Journal Description
Machines
Machines
is an international, peer-reviewed, open access journal on machinery and engineering, published monthly online by MDPI. The International Federation for the Promotion of Mechanism and Machine Science (IFToMM) is affiliated with Machines and its members receive a discount on the article processing charges.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, and other databases.
- Journal Rank: JCR - Q2 (Engineering, Mechanical) / CiteScore - Q1 (Control and Optimization)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 15.9 days after submission; acceptance to publication is undertaken in 2.9 days (median values for papers published in this journal in the first half of 2026).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
- Journal Cluster of Mechanical Manufacturing and Automation Control: Aerospace, Automation, Drones, Journal of Manufacturing and Materials Processing, Machines, Robotics and Technologies.
- Companion journals for Machines include: Industries and Precision.
Impact Factor:
3.0 (2025);
5-Year Impact Factor:
2.9 (2025)
Latest Articles
Progressive Attention-Guided Two-Stage Transfer Learning for Few-Shot Cross-Condition Bearing Fault Diagnosis
Machines 2026, 14(9), 1010; https://doi.org/10.3390/machines14091010 (registering DOI) - 4 Sep 2026
Abstract
Cross-condition bearing fault diagnosis suffers from severe performance degradation due to domain shift across different operating conditions, especially when only a few labeled target-domain samples are available. To address this challenge, this paper proposes a progressive attention-guided two-stage transfer learning framework for few-shot
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Cross-condition bearing fault diagnosis suffers from severe performance degradation due to domain shift across different operating conditions, especially when only a few labeled target-domain samples are available. To address this challenge, this paper proposes a progressive attention-guided two-stage transfer learning framework for few-shot bearing fault diagnosis across different fixed operating points. First, the raw time-domain vibration signals are fused with frequency-domain representations extracted by short-time Fourier transform (STFT) to enhance fault feature representation. Then, a progressive attention-guided feature learning strategy is developed by integrating dual efficient channel attention (ECA) modules into a deep one-dimensional convolutional neural network (1D-CNN), enabling the network to adaptively emphasize fault-sensitive features while suppressing redundant information. Subsequently, a two-stage transfer learning strategy is designed, consisting of transferable feature learning from the source domain and few-shot adaptation to the target domain. During target-domain adaptation, key feature extraction layers are frozen, and a sample-balanced optimization mechanism is introduced to alleviate the dominance of source-domain samples during joint training. Experimental results on the Case Western Reserve University (CWRU) bearing dataset demonstrate that the proposed method achieves an average accuracy of 99.96% across three cross-condition transfer tasks. Furthermore, experiments conducted on a self-built shaft system dataset show that the proposed method achieves an average accuracy of 87.11% under three representative transfer scenarios. The results verify that the proposed framework effectively mitigates domain shift and enables accurate bearing fault diagnosis with limited labeled target-domain samples.
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(This article belongs to the Section Machines Testing and Maintenance)
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Open AccessArticle
Deep Learning-Based Anomaly Detection in Electric Motor Production Using Mel-Spectrogram Representations and a Hybrid Neural Network
by
Jernej Mlinarič, Boštjan Pregelj and Gregor Dolanc
Machines 2026, 14(9), 1009; https://doi.org/10.3390/machines14091009 (registering DOI) - 4 Sep 2026
Abstract
End-of-Line (EoL) quality inspection of electric motors requires reliable detection of manufacturing faults before products leave the production line. However, conventional supervised deep learning approaches depend on a sufficient number of labeled instances of faulty motors, which are scarce in high-quality manufacturing environments.
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End-of-Line (EoL) quality inspection of electric motors requires reliable detection of manufacturing faults before products leave the production line. However, conventional supervised deep learning approaches depend on a sufficient number of labeled instances of faulty motors, which are scarce in high-quality manufacturing environments. This limits their applicability to newly introduced products and previously unobserved fault types. This paper presents an unsupervised deep learning framework for anomaly detection in motor acoustic and vibration signals, designed for EoL quality inspection in manufacturing. The proposed method leverages Mel-frequency spectrograms (MFSs) as input features and employs a hybrid neural network combining a convolutional neural network (CNN) and bidirectional gated recurrent units (BiGRUs), effectively capturing both local spectral patterns and temporal dependencies. The method is evaluated on real industrial production data from over 2400 motors, of which approximately 4.3% were faulty, reflecting the highly imbalanced nature of high-quality manufacturing. The model was trained exclusively on healthy motor data and therefore does not require labeled faulty samples during training. Experimental results demonstrate strong discrimination between healthy and faulty motors, indicating that the proposed approach is suitable for automated EoL quality inspection in manufacturing environments where labeled faulty data are scarce.
