Polyimide (PI) based tribological composites are widely used in demanding engineering environments, where combined heat and humidity may significantly deteriorate their surface stability and wear resistance. In this work, TiO2 reinforced PI/carbon fiber (PI/CF) composites were prepared to investigate their tribological behavior under hygrothermal ageing conditions. Accelerated ageing experiments (90 degrees C, 95% RH) were performed to evaluate moisture absorption characteristics, thermal stability, surface chemical evolution, and tribological performance of the composites. The results indicate that the incorporation of TiO2 effectively suppresses moisture uptake and improves the stability of the load-bearing surface during sliding. Among the investigated compositions, the composite containing 5 wt% TiO2 exhibits the best tribological performance after ageing, with the wear rate reduced by 49.3% compared with the TiO2 free composite. Morphological observations reveal that a moderate TiO2 content promotes the formation of a mechanically stable sliding interface, whereas excessive TiO2 leads to particle agglomeration and surface damage. To further elucidate the underlying mechanisms, molecular dynamics simulations were conducted to analyze the structural evolution of aged PI systems with different TiO2 contents. The simulation results demonstrate that an intermediate TiO2 content reduces free volume, enhances cohesive energy density, and restricts polymer chain mobility, which contributes to improved resistance against hygrothermal degradation. The combined experimental and molecular dynamics analysis provides new insights into the tribological durability of PI based composites in harsh hygrothermal environments.

The stator design with one-end hinged rotation and variable rectangular cross-section endows the V-shaped linear ultrasonic motor (VLUSM) with the advantages of a high thrust-to-weight ratio and ease of precision integration. However, as the stator rotates about the hinge point, its centroid generates an additional effect induced by such rotational motion. Based on the established whole-machine dynamic model of the VLUSM, numerical simulation analysis is conducted in this study, which reveals the centroid motion effect on the dynamic variation characteristics of the drive foot trajectory and the regulatory mechanism of evolution process of the contact force. The periodic rotation of the stator centroid injects a fundamental frequency harmonic component into the displacement field, which gives rise to the harmonic superposition effect in the displacement trajectory. In addition, the mechanical coupling mechanism is dominated by centroid motion, enabling dynamic regulation of the contact force. Periodic migration and regular scaling of the driving foot trajectory are observed in experiments, which confirm the additional effect of centroid motion. The complex dynamic coupling relationship between stator and mover is explained indirectly by the influence of joint environmental parameters on mover motion, which provides reference for optimization of VLUSM structure and control.

For the conventional inertial piezoelectric actuator using a non-resonant drive method, the speed and driving force are limited by the fact that the piezoelectric ceramic stack can only be driven at low frequencies. A resonant inertial linear ultrasonic motor (RILUM) with a plate-type stator is proposed in this study. Only one triangular wave signal is used to simultaneously excite two bending vibrations of the stator with a frequency ratio of 1:2 to achieve asymmetric displacements on the drive end, which drives the motion of the mover. Then, the commercial software automatic dynamic incremental nonlinear analysis (ADINA) is adopted to verify the feasibility and analyze the dynamic characteristics. Finally, the prototype is fabricated and tested for vibration characteristics and output performance. The experimental results show that the maximum no-load speeds of the prototype are 64.3 and 64.64 mm/s for forward and backward motion, respectively; the resolutions are 18 nm; and the maximum loads are 5.5 N. This work can achieve excellent no-load speeds, loading capacities, and resolutions in both directions by using only one signal, and it provides a new idea for the design of the resonance inertial ultrasonic motor (IUSM).

Addressing the challenge of increased energy consumption in bistable electromagnets within the aerospace and automation sectors, this study explores the structural optimization of a novel bistable solenoid using the NSGA-II multi-objective optimization algorithm. To boost the amplification factor of the bridge mechanism and enhance the overall performance of the variable-air-gap bistable solenoid, the bridge micro-displacement amplification mechanism and the parameters of key solenoid components are optimized, as these are crucial to the solenoid’s function. Finite element simulations of the optimized bridge mechanism are conducted to assess whether the magnification characteristics and maximum principal stress meet the expected optimization outcomes. Furthermore, electromagnetic simulations of the electromagnet are carried out post-optimization to validate the results. The simulation findings indicate that the magnification of the bridge-type micro-displacement amplification mechanism, following genetic algorithm optimization, can reach a factor of 16.38. Additionally, the number of ampere turns required for state switching, while maintaining a holding force of 35.8 N in the bistable electromagnet optimized through the multi-objective optimization algorithm, is found to be 2100, aligning with the optimization predictions. The newly simulated bistable solenoid structure demonstrated an energy reduction efficiency of 36.4%. Based on the parameters derived from the optimization results, a bistable electromagnet mechanism is fabricated, and both the mechanism’s performance and the ampere turns required for state switching are experimentally validated. Ultimately, the mechanism achieves an energy consumption reduction efficiency of 30.69%, offering a novel perspective for future research in this field.

