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15 pages, 4549 KiB

Open AccessCommunication

A Novel Electronic Chip Detection Method Using Deep Neural Networks

by Huiyan Zhang, Hao Sun, Peng Shi and Luis Ismael Minchala

Machines 2022, 10(5), 361; https://doi.org/10.3390/machines10050361 - 10 May 2022

Cited by 2 | Viewed by 2442

Abstract

Electronic chip detection is widely used in electronic industries. However, most existing detection methods cannot handle chip images with multiple classes of chips or complex backgrounds, which are common in real applications. To address these problems, a novel chip detection method that combines [...] Read more.

Electronic chip detection is widely used in electronic industries. However, most existing detection methods cannot handle chip images with multiple classes of chips or complex backgrounds, which are common in real applications. To address these problems, a novel chip detection method that combines attentional feature fusion (AFF) and cosine nonlocal attention (CNLA), is proposed, and it consists of three parts: a feature extraction module, a region proposal module, and a detection module. The feature extraction module combines an AFF-embedded CNLA module and a pyramid feature module to extract features from chip images. The detection module enhances feature maps with a region intermediate feature map by spatial attentional block, fuses multiple feature maps with a multiscale region of the fusion block of interest, and classifies and regresses objects in images with two branches of fully connected layers. Experimental results on a medium-scale dataset comprising 367 images show that our proposed method achieved

m A P^{0.5} = 0.98745

and outperformed the benchmark method. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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15 pages, 5217 KiB

Open AccessArticle

Experimental Characterization of A-AFiM, an Adaptable Assistive Device for Finger Motions

by Jhon Freddy Rodríguez-León, Eduardo Castillo-Castañeda, José Felipe Aguilar-Pereyra and Giuseppe Carbone

Machines 2022, 10(4), 280; https://doi.org/10.3390/machines10040280 - 15 Apr 2022

Cited by 4 | Viewed by 2615

Abstract

Robot rehabilitation devices are attracting significant research interest, aiming at developing viable solutions for increasing the patient’s quality of life and enhancing clinician’s therapies. This paper outlines the design and implementation of a low-cost robotic system that can assist finger motion rehabilitation by [...] Read more.

Robot rehabilitation devices are attracting significant research interest, aiming at developing viable solutions for increasing the patient’s quality of life and enhancing clinician’s therapies. This paper outlines the design and implementation of a low-cost robotic system that can assist finger motion rehabilitation by controlling and adapting both the position and velocity of fingers to the users′ needs. The proposed device consists of four slider-crank mechanisms. Each slider-crank is fixed and moves one finger (from the index to the little finger). The finger motion is adjusted through the regulation of a single link length of the mechanism. The trajectory that is generated corresponds to the natural flexion and extension trajectory of each finger. The functionality of this mechanism is validated by experimental image processing. Experimental validation is performed through tests on healthy subjects to demonstrate the feasibility and user-friendliness of the proposed solution. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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41 pages, 10084 KiB

Open AccessArticle

The Design Process of an Optimized Road Racing Bicycle Frame

by Alexandros G. Kitselis, Chrysavgi S. Nikolakea and Dimitrios E. Manolakos

Machines 2022, 10(2), 149; https://doi.org/10.3390/machines10020149 - 18 Feb 2022

Cited by 1 | Viewed by 9937

Abstract

This paper recommends an alternative designing process for a superior road racing bicycle frame manufactured from composite materials that is much faster than typically used design processes. The main design goal is for the rider to be faster under the same riding conditions [...] Read more.

This paper recommends an alternative designing process for a superior road racing bicycle frame manufactured from composite materials that is much faster than typically used design processes. The main design goal is for the rider to be faster under the same riding conditions and with the same effort made. This performance gain is the result of a combined structural and aerodynamic optimization process used during the design process along with the selection of the materials. As the needs of the rider are the focus of this design proposal, the optimization can be carried out only after they are understood. The main difference in this approach compared to the typically used methodology is that, instead of analyzing the frame as a whole from the beginning of the design process and the CFD and CAE iterations, we examine each candidate part of the frame separately. After evaluating the parts’ performances, we select those that performed better to create a single frame. This final frame design is used to choose the appropriate layup that would meet the performance needs of the riders and the necessary safety regulations. The benefit of this approach is that the design time is reduced, allowing the product to reach the market faster. Furthermore, it is more convenient and easier to make any modifications required by marketing or regulations. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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16 pages, 6658 KiB

Open AccessArticle

A Systematic Analysis of Printed Circuit Boards Bending during In-Circuit Tests

by Rui Oliveira, Luís Freitas, Diogo Costa, José Vicente, Arminda Manuela Gonçalves, Teresa Malheiro and José Machado

Machines 2022, 10(2), 135; https://doi.org/10.3390/machines10020135 - 13 Feb 2022

Cited by 5 | Viewed by 3223

Abstract

When performing In-Circuit Tests (ICTs) of Printed Circuit Boards (PCBs), there are certain phenomena related with strain analysis that must be known in order to obtain stronger and more accurate testing results. During testing, PCBs are often subjected to mechanical bending efforts that [...] Read more.

