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Machines, Volume 9, Issue 4 (April 2021) – 14 articles

Cover Story (view full-size image): Trochoidal milling is a promising alternative strategy for the milling of slots, which involves a trochoidal path for the cutting tool center and allows reduced cycle times, lower cutting forces, machine tool load and vibrations, as well as improved tool life and productivity. As the quality of the machined surface is also of major importance in the field of manufacturing, the capabilities of trochoidal milling strategy were investigated in comparison to the conventional slot milling strategy by two series of experiments. It was revealed that the trochoidal milling strategy can outperform the conventional strategy in terms of surface quality, given that appropriate parameter values are selected. Further experiments led to the determination of the correlation between surface roughness, cooling strategy and trochoidal path characteristics. View this paper
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23 pages, 5649 KiB  
Article
A Synergy of Innovative Technologies towards Implementing an Autonomous DIY Electric Vehicle for Harvester-Assisting Purposes
by Dimitrios Loukatos, Evangelos Petrongonas, Kostas Manes, Ioannis-Vasileios Kyrtopoulos, Vasileios Dimou and Konstantinos G. Arvanitis
Machines 2021, 9(4), 82; https://doi.org/10.3390/machines9040082 - 19 Apr 2021
Cited by 18 | Viewed by 3822
Abstract
The boom in the electronics industry has made a variety of credit card-sized computer systems and plenty of accompanying sensing and acting elements widely available, at continuously diminishing cost and size levels. The benefits of this situation for agriculture are not left unexploited [...] Read more.
The boom in the electronics industry has made a variety of credit card-sized computer systems and plenty of accompanying sensing and acting elements widely available, at continuously diminishing cost and size levels. The benefits of this situation for agriculture are not left unexploited and thus, more accurate, efficient and environmentally-friendly systems are making the scene. In this context, there is an increasing interest in affordable, small-scale agricultural robots. A key factor for success is the balanced selection of innovative hardware and software components, among the plethora being available. This work describes exactly the steps for designing, implementing and testing a small autonomous electric vehicle, able to follow the farmer during the harvesting activities and to carry the fruits/vegetables from the plant area to the truck location. Quite inexpensive GPS and IMU units, assisted by hardware-accelerated machine vision, speech recognition and networking techniques can assure the fluent operation of a prototype vehicle exhibiting elementary automatic control functionality. The whole approach also highlights the challenges for achieving a truly working solution and provides directions for future exploitation and improvements. Full article
(This article belongs to the Special Issue Intelligent Mechatronics Systems)
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14 pages, 31448 KiB  
Article
Development of a New Finishing Process Combining a Fixed Abrasive Polishing with Magnetic Abrasive Finishing Process
by Yanhua Zou, Ryunosuke Satou, Ozora Yamazaki and Huijun Xie
Machines 2021, 9(4), 81; https://doi.org/10.3390/machines9040081 - 12 Apr 2021
Cited by 13 | Viewed by 4244
Abstract
High quality, highly efficient finishing processes are required for finishing difficult-to-machine materials. Magnetic abrasive finishing (MAF) process is a finishing method that can obtain a high accuracy surface using fine magnetic particles and abrasive particles, but has poor finishing efficiency. On the contrary, [...] Read more.
High quality, highly efficient finishing processes are required for finishing difficult-to-machine materials. Magnetic abrasive finishing (MAF) process is a finishing method that can obtain a high accuracy surface using fine magnetic particles and abrasive particles, but has poor finishing efficiency. On the contrary, fixed abrasive polishing (FAP) is a polishing process can obtain high material removal efficiency but often cannot provide a high-quality surface at the nano-scale. Therefore, this work proposes a new finishing process, which combines the magnetic abrasive finishing process and the fixed abrasive polishing process (MAF-FAP). To verify the proposed methodology, a finishing device was developed and finishing experiments on alumina ceramic plates were performed. Furthermore, the mechanism of the MAF-FAP process was investigated. In addition, the influence of process parameters on finishing characteristics is discussed. According to the experimental results, this process can achieve high-efficiency finishing of brittle hard materials (alumina ceramics) and can obtain nano-scale surfaces. The surface roughness of the alumina ceramic plate is improved from 202.11 nm Ra to 3.67 nm Ra within 30 min. Full article
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2 pages, 165 KiB  
Editorial
Italian Advances on MMS
by Vincenzo Niola and Domenico Mundo
Machines 2021, 9(4), 80; https://doi.org/10.3390/machines9040080 - 12 Apr 2021
Viewed by 1448
Abstract
The aim of this Special Issue is to disseminate recent developments in the field of Mechanism and Machine Science achieved by the Italian community through international collaborations, ranging from theoretical contributions to experimental and practical applications [...] Full article
(This article belongs to the Special Issue Italian Advances on MMS)
14 pages, 4696 KiB  
Article
Vibration and Stability Analysis of a Bearing–Rotor System with Transverse Breathing Crack and Initial Bending
by Yuehua Wang, Xin Xiong and Xiong Hu
Machines 2021, 9(4), 79; https://doi.org/10.3390/machines9040079 - 8 Apr 2021
Cited by 8 | Viewed by 3012
Abstract
This paper focuses on the stability and nonlinear response of a bearing-rotor system affected by a transverse crack and initial bending which was thought to be part of an unbalance or had been neglected before. The differences of breathing functions for the transverse [...] Read more.