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(This article belongs to the Special Issue Process Monitoring and Quality Optimization in Manufacturing Engineering)
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Open AccessReview
Driveline Efficiency in Electric Vehicles: A Review of Architectures and Gearbox Power Losses
by
Adolfo Senatore and Attila Csobán
Machines 2026, 14(9), 1008; https://doi.org/10.3390/machines14091008 (registering DOI) - 4 Sep 2026
Abstract
Optimizing transmission efficiency is critical for advancing electric vehicle (EV) technology. This review paper covers advanced driveline schemes for electric cars and electric heavy vehicles through a selection and analysis of articles published over the past decade, focusing on passenger and commercial electric
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Optimizing transmission efficiency is critical for advancing electric vehicle (EV) technology. This review paper covers advanced driveline schemes for electric cars and electric heavy vehicles through a selection and analysis of articles published over the past decade, focusing on passenger and commercial electric vehicle drivetrains, transmission efficiency modeling, gear optimization, and tribological and NVH outcomes. The selected sources are grouped into analytical themes to map current academic and industrial developments in transmission topologies, specifically comparing single-speed reduction units with two-speed and multi-speed configurations. A comparative summary is discussed to consolidate the characteristics, complexity, efficiency impact, and typical applications of the various gearbox types. The review article is complemented by an examination of loss mechanisms through the lens of international tribological research. Key focal points include mechanical power losses, gear and bearing friction, and the trade-offs associated with low-viscosity fluids for electric vehicles to provide a comprehensive support resource for researchers and designers in the field of transmissions for EVs. Future development trajectories are delivered regarding the increase in efficiency and specific challenges of EV gearboxes.
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(This article belongs to the Special Issue Advanced Intelligent Control for Cyber–Physical Systems)
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Interface-DOF-Reduced Craig–Bampton Substructuring for Efficient Dynamic Characteristic Prediction of Shaft Generator Systems
by
Jimin Seo and Seunghun Baek
Machines 2026, 14(9), 1007; https://doi.org/10.3390/machines14091007 - 3 Sep 2026
Abstract
This study applies a Craig–Bampton (CB) substructure reduction procedure to the prediction of natural frequency changes upon rotor replacement in a shaft generator shafting system and quantifies its accuracy and computational cost for that configuration. Because the shafting conditions are determined by the
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This study applies a Craig–Bampton (CB) substructure reduction procedure to the prediction of natural frequency changes upon rotor replacement in a shaft generator shafting system and quantifies its accuracy and computational cost for that configuration. Because the shafting conditions are determined by the customer, performing full finite element analysis or experimental modal analysis (EMA) for every design change is impractical. The shafting system is divided into shaft and rotor substructures, and CB reduced-order models are constructed independently for each substructure. A three-stage verification framework—FE analysis versus EMA, the CB reduced-order model versus FE analysis, and the CB reduced-order model versus EMA—is employed to separate FE model error from CB reduction error. The CB pipeline reproduced the bending modes of the assembly with a maximum error of 0.26% against the parent finite element model, with a subspace MAC of 1.0000 for every mode group below 720 Hz, while reducing the model from 192,678 to 5379 degrees of freedom. With 20% of the interface degrees of freedom retained, the first three bending modes are predicted within 0.60%, and the reduced model comprises 1173 degrees of freedom, a reduction of 99.39%. The first bending mode error varies monotonically with the retention level, and the errors of all three bending modes remain bounded below 0.60% down to 20% retention. For the annular interface examined, the error-retention relation, therefore, provides a quantitative basis for selecting a retention level against a stated error tolerance, but its extension to other interface topologies, mesh densities, and mode ranges remains to be established.
Full article
(This article belongs to the Special Issue Advanced Planning, Perception, and Control for Autonomous Vehicles and Robots)
Open AccessReview
Generative AI vs. Traditional Machine Learning for Energy-Efficient and Circular Manufacturing in Industry 5.0: A Life-Cycle-Based Framework for Sustainable Manufacturing
by
Izabela Rojek and Dariusz Mikołajewski
Machines 2026, 14(9), 1006; https://doi.org/10.3390/machines14091006 - 3 Sep 2026
Abstract
This study proposes an integrated Industry 5.0 framework that compares and combines generative artificial intelligence (GenAI) with traditional machine learning (ML) to enhance the sustainability of manufacturing systems. This framework supports energy-efficient process optimisation, waste minimisation, material recycling and environmentally friendly production planning
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This study proposes an integrated Industry 5.0 framework that compares and combines generative artificial intelligence (GenAI) with traditional machine learning (ML) to enhance the sustainability of manufacturing systems. This framework supports energy-efficient process optimisation, waste minimisation, material recycling and environmentally friendly production planning through data-driven decision-making. GenAI is more commonly used to generate sustainable process configurations and alternative eco-design solutions, whilst traditional ML models predict energy consumption, emissions and material losses in real time. It is proposed that a life cycle assessment (LCA) be carried out to estimate the environmental impact at all stages of production. Preliminary analyses indicate significant potential for reducing resource consumption, improving the circular economy, and supporting more sustainable and resilient manufacturing ecosystems and supply chains.