When performing In-Circuit Tests (ICTs) of Printed Circuit Boards (PCBs), there are certain phenomena related with strain analysis that must be known in order to obtain stronger and more accurate testing results. During testing, PCBs are often subjected to mechanical bending efforts that induce excessive strain. This study focuses on the building of a Finite Elements Analysis (FEA) methodology that prevents excessive bending strain in critical points of a PCB during an ICT. To validate this methodology, a set of experimental tests, matched with a set of FEA, were carried out. Thus, companies, before the development of an ICT machine (fixture), will be able to use this FEA methodology to predict whether the maximum strain of a PCB under study, when subjected to its ICT, will damage it, thus reducing unnecessary production costs. A guideline was thus designed to enable the creation of the most representative Finite Elements Model (FEM) for any PCB, based on its amount and direction of copper traces. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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15 pages, 7070 KiB

Open AccessArticle

Experimental Study on Support Vector Machine-Based Early Detection for Sensor Faults and Operator-Based Robust Fault Tolerant Control

by Mingcong Deng, Yuki Tanaka and Ximei Li

Machines 2022, 10(2), 123; https://doi.org/10.3390/machines10020123 - 10 Feb 2022

Cited by 3 | Viewed by 1786

Abstract

Considering sensor faults for a thermoelectric cooler actuated by Peltier devices, this work proposes an operator-based robust nonlinear fault tolerant controller (FTC) integrated with early fault detection using a support vector machine (SVM). Firstly, a physical model is formulated based on the law [...] Read more.

Considering sensor faults for a thermoelectric cooler actuated by Peltier devices, this work proposes an operator-based robust nonlinear fault tolerant controller (FTC) integrated with early fault detection using a support vector machine (SVM). Firstly, a physical model is formulated based on the law of heat transfer, and the estimated model is derived based on Volterra identification. Then, an operator-based robust nonlinear control system is employed to compensate for uncertainties and to eliminate the effects of coupling. Furthermore, FTC integrated with SVM-based early fault detection is designed to improve the safety performance in the case of sensor faults. The simulation results indicate that SVM-based fault detection can shorten the detection time in comparison to the conventional method without the SVM classier. The experiment results are utilized to verify the tracking performance of the proposed FTC method in the case study. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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15 pages, 4135 KiB

Open AccessEditor’s ChoiceArticle

Fundamental Design and Modelling of the Superconducting Magnet for the High-Speed Maglev: Mechanics, Electromagnetics, and Loss Analysis during Instability

by Zhihao Wu, Jianxun Jin, Boyang Shen, Luning Hao, Youguang Guo and Jianguo Zhu

Machines 2022, 10(2), 113; https://doi.org/10.3390/machines10020113 - 3 Feb 2022

Cited by 11 | Viewed by 3539

Abstract

The high-temperature superconductor (HTS) has been recognised as one of the most up-and-coming materials thanks to its superior electromagnetic performance (e.g., zero resistance). For a high-speed maglev, the HTS magnet can be the most crucial component because it is in charge of both [...] Read more.

The high-temperature superconductor (HTS) has been recognised as one of the most up-and-coming materials thanks to its superior electromagnetic performance (e.g., zero resistance). For a high-speed maglev, the HTS magnet can be the most crucial component because it is in charge of both the levitation and the propulsion of the maglev. Therefore, a fundamental study of HTS magnets for maglev is crucial. This article presents the fundamental design and modelling of the superconducting magnet for a high-speed maglev, including mechanics, electromagnetics, and loss analysis during instability. First, the measurements of the superconducting wire were performed. The HTS magnet was primarily designed and modelled to fulfil the basic electromagnetic requirements (e.g., magnetic field) in order to drive the maglev at a high speed. The modelling was verified by experimental tests on a scale-down HTS magnet. A more professional model using the H-formulation based on the finite element method (FEM) was built to further investigate some deeper physical phenomenon of the HTS magnet (e.g., current density and loss behaviours), particularly in situations where the high-speed maglev is in the normal steady state or encountering instability. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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23 pages, 5029 KiB

Open AccessArticle

Speed-Sensorless Control of Induction Machines with LC Filter for Geothermal Electric Submersible Pumping Systems

by Julian Kullick and Christoph M. Hackl

Machines 2022, 10(2), 87; https://doi.org/10.3390/machines10020087 - 25 Jan 2022

Cited by 2 | Viewed by 2670

Abstract

A speed-sensorless state-feedback controller for induction machines (IMs) with LC filter is proposed. The speed and state estimation is based on a speed-adaptive observer, requiring only the measurement of the filter input currents. The motor currents are controlled by a state-feedback controller with [...] Read more.