The conventional microstepping driving method suffers from significant periodic speed oscillations under ultra-low-speed conditions, which fail to meet the stringent demand for smooth operation of ultrasonic motors in semiconductor packaging. Most existing theories and simulations of ultrasonic motors adopt a macroscopic mechanical perspective; after extensive linearization and idealization, they can only provide preliminary mechanism analysis and fail to achieve precise quantitative computation. Moreover, they neglect critical factors such as the microstructure of contact surfaces, preload distribution, and vibration mode transmission, making it difficult to reflect the true characteristics of the motor—including strong nonlinearity, multiphysics coupling, and complex interface behavior—resulting in considerable discrepancies between theory and experiment. In this paper, a macro-micro multi-scale finite element model of a traveling-wave ultrasonic motor is established using ADINA and HyperMesh, fully accounting for the strong nonlinearity and multiphysics coupling effects. Based on the ultrasonic friction reduction theory and the beat traveling wave mechanism, the stator deformation, interface zoning characteristics, and torque output of the superimposed pulse driving method and the microstepping driving method are systematically compared. The simulated stator mode shapes are validated by laser scanning vibrometry experiments, and multiple speed tests ranging from 200 to 320 arcsec/s are conducted. Simulation results show that at a target speed of 900 arcsec/s, the superimposed pulse driving method reduces the speed fluctuation rate from 228% to 32%. Experimental results confirm that the speed fluctuation rate of the superimposed pulse driving method is consistently much lower than that of the microstepping driving method across the entire tested speed range. This study reveals the low-speed smooth operation mechanism of the superimposed pulse driving method, characterized by single-peak dominance and smooth alternation between the driving and braking zones, thereby fundamentally overcoming the inherent shortcomings of the traditional microstepping driving method. The proposed model can effectively replace costly direct interface measurements, providing a new method and reference for ultra-low-speed precision control of ultrasonic motors and for investigating the driving mechanisms of similar motors.

Accurate and efficient dynamic modeling is crucial for the stable operation and optimization of piezoelectric actuators. However, existing methods often face a trade-off between model accuracy and computational speed. To address the piezoelectric and contact/friction nonlinearities of the V-shaped piezoelectric actuator (VPEA), this paper proposes a hybrid physics-based and data-driven modeling approach. First, an electromechanical coupling physics-based model of the VPEA is established, encompassing key mechanisms such as stator vibration, stator-rotor contact, and rotor dynamics, to generate sufficient and accurate training data. Subsequently, a backpropagation neural network (BPNN) is constructed, and its initial weights and thresholds are optimized using the grey wolf optimizer (GWO), resulting in a GWO-BPNN prediction model. Experimental comparisons demonstrate the superior performance of this model in predicting output speed and input current, achieving coefficients of determination (R2) of 0.99 and 0.992, respectively. These results significantly outperform models based on random forest, support vector machine, and BPNN optimized by genetic algorithm (GA) or particle swarm optimization (PSO). Furthermore, the computational response time of the proposed model is reduced by over 99% compared to the physics-based model, with the GWO converging 16.7% faster than GA and PSO. Utilizing this model, the influence of key parameters-including excitation voltage, preload, and external load-on the operational characteristics of the VPEA is analyzed. By further integrating the PSO algorithm for operational parameter optimization, a maximum operational efficiency of 26.57% is achieved, and the high-efficiency operating zone is identified. The results confirm that the proposed hybrid modeling method offers both high prediction accuracy and high computational efficiency, providing an effective solution for performance analysis and operational optimization of nonlinear piezoelectric actuators.

