Machines — Open Access Journal

The purpose of this research was to determine the optimal geometry of a variable pitch conical helicoid to be used in a pressing machine for grape pomace, also known as grape marc. This study attempted to understand if the optimized geometry of the considered helicoid after every pitch resulted in volume decrease DV_c, equal to that obtained during the pressing phase of grape pomace DV_p, using an optimized membrane press. The conical helicoid with variable pitch was replaced in a machine that offered continuous pressing of grape pomace using a cylindrical helicoid with constant pitch (constant pressure distribution, not optimized, along the cochlea axis). As this was a machine already available in the market, the overall dimensions were already established—5.95 m in length and 1.5 m in width. The pressure distribution p₁ and volume change DV_p, obtained during the grape pomace pressing phase in the optimized membrane press (producing high-quality wine) was taken into consideration in this research. Furthermore, the optimized pressure distribution p₁ was applied in seven phases during the pressing process, and a consequent volume change value DV_p was obtained for each phase. Therefore, this study determined the geometry of the variable pitch conical helicoid, which, after every pitch, resulted in volume changing DV_c that was similar to the volume changing DV_p obtained by the optimized membrane press. For this scope, calculations were realized using the Mathematica 10 program code, which, on being assigned the overall dimensions, slope angle of the helicoid, and volume for the first pitch value, determined the radius and pitch values of the helicoid, total volume, and volume change DV_c. It was also noted that by appropriately varying the geometric parameters (taper and pitch of the helicoid), different options of pressure distribution on grape pomace can be obtained, thus enabling improvement and optimization of product quality. Full article

In this study, fluid–structure interaction (FSI) modeling was applied for predicting the fluid flow in a specific peristaltic pump, composed of one metallic roller and a hyperelastic tube pumping a viscous Newtonian fluid. Hyperelastic material dynamics and turbulence flow dynamics were coupled in order to describe all the physics of the pump. The commercial finite element software ABAQUS 6.14 was used to investigate the performance of the pump with a 3D transient model. By using this model, it was possible to predict the von Mises stresses in the tube and flow fluctuations. The peristaltic pump generated high pressure and flow pulses due to the interaction between the roller and the tube. The squeezing and relaxing of the tube during the operative phase allowed the liquid to have a pulsatile behavior. Numerical simulation data results were compared with one cycle pressure measurement obtained from pump test loop data, and the maximum difference between real and simulated data was less than 5%. The applicability of FSI modeling for geometric optimization of pump housing was also discussed in order to prevent roller and hose parts pressure peaks. The model allowed to investigate the effect of pump design variations such as tube occlusion, tube diameter, and roller speed on the flow rate, flow fluctuations, and stress state in the tube. Full article

Intelligent tire concept constitutes one of the approaches to increase the accuracy of active safety systems in vehicle technology. The possibility of detecting tire–road interactions instantaneously has made these systems one of the most important research areas in automotive engineering. This study introduces the use of cost-effective flex and polyvinylidene fluoride strain sensors to estimate some dynamic tire features in free-rolling and real working conditions. The proposed solution combines a microcontroller-based readout circuit for the two sensors with a wireless data transmission system. A suitable prototype was realized and first experimental tests were conducted, in the laboratory as well as on the road. The energy consumption of the wireless monitoring system was optimized. Simulated and experimental results validate the proposed solution. Full article

In model order reduction and system theory, the cross-gramian is widely applicable. The cross-gramian based model order reduction techniques have the advantage over conventional balanced truncation that it is computationally less complex, while providing a unique relationship with the Hankel singular values of the original system at the same time. This basic property of cross-gramian holds true for all symmetric systems. However, for non-square and non-symmetric dynamical systems, the standard cross-gramian does not satisfy this property. Hence, alternate approaches need to be developed for its evaluation. In this paper, a generalized frequency-weighted cross-gramian-based controller reduction algorithm is presented, which is applicable to both symmetric and non-symmetric systems. The proposed algorithm is also applicable to unstable systems even if they have poles of opposite polarities and equal magnitudes. The proposed technique produces an accurate approximation of the reduced order model in the desired frequency region with a reduced computational effort. A lower order controller can be designed using the proposed technique, which ensures closed-loop stability and performance with the original full order plant. Numerical examples provide evidence of the efficacy of the proposed technique. Full article