A speed-sensorless state-feedback controller for induction machines (IMs) with LC filter is proposed. The speed and state estimation is based on a speed-adaptive observer, requiring only the measurement of the filter input currents. The motor currents are controlled by a state-feedback controller with prefilter and integral control action, in order to achieve fast and asymptotic set point tracking. Observer and controller gains are calculated offline using linear quadratic regulator (LQR) theory and updated online (gain-scheduling) in order to attain stability and improve controller performance in the whole operation range. Implementation aspects, such as discretization of the control system and reduction of computational effort, are taken into account as well. The proposed control scheme is validated by simulations and experimental results, even for critical operating conditions such as speed zero-crossings. It is shown that the overall control system performs very well under various load- and speed conditions; while its tuning remains simple which makes it attractive for industrial application such as geothermal electric submersible pumping (ESP) systems. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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16 pages, 4583 KiB

Open AccessArticle

3D-FEM Approach of AISI-52100 Hard Turning: Modelling of Cutting Forces and Cutting Condition Optimization

by Anastasios Tzotzis, Nikolaos Tapoglou, Rajesh Kumar Verma and Panagiotis Kyratsis

Machines 2022, 10(2), 74; https://doi.org/10.3390/machines10020074 - 20 Jan 2022

Cited by 13 | Viewed by 3449

Abstract

In the present study, a 3D finite element (FE) model for machining AISI-52100 steel was proposed, with respect to three levels of cutting speed (100 m/min, 150 m/min and 200 m/min), feed (0.08 mm/rev, 0.11 mm/rev and 0.14 mm/rev), depth of cut (0.20 [...] Read more.

In the present study, a 3D finite element (FE) model for machining AISI-52100 steel was proposed, with respect to three levels of cutting speed (100 m/min, 150 m/min and 200 m/min), feed (0.08 mm/rev, 0.11 mm/rev and 0.14 mm/rev), depth of cut (0.20 mm, 0.30 mm and 0.40 mm) and tool nose radius (0.80 mm, 1.20 mm and 1.60 mm). Nine simulation tests were performed according to cutting conditions that were used in experimental studies, in order to verify the accuracy of the model. Next, the FE model was utilized to carry out thirty new simulation runs, with cutting conditions derived from the implementation of the central composite design (CCD). Additionally, a mathematical model was established for prediction purposes, whereas the relationship between the applied cutting parameters and their influence on the resultant cutting force was investigated with the aid of statistical methodologies such as the response surface methodology (RSM) and the analysis of variance (ANOVA). The comparison between the numerical and the statistical model revealed an increased level of correlation, superseding 90% in many tests. Specifically, the relative error varied between −7.9% and 11.3%. Lastly, an optimization process was performed to find the optimal cutting conditions for minimizing the resultant machining force, as per the standardized tool nose radius value. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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16 pages, 9947 KiB

Open AccessEditor’s ChoiceArticle

Design of a 3D-Printed Hand Exoskeleton Based on Force-Myography Control for Assistance and Rehabilitation

by Daniele Esposito, Jessica Centracchio, Emilio Andreozzi, Sergio Savino, Gaetano D. Gargiulo, Ganesh R. Naik and Paolo Bifulco

Machines 2022, 10(1), 57; https://doi.org/10.3390/machines10010057 - 13 Jan 2022

Cited by 38 | Viewed by 8834

Abstract

Voluntary hand movements are usually impaired after a cerebral stroke, affecting millions of people per year worldwide. Recently, the use of hand exoskeletons for assistance and motor rehabilitation has become increasingly widespread. This study presents a novel hand exoskeleton, designed to be low [...] Read more.

