High power density and energy efficiency are critical for achieving agile locomotion and sustained operation in miniature flapping-wing robots. Here, a pneumatic linear reciprocating oscillator is developed as an actuation solution. The oscillator leverages the Bernoulli principle to establish a positive feedback mechanism through coordinated interactions among a soft membrane, a piston, and the airflow. Experimental validation demonstrates that the oscillator-based flapping-wing robot can generate a lift of 0.43 N to enable take-off and sustained flight in unstructured environments. The minimal oscillation unit exhibits maximum input and output specific power of 710.5 W/kg and 220.7 W/kg, respectively, with peak energy conversion efficiency reaching 41.9% . This design represents a paradigm shift from conventional electromechanical systems, offering two fundamental advancements: (i) simplified robotic drive architectures through an oscillator-based mechanism, and (ii) a foundation for hybrid energy systems that reduce reliance on electricity.

To enhance both shock resistance and vibration isolation performance, this paper proposes a voice coil motor (VCM)-based active vibration isolator with axial-radial stiffness compensation. The compensator enables broadband isolation and impact resistance, while the skyhook-damping-inspired integral force feedback (IFF) control algorithm allows the lightweight isolator to simultaneously mitigate low-frequency vibrations and high-frequency shocks. Comprehensive experimental validation—including random excitation, frequency sweeps, bump tests, and impact tests—demonstrates effective vibration attenuation across 1–200 Hz, with 7 g bump shock tolerance and 40 kg drop-weight impact resistance, achieving a remarkable shock transmissibility of 0.0015.

In aerospace applications, unwanted vibrations pose a significant challenge, particularly in complex vibration environments that contain both low-frequency vibrations and narrowband disturbances. However, the frequencies of the narrowband disturbances are unknown, and the low-frequency vibrations are close to the measurement limits of inertial sensors. Therefore, a hybrid control algorithm is proposed, which combines filtered-x least mean square (FxLMS) and enhanced active disturbance rejection control (EADRC). Specifically, the normalized frequency estimator is first employed to obtain a preliminary estimate of the disturbance frequency and the Kalman filter (KF) is then utilized to smooth fluctuations, thereby addressing the frequency mismatch issue in the FxLMS. Furthermore, by introducing the concept of zero-pole compensation into the extended state observer, correction in the feedback loop enables active disturbance rejection control (ADRC) to achieve more precise control. Experimental results confirm that the proposed algorithm significantly suppresses low-frequency vibrations and four narrowband disturbances.

The efficient utilization of low-grade waste heat, a vast yet underutilized energy resource, is critical for advancing sustainable energy technologies and enabling self-powered systems. In this study, we propose and experimentally demonstrate a structurally innovative micro-scale organic Rankine cycle (mORC) energy harvester operating near-room-temperature (<= 60 degrees C), achieving three-stage heat-mechanical-electrical conversion. This architecture eliminates the conventional separation of the evaporator, expander, condenser, and working-fluid pump by integrating these modules into a single custom-fabricated glass component charged with HCFC-141b (1,1-dichloro-1-fluoroethane) as the working fluid. Vaporization-induced pressure difference drive the liquid column, causing the component to flip and initiate torsional oscillations, which in turn power an axial-flux permanent-magnet generator to produce electricity. Beyond structural innovation, we introduce a nonlinear coupled dynamic model that integrates the thermal, mechanical, and electromagnetic domains to predict system performance. By modeling the system as a weakly nonlinear Duffing oscillator, approximate analytical solutions are obtained using the method of multiple time scales. Furthermore, impedance matching through COMSOL Multiphysics (R) electromechanical simulations predicts an energy output of 13.08 mJ per cycle at an optimal load of similar to 900 Omega with an electromechanical efficiency of 72.1 %, while experiments confirm voltage consistency within 19 %. The high degree of structural integration together with the dedicated multiphysics modeling underscores the originality of this study, while its simplicity, modularity, and efficient low-temperature operation demonstrate the application value of harnessing near-room-temperature low-grade thermal energy to power self-sustaining devices.

