## 1 Introduction  
From the very beginning of aviation, in addition to the construction of the aircraft, the most demanding task was to master the aircraft piloting. The rapid development of civil aviation soon required the possibility of instrumental flying. Pilots had to be able to control the aircraft in conditions when visibility from the cockpit was so reduced that the flight was no longer safe. In 1929, to reduce the risk and cost of training, the American constructor [PERSON] constructed the Link Trainer flight simulator. The cockpit was mounted on a carrier which enabled change of position and orientation, depending on the given command, in the same way as a real aircraft. It is also crucial to have the same instruments which react accordingly. Today, flight simulators play an irreplaceable role in pilot training and certification. Their full potential was discovered when there was not enough time to train a large number of pilots on real planes. With these machines, pilots could learn how to fly under conditions in which flight by visual reference is not safe anymore. In such situations, the pilot needs to know how to control the aircraft, relying only on information collected from the instruments and its own vestibular system. Over time, flight simulators have become complex mechatronic systems, but their main purpose, to enable pilots to feel what they see with their eyes, remains the same. In order to achieve realistic simulation in all flight cases and all forces acting upon the pilot during the flight, a moving part of the simulator needs to have six degrees of freedom. The chosen mechanism with six degrees of freedom has to have a sufficiently large workspace to simulate aircraft motion, which is why the determination of motion boundaries is very important. A free rigid body has six degrees of freedom, it can perform six independent motions, three translations and three rotations. A kinematic chain is a series of bodies or segments connected together by joints. A kinematic chain can be simple or complex, and both can be divided into open and closed. One segment of a simple kinematic chain cannot be connected to more than two other segments, while one segment of a complex kinematic chain can be connected to more than two other segments. Open kinematic chains have segments that are connected to only one other segment, while all closed chain segments are connected to at least two other segments, as shown in Figure 1.  
Among many existing designs, parallel mechanisms (mechanisms with closed chains) based on the Stewart platform, defined in [1], are most frequently used for flight simulators. From this first work until today, this mechanism is a popular research topic in robotics with many research papers published about inverse and forward kinematics problems [2; 3], dynamics [4; 5; 6; 7], singularities and workspace estimation [8; 9; 10; 11]. In a paper [12] written in 1998, the authors presented a state-of-the-art review of the literature on the Stewart platform and mentioned papers are still the basis of research. A similar overview paper was written in 2016 [13]. Even after so many years (almost six decades) of research, there is still the opportunity to find a new or better way of practical use of this mechanism. Besides flight simulators, this mechanism is currently used, for instance, for machining tools [14], as part of medical instruments for precision surgeries [15], for high-precision vibration damping for spacecraft payload [16], within marine satellite tracking antenna stabilization system [17], for non-destructive inspection tool [18], for assembly of flaps [19], for testing of micro-electro-mechanical system dynamic inclinometer [20], for energy-efficient machining bed [21], gait rehabilitation [22; 23], stabilization system for optoelectronic devices [24], docking mechanism [25] and even for helicopter floating helideck [26]; additional applications are shown in [27].