This study reports on the numerical model development for the prediction of the material removal rate and surface roughness generated during electrical discharge machining (EDM). A simplified 2D numerical heat conduction equation along with additional assumptions, such as heat effect from previously generated crater on a subsequent crater and instantaneous evaporation of the workpiece, are considered. For the material removal rate, an axisymmetric rectangular domain was utilized, while for the surface roughness, a rectangular domain where every discharge resides at the end of previous crater was considered. Simulated results obtained by solving the heat equation based on a finite element scheme suggested that results are more realistic by considering instantaneous evaporation of the material from the workpiece and the effect of residual heat generated from each spark. Good agreement between our model and previously published data validated the newly proposed models and demonstrate that instantaneous evaporation, as well as residual heat, provide more realistic predictions of the EDM process. Full article

Mechanical parameters of the olive wood plate have been computed by data inversion of vibrational experimental tests. A numerical-experimental method has allowed the evaluation of the two transverse shear moduli and the four in-plane moduli of a thick orthotropic olive tree plate. Therefore, the natural flexural vibration frequencies of olive trees plates have been evaluated by the impulse technique. For our purposes, we define the objective function as the difference between the numerical computation data and the experimental ones. The Levenberg–Marquardt algorithm was chosen as optimization strategy in order to minimize the matching error: the evaluation of the objective function has required a complete finite element simulation by using the ANSYS code. As input, we have used the uniaxial test data results obtained from the olive plates. The converged elastic moduli with n = 10 natural modes were E₁ = 14.8 GPa, E₂ = 1.04 GPa, G₁₂ = 4.45 GPa, G₂₃ = 4.02 GPa, G₁₃ = 4.75 GPa, ν₁₂ = 0.42, and ν₁₃ = 0.42. The relative root mean square (RMS) errors between the experimental frequencies and the computed one is 9.40%. Then, it has been possible to obtain a good agreement between the measured and calculated frequencies. Therefore, it has been found that for plates of moderate thickness the reliability of the estimated values of the transverse shear moduli is good. Full article

This paper presents an experimental characterization of a two-stage planetary gearbox (TSPG) designed at the Laboratory of Robot Mechatronics (LARM2) in the University of Rome Tor Vergata. The TSPG operates differentially as function of the attached load and the internal friction forces caused for the contact between gears. Experiments under varying load conditions are developed in order to analyze the usefulness of the gearbox to avoid excessive torques on its internal elements. The analysis of the dynamic torques is presented as an indicator of stability in the gearbox operation. The results show that the actuation of the second operation stage reduces the torques 57% in the output shaft and 65% in the input shaft. The efficiency of the gearbox is estimated as 40% in presence of high internal friction forces. Full article

A new index for a precise calculation of a manipulator’s stiffness isotropy is introduced. The proposed index is compared with the conventionally used stiffness isotropy index by making use of the investigation on R-CUBE manipulator. The proposed index is shown to produce relatively more precise results from which a higher number of isotropic poses are detected. Full article

In the experimental identification of dynamic bearing coefficients, usually small perturbations around the static equilibrium position are assumed and linear coefficients are considered. In the literature, studies on non-linear effects in plain journal bearings, especially from a numerical point of view, are reported. Few similar studies can be found on tilting pad journal bearings (TPJB). The present work reports some peculiar aspects observed during the experimental identification procedure of TPJB linear dynamic coefficients. The tests are performed on a test bench designed for large size journal bearings operating at high peripheral speeds and static loads. A quasi-static procedure is developed to quickly check the results obtained from the usually adopted dynamic excitation. It consists of applying a slowly rotating force to the floating stator and measuring the relative displacement of the stator from the rotating shaft. Different levels of static and dynamic load are applied to two different TPJBs with four and five pads. Deformed orbits have been observed increasing the ratio between dynamic load and static load, suggesting the presence of non-linearity. Similar results are obtained with simple analytical models assuming suitably tuned non-linear stiffness terms. Full article