ABSTRACT Polyimide (PI)‐based tribological composites containing carbon fiber (CF), molybdenum disulfide (MoS 2 ), and other solid lubricants have been extensively studied. However, the role of hexagonal boron nitride (h‐BN) in regulating interfacial interactions and wear mechanisms in PI/CF/MoS 2 systems remains insufficiently understood. In this study, the effects of h‐BN incorporation on the mechanical and tribological behaviors of PI/CF/MoS 2 composites were systematically investigated through experimental characterization combined with molecular dynamics (MD) simulations. The results revealed that h‐BN addition improved hardness while reducing tensile strength and ductility due to the enhanced interfacial restriction and increased stress concentration. The tribological performance exhibited a non‐monotonic dependence on h‐BN content, with the optimal performance achieved at 5 wt.% h‐BN. Scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS) analyses suggested that an appropriate h‐BN content facilitated the formation of a relatively continuous transfer film, whereas excessive h‐BN promoted filler agglomeration and interfacial degradation, leading to accelerated wear. Furthermore, MD simulations suggested that the reduced molecular mobility and fractional free volume at the optimal h‐BN content were consistent with enhanced interfacial stability. The combined experimental and simulation results provide qualitative insights into the role of h‐BN in regulating filler dispersion, interfacial interactions, and molecular chain dynamics. These findings establish a structure–property relationship for designing high‐performance multi‐filler PI‐based tribological composites.

Adhesive technology is crucial for the assembly and reliability of engineered systems, such as ultrasonic motors used in aerospace environments, where adhesives must maintain high shear strength and thermal stability. This study investigated the temperature-dependent properties of adhesive layers in ultrasonic motors using a combination of experimental testing and molecular dynamics (MD) simulations. Four adhesive systems were prepared using two epoxy resins-resorcinol diglycidyl ether (RDGE) and 4,4-diaminodiphenylmethane tetraglycidylamine (TGDOM)-and two curing agents-m-cyclohexanedimethylamine (HXDA) and polyetheramine (D230). The results showed that the RDGE-D230 system exhibited the highest adhesive strength and was therefore selected for further analysis. Shear tests were conducted on the stator-piezoelectric ceramic interface and the rotor-friction material interface within a temperature range of 220-380 K. The results show that the shear strength decreases significantly with increasing temperature. The shear strength at the stator-ceramic interface decreases from 5.26 MPa at 220 K to 0.9 MPa at 340 K, and the shear strength at the rotor-friction material decreases from 4.96 MPa at 220 K to 0.53 MPa at 340 K. Molecular dynamics simulations indicate that increasing temperature enhances molecular mobility in the adhesive layer, and the fracture mode changes from brittle fracture to ductile fracture, manifested as an increase in mean square displacement and radius of gyration (from 8 & Aring; to 10.5 & Aring;). Simultaneously, the interaction energy between the adhesive and the substrate decreases with increasing temperature. These results elucidate the molecular mechanism of temperaturedependent adhesion and provide guidance for adhesive selection in high-temperature applications.

Ba(Cu0.5W0.5)O3 (BCuW)-doped [(Ba0.85Ca0.15)1-xDyx](Zr0.1Ti0.9)O3 (BCZT-xDy, x = 0.001, 0.03) ceramics were prepared by conventional ceramic processing via low-temperature sintering technique. Rather pure perovskite structure and densified morphology with irregular nearly spherical-shape grains are achieved in all ceramics due to liquid-phase sintering. All BCuW-doped BCZT-xDy ceramics present apparent dielectric frequency dispersion and relaxor ferroelectric characteristic due to ion substitution and adding BCuW. The ceramics prepared at optimized sintering temperatures have rather large strain and small strain hysteresis, showing prospect application in piezoelectric high-precision actuators.

In this paper, the useful life prediction of traveling wave ultrasonic motors is taken as the research object to explore the estimation method of motor life and analyze the main mechanisms affecting the life of motors. The degradation pattern of motor performance is stochastic and nonlinear, and two modes of remaining useful life prediction models were established based on Wiener process theory. The parameters of the model were estimated based on Maximum Likelihood Estimation and multidimensional search optimization method. The performance of each degradation model was evaluated by introducing Akai Information Criterion and error evaluation method. Through the construction of an ultrasonic motor life test system and the life test, experimental data that can reflect the degradation of motor performance were obtained. The feasibility of the proposed method was verified using simulated signals and experimental datasets of motors. Compared with the existing methods of remaining useful life prediction, the modeling approach proposed has its uniqueness and superiority.

