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Machines, Volume 10, Issue 6 (June 2022) – 84 articles

Cover Story (view full-size image): In air compressors (e.g., for fuel cell cars), the use of foil bearings provides many advantages. They have low friction, require little installation space and, due to media lubrication, do not require oils or peripheral equipment. Their full potential is shown at speeds of 100,000 rpm and more. On the downside, the frequent start–stop cycles in such applications are critical, as they can lead to higher wear and, thus, a shorter service life. With actively controllable bearings, an attempt is made to achieve better behavior in the start-up range. The cover picture shows an enhanced test rig which was used to examine the static switching states of such a bearing. The two test bearings (for each switching state) were compared in terms of lift-off speed, frictional torque, eccentricity, and stiffness. View this paper
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22 pages, 3183 KiB  
Review
Review and Comparison of Clearance Control Strategies
by Bingwei Gao, Wei Shen, Hao Guan, Wei Zhang and Lintao Zheng
Machines 2022, 10(6), 492; https://doi.org/10.3390/machines10060492 - 20 Jun 2022
Cited by 6 | Viewed by 1969
Abstract
The nonlinearity of clearance has a significant influence on the performance of a system while ensuring the reliability of the variable-speed transmission, and hinders the development of the controlled object according to the predetermined trajectory. Aimed at the transmission clearance problem in different [...] Read more.
The nonlinearity of clearance has a significant influence on the performance of a system while ensuring the reliability of the variable-speed transmission, and hinders the development of the controlled object according to the predetermined trajectory. Aimed at the transmission clearance problem in different systems, this study summarizes the existing literature and provides a reference for the research and compensation of clearance characteristics. First, the influence of clearance on system performance is analyzed and summarized, and it is shown that the existence of clearance causes problems, such as system response delay and limited cycle oscillation. Then, the control strategies for studying clearance are introduced, which are mainly divided into the control strategy based on the clearance model and the non-clearance model control strategy, and these are respectively explained. Finally, some opinions are proposed for the perfection and development of future clearance nonlinear control theory. Ideas for realizing the suppression of the adverse effects of clearances have their characteristics, and in practical applications, the difficulty of implementation and cost control should be comprehensively considered. In the future, to cope with complex and changeable environments, the clearance control strategy will continue to be optimized. Full article
(This article belongs to the Special Issue Nonlinear Control Applications and New Perspectives)
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2 pages, 160 KiB  
Editorial
Advanced Autonomous Machines and Design Developments
by Hamid Reza Karimi, Kai Cheng and Yanhua Zou
Machines 2022, 10(6), 491; https://doi.org/10.3390/machines10060491 - 20 Jun 2022
Viewed by 1226
Abstract
With the rapid technological development of machines in different applications such as vehicles, robotics, and manufacturing, concerns may arise with regard to complexity, safety, performance, and maintenance costs associated with the machine operation [...] Full article
(This article belongs to the Special Issue Advanced Autonomous Machines and Designs)
15 pages, 4687 KiB  
Article
Application of Kriging Model to Gear Wear Calculation under Mixed Elastohydrodynamic Lubrication
by Kunpeng Dong and Zhili Sun
Machines 2022, 10(6), 490; https://doi.org/10.3390/machines10060490 - 19 Jun 2022
Cited by 2 | Viewed by 1569
Abstract
The calculation of tooth wear under mixed elastohydrodynamic lubrication is very complex and requires consideration of many conditions such as load distribution in the tooth meshing zone, micro-convex elastoplastic deformation and tooth surface temperature. The accurate calculation of tooth wear requires a lot [...] Read more.
The calculation of tooth wear under mixed elastohydrodynamic lubrication is very complex and requires consideration of many conditions such as load distribution in the tooth meshing zone, micro-convex elastoplastic deformation and tooth surface temperature. The accurate calculation of tooth wear requires a lot of time and effort. In order to calculate tooth face wear under mixed elastomeric flow lubrication quickly and accurately, a new proxy model of tooth face wear is developed using the Kriging method. The pressure distribution required for the wear calculation was obtained utilizing the modified Reynolds equation and ZMC elasto-plastic model. The numerical calculation model of gear wear was derived using the modified Archard wear model. The Kriging model was used to construct a proxy model between gear parameters and tooth wear, and the degree of approximation and goodness of fit of the Kriging model were investigated. The results are as follows. The wear depth at each position is different, the smallest at the pitch, the largest near the tooth root, and the pinion has a larger wear depth than the gear. The Kriging model is highly efficient and accurate in its computation and overcomes the shortage of excessive time spent on the calculation of numerical calculation models. Full article
(This article belongs to the Section Friction and Tribology)
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20 pages, 13069 KiB  
Article
Tracking and Counting of Tomato at Different Growth Period Using an Improving YOLO-Deepsort Network for Inspection Robot
by Yuhao Ge, Sen Lin, Yunhe Zhang, Zuolin Li, Hongtai Cheng, Jing Dong, Shanshan Shao, Jin Zhang, Xiangyu Qi and Zedong Wu
Machines 2022, 10(6), 489; https://doi.org/10.3390/machines10060489 - 17 Jun 2022
Cited by 29 | Viewed by 5149
Abstract
To realize tomato growth period monitoring and yield prediction of tomato cultivation, our study proposes a visual object tracking network called YOLO-deepsort to identify and count tomatoes in different growth periods. Based on the YOLOv5s model, our model uses shufflenetv2, combined with the [...] Read more.
To realize tomato growth period monitoring and yield prediction of tomato cultivation, our study proposes a visual object tracking network called YOLO-deepsort to identify and count tomatoes in different growth periods. Based on the YOLOv5s model, our model uses shufflenetv2, combined with the CBAM attention mechanism, to compress the model size from the algorithm level. In the neck part of the network, the BiFPN multi-scale fusion structure is used to improve the prediction accuracy of the network. When the target detection network completes the bounding box prediction of the target, the Kalman filter algorithm is used to predict the target’s location in the next frame, which is called the tracker in this paper. Finally, calculate the bounding box error between the predicted bounding box and the bounding box output by the object detection network to update the parameters of the Kalman filter and repeat the above steps to achieve the target tracking of tomato fruits and flowers. After getting the tracking results, we use OpenCV to create a virtual count line to count the targets. Our algorithm achieved a competitive result based on the above methods: The mean average precision of flower, green tomato, and red tomato was 93.1%, 96.4%, and 97.9%. Moreover, we demonstrate the tracking ability of the model and the counting process by counting tomato flowers. Overall, the YOLO-deepsort model could fulfill the actual requirements of tomato yield forecast in the greenhouse scene, which provide theoretical support for crop growth status detection and yield forecast. Full article
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14 pages, 13588 KiB  
Article
Effect of Strain Hardening and Ellipticity on Elastic–Plastic Contact Behaviour between Ellipsoids and Rigid Planes
by Jian Chen, Wangyang Zhang, Chenglong Wang, Di Liu and Linbo Zhu
Machines 2022, 10(6), 488; https://doi.org/10.3390/machines10060488 - 17 Jun 2022
Cited by 3 | Viewed by 2199
Abstract
The contact behaviour between an ellipsoid and a rigid plane is significant in research on bearing and assembly joint surfaces. However, an empirical relationship between an elastic–plastic ellipsoid and a rigid plane has not been established. In this study, the elastic–plastic contact behaviour [...] Read more.
