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Abstract Battery remaining charging time (RCT) prediction can facilitate charging management and alleviate mileage anxiety for electric vehicles (EVs). Also, it is of great significance to improve EV users' experience. However, the RCT for a lithium-ion battery pack in EVs changes with temperature and other battery parameters. This study proposes an electrothermal model-based method to accurately predict battery RCT. Firstly, a characteristic battery cell is adopted to represent the battery pack, thus an equivalent circuit model (ECM) of the characteristic battery cell is established to describe the electrical behaviors of a battery pack. Secondly, an equivalent thermal model (ETM) of the battery pack is developed by considering the influence of ambient temperature, thermal management, and battery connectors in the battery pack to calculate the temperature which is then fed back to the ECM to realize electrothermal coupling. Finally, the RCT prediction method is proposed based on the electrothermal model and validated in the wide temperature range from − 20 ℃ to 45 ℃. The experimental results show that the prediction error of the RCT in the whole temperature range is less than 1.5%.

Abstract The lower limb exoskeletons are used to assist wearers in various scenarios such as medical and industrial settings. Complex modeling errors of the exoskeleton in different application scenarios pose challenges to the robustness and stability of its control algorithm. The Radial Basis Function (RBF) neural network is used widely to compensate for modeling errors. In order to solve the problem that the current RBF neural network controllers cannot guarantee the asymptotic stability, a neural network robust control algorithm based on computed torque method is proposed in this paper, focusing on trajectory tracking. It innovatively incorporates the robust adaptive term while introducing the RBF neural network term, improving the compensation ability for modeling errors. The stability of the algorithm is proved by Lyapunov method, and the effectiveness of the robust adaptive term is verified by the simulation. Experiments wearing the exoskeleton under different walking speeds and scenarios were carried out, and the results show that the absolute value of tracking errors of the hip and knee joints of the exoskeleton are consistently less than 1.5°and 2.5°, respectively. The proposed control algorithm effectively compensates for modeling errors and exhibits high robustness.

Abstract A built-in capacitive proximity sensing method for a charge-induction electrostatic film actuator is proposed. This actuator consists of two thin sheets that function as a stator and a slider. A stator is an insulating sheet with many strips of electrodes in it, whereas a slider is a dielectric sheet that has slight conductivity on its surface. By applying actuation voltage on stator electrodes, the slider that is placed on the stator is driven by electrostatic force. This research realized the simultaneous actuation and proximity sensing using the same electrodes by integrating a resonance-based capacitance measurement circuit into a driving circuit. The study investigated the impact of having a slider on sensing performance, confirming the feasibility of simultaneous sensing and driving. The implemented system achieved an interactive actuation that changed driving velocity according to the proximity distance of the human hand.

Abstract In the railway system, fasteners have the functions of damping, maintaining the track distance, and adjusting the track level. Therefore, routine maintenance and inspection of fasteners are important to ensure the safe operation of track lines. Currently, assessment methods for fastener tightness include manual observation, acoustic wave detection, and image detection. There are limitations such as low accuracy and efficiency, easy interference and misjudgment, and a lack of accurate, stable, and fast detection methods. Aiming at the small deformation characteristics and large elastic change of fasteners from full loosening to full tightening, this study proposes high-precision surface-structured light technology for fastener detection and fastener deformation feature extraction based on the center-line projection distance and a fastener tightness regression method based on neural networks. First, the method uses a 3D camera to obtain a fastener point cloud and then segments the elastic rod area based on the iterative closest point algorithm registration. Principal component analysis is used to calculate the normal vector of the segmented elastic rod surface and extract the point on the centerline of the elastic rod. The point is projected onto the upper surface of the bolt to calculate the projection distance. Subsequently, the mapping relationship between the projection distance sequence and fastener tightness is established, and the influence of each parameter on the fastener tightness prediction is analyzed. Finally, by setting up a fastener detection scene in the track experimental base, collecting data, and completing the algorithm verification, the results showed that the deviation between the fastener tightness regression value obtained after the algorithm processing and the actual measured value RMSE was 0.2196 mm, which significantly improved the effect compared with other tightness detection methods, and realized an effective fastener tightness regression.

Abstract This paper describes the development and the verification of flight test results of a differential pressure-based, two-dimensional low-airspeed sensor designed for the navigation or disturbance detection in small helicopters. The compact and lightweight sensor is integrated with the main rotor of a small helicopter and comprises two probes at both arm ends, a differential pressure sensor, rotary encoder with one magnet and two sensors, microcomputer, a wireless data link, and battery. It measures the differential pressure between the total pressures captured by two total-pressure probes at each rotor angle, instead of using static pressure probes. Thus, the airspeed of the fuselage can be evaluated from the low speed. Flight tests were conducted employing a reference ultrasonic two-dimensional airspeed sensor for comparison. The results demonstrated that the magnitude error of the airspeed is less than 2 m/s for low-airspeed flights ( $$

Abstract The Chinese express delivery industry processes nearly 110 billion items in 2022, averaging an annual growth rate of 200%. Among the various types of sorting systems used for handling express items, cross-belt sorting systems stand out as the most crucial. However, despite their high degree of automation, the workload for operators has intensified owing to the surging volume of express items. In the era of Industry 5.0, it is imperative to adopt new technologies that not only enhance worker welfare but also improve the efficiency of cross-belt systems. Striking a balance between efficiency in handling express items and operator well-being is challenging. Digital twin technology offers a promising solution in this respect. A realization method of a human–machine integrated digital twin is proposed in this study, enabling the interaction of biological human bodies, virtual human bodies, virtual equipment, and logistics equipment in a closed loop, thus setting an operating framework. Key technologies in the proposed framework include a collection of heterogeneous data from multiple sources, construction of the relationship between operator fatigue and operation efficiency based on physiological measurements, virtual model construction, and an online optimization module based on real-time simulation. The feasibility of the proposed method was verified in an express distribution center.

