Search

Mechanisms of machines completing a repeating operation have many applications in the processing industry. During the working cycle, the output link of the mechanism has one or more periods of dwell, while the input link moves continuously. The paper presents the graphical synthesis of 6-bar linkage mechanism with high class structure groups. The procedure is based on the synthesis at the extreme positions of the mechanism, simplifying the task to a problem with a finite number of precise positions. At the core of this procedure are simple, easily visible and understandable geometric constructions that are then used to form equations suitable for further analysis and optimization. Motion of the mechanism resulting from the synthesis has some inaccuracy - the output link moves during the dwell phase, completing an angle of ±0.5°, which is considered accurate enough for a wide range of practical applications.

The use of 3D models of the human bone system has great utility in the biomechanical study, due to the fact that these structures cannot be analyzed or tested in vivo. Within this paper, taking into consideration its real bone structure, the human femur CAD modelling is established. Firstly, a preliminary anatomical study is done, in order to highlight the fact that the thigh bone is a heterogeneous structure, consisting of several entities with different mechanical characteristics. The modelling starts from a homogenous 3D model of the femur, from which, every single separate entity is designed and finally they are assembled within a single product assembly. Therefore, the final result ensures a complex CAD structure, able to get assigned different material properties, specific for each entity this modelling furtherly allows the characteristic pathological structures studies of the referred entity or to simulate specific surgical interventions.

By analysing and comparing the existing solutions of universal gear reducers with helical gears of the leading manufacturers, it can be noticed the effort to increase the load capacity of the gear reducer within the same axis height. In this way, the manufacturers can offer smaller (cheaper) gear reducers, as well as to simultaneously increase the values of the largest gear ratios. This concept enables the offer of lower-stage (cheaper) gear reducers with higher gear ratios in certain segments of gear ratios. By these efforts, it is reached the maximum, but the further increase is possible only by changing the current concept of universal gear drives. Within this paper, it is given an overview and analysis of one of the possible new conceptual solutions of modern universal motor gear reducer.

Today, for almost all products, the appearance is very important. Thus, for example, the appearance of universal gear reducers was not given so much attention, but today there are many very interesting solutions of shape, colour and graphic design. It should have in mind that universal gear reducers have much complex construction comparing them with special gear reducers. In the same time, they have to provide different positions and way of mounting and different speeds with different powers (torques) at the output shaft. Particularly, it should be noticed, that within all universal gear reducers single-stage gear units are nowadays increasingly used because their gear ratio values are increased (values of gear ratio can go up to 15) so that these reducers largely cover most of the two-stage gear reducers with their gear ratio values, so thereby their exploitation is significantly increased. Single-stage gear reducers are very simple products, and today there is a large number of manufacturers of such product. However, their mounting dimensions and way of mounting are not defined by a standard, so there is a variety of units with different dimensions and way of mounting. Although, most manufacturers look up to dimensions of leading manufacturers (usually SEW) in order to ensure greater exchangeability of their gear units. It is interesting to note, that most manufacturers tend to adopt the design of housing that will be substantially different from competing solutions. The reason is probably to avoid the possibility of being accused of copying someone else’s solution. However, there are manufacturers that retain almost identical housing design as a competing solution (probably they bought the licence or the solution is copied without permission). This paper considers only the design solutions of single-stage gear reducer in order to indicate the expected directions of their further development.

High contact ratio (HCR) gearing is a special kind of the basic involute profile gearing with higher contact ratio, since there are always at least two pairs of teeth in contact. Compared to standard gearings, HCR gearings have greater load capacity, higher resistance and a lower relative noise level. Their main drawbacks are more complicated design than standard involute profiles, greater predisposition for interference, pointed tip thickness and undercut of teeth during production. There is also a larger possibility of some interference or pointed tooth tip occurring. All these issues represent serious design constraints which need to be resolved in the design phase. In this paper, a new method for HCR gearing design is proposed, which uses Generalized Particle Swarm Optimization Algorithm (GPSO) for gearing parameters optimization. This recently introduced global optimization method enables finding of global optimal solution(s), ensuring that all relevant design and function constraints are satisfied.