Full article
(This article belongs to the Special Issue Sustainable Manufacturing and Green Processing Methods, 2nd Edition)
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Open AccessArticle
Machine Learning-Based Prediction of Machinability Responses in Meso-Scale Ultrasonic Vibration-Assisted End Milling (UVAEM) of Inconel 718 Superalloy: A Comparative Study of GPR, SVR, Random Forest, and Ridge Regression
by
Danyal Zahid, Muhammad Salman Khan, Muhammad Rizwan Ul Haq and Mushtaq Khan
Machines 2026, 14(9), 1005; https://doi.org/10.3390/machines14091005 - 3 Sep 2026
Abstract
Meso-scale ultrasonic vibration-assisted end milling (UVAEM) is an advanced manufacturing technique. UVAEM of Inconel 718 superalloy presents significant modeling challenges due to complex thermo-mechanical interactions and meso-scale size effects. This study introduces a machine learning framework that systematically compares Gaussian Process Regression (GPR),
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Meso-scale ultrasonic vibration-assisted end milling (UVAEM) is an advanced manufacturing technique. UVAEM of Inconel 718 superalloy presents significant modeling challenges due to complex thermo-mechanical interactions and meso-scale size effects. This study introduces a machine learning framework that systematically compares Gaussian Process Regression (GPR), Support Vector Regression (SVR), Random Forest (RF), and Ridge Regression for predicting cutting force, tool wear, and surface roughness, thereby contributing to sustainable manufacturing. Experiments followed a Taguchi L16 orthogonal array with two replicates (n = 32), varying cutting speed (10–40 m/min), feed rate (0.01–0.025 mm/tooth), depth of cut (0.10–0.25 mm), vibration amplitude (0–9 μm), and tool coating (TiAlN, TiSiN, nACo, Uncoated). Tool coating was one-hot encoded, and strict leave-one-out cross-validation (LOOCV) with within-fold standardization ensured unbiased generalization metrics. Following nested hyperparameter tuning, SVR achieved the highest accuracy (R2 = 0.9552, 0.9473, 0.9294), marginally outperforming GPR (R2 = 0.9543, 0.9420, 0.9290). Ridge regression was competitive for tool wear (R2 = 0.9235), while random forest ranked last due to limited ensemble diversity at n = 32. Pearson correlation identified depth of cut as the dominant driver of cutting force and surface roughness (r = 0.767, 0.759), cutting speed as the primary driver of tool wear (r = 0.663), and vibration amplitude as consistently beneficial across all three responses. SVR and GPR are recommended as reliable surrogate models for process optimization in UVAEM of Inconel 718.
Full article
(This article belongs to the Special Issue Advanced Manufacturing Processes and Technologies: Trends and Innovations)
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Open AccessArticle
RDIC-MSCKF: Risk–Direction-Decoupled and Innovation-Calibrated MSCKF for Stereo Visual-Inertial Odometry
by
Zhidu Huang, Wei Huang, Jianna Ouyang, Haibin Hu, Shen Dong and Bo Dong
Machines 2026, 14(9), 1004; https://doi.org/10.3390/machines14091004 - 3 Sep 2026
Abstract
Filtering-based stereo visual-inertial odometry often assigns fixed or uniformly scaled covariance to tracks accepted by the front-end, although accepted observations can differ in terms of tracking reliability, local directional identifiability, and agreement with the batch-level innovation model. This issue is important for UAV-based
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Filtering-based stereo visual-inertial odometry often assigns fixed or uniformly scaled covariance to tracks accepted by the front-end, although accepted observations can differ in terms of tracking reliability, local directional identifiability, and agreement with the batch-level innovation model. This issue is important for UAV-based multisensor inspection platforms, where pose estimates support autonomous flight, measurement registration, repeatable survey lines, and multisensor data fusion. This paper presents RDIC-MSCKF, a Risk–Direction-Decoupled and Innovation-Calibrated MSCKF, where innovation calibration denotes bounded empirical scaling within the visual update. RDIC-MSCKF maps robust tracking diagnostics to a bounded standard-deviation multiplier and uses a robust local photometric information matrix to add penalty-only anisotropic covariance along weak image directions. The resulting observation covariance is preserved during MSCKF landmark elimination through full projected-covariance whitening. In parallel with feature-block innovation gating, bounded minimum measurement-noise inflation is estimated from the pre-gate innovation population and applied through a Kalman-equivalent modal update. On ten evaluated EuRoC MAV sequences, RDIC-MSCKF obtains lower ATE RMSE than the S-MSCKF baseline on nine sequences; averaged over five runs per sequence, the mean RMSE decreases from 0.1869 m to 0.1236 m, corresponding to a 33.8% reduction, and the sequence-mean P90 error decreases by 32.0%. Runtime profiling on five representative EuRoC sequences gives a 26.32 ms mean and 37.33 ms P95 per-frame processing time for RDIC-MSCKF, with 0.01% of profiled frames above the 50 ms reference. Outdoor UAV flights with RTK reference trajectories further demonstrate lower Sim(2)-aligned horizontal RMSE than S-MSCKF on all three evaluated flights.