Abstract Inconel 718 (IN718) alloy is widely applied to fabricate high temperature resistant or corrosion resistant parts due to its excellent mechanical performance. However, the machining of IN718 alloy is difficult as it may cause serious tool wear and poor surface quality (SQ) of the workpiece. In this work, grinding experiments on IN718 alloy at different speeds were conducted by using a CBN grinding wheel. The relationship between grinding speed, SQ and subsurface damage (SSD) was well studied. With increasing grinding speed, surface roughness decreased, and SQ was greatly improved. Meanwhile, the microhardness of the grinding surface declined as the grinding speed increased. The SSD depth was almost unchanged when the grinding speed was lower than 15 m/s, then it decreased with higher grinding speeds. It was attributed to the mechanical-thermal synergistic effect in the grinding process. The results indicated that increasing grinding speed can effectively improve the SQ and reduce the SSD of IN718 alloy. The conclusion in the work may also provide insight into processing other hard-to-machining materials.

Abstract Detecting contact when fingers are approaching an object and estimating the magnitude of the force the fingers are exerting on the object after contact are important tasks for a multi-fingered robotic hand to stably grasp objects. However, for a linkage-based under-actuated robotic hand with a self-locking mechanism to realize stable grasping without using external sensors, such tasks are difficult to perform when only analyzing the robot model or only applying data-driven methods. Therefore, in this paper, a hybrid of previous approaches is used to find a solution for realizing stable grasping with an under-actuated hand. First, data from the internal sensors of a robotic hand are collected during its operation. Subsequently, using the robot model to analyze the collected data, the differences between the model and real data are explained. From the analysis, novel data-driven-based algorithms, which can overcome noted challenges to detect contact between a fingertip and the object and estimate the fingertip forces in real-time, are introduced. The proposed methods are finally used in a stable grasp controller to control a triple-fingered under-actuated robotic hand to perform stable grasping. The results of the experiments are analyzed to show that the proposed algorithms work well for this task and can be further developed to be used for other future dexterous manipulation tasks.

Abstract Plastoelastohydrodynamic lubrication of rough surfaces (R-PEHL) is a cutting-edge area of research in interface fluid-structure coupling analysis. The existing R-PEHL model calculates the elastic-plastic deformation of rough surface by the Love equation in a semi-infinite space smooth surface, which deviates from the actual surface. Therefore, it is an innovative work to study the exact solution of elastic-plastic deformation of rough surface and its influence on the solution results of R-PEHL model. In this paper, a new contact calculation model of plastoelastohydrodynamic lubrication (PEHL) with three-dimensional (3D) rough surface is proposed by integrating numerical method of EHL and finite element method. The new model eliminates an original error introduced by the assumption of semi-infinite space in contact calculation, providing wide applicability and high accuracy. Under the given rough surfaces and working conditions, the study reveals that: (1) the oil film pressure calculated by the new model is lower than that of the smooth surface in semi-infinite space by 200–800 MPa; (2) the Mises stress of the new model is 2.5%–26.6% higher than that of the smooth surface in semi-infinite space; (3) compared with the semi-infinite space assumption, the rough surface plastic deformation of the new model is increased by 71%–173%, and the local plastic deformation singularity may appear under the semi-infinite space assumption; (4) the plastic deformation caused by the first contact cycle on the rough surface of the new model accounts for 66.7%–92.9% of the total plastic deformation, and the plastic deformation of the semi-infinite space accounts for 50%–83.3%. This study resolves the contradiction between the smooth surface assumption and the rough surface in the existing R-PEHL model, establishing a solid logic foundation for the accurate solution of R-PEHL model.

Abstract The tribological properties of self-lubricating composites are influenced by many variables and complex mechanisms. Data-driven methods, including machine learning (ML) algorithms, can yield a better comprehensive understanding of complex problems under the influence of multiple parameters, typically for how tribological performances and material properties correlate. Correlation of friction coefficients and wear rates of copper/aluminum-graphite (Cu/Al-graphite) self-lubricating composites with their inherent material properties (composition, lubricant content, particle size, processing process, and interfacial bonding strength) and the variables related to the testing method (normal load, sliding speed, and sliding distance) were analyzed using traditional approaches, followed by modeling and prediction of tribological properties through five different ML algorithms, namely support vector machine (SVM), K-Nearest neighbor (KNN), random forest (RF), eXtreme gradient boosting (XGBoost), and least-squares boosting (LSBoost), based on the tribology experimental data. Results demonstrated that ML models could satisfactorily predict friction coefficient and wear rate from the material properties and testing method variables data. Herein, the LSBoost model based on the integrated learning algorithm presented the best prediction performance for friction coefficients and wear rates, with R 2 of 0.9219 and 0.9243, respectively. Feature importance analysis also revealed that the content of graphite and the hardness of the matrix have the greatest influence on the friction coefficients, and the normal load, the content of graphite, and the hardness of the matrix influence the wear rates the most.

Tunnel boring machine (TBM) reducers are important components of TBM's cutter-head drive system. In order to reveal the dynamic characteristics of the two-stage planetary gear transmission system of the TBM reducer, the influence factors such as tooth surface friction, the time-varying meshing stiffness, the backlash and meshing error of the two-stage planetary gear transmission system of the TBM reducer are considered. The torsional dynamics model of the two-stage planetary gear transmission system of the TBM reducer is established by the lumped parameter method, and its dynamic characteristics are solved and analyzed. The inherent characteristic analysis results show three vibration modes of the planetary gear train: rigid body vibration mode, torsional vibration mode and the planetary gear vibration mode; the vibration displacement of each gear and the dynamic meshing force between the gear pairs are obtained from the dynamic response analysis. The result lays the foundation for the dynamic optimization design of planetary gear trains.