This paper focuses on the stability and nonlinear response of a bearing-rotor system affected by a transverse crack and initial bending which was thought to be part of an unbalance or had been neglected before. The differences of breathing functions for the transverse breathing crack caused by initial bending is presented here, and the calculation of time-varying finite elements stiffness matrix of the cracked shaft is improved by replacing traditional the approximate crack segment with an exact area. After establishing the dynamic model of the cracked rotor with initial bending, vibrational characteristics such as amplitude-speed diagram, frequency spectrogram and bifurcations are investigated in detail. The eigenvalues of the transition matrix are calculated and analyzed as an indicator of dynamic stability with the growths of crack depth and initial bending. Many differences are found between the two cases of dynamic response of rotor system by numerical simulation. The frequency change with the growth of initial bending is opposite to the change with the growth of crack depth, and the shapes of amplitude-speed also having great different features. Stable regions are reduced and extended laterally by initial bending. All these results obtained in this paper will contribute to identify the bending fault and assess the stability of the bearing-rotor systems. Full article
(This article belongs to the Special Issue Condition Monitoring for Non-stationary Rotating Machines)
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19 pages, 3684 KiB  
Article
Cybersecurity Risk Assessment in Smart City Infrastructures
by Maxim Kalinin, Vasiliy Krundyshev and Peter Zegzhda
Machines 2021, 9(4), 78; https://doi.org/10.3390/machines9040078 - 4 Apr 2021
Cited by 58 | Viewed by 10571
Abstract
The article is devoted to cybersecurity risk assessment of the dynamic device-to-device networks of a smart city. Analysis of the modern security threats at the IoT/IIoT, VANET, and WSN inter-device infrastructures demonstrates that the main concern is a set of network security threats [...] Read more.
The article is devoted to cybersecurity risk assessment of the dynamic device-to-device networks of a smart city. Analysis of the modern security threats at the IoT/IIoT, VANET, and WSN inter-device infrastructures demonstrates that the main concern is a set of network security threats targeted at the functional sustainability of smart urban infrastructure, the most common use case of smart networks. As a result of our study, systematization of the existing cybersecurity risk assessment methods has been provided. Expert-based risk assessment and active human participation cannot be provided for the huge, complex, and permanently changing digital environment of the smart city. The methods of scenario analysis and functional analysis are specific to industrial risk management and are hardly adaptable to solving cybersecurity tasks. The statistical risk evaluation methods force us to collect statistical data for the calculation of the security indicators for the self-organizing networks, and the accuracy of this method depends on the number of calculating iterations. In our work, we have proposed a new approach for cybersecurity risk management based on object typing, data mining, and quantitative risk assessment for the smart city infrastructure. The experimental study has shown us that the artificial neural network allows us to automatically, unambiguously, and reasonably assess the cyber risk for various object types in the dynamic digital infrastructures of the smart city. Full article
(This article belongs to the Special Issue Mechatronic System for Automatic Control)
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24 pages, 7274 KiB  
Article
Research on Motion Planning Based on Flocking Control and Reinforcement Learning for Multi-Robot Systems
by Minghui Wang, Bi Zeng and Qiujie Wang
Machines 2021, 9(4), 77; https://doi.org/10.3390/machines9040077 - 1 Apr 2021
Cited by 23 | Viewed by 4045
Abstract
Robots have poor adaptive ability in terms of formation control and obstacle avoidance control in unknown complex environments. To address this problem, in this paper, we propose a new motion planning method based on flocking control and reinforcement learning. It uses flocking control [...] Read more.