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(This article belongs to the Special Issue Intelligent Robots and Mechatronic Systems for Complex Outdoor Infrastructure: Perception, Fusion, SLAM and Robust Control)
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Open AccessArticle
Geometric Parameter Effects on Lift Enhancement of a Circulation-Control Airfoil for Aerodynamically Alleviated Marine Vehicles Under Fixed Ground Effect
by
Yajun Shi, Yani Song, Xiaoxu Du, Guang Pan and Dong Song
Machines 2026, 14(9), 1003; https://doi.org/10.3390/machines14091003 - 3 Sep 2026
Abstract
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Circulation control is an efficient active flow control technique that enhances aerodynamic lift by injecting a tangential jet near the trailing edge, altering the circulation around the airfoil. This study investigates the influence of three key geometric parameters—Coanda surface radius, slot height, and
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Circulation control is an efficient active flow control technique that enhances aerodynamic lift by injecting a tangential jet near the trailing edge, altering the circulation around the airfoil. This study investigates the influence of three key geometric parameters—Coanda surface radius, slot height, and jet angle—on the aerodynamic performance of a NACA4309-based circulation-control airfoil (NACA4309-CCA) operating under a fixed ground clearance (hg/c = 0.14), representative of high-speed aerodynamically alleviated marine vehicles. Numerical simulations are performed using the Reynolds-averaged Navier–Stokes equations with the SST k-ω turbulence model. The results show that increasing r/c enhances lift up to a limit (r/c ≈ 0.017), beyond which flow separation occurs, reducing lift. For a fixed momentum coefficient (=0.01), an optimal h/c = 0.0007 balances jet momentum and mass flow, yielding the highest lift. The jet angle study reveals that the maximum lift (CL = 2.684) is achieved at θ ≈ 10°, but θ = 0° (CL = 2.581) is recommended for practical implementation due to simpler geometry and stable attachment, with only a 3.84% loss in lift relative to the maximum. The findings provide comparative numerical trends for the design of circulation-control systems on aerodynamically alleviated marine vehicles under the investigated conditions.
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Open AccessArticle
Effects of Tire Dynamics on Vehicle Safety: A Simulation-Driven Comparison of New and Service-Aged Tires Under Variable Inflation Pressures and Loads
by
Mykola Karpenko, Paulius Skačkauskas, Gabrielius Mejeras, Maksym Delembovskyi and Michał Stosiak
Machines 2026, 14(9), 1002; https://doi.org/10.3390/machines14091002 - 3 Sep 2026
Abstract
The research paper presents a simulation-driven investigation into the effects of tire dynamics on vehicle safety by examining the influence of inflation pressure and load variability in both new and service-aged pneumatic tires. The proposed methodology combines finite element analysis with experimental measurements
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The research paper presents a simulation-driven investigation into the effects of tire dynamics on vehicle safety by examining the influence of inflation pressure and load variability in both new and service-aged pneumatic tires. The proposed methodology combines finite element analysis with experimental measurements to accurately characterize tire behaviour while avoiding the complexity associated with detailed composite material modelling. Pre-experimental data are employed to calibrate and validate the numerical model, enabling realistic prediction of tire dynamic responses under various operating conditions. The developed approach facilitates the assessment of tire performance across a range of inflation pressures and vertical loads, allowing a comparative evaluation of new and service-aged tires in terms of deformation characteristics and dynamic stability. Furthermore, the numerical simulations investigate how pressure loss and load variability affect tire blowout conditions and braking performance, both of which are relevant to overall vehicle safety. The results demonstrate that tire aging, together with improper inflation pressure and increased loading, significantly influences tire dynamic behaviour and vehicle stability, leading to measurable changes in braking distance and road-holding capability. The proposed simulation-driven framework provides an efficient and reliable tool for evaluating service-aged tire performance under realistic service conditions and supports the development of safer tire designs and maintenance strategies aimed at improving road traffic safety.
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(This article belongs to the Special Issue Recent Analysis and Research in the Field of Vehicle Traffic Safety, 2nd Edition)
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A Cross-Validated Reassessment of Regression and Machine-Learning Models for AISI 1045 End Milling
by
Prakash Marimuthu, Jana Petru and Thenarasu Mohanavelu
Machines 2026, 14(9), 1001; https://doi.org/10.3390/machines14091001 - 2 Sep 2026
Abstract
Machining-induced residual stress, cutting force, and temperature govern the fatigue life, dimensional stability, and surface integrity of milled components, yet predictive models for these responses are still routinely validated only in-sample, concealing overfitting on small, single-laboratory datasets. This study re-examines a published AISI
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Machining-induced residual stress, cutting force, and temperature govern the fatigue life, dimensional stability, and surface integrity of milled components, yet predictive models for these responses are still routinely validated only in-sample, concealing overfitting on small, single-laboratory datasets. This study re-examines a published AISI 1045 end-milling dataset (N = 24, combining one-factor-at-a-time and Taguchi L9 trials) using six regression paradigms: Multiple Linear Regression (MLR), random forest, gradient boosting, Support Vector Regression (SVR), Gaussian process regression (GPR), and a shallow neural network (ANN)—under leave-one-out cross-validation (LOO-CV). The previously reported in-sample R2 of 0.84 (from a smaller n = 9 subset) was substantially higher than the LOO-CV R2 of 0.167 obtained here on the full dataset; although this gap cannot be attributed to cross-validation alone, it shows a substantial in-sample/out-of-sample performance gap. SVR gave the strongest, bootstrap- and nested-CV-confirmed cross-validated residual-stress prediction (R2 = 0.575); its apparent force advantage (R2 = 0.558) was statistically indistinguishable from GPR and did not survive nested tuning, so it is reported cautiously. GPR was narrowly best for temperature (R2 = 0.492); the ANN and SVR underperformed the linear baseline there, though nested tuning traced this largely to a fixed hyperparameter rather than the kernel method itself. Random forest permutation importance identified feed rate as the dominant residual-stress predictor, consistent with the original ANOVA. The contribution is a cross-validated, multi-paradigm reassessment with explicit uncertainty and sensitivity analysis, together with a candidate low-cost screening surrogate for AISI 1045 process planning—not a replacement for XRD or FE—and a broader caution to match model complexity to sample size.