Voluntary hand movements are usually impaired after a cerebral stroke, affecting millions of people per year worldwide. Recently, the use of hand exoskeletons for assistance and motor rehabilitation has become increasingly widespread. This study presents a novel hand exoskeleton, designed to be low cost, wearable, easily adaptable and suitable for home use. Most of the components of the exoskeleton are 3D printed, allowing for easy replication, customization and maintenance at a low cost. A strongly underactuated mechanical system allows one to synergically move the four fingers by means of a single actuator through a rigid transmission, while the thumb is kept in an adduction or abduction position. The exoskeleton’s ability to extend a typical hypertonic paretic hand of stroke patients was firstly tested using the SimScape Multibody simulation environment; this helped in the choice of a proper electric actuator. Force-myography was used instead of the standard electromyography to voluntarily control the exoskeleton with more simplicity. The user can activate the flexion/extension of the exoskeleton by a weak contraction of two antagonist muscles. A symmetrical master–slave motion strategy (i.e., the paretic hand motion is activated by the healthy hand) is also available for patients with severe muscle atrophy. An inexpensive microcontroller board was used to implement the electronic control of the exoskeleton and provide feedback to the user. The entire exoskeleton including batteries can be worn on the patient’s arm. The ability to provide a fluid and safe grip, like that of a healthy hand, was verified through kinematic analyses obtained by processing high-framerate videos. The trajectories described by the phalanges of the natural and the exoskeleton finger were compared by means of cross-correlation coefficients; a similarity of about 80% was found. The time required for both closing and opening of the hand exoskeleton was about 0.9 s. A rigid cylindric handlebar containing a load cell measured an average power grasp force of 94.61 N, enough to assist the user in performing most of the activities of daily living. The exoskeleton can be used as an aid and to promote motor function recovery during patient’s neurorehabilitation therapy. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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23 pages, 6172 KiB

Open AccessArticle

In-Process Chatter Detection Using Signal Analysis in Frequency and Time-Frequency Domain

by Michele Perrelli, Francesco Cosco, Francesco Gagliardi and Domenico Mundo

Machines 2022, 10(1), 24; https://doi.org/10.3390/machines10010024 - 28 Dec 2021

Cited by 13 | Viewed by 3624

Abstract

All machining processes involve vibrations generated by structural sources such as a machine’s moving parts or by the interaction between cutting tools and work-pieces. Relative vibrations between the work-pieces and the cutting tool are the most relevant from the point of view of [...] Read more.

All machining processes involve vibrations generated by structural sources such as a machine’s moving parts or by the interaction between cutting tools and work-pieces. Relative vibrations between the work-pieces and the cutting tool are the most relevant from the point of view of the regenerative chatter phenomenon. In fact, these vibrations can lead to a chip yregeneration effect, which results in unwanted consequences, rapidly degenerating towards a very poor quality of surface finishing or, in case of severe chatter conditions, to machine-tool or work-piece damage. In the past decades, two different approaches for chatter avoidance were proposed by the scientific community, and they are commonly referred to as Out-of-Process (OuP) and in-Process (iP) solutions. The OuP solutions are off-line approaches, which allow to properly set the working parameters before machining starts. Ip solutions are on-line techniques, which allow to dynamically change the working parameters during machining by using single or multiple sensors. By monitoring the machining process, iP algorithms try to keep the machining process in stable working conditions while keeping high productivity levels. This study dealt with a novel iP chatter-detection strategy based on the Power Spectral Density (PSD) analysis and on the Wavelet Packet Decomposition (WPD) of different sensor signals. The preliminary results demonstrate the stability and feasibility of proposed indicators for chatter detection in industrial application. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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24 pages, 5126 KiB

Open AccessArticle

Effects of Currents on Human Freestyle and Breaststroke Swimming Analyzed by a Rigid-Body Dynamic Model

by Yinxiang Bao, Hongbin Fang and Jian Xu

Machines 2022, 10(1), 17; https://doi.org/10.3390/machines10010017 - 24 Dec 2021

Cited by 6 | Viewed by 4179

Abstract

Swimming is a kind of complex locomotion that involves the interaction between the human body and the water. Here, to examine the effects of currents on the performance of freestyle and breaststroke swimming, a multi-body Newton-Euler dynamic model of human swimming is developed. [...] Read more.

Swimming is a kind of complex locomotion that involves the interaction between the human body and the water. Here, to examine the effects of currents on the performance of freestyle and breaststroke swimming, a multi-body Newton-Euler dynamic model of human swimming is developed. The model consists of 18 rigid segments, whose shapes and geometries are determined based on the measured data from 3D scanning, and the fluid drags in consideration of the current are modeled. By establishing the interrelations between the fluid moments and the swimming kinematics, the underlying mechanism that triggers the turning of the human body is uncovered. Through systematic parametric analyses, the effects of currents on swimming performance (including the human body orientation, swimming direction, swimming speed, and propulsive efficiency) are elucidated. It reveals that the current would turn the human body counterclockwise in freestyle swimming, while clockwise in breaststroke swimming (which means that from the top view, the human trunk, i.e., the vector pointing from the bottom of feet to the top of the head, rotates counterclockwise or clockwise). Moreover, for both strokes, there exists a critical current condition, beyond which, the absolute swimming direction will be reversed. This work provides a wealth of fundamental insights into the swimming dynamics in the presence of currents, and the proposed modeling and analysis framework is promising to be used for analyzing the human swimming behavior in open water. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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21 pages, 3548 KiB

