The large-scale hydraulic manipulator is a key type of construction machine. Vibration remains a major challenge in large-scale hydraulic manipulators owing to the low system damping, large inherent inertia, and strong external excitation. However, existing vibration suppression methods struggle to maintain a safe working position while suppressing vibration. To address these challenges, a pressure feedback vibration suppression method considering position safety based on an independent metering system is proposed. An independent metering system is used to increase the control degrees of freedom. The valve on the bearing chamber side seals the cylinder to constrain the manipulator position within a safe range, whereas the valve on the non-bearing chamber side controls vibration. A linear relationship between bearing chamber pressure and hydraulic cylinder position can be established, enabling vibration suppression and position holding using pressure control alone. To enhance pressure control performance, an improved active disturbance rejection control (ADRC) incorporating a radial basis function neural network based extended state observer (RBFNN-ESO) is proposed. The improved ADRC increases the state-observation speed and enhances disturbance-rejection performance. Experiments under different postures show that the proposed method achieves a vibration suppression rate of 54.39% while maintaining a safe position.

Piston pumps are widely used in equipment such as aircraft and ultra-long-arm pump trucks. Slippers are core components of piston pumps, typically made of P31CL copper-zinc alloy. Their friction and wear properties directly affect the efficiency and reliability of pumps and even equipment. However, traditional casting and forging processes have weak anti-wear and anti-friction properties, respectively. For that, this study proposes a new strengthening strategy to simultaneously improve friction and wear properties. The new strengthening strategy uses specific process parameters to perform high-frequency twice ultrasonic surface rolling (HFT-USR) on the P31CL alloy, which markedly introduces residual compressive stress, a fibrous subsurface microstructure, low roughness, and specific-direction surface textures. These alterations enhance load-carrying capacity, microstructural stability, and hydraulic oil redistribution at the sliding interface. As a result, the new strengthening strategy reduces friction and wear by 14.5% and 79.4%, respectively, compared to traditional processes. Besides, the results demonstrate the directional dependence of tribological behavior and highlight the importance of matching the friction-sliding and ultrasonic-rolling directions.

Ti-6Al-4V alloy is widely employed in aircraft engine turbine blades, compressor discs, and valves, which generally suffer high-temperature wear failure, causing component damage and serious safety incidents. However, the tribological failure induced by time-dependent wear evolution at high temperatures remains poorly understood. Herein, this study systematically investigates the high-temperature wear behaviors of Ti-6Al-4V at 350 degrees C and 550 degrees C, whose worn characteristics are compared with those at room temperature. The time-dependent evolution mechanisms of high-temperature wear are clarified by combining the worn morphology, tribo-oxide layer formation, and plastic deformation behaviors. The results show the high-temperature wear process of Ti-6Al-4V undergoes two distinct stages: initial running-in stage dominated by adhesive wear and stable wear stage governed by protective tribo-oxide layer and surface softening. Within initial sliding period, the wear rate at high temperatures is significantly higher compared to that at room temperature, which is owing to the worn surface softening induced by high temperatures. Nevertheless, with extension of sliding time, the oxide layer on worn surface becomes continuous and thick at high temperatures, causing a growth deceleration of wear rate. Conversely, the wear rate exhibits a sharp increase over time at room temperature. Although prolonged exposure promotes subsurface grain coarsening that aggravates softening, thermally activated dislocations remain the primary driver of thermal softening. The protective and lubricating benefits conferred by oxide layer outweigh adverse effects associated with surface softening. The dominant wear mechanism at high temperatures transitions from adhesive wear accompanied by slight oxidative wear to severe oxidative and adhesive wear.