Robots have poor adaptive ability in terms of formation control and obstacle avoidance control in unknown complex environments. To address this problem, in this paper, we propose a new motion planning method based on flocking control and reinforcement learning. It uses flocking control to implement a multi-robot orderly motion. To avoid the trap of potential fields faced during flocking control, the flocking control is optimized, and the strategy of wall-following behavior control is designed. In this paper, reinforcement learning is adopted to implement the robotic behavioral decision and to enhance the analytical and predictive abilities of the robot during motion planning in an unknown environment. A visual simulation platform is developed in this paper, on which researchers can test algorithms for multi-robot motion control, such as obstacle avoidance control, formation control, path planning and reinforcement learning strategy. As shown by the simulation experiments, the motion planning method presented in this paper can enhance the abilities of multi-robot systems to self-learn and self-adapt under a fully unknown environment with complex obstacles. Full article
(This article belongs to the Section Robotics, Mechatronics and Intelligent Machines)
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16 pages, 6387 KiB  
Article
Performance Prediction of a Turbodrill Based on the Properties of the Drilling Fluid
by Delong Zhang, Yu Wang, Junjie Sha and Yuguang He
Machines 2021, 9(4), 76; https://doi.org/10.3390/machines9040076 - 31 Mar 2021
Cited by 9 | Viewed by 2811
Abstract
High-temperature geothermal well resource exploration faces high-temperature and high-pressure environments at the bottom of the hole. The all-metal turbodrill has the advantages of high-temperature resistance and corrosion resistance and has good application prospects. Multistage hydraulic components, consisting of stators and rotors, are the [...] Read more.
High-temperature geothermal well resource exploration faces high-temperature and high-pressure environments at the bottom of the hole. The all-metal turbodrill has the advantages of high-temperature resistance and corrosion resistance and has good application prospects. Multistage hydraulic components, consisting of stators and rotors, are the key to the turbodrill. The purpose of this paper is to provide a basis for designing turbodrill blades with high-density drilling fluid under high-temperature conditions. Based on the basic equation of pseudo-fluid two-phase flow and the modified Bernoulli equation, a mathematical model for the coupling of two-phase viscous fluid flow with the turbodrill blade is established. A single-stage blade performance prediction model is proposed and extended to multi-stage blades. A Computational Fluid Dynamics (CFD) model of a 100-stage turbodrill blade channel is established, and the multi-stage blade simulation results for different fluid properties are given. The analysis confirms the influence of fluid viscosity and fluid density on the output performance of the turbodrill. The research results show that compared with the condition of clear water, the high-viscosity and high-density conditions (viscosity 16 mPa∙s, density 1.4 g/cm3) will increase the braking torque of the turbodrill by 24.2%, the peak power by 19.8%, and the pressure drop by 52.1%. The results will be beneficial to the modification of the geometry model of the blade and guide the on-site application of the turbodrill to improve drilling efficiency. Full article
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15 pages, 5120 KiB  
Article
Investigation on the Surface Quality Obtained during Trochoidal Milling of 6082 Aluminum Alloy
by Nikolaos E. Karkalos, Panagiotis Karmiris-Obratański, Szymon Kurpiel, Krzysztof Zagórski and Angelos P. Markopoulos
Machines 2021, 9(4), 75; https://doi.org/10.3390/machines9040075 - 30 Mar 2021
Cited by 19 | Viewed by 3933
Abstract
Surface quality has always been an important goal in the manufacturing industry, as it is not only related to the achievement of appropriate geometrical tolerances but also plays an important role in the tribological behavior of the surface as well as its resistance [...] Read more.
Surface quality has always been an important goal in the manufacturing industry, as it is not only related to the achievement of appropriate geometrical tolerances but also plays an important role in the tribological behavior of the surface as well as its resistance to fatigue and corrosion. Usually, in order to achieve sufficiently high surface quality, process parameters, such as cutting speed and feed, are regulated or special types of cutting tools are used. In the present work, an alternative strategy for slot milling is adopted, namely, trochoidal milling, which employs a more complex trajectory for the cutting tool. Two series of experiments were initially conducted with traditional and trochoidal milling under various feed and cutting speed values in order to evaluate the capabilities of trochoidal milling. The findings showed a clear difference between the two milling strategies, and it was shown that the trochoidal milling strategy is able to provide superior surface quality when the appropriate process parameters are also chosen. Finally, the effect of the depth of cut, coolant and trochoidal stepover on surface roughness during trochoidal milling was also investigated, and it was found that lower depths of cut, the use of coolant and low values of trochoidal stepover can lead to a considerable decrease in surface roughness. Full article
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10 pages, 2903 KiB  
Communication
Iron Loss Analysis of a Concentrated Winding Type Interior Permanent Magnet Synchronous Motor with Single and Dual Layer Magnet Shape
by Chan-Ho Baek, Hyo-Seob Shin and Jang-Young Choi
Machines 2021, 9(4), 74; https://doi.org/10.3390/machines9040074 - 29 Mar 2021
Cited by 3 | Viewed by 2860
Abstract
In this study, the iron losses of high flux density concentrated winding-type interior permanent magnet synchronous motors for three different magnet shapes (single-V, single-flat, and dual-delta) and rotor structures are analyzed and compared. Iron loss is analyzed using the classical Steinmetz equation (CSE) [...] Read more.