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(This article belongs to the Topic Digital Manufacturing Technology)
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Open AccessArticle
Chebyshev Surrogate Modeling and Robust Multi-Objective Optimization of Dynamic Transmission Error in Harmonic Drives Under Parameter Uncertainty
by
Qiushi Hu, Haofei Zhang, Yanfei Wang and Kelong Zhao
Machines 2026, 14(9), 1000; https://doi.org/10.3390/machines14091000 - 2 Sep 2026
Abstract
To address the influence of multi-source probabilistic uncertain parameters on the dynamic transmission error (DTE) of harmonic drives, this paper proposes a robust DTE modeling and multi-objective optimization method. First, a Chebyshev surrogate model is constructed by integrating the measured static transmission error
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To address the influence of multi-source probabilistic uncertain parameters on the dynamic transmission error (DTE) of harmonic drives, this paper proposes a robust DTE modeling and multi-objective optimization method. First, a Chebyshev surrogate model is constructed by integrating the measured static transmission error (STE) probability model, system dynamic equations, and identified nominal parameters. Prototype validations show a prediction mean absolute percentage error (MAPE) of 8.14% and a mean absolute error (MAE) of 7.761″. Meanwhile, compared to the original dynamic equations, the surrogate model reduces the single-evaluation time from 0.147 s to 0.000003 s (a 49,000-fold acceleration), effectively overcoming the efficiency bottleneck of numerical integration in dynamic response evaluation. Secondly, to achieve the collaborative optimization of system transmission accuracy and anti-disturbance robustness, a Chebyshev–AMP–MOPSO algorithm integrating a diversity entropy state-driven weight and a pyramid-hierarchical dual-track search strategy is proposed, which improves upon the issues of local convergence and uneven solution set distribution in the classical MOPSO and NSGA-II algorithms. On this basis, parameter optimization under three decision preferences was completed. The accuracy-first scheme reduces the DTE mean by 3.67%, the robustness-first scheme reduces the standard deviation by 9.36%, and the balanced scheme improves both. Finally, comparative tests on five prototypes show the actual dynamic parameters’ deviation (Di) relative to the theoretical optimal configuration exhibits a consistent corresponding trend with measured DTE means. Prototypes with the minimum (Di = 0.365) and maximum (Di = 0.474) deviations yield the lowest and highest measured means, respectively, matching theoretical optimization expectations.
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(This article belongs to the Special Issue Advances in Precision Mechanical Transmission Systems: Design, Dynamics, and Applications)
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Open AccessReview
Progress and Perspectives on Thermal Design Methods of Machine Tools: A Critical Review
by
Qiang Li and Haolin Li
Machines 2026, 14(9), 999; https://doi.org/10.3390/machines14090999 - 2 Sep 2026
Abstract
Thermal error remains a primary bottleneck restricting the machining accuracy of precision CNC machine tools. As a proactive, source-level countermeasure, thermal design has become increasingly critical for achieving the accuracy targets required by advanced manufacturing sectors. This paper presents a critical review of
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Thermal error remains a primary bottleneck restricting the machining accuracy of precision CNC machine tools. As a proactive, source-level countermeasure, thermal design has become increasingly critical for achieving the accuracy targets required by advanced manufacturing sectors. This paper presents a critical review of machine-level thermal design methodologies, categorizing existing approaches into three principal technical routes: temperature control, material improvement, and structural optimization. For each route, we critically examine the underlying theoretical foundations, representative implementations, and reported effectiveness, with particular emphasis on the persistent gap between academic research and industrial practice. Our analysis reveals that the majority of existing thermal design efforts focus on reducing the magnitude of thermal deformation, while paying limited attention to its spatial distribution. This imbalance, we argue, limits the potential synergies between thermal design and thermal compensation, as spatially complex deformation fields are intrinsically more difficult to model and correct than regular patterns. To address this gap, we propose a paradigm shift from “amplitude minimization” to “deformation mode regularization”: actively shaping the spatial distribution and temporal evolution of thermal deformation to render it more predictable, repeatable, linear, and readily compensable. The review concludes by outlining a forward-looking framework that integrates thermal deformation mode regularization, digital twin-based thermal state perception, and design-for-compensation principles, offering both theoretical foundations and practical guidelines for thermal design in high-precision machine tools.
