Search Results (9,275)

The valve serves as the actuating component within the valve mechanism. Under braking conditions, the valve is prone to swaying, which significantly compromises the reliability and service life of the engine. Hence, this paper focuses on researching the deviation characteristics of engine valves. Through a three-dimensional numerical simulation, we analyze the flow field around the valve in the instantaneous states. Our research has revealed that the flow surrounding the valve exhibits a complex multi-vortex structure. Specifically, we observed the evolution pattern of the asymmetric multi-vortex flow along the valve axis within three distinct zones: the asymmetry increase zone, the symmetric development zone, and the asymmetry re-increase zone. The asymmetry increase zone and the asymmetry re-increase zone are located in the curved section and the cylindrical body of the valve, respectively. These zones are the primary contributors to the lateral force acting on the valve, which in turn induces deviation. Based on these analysis results, further research must be conducted on the dynamic characteristics of the flow during valve movement and on optimizing the valve structure through flow control strategies. Full article

Polydimethylsiloxane (PDMS) films doped with graphene nanoplatelets (GNP) with an embossed surface-relief grating were investigated as photothermal actuated sensors. The films were initially characterized using controlled environmental heating where the wavelength of a diffracted white-light probe beam measured at a fixed angle increased monotonically with temperature due to thermal expansion of the grating. An asymmetric double sigmoidal function tracked the shift in peak diffraction wavelength. The observed thermal response is consistent with the thermal expansion of a freestanding PDMS composite film. When a continuous-wave (CW) laser was incident on the film, intensity-dependent photothermal expansion caused a transient deformation in the grating. The photomechanical behavior of the grating, tracked by the diffracted probe beam with a miniature spectrometer, was then shown to act as a laser power meter. These results demonstrate that photomechanical materials can be used as add-ons to existing optical spectroscopy devices for power-sensing applications. Full article

Acoustic microactuation technology has emerged as an effective approach for fabrication of micro- and nanoscale objects, enabling precise processing and shaping control of microscale materials by efficiently transmitting ultrasonic vibration energy and focusing energy locally. In this work, the proposed platform is regarded as an acoustically driven micromachine, in which ultrasonic excitation acts as the primary microactuation mechanism. Micrometer-scale copper wires are widely used in microelectronics and precision manufacturing. However, their small dimensions and low rigidity make fixation and forming particularly challenging. To achieve controllable forming of fine copper wires, this study introduces an ultrasonic vibration energy-focusing principle and investigates an ultrasonic post-processing method tailored for such materials, with the aim of enhancing processing stability and forming accuracy. An ultrasonic processing experimental platform for copper wires was established, and multiple micro-tool designs—including glass fiber, 304 stainless steel wire with support, and elastic hard 304 stainless steel—were evaluated. Single-point and continuous processing experiments were conducted by varying micro-tool materials and support configurations, and the influence of feed speed on processing width and depth was systematically analyzed. The results indicate that a hard 304 stainless steel micro-tool supported by a hard plastic ring provides the best overall performance. Feed speed has a significant effect on processing depth, with a maximum average depth of approximately 0.95 μm achieved at a feed speed of 1 mm/min. These findings demonstrate the feasibility of ultrasonic processing for the effective forming of fine copper wires and confirm that appropriate micro-tool design and feed speed are critical for achieving stable and reliable processing results. The proposed system employs an ultrasonically actuated micro-tool to perform post-processing on micrometer-scale copper wires. The ultrasonic vibration serves as a microactuation mechanism that enhances local deformation and material response during micro-machining. Full article

The behavior of shape memory alloy (SMA) materials is more complex than linear isotropic metals because of their nonlinear thermomechanical coupling. When an SMA material is mechanically stressed or joule-heated, phase transformation happens in the material, and accordingly some material properties dramatically change. In any loading or unloading scenario, the initial state of the material should be known because it significantly affects its behavior. Stress and strain alone are not enough to describe such materials. Temperature and martensitic fraction are also required to simulate SMA materials accurately. This paper presents a MATLAB application, called “SMA Simulator,” that was developed to simulate the nonlinear behavior of SMA wires under mechanical or thermal loads. This tool is very effective in helping users understand the shape memory and pseudoelastic effects in such smart materials, as it allows for plotting the loading path in the 3D stress–strain–temperature space while monitoring the evolution of the martensitic fraction. Any load–unload scenario can be studied, including multiple consecutive partial loading cycles. Since the application is not based on any numerical method that would require extensive meshing, the computational time is minimal, allowing users to perform more simulations and acquire results instantaneously. Full article