For aerospace field, vibration suppression is critical for flexible structures and precision equipment. To resolve the stiffness-mass conflict, this paper develops a five-magnet magnetic spring-beam structure with positive and negative stiffness in parallel (PNSP-FMSS). The system comprises a beam, four symmetrically distance-adjustable magnets and one moving magnet in mutual attraction. Theoretical modeling analyzes magnet parameters' effects on magnetic force and stiffness. Results show that the system exhibits negative/positive stiffness or bistable behavior, by adjusting horizontal distances (L, R) and widths (B, Bo) of magnets. Focusing on the beam's first-order vibration mode exclusively, the displacement transmissibility is derived using harmonic balance method, reveals how excitation amplitude, damping ratio, and magnet distance influence vibration performance. Experimental validation confirms the theoretical results that adjusting magnet distance, stiffness is significantly decreased from 218 N m-1 to 20 N m-1, resonant frequency is reduced from 17 Hz to 5.27 Hz, resonant peak is reduced from 28.5 dB to 16.8 dB, and vibration amplitude is reduced from 0.01 g to 1.52 & times;10-3 g. When L + R approximate to B + Bo, the system demonstrates experimentally confirmed bistable behavior with tunable stable points. The proposed PNSP-FMSS provides foundational research for enhancing low-frequency vibration isolation or energy harvesting.

As a typical variable-section structure, the flexible wing has attracted considerable attention in the aerospace field due to its advantages in load-bearing capacity, stiffness distribution and mass optimization. However, the variation in geometric and physical properties along the structural length significantly increases the complexity of dynamic modeling, consequently leading to pronounced changes in the mode shapes. To address this challenge, the paper establishes linear dynamic equations of flexible wings based on the Euler-Bernoulli beam theory and Lagrange's principle. Building on this foundation, a dimensionless variable transformation is applied to normal ize the geometric and physical parameters in the governing equations, thereby simplifying the coupling among different variables. Subsequently, a special function expansion method is employed to formalize the mode shapes as a linear combination of Bessel and Meijer-G functions, ensuring the satisfaction of boundary conditions and ef fectively capturing the influence of cross-sectional variations on modal characteristics. On this basis, an improved mode shape function for variable cross-section cantilever beams is developed. This method enables rapid determi nation of natural frequencies and mode shape functions without iterative procedures or approximate truncation, significantly improving computational efficiency while maintaining high accuracy, thus making it well-suited for efficient dynamic analysis of complex structures. The results indicate that the natural frequencies and mode shape curves obtained by this method are in good agreement with the ANSYS results, the existing literature, and the experimental tests, thereby verifying the rationality and effectiveness of the proposed method.

This study presents a novel dual-mode pneumatic gravity compensation device, which comprises a pneumatic cylinder, a rope-pulley system, and a gear mechanism. It employs a rope-pulley mechanism that allows the compensation force to depend solely on the load mass and remain independent of any joint rotation angle, thereby eliminating the need for complex control algorithms. The device operates in two modes-active and passive-adapting to varying operational conditions. In active mode, dynamic gravity compensation is achieved by regulating air pressure through an empirically calibrated constant pressure offset. In passive mode, a sealed vacuum chamber is created on one side of the cylinder, allowing atmospheric pressure alone to generate the required compensation force for a given load, without any external energy supply during operation. A prototype was constructed to validate the aforementioned principle. The results show that the device can maintain joint torque near zero, allowing the load to remain in a "0-gravity" suspended state. To demonstrate improved energy efficiency and performance in robotic systems, this study applies the gravity compensation device to a robotic arm and a floating backpack. The device enables the robotic arm to support loads beyond the motor's torque limit while reducing energy consumption in the joints. In addition, it offers power-off self-holding capabilities and simplifies the drag-teaching process. In the floating backpack application, the device effectively mitigates shoulder impact during exercise, reducing peak shoulder pressure by 59.7%.

Air springs play a vital role in vehicle suspension systems. This paper investigates their dynamic and static characteristics through experimental and simulation analysis, examining the effects of inflation pressure (0.2–0.6 MPa) and wall thickness (3.5–5.5 mm). A fluid-structure interaction model was established using ABAQUS. Optimisation was achieved through response surface methodology combined with a genetic algorithm, resulting in a 28.6% reduction in transmission rate at 5 Hz and a 23.7% improvement in dynamic stiffness curve flatness. The reliability of the optimised design was validated through 500,000 cycles of load testing.

In spacecraft, precision equipment is severely affected by vibration excitation generated by rotor imbalance in the Control Moment Gyroscope (CMG), which is the core actuator for low-frequency attitude adjustments. Active vibration isolation (AVI) has been extensively studied by many scholars. However, traditional actuators suffer from contact friction and response delay; feedback and feedforward control alone have performance bottlenecks. As a result, the low-frequency tracking and mid-frequency isolation performance of CMG AVI are severely limited. Therefore, this paper proposes a magnetic levitation vibration isolation system (MLVIS) with composite control to optimize the tracking and AVI performance. In terms of structure, a magnetic levitation actuator is used to eliminate slow response and friction hysteresis. For the control algorithm, a composite strategy integrating integral force feedback and filtered-x recursive least squares is adopted. Through mutual compensation between the two control methods, this composite strategy mitigates the inherent time delay of feedback control and the instability of feedforward control. Experimental results show that the tracking error in the low-frequency band is 2.71% and 11.67% under single- and dual-frequency excitation, respectively, while 91.86% attenuation of the natural-frequency vibration amplitude is achieved in the mid-frequency band. These results verify the tracking and AVI performance of the MLVIS.