Axial piston pumps are the power sources of actuating mechanisms for new-generation aircraft movable wing surfaces. The inevitable tilt of the internal cylinder block may cause leakage and local rub-impact, thereby reducing pump reliability. Therefore, monitoring the tilting angle is essential for early warning and control feedback to prevent severe tilting failures. However, existing methods usually rely on multiple eddy-current sensors inserted through the pump housing, which increases cost, leakage risk, and space occupation. To address this issue, this study proposes a virtual dual-axis angle sensor based on a physics-informed bidirectional long short-term memory (PI-BiLSTM) network. The proposed method estimates the dynamic tilting angle in real time using only the pump’s inherent hydraulic pressure signals. First, a BiLSTM is designed to capture the temporal features of the pressure signals, and periodic features are introduced as prior knowledge into the network input. Second, a wear-related mapping model between the hydraulic pressure signals and the cylinder block tilting angle is derived and embedded into the physics loss as a penalty term. Meanwhile, the intermediate four-point displacements are used to construct the data loss instead of the final output, which helps suppress error amplification during weak-signal inference. Finally, experiments under different operating conditions and wear states are conducted to compare the proposed virtual sensor with actual sensor measurements. The results show that the proposed method achieves an average prediction error of 2.48% and remains insensitive to pump wear.

Reliable start-up of swash plate axial piston motors is essential for improving the rapid response and operational reliability of aerospace control systems. However, accurate prediction of the start-up process remains challenging because rigid body motion, transient friction, and lubrication state evolution are strongly coupled. To address this problem, this study proposes a coupled tribo-dynamic model for the start-up process of swash plate axial piston motors. The model combines Stribeck friction theory with molecular-mechanical friction theory to describe the evolution of key friction pairs from static friction to dynamic sliding during start-up. Friction coefficient tests and start-up performance experiments are conducted to validate the proposed model. The results show that the predicted start-up pressure and rotational speed agree well with the experimental data, with maximum errors within 7%. The torque loss analysis indicates that the valve plate-cylinder pair is the dominant source of resistance, accounting for approximately 64% of the total torque loss. Increasing the swash plate angle from 7° to 13° markedly increases the average input torque and shortens the start-up duration. These results reveal the dominant torque loss mechanism during motor start-up and provide theoretical guidance for improving the transient response and start-up performance of swash plate axial piston motors.

The cam-lobe hydraulic motors, as the core actuating components, determine the service life of heavy-duty equipment. Their multiple cam roller-cam ring pairs have become prone to failure with the upgrading of operating pressure level, in which the cam rollers with a 3 cm length will be subjected to an additional force of 1.4 tons. However, traditional cam roller design is difficult to adapt to heavy-load and even alternating conditions caused by the multi-lobe cam ring. For that, this paper proposes the cam roller micro-geometric design integrating full-cycle alternating characteristics, which can homogenize and minimize deformation and pressure distributions of the cam roller-cam ring pair, especially under heavy loads, thereby improving the lifespan of the motor. Specifically, a thermal elastohydrodynamic lubrication model (TEHL) incorporating micro surface morphology is established to obtain pressure and deformation distribution of the cam roller-cam ring pair. On the basis of the results from the TEHL model, a multi-strategy adaptive hybrid optimization (MAHO) algorithm is developed to robustly design the micro-geometric shape of the cam roller, thereby coping with both alternating states in a full cycle and machining error. The designed cam roller achieves a reduction in peak pressure of 24.8-28.3% and increases fatigue life by 17.3-27.8 times theoretically. The actual bench tests of the motors demonstrate that the designed cam roller achieves a service life of 1030 h under high-pressure conditions, representing a 19.4-fold improvement over the original design. Furthermore, the failure mode shifts from "simultaneous rapid damage of cam rollers and cam ring" to "gradual cam ring fatigue preceding cam roller failure". This study significantly enhances the service life of cam-lobe hydraulic motors under high-pressure conditions, laying a critical technical foundation for the long-term durability and high power density of heavy-duty equipment.