To solve the problem of high driving voltage of traditional traveling wave rotary ultrasonic motor (TRUM), a low-voltage traveling wave rotary ultrasonic motor is proposed by using a piezoelectric bimorph. First, the whole structure of the motor is proposed, the principle of low-voltage drive is revealed, and the arrangement of the piezoelectric bimorph is designed. Secondly, the finite element (FE) simulation of the stator and the whole machine is carried out to study the influence of different conditions on the output performance of the motor. Finally, a prototype is made and an experimental platform is built to verify the feasibility and correctness of the design. The research results indicate that this design retains the advantages of traditional structures while also possessing the advantages of low-voltage driving.

With the diversification and multifunctionality of space missions, micro-nano satellites need to carry more payloads in deep space orbits with harsh lighting conditions. Traditional built-in batteries and fixed deployable solar wings offer limited energy, making it difficult to meet these demands. Although solar wing drive mechanisms powered by stepper motors and harmonic reducers improve power output, their large size, weight, and complexity render them unsuitable for micro-nano satellites. This paper presents a solar array drive assembly driven by an ultrasonic motor, designed for micro-nano satellites operating in the halo orbit at the Lagrange L2 point of the Earth-Moon system. This design addresses the need for miniaturization and lightweight construction while enhancing energy supply. Key components, including the yaw axis pointing mechanism, solar panel assembly, angular displacement detection, energy transmission system, and ultrasonic motor, are optimized for size and weight reduction. To identify the optimal energy-saving drive method, a dynamic model of the SADA system is established, and a novel low-power driving method for the ultrasonic motor-driven solar wing is proposed. A prototype with a volume of less than 0.5U and a mass under 0.2 kg was fabricated. Experimental results show that the output torque of the ultrasonic motor exceeds 0.0581 N m, with the number of driving signal cycles n positively correlated with the total rotation angle theta of the solar wing. When n =1000 and the interval time Tm = 1.35 h, the mechanism achieves its lowest energy consumption cost, allowing the solar wing to operate at 12.1 degrees per day, saving over 23.8 % of energy compared to continuous drive methods.

The working of the ultrasonic motor directly relies on the micron-amplitude & high-frequency vibrations of the stator in contact with the friction layer. Therefore, the multi-scale rough surface features on the contact surface, which are also at the micron level, cannot be neglected. A novel contact model considering rough surface of different scales is proposed in this paper, and the impact of different scale features on output characteristics is studied. First, the equivalent stiffness coefficient and surface clearance value related to the applied preload on the contact surface are derived using the probability statistics method. Then, the surface data collected by the profilometer are decomposed into microscopic roughness and mesoscopic waviness using wavelet transform. The roughness data are substituted into the probability statistics method, and the waviness is used to adjust the amplitude function. Subsequently, the time-varying working dead zone is obtained using the discrete method, and the output characteristics are obtained by Coulomb friction. The influence of model variables such as microscopic roughness, mesoscopic waviness, preload, stator amplitude, and material properties on the output characteristics is analyzed through simulation analysis. The collected experimental data of the mechanical characteristic curve are highly consistent with the simulation results, verifying the accuracy of the proposed multi-scale contact model. This model can be applied to other types of ultrasonic motors and provides a new perspective for improving motor performance, as well as a theoretical foundation for the study of contact surface texture.

Miniaturized bionic underwater robots hold significant development potential in areas such as resource exploration, underwater rescue, and military operations due to their superior biomimetic and flexible design. However, there are challenges in developing miniaturized underwater robots in terms of operating mechanisms and structural design. In this study, inspired by the efficient jet propulsion mechanisms of cephalopods, a miniaturized underwater robot driven by a linear piezoelectric actuator is designed and developed. The proposed design adopts a direct drive linear piezoelectric actuator, which eliminates the requirement for complex transmission mechanisms, thereby reducing structural complexity. To systematically evaluate the operation performance, a coupling simulation is developed to investigate the fluid-structure interaction and optimize the nozzle diameter. Experimental validation is conducted to investigate the influence of the nozzle diameter on the thrust force and swimming velocity. The results reveal that a nozzle diameter of 25 mm yields optimal performance, with the prototype achieving a maximum thrust force of 56 mN and a swimming velocity of 0.4 BL/s. This research not only demonstrates the feasibility of applying the linear piezoelectric actuator for underwater propulsion in a simple and efficient approach but also provides a design method for the development of compact, high-performance miniaturized bionic robots.

The journal retracts the article “Design and Dynamic Simulation of a Novel Traveling Wave Linear Ultrasonic Motor” [...]