Objective To observe the effects of neuromuscular exercise(NEMEX)training combined with semiconductor la-ser therapy on patients with knee osteoarthritis(KOA).Methods A total of 60 patients with knee osteoarthritis who were treated in the Rehabilitation Medicine Department of the First Affiliated Hospital of Bengbu Medical University from August 2023 to March 2024 were selected and randomly divided into control group and observation group using a random number table method,with 30 cases in each group.The control group received conventional rehabilitation treatments,including joint mobilization and medium-fre-quency electrical stimulation,along with semiconductor laser therapy at a wavelength of 808 nm and an irradiation power of 400-800 mW,continuous irradiation,20 minutes per session,once daily,five times weekly for a total of four weeks.The observation group received NEMEX training in addition,including 10 minutes of warm-up exercise;40 minutes of NEMEX training(stability,posture orientation,lower limb muscle strength training,and functional exercises);and a 10-minute cool-down exercise(involving gait adjustment and stretching),once daily,five times weekly for four weeks.Before and after treatment,Visual Analog Scale(VAS)was used to assess the degree of pain;Western Ontario and McMaster University Osteoarthritis Index(WOMAC)and Lysholm Knee Score were used to assess knee joint function;Berg Balance Scale(BBS)was used to assess balance function;the surface electromy-ography system was used to record the root mean square(RMS)of surface electromyography(sEMG)signals of the quadriceps and hamstring muscles during the squatting and standing of the affected knee joint,and the co-contraction rate(CR)was calculated;the adverse events during the treatment process of the two groups were compared.Results(1)VAS,WOMAC,Lysholm,and BBS scores:compared with those before treatment,VAS and WOMAC scores in both groups after treatment decreased significantly(P<0.05),while Lysholm and BBS scores increased significantly,and the differences were statistically significant(P<0.05).Compared with the control group,VAS and WOMAC scores in the observation group after treatment decreased significantly(P<0.05),while Lysholm and BBS scores were significantly higher,and the differences were statistically significant(P<0.05).(2)CR:compared with that before treatment,CR in the observation group after treatment decreased statistically,and the difference was statistically sig-nificant(P<0.05),while there was no statistically significant difference in CR in the control group after treatment(P>0.05).Com-pared with the control group,CR in the observation group after treatment was lower,and the differences was statistically significant(P<0.05).(3)Safety:no adverse events were observed in either group during treatment,and patients exhibited good compliance,in-dicating a high level of safety.Conclusion NEMEX training combined with semiconductor laser therapy can effectively improve pain,knee joint function,balance function,and muscle coordination and control around the knee joint of patients with KOA,which is worthy of clinical application.

The bistable vibration isolator (BVI) has attracted the interest in the field of nonlinear vibration isolation. The tunable symmetric and asymmetric BVIs can be generated through nonlinear magnetic repulsion forces and linear structures. However, the intricate structures of magnet-based BVI systems currently available are responsible for their limited versatility and flexibility, ultimately leading to a deficiency in general theory regarding vibration isolation. Notably, the deficiency includes inadequate understanding of the impact of structural asymmetry on isolation performance, highlighting the need for further research. This paper proposes a magnet-based BVI and the axial nonlinear magnetic force analysis model utilizing the filament method. By utilizing the harmonic balance method, analytical formulas for the displacement transmissibility of both symmetric and asymmetric magnet-based BVIs (SBVIs and ABVIs) are derived. The influence of different parameters on the bistable shape, the snap-though behavior and the vibration isolation performance has been revealed. An experimental platform is established for verification and analysis. Theoretical and experimental analysis show that there is a contradiction between the isolation bandwidth and allowable excitation amplitude, and compared to the symmetric bistable structures, the asymmetric bistable shape involves more structural parameters. Nonetheless, the ABVI exhibits better adjustability and adaptivity for different excitation amplitudes, which leads to the unique advantages for vibration isolation. Additionally, the ABVI exhibits superior flexibility, enabling the dynamic performance of the system to be tailored to compensate for potential linear stiffness mismatches through installation modifications.