Full article
(This article belongs to the Section Machine Design and Theory)
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Open AccessArticle
Data-Driven Model Predictive Control for Speed Temperature Drift Compensation of Rotary Traveling Wave Ultrasonic Motors
by
Xue Qi, Haozhe Ding, Meiting Zhao, Lina Zhang, Jiacheng Lv, Pengying Xu, Zhihui Liu and Lei Fan
Machines 2026, 14(9), 998; https://doi.org/10.3390/machines14090998 - 1 Sep 2026
Abstract
This paper proposes a data-driven model predictive control (MPC) framework for high-precision speed control of rotary traveling wave ultrasonic motors (RTWUSMs) under temperature drift. To address the strong nonlinearity and time-varying thermal characteristics of RTWUSMs, a Koopman–convolutional neural network–long short-term memory (Koopman–CNN–LSTM) prediction
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This paper proposes a data-driven model predictive control (MPC) framework for high-precision speed control of rotary traveling wave ultrasonic motors (RTWUSMs) under temperature drift. To address the strong nonlinearity and time-varying thermal characteristics of RTWUSMs, a Koopman–convolutional neural network–long short-term memory (Koopman–CNN–LSTM) prediction model with radial basis function (RBF) observable features is constructed. The model maps the nonlinear electromechanical coupling and friction-driven dynamics of the motor into a linear invariant subspace, achieving high prediction accuracy while maintaining low computational complexity. On this basis, a data-driven MPC scheme is designed, which eliminates the dependence on accurate analytical plant models and compensates for thermal-induced speed drift through online driving frequency adjustment. The experimental results show that under 900 s of continuous operation, the proposed scheme achieves a relative steady-state speed error of 0.37%, which is significantly better than typical temperature drift compensation methods. This scheme can also provide stable tracking performance under load torques of 0.5 N·m and 1.0 N·m, providing a practical solution for the long-term stable speed regulation of RTWUSM in precision drive applications.
Full article
(This article belongs to the Section Electrical Machines and Drives)
Open AccessArticle
A Risk-Aware Safety Framework for UWB-Localized Quadrotors: Geometry-Aware Error Compensation and Belief-Space Collision Avoidance
by
Yufei Yang, Junjie Cao and Yaohua Shen
Machines 2026, 14(9), 997; https://doi.org/10.3390/machines14090997 - 1 Sep 2026
Abstract
Ultra-wideband (UWB) positioning provides cost-effective localization for quadrotors in global navigation satellite system (GNSS)-denied environments, but geometry-dependent, heavy-tailed errors challenge state estimation and safety-critical control. This paper presents a risk-aware framework linking geometry-aware error quantification with belief-space collision avoidance under a fixed four-anchor
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Ultra-wideband (UWB) positioning provides cost-effective localization for quadrotors in global navigation satellite system (GNSS)-denied environments, but geometry-dependent, heavy-tailed errors challenge state estimation and safety-critical control. This paper presents a risk-aware framework linking geometry-aware error quantification with belief-space collision avoidance under a fixed four-anchor UWB configuration. Specifically, horizontal dilution of precision (HDOP) and nearest-anchor distance are used as spatial features in a Student’s-t process regression (STPR) model to predict UWB positioning errors and quantify the associated uncertainty. The compensated UWB measurements are then fused with inertial data through a Kalman filter to obtain a Gaussian belief state. A belief control barrier function (BCBF) maps ellipsoidal collision regions to a unit sphere, approximates them using tangent half-spaces, and is embedded in nonlinear model predictive control (NMPC). In outdoor flight experiments, the positioning RMSE is reduced to 0.071 m by the proposed STPR-KF method, compared with 0.299 m for raw UWB and 0.292 m for conventional KF. Feasible risk-aware obstacle avoidance and adjustable safety clearance are further demonstrated through numerical simulations. The feasibility of linking geometry-aware UWB error characterization with belief-space safety constraints for UWB-localized quadrotor navigation is therefore indicated.
Full article
(This article belongs to the Special Issue Multi-Spacecraft Coordination and Intelligent Aircraft Autonomous Control)
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Open AccessArticle
Surrogate-Assisted Coordinated Optimization of Mechanism Parameters and Motion Trajectories for a Variable-Link-Length Robotic Manipulator
by
Jingdong Qu, Jinfei Liu, Hua Huang, Ming Chen and Yifan Zhu
Machines 2026, 14(9), 996; https://doi.org/10.3390/machines14090996 - 1 Sep 2026
Abstract
Fixed-link manipulators have limited adaptability to changes in task locations and obstacle layouts, while sequential mechanism design and trajectory planning restrict their coordinated performance. This study proposes a surrogate-assisted bilevel optimization method for a four-degree-of-freedom PRRR variable-link-length manipulator. The three link lengths are
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Fixed-link manipulators have limited adaptability to changes in task locations and obstacle layouts, while sequential mechanism design and trajectory planning restrict their coordinated performance. This study proposes a surrogate-assisted bilevel optimization method for a four-degree-of-freedom PRRR variable-link-length manipulator. The three link lengths are treated as outer-layer mechanism variables, whereas B-spline control points and trajectory duration are optimized in the inner layer subject to joint, motion, endpoint, and collision constraints. An objective-decoupled surrogate predicts trajectory duration, path length, jerk cost, and minimum clearance, and is embedded in an adaptive reference vector-guided multi-operator multi-objective beluga whale optimization algorithm. The framework combines inverse-kinematics prescreening, surrogate evaluation, high-fidelity trajectory re-optimization, dense constraint verification, and preference-based decision-making. Blind-test, ablation, and high-fidelity verification results show that the method efficiently identifies high-quality, physically feasible mechanism–trajectory candidates. Factorial analysis of an obstacle-constrained handling task indicates that trajectory optimization primarily improves smoothness and clearance, whereas mechanism adaptation redistributes joint motion and further enhances overall trajectory quality. Physical experiments demonstrate the executability of the selected mechanism–trajectory solutions without observed cylinder collision or joint-limit activation in the tested trials. These results demonstrate that the proposed framework provides an effective approach to task-adaptive mechanism–trajectory co-optimization in constrained environments.