ABSTRACT Hydraulic quadruped robots exhibit exceptional terrain adaptability, offering significant potential for environmental exploration and military transportation. However, conventional hydraulic architectures are often plagued by excessive weight, complex pipeline network and mechanical interference, which restrict the improvement of its compactness and flexibility. To address these issues, this paper proposes a tubeless limb leg unit (LLU) featuring an electro‐hydraulic hybrid drive and topologically optimized structural components. By exploring the relationship between motion capability and joint performance parameters, a hybrid drive configuration integrating rotary and linear (RL) actuators is proposed, achieving full integration of actuators and hydraulic flow channels within the LLU. Furthermore, a lightweight reconstruction of critical thigh components is executed using the variable density penalty method combined with a lattice‐filling strategy to mitigate local stress concentrations, which reduces redundant mass by 37% without compromising structural integrity. Subsequently, a compact hydraulic power system is constructed, and an integrated control and simulation platform based on the robot operating system (ROS) framework is designed. Experimental validation demonstrates that the robot exhibits better dynamic stability during standing, trot gait, heavy payload, uneven terrain, and disturbance recovery tests.

Vertical jumping performance of the limb leg unit (LLU) significantly impacts the movement of legged robots. In this article, a multiobjective joint optimization method for the trajectory generator and controller coupling parameters is proposed. This method constructs a quasi-realistic simulation model with physical feasibility constraints, ensuring an accurate representation of the physical prototype performance. Subsequently, the design variables and objectives are defined considering the inherent coupling relationships and complex evaluation metrics of the LLU. By leveraging data from the proposed model, the empirical objective functions are formulated in the form of a response surface model and used to analyze the influence of variables on different objectives. An improved genetic algorithm with weight selection is proposed to prioritize maximizing the jump height while satisfying the optimization objectives. Finally, the accuracy of the quasi-realistic model is validated by experiments and the results demonstrate an increase of 11.95% in jump height and a decrease of 6.60% in force ratio compared with the conventional method. The joint optimization method can serve as a valuable reference for parameter selection in other multivariable, multiobjective, and multiconstraint problems.

Speed pulsation of the hydraulic motor not only reflects its inherent characteristics but also significantly affects its output stability and operation safety. However, there is still a significant challenge to reveal the speed pulsation mechanism owing to the complex friction and leakage characteristics of multi-interfaces in the hydraulic motor, especially under low speeds. To address this issue, this study proposes an innovative multi-interface fusion speed pulsation model that comprehensively incorporates the friction and leakage losses for high-torque hydraulic motors. Firstly, a coupled rigid-fluid dynamics framework is established to determine the speed pulsation behavior. Within this framework, multiple methods are employed to describe the friction and leakage losses in different interfaces according to their lubrication characteristics. Furthermore, a dedicated speed pulsation test rig is developed to experimentally validate the proposed model. Finally, the influence of multi-interface friction and leakage on the speed pulsation behavior is quantitatively revealed, providing new insights into the intrinsic pulsation mechanism and offering valuable guidance for the design optimization of high-torque hydraulic motors.

Electro-hydraulic control valve (EHCV) with integrated controller commonly utilizes a linear variable displacement transformer (LVDT) to measure spool displacement and achieve closed-loop control. However, the switching power drive circuit controlled by pulsewidth modulation (PWM) within the controller introduces ripple interference to the electrical signal. In addition, as an inductive component, the LVDT exhibits hysteresis in its inductive signal, making the design of a high-precision conditioning circuit complicated and limiting the precision of spool displacement measurement. Based on the LVDT signal-conditioning hardware architecture, this study enables efficient and precise signal phase adjustments, achieving adaptive sampling (AS) to mitigate ripple interference. Noise-suppressing high-precision demodulation is further achieved through sampling position optimization (SPO), forming a novel digital conditioning method for spool displacement measurement in EHCVs. The experimental results of signal demodulation indicate that the proposed high-precision digital conditioning method effectively reduces the noise level of the standard spool displacement signal (SSDS). The SSDS's mean precision is improved to 0.21%, and its mean maximum error is limited to 0.12%. The dynamic and static experimental results of the EHCV further validate that the high-precision digital conditioning method significantly enhances the valve performance.