The contact behaviour between an ellipsoid and a rigid plane is significant in research on bearing and assembly joint surfaces. However, an empirical relationship between an elastic–plastic ellipsoid and a rigid plane has not been established. In this study, the elastic–plastic contact behaviour between a deformable ellipsoid and a rigid plane was investigated by establishing a new finite element model. The proposed elastic–plastic ellipsoid contact model was designed considering the effects of the ellipticity and strain-hardening rate of the ellipsoid. The strain-hardening rate and ellipticity of the ellipsoid affected the contact area, load and mean pressure. Furthermore, the effect gradually increased with an increase in interference. New dimensionless empirical formulas for determining the contact load and contact area were proposed based on the analysis. The proposed model was validated by comparing the obtained results with previous experimental results and those of theoretical models. This study can be used to predict the elastic–plastic contact parameters between a single ellipsoid and a rigid body, such as bearings, gears and cams. It can also be used to investigate the elastic–plastic contact behaviour between anisotropic rough surfaces composed of asperities with different radii of curvature. Full article
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16 pages, 1792 KiB  
Article
DMnet: A New Few-Shot Framework for Wind Turbine Surface Defect Detection
by Jinyun Yu, Kaipei Liu, Liang Qin, Qiang Li, Feng Zhao, Qiulin Wang, Haofeng Liu, Boqiang Li, Jing Wang and Kexin Li
Machines 2022, 10(6), 487; https://doi.org/10.3390/machines10060487 - 16 Jun 2022
Cited by 4 | Viewed by 1997
Abstract
In the field of wind turbine surface defect detection, most existing defect detection algorithms have a single solution with poor generalization to the dilemma of insufficient defect samples and have unsatisfactory precision for small and concealed defects. Inspired by meta-learning ideology, we devised [...] Read more.
In the field of wind turbine surface defect detection, most existing defect detection algorithms have a single solution with poor generalization to the dilemma of insufficient defect samples and have unsatisfactory precision for small and concealed defects. Inspired by meta-learning ideology, we devised a cross-task training strategy. By exploring the common properties between tasks, the hypothesis space shrinks so that the needed sample size that satisfies a reliable empirical risk minimizer is reduced. To improve the training efficiency, a depth metric-based classification method is specially designed to find a sample-matching feature space with a good similarity measure by cosine distance. Additionally, a real-time feedback session is innovatively added to the model training loop, which performs information enhancement and filtering according to the task relevance. With dynamic activation mapping, it alleviates the information loss during traditional pooling operations, thus helping to avoid the missed detection of small-scale targets. Experimental results show that the proposed method has significantly improved the defect recognition ability under few-shot training conditions. Full article
(This article belongs to the Section Machines Testing and Maintenance)
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22 pages, 7081 KiB  
Article
Increasing Safety in Ultralight Aviation with a Wankel-Based Series/Parallel Hybrid Electric Power System
by Teresa Donateo and Davide Cavalera
Machines 2022, 10(6), 486; https://doi.org/10.3390/machines10060486 - 16 Jun 2022
Cited by 7 | Viewed by 2852
Abstract
The goal of this investigation is to propose a series/parallel hybrid electric power system for ultralight aviation designed to improve safety and, possibly, reduce fuel consumption. The power system consists of a Wankel engine, two electric machines, a battery, and a planetary gear [...] Read more.
The goal of this investigation is to propose a series/parallel hybrid electric power system for ultralight aviation designed to improve safety and, possibly, reduce fuel consumption. The power system consists of a Wankel engine, two electric machines, a battery, and a planetary gear set, all acquired from the automotive market. After a preliminary design based on takeoff power, the system is simulated over a typical flight mission and in case of engine failure for a first validation of the proposed powertrain. The investigation also shows a comparison in terms of performance and fuel consumption between the initial configuration (reciprocating piston engine), a non-hybrid Wankel arrangement, and the proposed hybrid electric configurations by using in-house simulation software. A heuristic energy management strategy is proposed as well. During a typical mission, the new powertrain works as a parallel hybrid during takeoff and climb, thus ensuring high performance and safety. During the cruise, the system behaves like a parallel hybrid with a continuously variable transmission that makes the engine work always at high efficiency. The battery is partially recharged during the descent by the extra power of the engine. The preliminary results reported in this work predict an improvement in fuel consumption by about 20% compared with the initial piston engine configuration and 28% compare with the non-hybrid Wankel powertrain, despite the larger takeoff weight. Full article
(This article belongs to the Section Vehicle Engineering)
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18 pages, 3992 KiB  
Article
Rolling Bearing Fault Diagnosis Based on Multiscale Permutation Entropy and SOA-SVM
by Xi Zhang, Hongju Wang, Mingming Ren, Mengyun He and Lei Jin
Machines 2022, 10(6), 485; https://doi.org/10.3390/machines10060485 - 16 Jun 2022
Cited by 15 | Viewed by 2081
Abstract
The service conditions of underground coal mine equipment are poor, and it is difficult to accurately extract the fault characteristics of rolling bearings. In order to better improve the accuracy of the fault identification of rolling bearings, a fault-detection method based on multiscale [...] Read more.