To enhance the low-frequency vibration suppression capability of cantilever beams, a magnetically tunable piezoelectric cantilever beam structure (MTPCBS) is proposed in this paper. A magnetic spring with negative stiffness (NSMS) is fixed at the free end of a cantilever beam, forming a quasi-zero-stiffness structure. Meanwhile, a macro-fiber composite (MFC) patch is bonded near the root of the beam to implement active skyhook damping control for active vibration control. A theoretical model of the cantilever beam, NSMS, and MFC is established, and the displacement transmissibility of the MTPCBS is derived. The influences of the magnet distance of the NSMS and the control gain of the controller are investigated via simulation. Experimental results indicate that compared to the single beam, the effective vibration isolation frequency of the proposed MTPCBS shifts from 15.3 Hz to 4.6 Hz. When subjected to random vibration excitation ranging from 1 to 80 Hz, the root mean square (RMS) value of vibration decreases from 0.03 g to 1.77 × 10−3 g, with the vibration attenuation rate improving from −50% to 91%. The proposed MTPCBS and active–passive vibration control method for cantilever beams significantly enhances low-frequency vibration suppression capabilities, providing a feasible strategy for achieving broadband vibration suppression.

To achieve high-load vibration isolation at low frequencies, this paper proposes an adjustable negative stiffness quasi-zero stiffness (QZS) system based on Euler beam buckling. By altering the number and height of sliders, the negative stiffness of the isolation system can be adjusted to suit varying operating conditions. The dynamics of the QZS system are discussed using the Euler beam mechanical model. Its load-bearing capacity and vibration damping performance were verified through universal testing machines and random excitation experiments. Experimental results demonstrate that the proposed QZS isolator achieves a minimum natural frequency of 2.5 Hz while supporting a load capacity of $\mathbf{6 0 ~ k g}$, with vibration attenuation reaching -30 dB at $\mathbf{5 0 ~ H z}$.

The strategy of linear compensation for nonlinear stiffness to flexibly adjust the degree of stiffness is widely applied in the field of vibration reduction but remains relatively uncommon in the domain of energy harvesting. This article explores the utilization of a piezoelectric stack energy harvester that compensates for nonlinear stiffness through linear stiffness [compensated-nonlinearity piezoelectric energy harvester (CPEH)], thereby effecting a broad-spectrum shift in the energy-harvesting frequency band. A two-degree-of-freedom theoretical model is formulated to anticipate the bandwidth shift phenomenon, subsequently validated using specific experimental data. The investigation delves into the influence of system parameters on the output performance of the CPEH, substantiating the impact of linear compensation on bandwidth translation. For instance, employing a linear stiffness of 0.33 N/mm to compensate for the 256-mT magnetic spring in the 4.8-9-Hz operating bandwidth shifts to 13.7-18.9 Hz. Through automotive application experiments, the feasibility of energy harvesting in practical scenarios has been validated, achieving a theoretical voltage of 4.87 V under idle low gear conditions. Additionally, temperature testing experiments have confirmed the potential for real-time power supply. A design guideline is presented for optimizing energy-harvesting performance through parameter analysis.

Marine intelligent sensing equipment is essential for collecting marine resources, and its development has increasingly advanced. However, increasing battery pollution necessitates an urgent search for alternative energy sources. This study proposes a novel compact magnetoelectric-electromagnetic hybrid energy harvester (MEEM-HEH) to enhance the low voltage characteristics of traditional electromagnetic generators (EMGs). To adapt to the low frequency characteristics of waves (< 2 Hz), a quasi-zero stiffness mechanism is designed to address the ultra-low frequency limitations of parallel magnet mechanisms in the hybrid generator. Additionally, a coupled negative stiffness mechanism is developed to increase the energy density of the generator. The effectiveness of the MEEM-HEH is verified experimentally. At excitation frequencies ranging from 0.5 to 1.5 Hz, the magnetoelectric generator (MEG) achieves an output power density of 28.67 W m(-3), whereas the EMG reaches 450.19 W m(-3) at 50 Omega. The maximum output power of the MEEM-HEH is 18.05 mW. The effectiveness is also tested in a real marine environment. This work offers a potential solution for hybrid generators that target ultra-low frequency wave energy.

In this Letter, we propose fractal-based piezoelectric energy harvesters (PEHs) for broadband energy scavenging. The introduction of fractal topology into transducers significantly alleviates the inherent limitation of a narrow working bandwidth in commonly used cantilever PEHs. We conduct a finite element analysis and experiments to exploit the performance of fractal cantilever PEHs with different iteration times. Our findings reveal that the higher-order fractal structures generate an increased number of eigenfrequencies as well as modal patterns within a certain range of working bandwidth (i.e., <50 Hz). Experimental results indicate that the efficient energy harvesting bandwidth of the fractal PEHs of iterative levels 1 and 2 is 2.05 and 2.15 times, respectively, larger than the conventional PEHs (i.e., level 0). In addition, the harvested voltage and power of fractal PEHs can be enhanced by attaching a proof mass to compensate for the energy loss in producing iterations. This method exhibits superiority over capturing energy in low-frequency vibration environments, such as wave energy and human movement energy.