The deep groove ball bearing is one of the most important components of the rotary motion system and is the research subject in this paper. After factory assembly, new ball bearings need to pass quality control. The conventional approach relies on measuring the vibration amplitudes for each unit and sorting them into classes according to the vibration level. In this paper, based on experimental research, models are created to predict the vibration class and analyze the dynamic behavior of new ball bearings. The models are based on artificial neural networks. A feedforward multilayer perceptron (MLP) was applied, and a backpropagation learning algorithm was used. A specific method of training groups of artificial neural networks was applied, where each network provided an answer to the input within the group, and the final answer was the mean value of the answers of all networks in the group. The models achieved a prediction accuracy of over 90%. The main aim of the research was to construct models that are able to predict the vibration class of a new ball bearing based on the geometric parameters of the bearing rings. The models are also applied to analyze the influence of surface roughness of the raceways and the internal radial clearance on bearing vibrations. [ABSTRACT FROM AUTHOR]

The operating principle of rolling bearings generates vibrations that come from the periodic change in the stiffness of the bearing. The vibration level of the bearing depends on a large number of factors such as waviness, surface roughness of the raceways, deviation of the raceway radius, exploitation conditions, amount of lubrication in the bearing and other. This paper presents the influence of the roughness of the raceways and the amount of lubrication on the level of vibrations of the ball bearing, designation 6006. The determination of the influence of these parameters was done experimentally. The experiment was performed according conditions prescribed by ISO 15242-2, and the analysis of the measured signals was performed according to the guidelines given by the standard ISO 15242-1.

Possible concept solutions of chain drives are analysed in this paper in order to point out the benefits of chain drive application and, in particular, the possibility of application of multi-level chain drive. The paper also analyses the possibility of replacing the gear drives with chain drives, which, in the case of short-term drive and using the same direction of rotation, enables a slightly simpler drive solution. The paper doesn’t consider difference between the roller and gear chains application because these two types of chains can be used very successfully. Also, the possibility of using timing belt drive is not considered, but it can be also used very successfully in this type of drive, but only as a transmission of motion.

The problem of defining the load (nominal torque on the output shaft - T2N) of universal gear drives depending on the size of the gear ratio is analysed in this paper. It is logical that the load capacity of gear drive depends on the weakest gear component. Since the gears are the most expensive components of gear unit, it tends to maximize their performance. However, for low gear ratio, i.e. for high speeds, the bearings often limit their load capacity since the same bearings are used in all transmission ratios because it is not practiced to oversize the bearings at low speeds. Nowadays, when high values of gear ratio are used, it is interesting to consider the dependence of the nominal torque at the output regarding to gear ratio and operating life of the unit.

In this paper we present a design method for a modular device used in different types of HIGH TIBIAL OSTEOTOMY surgical procedures. The requirements, necessities and functions of this modular device are presented in the first part of the article. An important aspect is the fact that the device must be designed in a manner which permit to use it for all types of HIGH TIBIAL OSTEOTOMY: opening wedge osteotomies, closing wedge osteotomies, medial osteotomies, lateral osteotomies, uniplanar osteotomies or biplanar osteotomies. This fact is possible using modular elements for the main parts of the devices. The researches could be the starting point for others researches regarding the appropriate materials and the possibility to execution customized several parts of the modular device using Additive Manufacturing facilities.

Gear transmissions are relatively simple mechanisms whose quality, price, delivery time and design appearance are almost equal. This is the common reason why it is very difficult for all gear manufacturers to ensure the successful placement of their products on the market. However, regardless of their simplicity, gear transmissions may have different design and technical solutions, and due to different limitations of individual components, the calculation of load capacity and other technical characteristics can be quite complicated. In accordance with the basic settings of Industry 4.0, smart transmissions are being developed that will be able to provide a certain advantage over the competition and thus, for sure, ensure the successful business of these innovative companies. This paper describes the basic principles of construction using new technologies, primarily using the Internet of Things and digital twins. The paper includes an analysis of approaches to the creation of Digital Twins. Describe why Industry 4.0 is so different and specific, define what is Cyber-physical systems and the Internet of Things, and what is predictive monitoring with using different sensors. [ABSTRACT FROM AUTHOR]

In the area of universal gear reducers, standard does not prescribe relations between load capacity, gear ratios and axis heights. Therefore, larger load capacity of some gear reducers manufacturers has advantage for lower gear ratio and, vice versa, smaller load capacity of the gearbox achieves higher values of gear ratio. However, there are some manufacturers who produce gear reducers with smaller or larger load capacity for higher or lower gear ratio, within the same axis height. This paper deals with analysis of justification of applying two gear sets, especially in the case when so-called intermediate sizes of gear reducer are not used.