The service conditions of underground coal mine equipment are poor, and it is difficult to accurately extract the fault characteristics of rolling bearings. In order to better improve the accuracy of the fault identification of rolling bearings, a fault-detection method based on multiscale permutation entropy and SOA-SVM is proposed. First, the whale optimization algorithm is used to select the modal analysis number K and the penalty factor α of the variational mode decomposition algorithm. Then, the vibration signal of rolling bearings is dissolved according to the optimized variational mode decomposition algorithm, and the multi-scale permutation entropy of the main intrinsic mode function is calculated. Finally, the feature values of the matrix are entered into the SVM algorithm optimized by the seagull optimization algorithm to obtain the classification result. The experimental results based on the published rolling bearing datasets of Western Reserve University show that the identification success rate of the proposed method can reach 98.75%. The fault detection of the rolling bearings can be completed accurately and efficiently. Full article
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15 pages, 3971 KiB  
Article
Profile Analysis of Spur Gear Shaping Cutters Based on Sharpened Cutting Edges
by Chin-Lung Huang and You-Chuan Wei
Machines 2022, 10(6), 484; https://doi.org/10.3390/machines10060484 - 16 Jun 2022
Viewed by 2463
Abstract
Spur shaping cutters, the most versatile gear cutting tools, are used to produce gears that are limited in general cutting cases, such as internal gears and stacked gears. The side clearance angle, which is formed by the profile shifting on the tooth surface, [...] Read more.
Spur shaping cutters, the most versatile gear cutting tools, are used to produce gears that are limited in general cutting cases, such as internal gears and stacked gears. The side clearance angle, which is formed by the profile shifting on the tooth surface, and the rake angle, which increases the cutting efficiency and reduces the wearing of the cutting edge, are designed to create better cutting conditions. However, these cutting angles cause errors in the profile of the cutter edge. In this study, mathematical models of the Isoform® shaping cutter generation method and a model of the cutter edge formed by the conical cutter face were derived to verify the profile error of the cutter edge. A mathematical model to determine the profile error through the corresponding cutter enveloping gear is also proposed. Finally, mathematical models were also derived to correct and reduce the profile error at the major cutter face and the results at the other cutter faces. The numerical results, namely, the profile error curves, show that the corrected cutter has better profile accuracy for the normal usable cutter life. Full article
(This article belongs to the Section Machine Design and Theory)
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25 pages, 8215 KiB  
Article
Mixed Lubrication Modeling of Multi-Lip Reciprocating Seals Based on Elastohydrodynamic Lubrication Theory
by Donghong Cheng, Lichen Gu and Yu Sun
Machines 2022, 10(6), 483; https://doi.org/10.3390/machines10060483 - 16 Jun 2022
Cited by 5 | Viewed by 2152
Abstract
Multi-lip reciprocating seals are extensively used in the subject of engineering equipment. However, the current research on the tribology of reciprocating seals mainly focused focuses on the numerical analysis of single-lip seals. In order to study the sealing performance of multi-lip seals, this [...] Read more.
Multi-lip reciprocating seals are extensively used in the subject of engineering equipment. However, the current research on the tribology of reciprocating seals mainly focused focuses on the numerical analysis of single-lip seals. In order to study the sealing performance of multi-lip seals, this paper takes double-acting seal (DAS) as the research object, and establishes a multi-lip mixed elastohydrodynamic lubrication (M-EHL) numerical simulation model from the perspective of solid mechanics, fluid mechanics, contact mechanics, and deformation mechanics. The sealing characteristics under different working conditions (sealed pressure, piston rod extension speed, and seal surface roughness) were analyzed by numerical calculation, and the variation trend of friction force corresponding to the experimental results was obtained. The model can provide a modeling guidance basis for the M-EHL characteristic analysis and structural optimization design of multi-lip reciprocating seals in the mechanical field. Full article
(This article belongs to the Special Issue Elastohydrodynamic Lubrication)
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26 pages, 9917 KiB  
Article
Multi-Objective Optimization Design for a Novel Parametrized Torque Converter Based on an Integrated CFD Cascade Design System
by Zilin Ran, Wenxing Ma, Kaifeng Wang and Bosen Chai
Machines 2022, 10(6), 482; https://doi.org/10.3390/machines10060482 - 15 Jun 2022
Cited by 4 | Viewed by 2021
Abstract
Advanced cascade design theories and methods are crucial to the rapid development of torque converters. Therefore, the study proposed a new parametric design method for a hydrodynamic torque converter cascade. The method is embodied by using a cubic non-uniform rational B-splines (NURBS) open [...] Read more.
Advanced cascade design theories and methods are crucial to the rapid development of torque converters. Therefore, the study proposed a new parametric design method for a hydrodynamic torque converter cascade. The method is embodied by using a cubic non-uniform rational B-splines (NURBS) open curve and closed curve, respectively, to carry out the parametric design of the unit blade camberline and unit blade thickness distribution, and the curvature of the designed blade curve is continuous. Then, the author developed batch and script files in the Isight platform for a fully automated integrated design of the hydrodynamic torque converter, including cascade parametric modeling, meshing, computational fluid dynamics (CFD) simulation, post-processing, and optimization design. A three-dimensional cascade integrated optimization design system of the hydrodynamic torque converter is established with CFD technology as the bottom layer design, a control file as the middle layer, and an optimization algorithm as the top layer drive. Finally, multi-objective optimization was carried out for the key cascade parameters (camberline peak height). Compared with the original blade, the optimized NURBS blade increased by 7.207% in high-efficiency region width (Gη), and the optimized blade increased by 2.673% in peak efficiency (ηmax) to meet the actual engineering requirements. The new parametric design method of the blade shape and the integrated optimization design system of a three-dimensional cascade of torque converter proposed in this paper significantly reduces the design costs and shortens the design cycle of the torque converter, which will provide a valuable reference for engineers of turbomachinery. Full article
(This article belongs to the Special Issue Emerging Techniques and Their Application in Turbomachinery)
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21 pages, 6367 KiB  
Article
A Rolling Bearing Fault Diagnosis Method Based on Enhanced Integrated Filter Network
by Kang Wu, Jie Tao, Dalian Yang, Hu Xie and Zhiying Li
Machines 2022, 10(6), 481; https://doi.org/10.3390/machines10060481 - 15 Jun 2022
Cited by 3 | Viewed by 1924
Abstract
Aiming at the difficulty of rolling bearing fault diagnosis in a strong noise environment, this paper proposes an enhanced integrated filter network. In the method, we firstly design an enhanced integrated filter, which includes the filter enhancement module and the expression enhancement module. [...] Read more.
