Applied Mechanics and Materials Vols. 809-810

Abstract: Vibration based fault detection and diagnose analysis is a well established field in machine or monitoring supervision. The vibration diagnose is also suited for the miniature ball bearings monitoring. The typical balls size starts at 3 mm with the bearing outer diameter of maximum 20 mm. Ball bearings of this size are ideal for precision mechanisms, they are able to carry light loads and they are perfect for handheld medical equipment and tools which must be very small but also very precise and durable. The paper presents experiments carried out on a fully instrumented universal CETR micro-tribometer at room temperature. The tested miniature ball bearing, lightly loaded and operating at low speeds, is subjected to dry and lubrication conditions with two different oil viscosities. A comparative study is realized concerning the vibration diagnose potential using the FFT analysis of the bearing acquired signals. Statistical analysis of the vibration signals is a key point in the detection of the overall vibration level of bearings lubricated with oils of different viscosities.

Abstract: The authors investigated experimentally the friction torque in a thrust ball bearing operating at very low axial load and lubricated with mineral oils. The experiments were conducted using spin-down methodology and the results were compared with the theoretical values determined by the SKF methodology for friction torque. The values of the friction torque obtained in the experiments are higher than the analytical values obtained with SKF equations, the differences being explained by the important influence of the friction in balls–cage contacts.

Abstract: This paper presents the dynamic characteristics and the proposed positioning performance of the system to them investigated experimentally. In this research, we developed the positioning system and we evaluated positioning accuracy. The developed system uses a servo motor for motion actuation. In this paper, we focused on studying the dependency of the positioning error – elementary errors – the position of the conducting element for the mechanism of the transformation of the rotation translation movement, representatively the mechanism screw – screwdriver and on emphasizing the practical consequences in the field of design, regulation and exploitation of the correct identification of all the initial errors in the structure of the mechanism, their character and the selection for an ultimate calculus of these which are of a real practical importance.

Abstract: District heating systems operating under dynamic conditions without proper hydronic balancing is one of the causes of discomfort for heating consumers. Moreover, from the point of view of producers, unbalanced heating networks generate low energy efficiency. The study analyzes the operation conditions in three cases, on the same network: the first simulates the operating conditions of the network without balancing, the second when just balancing valves set to corresponding nominal flow rate values are used and the third when balancing valves and differential pressure controllers are used, the so-called total balancing method. Results highlight the importance of the hydraulic balancing under steady state and dynamic operating conditions, as a source to increase the energy efficiency and assure thermal comfort by better distribution of fluid flow rates between consumers.

Abstract: Global challenges related to fossil fuels depletion, climate changes and growth of population with a higher comfort demand require a significant change of heating and cooling perspective in the building sector, from currently mainly fossil combustion to renewable energy sources. Solar heating and cooling may have an important role in providing an economically feasible and environmentally sustainable long-term solution to these essential requirements. This paper presents a brief overview on the available solar cooling technologies focus on thermally driven methods. A market study is also carried out and the potential of solar cooling is emphasized.

Abstract: Multiaxial experiments are necessary to determine materials behavior subjected to complex stress state corresponding to real operating conditions under complex loadings. Stresses applied in biaxial experiments are closely to the stresses that materials experience during their function life. Because of reduced acquisition cost, operation cost and maintenance costs devices attached to the universal testing machine are beginning to be used in ever more applications. The present paper examines a new type of mechanism used to test biaxial cruciform specimens in order to evaluate stress state in planar biaxial tensile testing.

Abstract: The specific objectives of rehabilitation medicine are maintaining and recovering human body functions, as well as preventing dysfunctionalities by means of kinetic and orthotic techniques and a variety of equipment for support and adaptation. The latter are medical systems facilitating the exercise of muscles at constant or variable speeds according to professional recommendations. The paper presents and discusses the control of rehabilitation equipment designed for the passive mobilisation exercises of joints. The novelty of such equipment resides in its actuation by pneumatic muscles, as well as in its control by means of an SPC 200 controller and WinPISA software. The paper presents a number of examples of rehabilitation programmes and the corresponding motion graphs of the rehabilitation equipment sliding block.

Abstract: Planetary speed reducers are used as the actuating module of the revolute joints for the industrial robots as a result of their specific advantages given by high transmission ratios, efficiencies and reliability. However, planetary speed reducers are currently used with variable high speed electric motors, which leads to increased peripheral speeds for the gears and planet carrier, leading in turn to increased noise during operation. Therefore it becomes necessary to manufacture the gears and planet carrier in an upper precision class, leading to significantly increased costs for the entire planetary transmission. Throughout this paper, novel solutions for planetary speed reducers are proposed, characterized by reduced peripheral speeds of the moving elements. For all the structural variants proposed, the summation method (Svamp’s rule) was applied in order to establish mathematical expressions for the transmission ratios. Subsequently, expressions for the peripheral speeds, corresponding to each moving element were derived, and expressed as a function of the number of revolutions of the input shaft. The method described in this paper was applied for each structural variant proposed, the results obtained being compared and analysed, leading to the optimal variant, characterized by a reduced level of noise and vibrations. Based on the mathematical expressions previously derived, a series of graphical representations of peripheral speeds as a function of the number of revolutions for the input shafts were elaborated for each structural variant proposed. At the same time, some recommendations useful for both designers and manufacturers of planetary speed reducers were made, based on the obtained results.

Abstract: Planetary speed reducers are used in the actuation of the revolute kinematic joints thanks to their specific advantages. However, in order to achieve a good positioning accuracy for the kinematic chains, these must have reduced backlash and high torsional stiffness. Therefore the deformations of the elements composing the mechanical structure under the action of gearing forces should be as low as possible, thus leading to backlash reduction. This also becomes important since the presence of backlash in the structure of the planetary speed reducer affects the stability of the overall kinematic chain. In this paper, a novel computation method for bearing deflections is proposed, starting from the kinematic diagram of the planetary speed reducer. Having known the kinematic diagram, it becomes possible to compute the gearing forces, keeping in mind the non-uniform power distribution on the planetary gears. The bearing reactions were computed in two cases: when the planetary gears are free to spin on the planetary carrier and when the planetary gears are fixed on the planet carrier, being supported at the extremities. Based on the computed values for bearing reactions, the corresponding deflections are determined. Once the values of the bearing reactions and deflections had been determined, the load-deflection and stiffness-deflection diagrams were elaborated for ball and roller bearings, allowing the determination of the bearing type that ensures low deflections and high stiffness. Based on the results, some recommendations are made, allowing the reduction of bearing deflections, and increasing the torsional stiffness.

Abstract: In this paper the authors present some of the results of research on the behavior of high entropy alloys used in ballistic protection structures. Bullet impact testing methodology and results on layered Ballistic Packages that incorporate high entropy alloys (HEA) are presented. The paper details the technological processes used to improve the mechanical characteristics of Ballistic Packages. The optimization of the high entropy alloy based layered ballistic composite structures is also investigated. Testing methodology of ballistic boxes, the special heat treatment processes, the homogenization and the artificial aging of high entropy alloys, designed and applied during scientific research; represent the novelties of the article. Ballistic Packages are layered structures which include combinations of the following materials: HEA, armored steel, ceramic plates and laminated polyamide fibers arranged in a predetermined order depending on the constructive version. Ballistic Boxes behavior was investigated by ballistic experimental methods and numerical simulation methods. For the numerical simulation a FEM with an explicit numerical code was used. The numerical and test results are consistent in underling the ballistic protection effectiveness of the investigated configuration.