Jidoka, although no direct translation, it is thought of as autonomous defect control. A way in which the process can be developed to prevent defects happening, and if they do, stop them from propagating downstream.
As Shingo once said “Humans are animals that make mistakes”. This is absolutely true, therefore people cannot be assumed to spot or prevent all instances of defects. The need to create a self-assessing system is essential, especially when dealing with large scale production and products which must meet strict tolerances.
Jidoka helps reduce waste such as over-processing, over-production, and obviously defects, but not only does it reduce this, it also reduces the consequences of these wastes. These wastes introduce instability by disrupting the flow (Mura), and also stress the process, with the extra effort being (Muri). A Lean system cannot tolerate the consequences defects pose upon it.
In conventional approaches to defects, inspection would be the immediate answer. However 100% inspection is inefficient, costly, and simply not feasible in large scale production. Another typical answer would be SPC (statistical process control) however this also has it’s problems, and cannot prevent all defects from transpiring.
It is also possible to focus on the process, rather than inspecting parts, inspecting the process with techniques such as SixSigma. Jidoka does not discard these options, but it does offer an alternative approach to defect issues.
Jidoka aims to find the root-cause of problems, and make it impossible for them to return. It is an ongoing system of defect control, and therefore should not be thought of as a one-stop fix to problems.
Jidoka has three main areas:
- Process control
- A capable process will not create substandard parts
- Early detection of errors, then preventing propagation
- Immediately taking corrective action, once an error is discovered
Jidoka is one of the main pillars in the “House of Lean” and within itself there are 6 main sections:
- Line MUST stop if defects are found. (Although management tend to be against this methodology). The process should be designed to spot errors and stop automatically.
- In-Station QC
- This is simply applying QC within a station or work area, preventing incorrect parts being moved to the next station.
- Solving Root Causes
- Often the root cause isn’t obtained, so a method such as 5 Whys should be used here.
- Person-Machine Separation
- This allows people to notice abnormal situations, which otherwise would be moved to the next machine without question.
- Visual management allows clear and concise feedback information on defects and other relative information.
- Error Proofing
- Fool proofing doesn’t exist: fools can be employed, but it is possible to prevent them making errors. Poka Yoke techniques are key to preventing the possibility of defects.
So what are the action to be taken if an error is found?
The line can either stop, giving sufficient time to solve the root cause, or there can be a warning that a substandard part/component has been produced. In this case, the seriousness of the defect will command which action is best suited for the situation.
So in summary, we must prevent defects at the source, and if not possible to remove, we must prevent their propagation. 100% inspection is also our aim, but this should be autonomous, not NNVA, as in people inspecting products. As a last note, use Poka Yoke extensively.