Aiming at the difficulty of rolling bearing fault diagnosis in a strong noise environment, this paper proposes an enhanced integrated filter network. In the method, we firstly design an enhanced integrated filter, which includes the filter enhancement module and the expression enhancement module. The filter enhancement module can not only filter the high-frequency noise to extract useful features of medium and low-frequency signals but also maintain frequency and time resolution to some extent. On this basis, the expression enhancement module analyzes fault features intercepted by the upper network at multiple scales to get deep features. Then we introduce vector neurons to integrate scalar features into vector space, which mine the correlation between features. The feature vectors are transmitted by dynamic routing to establish the relationship between low-level capsules and high-level capsules. In order to verify the diagnostic performance of the model, CWRU and IMS bearing datasets are used for experimental verification. In the strong noise environment of SNR = −4 dB, the fault diagnosis precisions of the method on CWRU and IMS reach 94.85% and 92.45%, respectively. Compared with typical bearing fault diagnosis methods, the method has higher fault diagnosis precision and better generalization ability in a strong noise environment. Full article
(This article belongs to the Special Issue Advances in Bearing Modeling, Fault Diagnosis, RUL Prediction)
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15 pages, 4848 KiB  
Article
A Computer-Assisted Preoperative Path Planning Method for the Parallel Orthopedic Robot
by Jian Li, Rui Cui, Peng Su, Lifang Ma and Hao Sun
Machines 2022, 10(6), 480; https://doi.org/10.3390/machines10060480 - 15 Jun 2022
Cited by 6 | Viewed by 1839
Abstract
Background: Trajectory planning is the premise of the control of orthopedic robots, which is directly related to the safety of the human body. However, to date, the trajectory of orthopedic robots has been restricted to lines and spline curves. This limits the flexibility [...] Read more.
Background: Trajectory planning is the premise of the control of orthopedic robots, which is directly related to the safety of the human body. However, to date, the trajectory of orthopedic robots has been restricted to lines and spline curves. This limits the flexibility of the robot and leads to unsatisfactory performance. In this paper, a trajectory planning method based on improved RRT* and B-spline curve is proposed in order to improve the control accuracy and flexibility. Method: Firstly, combined with the shortcomings of current trajectory planning methods and bone docking task analysis, the characteristics of the trajectory for orthopedic robot are illustrated, and the problem is described. Secondly, a sampling strategy and an extension strategy are proposed to solve the optimal problem of the RRT* algorithm. Meanwhile, B-spline curve is selected for path smoothing. Thirdly, based on our orthopedic robot, kinematics analysis is introduced briefly, and hypotonic polynomial is used to fit the joint variables. Finally, a comparative study of the improved RRT*, RRT*, and other algorithms are completed, and the feasibility of the robot’s trajectory is verified by algorithm simulation and platform simulation. Results: Compared with RRT*, shorter path and high node utilization are shown in the improved RRT*, which cut down about 1mm in the average path length and increased about half in the average node utilization. In the meantime, the fitting results are accepted, and the results of algorithm simulation and platform simulation showed good consistency and feasibility. Conclusions: This study revealed that the improved RRT* was superior to RRT*, and the proposed method could be used for the trajectory planning of parallel orthopedic robots, which has some significance for bone fracture and deformity correction. Full article
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15 pages, 4165 KiB  
Article
Reducing Helicopter Vibration Loads by Individual Blade Control with Genetic Algorithm
by Renguo Yang, Yadong Gao, Huaming Wang and Xianping Ni
Machines 2022, 10(6), 479; https://doi.org/10.3390/machines10060479 - 15 Jun 2022
Cited by 6 | Viewed by 2381
Abstract
A rotor that can realize individual blade pitch control was designed. This paper focuses on finding the trend of helicopter vibration loads after applying multiple high-order harmonic control. The Glauert inflow model was introduced to calculate the induced velocity of rotor blades in [...] Read more.
A rotor that can realize individual blade pitch control was designed. This paper focuses on finding the trend of helicopter vibration loads after applying multiple high-order harmonic control. The Glauert inflow model was introduced to calculate the induced velocity of rotor blades in a rotor disk plane, and the Leishman Beddoes (L-B) unsteady dynamic model was employed to calculate the aerodynamic forces of each section of a rotor blade. It was found that the influence of each high-order harmonic control on individual blade vibration load reduction is similar in different advanced ratios. After these calculations, the genetic algorithm was used to calculate the best combination of amplitude and phase of the higher order harmonic under a specific flight state. Under the effect of high harmonic input, the vibration loads of the hub could be reduced by about 65%. These results can be theoretically applied to design control law to reduce helicopter vibration loads. Full article
(This article belongs to the Special Issue Bio-Inspired Smart Machines: Structure, Mechanisms and Applications)
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26 pages, 9632 KiB  
Review
Optimization Approaches and Techniques for Automotive Alternators: Review Study
by Omar Talal Mahmood, Wan Zuha Wan Hasan, Luthffi Idzhar Ismail, Suhaidi Shafie, Norhafiz Azis and Nor Mohd Haziq Norsahperi
Machines 2022, 10(6), 478; https://doi.org/10.3390/machines10060478 - 15 Jun 2022
Viewed by 2921
Abstract
Optimization and improvement of the electrical system are applied to cope with the increased demand for electrical power in the vehicular system; they must be carried out in many ways to ensure that the vehicles are provided with the necessary electricity for their [...] Read more.
Optimization and improvement of the electrical system are applied to cope with the increased demand for electrical power in the vehicular system; they must be carried out in many ways to ensure that the vehicles are provided with the necessary electricity for their performance work electrical equipment. This paper reviews the various optimization approaches for the alternator used in automotive applications and discusses the advantages and disadvantages of each method. The optimization is achieved to the field excitation current that influences the alternator output voltage, and the other techniques designed a controller to optimize the output power of the alternator using power electronic converters. The most suitable approaches are those approaches that use real-time optimization and self-optimization methods. Combining the above two methods can achieve the best results, higher efficiency, stable performance, and a large amount of power produced by the alternator. Full article
(This article belongs to the Section Electromechanical Energy Conversion Systems)
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18 pages, 3299 KiB  
Article
Rolling Bearing Fault Diagnosis Based on Nonlinear Underdetermined Blind Source Separation
by Hong Zhong, Yang Ding, Yahui Qian, Liangmo Wang and Baogang Wen
Machines 2022, 10(6), 477; https://doi.org/10.3390/machines10060477 - 14 Jun 2022
Cited by 1 | Viewed by 1640
Abstract
One challenge of bearing fault diagnosis is that the vibration signals are often a nonlinear mixture of unknown source signals. In addition, the practical installation position also limits the number of observed signals. Hence, bearing fault diagnosis is a nonlinear underdetermined blind source [...] Read more.