Active vibration control is crucial for mitigating harmful resonant vibrations in structures subjected to harmonic loads. While antiresonant (zero-placement) methods are effective for this purpose, existing state-feedback solutions require full state measurement, and output-feedback approaches often prioritize resonance assignment over direct harmonic cancellation. This work bridges this gap by proposing a novel systematic design for a proportional–derivative (PD) output-feedback controller to achieve antiresonance for second-order linear systems with a time delay in the actuators. The method first computes a homogeneous gain solution. It then leverages the parametrization of all antiresonant solutions as a constraint within a genetic algorithm optimization. The algorithm optimizes both the stability margin, characterized by an $M_s$-disk criterion, and the number of encirclements of the critical point $(-1,0)$ in the complex plane, as assessed by the Generalized Nyquist Stability Criterion. The proposed approach provides a practical, optimized output-feedback strategy for precise rejection of harmonic disturbances, as demonstrated through a collection of numerical examples from real-world applications. The results confirm the method’s effectiveness in synthesizing stabilizing controllers that enforce antiresonance while ensuring robust stability margins. Full article

The paper presents the results of numerical and experimental investigations of a novel low-profile piezoelectric inertial linear actuator designed for a high-payload application. The actuator structure is based on a rectangular piezoelectric bimorph plate with centrally located trapezoidal toothed rings. The actuator operates in the second longitudinal vibration mode of the plate, which is excited by a sawtooth electric signal. Trapezoidal teeth are used to transfer longitudinal vibrations of the plate to the slider and, this way, generate linear motion. The use of trapezoidal teeth reduces the stumbling effect at high preload forces and as a result increases the actuator’s ability to operate under high preload forces and drive higher payloads. Numerical simulations indicated that the actuator exhibits a resonance frequency of 68.49 kHz, with the trapezoidal tooth achieving a maximum displacement amplitude of 188.25 µm at a voltage of 200 V_p-p. Furthermore, numerical analysis revealed that the trapezoidal tooth deflection in the out-of-plane direction under an axial load of 25 N reached 2.07 nm/N, demonstrating structural stability under high preload conditions. The results of experimental investigations have shown that the actuator can provide up to 75.16 mm/s at a linear motion speed of 200 V_p-p and an output force of 18.88 N at the same excitation signal amplitude. In addition, the 15 N load actuator was indicated to achieve a linear motion accuracy of 11.5 µm per step. Full article

Unmanned spherical robots are autonomous mobile platforms with a fully enclosed spherical shell, providing high stability and strong adaptability to complex terrains. However, existing pendulum or flywheel spherical robots often suffer from limited maneuverability, whereas complex hybrid actuation schemes tend to compromise system stability. To address these issues, this study proposes an improved pendulum-driven spherical robot with a mechanically decoupled actuation design, integrating a pendulum system and a circular gear rack turning mechanism. This design enables smooth linear rolling as well as rapid in-place rotation, significantly enhancing maneuverability and motion flexibility on complex terrains. A dynamic model of the spherical robot is established to describe the decoupled actuation mechanism, and a fuzzy proportional–derivative (PD) control strategy is designed for rolling and steering control. Simulation and prototype experiments were conducted to evaluate trajectory tracking, steering response, and terrain adaptability. The results demonstrate that the proposed spherical robot achieves path following and in-place turning with robust mobility. Full article

This study proposes a tension-spring-based unidirectional rotational stiffness mechanism (TS-URM) and its implementation in a Unidirectional Series Elastic Actuator (USEA). Unlike conventional bidirectional rotary SEAs, the proposed design is structurally optimized for unidirectional torque transmission, improving deformation utilization efficiency in pulling-type applications. An analytical model was derived to establish the geometric relationship between spring elongation and rotational deformation, enabling explicit formulation of the torque–angle relationship. The influence of the installation angle on stiffness linearity was systematically analyzed, and a multilayer spring configuration was optimized to achieve a target rotational stiffness of approximately 42 Nm/rad. A preload adjustment mechanism was incorporated to eliminate nonlinear behavior in the initial operating region. Experimental results validated the analytical model and demonstrated stable unidirectional force control up to 130 N with steady-state errors within 1 N. The proposed mechanism provides predictable stiffness characteristics and an efficient structural solution for compact USEA systems. Full article

