Jidoka is a device that will stop a process if an error (defective part) occurs. It supports the principle of one piece flow in that no faulty part is passed to the next process and errors are resolved at source and in a timely manner.
All evidence of the creation of the fault is maintained so that it can be eliminated forever because the process is evaluated and changed to remove the possibility of making the same mistake again.
The purpose is to free equipment from the necessity of constant human attention, separate people from machines and allow workers to staff multiple operations. This form of Jidoka relates closely to Shigeo Shingo's concept of Poka-yoke.
Jidoka, as applied to manned operations, refers to the practice of stopping the entire line or process when something a defect is detected. This is another component part of continuous improvement.
You will find a number of resources to assist you in your understanding of lean - please feel free to browse our content and let us know if you require anything further.