One challenge of bearing fault diagnosis is that the vibration signals are often a nonlinear mixture of unknown source signals. In addition, the practical installation position also limits the number of observed signals. Hence, bearing fault diagnosis is a nonlinear underdetermined blind source separation (UBSS) problem. In this paper, a novel nonlinear UBSS solution based on source number estimation and improved sparse component analysis (SCA) is proposed. Firstly, the ensemble empirical mode decomposition (EEMD), correlation coefficient (CC), and adaptive threshold singular value decomposition (ATSVD) joint approach is proposed to estimate the source number. Then, the observed signals are transformed into the time−frequency domain by short−time Fourier transform (STFT) to meet the sparsity requirement of SCA. The frequency energy is adopted to increase the accuracy of fuzzy C−means (FCM) clustering, so as to ensure the accuracy estimation of the mixing matrix. The L1−norm minimization is utilized to recover the source signals. Simulation results prove that the proposed UBSS solution can exactly estimate the source number and effectively separate the simulated signals in both linear and nonlinear mixed cases. Finally, bearing fault testbed experiments are conducted to verify the validity of the proposed approach in bearing fault diagnosis. Full article
(This article belongs to the Section Machines Testing and Maintenance)
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16 pages, 3220 KiB  
Article
Influence and Suppression Method of the Eddy Current Effect on the Suspension System of the EMS Maglev Train
by Qing Yang, Zhenxiang Chi and Lianchun Wang
Machines 2022, 10(6), 476; https://doi.org/10.3390/machines10060476 - 14 Jun 2022
Cited by 3 | Viewed by 1975
Abstract
The suspension system of the EMS (Electro-Magnetic Suspension) medium-and-low-speed maglev train is affected by the eddy current effect when the train is in motion. This is a crucial problem related to the improvement of train operation speed. In this article, this phenomenon is [...] Read more.
The suspension system of the EMS (Electro-Magnetic Suspension) medium-and-low-speed maglev train is affected by the eddy current effect when the train is in motion. This is a crucial problem related to the improvement of train operation speed. In this article, this phenomenon is analyzed and the method of suppressing the eddy current effect is put forward. Firstly, theoretical analysis and experimental verification are carried out. It is worth mentioning that the experimental data, which thoroughly show how the suspension current changes with the maglev train speed under the influence of the eddy current effect, are collected and published for the first time, which strongly confirms the accuracy of the theoretical analysis. Secondly, an improved scheme to suppress the influence of the eddy current effect is proposed from the perspective of the rail structure for the first time and simulation results verify the effectiveness of the improved scheme. This research makes important progress on the improvement of the rail used in the maglev train. Full article
(This article belongs to the Section Vehicle Engineering)
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15 pages, 1701 KiB  
Article
Comprehensive Design and Analysis of Rotor Stress for HSPMM Considering Cooling Method
by Yingzhe Lin, Yunkai Huang and Tao Zhang
Machines 2022, 10(6), 475; https://doi.org/10.3390/machines10060475 - 14 Jun 2022
Cited by 2 | Viewed by 2452
Abstract
In the design process of a high-speed motor, a reasonable rotor stress analysis is a necessary prerequisite to guarantee its safe and reliable operation. In this paper, the comprehensive design and analysis of the rotor stress of a 200 kW 20,000 r/min high-speed [...] Read more.
In the design process of a high-speed motor, a reasonable rotor stress analysis is a necessary prerequisite to guarantee its safe and reliable operation. In this paper, the comprehensive design and analysis of the rotor stress of a 200 kW 20,000 r/min high-speed permanent magnet motor (HSPMM) with magnetic bearing are carried out. Firstly, the stress distribution characteristics of rotors with different permanent magnet structures and different thermal expansion coefficients of filling materials are analyzed and compared. Secondly, the rotor design is determined through a comprehensive comparative analysis of different sleeve thicknesses and shrink fit. Furthermore, considering the axial temperature gradient due to the axial ventilation cooling method adopted by the prototype, the rotor stress is checked through the coupling calculation of fluent and static stress. Finally, several long-period running tests are carried out, showing the good agreement between the calculated and measured results, and the safe and reliable operation of the prototype verifies the correctness of the above theoretical analysis. Full article
(This article belongs to the Section Machine Design and Theory)
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15 pages, 1954 KiB  
Article
Integrated Smart Warehouse and Manufacturing Management with Demand Forecasting in Small-Scale Cyclical Industries
by Yuk-Ming Tang, George To Sum Ho, Yui-Yip Lau and Shuk-Ying Tsui
Machines 2022, 10(6), 472; https://doi.org/10.3390/machines10060472 - 14 Jun 2022
Cited by 13 | Viewed by 5298
Abstract
In the context of the global economic slowdown, demand forecasting, and inventory and production management have long been important topics to the industries. With the support of smart warehouses, big data analytics, and optimization algorithms, enterprises can achieve economies of scale, and balance [...] Read more.
In the context of the global economic slowdown, demand forecasting, and inventory and production management have long been important topics to the industries. With the support of smart warehouses, big data analytics, and optimization algorithms, enterprises can achieve economies of scale, and balance supply and demand. Smart warehouse and manufacturing management is considered the culmination of recently advanced technologies. It is important to enhance the scalability and extendibility of the industry. Despite many researchers having developed frameworks for smart warehouse and manufacturing management for various fields, most of these models are mainly focused on the logistics of the product and are not generalized to tackle the specific manufacturing problem facing in the cyclical industry. Indeed, the cyclical industry has a key problem: the big risk which high sensitivity poses to the business cycle and economic recession, which is difficult to foresee. Despite many inventory optimization approaches being proposed to optimize the inventory level in the warehouse and facilitate production management, the demand forecasting technique is seldom focused on the cyclic industry. On the other hand, management approaches are usually based on the complex logistics process instead of integrating the inventory level of the stock, which is very crucial to composing smart warehouses and manufacturing. This research study proposed a digital twin framework by integrating the smart warehouse and manufacturing with the roulette genetic algorithm for demand forecasting in the cyclical industry. We also demonstrate how this algorithm is practically implemented for forecasting the demand, sustaining manufacturing optimization, and achieving inventory optimization. We adopted a small-scale textile company case study to demonstrate the proposed digital framework in the warehouse and demonstrate the results of demand forecasting and inventory optimization. Various scenarios were conducted to simulate the results for the digital twin. The proposed digital twin framework and results help manufacturers and logistics companies to improve inventory management. This study has important theoretical and practical significance for the management of the cyclical industry. Full article
(This article belongs to the Special Issue Digital Twin Applications in Smart Manufacturing)
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16 pages, 7664 KiB  
Article
Proximate Model of Gear Drive Units Based on Dimensional Analysis for Wear Process Evaluation
by Wenhua Wang, Wei Yuan, Yuqi Zhu, Qianjian Guo, Baotao Chi, Haixiao Wang and Xianhai Yang
Machines 2022, 10(6), 474; https://doi.org/10.3390/machines10060474 - 13 Jun 2022
Viewed by 1773
Abstract
Excessive wear of gears will not only cause noise and vibration in the transmission system, but also reduce transmission efficiency and accuracy in severe cases, causing irreversible losses to the transmission system. It is desirable to develop a micro-gear unit model for evaluating [...] Read more.