The fusion of different technologies is the base of the fourth industrial revolution. Companies are encouraged to integrate new tools in their production processes in order to improve working conditions and increase productivity and production quality. The integration between information, communication technologies and industrial automation can create highly flexible production models for products and services that can be customized through real-time interactions between consumer, production and machinery throughout the production process. The future of production, therefore, depends on increasingly intelligent machinery through the use of digital systems. The key elements for future integrated devices are intelligent systems and machines, based on human–machine interaction and information sharing. To do so, the implementation of shared languages that allow different systems to dialogue in a simple way is necessary. In this perspective, the use of advanced prototyping tools like Open-Source programming systems, the development of more detailed multibody models through the use of CAD software and the use of self-learning techniques will allow for developing a new class of machines capable of revolutionizing our companies. The purpose of this paper is to present a waypoint navigation activity of a custom Wheeled Mobile Robot (WMR) in an available simulated 3D indoor environment by using the Gazebo simulator. Gazebo was developed in 2002 at the University of Southern California. The idea was to create a high-fidelity simulator that gave the possibility to simulate robots in outdoor environments under various conditions. In particular, we wanted to test the high-performance physics Open Dynamics Engine (ODE) and the sensors feature present in Gazebo for prototype development activities. This choice was made for the possibility of emulating not only the system under analysis, but also the world in which the robot will operate. Furthermore, the integration tools available with Solidworks and Matlab-Simulink, well known commercial platforms of modelling and robotics control respectively, are also explored. Full article

The optimization of wind energy conversion efficiency has been recently boosting the technology improvement and the scientific comprehension of wind turbines. In this context, the yawing behavior of wind turbines has become a key topic: the yaw control can actually be exploited for optimization at the level of single wind turbine and of wind farm (for example, through active control of wakes). On these grounds, this work is devoted to the study of the yaw control optimization on a 2 MW wind turbine. The upgrade is estimated by analysing the difference between the measured post-upgrade power and a data driven model of the power according to the pre-upgrade behavior. Particular attention has therefore been devoted to the formulation of a reliable model for the pre-upgrade power of the wind turbine of interest, as a function of the operation variables of all the nearby wind turbines in the wind farm: the high correlation between the possible covariates of the model indicates that Principal Component Regression (PCR) is an adequate choice. Using this method, the obtained result for the selected test case is that the yaw control optimization provides a 1% of annual energy production improvement. This result indicates that wind turbine control optimization can non-negligibly improve the efficiency of wind turbine technology. Full article

To meet the needs of present-day robotics, a family of gripping flexible fingers has been designed. Each of them consists of a number of independent and flexible modules that can be assembled in different configurations. Each module consists of a body with a flexible central rod and three longitudinally positioned shape memory alloy (SMA) wires. When heated by the Joule effect, one to two SMA wires shorten, allowing the module to bend. The return to undeformed conditions is achieved in calm air and is guaranteed by the elastic bias force exerted by the central rod. This article presents the basic concept of the module and a simple mathematical model for the design of the device. Experimental tests were carried out on three prototypes with bodies made of different materials. The results of these tests confirm the need to reduce the antagonistic action of the inactive SMA wires and led to the realization of a fourth prototype equipped with an additional SMA wire-driven locking/unlocking device for these wires. The preliminary results of this last prototype are encouraging. Full article

In this paper, the mechanical behavior of concrete twin-shaft mixers is analyzed in terms of power consumption and exchanged forces between the mixture and the mixing organs during the mixing cycle. The mixing cycle is divided into two macro phases, named transient and regime phase, where the behavior of the mixture is modeled in two different ways. A force estimation and power consumption prediction model are presented for both the studied phases and they are validated by experimental campaigns. From the application of this model to different machines and by varying different design parameters, the optimization of the power consumption of the concrete twin-shaft mixers is analyzed. Results of this work can be used to increase productivity and profitability of concrete mixers and reduce energy waste in the industries which involve mixing processes. Full article

This paper presents a semi-automated design algorithm for computing straight bevel gear involute profiles. The proposed formulation is based on the Tredgold approximation method. It allows the design of a pair of bevel gears with any desired number of teeth and relative axes inclination angles by implementing additive manufacturing technology. A specific case study is discussed to calculate the profiles of two straight bevel gears of a biomedical application. Namely, this paper illustrates the design of the bevel gears for a new laparoscopic robotic system, EasyLap, under development with a grant from POR Calabria 2014–2020 Fesr-Fse. A meshing analysis is carried out to identify potential design errors. Moreover, finite element-based tooth contact analysis is fulfilled for determining the vibrational performances of the conjugate tooth profiles throughout a whole meshing cycle. Simulation results and a built prototype are reported to show the engineering feasibility and effectiveness of the proposed design approach. Full article