Linear ultrasonic motors (LUSMs) occupy an important position in the field of high-precision actuation due to their advantages of simple structure, high control accuracy and direct linear motion generation. This review first classifies LUSMs according to wave modes into traveling wave linear ultrasonic motors (TWLUSMs) and standing wave linear ultrasonic motors (SWLUSMs). Among them, TWLUSMs include the straight beam type and the annular beam type, while SWLUSMs consist of the single-foot type and the multi-foot type. In addition, the working principles of TWLUSMs and SWLUSMs are elaborated. The structural characteristics and performance parameters of different types of ultrasonic motors (USMs) are sorted out, and the analysis shows that SWLUSMs are significantly superior to TWLUSMs in terms of output speed and output force. This review summarizes the application status of LUSMs in fields such as biomedicine, deep-sea exploration, aerospace and precision manufacturing, and finally outlines the development trends of LUSMs from the aspects of miniaturization and lightweighting, extreme environment adaptability and intelligent upgrade. This review provides a comprehensive reference for the structural design, performance improvement and application expansion of LUSMs. Full article

The vibration signals of Electro-Hydrostatic Actuators (EHAs) exhibit strong non-linearity and non-stationarity, particularly under complex coupling mechanisms, making the extraction of intrinsic fault features computationally challenging. Conventional deep learning approaches often lack mathematical interpretability and struggle to decouple superimposed fault signatures from incomplete datasets. To address these issues, this paper proposes the Enhanced Continuous Wavelet Transform Capsule Network (ECWTCN), an intelligent decoupled diagnosis framework designed for multiscale signal analysis. The architecture integrates a wavelet-kernel convolution layer to extract physically interpretable time–frequency features across multiple scales, effectively capturing transient impulses associated with incipient faults. Furthermore, a novel maximized aggregation routing algorithm is introduced to optimize the dynamic routing process, enhancing global feature aggregation. A distinct advantage of the ECWTCN is its capability to generalize distinct fault patterns, enabling the identification of unseen compound faults by training exclusively on normal and single-fault samples. Comparative experiments show that the proposed method delivers strong multi-label classification performance under operating condition A, achieving a Subset Accuracy of 93.7% and a Label Ranking Average Precision of 0.998. Complexity analysis further confirms the method’s efficiency in terms of FLOPs and parameter size. This work presents a robust, lightweight, and mathematically interpretable solution for the analysis of complex signals in high-reliability equipment. Full article

Ionic polymer–metal composites consist of an ion-conducting polymer–gel membrane sandwiched between two flexible electrodes, representing a class of soft electroactive materials capable of large deformation under low voltage. The gel membrane, swollen with solvent, facilitates ion migration under an electric field, enabling actuation. Tailoring the interfacial architecture between the electrode and the polymer–gel membrane is pivotal for advancing high-performance IPMC actuators. This study presents a comparative investigation of three core–shell nanocomposite electrodes, fabricated via in situ polymerization, for IPMC applications. Among these, the polyaniline-coated multi-walled carbon nanotube composite exhibits a deliberately designed hierarchical structure, with a specific surface area of 32.345 m²·g⁻¹ and a conductive doped polyaniline shell, as confirmed through XPS analysis. This optimized interface enables superior charge storage and transport, endowing the corresponding electrode with a specific capacitance of 40.28 mF·cm⁻² at 100 mV·s⁻¹—3.2 times greater than that of conventional silver-based electrodes—along with a reduced sheet resistance. When integrated with a Nafion ion–gel membrane, the PANI@MWCNT electrode achieves a 67% increase in force density and a larger displacement output compared to standard devices, directly correlated with its enhanced electrical and electrochemical properties. This work highlights the critical role of core–shell interfacial engineering in governing electromechanical performance at the electrode–gel interface and offers a practical design strategy for developing high-performance, cost-effective IPMC actuators for soft robotics, flexible electronics, and related applications. Full article