Considering the fact that ships at sea will be affected by waves, sea breeze and air currents, which usually results in serious interference of equipment that needs to work in a stable environment, such as lifting platforms, radar signal capture, etc. In response to the above problems, the S-RPS-SPS parallel mechanism is established to stabilize the platform. It can realize the roll angle of the rotation around the X axis and the pitch angle of rotation around the Y axis; it can also indirectly eliminate the rotation of the hull on these two axes. Model this parallel mechanism in Solidworks software and verify the degrees of freedom. The relation between the length of two driving rods and the pose angle of the moving platform is calculated by the method of inverse pose solution. Two sets of data are obtained by inputting different angles in the range of the rotating angle of the moving platform and the expansion length of the driving rod. The calculation formula, rotation angle range and coordinates are simulated by algorithms in Matlab software, and the correctness of the moving platform pose is verified. The simulation results show that the accuracy and reliability of this mechanism in terms of kinematics are well guaranteed.

In order to solve the problem of high complexity and large amount of computation for kinematics of industrial robots, conformal geometric algebra (CGA) is introduced to the construction of kinematics model of industrial robots. In the forward kinematics solving process, the motion expressions of each joint are obtained by using the translation and rotation operators in CGA, and then the pose of the end-effector of the robot is obtained. In the process of solving the inverse kinematics, cross product of the constructed basic geometry is carried out to obtain the position of each joint node, the lines and planes through the joint node are constructed, the inner product is made in the CGA frame to obtain the cosine expression of all joint angles, and then all the solutions of the robot's inverse kinematics are solved. Finally, the MOTOMAN-HP20D 6-DOF industrial robot is used for example calculation, and the accuracy and effectiveness of the algorithm is verified by Matlab/Simulink software, which lays the foundation for the subsequent motion control of the robot.

In order to reduce the movement energy consumption of the hydraulic excavator and realize the reasonable and effective operation of each joint, a joint interpolation method based on a T-type velocity curve is proposed to realize the optimal energy consumption trajectory planning of the hydraulic excavator. In this method, the speed of each joint is set as uniform acceleration, constant velocity, and uniform deceleration to ensure the stability of the hydraulic excavator in the operation process. Under the constraint conditions of the joint angle, angular velocity, and angular acceleration, the improved adaptive genetic algorithm is used to optimize the uniform acceleration (deceleration) and constant velocity motion time of each joint, obtain the optimal motion curve of each joint, and realize the optimal energy consumption trajectory planning of the hydraulic excavator. The interpolation programming method based on the T-type velocity curve is simulated and compared with the interpolation results of the quartic polynomial under the same conditions. The experimental results show that the trajectory planned by this method has low energy consumption, avoids unnecessary movement of each joint, effectively reduces friction loss, and makes the excavator complete the operation smoothly and with low energy consumption.

Nonlinear transmission by special mechanism has been applied in the mechanical flight control system. Through approximate fitting of transmission requirements, the design parameters of the mechanism can be solved. The mechanism designed by this method cannot accurately fulfill the transmission constraint condition, so it has not been applied in the mechanical aircraft engine control system. Based on the characteristic of the mechanical aircraft engine control system, the four-bar mechanism is substituted by the five-bar mechanism to realize nonlinear transmission. The mechanism design parameters are divided into optimization decision parameters and transmission control parameters by analyzing the principle of five-bar mechanism design parameters, the mechanism solving method and optimization design method are built to directly solve the mechanism design parameters and make the transmission characteristic fulfill the constraint condition precisely. Then the maximum transmission ratio and mechanism wear factor are used as the objective function to optimize the mechanism design to improve system performance and service life. Furthermore, it is proved by the engine control system design example and ground test that this method is reasonable and practicable with practical value in engineering.

Gear shifting mechanism is one of the most critical components in the shifting transmission system, and its performance directly affects the power performance and stability of the transmission system. In this study, the dynamic equations of the gear shifting mechanism of the two-stage planetary gear transmission system are established, and the influence of the external excitation frequency on the complex dynamic characteristics of the transmission system is studied. Through bifurcation diagram, time domain response diagram, phase diagram, Poincare section diagram and spectrum diagram, the chaotic vibration characteristics of the two-stage planetary gear transmission system are learned, and the stable vibration range of the external excitation frequency is obtained. The proportional differential control method is used to control the chaotic vibration of the gear shifting mechanism, and the chaotic vibration is adjusted to a stable single period vibration. The research results lay a foundation for improving the stability of the shift planetary transmission system.

By processing the rigid-body poses by the spherical four-bar rigid-body guidance mechanism in the standard installation position, it is found that the pose feature curves, which are generated by taking the processing to the output curves of the mechanism, lie on circles. The formation mechanism of pose feature curves is analyzed, and the internal relationship between the center angle of the adjacent feature points on the pose feature circles and the coupler angle of the spherical four-bar mechanism is revealed. An input angles determination method is proposed for the spherical four-bar rigid body guidance mechanism in the standard installation position. Then, the method is extended to the spherical four-bar rigid-body guidance mechanism in a general installation position. By optimizing the installation angle parameters of the two-dimensional mechanism and the relative input angle of the two-dimensional mechanism to realize the input angles supplement of the spherical four-bar rigid-body guidance mechanism at the general installation position. Use numerical atlas method to solve the motion generation of the spherical four-bar mechanism without prescribed input angles. Finally, the feasibility and effectiveness of the proposed method are demonstrated by examples.

Taking the point contact gear with circular-parabola configuration as the research object, based on the Adams dynamic analysis software, dynamic characteristics and the variable law of tooth surfaces are studied in this study. Firstly, according to space meshing theory, tooth surfaces equation of the point contact gear with circular-parabola configuration is derived, and three-dimensional solid models of gear pairs are established by the given design parameters. Secondly, the virtual prototype of point contact gears with circular-parabola configuration is established utilizing Adams software. Through simulation process, variation law of normal contact force, circumferential force, radial force and axial force of the gear are discussed. Change law of normal contact force under the same parameters and working conditions are analyzed between the point contact gear with circular-parabola configuration and general involute helical gears. Influences of meshing stiffness on normal contact force of the gear are also discussed. Research results show that the dynamic performance of point contact gears with circular-parabola configuration is better than that of general involute helical gears under the same parameters and working conditions. Meshing stiffness has a certain influence on the dynamic performance of tooth surfaces. For a reasonable variable range, the transmission process will be more stable with the increase of the meshing stiffness. The study can provide a basis for the design of point contact gears with circular-parabola configuration.