The paper presents the development of neck mechanism for humanoid robots. The research was conducted within the project which is developing a humanoid robot Marko that represents assistive apparatus in the physical therapy for children with cerebral palsy.There are two basic ways for the neck realization of the robots. The first is based on low backlash mechanisms that have high stiffness and the second one based on the viscoelastic elements having variable flexibility. We suggest low backlash differential gear mechanism that requires small actuators. Based on the kinematic-dynamic requirements a dynamic model of the robots upper body is formed. Dynamic simulation for several positions of the robot was performed and the driving torques of neck mechanism are determined.Realized neck has 2 DOFs and enables movements in the direction of flexion-extension 100°, rotation ±90° and the combination of these two movements. It consists of a differential mechanism with three spiral bevel gears of which the two are driving and are identical, and the third one which is driven gear to which the robot head is attached. Power transmission and motion from the actuators to the input links of the differential mechanism is realized with two parallel placed gear mechanisms that are identical.Neck mechanism has high carrying capacity and reliability, high efficiency, low backlash that provide high positioning accuracy and repeatability of movements, compact design and small mass and dimensions.

Within the universal motor helical gear reducer, single row deep groove ball bearings are usually used, but for larger driver dimensions and heavily loaded shafts, spherical roller bearings are used. In order to achieve the maximum load capacity of the gearbox, within the same axis height, relatively large single-row ball bearings are necessary. In some cases, due to dimensions constraints, they cannot be installed in the gearbox, so many manufacturers, in certain cases, use somewhat smaller and more expensive single-row cylindrical roller bearings. Though these bearings are not specifically designed to transmit axial forces, they can bear axial loads. The idea of this paper is to point out this problem and the benefits that come from the use of cylindrical roller bearings. [ABSTRACT FROM AUTHOR]

Within this paper is described an analytical model for the analysis of quasistatic load distribution in four contact ball bearings. The quasistatic model was developed on the basis of the static model, applying Hertz's theory of contact and John-Harris's load distribution on ball. In this paper, the model is extended by introducing parameters such as positive/negative clearances into static equilibrium equations. Behavior analysis of the four point contact ball bearing (FKL LSQFR 308) was performed for different operating conditions. Within certain analyzes, the analysis of the influence of conceptual parameters (positive/negative clearances) on the operational characteristics of bearings was performed. The change in external load also varied. Verification of the static behavior of the ball bearing LSQFR 308 was performed by comparing the results obtained by quasistatic modeling and the results obtained using the finite element method. [ABSTRACT FROM AUTHOR]

Ball bearings can be found in all machines with rotary movement. Dynamic behavior analysis of ball bearings is a phenomenon that has been studied for many years. Previous studies on the dynamic behavior of ball bearings are based on describing the state of ball bearings using mathematical models. In addition to mathematical description, computers simulations based on finite element methods are also applied. This paper presents study of the dynamic behavior of ball bearings using artificial neural networks. Artificial neural network models are able to predict the amplitude of vibration that will generate the analyzed bearings depending on the lubrication. In this way, by the application of artificial neural networks bearing dynamic behavior can be predicted depending on the geometric parameters and lubrication. [ABSTRACT FROM AUTHOR]

This paper presents the development of the waist mechanism for humanoid robots. The research was conducted within the project which is developing a humanoid robot Marko that represents assistive technology in physical therapy for children with cerebral palsy. There are two basic ways for realization of the robot trunk. The first is based on multi-joint viscoelastic structures that have variable flexibility and the second one is based on low backlash mechanisms with one joint that has high stiffness. Based on the kinematic-dynamic requirements a dynamic model of the robot upper body is formed. Dynamic simulation for several positions of the robot was performed and the driving torques of the waist mechanism are determined. Realized waist has 1 DOF and enables movements in the direction of flexion-extension 90°. It consists of a gear mechanism with bevel and helical gears. It has a high carrying capacity and reliability, high efficiency and low backlash that provide high positioning accuracy and repeatability of movements. [ABSTRACT FROM AUTHOR]

The problem of worm gear heating is analysed in this paper. In most of cases, this heating has great impact on load capacity of worm gears, but in a great measure defines efficiency of worm gear transmission. Heating of worm gear is restricted by thermal power capacity of the gearbox. Thermal power capacity of the gearbox is defined as the biggest input power of the gearbox which could be transmitted by the gear unit, with the condition that power losses can be given to the surrounding without overheating of the gearbox, in the case of normal air temperature. Determination of the operating temperature represents the main problem for defining thermal power capacity of the gearbox. The highest operating temperature represents a limit until the gearbox (the oil in the gearbox) can be heated, but also in dependence of surrounding temperature (the ambient temperature where the gearbox operates). Influence of these temperatures is analysed in this paper. [ABSTRACT FROM AUTHOR]