Open AccessArticle

Implementation of Hardware-Based Expert Systems and Comparison of Their Performance to Software-Based Expert Systems

by Noah Ritter and Jeremy Straub

Machines 2021, 9(12), 361; https://doi.org/10.3390/machines9120361 - 17 Dec 2021

Cited by 4 | Viewed by 4113

Abstract

Expert systems are a form of highly understandable artificial intelligence that allow humans to trace the decision-making processes that are used. While they are typically software implemented and use an iterative algorithm for rule-fact network processing, this is not the only possible implementation [...] Read more.

Expert systems are a form of highly understandable artificial intelligence that allow humans to trace the decision-making processes that are used. While they are typically software implemented and use an iterative algorithm for rule-fact network processing, this is not the only possible implementation approach. This paper implements and evaluates the use of hardware-based expert systems. It shows that they work accurately and can be developed to parallel software implementations. It also compares the processing speed of software and hardware-based expert systems, showing that hardware-based systems typically operate two orders of magnitude faster than the software ones. The potential applications that hardware-based expert systems can be used for and the capabilities that they can provide are discussed. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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22 pages, 2437 KiB

Open AccessArticle

Time-Delay Luenberger Observer Design for Sliding Mode Control of Nonlinear Markovian Jump Systems via Event-Triggered Mechanism

by Min Cheng, Chunyang Zhang, Jin Qiu, Zhengtian Wu and Qing Gao

Machines 2021, 9(11), 259; https://doi.org/10.3390/machines9110259 - 30 Oct 2021

Cited by 2 | Viewed by 2172

Abstract

This paper is focused on the stabilization of Takagi–Sugeno fuzzy model-based Markovian jump systems with the aid of a delayed state observer. Due to network-induced constraints in the communication channel, a delay partition method combined with an event-triggered mechanism is proposed to design [...] Read more.

This paper is focused on the stabilization of Takagi–Sugeno fuzzy model-based Markovian jump systems with the aid of a delayed state observer. Due to network-induced constraints in the communication channel, a delay partition method combined with an event-triggered mechanism is proposed to design the observer. Then, a novel integral sliding surface is designed, based on which sliding mode dynamics is obtained. Further, according to stochastic stability theory, feasible conditions are provided to ensure the sliding mode dynamics and the error dynamics have an H_∞ attenuate level γ. The challenge is to deal with the issue that transition rates may be totally unknown. Moreover, an observer-based sliding mode controller is constructed to ensure the finite-time reachability of the predefined sliding surface. Finally, a numerical example based on a robotic manipulator is given to verify the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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14 pages, 3262 KiB

Open AccessArticle

Key-Phase-Free Blade Tip-Timing for Nonstationary Test Conditions: An Improved Algorithm for the Vibration Monitoring of a SAFRAN Turbomachine from the Surveillance 9 International Conference Contest

by Alessandro Paolo Daga, Luigi Garibaldi, Changbo He and Jerome Antoni

Machines 2021, 9(10), 235; https://doi.org/10.3390/machines9100235 - 13 Oct 2021

Cited by 6 | Viewed by 2302

Abstract

A turbomachine is a fundamental engineering apparatus meant to transfer energy between a rotor and a fluid. Turbomachines are the core of power generation in many engineering applications such as electric power generation plants, aerospace, marine power, automotive etc. Their relevance makes them [...] Read more.

A turbomachine is a fundamental engineering apparatus meant to transfer energy between a rotor and a fluid. Turbomachines are the core of power generation in many engineering applications such as electric power generation plants, aerospace, marine power, automotive etc. Their relevance makes them both mission critical and safety critical in many fields. To foster reliability and safety, then, continuous monitoring of the rotor is more than desirable. One promising monitoring technique is, with no doubt, the Blade Tip-Timing, which, being simple and non-invasive, can be easily implemented on many different rotors. Blade Tip-Timing is based on the recording of the time of arrival of the blades passing in front of a probe located at a fixed angular position. The non-contact nature of the measurement prevents influences on the measured vibration, that can be recovered for all the blades simultaneously, possibly even online. In this regard, a novel algorithm is presented in this paper for obtaining a good estimate of the vibration of the blades with minimum system complexity (i.e., only one Blade Tip-Timing probe) and minimum computational effort, so to create a simple vibration monitoring system, potentially implementable online. The methodology was tested on a dataset from a SAFRAN turbomachine made available during the Surveillance 9 international conference for a diagnostic contest. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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22 pages, 7388 KiB