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(This article belongs to the Section Machine Design and Theory)
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Open AccessArticle
Static–Dynamic Performance Improvement of LV500 Horizontal CNC Lathe via Bed–Saddle Collaborative Optimization and Laser Interferometer Validation
by
Lei Qin, Changyuan Sun, Luji Wu, Jinyu Geng, Longjie Li and Baozhou Shi
Machines 2026, 14(9), 995; https://doi.org/10.3390/machines14090995 - 1 Sep 2026
Abstract
To improve the static and dynamic stiffness of the LV500 horizontal CNC lathe and reduce machining errors, this study focuses on integrated structural simulation, bed–saddle collaborative optimization, and standardized precision evaluation. A whole-machine structural model is established in SolidWorks, and static, modal, and
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To improve the static and dynamic stiffness of the LV500 horizontal CNC lathe and reduce machining errors, this study focuses on integrated structural simulation, bed–saddle collaborative optimization, and standardized precision evaluation. A whole-machine structural model is established in SolidWorks, and static, modal, and harmonic response co-simulations are performed in ANSYS, followed by multi-objective optimization of the two key weak components. MATLAB is used to process the dynamic simulation data. Based on a Renishaw XL-80 laser interferometer and the accompanying CARTO software, axis accuracy detection and measurement uncertainty evaluation are performed, forming a reproducible full-process engineering analysis system applicable to similar machine tools. The simulation results show that the maximum structural deformation after optimization is 0.016 mm, and the first-order natural frequency increases from 86.99 Hz to 92.55 Hz. Experimental tests demonstrate positioning accuracies of 3.0 μm (U = 0.38 μm, k = 2) for the X-axis and 3.3 μm (U = 0.45 μm, k = 2) for the Z-axis. Owing to the enhanced static–dynamic stiffness after structural optimization, the workpiece machining error can be stably controlled within 0.01 mm. In this study, a unified whole-machine model enables continuous static and dynamic analysis. The coupling stiffness of assembled components is considered in the modeling process, and the static and dynamic performance of the whole machine is improved through dual-component collaborative optimization. The inclusion of metrological-level uncertainty evaluation enhances the reliability of the experimental data. The proposed method provides a standardized engineering scheme for the static and dynamic performance optimization of similar horizontal CNC lathes.
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(This article belongs to the Special Issue Advanced Design, Manufacturing, and Applications of Precision Machine Tools)
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Open AccessArticle
Research on the Characteristics of an Electro-Mechanical Direct Drive System for Heavy-Duty Manipulators
by
Zepeng Li, Yuxin Yang, Long Quan, Xiangyu Wang, Yunxiao Hao and Lei Ge
Machines 2026, 14(9), 994; https://doi.org/10.3390/machines14090994 - 1 Sep 2026
Abstract
Heavy-duty manipulators are generally driven by hydraulic systems. The control valves in these systems cause substantial throttling losses, resulting in low overall system energy efficiency. To address this problem, this study proposes an electro-mechanical direct drive system (EMDDS) based on an electro-mechanical actuator
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Heavy-duty manipulators are generally driven by hydraulic systems. The control valves in these systems cause substantial throttling losses, resulting in low overall system energy efficiency. To address this problem, this study proposes an electro-mechanical direct drive system (EMDDS) based on an electro-mechanical actuator (EMA) for energy-efficient actuation of heavy-duty manipulators. A supercapacitor energy-management strategy combining current feedforward with voltage feedback is also developed to recover and reuse the gravitational potential energy of the manipulator efficiently. System parameters were selected for the boom of a 6 t excavator, after which a multidisciplinary co-simulation model was established and an experimental prototype was built for validation. The simulation and experimental results show that the proposed system incurs no throttling loss during operation and achieves high drive efficiency. The system recovers and reuses gravitational potential energy with an efficiency of up to 46.4%. Compared with the load-sensing (LS) system, the EMDDS reduces energy consumption over one boom raising and lowering cycle from 42.25 kJ to 16.86 kJ, a reduction of 60.1%. The analysis and experiments provide a basis for developing energy-efficient electric drives and potential-energy recovery technologies for heavy-duty manipulators.
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(This article belongs to the Section Electromechanical Energy Conversion Systems)
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Open AccessArticle
Study on the Influence of Structural Parameters on the Performance of an Internal Feedback Hydrostatic Bearing
by
Xiaochen Song, Xinzhou Wang, Xiaosen Lv, Shuguo Zheng, Mingcheng Zhai, Rencheng Zheng and Jianbin Liu
Machines 2026, 14(9), 993; https://doi.org/10.3390/machines14090993 - 1 Sep 2026
Abstract
Hydrostatic spindles are key components in high-precision grinding machines. In this paper, an internal feedback radial–thrust combined hydrostatic bearing is proposed to improve the load-carrying performance of conventional hydrostatic spindles. The throttling structure is integrated into the bearing inner surface, and an internal
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Hydrostatic spindles are key components in high-precision grinding machines. In this paper, an internal feedback radial–thrust combined hydrostatic bearing is proposed to improve the load-carrying performance of conventional hydrostatic spindles. The throttling structure is integrated into the bearing inner surface, and an internal feedback throttling configuration is developed to enhance pressure regulation and reduce nterference between oil pockets. Based on fluid lubrication theory and the hydraulic resistance network method, a theoretical model of the combined bearing is established, and a systematic parameter design method is developed. The governing equations of flow, pressure, load-carrying capacity, and stiffness are derived for performance prediction and structural design. Furthermore, finite element simulations are conducted to investigate the effects of key parameters. The simulation results show that, at a supply pressure of 4 MPa, the radial stiffness reaches 2559.3 N/μm and the axial stiffness reaches 423.1 N/μm. The simulation results are compared with the theoretical predictions, showing good agreement and providing numerical verification of the proposed theoretical model.
