# Integrated Multilevel Production Planning Solution According to Industry 5.0 Principles
## 2 Related Works--Literature Review
### Challenges for the Production Planning in Industry 5.0
This is why the EU has presented the Industry 5.0 concept, a human-centered digital manufacturing system that would enable it to overcome the obstacles and challenges set by the implementation of Industry 4.0 [65]. The human-related challenge that remains is the time-consuming learning and adaptation to newly implemented systems. The learning curve must be reduced so that not only current but also new workers can start to use the new system in as short a time as possible [18; 19; 66]. Finally, three very important characteristics of Industry 5.0 must be considered when creating a new production planning system, namely, sustainability and resilience [14; 43]. Each manufacturer has its own specific demands; therefore, each implemented segment of Industry 5.0 should be highly customized but developed according to the general principles of the digital manufacturing concept. The production planning and scheduling system should be sustainable to avoid major changes in the near (or distant) future, with a possibility of modification in terms of flexibility and upgrades. The system should also be resilient to unpredicted and dynamic events within and outside of the system. As for the implementations of Industry 5.0 principles, many sources have showcased in case studies that there is no universal solution in providing a human-centric, sustainable, and resilient solution for multiple segments of manufacturing companies, therefore it has been suggested that an individual approach is most suitable. This means that the inclusion of multiple levels of the organization leads to a beneficial solution for any new technology implementation or its modification [43], while hybrid approaches can be developed for estimating the lead times of engineering activities considering both the capacity constraints for engineering resources and the characteristics of new engineering projects [63]. Therefore, the explicit guideline of a production planning system in an Industry 5.0 environment is not clearly defined in the literature, especially for the design-to-order systems, but certain segments are clear and were used for the design of the novel integrated production planning system in this research:  
* Real-time data availability and analytics. The data should be properly structured to avoid the appearance of data-related waste but should also be understandable to the specific user. Every modification should be visible in real time to each user to avoid misinterpretations and wrong decisions. * Decentralized decision-making. With available data adjusted to a specific user, the data-driven decisions can be made decentralized and more accurate. * Internet technologies and cloud computing. The data should be stored on the cloud and available from different platforms. * Complexity reduction. The system should be simple, user-friendly, and easy to use and to learn. * Sustainability and resilience. The production planning system should remain open to future modifications and upgrades which do not demand very complex tasks and high investments, such as a simple modification which enables the accurate and effective functioning in the future without disruptions. These findings from the literature were a guideline for the development of a new integrated production planning system according to Industry 5.0 principles that was implemented and proven in practice for a leading power transformer manufacturer in Croatia.