In this study, the iron losses of high flux density concentrated winding-type interior permanent magnet synchronous motors for three different magnet shapes (single-V, single-flat, and dual-delta) and rotor structures are analyzed and compared. Iron loss is analyzed using the classical Steinmetz equation (CSE) based on the frequency separation approach using the iron loss material table, and each rotor type is compared. In addition, to validate the hysteresis loss for each rotor type, two additional analyses are performed. In the methods considered, the number of minor loops is counted, and the area is calculated based on DC bias. The eddy current loss is compared using two approaches: CSE base frequency separation and the homogenization method considering the skin effect. This study primarily focuses on the comparison of relative iron losses based on different rotor topologies instead of absolute comparisons. Full article
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13 pages, 3953 KiB  
Communication
Experimental Investigation Using Acoustic Emission Technique for Quasi-Static Cracks in Steel Pipes Assessment
by Mohamed Shehadeh, Ahmed Osman, Aly Abdelbaky Elbatran, John Steel and Robert Reuben
Machines 2021, 9(4), 73; https://doi.org/10.3390/machines9040073 - 29 Mar 2021
Cited by 7 | Viewed by 2607
Abstract
Acoustic emission (AE) is a phenomenon where transient waves of stress are generated during deformed material, which is applied to detect and monitor the cracks and cracks propagation. The majority of related literature studied simulated wave sources, which were utilized for a single [...] Read more.
Acoustic emission (AE) is a phenomenon where transient waves of stress are generated during deformed material, which is applied to detect and monitor the cracks and cracks propagation. The majority of related literature studied simulated wave sources, which were utilized for a single point of a pipe and have been strictly controlled by temporal characteristics. Therefore, the realistic wave sources which do not have known temporal characteristics are studied in the present work. The realistic source is quasi-static crack propagation under three-point bending. The distortions of AE signals are experimentally evaluated by testing the AE signals of crack propagation using simulated sources. A variety of stress intensities are applied on a steel pipe to determine the effect of stress type and intensity on the characteristics of the source using time and frequency domains. Machines are mounted on the steel pipe to locate and reconstitute the features of time and frequency domain of the AE sources. It is concluded that the AE energy was sensitive to the crack size which was concerning to the transition of plane-stress to plane-strain. The potential of AE technique for identifying the nature, intensity and location of crack propagation is demonstrated. Full article
(This article belongs to the Section Machines Testing and Maintenance)
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22 pages, 5733 KiB  
Article
Numerical and Experimental Investigation of Flow and Heat Transfer in Heat Exchanger Channels with Different Dimples Geometries
by Pingting Ying, You He, Hesheng Tang and Yan Ren
Machines 2021, 9(4), 72; https://doi.org/10.3390/machines9040072 - 26 Mar 2021
Cited by 10 | Viewed by 3138
Abstract
The heat exchanger is widely applied to many axial piston machines, and its structure significantly affects the heat transfer performance. Flow characteristic and heat transfer performance in heat exchanger channels with different dimples geometries are numerically and experimentally analyzed in this research work. [...] Read more.