In order to solve the problem of waste lithium-ion battery recycling, a robot end-effector is designed to carry the battery weight and adapt to different sizes in the process of sorting. In this study, each mechanism of the end-effector is introduced. The kinematic model of the six-bar mechanism is established by further checking the toe-bar six-bar mechanism. The rod length and position parameters of six-bar mechanism are optimized by genetic algorithm-BFGS （GA-BFGS） quasi-Newton method and particle swarm optimization-BFGS (PSO-BFGS) quasi-Newton method, and the dynamics model of the six-bar mechanism is established. The driving force required by no load and the radial force in the handling process under the limit condition are calculated and simulated. This study provides a new idea of the six-bar drive mechanism, and provides reference for the research and development of the waste lithium-ion battery sorting equipment.

Considering the effects of time-varying load, time-varying excitation, longitudinal stiffness, radial stiffness and bending stiffness of each pulley, the dynamic analysis model of the inner and outer engine front-end accessory drive system is established by Simdrive software. The static characteristics of the system are evaluated. Galerkin method is used to discretize the system space, the implicit multi-step method is used to solve the dynamic characteristics of the system under acceleration conditions, and the influencing factors of the accessory pulley speed fluctuation, tension fluctuation and belt-pulley slip characteristics are obtained. Based on the analysis results, an improvement plan is proposed to appropriately increase the initial tension and the crankshaft wheel wrap angle, and add an automatic tensioner at the No.2 idler gear. The comparison analysis shows that the dynamic characteristics of the engine front-end accessory drive system are improved effectively when adding automatic tensioner.

Due to the complex marine environment, ship engines are under the harsh working conditions of high humidity and high salinity for a long time, which seriously aggravates the frictional wear of engine chains and thus affects the working stability and the fatigue life of engines. Based on this, this study designs the surface textures on the chain pin in three shapes—square, sine and circular. Combining experiments and simulations, the influence of texture shape, area occupancy and depth on the friction and wear resistance is studied in order to provide new ideas and theoretical basis for solving the long-term engine chain wear problem. The results show that the presence of the texture reduces the elemental Cr content of the surface after wear and thus improves the surface wear resistance compared to a smooth no-texture surface. Among the three texture shapes, the sinusoidal texture exhibites the best friction reduction and wear resistance performance, and the highest friction reduction rate of about 31. 9% is achieved under high speed and light load conditions. The sinusoidal texture has the shallowest surface wear marks, and the wear process is mainly micro-motion wear, accompanied by slight adhesive wear.

Gear modification is an important technology in improving the meshing state, transmission accuracy and efficiency. However the existing modification methods and instrumental softwares are difficult to ensure the geometric quality and efficiency of gear modification. Therefore, a new gear modification method based on spatial lattice is proposed in this study. Firstly, according to the requirements of modification accuracy, the gear surface is discretized into regular spatial lattice, and the modification amount is mapped to the corresponding spatial point. The adjusted spatial lattice is then constructed into regular quadratic B-spline curves. Then, the modified gear surface is obtained by optimizing the mesh curve, and the new gear surface of the whole gear 3D model is updated adaptively. Finally, the method is seamlessly integrated into the 3D design software NX platform, and a gear accurate modification design system is developed. The result of the example shows that the method realizes the precise modification of the gear surface through the dual control of the modification position and the modification amount, and the high-quality gear profile surface is obtained, which improves the efficiency and practicality of the gear modification while ensuring the accuracy.

For traditional machine learning algorithms, visual recognition algorithms have low recognition accuracy and slow running time. This research studies the scene of the robot doing housework in the family scene, and uses the RGB image information as input to complete the grasping pose estimation of the target object. Based on the object detection model YOLOv5s, the network architecture is built by combining data enhancement and transfer learning with its advantages of lightweight and fast speed. After building a family scene data set to enhance the data of a small number of training samples, the model is trained on the target data set using transfer learning, and the parameters are fine-tuned at the same time. The positioning information of the target object is transformed into the grasping pose of the robotic arm through coordinate transformation, and the robotic arm is controlled to finally complete the grasping task with a fixed grasping posture. Finally, the effectiveness of the algorithm is verified by building an experimental platform and manipulating the UR5 robotic arm to carry out actual grasping experiments. The proposed method based on target detection is fast, has high real-time performance, and has a false/missed recognition rate of less than 2%. The application in the robotic arm can efficiently complete the task.

To improve the carrying capacity of the robot, reduce the energy consumption of the driving motor and make the wheel-leg mode switching smooth and efficient, a reconfigurable decoupled parallel mobile robot configuration is proposed, and the configuration synthesis research and decoupling and singularity analysis are carried out. According to the expected degree of freedom of the robot's mechanical leg, four main motion limbs are synthesized. The 58 constraint limbs are synthesized based on the de-constraint method of the screw theory. Based on the virtual chain method of the screw theory, the 3R spherical parallel mechanism is synthesized as the bearing limb of the mechanical leg. Then two robot examples are given. Taking one of the robots as an example, the input-output equation is established, and the decoupling of the mechanical leg is analyzed. The singular configuration of the reconfigurable unit is verified by the reduction to absurdity, and the singular type is judged based on Grassmann line geometry. Finally, the influence of the singularity of the bearing limb on the motion output of the mechanical leg is analyzed. The mechanical leg of the robot adopts a parallel limb chain configuration, which has strong bearing capacity. The robot realizes wheel-leg switching based on constraint singularity, which makes the switching action more stable. The configurability of the mechanical leg reduces the energy consumption of the drive motor. Each drive of the mechanical leg is decoupled from the other, which reduces the control difficulty and makes the wheel-leg mode switching of the mechanical leg more efficient.