The reliability of gold-plated electrical connectors is frequently compromised by severe adhesive wear and the tribological failure of traditional conductive coatings. Although graphene exhibits exceptional intrinsic lubricity and electrical conductivity, its weak physical adsorption onto metal substrates often leads to premature delamination and unstable electrical contact during sliding. To address these limitations, this study develops a high-performance conductive lubricating coating based on thiol-functionalized reduced graphene oxide (thiolRGO). Capitalizing on the strong affinity between sulfur and gold, thiol-RGO nanosheets are covalently anchored onto Au substrates via Au-S bonds. Multi-scale characterizations, including conductive atomic force microscopy (C-AFM) and nanoscratch tests, demonstrate that this "chemical anchoring effect" significantly enhances the interfacial adhesion strength compared to physically adsorbed pristine graphene. Macroscopic current-carrying friction evaluations reveal that the thiol-RGO coating achieves a superior synergistic balance between tribological and electrical performances, maintaining a low coefficient of friction and stable contact resistance comparable to that of bare Au under sliding electrical conditions. Post-test analyses confirm that the robustly anchored thiol-RGO facilitates the formation of a persistent conductive lubricating film, effectively smoothing substrate asperities and preventing direct metal-to-metal contact. This work proposes a scalable and robust technical strategy for designing next-generation high-performance lubricants in precision electronic systems.

Accurate identification of dynamic parameters is essential for precise motion control and autonomous operation of heavy-duty hydraulic manipulators. However, due to their low-speed motion property, conventional approaches fail to simultaneously excite all parameters. To overcome this issue, a sequential parameter identification approach for heavy-duty hydraulic manipulators is proposed. All parameters are categorized based on their dynamic characteristic, and then distinct excitation trajectories have been designed to separately stimulate and identify each parameter. Dynamic parameters are fully excited, which is reflected in a reduced condition number of the observation matrix. Furthermore, an approach that ensures the physical feasibility of the identified parameters is constructed, which makes them more suitable for application in nonlinear control. The performance of the proposed method is evaluated with various identification methods, including traditional least squares, weighted least squares, and the method only considering physical feasibility. The results indicate a substantial decrease in torque prediction error compared to these methods. Specifically, the prediction accuracy of the joint torque using the proposed method has been improved by approximately 5.63% to 27.06%.

PurposeFor the purpose of studying the stability and stick-slip vibration characteristics of the coke pushing system, a dynamic model used to describe the friction self-excited vibration system is established in the article.Design/methodology/approachThe Stribeck friction model is introduced into the established dynamic model and the theoretical calculation and numerical simulation are carried out. The critical instability speed of the coke pushing system is 0.45 by theoretical calculation, and the numerical simulation results verify the correctness of the theoretical calculation. In order to control the stability and stick-slip vibration of the coke pushing system, a linear and nonlinear state feedback controller is designed in this paper.FindingsStick-slip vibration emerges in the coke pushing system when its operating speed is below the critical instability speed of 0.45, while the system stabilizes at speeds above this threshold. The linear gain of the state feedback controller can reduce the critical instability speed of the coke pushing device to achieve stable operation at lower operating speeds. Meanwhile, its nonlinear gain can reduce the limit cycle size, suppress stick-slip vibration amplitude and significantly improve the vibration state of the whole system.Originality/value(1) A dynamic model used to describe the friction self-excited vibration of the coke pushing system is established. (2) Design a linear and nonlinear state controller to control the stability and stick-slip vibration of the coke pushing system. (3) Investigate the effect of linear and nonlinear state controllers' linear gain on the critical instability speed and nonlinear gain on the vibration limit cycle size of the coke pushing system.