Open AccessArticle

A Data-Driven Framework for Early-Stage Fatigue Damage Detection in Aluminum Alloys Using Ultrasonic Sensors

by Susheel Dharmadhikari, Chandrachur Bhattacharya, Asok Ray and Amrita Basak

Machines 2021, 9(10), 211; https://doi.org/10.3390/machines9100211 - 25 Sep 2021

Cited by 7 | Viewed by 3023

Abstract

The paper presents a coupled machine learning and pattern recognition algorithm to enable early-stage fatigue damage detection in aerospace-grade aluminum alloys. U- and V-notched Al7075-T6 specimens are instrumented with a pair of ultrasonic sensors and, thereafter, tested on an MTS apparatus integrated with [...] Read more.

The paper presents a coupled machine learning and pattern recognition algorithm to enable early-stage fatigue damage detection in aerospace-grade aluminum alloys. U- and V-notched Al7075-T6 specimens are instrumented with a pair of ultrasonic sensors and, thereafter, tested on an MTS apparatus integrated with a confocal microscope and a digital microscope. The confocal microscope is focused on the notch root of the specimens, whereas the digital microscope is focused on the side of the notch. Two features, viz., the crack opening displacement (COD) and the crack length, are extracted during the tests in addition to the ultrasonic signal data. These signal data are analyzed using a machine learning framework that is built upon a symbolic time-series algorithm. This framework is interrogated for crack detection in the crack coalescence (CC) regime defined by COD of ~3 μm and detected through the confocal microscope. Additionally, the framework is probed in the crack propagation (CP) regime characterized by a crack length of ~0.2 mm and detected via the digital microscope. For the CC regime, training accuracies of 79.82% and 81.94% are achieved, whereas testing accuracies of 68.18% and 74.12% are observed for the U- and V-notched specimens, respectively. For the CP regime, overall training accuracies of 88.3% and 91.85% are observed, and accordingly, testing accuracies of 81.94% and 85.62% are obtained for the U- and V-notched specimens, respectively. The results show that a combined machine learning and pattern recognition algorithm enables robust and reliable fatigue damage detection in aerospace structural components. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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13 pages, 4787 KiB

Open AccessEditor’s ChoiceArticle

Three-Phase Induction Motors Online Protection against Unbalanced Supply Voltages

by Khaled Laadjal, Mohamed Sahraoui, Abdeldjalil Alloui and Antonio J. Marques Cardoso

Machines 2021, 9(9), 203; https://doi.org/10.3390/machines9090203 - 20 Sep 2021

Cited by 15 | Viewed by 4598

Abstract

Three-phase induction motors (IMs) are the main workhorse in industry due to their many advantages as compared to other types of industrial motors. However, the efficiency and lifetime of IMs can be considerably affected by some operating conditions, in particular those related to [...] Read more.

Three-phase induction motors (IMs) are the main workhorse in industry due to their many advantages as compared to other types of industrial motors. However, the efficiency and lifetime of IMs can be considerably affected by some operating conditions, in particular those related to unbalanced supply voltages (USV), which is quite a common condition in industrial plants. Therefore, early detection and a precise severity estimation of the USV for all working conditions can prevent major breakdowns and increase reliability and safety of industrial facilities. This paper proposes a reliable method allowing for a precise and online detection of the USV condition, by monitoring a pertinent indicator calculated using the voltage symmetrical components. The effectiveness of the proposed method is validated experimentally for several different working conditions, and a comparison with other indicators available in the literature is also performed. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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Review

Jump to: Research, Other

78 pages, 3001 KiB

Open AccessReview

A Comprehensive Survey on Fault Tolerance in Multiphase AC Drives, Part 2: Phase and Switch Open-Circuit Faults

by Alejandro G. Yepes, Ignacio Gonzalez-Prieto, Oscar Lopez, Mario J. Duran and Jesus Doval-Gandoy

Machines 2022, 10(3), 221; https://doi.org/10.3390/machines10030221 - 21 Mar 2022

Cited by 50 | Viewed by 5717

Abstract

Multiphase machines are very convenient for applications that require high reliability. In this two-part survey, the state of the art about fault tolerance in multiphase drives is reviewed. In Part 1, an overview including numerous fault types was presented, along with fundamental notions [...] Read more.

