**1. Introduction**

Obtaining appropriate reliability and quality of products requires proper methods of enterprise management, production, and the means necessary for its implementation [1]. These methods allow for the coordination and integration of all company functions [2]. One of the elements affecting the high quality of a product is the condition of technological machines maintained in enterprises [3–5]. Its suitability and technical condition largely determine the quality and competitiveness of a product.

Maintenance management is a critical issue amongst management activities of manufacturing organizations [6–8]. Therefore, in recent years, intensive efforts have been made to propose and improve maintenance strategies that aim to extend the useful life of every piece of existent equipment, increase its availability, and guarantee higher levels of reliability [9–11].

In recent decades, maintenance was regarded as a necessary evil in managing an organization, because it was limited to the appropriate functions that are usually performed in emergency situations, such as a machine failure. However, this practice is no longer acceptable, because the role of maintenance has been recognized as a strategic element of generating revenues for the organization [1].

The maintenance process in enterprises was not always carried out in a way that ensures the minimization of outlays while maximizing the achieved effects in service and maintenance processes. In practice, obtaining the maximum benefits from the operation of a technological machine system requires an optimal solution to a number of tasks [12,13]. For a larger number of machines, it creates the need for appropriate system modelling, simulation research, and optimization of partial and complex tasks based on the adopted optimization criteria [14]. Accordingly, the company must establish a maintenance system that enables these activities to be carried out in an optimal manner from the point of view of resource pro-vision and its effectiveness [15]. These activities are usually carried out in accordance with a specific exploitation strategy that has been developed with the development of production systems. Most of the enterprises with foreign capital managed to organize effective maintenance [16]. However, small and medium enterprises are still looking for the right method for their reorganization as well as for the right way of supervising technological machines and equipment that would allow for improving effectiveness as well as for using it in a manufacturing process. That is why, some organizations have started implementing lean methods and tools in the area of maintenance defined as lean maintenance [17]. Lean maintenance is a proactive maintenance strategy whose main goal is to support reliability in the most effective, cost-effective way possible, which means keeping costs to a minimum while ensuring high efficiency and productivity. This philosophy is mainly based on the concept of total productive maintenance (TPM), the idea of which is to involve all employees at every level of the organization in maintenance and management tasks [18].

This paper presents the possibilities of using intelligent systems to support decision-making processes in the implementation of the lean maintenance concept. The aim of the article is to indicate the methods and tools of lean maintenance, which have the greatest impact on increasing the effectiveness of the enterprise. The obtained research results indicate which lean maintenance methods and tools should be implemented in the company in the first place to increase the efficiency, quality, and availability of its production processes. This problem is particularly important from the point of view of small- and medium-sized enterprises, which do not always have adequate human or financial resources to implement modern concepts in a wide range. The methodology used in the work is based on the use of artificial intelligence methods (decision trees, rough set theory), which allows for the identification of factors influencing the effectiveness of lean maintenance implementation by enterprises. The second chapter of the article contains the background. Section 3 describes the problem formulation and methodology. Section 4 presents the results of research on the use of the overall equipment effectiveness (OEE) indicator in enterprises and the concept of using artificial intelligence (AI) methods to assess the effectiveness of the implementation of the lean maintenance concept. The work is summarized with conclusions and a proposal for further work.

#### **2. Literature Review**

#### *2.1. Lean Manufacturing as the Foundation of Lean Maintenance*

Global industry in the 21st century motivates companies to seek and implement a more competitive production system. Many of them implement or plan to implement lean manufacturing. Lean manufacturing philosophy is mainly used in industry to increase efficiency and productivity. It was developed in the 1990s and is mainly based on the Toyota Production System (TPS) [19].

The basis of this concept is the elimination of unnecessary losses that have a significant impact on productivity and profit. These losses can be divided into three main types: Muda, Mura, and Muri. Muda identifies seven types of waste, which include transportation, supplies, redundant movement, waiting, overproduction, over processing, and defects. Mura means unevenness, non-uniformity,

and irregularity and is the reason for the existence of any of the seven wastes. Finally, Muri means overburden, beyond one's power, excessiveness, impossible, or unreasonableness and can result from Mura and, in some cases, can be caused by excessive removal of Muda from the process [20–22].

Production using the lean manufacturing philosophy should consist of reducing the amount of losses related to people, inventory, time to market, and production space, so as to obtain a highly reactive demand for customer needs, while producing high-quality products in the most efficient and cost-effective manner [23]. Lean manufacturing can be a cost reduction mechanism, and if properly implemented, it will make it a world-class organization [24], and importantly, lean manufacturing can be used in all industries [19,25].

Many organizations have embarked on the practice of using "lean tools" primarily to eliminate wasted production. It is widely recognized that organizations that have applied lean manufacturing methods have significant cost and quality advantages over those that continue to use traditional manufacturing [23]. It turns out that organizations pay more and more attention to maintenance, which is why some organizations have started to practice lean maintenance in addition to lean manufacturing.

Lean maintenance is a concept that implements activities aimed at increasing the effectiveness of technical infrastructure. These activities are related to the elimination of losses in maintenance, such us [18,19]:


Duran et al. [26] show the connection between the sources of waste in lean manufacturing and lean maintenance (Table 1).


**Table 1.** Relationships between sources of waste in lean manufacturing and lean maintenance.

The elimination of waste is most often carried out by implementing lean tools such as 5S, standardized work, Kaizen, Poka-Yoke, and value stream mapping (VSM) [27,28]. They are most commonly applied to make production processes more effective and to reduce lead-time or cost of production, but they can also be applied for maintenance operations. As the most common examples of application lean tools in the maintenance area, the implementation of the standardized work for

maintenance operators, the Andon system to initiate corrective maintenance, or using VSM to identify and eliminate waste in maintenance operations can be distinguished [29]. However, the fundamental elements of lean philosophy and total productive maintenance (TPM) must be implemented before application of such specific tools [30].