This paper presents the design of Rene Artificiale Portatile (RAP), a novel wearable and portable device for extracorporeal blood ultrafiltration, capable of providing remote treatment of fluid overload in patients with kidney diseases and/or congestive heart failure. The development of the device is based on a new design paradigm, since the layout of the device is box-shaped, as to fit a backpack or a trolley case, differentiating it from other existing devices. The efficient layout and component placement guarantee minimalization and ergonomics, as well as an efficient and cost-effective use. The redundant control architecture of the device has been implemented to ensure a high level of safety and an effective implementation of the clinical treatment. The consistency of the design and its effective implementation are assessed by the results of the preliminary in-vitro tests presented and discussed in this work. Full article

This paper describes an experimental investigation conducted on magneto-rheological elastomers (MREs) with the aim of adopting these materials to make mounts to be used as vibration isolators. These materials, consisting of an elastomeric matrix containing ferromagnetic particles, are considered to be smart materials, as it is possible to control their mechanical properties by means of an applied magnetic field. In the first part of the paper, the criteria adopted to define the characteristics of the material and the experimental procedures for making samples are described. The samples are subjected to a compressive static test and are then, adopting a testing machine specially configured, tested for shear periodic loads, each characterized by a different constant compressive preload. The testing machine is equipped with a coil, with which it is possible to vary the intensity of the magnetic field crossing the sample during testing to evaluate the magneto-rheological effect on the materials’ characteristics in terms of stiffness and damping. Full article

In the recent years, distributed energy production has been one of the main research topics about renewable energies. The decentralization of electric production from wind resources raises the issues of reducing the size of generators, from the MW scale of industrial wind farm turbines to the kW scale, and possibly employing them in urban areas, where the wind flow is complex and extremely turbulent because of the presence of buildings and obstacles. On these grounds, the use of small-scale vertical axis small wind turbines (VASWT) is a valid choice for on-site generation (OSG), considering their low sensitivity with respect to turbulent flow and that there is no need to align the turbine with wind direction, as occurs with horizontal axis small wind turbines (HASWT). In addition, VASWTs have a minor acoustic impact with respect to HASWTs. The aim of this paper is to study the interactions that take place between a 1.2 kW, vertical axis, Darrieus VASWT turbine and a small, experimental building, in order to analyze the noise and the vibrations transmitted to the structure. One method to damp the vibrations is then assessed through spectral analysis of data acquired through accelerometers located both in the mast of the wind turbine and at the building walls. The results confirm the usefulness of dampers to increase the building comfort regarding vibrations. Full article

In recent decades, the power grid’s configuration is shifting towards a smart grid where responsive loads and energy storage systems (ESS) are finding an increased role in the power system operation. In the presented work, a mathematical formulation for frequency response analysis of a multi-machine power system is developed, considering the individual and combined roles of ESS and responsive loads. The validity of the developed model is demonstrated with the help of multiple case studies, which consider the various configurations of the power system. Moreover, different combinations of capacities of generation units, ESS and responsive loads are also simulated. With the help of mathematical model and simulation results, it is demonstrated that ESS and responsive loads may improve the economy and performance of the power system even during the failure of a certain portion of generation capacity. Though the case studies consider non-reheat turbines only, the mathematical model and conclusions are equally valid for other types of turbines as well. Full article

Processing in planetary ball mills is well suited to a large number of applications because they are easy to operate and versatile, grinding faster than other mills. Research related to planetary mills are mainly about the process evaluation, and there are few studies on the mechanical design of such equipment. This paper describes the decision process in the design of an innovative planetary mill in which design for manufacture and assembly (DFMA) principles were used to provide compact equipment made of simple and standardized parts. We developed a friction wheel mechanism with an additional degree of freedom that improves transmission and facilitates assembly, reducing the need for adjustment. It can be applied to different equipment that relies on planetary motion or rotating devices. A prototype was built, and its grinding performance surpasses that of other types of traditional mill. The mean particle size of alumina powder was reduced from 4.2 µm to 0.9 µm in 60 minutes. Full article