Excessive wear of gears will not only cause noise and vibration in the transmission system, but also reduce transmission efficiency and accuracy in severe cases, causing irreversible losses to the transmission system. It is desirable to develop a micro-gear unit model for evaluating the wear process and predicting the failure time of large gear units (such as wind turbine gear units), reducing losses due to sudden failures. Based on the Buckingham pi-theorem of dimensional analysis and Hertz formula, the similarity ratio of each parameter of the gear wear process was proposed. The maximum equivalent stress is calculated by establishing the FEM model and comparing it with the theoretical contact stress calculated by the Hertz formula, and the results were relatively consistent. Two pairs of gear friction and wear experiments with similar parameters were carried out to compare the wear evolution performance of two similar gears. The friction performance process of the test gears was observed by particle counter and analytical ferrograph. The results show that the friction and wear processes of the two groups of gears with similar parameters have a certain correlation, which was consistent with the proposed similarity model. The similarity model combined with the observation results of abrasive particles has a certain application value for the evaluation of the wear state of the transmission system. Full article
(This article belongs to the Section Friction and Tribology)
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17 pages, 6166 KiB  
Article
Dynamic Characteristic Analysis of the Multi-Stage Centrifugal Pump Rotor System with Uncertain Sliding Bearing Structural Parameters
by Lijun Lin, Mingge He, Wensheng Ma, Qingyuan Wang, Haiyan Zhai and Congying Deng
Machines 2022, 10(6), 473; https://doi.org/10.3390/machines10060473 - 13 Jun 2022
Cited by 5 | Viewed by 1859
Abstract
The traditional dynamic characteristic analysis of the multi-stage centrifugal pump rotor system is developed assuming the bearing structural parameters with constant values. However, the manufacturing errors will cause the structural parameters to vary around their nominal values and then affect the dynamic characteristics [...] Read more.
The traditional dynamic characteristic analysis of the multi-stage centrifugal pump rotor system is developed assuming the bearing structural parameters with constant values. However, the manufacturing errors will cause the structural parameters to vary around their nominal values and then affect the dynamic characteristics of the bearing-rotor system. Thus, this paper proposes a method for analyzing the dynamic characteristics of the bearing-rotor system with uncertain bearing structural parameters. First, dynamic characteristic coefficients of the sliding bearing are identified to establish the dynamic model of the rotor system, and its dynamic characteristics are analyzed through finite element simulations. Next, the sliding bearing structural parameters are taken as the variables to establish an optimization model, which is solved by the improved particle swarming optimization algorithm to obtain the extreme critical speed of the rotor system. A case study was carried out on a multi-stage centrifugal pump. The obtained extreme values of the critical speeds were close to those calculated using the multiple samples generated by the Monte Carlo method, indicating that the proposed method can provide accurate variation ranges of critical speeds efficiently and lay a theoretical basis for selecting robust operational speeds and designing the rotor system of the multi-stage centrifugal pump. Full article
(This article belongs to the Special Issue Emerging Techniques and Their Application in Turbomachinery)
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14 pages, 1354 KiB  
Article
A Local Density-Based Abnormal Case Removal Method for Industrial Operational Optimization under the CBR Framework
by Xiangyu Peng, Yalin Wang, Lin Guan and Yongfei Xue
Machines 2022, 10(6), 471; https://doi.org/10.3390/machines10060471 - 12 Jun 2022
Cited by 3 | Viewed by 1714
Abstract
Operational optimization is essential in modern industry and unsuitable operations will deteriorate the performance of industrial processes. Since measuring error and multiple working conditions are inevitable in practice, it is necessary to reduce their negative impacts on operational optimization under the case-based reasoning [...] Read more.
Operational optimization is essential in modern industry and unsuitable operations will deteriorate the performance of industrial processes. Since measuring error and multiple working conditions are inevitable in practice, it is necessary to reduce their negative impacts on operational optimization under the case-based reasoning (CBR) framework. In this paper, a local density-based abnormal case removal method is proposed to remove the abnormal cases in a case retrieval step, so as to prevent performance deterioration in industrial operational optimization. More specifically, the reasons as to why classic CBR would retrieve abnormal cases are analyzed from the perspective of case retrieval in industry. Then, a local density-based abnormal case removal algorithm is designed based on the Local Outlier Factor (LOF), and properly integrated into the traditional case retrieval step. Finally, the effectiveness and the superiority of the local density-based abnormal case removal method was tested by a numerical simulation and an industrial case study of the cut-made process of cigarette production. The results show that the proposed method improved the operational optimization performance of an industrial cut-made process by 23.5% compared with classic CBR, and by 13.3% compared with case-based fuzzy reasoning. Full article
(This article belongs to the Special Issue Deep Learning-Based Machinery Fault Diagnostics)
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19 pages, 6704 KiB  
Article
3D Pipe Forming of a New Bending Machine with a 3PUU–3RPS Hybrid Mechanism
by Shuai Zhang, Yusen Li, Zhenming Yue, Zhongran Zhang, Lianpeng Su, Biao Yan and Jun Gao
Machines 2022, 10(6), 470; https://doi.org/10.3390/machines10060470 - 12 Jun 2022
Viewed by 3066
Abstract
To achieve the spatial variable curvature bending process of metal pipes, one 3PUU–3RPS hybrid mechanism designed for the free-bending forming of pipes is presented in this study. Its kinematics model was conducted based on theoretical analysis, and the obtained result was validated through [...] Read more.