Tooth surface twisting is a kind of processing error generated when the spiral herringbone gear is formed and grinded. In order to reduce the tooth surface distortion and improve the grinding accuracy, a gear reverse twisting processing calculation method is proposed based on reverse thinking to reduce the processing error caused by the tooth surface distortion. According to the meshing coordinate system of the shaping and grinding herringbone gear space, the contact line at multiple positions of the standard gear tooth surface, tooth surface twisting and tooth surface anti-twisting is solved, and the reverse distortion model of the tooth surface of the herringbone gear is established by calculating the curvature of the tooth surface method and the amount of spiral modification. The contact line optimization of the gears before and after the shaping is combined with the Monte Carlo method; and the transmission error of the tooth surface anti-twisting and the tooth surface twisting; and also the tooth surface contact stress are analyzed by the finite element method. Finally, the dynamic characteristics of the tooth surface twist and the tooth surface anti-twist after the shape are compared. The results show that the tooth surface anti-twisting machining can effectively reduce the error of the tooth surface processing principle of the herringbone gear and improve the grinding accuracy of the herringbone gear.

In order to accurately calculate the meshing efficiency of the new internal S-gears, a time-varying friction model of the elastohydrodynamic lubrication is established considering the surface sliding of the gear tooth, lubricating oil condition and load. The lubrication mechanism of the meshing tooth surface is analyzed, and the sliding friction coefficient and friction loss power are calculated by tooth contact analysis (TCA) and loaded tooth contact analysis. On this basis, instantaneous meshing efficiency and average meshing efficiency of internal S-gears within one meshing cycle are obtained. The results show that the new internal S-gears have higher meshing efficiency than the involute gears under the same design parameters. The meshing efficiency of the new internal S-gears is improved after the tooth direction modification and increases positively with the tooth direction modification.

Quadruped robots based on the bionic principle are the hot topic of many scholars at home and abroad. In order to satisfy the stationary motion requirements of quadruped robots, a non-impact foot trajectory form combining the improved constant velocity motion law in the vertical direction and the bionic motion law in the forward direction is proposed, and its piecewise function expression is derived. In order to solve the problems of multiple drives and weak leg stiffness of quadruped robots, a new leg mechanism with single degree of freedom is proposed, which is composed of two crank-rocker mechanisms, a synchronous belt drive and an external meshing cylindrical gear drive. The kinematics model of the mechanism is established and the coordinates of the foot end are derived. The optimal motion size and initial position of each component of the mechanism are optimized by using the genetic algorithm and the general nonlinear optimization method with the approximation degree of non-impact foot trajectory as the objective. A 3D modeling software is used to build a simplified virtual prototype model, which is imported into Adams software for Trot gait simulation test, and the motion effect reaches the expected design. The proposed non-impact trajectory can be used as reference for foot trajectory planning of other legged robots. The optimal design method of the multi-link leg mechanism composed of two crank-rocker mechanisms provides a basis and innovative ideas for the leg design of legged robots.

As a key component of the integrated transmission device of tracked armored vehicles, the confluence planetary row has the advantages of high transmission efficiency, high load capacity and compact space structure, but its working condition is very complex and variable, and the vibration characteristics under the extreme high and low temperature environment directly affect the service performance of the integrated transmission device. In this study, a comprehensive test rig for the vibration of the confluence planetary row is designed and built, and the dynamic characteristics tests of the confluence planetary row gear system are carried out under normal temperature conditions and temperature rise conditions. The results show that under normal temperature conditions, the rotational speed and load power have a greater influence on the system vibration amplitude; and under temperature rise conditions, when the temperature is constant, the load power has a greater influence on the system vibration amplitude in the low frequency band, and the rotational speed plays a dominant role in the high frequency band. When the speed and load power are certain, the influence of temperature on the low frequency region is more obvious, and the higher the temperature, the more obvious the influence will be. The research results have theoretical and application values for condition monitoring and health maintenance of the confluence planetary row under complex working conditions.

Based on the calculation method of thermal deformation of spur gears, a calculation and analysis model of thermal deformation with equivalent spur gears as the object is formed. According to the difference between different types of gears and equivalent spur gears, the calculation methods of thermal deformation of helical cylindrical gears and straight bevel gears are deduced. The proposed methods are compared and verified by finite element simulation. Finally, the method is extended to the calculation of thermal deformation of spiral bevel gears. The results show that the thermal deformation of the tooth surface calculated by the proposed method is in good agreement with the finite element simulation results, which can truly reflect the deformation degree of the tooth surface after heating. The numerical difference at the maximum thermal deformation is less than 8%. This method provides a new idea for the calculation of thermal deformation of gears with complex tooth surfaces.

In response to the problem that the error value is usually set as a constant value in the tooth contact analysis (TCA) model of cycloidal needle tooth transmission, which makes the calculation results unreasonable, and the calculation does not converge in the calculation process, an analysis model of cycloidal pinwheel transmission error including multi-factors such as shaping modification and processing error is established. After analyzing the vector equation of the meshing point, a method to solve the problem of numerical non-convergence is proposed, that is, to find the meshing point with equal normal vector in the obtained point with equal ordinate and abscissa on the cycloid wheel and the needle tooth. After analyzing the form of the rotary body error, a method to solve the unreasonable calculation results is proposed, that is, the cycloid circumferential joint error, the cycloid tooth profile radial runout error and the needle tooth center circle radius error change periodically in the tolerance band. RV-80E reducer is taken as the test object, and the correctness of the theoretical model is verified by comparing the test results. The influence of each error on the transmission error is studied, and the sensitivity analysis of each error is carried out. The results show that the needle tooth radius error and the normal clearance under the comprehensive action of the needle tooth and the needle tooth shell gap are the important factors affecting the transmission error.