Multiphase machines are very convenient for applications that require high reliability. In this two-part survey, the state of the art about fault tolerance in multiphase drives is reviewed. In Part 1, an overview including numerous fault types was presented, along with fundamental notions about multiphase drives. Here, in Part 2, the focus is placed on phase/switch open-circuit (OC) faults in particular, which have received the most attention in the literature. Phase OC failures involve OCs in stator phases or in converter-machine connections, and switch/diode OCs are frequently dealt with similarly or identically. Thanks to the phase redundancy of multiphase drives, their operation can be satisfactorily continued under a certain number of OCs. Nonetheless, the procedure to follow for this purpose is far from unique. For given OC fault conditions, numerous fault-tolerant possibilities can be found in the literature, each of them with different advantages and disadvantages. Moreover, a great variety of methods have also been devised to detect and diagnose phase/switch OC failures so that, as soon as possible, the most appropriate fault-tolerance measures are applied. Thus, given the broad literature about tolerance to phase/switch OC faults in multiphase drives, the survey presented here is expected to be of great interest for the research community and industry. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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134 pages, 7014 KiB

Open AccessEditor’s ChoiceReview

A Comprehensive Survey on Fault Tolerance in Multiphase AC Drives, Part 1: General Overview Considering Multiple Fault Types

by Alejandro G. Yepes, Oscar Lopez, Ignacio Gonzalez-Prieto, Mario J. Duran and Jesus Doval-Gandoy

Machines 2022, 10(3), 208; https://doi.org/10.3390/machines10030208 - 14 Mar 2022

Cited by 70 | Viewed by 8321

Abstract

Multiphase drives offer enhanced fault-tolerant capabilities compared with conventional three-phase ones. Their phase redundancy makes them able to continue running in the event of faults (e.g., open/short-circuits) in certain phases. Moreover, their greater number of degrees of freedom permits improving diagnosis and performance, [...] Read more.

Multiphase drives offer enhanced fault-tolerant capabilities compared with conventional three-phase ones. Their phase redundancy makes them able to continue running in the event of faults (e.g., open/short-circuits) in certain phases. Moreover, their greater number of degrees of freedom permits improving diagnosis and performance, not only under faults affecting individual phases, but also under those affecting the machine/drive as a whole. That is the case of failures in the dc link, resolver/encoder, control unit, cooling system, etc. Accordingly, multiphase drives are becoming remarkable contenders for applications where high reliability is required, such as electric vehicles and standalone/off-shore generation. Actually, the literature on the subject has grown exponentially in recent years. Various review papers have been published, but none of them currently cover the state-of-the-art in a comprehensive and up-to-date fashion. This two-part paper presents an overview concerning fault tolerance in multiphase drives. Hundreds of citations are classified and critically discussed. Although the emphasis is put on fault tolerance, fault detection/diagnosis is also considered to some extent, because of its importance in fault-tolerant drives. The most important recent advances, emerging trends and open challenges are also identified. Part 1 provides a comprehensive survey considering numerous kinds of faults, whereas Part 2 is focused on phase/switch open-circuit failures. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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37 pages, 1941 KiB

Open AccessEditor’s ChoiceReview

Motion Planning for Mobile Manipulators—A Systematic Review

by Thushara Sandakalum and Marcelo H. Ang, Jr.

Machines 2022, 10(2), 97; https://doi.org/10.3390/machines10020097 - 27 Jan 2022

Cited by 65 | Viewed by 14170

Abstract

One of the fundamental fields of research is motion planning. Mobile manipulators present a unique set of challenges for the planning algorithms, as they are usually kinematically redundant and dynamically complex owing to the different dynamic behavior of the mobile base and the [...] Read more.

One of the fundamental fields of research is motion planning. Mobile manipulators present a unique set of challenges for the planning algorithms, as they are usually kinematically redundant and dynamically complex owing to the different dynamic behavior of the mobile base and the manipulator. The purpose of this article is to systematically review the different planning algorithms specifically used for mobile manipulator motion planning. Depending on how the two subsystems are treated during planning, sampling-based, optimization-based, search-based, and other planning algorithms are grouped into two broad categories. Then, planning algorithms are dissected and discussed based on common components. The problem of dealing with the kinematic redundancy in calculating the goal configuration is also analyzed. While planning separately for the mobile base and the manipulator provides convenience, the results are sub-optimal. Coordinating between the mobile base and manipulator while utilizing their unique capabilities provides better solution paths. Based on the analysis, challenges faced by the current planning algorithms and future research directions are presented. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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25 pages, 1333 KiB

Open AccessEditor’s ChoiceReview

A Review of Thermal Monitoring Techniques for Radial Permanent Magnet Machines

by Tianze Meng and Pinjia Zhang

Machines 2022, 10(1), 18; https://doi.org/10.3390/machines10010018 - 24 Dec 2021

Cited by 16 | Viewed by 4613

Abstract

Permanent magnet machines are widely applied in motor drive systems. Therefore, condition monitoring of permanent magnet machines has great significance to assist maintenance. High temperatures are accountable for lots of typical malfunctions and faults, such as demagnetization of the permanent magnet (PM) and [...] Read more.

