poka-yoke systems, anomaly detection can be done in three main ways:
To support Poka-Yoke systems, one of the most common forms of visual management used is Andon.
Andon, an archaic Japanese term originally used to refer to paper lanterns, in the modern industrial context refers to a visual warning system used to call for assistance when an abnormal situation occurs. It helps to quickly identify problems in the process, facilitating a timely and effective response.
One of the most famous examples of this system in the automotive industry is the andon cord developed by Toyota. This is a cord running along the entire production line that, when pulled, interrupts the flow of production and simultaneously activates the problem solving process. The seemingly drastic decision to interrupt the flow can be made directly by the operator, representing a perfect example of widespread empowerment.