Asymmetric gears are a new type of involute gears with different pressure angles on each side of a gear tooth. Gear tooth profile parameters have a great influence on the performance of a gear pair, such as its tooth profile shape, motion characteristics, bearing capacity, transmission efficiency, dynamic characteristics and so on. Asymmetric tooth geometry formulas based upon a rack-type tool are derived following Litvin's vector approach. Then a precise calculation model for meshing stiffness of asymmetric gear is proposed and validated to be effective by comparing with a finite element model separately. Further, the influence of cutting tool tip fillet radius, gear pressure angle and contact ratio on gear meshing stiffness is quantified parametrically. The research results indicate that gear meshing stiffness can be improved effectively with the increase of pressure angle and cutting tool fillet radius. The influence of the pressure angle is relatively greater. With the increase of the pressure angle, not only will the thickness of tooth root increase, which is beneficial to improve the bearing capacity of the gear, but also the thickness of tooth tip and contact ratio will decrease, which is prone to evoke tooth tip fractures. In asymmetric tooth profile design, it is suggesting that the involute pressure angles are set according to actual working conditions.

In order to reduce the drag torque under high speed conditions, the equivalent radius is introduced into the traditional low speed torque model of a wet clutch with track vehicle, and the calculation model of the drag torque with radial groove is derived. An optimization design model is established with 3 working condition parameters of the clutch and 5 structural parameters of the friction plate as design variables, and the minimum drag torque as the optimization objective. The objective function is solved based on the whale optimization algorithm (WOA) , and the drag torque is reduced by 35.6% after optimization. The dynamic response model of the objective function is established by Simulink software, and the optimization results are verified. The results show that the optimization method is effective and can provide some reference for structural design and parameter optimization of wet clutches.

Aiming at the problem of parameter design of marine wedge gear propeller shaft clutches, the design and research of marine wedge gear propeller shaft clutches are carried out. The variation of the critical friction coefficient required for the self-locking of the marine wedge gear propeller shaft clutch with the pressure angle and wedge angle of the wedge gear is theoretically analyzed and verified by the simulation. The multi-body dynamic model of marine wedge gear propeller shaft clutches is established, and the engagement process with the tooth error is studied. The results show that the marine wedge gear propeller shaft clutch reduces the accuracy requirement of the tooth alignment process. When there is an error within 0.4° in the engagement process, the engagement can be completed under its own guidance. The formula of self-locking critical friction coefficient derived in this study can be used to guide the design of marine wedge gear propeller shaft clutches.

It is possible to calculate the oil film thickness and the pressure distribution on the Hertzian contact surface of bearings, gears, traction drives, etc. by the EHL theory by Dowson et al.. For these calculations, it is important to determine the high pressure viscosity and high pressure density of lubricant. In a previous report, I constructed a theory of the relationship between viscosity, temperature and pressure. And the van der Waals type viscosity equation was derived. Similarly, in this study, I constructed a theory of the relationship between density, temperature and pressure. As a result, it was found from the dimensional analysis that 1/3 power of density (line density) was negatively proportional to temperature. This linear equation was found to be a van der Waals type line density equation which consists of three eigen constants: absolute zero line density ρt=01/3, line density constant 1/G and pressure constant H/G. Furthermore, the pressure constant H/G of the line density equation is equivalent to the PR of the liquid state equation and the pressure constant C/B of the van der Waals type viscosity equation. And I report the results of estimating the high pressure density of various lubricants by the line density equation.

This study examined the effects of polytetrafluoroethylene (PTFE) and Eichhornia crassipes carboxymethyl cellulose (EC-CMC) polymers in base jatropha lubricant and employed commercial shell lubricant as the reference. Wear reduction and coefficient of friction (COF) were measured using 1 mass% polymer concentrations. Characterization analysis showed that the formulation processes required functional groups like carbonyl, alkene, aliphatic CH2 and CH3 group that the Fourier Transmission Infrared (FT-IR) studies indicated were necessary for lubrication. According to the frictional analysis, the polymers’ tribological performance was influenced by changes in both load and operational speed. At 40 kg and 1200 rpm, PTFE and EC-CMC reduced COF by 53.7% and 49.8%, respectively, compared to base jatropha. However, commercial shell oil produced exceptional performance.

The durability of super-low friction of hydrogenated carbon nitride (CNx:H) coatings sliding against Si3N4 balls in high-vacuum (HV) environments and the phenomena that occur at the interface were clarified. In an HV, CNx:H achieved super-low friction (µ

Indentations in rolling bearings from particle contamination introduce surface damage because they disturb lubrication and produce stress concentrations. In this article, a methodology is proposed where non-failed bearings that have been running in the field are inspected, indentations are counted and their geometry is characterized. With this information and the use of a mathematical model previously developed, the inferred damage in the bearing can be estimated and with this also the actual contamination parameter, ηc as described in the ISO 281 standard. In this way giving more certainty on the real contamination conditions in the application than other indirect assessment methods.

Abstract With remarkable learning capabilities and swift operational speeds, artificial intelligence (AI) can assist researchers in swiftly extracting valuable patterns, trends, and associations from subjective information. Tribological behaviors are characterized by dependence on systems, evolution with time, and multidisciplinary coupling. The friction process involves a variety of phenomena, including mechanics, thermology, electricity, optics, magnetics, and so on. Hence, tribological information possesses the distinct characteristics of being multidisciplinary, multilevel, and multiscale, so that the application of AI in tribology is highly extensive. To delineate the scope, classification, and recent trends of AI implementation in tribology, this review embarks on exploration of the tribology research domain. It comprehensively outlines the utilization of AI in basic theory of tribology, intelligent tribology, component tribology, extreme tribology, bio-tribology, green tribology, and other fields. Finally, considering the emergence of “tribo-informatics” as a novel interdisciplinary field, which combines tribology with informatics, this review elucidates the future directions and research framework of “AI for tribology”. In this paper, tribo-system information is divided into 5 categories: input information (I), system intrinsic information (S), output information (O), tribological state information (Ts), and derived state information (Ds). Then, a fusion method among 5 types of tribo-system information and different AI technologies (regression, classification, clustering, and dimension reduction) has been proposed, which enables tribo-informatics methods to solve common problems such as tribological behavior state monitoring, behavior prediction, and system optimization. The purpose of this review is to offer a systematic comprehension of tribo-informatics and to inspire new research ideas of tribo-informatics. Ultimately, it aspires to enhance the efficiency of problem-solving in tribology.