Permanent magnet machines are widely applied in motor drive systems. Therefore, condition monitoring of permanent magnet machines has great significance to assist maintenance. High temperatures are accountable for lots of typical malfunctions and faults, such as demagnetization of the permanent magnet (PM) and inter-turn short circuit of stator windings. Therefore, temperature monitoring of the PM and stator windings is essential for reliable operation. In this paper, an overview introducing and evaluating existing thermal monitoring methods is presented. First, the mechanism of thermal-caused failures for the PM and stator windings is introduced. Then, the design procedure and principles of existing temperature monitoring methods are introduced and summarized. Next, the evaluations and recommendations of application feasibility are demonstrated. Finally, the potential future challenges and opportunities for temperature monitoring of the PM and stator windings are discussed. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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26 pages, 1015 KiB

Open AccessEditor’s ChoiceReview

Fault Detection and Condition Monitoring of PMSGs in Offshore Wind Turbines

by Nuno M. A. Freire and Antonio J. Marques Cardoso

Machines 2021, 9(11), 260; https://doi.org/10.3390/machines9110260 - 30 Oct 2021

Cited by 15 | Viewed by 4885

Abstract

Research on fault detection (FD) and condition monitoring (CM) of rotating electrical generators for modern wind turbines has addressed a wide variety of technologies. Among these, permanent magnet synchronous generators (PMSGs) and the analysis of their electromagnetic signatures in the presence of faults [...] Read more.

Research on fault detection (FD) and condition monitoring (CM) of rotating electrical generators for modern wind turbines has addressed a wide variety of technologies. Among these, permanent magnet synchronous generators (PMSGs) and the analysis of their electromagnetic signatures in the presence of faults deserve emphasis in this paper. PMSGs are prominent in the offshore wind industry, and methods for FD and CM of PMSGs based on electromagnetic measurements are extensively discussed in academia. This paper is a concise review of FD and CM in wind turbines and PMSGs. Terminology and fundamentals of PMSG’s operation are introduced first, aiming to offer an easy read and good reference to a broad audience of engineers and data scientists. Experience and research challenges with stator winding failures are also discussed. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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15 pages, 10930 KiB

Open AccessConcept Paper

Investigation of Surface Modification of 60CrMoV18-5 Steel by EDM with Cu-ZrO₂ Powder Metallurgy Green Compact Electrode

by Maria Balanou, Panagiotis Karmiris-Obratański, Beata Leszczyńska-Madej, Emmanouil L. Papazoglou and Angelos P. Markopoulos

Machines 2021, 9(11), 268; https://doi.org/10.3390/machines9110268 - 3 Nov 2021

Cited by 12 | Viewed by 2162

Abstract

Electrical discharge machining (EDM) is a non-conventional machining process, which is mostly used for machining of difficult-to-cut materials. These materials are often used in engineering applications that require improved surface properties; thus, surface modification is desirable in these cases. In the recent past, [...] Read more.

Electrical discharge machining (EDM) is a non-conventional machining process, which is mostly used for machining of difficult-to-cut materials. These materials are often used in engineering applications that require improved surface properties; thus, surface modification is desirable in these cases. In the recent past, it has been observed that EDM is an alternative surface modification process due to migration of material from the electrode to the workpiece surface. Surface modification can be done with powder metallurgy (P/M) electrode as tool. The aim of this work is to examine the surface modification of the tool steel Calmax (Uddeholm) by EDM process using Cu-30 wt.% ZrO₂ P/M green compact electrode. The influence of peak current (Ip) and pulse-on (Ton) on the Material Transfer Rate (MTR) and Surface Roughness (SR) was investigated and the surface characteristics were also evaluated by scanning electron microscopy (SEM). The experimental results confirm the material migration from the electrode to the machined surface and show that the higher MTR of 46.5 mgr/min is achieved on the combination of Ip = 9 A and Ton = 25 μs and the Ra varies from 3.72 μm to 7.12 μm. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the First Impact Factor of Machines)

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