High-power cam-lobe hydraulic motors serve as the core driving components in heavy-load rotary machinery. The internal hybrid journal bearings (roller-piston pairs) are prone to premature failure under mixed lubrication conditions involving heavy loads, alternating stresses, and impact forces, which severely compromise the motor’s reliability. While applying the hydraulic oil-reactive lubricating graphite-like coating with the specific-proportion tungsten (W-GLC) that can react with hydraulic oil to generate a lubricating film, the tribological properties of bearings are significantly enhanced. However, the evolutionary failure mechanism of this coating on the hybrid journal bearings remains unclear, limiting their longer life design. For that, this study focuses on investigating the evolutionary behaviors and failure mechanisms of the W-GLC coating in hybrid journal bearings. A self-developed quasi-actual rig is used to monitor variation in friction torque and hydrostatic leakage for coated hybrid journal bearings during service. Moreover, the microscopic characteristics of the bearing surfaces are measured at different time stages. The results indicate that the wear region of the coating on the bearing progressively expands from the center of the piston toward the edges, which leads to a continuous rise in leakage. This process subsequently triggers an accelerated temperature rise and weakens the load-bearing capacity of the oil film, thereby forming an accelerated failure mechanism driven by the coupling among wear, leakage, and heat. Furthermore, the wear mode evolves continuously throughout the experimental process, which involves a transition from initial abrasive wear to a coupled multi-mechanism wear regime. Simultaneously, the WS2 lubricating film generated in situ during the friction process plays a critical role in damage compensation during the steady-wear stage.

Hydraulic energy converters are components that can realize the conversion between mechanical energy and hydraulic energy. Their powers can be as high as 2 x 10(6) W or more. For a high-power component, even if its efficiency is increased by 1 %, it will bring huge energy savings. However, current research mainly focuses on improving the efficiency of high-speed hydraulic energy converters via enhancing hydrodynamic effect, with little attention paid to low-speed hydraulic energy converters (<500 r/min). For that, this study develops a self-reactive lubricating graphite-like coating specifically for hydraulic energy converters to reduce mechanical friction that leads to low efficiency at low speeds. The self-reactive lubricating graphite-like coating is composed of two elements: carbon and tungsten. The results of the ring-block tests show that the coating with an atomic ratio (carbon: tungsten) of 0.51:0.49 has lower friction and temperature rise under three load conditions. Its mechanism is that an appropriate content of tungsten can react with additives in hydraulic oil to form a lubricating film, such as WS2 and PO3-, thereby reducing friction. Afterwards, the preferred coating is applied to the pistons in a high-power cam-lobe hydraulic motor. The friction torque of the piston-roller friction pairs is tested on a homemade quasi-actual testing rig, and the results showed that the self-reactive lubricating graphite-like coating could reduce the friction torque by 14 %. The present study provides a new approach to improve the mechanical efficiency of hydraulic energy converters, and can also increase the starting torque to reduce the installed power.

Abstract The running-in process is critical to the efficiency and service life of the valve plate pair (VPP) in axial piston pumps. Stepped speed variations during the running-in process have a significant impact on the VPP’s tribological characteristics. This study investigates the effects of speed step number, variation direction, and time proportion on the VPP's running-in tribological performance. Friction and wear tests were conducted using a ring-on-block tribometer. The results demonstrate that increasing the speed step number can reduce the size of abrasive particles and Spk values. However, excessive steps drastically reduce the Svk value by approximately 82.44%, thereby compromising the surface's oil retention capability. Acceleration running-in significantly outperforms deceleration running-in. Compared to deceleration running-in, the friction coefficient decreases by 63.89%, and the wear rate is halved. In contrast, deceleration running-in induces deeper micro-cutting marks and adhesive wear. Furthermore, optimizing the time distribution by extending the low-speed stage can minimize surface damage and abrasive wear. These findings suggest that a multi-stage acceleration strategy with an optimized time proportion can effectively enhance the running-in quality and tribological performance of VPPs.

Cloud-side inference gives imitation-learning policies access to greater computational resources, but communication and computation delays can degrade control performance. To compensate for these delays, we propose RAPAC-DP, a response-aligned pending-action compensation framework designed for both diffusion- and flow-based action generators. RAPAC-DP encodes the actions already scheduled for execution before the cloud response arrives into a pending-action sequence that serves as the conditioning input to a parameter-efficient compensation pathway. When delay effects are negligible, bypassing this pathway exactly recovers the frozen base policy. For training, RAPAC-DP constructs delay-conditioned samples from delay-free demonstrations, requiring neither explicit system dynamics nor additional delayed demonstrations. At the largest fixed delay tested on Kinetix, RAPAC-DP retained 81.4