This paper utilizes a multi-magnet configuration to form nonlinear magnetic negative stiffness and to construct a multi-magnet coupled bistable piezoelectric energy harvester (MC-BPEH). By adjusting the distance between adjustable magnets and fixed magnets and increasing the number of adjustable magnets, the MC-BPEH achieves high output voltage and power and wide bandwidth for energy collection. The effect of magnetic distances and quantities on the magnetic force, nonlinear magnetic negative stiffness, potential energy well, and magnetic flux density of the system is scrutinized. The dynamic responses and energy harvesting performance of the MC-BPEH are characterized by frequency-sweep and fixed-frequency experiments. The maximum power output and power density of the MC-BPEH with four adjustable magnets is 12 mW and 1.17 mW/cm3 3 at the optimal resistance of 300 k Omega, approximately 78 % and 72 % higher than the counterparts with two adjustable magnets under 0.5g excitation level, respectively. The device is also demonstrated to light up 93 LEDs. These results show that the introduction of multiple magnets into a piezoelectric energy harvester brings the redistribution of magnetic flux density and improves the energy harvesting performance of the proposed MC-BPEH. The optimized method proposed in this study is beneficial for developing high-performance and broadband energy harvesters for low- frequency and large-amplitude application scenarios.

Simpler structure, better adaptability to variable loads, and wider linear stable region have always been pursued by nonlinear quasi zero stiffness (QZS) isolator. Inspired by the balancing and stabilizing effect of the leg and wing in the take-off and landing of birds, this paper proposes a novel bio-inspired QZS vibration isolator (BI-QZSVI). The BI-QZSVI is composed of two primary components: the legged negative stiffness structure, which comprises a two-link mechanism and a set of oblique springs, and a pair of vertical springs that imitate wings. A static model is established based on the virtual work principle, the nonlinear dynamic model is then constructed using Lagrangian equations, and an analytical solution is derived through implementation of the harmonic balance method. An experimental platform is established to verify the effectiveness of the theoretical results. The results reveal that the proposed isolator outperforms existing typical isolators by offering a larger quasi-zero stiffness region, as evidenced by the two proposed range and linearity indexes. The unique structure effectively tackles geometric nonlinearity to establish a linear relationship between the load and stiffness. Notably, the negative stiffness of the isolator exhibits exceptional linearity throughout the entire stroke, ensuring a broad stability region even under high excitation levels. Furthermore, the isolator demonstrates remarkable efficacy in reducing vibrations with frequencies exceeding 3 Hz. Overall, the proposed isolator is an efficient low-frequency isolator with simple structure, strong adaptability, and wide linear range.

Underwater adsorption is the key function of underwater robot operation, in order to complete the underwater wall fixation, underwater object capture and other operations. The underwater adhesion mechanism based on vibration control has the advantage of using the liquid viscosity to pull the object surface at a certain distance and control the adhesion effect by frequency. A disc of 0.5mm thickness and 100mm diameter can accommodate the adhesion of different rough planes at 50Hz, a curved cup can be pulled and grabbed at a distance of 7mm at 100Hz, when 0.5mm thick silicone spacers were attached to the bottom of the drive disc, the loading mass of the disc adhesion was increased from 76g to 1056g at a vibration frequency of 150Hz. In short, the underwater vibration adhesion of rigid body is a new adhesion mechanism, which is expected to provide new ideas and applications in the field of underwater grasping.

Abstract The skyhook control technology is widely used in active vibration isolation and has proven effective. However, the absolute speed sensor used in the skyhook control technology is easily affected by external factors and may be easily damaged. There are few application scenarios for the skyhook control technology. To overcome this limitation, a brand-new approach is proposed for the design of an isolator that involves a voice coil motor (VCM) and an accelerometer. First of all, the proposed structure is introduced, and the dynamic model is established to achieve an analytical solution. Then, an integral acceleration feedback (IAF) algorithm is introduced and simulations are carried out. Finally, a prototype is constructed to verify its vibration isolation performance. From the experimental results, it can be concluded that the proposed active vibration control system (AVCS) can effectively reduce the peak value near the natural frequency, with a peak value reduction of 14.77 dB. Compared with the simulation results, the peak change rate at 12.5 Hz is 3.92%. AVCS with IAF can be applied to more application scenarios with a similar isolation effect to skyhook control technology.