The heat exchanger is widely applied to many axial piston machines, and its structure significantly affects the heat transfer performance. Flow characteristic and heat transfer performance in heat exchanger channels with different dimples geometries are numerically and experimentally analyzed in this research work. The objective is to present details of flow field structure and heat transfer mechanisms for the dimpled channel. The realizable k-ε turbulence model was employed in the numerical simulations with the Re range from 3500 to 20,000. The temperature contour, local streamlines, friction factor, and Nu were presented to illustrate the heat transfer enhancement mechanisms. From this investigation, it is found that dimples cause downward flow, improve the flow mixing and reattachment, interrupt the boundary layer and form periodic impingement flows and then greatly improve the heat transfer. The heat transfer coefficient of hemispherical dimple channels with the three kinds of dimple radius–depth ratios is the highest, and it is about 27.2% higher than that of the traditional rhombus dimple channel. Comparing to the rhombus dimpled channel, the lower flow friction performance of the hemispherical dimple channel depends on the lower dimple radius–depth ratio. The hemispherical dimpled channel present better overall thermal performance due to the strength and extent of the recirculation flow reduction. Full article
(This article belongs to the Section Machine Design and Theory)
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21 pages, 19636 KiB  
Article
Characterization of the Compressive Load on a Lithium-Ion Battery for Electric Vehicle Application
by Seyed Saeed Madani, Erik Schaltz and Søren Knudsen Kær
Machines 2021, 9(4), 71; https://doi.org/10.3390/machines9040071 - 25 Mar 2021
Cited by 5 | Viewed by 5648
Abstract
Lithium-ion batteries are being implemented in different large-scale applications, including aerospace and electric vehicles. For these utilizations, it is essential to improve battery cells with a great life cycle because a battery substitute is costly. For their implementation in real applications, lithium-ion battery [...] Read more.
Lithium-ion batteries are being implemented in different large-scale applications, including aerospace and electric vehicles. For these utilizations, it is essential to improve battery cells with a great life cycle because a battery substitute is costly. For their implementation in real applications, lithium-ion battery cells undergo extension during the course of discharging and charging. To avoid disconnection among battery pack ingredients and deformity during cycling, compacting force is exerted to battery packs in electric vehicles. This research used a mechanical design feature that can address these issues. This investigation exhibits a comprehensive description of the experimental setup that can be used for battery testing under pressure to consider lithium-ion batteries’ safety, which could be employed in electrified transportation. Besides, this investigation strives to demonstrate how exterior force affects a lithium-ion battery cell’s performance and behavior corresponding to static exterior force by monitoring the applied pressure at the dissimilar state of charge. Electrochemical impedance spectroscopy was used as the primary technique for this research. It was concluded that the profiles of the achieved spectrums from the experiments seem entirely dissimilar in comparison with the cases without external pressure. By employing electrochemical impedance spectroscopy, it was noticed that the pure ohmic resistance, which is related to ion transport resistance of the separator, could substantially result in the corresponding resistance increase. Full article
(This article belongs to the Section Vehicle Engineering)
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20 pages, 7884 KiB  
Article
Optimal Control of the Positional Electric Drive and Its Implementation
by Vladimir Dotsenko, Roman Prokudin and Alexander Litvinenko
Machines 2021, 9(4), 70; https://doi.org/10.3390/machines9040070 - 24 Mar 2021
Cited by 2 | Viewed by 1910
Abstract
The article deals with the optimal control of the positional electric drive of the stator element of a segment-type wind turbine. The calculation options charts current in the assumption of the minimum energy consumption and the implementation of line chart current using the [...] Read more.
The article deals with the optimal control of the positional electric drive of the stator element of a segment-type wind turbine. The calculation options charts current in the assumption of the minimum energy consumption and the implementation of line chart current using the phenomenon of capacitor discharge. The analysis of the implementation is expressed in a jump-like change in current and a triangular graph of the speed change. This article deals with small capacity synchronous wind turbine generators with a segment type stator. These units have the possibility of intentionally changing the air gap between the rotor and stator. This allows: (1) Reduce the starting torque on the rotor shaft, which will allow the rotor to pick up at low wind speeds. (2) Equivalent to change of air gap in this case is change of excitation of synchronous generators. Thus, the purpose of the article is to consider a method of excitation of generators in a segmented design, by controlling the gap with the electric drive, while providing control should be carried out with minimal losses. Full article
(This article belongs to the Special Issue Mechatronic System for Automatic Control)
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1 pages, 194 KiB  
Addendum
Addendum: Suchy, L.; et al. Influence of Hub Parameters on Joining Forces and Torque Transmission Output of Plastically Joined Shaft–Hub–Connections with a Knurled Contact Surface. Machines 2018, 6, 16
by Lukas Suchy, Erhard Leidich, Thoralf Gerstmann and Birgit Awiszus
Machines 2021, 9(4), 69; https://doi.org/10.3390/machines9040069 - 24 Mar 2021
Viewed by 1358
Abstract
The authors, while validating calculations, found discrepancies with Equations (9) and (10) in their paper [...] Full article
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