To achieve the spatial variable curvature bending process of metal pipes, one 3PUU–3RPS hybrid mechanism designed for the free-bending forming of pipes is presented in this study. Its kinematics model was conducted based on theoretical analysis, and the obtained result was validated through ADAMS simulation. Through the theoretical analysis, the inverse position model of the proposed mechanical construction, which can show the relationship between the motion and the drive of the working platform, was presented. The velocity Jacobian matrix was also obtained and analyzed by establishing the inverse velocity model and inverse acceleration model. In addition, the static stiffness analysis of the proposed mechanical construction was also conducted in ABAQUS. Finally, by investigating its working space, the capability of 3PUU–3RPS mechanism was proved. Full article
(This article belongs to the Topic Designs and Drive Control of Electromechanical Machines)
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22 pages, 10047 KiB  
Article
Composite Fault Diagnosis of Rolling Bearing Based on Chaotic Honey Badger Algorithm Optimizing VMD and ELM
by Jie Ma, Sen Yu and Wei Cheng
Machines 2022, 10(6), 469; https://doi.org/10.3390/machines10060469 - 12 Jun 2022
Cited by 9 | Viewed by 2110
Abstract
In order to effectively extract the characteristic information of bearing vibration signals and improve the classification accuracy, a composite fault diagnosis method of rolling bearing based on the chaotic honey badger algorithm (CHBA), which optimizes variational mode decomposition (VMD) and extreme learning machine [...] Read more.
In order to effectively extract the characteristic information of bearing vibration signals and improve the classification accuracy, a composite fault diagnosis method of rolling bearing based on the chaotic honey badger algorithm (CHBA), which optimizes variational mode decomposition (VMD) and extreme learning machine (ELM), is proposed in this paper. Firstly, aiming to solve the problem that the HBA optimization process can easily fall into local optimization and slow convergence speed, sinusoidal chaotic mapping is introduced to improve HBA, and the advantages of CHBA are verified by 23 benchmark functions. Then, taking the Gini index of the square envelope (GISE) as the fitness function, the VMD is optimized with CHBA to obtain the optimal number of modes K and the quadratic penalty factor. Secondly, the first four IMF components with the largest GISE values are selected, and the IMF components are grouped by the “Systematic Sampling Method (SSM)” to calculate the signal energy to form the fault feature vector. Finally, taking the classification error rate as the fitness function, the feature vector is input into the ELM model optimized by CHBA to classify and identify different types of faults. Through experimental analysis, and compared with BP, ELM, GWO-ELM, and HBA-ELM, this method has better diagnosis results for composite faults, and the accuracy of fault classification can reach 100%, which provides a new way to solve the problem of composite fault diagnosis. Full article
(This article belongs to the Section Machines Testing and Maintenance)
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17 pages, 14762 KiB  
Article
Design and Modeling of a Bio-Inspired Compound Continuum Robot for Minimally Invasive Surgery
by Gang Zhang, Fuxin Du, Shaowei Xue, Hao Cheng, Xingyao Zhang, Rui Song and Yibin Li
Machines 2022, 10(6), 468; https://doi.org/10.3390/machines10060468 - 11 Jun 2022
Cited by 15 | Viewed by 3613
Abstract
The continuum robot is a new type of bionic robot which is widely used in the medical field. However, the current structure of the continuum robot limits its application in the field of minimally invasive surgery. In this paper, a bio-inspired compound continuum [...] Read more.
The continuum robot is a new type of bionic robot which is widely used in the medical field. However, the current structure of the continuum robot limits its application in the field of minimally invasive surgery. In this paper, a bio-inspired compound continuum robot (CCR) combining the concentric tube continuum robot (CTR) and the notched continuum robot is proposed to design a high-dexterity minimally invasive surgical instrument. Then, a kinematic model, considering the stability of the CTR part, was established. The unstable operation of the CCR is avoided. The simulation of the workspace shows that the introduction of the notched continuum robot expands the workspace of CTR. The dexterity indexes of the robots are proposed. The simulation shows that the dexterity of the CCR is 1.472 times that of the CTR. At last, the length distribution of the CCR is optimized based on the dexterity index by using a fruit fly optimization algorithm. The simulations show that the optimized CCR is more dexterous than before. The dexterity of the CCR is increased by 1.069 times. This paper is critical for the development of high-dexterity minimally invasive surgical instruments such as those for the brain, blood vessels, heart and lungs. Full article
(This article belongs to the Special Issue Bio-Inspired Smart Machines: Structure, Mechanisms and Applications)
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20 pages, 5081 KiB  
Article
Investigation of the Aerodynamic Performance of the Miller Cycle from Transparent Engine Experiments and CFD Simulations
by Marcellin Perceau, Philippe Guibert, Adrian Clenci, Victor Iorga-Simăn, Mihai Niculae and Stéphane Guilain
Machines 2022, 10(6), 467; https://doi.org/10.3390/machines10060467 - 11 Jun 2022
Cited by 2 | Viewed by 2288
Abstract
This paper assesses the effect of the Miller cycle upon the internal aerodynamics of a motored transparent spark ignition engine via CFD simulation and particle image velocimetry. Since the transparent Miller engine does not allow for measurements in the roof of the combustion [...] Read more.
This paper assesses the effect of the Miller cycle upon the internal aerodynamics of a motored transparent spark ignition engine via CFD simulation and particle image velocimetry. Since the transparent Miller engine does not allow for measurements in the roof of the combustion chamber, the extraction of information regarding the aerodynamic phenomena occurring here is based on CFD simulation, i.e., the results of the CFD simulation are used to allow for the extrapolation of the experimental data; thus, they are used to complete the picture regarding the aerodynamic phenomena occurring inside the whole cylinder. The results indicate that implementing the early intake valve closing strategy to obtain the Miller cycle has a negative impact on the mean kinetic energy, turbulent kinetic energy, and fluctuating velocity toward the end of the compression stroke, thus affecting, the combustion process. This supports the need to intensify the internal aerodynamics when applying the Miller cycle such that the turbulence degradation is not too big and, consequently, to still gain efficiency in the Miller cycle. Full article
(This article belongs to the Special Issue Optimization and Flow Characteristics in Advanced Fluid Machinery)
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26 pages, 4153 KiB  
Article
Mechanical Design and a Novel Structural Optimization Approach for Hexapod Walking Robots
by Ervin Burkus, Ákos Odry, Jan Awrejcewicz, István Kecskés and Péter Odry
Machines 2022, 10(6), 466; https://doi.org/10.3390/machines10060466 - 11 Jun 2022
Cited by 6 | Viewed by 2543
Abstract
This paper presents a novel model-based structural optimization approach for the efficient electromechanical development of hexapod robots. First, a hexapod-design-related analysis of both optimization objectives and relevant parameters is conducted based on the derived dynamical model of the robot. A multi-objective optimization goal [...] Read more.
