The Jidoka principle in production and logistics
The Jidoka principle describes the ability of a machine, a plant or an entire system to switch itself off in case of errors, quality and production problems. Jidoka forms the second supporting pillar in the Toyota Production System (TPS) alongside the just-in-time principle and is an important factor in lean management and quality assurance. Via sensors, limit switches or other devices, malfunctions or occurring errors are detected, which leads to the above-mentioned automatic shutdown of the machine. This increased degree of autonomy of the system is called autonomation (automation + autonomy); one also speaks of intelligent automation or automation with a human touch.
Jidoka in production
Jidoka’s decisive point of view is to check the manufactured materials during the ongoing production process instead of only detecting possible defects afterwards. This allows an intensive search for the cause of the problems and can result in a loss of productivity in the short term, but in the long term, it increases reliability and thus also profits. Jidoka acts as a cost-efficient intermediate step towards complete automation, where any faults that occur are not only detected by the machine itself but also corrected. The system is enabled to do this by means of certain components, such as sensors. All deviations from normal operation (anomalies) are detected and, if possible, automatically corrected; if the latter is not possible, the machining process is also automatically stopped and visually signalled to the responsible employees.
The Toyota term “jido” is applied to a machine with a built-in device for making judgments, whereas the regular Japanese term “jido” (automation) is simply applied to a machine that moves on its own. Jidoka refers to “automation with a human touch,” as opposed to a machine that simply moves under the monitoring and supervision of an operator.
Advantages in production
- One hundred per cent control is no longer necessary in the context of quality assurance since errors are automatically detected in advance.
- Rejects or rework are reduced or even completely eliminated, as faulty part processing is detected immediately; as a result, no defective parts are passed on to downstream processes.
- Machines do not continue to wear out due to faulty processes and parts.
- Plants and individual machines no longer need to be monitored by employees; pure monitoring is considered a waste of time. As a result, one employee can operate several plants simultaneously, in the certainty that no missing parts are produced (Multi-Process Handling).
The Jidoka principle in intralogistics
The Jidoka principle also applies to intralogistics, but in a different way. In the warehouse, for example, it is also important to avoid waste. The corresponding types of waste can be as follows: unnecessary transport due to excessively long distances, unnecessary stock due to incorrect disposition, rework due to picking errors or waiting time due to missing information, employees, materials or parts. In the context of lean warehousing, Jidoka represents a method that drives quality management, cushions increasing cost and efficiency pressure, supports the growing share of value-added services and spreads the use of conveyor and automation technology.
Examples are automation processes within goods receipt, picking, inventory and returns processing. Thus, within a warehouse management system, individual work steps are automated and computer-aided controlled on the basis of stored information. In goods receipt, for example, the goods control begins with the notification(advice note) of the goods. Based on the notification information, the process steps in goods receipt are automatically defined before the actual delivery. The receipt of the goods into the logistics centre or distribution centre describes not only the putaway but also a comparison of the existing data: article, weight, quantity, article number. By means of a dialogue, the employee can see in real-time what exactly has been recorded and whether the goods (delivery note data) match the information of the person notified (usually supported by systems such as ERP and WMS). In order to be able to complete the goods receipt process section, the data must be confirmed; only then the goods are received in full – as a rule, these control mechanisms take effect at the so-called identification point (I-point) and automatically follow a specific sequence, for example, when the employee triggers it via scan.
In picking, there are several variants of how the goods to be placed in stock or removed from stock are automatically checked during picking. On the one hand, the picking method Pick-by-Visions, for example, offers the possibility to guide the employee error-free by means of detailed information (graphics, photos, text); on the other hand, picking processes such as Pick-by-Scan, Pick-by-Light and Pick-by-Robot are designed in such a way that the warehouse management system itself shows the employee exactly which article must be touched – quantity checks are automatically carried out during the picking process. If the system quantity does not match the quantity in the compartment, the compartment is responsible for a clarification case. A clarification case can also be the trigger for replenishment.
Editor’s note: In contrast to the Jidoka principle in production, intralogistics conveyor systems, such as a pocket sorter or general sorters within a picking zone, are not switched off when, for example, product defects are detected. The faulty products merely have to be removed from the actual material flow and handled separately.
Manual processes offer flexibility
The extension of the Jidoka principle in intralogistics is opposed by the chaku-chaku principle, which is also included in the TPS. Here, system performance is made more flexible by increasing personnel deployment while at the same time dispensing with complicated conveyor technology. If, for example, a distribution centre relies on a wide range of articles, but expects demand to fluctuate (seasonally), and chaotic storage is also favoured, then manual work steps are often more sensible than using automated technology (see manual order picking).
Summary of Jidoka principle
The application of the Jidoka principle enables machines and software to recognise errors that occur in the running process and, if necessary, to correct them or stop the current process. In this way, production errors cannot spread throughout the entire downstream process, which in turn avoids later reworking or postponement of the production sequence. This autonomous and automatic quality assurance is an important pillar in lean manufacturing with its origin in the Toyota production system. Within logistics centres, similar, mostly software-based control mechanisms are implemented in warehouse management systems or ERP systems. In contrast to production facilities, no equipment has to be stopped in intralogistics.