The issue of design and dimensioning of HCR gearing, particularly of the gearings with an internal engagement, it nowadays, especially in the design of hybrid cars drives, highly topical. This kind of gearing has many advantages in operation, but at the same time it is more complicated in stage of its design and load capacity calculation. Authors in this contribution present some results of temperature scuffing research of internal and external HCR gearing. There are given the equations for calculation of warm scuffing resistance of both external and internal HCR gearing derived according to the integral temperature criterion. [ABSTRACT FROM AUTHOR]

The temperature of rubber or rubber-metal springs increases under cyclic loading, due to hysteresis losses and low rubber thermal conductivity. Hysteresis losses correspond to energy dissipation from the rubber, which is primarily converted into heat. This well-known phenomenon, called heat build-up, is the primary reason for rubber aging. Increase in temperature within the rubber com-pound leads to degradation of its physical and chemical properties, increase in stiffness and loss of damping capability. This paper presents a novel procedure of heat generation prediction in rubber or rubber-metal springs. The procedure en-compasses the prediction of hysteresis loss, i. e. dissipated energy within the rubber, by finite element analysis and application of a modern viscoplastic rubber constitutive model. The obtained dissipated energy was used as an input for transient thermal analysis. Verification of the proposed procedure was performed by comparison of simulation results with experimentally obtained data during the dynamic loading of the rubber specimen. The proposed procedure is highly computationally efficient and it enables time integration, which can be problematic in coupled mechanical thermal analysis. [ABSTRACT FROM AUTHOR]

A considerable slide exists between the flanks of worm and gear during the work, which results in flank wear and considerable loss of energy. The energy is, there-by, converted into heat, which leads to the warming-up of gear drive, compromising its correct operation, and to scuffing in critical cases. Oil temperature has an important role in thermal stability. Viscosity depends on temperature. Viscosity significantly affects the processes in the contact zone, i. e. the energy losses, and hence the temperature. Optimal lubrication can be provided only in the relevant field of temperatures. The paper presents experimental and theoretical research on the effect of temperatures and thermal stability of a worm and gear set with a gear made of sintered steel Fe1.5Cr0.2Mo on their ability and appearance of boundary conditions. [ABSTRACT FROM AUTHOR]

This paper analyzes possibilities of reducing the number of necessary gears in the family of universal motor gear reducers with helical gears, since both the production and storage of a large number of different gears cost a lot and impose a great burden for any gear manufacturer, as it can be seen from literature [1,2] that focuses on this problem. The paper particularly emphasizes the necessity of narrowing down the assortment of gear reducers and the possibility of changing the design solution between the pinion and the electric motor as they represent the basic possibilities for reducing the number of necessary gears. The paper also points out the need for a special selection of preferred gear ratios and corresponding gears as one of the possibilities for reducing the total number of gears. This can certainly result in faster delivery of a gearbox with the preferred gear ratio. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to determine the effect of the air torque position (ATP) damper hysteresis on the accuracy of air velocity measurements and the adequacy of the ATP damper mathematical model tested in the present study. A total of three dampers with non-cascading blades were examined: a damper with a single flat blade, a damper with two opposed flat blades, and a damper with two flat blades - one of which is a measuring blade and the other is fixed in the horizontal direction. Furthermore, a total of two damper installation locations in a duct system were examined as well: at the duct exit with a straight duct section preceding the damper and within the duct itself with straight duct sections both preceding and following the damper. The ATP damper hysteresis was found to exert a significant effect on the accuracy of air velocity measurements and the adequacy of the ATP damper mathematical model tested if the ATP damper is more open, i.e. with lower blade angles of attack. Moreover, the ATP damper installed at the duct exit was found to be more susceptible to hysteresis effects than the damper located within the duct. • ATP damper hysteresis exerts a significant effect if the damper is more open. • ATP damper installed at the duct exit was found to be more susceptible to hysteresis. • A fixed ATP damper blade in horizontal direction could mitigate effect of hysteresis. • The effect of hysteresis could be reduced by fixing blade angle during measurements. [ABSTRACT FROM AUTHOR]