Aiming at requirements in stepping motion of ultrasonic motors in space laser communication, a novel beat traveling wave pulse drive control (BTWPDC) method is proposed. Utilizing the special motion form of ultrasonic motors driven by the beat traveling wave, parameters are controlled so that the power-off speed is sufficiently low, and a pulse cycle is composed by setting a suitable excitation interval. An experimental platform based on FPGA is established to generate the required signals and verify the effect. The experimental data show that compared with the conventional pulse drive method, jitter in the stepping process, which has a maximum value above 15% of the step length, is effectively weak to realize almost jitter-free stepping under open-loop control. Meanwhile, the step resolution is significantly improved to stable 2 urad and even higher. This method solves the jitter in stepping motion and improves the step resolution for ultrasonic motors.

An inertial linear ultrasonic motor with a novel double-stator structure is proposed for achieving higher performance and resolution in this paper. Utilizing a symmetrical structure and single sawtooth wave signal, the prototype is capable of outputting effective linear motion based on inertial movement. The validity and rationality of the prototype are investigated by conducting finite element analyses. The experimental setups are built up to acquire the output characteristics of the motor. The experimental results indicate that the motor can achieve a maximum output velocity of 8.746 mm/s and thrust force of 1.645 N, which is almost twice the output performance of a motor with a single stator. The displacement solution of the motor can be adjusted by changing the amplitude of the voltage, with a resolution of 27 nm. Simultaneously, the relationships between the output characteristics and the input parameters are measured and analyzed during the experiments. Compared to the actuators with complex structures and multi-signal drives, the proposed motor exhibits the merits of higher output performance with the double-stator structure, providing an alternative direction for the further development of the inertial linear ultrasonic motor.

To achieve higher output performance in precision applications, and in order to gain deeper insight into operation principle, a dynamic model is established including the transmission relationship between the stators, the driving shaft, and the mover based on a slip-slip type inertial linear piezoelectric actuator with double stators. The influence of stator material and symmetry ratio of the excitation signal on the vibration characteristics of the stator and the output performance are investigated. This study reveals the relationship between these factors through a combination of simulations and experiments. Prototypes using several materials are machined and assembled, and the vibration characteristics and output performance are rigorously tested. The results obtained from the experimental measurements are consistent with the simulation results, confirming the validity and rationality of the dynamic model. The experimental results of the stator, as well as the actuator, are analyzed. It can be concluded that the actuator is able to output a larger effective displacement in one motion period with the increased symmetry ratio of the triangular wave signal, applied with a higher operating frequency, resulting in a higher output velocity of 42 mm s(-1) and a larger load of 300 g with the steel stator, and a higher displacement resolution of 18 nm can be achieved using the AL alloy stator. This research not only provides an effective method for enhancing and selecting the desired output performance for the researched actuator but also can be extended to other slip-slip type inertial linear piezoelectric actuators.

Space pointing mechanisms are crucial for controlling the movement of solar arrays, which can significantly improve power generation. So the solar array drive assembly plays a key role in advancing space technology. However, most current solar array drive assemblies face challenges related to weight and size. Therefore, this paper presents a lightweight design solution: a solar array drive assembly powered by ultrasonic motors that meet the requirements for the lightweight design. Firstly, a coordinate transformation in geosynchronous orbit is established to analyze the design requirement of the mechanism’s degree of freedom. Next, the structural composition and working principle of the mechanism is introduced. To achieve precise pointing motion, forward and inverse kinematic models are developed, followed by an analysis of the mechanism’s workspace and error model. The solar array drive assembly proposed in this paper is expected to be applied in micro-satellites and special orbiting spacecraft in the future.

This study aims to investigate the shear behavior of epoxy resin adhesives at different temperatures, and to reveal the shear mechanism through experimental tests and molecular dynamics(MD) simulations. The shear strength at different temperatures was experimentally tested. With the increase of temperature, the shear strength decreases obviously. Then, the three-layer shear model was constructed based on the experimental process, and shear simulations were conducted at the corresponding temperatures. The simulations reveal that with increasing temperature, the adhesive exhibit more intense thermal motion, leading to a decrease in cohesive energy density. Additionally, as the temperature rises, the energy of the system increases, rendering it more unstable and resulting in a decrease in shear strength. This study provides valuable insights into the temperature effects on the shear process of epoxy resin adhesives.