## 2 Related Work  
Phollower has been designed and developed as an AMR for the industrial and civil indoor environments. In operation, such a complicated device is challenged by adverse and unspecified situations that may result in hazardous behavior [2]. It is indisputable that safety is a crucial characteristic here. Therefore, from the early beginning, all the safety requirements for machinery had to be applied in the whole development process in accordance with Directive 2006/42/EC of the European Parliament and of the Council of Europe [3; 4]. This directive includes a set of standards and must be fulfilled by any machinery intended to be placed on the European market. In the case of mobile platforms, compliance with the following standards is required:  
* EN ISO 12100: General principles for design,
* EN 60204-1: Safety of machinery, electrical equipment,
* EN 1175-1+A1: Safety of industrial trucks, requirement for battery powered trucks, and
* EN 1525: Driverless trucks and their systems.  
Safety must be quantified, and it must be shown with confidence that the vehicle is safe. Several approaches for vehicle safety validation can be found in the literature:  
* worst-case scenarios, using the assumption that less demanding situations are handled if the worst-case is handled. This is done by directed testing, and it is the most straightforward and yet valid approach;* to use models to verify that different parts of the AMR work together safely. This requires valid models for everything that can affect the system, which is time-consuming and not always applicable;
* to use field tests and from their results show statistically the vehicle is safe enough, where the Extreme Value Theory statistic method can be used [5] with a high validity and lower amount of data required.  
Three different safety concepts were proposed and discussed in [6] to design a safe environment for indoor AMRs. They include the safety ring for reliable object detection, safe navigation, and environmental awareness. However, not all proposed concepts for MiR100 [6] have been implemented, and their mutual evaluation is still missing. For [7], safe and robust movement in a complex 3D environment, scenarios were obtained by the combination of variable step-size rapidly exploring random-tree (RRT) method for global path planning together with the local planner for safe path optimization. A solution for the quantitative derivation of the collision risk with the speed control strategies for safe indoor navigation was presented in [8]. The safety speed margin and minimum time for path optimization were chosen as the two criteria by which safety was guaranteed. Safe and rapid AMR navigation in greenhouses was proposed in [9].  
A modification of differential evolution optimization algorithm was introduced to find optimal and safe navigation points to avoid damage of agricultural products. An exciting safety approach is the detection of \"smartphone zombies\" that was shown in [10] using Light Detection and Ranging (LiDAR) point cloud streams and an enhanced segmentation-based method. It enables the AMR to recognize and avoid pedestrians with smartphones and thereby navigate safely. Potential safety and security features during the design level phase of AMR development were studied in [11], but the presented solutions suffer from low latency in communication systems. Commercial AMRs with comparable technology to Phollower [12; 13; 14; 15; 16] mostly use safety LiDAR system with probabilistic algorithms.