Miloš Matejić

In robotics and industrial automation, cycloidal reducers are widely used due to their high transmission ratios, compact design, and low backlash. However, their specific kinematics and multiple simultaneous contacts result in complex stress and deformation states, particularly in the cycloidal gear-tooth region. Most previous studies analyzed the stress–strain state only at isolated angular positions of the cycloidal gear, while the behavior of a single tooth during the complete meshing cycle has remained insufficiently investigated. For this reason, this paper presents a combined analytical–numerical approach based on the finite element method (FEA) for the analysis of a single cycloidal gear tooth throughout the entire meshing cycle with the rollers of the ring gear. The results showed that higher Von Mises stress values occur in contacts between convex and concave surfaces than in contacts between two convex surfaces. In addition, the analysis enabled the identification of the most critical angular positions during operation and provided a more detailed insight into the evolution of stress distribution during meshing.

Reliable prediction of carrying capacity is essential for efficient design of all carrying structures, including pallet racks. Precise or simplified analytical models are surely indispensable in engineering practice, but when considering racking structures, they still remain limited primarily by specific beam-to-column connections. This study proposes a semi-empirical, machine learning-driven approach for predicting the behavior of rack elements, i.e., upright frames, as a function of three structurally distinct connection types and appropriate racking element properties. Random Forest was selected for feature screening based on comparative analysis of six ML algorithms, and the retained parameters were used to develop interpretable power-law models. Within this research, upright cross-section area and beam-level height were retained as main influential parameters for the first two considered connection types, whereas upright cross-section moment of inertia, beam-level height and beam cross-section height governed the third type. These differences indicate that the contribution of each input parameter to capacity prediction varied among connection types. Grouped correction factors were introduced to account for deviations associated with upright profile and beam-level height, with additional differences specifically for the third connection type. The adopted models achieved near-exact agreement with the upright frame carrying capacities within the calibration domain. Although the resulting coefficients are specific to the analyzed rack structures, the proposed sequence provides a transferable framework for converting large structural datasets into simplified and interpretable engineering models.

Accurate reciprocating tribological testing depends on the mechanical design, kinematic stability, and load application strategy of the testing apparatus. This paper presents the design, construction, and validation of a custom-built linear reciprocating tribometer developed for controlled laboratory testing. The tribometer provides a programmable stroke of up to 500 mm and a sliding-velocity range of 0.1–50 mm/s. The tribometer was validated through finite element analysis, repeated friction tests, and noise measurements. FEM results showed a maximum displacement of 0.1664 mm and a maximum von Mises stress of 7.47 MPa for the moving plate assembly under a 100 N load, while the loading portal exhibited a maximum localized displacement of 0.017 mm and a maximum stress of approximately 13 MPa under combined loading. These conditions correspond to the maximum design load of the developed tribometer. Repeated tests at 10, 15, and 20 mm/s yielded coefficients of variation of 2.84%, 5.90%, and 14.62%, respectively. Acoustic measurements showed standard deviation values in the range 1.868–3.119 dB. The obtained results confirm stable operation, limited structural deformation, and satisfactory repeatability within the analyzed operating range, indicating that the developed tribometer is suitable for controlled reciprocating tribological experiments under representative laboratory conditions.

The importance of tribology lies in understanding material characteristics that directly affect the reliability and service life of machine elements. In addition to determining tribological properties, it is necessary to provide experimental conditions that correspond to real operating conditions in order to obtain relevant data on the behavior of two materials in contact. This paper presents the development, construction, and experimental testing of a device for measuring friction force in the contact between two materials. The tribometer described in this study belongs to the Pin-on-Disc type. The normal load is applied by a mechanical system based on weights and a lever mechanism. The variation of friction force is monitored in real time using a load cell and a data acquisition system. Within the experimental study, six test series were conducted. The coefficient of friction was analyzed for the contact between a steel disc and pins made of different materials (steel, brass, and aluminum). After several experimental test series, the obtained results were analyzed. The results of the experimental testing confirm the reliability of the developed tribometer.

Understanding the tribological behavior of additively manufactured polymers is essential for their reliable use in sliding components. Tribological tests were performed on a linear reciprocating tribometer pin-on-plate configuration using a polycarbonate sample (PC–PC). To assess the influence of additive-manufacturing-induced anisotropy, three build orientations (0°, 45°, 90°) were examined. Two normal loads of 39.24 N and 58.86 N, and two sliding velocities of 15 and 20 mm/s were selected to represent typical low-load operating conditions of polymeric components. Tests were conducted in dry contact and with two commercial lubricants exhibiting distinct rheological characteristics. Surface topography was characterized before and after testing to evaluate orientation-dependent roughness evolution, while rheological measurements provided effective viscosities at shear rates corresponding to imposed velocities. Frictional behavior was analyzed through the Stribeck parameter, showing that all configurations operated within boundary or early mixed lubrication regimes. Longitudinal specimen layer orientation (90°) was expected to give the lowest friction. In fact, dominant lowest friction in most of the examination regimes gave the 45° build orientation, whereas the 0° orientation hindered lubricant entrainment and produced the highest boundary interaction. Differences in lubricant viscosity influenced Stribeck positioning and the magnitude of friction reduction, demonstrating strong coupling between layer orientation, roughness evolution, and lubrication performance.

Gears are fundamental machine elements used in various industries due to their durability, ability to transmit high torques, and high precision. Modern demands for gear manufacturing involve improving production methods in order to achieve greater efficiency while maintaining the prescribed tolerances. The focus of this study is on the fast, simple, and cost-effective manufacturing of gears and the geometric analysis of gears produced in such a way. For the purpose of this research, six pairs of cylindrical spur gears with straight teeth and involute profiles were fabricated. The gears were manufactured by laser cutting on a BODOR C6 machine, using low-alloy structural steel grade S355. After production, the gears were measured using a TESA Micro-Hite coordinate measuring machine, supported by PC-DMIS Gear software, in accordance with ISO 1328-1. The measured parameters were analyzed, identifying the potential applicability of laser cutting as a viable gear production method. In conclusion, recommendations for the use of such gears are provided. Further research will include the investigation of functional parameters of laser-cut gears, such as efficiency, noise, vibration, and more.

Cycloid power transmissions belong to the group that can be classified as planetary gear trains. These power transmissions, reducers, are part of the latest generation of power transmissions, related to the conventional ones. Cycloid power transmissi...