Film cooling protects high-temperature components and generates complex vortex structures through the interaction between the mainstream flow and the injected coolant. Additionally, the process of applying thermal barrier coatings introduces imperfect cooling holes. A numerical simulation study is conducted on two geometric configurations: inclined perfect and imperfect holes arranged in a single row on a flat plate to investigate the effects of flow field vortex structures and hole imperfections. The k-epsilon turbulent model is employed to analyse the impact of varying blowing ratios and defect positions on flow field structure and cooling efficiency, with vortex dynamics providing explanatory insights. As the blowing ratio increases, the kidney vortex associated with the perfect holes progressively detaches from the wall, reducing film cooling efficiency. The kidney vortex originates from the shear interaction between the mainstream and the impinging jet, predominantly influenced by the vortex stretching component. Imperfect holes influence the distribution state of the kidney vortex, with weakened roll-up phenomena observed at the IT4 defect location. Consequently, a noticeable enhancement in film cooling effectiveness is achieved near the proximal end of the hole.

The Reynolds number (Re) is an important parameter that can affect compressor performance. This study experimentally and numerically investigated the effect of Re variations on the efficiency and stall mechanisms for a three-stage axial flow compressor. In the experiment, the total pressure ratio, polytropic efficiency, and stalling mass flow rate were measured in a Re range varying from 1,100,000 to 55,000 to elucidate the Re effects. Unsteady three-dimensional numerical simulations were implemented to understand the stall mechanisms. The results indicate that the compressor efficiency and stall–pressure ratio begin to decrease remarkably as Re is reduced below a critical value, which is 220,000 in the case of the compressor studied. At a low Re, losses caused by the secondary flow near the hub and shroud increase remarkably, and the extended boundary layer separations at the blade suction surface further decrease the efficiency. The variation in Re changes the stall-initiated location. At higher Reynolds numbers, the interaction between the corner separation at the hub of stator 1 and the leakage flow through the blade tip gap induces a large vortex, which seriously blocks the blade passage. The blocking effect spreads to the aft stage and extends to higher spans, which results in the stall of the whole compressor. However, the blocking effect at the hub disappears at Re =55,000, and the interaction of the blade boundary layer separation near the shroud of rotor 1 and the tip leakage vortex causes a large blockage and then induces stall. The Re variation changes the radial flow transportation because of the varying effect on the aerodynamic performance of each blade element at different spans. This significantly influences the extent of the vortex near the end wall and ultimately changes the stall mechanisms.

Radial pre-swirl systems are widely applied in the aviation industry to supply cooling air to high-pressure turbine blades in aircraft engines. The efficiency of the film cooling can significantly decline when the air pressure is insufficient. This study explored the synergistic optimization of pre-swirl nozzles and receiver holes to improve the pressure ratio of a radial pre-swirl system. To attain this objective, we established a surrogate model using an artificial neural network and adopted the particle swarm optimization algorithm to pinpoint the optimized geometric parameters within the defined design scope. The results revealed that the optimal performance was achieved when the pre-swirl-nozzle tangential angle reached 40.4368°, the receiver-hole axial angle reached 2.0286°, and the tangential angle reached 30°. Additionally, multiple computational simulations were performed under diverse operational conditions to validate the efficacy of this optimization. The results revealed a significant enhancement in the pressure-boosting efficiency of the radial pre-swirl system, with negligible impact on temperature increment. The optimized model exhibited a 16.93% higher pressure ratio and 1.6% higher temperature ratio than the baseline model. This improvement can be attributed to enhancements in the flow field and reductions in local losses.

This study investigates the cooling features of sweeping jets with phase changes, providing insights into how parameters affect heat transfer. The study aims to improve heat transfer by investigating the cooling effects of a sweeping jet impinging on a concave wall. The Eulerian-Lagrangian particle tracking method was used to examine the impact of Reynolds number, droplet diameter, mist capacity, and impingement distance on heat transfer properties during the sweeping jet impingement cooling. Increasing the Reynolds number from 20,000 to 35,200 results in a 7.1% and 3.3% decrease in average temperature at the axial centerline of the impingement wall, attributed to the cooling effect from droplet phase change. Decreasing droplet diameter from 20 µm to 10 µm reduces temperature amplitude by 11K. At 5% and 7.5% mist ratios, the cooling performance is similar to that of dry air. However, a mist injection of 10% significantly amplifies the cooling effect by 18.8%, providing a more efficient cooling experience. This investigation provides essential perspectives on impingement cooling, offering insights into the impact of various parameters on heat transfer enhancement.

The sport of half-pipe skiing, characterized by its dynamic maneuvers and high-speed descents, often faces challenges posed by unpredictable wind conditions. To address this, an advanced wind-blocking system incorporating an air curtain capable of generating a jet flow is proposed. This pioneering design offers a dual advantage: the system can significantly reduce the windbreak size in the vertical dimension while maintaining a satisfactory wind-blocking effect. A comprehensive study is conducted to analyze the effects of the height of the windbreak and the jet emission angle from the air curtain. When the jet speed is 40 m/s, a 50° emission angle and a 2 m height of the windbreak result in an optimal wind-blocking effect. Furthermore, delving deeper to understand the underpinnings of this phenomenon, we discovered that a counterrotating vortex pair, which forms in the presence of this jet under crossflow conditions, plays a pivotal role in augmenting the wind-blocking capabilities of the system.