The rapid development of Autonomous Underwater Vehicles (AUVs) has increased the demand for propulsion systems that balance thrust density, hydrodynamic efficiency, and acoustic discretion. This study presents a comprehensive numerical investigation of the performance of the Blue Robotics T500 thruster, embedded within the RAS-HA-X25 AUV’s internal conduit. Using transient Computational Fluid Dynamics (CFD) within the OpenFOAM framework, this research assesses the propulsive characteristics of the thruster across six distinct outlet geometries, including convergent jet nozzles and multi-lobed “daisy” configurations. To improve computational efficiency for parametric design, a calibrated actuator disc model was developed and validated against resolved-rotor simulations, revealing a 15% discrepancy attributed to tip leakage and hub vortex effects. Results show that at the operational advance ratio ($J=0.167$), the 60 mm convergent nozzle is the optimal configuration for maximising thrust, achieving a peak net thrust of 42 N. In contrast, the daisy-type lobed geometries, while causing a 50% reduction in absolute thrust compared to a standard cylindrical pipe, significantly homogenise the exit-plane velocity distribution and reduce swirl intensity. These findings indicate that lobed terminations provide a viable mechanism for reducing hydroacoustic signatures, offering a strategic “stealth” advantage for low-observable underwater platforms where acoustic discretion is prioritised over pure thrust density. This study establishes a robust methodology for optimising embedded propulsion modules in next-generation autonomous and hybrid underwater vehicles. Full article

A piezoelectric actuator (PEA) is a fundamental part of a high-precision motion system, yet its performance is critically constrained by inherent nonlinearities such as the velocity dead zone and hysteresis. To overcome these limitations and the associated time-varying dynamics, this study introduces a novel control framework for a dual-mode standing wave PEA. The framework integrates a Global Linearized Sparse Prediction (GLSP) model with an Adaptive Kalman Observer-based Model Predictive Control (AKOBMPC) strategy, specifically designed for velocity dead-zone compensation. The GLSP model employs Koopman operator theory to lift the complex, nonlinear electromechanical and contact dynamics into a linear invariant subspace. Incorporated with a deep learning-based structured pruning mechanism, the model achieves an effective balance between prediction accuracy and computational efficiency, facilitating real-time implementation. Leveraging this high-fidelity model, the AKOBMPC algorithm is developed to estimate unmeasurable disturbances and optimize the control sequence for precise velocity tracking. Experimental results demonstrate the GLSP model’s accurate prediction of system behavior under varying loads and excitation frequencies. The proposed controller effectively suppresses the velocity dead zone, achieving tracking errors within ±0.35 mm/s for a 40.00 mm/s trapezoidal reference and within ±0.50 mm/s for sinusoidal tracking. These results confirm the superior performance of the AKOBMPC scheme over conventional methods, offering a robust solution for high-precision velocity regulation in PEA system and contributing to the advancement of next-generation precision actuator. Full article

The FOCUS mission is an integrative project developed at the Universidad Nacional de San Martín (UNSAM), Argentina, featuring a constellation of small satellites equipped with X-band Synthetic Aperture Radar (SAR) sensors. Designed with autonomous orbit control, the mission enables Interferometric SAR (InSAR) applications for critical infrastructure monitoring, providing scalable and cost-effective global observation capabilities. This paper presents the modeling, design, and numerical evaluation of the Attitude and Orbit Determination and Control System (AODCS) for the FOCUS mission. The analysis incorporates realistic constraints, including actuator saturation, sensor noise, underactuation effects, and hardware limitations—specifically regarding magnetorquer magnetic moments, reaction wheel capacities, and propulsion unit impulse bounds. Utilizing the NASA 42 attitude and orbit simulator, numerical simulations were conducted to assess stability, pointing accuracy, and agile maneuver tracking through specialized guidance laws. The results confirm that the proposed AODCS architecture achieves stable, responsive performance and supports continuous orbit maintenance, ensuring adequate target acquisition per orbit. Additionally, the selection of star trackers allows achieving a secondary objective through the detection of Resident Space Objects. Full article

This paper investigates a finite-time prescribed performance control (PPC) problem for a class of nonlinear engineering systems subject to actuator input saturation. By introducing a performance transformation framework, the tracking error is constrained within predefined bounds with guaranteed finite-time convergence. To address the strict-feedback structure and input constraints simultaneously, a dynamic surface control (DSC) technique is employed to avoid the explosion of complexity. A novel saturation-compensated control law is constructed to ensure closed-loop stability without requiring the persistence of excitation or exact knowledge of system dynamics. Lyapunov-based analysis rigorously proves that all closed-loop signals are bounded and the prescribed performance is achieved within a finite time. The simulation results demonstrate the effectiveness of the proposed approach under actuator saturation, highlighting its applicability to constrained engineering process control systems. Full article