## 3 Analysis of Joint Loading Under Different Drive Mechanism Variants
For the purpose of dynamic simulation in MSC Adams, a 3D model of the loader was developed based on the Komatsu WA320-6, with its components connected via rotational and translational joints. The members of the loader's kinematic chain are subjected to gravitational forces and digging resistance forces obtained through the DEM simulation. The resistance forces \(W_{x}\) and \(W_{y}\) act at the center of the cutting edge tip of the bucket. The actuator displacement and the resistance force were defined using step functions to ensure  
Figure 3: Resistance force during loading operation determined by numerical simulation DEM (**a,b**). a more realistic representation of the actuator behavior and external loading, while also improving the numerical stability and convergence of the simulation. Based on the simulation results, Figure 4 shows the variation of the normal forces \(F_{in}\) (\(i\) = 3, 4, 5) at the joints \(O_{3}\), \(O_{4}\), and \(O_{5}\) of the kinematic pairs for each generated manipulator mechanism variant V.001, V.108, and V.135--in a function of the duration of the manipulation task. The results indicate that the manipulator mechanism variant V.108, which has larger transformation parameters (larger size of hydraulic cylinders), exhibits significantly higher normal forces \(F_{in}\), compared to the variant V.135, which has smaller transformation parameters. Figure 4: Normal forces \(F_{in}\) in revolute joints: (**a**) \(O_{3}\) joint, (**b**) \(O_{4}\) joint, and (**c**) \(O_{5}\) joint for selected variants of manipulator mechanisms V.001, V.108, and V.135. During the loading operation (\(t\) = 0-6 s), the maximum intensities of normal forces occur across all joints. The highest normal force is \(F_{3t}\), acting at the joint \(O_{3}\) (Figure 4a), which belongs to the kinematic pair between the front structure-motion member and the arm (\(L_{2}\)-\(L_{3}\)). The normal force \(F_{5t}\) (Figure 4c) acting at the joint \(O_{5}\) in the kinematic pair connecting the arm and the double-arm lever (\(L_{3}\)-\(L_{5}\)) is noticeably lower. The lowest intensity is observed in the normal force \(F_{4t}\) (Figure 4b) acting at the joint \(O_{4}\) of the kinematic pair between the arm and the bucket (\(L_{3}\)-\(L_{4}\)). In addition to normal forces, the simulation determines the required power \(N_{ut(\text{V},001)}\), \(N_{ut(\text{V},108)}\), and \(N_{ut(\text{V},135)}\) (Figure 5), which is necessary to overcome frictional resistance in the joints of the kinematic pairs for the selected manipulator mechanism variants. These power losses were analyzed during manipulation tasks involving a loading method based on a stepped bucket trajectory (Figure 5a) and a loading method based on a parabolic bucket trajectory (Figure 5b). The results indicate that the manipulator mechanism variants exhibit differing levels of frictional resistance during the simulated tasks. The V.108 variant, characterized by larger transformation parameters, requires significantly greater power to overcome joint friction compared to the V.135 variant, which has smaller transformation parameters, under identical manipulation conditions. Figure 5: Power \(N_{ut}\) required to overcome frictional resistance in joints of selected variants of manipulator mechanisms V.001, V.108 and V.135 for: (**a**) stepped bucket trajectory and (**b**) parabolic bucket trajectory. The conducted analysis indicates that the transmission parameters of drive mechanisms significantly influence the tribological performance of kinematic pair joints and that a minimum power loss criterion enables the identification of drive mechanism variants that ensure both energy efficiency and reduced power loss in the revolute joints of the kinematic pairs.