This paper presents a novel model-based structural optimization approach for the efficient electromechanical development of hexapod robots. First, a hexapod-design-related analysis of both optimization objectives and relevant parameters is conducted based on the derived dynamical model of the robot. A multi-objective optimization goal is proposed, which minimizes energy consumption, unwanted body motion and differences between joint torques. Then, an optimization framework is established, which utilizes a sophisticated strategy to handle the optimization problems characterized by a large set of parameters. As a result, a satisfactory result is efficiently obtained with fewer iterations. The research determines the optimal parameter set for hexapod robots, contributing to significant increases in a robot’s walking range, suppressed robot body vibrations, and both balanced and appropriate motor loads. The modular design of the proposed simulation model also offers flexibility, allowing for the optimization of other electromechanical properties of hexapod robots. The presented research focuses on the mechatronic design of the Szabad(ka)-III hexapod robot and is based on the previously validated Szabad(ka)-II hexapod robot model. Full article
(This article belongs to the Special Issue Modeling, Sensor Fusion and Control Techniques in Applied Robotics)
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20 pages, 1168 KiB  
Article
Constrained Image-Based Visual Servoing of Robot Manipulator with Third-Order Sliding-Mode Observer
by Xiuyan Peng, Jiashuai Li, Bing Li and Jiawei Wu
Machines 2022, 10(6), 465; https://doi.org/10.3390/machines10060465 - 11 Jun 2022
Cited by 1 | Viewed by 2360
Abstract
A new image-based robot visual servo control strategy based on a third-order sliding-mode observer (TOSM) model predictive control is proposed in this study. This new control strategy solves the problem of robot visual servo control with system constraints and time-varying disturbances when the [...] Read more.
A new image-based robot visual servo control strategy based on a third-order sliding-mode observer (TOSM) model predictive control is proposed in this study. This new control strategy solves the problem of robot visual servo control with system constraints and time-varying disturbances when the camera and model of the robot manipulator are uncertain and the joint velocity is unknown. In the proposed method, the joint velocity and system centralized uncertainties are estimated simultaneously based on a third-order sliding-mode observer, and the image-based visual servoing problem is transformed into a nonlinear optimization problem based on a model predictive control method considering both visibility constraints and actuator constraints, which minimizes the predicted trajectory cost function to generate the control signal for each cycle. Simulations were carried out to verify the effectiveness of the proposed control scheme. Full article
(This article belongs to the Topic Recent Advances in Robotics and Networks)
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15 pages, 3152 KiB  
Article
Fractal Model of Contact Thermal Stiffness
by Yunshuai Chen, Pengyang Li, Jian Sun, Miao Shang and Limin Shao
Machines 2022, 10(6), 464; https://doi.org/10.3390/machines10060464 - 10 Jun 2022
Cited by 2 | Viewed by 1626
Abstract
The continuity, self-similarity, and self-affinity of a microscopic contact surface can be described by the Weierstrass–Mandelbrot (W–M) function in fractal theory. To address the problems that the existing normal contact load fractal model does not take into account the effect of thermal stress [...] Read more.
The continuity, self-similarity, and self-affinity of a microscopic contact surface can be described by the Weierstrass–Mandelbrot (W–M) function in fractal theory. To address the problems that the existing normal contact load fractal model does not take into account the effect of thermal stress and is not applicable to the temperature variation in the joint surface of the giant magnetostrictive ultrasonic vibration systems, a fractal model of thermal–elastic–plastic contact normal load fractal is established based on fractal theory. The model is an extension of the traditional model in terms of basic theory and application scope, and it takes into account the effects of temperature difference, linear expansion coefficient, fractal dimension, and other parameters. Finally, the effect of the temperature difference at the joint surface on the normal load of the thermoelastic contact is revealed through numerical simulations. The results show that the nonlinearity of the contact stiffness of the thermoelastic joint surface is mainly related to the surface roughness and the fractal dimension, while the effect of the temperature change on the joint surface properties within a certain range is linear. Full article
(This article belongs to the Section Friction and Tribology)
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14 pages, 2653 KiB  
Article
Stability and Dynamic Walk Control of Humanoid Robot for Robot Soccer Player
by Rudolf Jánoš, Marek Sukop, Ján Semjon, Peter Tuleja, Peter Marcinko, Martin Kočan, Maksym Grytsiv, Marek Vagaš, Ľubica Miková and Tatiana Kelemenová
Machines 2022, 10(6), 463; https://doi.org/10.3390/machines10060463 - 10 Jun 2022
Cited by 9 | Viewed by 3022
Abstract
Robotic football with humanoid robots is a multidisciplinary field connecting several scientific fields. A challenging task in the design of a humanoid robot for the AndroSot and HuroCup competitions is the realization of movement on the field. This study aims to determine a [...] Read more.
Robotic football with humanoid robots is a multidisciplinary field connecting several scientific fields. A challenging task in the design of a humanoid robot for the AndroSot and HuroCup competitions is the realization of movement on the field. This study aims to determine a walking pattern for a humanoid robot with an impact on its dynamic stability and behavior. The design of the proposed technical concept depends on its stability management mechanism, walking speed and such factors as the chosen stability approaches. The humanoid robot and its versatility, along with the adaptability of the terrain, are somewhat limited due to the complexity of the walking principle and the control of the robot’s movement itself. The technical concept uses dynamic stability as the potential force of the inertial bodies and their parts so that the humanoid robot does not overturn. The total height of the robot according to the rules of the competition will be 50 cm. In the performed experiment, only the lower part of the humanoid robot with added weight was considered, which is more demanding due to the non-use of the upper limbs for stabilization. The performed experiment verified the correctness of the design, where the torso of the robot performed eight steps in inclinations of a roll angle +4/−2° and a pitch angle +4/−6°. Full article
(This article belongs to the Topic Motion Planning and Control for Robotics)
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