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(This article belongs to the Section Machine Design and Theory)
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Open AccessArticle
Point Cloud-Based Measurement of Switch Rail-to-Sleeper Longitudinal Displacement with Multi-Bolt Reference
by
Cuijun Dong, Qingzhou Mao, Shihao Zhang, Zongming Zhang, Yixuan Shi, Wei Hu, Jizhong Zheng and Dehui Lai
Machines 2026, 14(9), 992; https://doi.org/10.3390/machines14090992 - 1 Sep 2026
Abstract
The longitudinal displacement of the switch rail relative to the sleeper is a critical defect affecting the safety of railway switching operations, as the sleeper serves as the mounting base for the switch machine. Existing measurement methods that rely on the stock rail
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The longitudinal displacement of the switch rail relative to the sleeper is a critical defect affecting the safety of railway switching operations, as the sleeper serves as the mounting base for the switch machine. Existing measurement methods that rely on the stock rail as a reference are susceptible to reference drift and cannot directly capture the displacement of the switch rail relative to its actuation base. This paper proposes a measurement method for the longitudinal displacement of the switch rail relative to the sleeper using the centers of multiple anchor bolts as reference benchmarks. Based on the fact that both the anchor bolts and the switch machine are fixed to the sleeper, the displacement of the switch rail relative to the bolt centers is equivalent to its displacement relative to the switch machine. Multiple anchor bolt centers on the sleeper are used to establish a stable reference frame. A self-developed mobile measurement device is employed to acquire three-dimensional structured light point clouds of the switch rail area. The coordinates of multiple anchor bolt centers are extracted through hexagon fitting. Abnormal coordinates are eliminated via joint adjustment of the multi-bolt centers, establishing a stable spatial reference frame that enables precise measurement of the longitudinal displacement of the switch rail relative to the sleeper. Field experiments on an operational No. 18 turnout successfully extracted the switch rail tip position and a longitudinal misalignment of −2 mm between the two switch rails. In simulation experiments, a creep displacement of 10 mm and multiple gross errors were artificially introduced; after three iterations, the final measured creep was 9.65 mm, with a deviation of only 0.35 mm, verifying the method’s accuracy and robustness under adverse conditions. Additional experiments on a No. 12 turnout with straight and curved switching states demonstrated that the standard deviation of the longitudinal spacing measurements between bolt centers was 1.17 mm under track switching conditions, confirming the method’s stability in the presence of switch machine movement. The proposed method achieves non-contact, automated measurement of the switch-rail-to-sleeper relative displacement, providing a practical technical pathway for turnout condition monitoring.
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(This article belongs to the Special Issue Innovations in Railway Vehicle System: Design, Monitoring and Maintenance)
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Open AccessArticle
Geometric Improvement of High-Pressure Bifurcated Pipes for Enhanced Flow and Energy Characteristics Under Hydraulic Short-Circuit Operation
by
Shang Zhu, Ming Xia, Shizhe Liu, Fangxu Ji, Jing Yang and Zhengwei Wang
Machines 2026, 14(9), 991; https://doi.org/10.3390/machines14090991 - 1 Sep 2026
Abstract
Hydraulic short-circuit (HSC) operation is an important approach to enhancing the operational flexibility of pumped-storage power plants (PSPPs). However, under this new operating mode, the flow characteristics in the bifurcated pipe deteriorate significantly, posing a threat to the efficiency of the piping system
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Hydraulic short-circuit (HSC) operation is an important approach to enhancing the operational flexibility of pumped-storage power plants (PSPPs). However, under this new operating mode, the flow characteristics in the bifurcated pipe deteriorate significantly, posing a threat to the efficiency of the piping system and potentially affecting the inflow conditions for the turbine. In this study, six improved bifurcated pipe models were designed, and their internal flows under pumping, generating, and HSC modes were numerically simulated. Entropy production theory and vortex identification method were employed for flow field analysis. The results show that local modifications confined to the bifurcation are insufficient to simultaneously improve energy characteristics across different modes. In contrast, the bypass pipe enables early flow diversion, weakening the original high-dissipation regions while introducing controllable additional losses. M6 achieves an average energy loss reduction of 47.85% in the mid-to-high flow split ratio range (FSR > 0.3). A strong correlation is observed between vortex suppression and energy loss reduction: the bypass pipe substantially shortens the main vortex length at the inlet section of the generating branch, while simultaneously inducing new shear vortices at the junction; adjustment of its installation position is expected to further shorten their extension, thereby ensuring the normal operation of the turbine. This study provides a new technical pathway for extending the operating range of HSC operation and contributes to enhancing the grid-regulation capability of PSPPs.
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(This article belongs to the Special Issue Health Condition Monitoring, Intelligent Operation and Maintenance of Wind Turbines)
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