The self-starting performance of vertical-axis wind turbines (VAWTs) is crucial for their widespread utilization. Conventional evaluation methods using the static torque coefficient (CTS) or self-starting time have limitations. "The minimum 1st derivative of angular acceleration in the lift acceleration state" is proposed to serve as a suitable indicator for the completion of self-starting. Understanding the behavior of the self-starting process in VAWTs is crucial for optimizing power output. A comprehensive methodology is used that integrates experiments and computational fluid dynamics (CFD). Wind tunnel experiments are conducted to evaluate the self-starting and power output performance of the turbines. CFD is employed utilizing the Fluent 6DOF module to investigate the torque and flow field characteristics during the self-starting process. Additionally, the objectives of our study are to investigate the effect of static evaluation methods on the dynamic start-up process and to explore the effects of airfoil type, pitch angle, and inlet wind speed on the self-starting behavior of turbines. The results indicate that a high CTS ensures initial rotation, but the subsequent self-starting time remains independent of this factor. Increasing the pitch angle enhances the self-starting performance. At an inlet speed of 5 m/s, for the NACA2418 airfoil turbine, the self-starting times for pitch angles of 10° and 5° are reduced by 20% and 12%, respectively, compared to that for 0°. The NACA0018 airfoil turbines with pitch angles of 0° and 5° fail to complete self-starting. The airfoil type also plays a crucial role, with the NACA2418 airfoil demonstrating superior self-starting performance and power performance. Furthermore, the minimum self-starting wind speed of the NACA0018 airfoil turbine was explored and determined be between 5.5 m/s and 6 m/s. The utilization of this novel self-starting evaluation method addresses the limitations of traditional approaches, providing a more universally applicable interpretation of the characteristics of turbine self-starting behavior.

Unmanned Combat Aerial Vehicles (UCAVs) are designed to be lightweight and compact, which can impact their overall lift and aerodynamic capabilities. This study focuses on enhancing the Coefficient of Lift (CL) by optimising the Back Sweep Angle in the Lambda wing-UCAV. The model's baseline geometry remains unchanged during the experimental and numerical analysis, while different back sweep angles ranging from δ=00 to δ=500 are investigated at varied free-stream velocities and angles of attack. This helps to understand the generation of induced lift in the intricate shapes of the Lambda Wing. The results indicate a 5% to 10% increase in the lift for every 100 increments of the Back Sweep Angle, and the vortices' strength increases and reaches a maximum at δ=400. At greater angles (δ >400), the lift drops gradually with the Reynolds number. The stagnation point shifts from 25% to 35% along the chord towards the pressure surface as the angles of attack increase from α=50 to α=100. The angle of attack α>100.

To enhance the aerodynamic performance of an ultra-compact S-shaped convergent-divergent nozzle and mitigate flow separation, numerical simulations were conducted using FLUENT software. The study employed the k-ω shear stress transport turbulent model to investigate a flow control method involving blowing. Detailed analysis was performed on the impact of blowing position, angle, and pressure ratio on controlling flow separation. The findings indicate that as the blowing position moves backward, the flow separation area diminishes. Additionally, downstream flow separation ceases at smaller blowing angles within the separation zone. However, excessively large blowing angles tend to create an “aerodynamic wall,” causing significant upstream flow loss and nozzle performance degradation. Enhancing the blowing pressure ratio, given proper mixing with low-energy fluid and no interference with the main flow, can improve the nozzle's aerodynamic performance. Under the optimal blowing scheme, the total pressure recovery coefficient and thrust coefficient are increased by approximately 0.52% and 3.75%, respectively, when compared with those of the reference nozzle.

Traveling wave is an innovative active flow control technique that can remarkably mitigate flow separation. This paper employs numerical simulation to examine how traveling wave structures affect the NACA0012 airfoil. The traveling wave structure is situated at 0.5%c from the leading edge. In the chord direction, its projection length is 0.1c. Through numerical simulation, the impacts of dimensionless length-width ratio and velocity of traveling wave on flow separation are investigated, and the relationship between the traveling wave's optimal parameters and angle of attack is explored. The outcomes demonstrate that traveling waves with suitable length-width ratios and velocities can effectively suppress flow separation. When AoA=16°, traveling wave airfoil with dimensionless velocity U=1.1 and length-width ratio A=1 achieves the best performance, and its lift-drag ratio is 9.24 times that of the original NACA0012 airfoil. The optimal dimensionless length-width ratio and velocity of the traveling wave airfoil are associated with the angle of attack, and different parameters need to be chosen at various angles of attack to attain optimum effect.

Present research study analyses the suitability of baffled reactor vessels with large diameter agitated using the Rushton Turbine (RT) impeller maintained at standard clearance condition for the solid-liquid suspension process. The mean and turbulent flow fields associated with reactor vessels of various diameter were simulated using Computational Fluid Dynamics (CFD) approach. The impeller rotation was modelled using Multiple Reference Frame (MRF) technique and entrainment of air was simulated using Volume of Fluid (VOF) method respectively. The increase in the diameter of reactor vessel keeping impeller at standard clearance condition lead to the transition from double to single loop pattern with considerable decrease in the power number. In large reactor vessels, a low pressure zone is developed below the impeller which deflects the discharge streams and trailing vortices towards bottom surface of the reactor vessel causing the formation of single loop down-pumping pattern. The downward propagation of trailing vortices weaken the flow separation region behind the impeller blades which in turn decreases the form drag and power number of the impeller. The development of single loop down-pumping pattern, high magnitudes of axial velocity, vortex and turbulence fields near vessel bottom and inferior entrainment of air makes the large reactor vessels suitable for the solid-liquid suspension process. The high magnitudes of axial velocity developed below the impeller of large reactor vessel with same power consumption as compared to low clearance vessel makes the former vessel configuration more suitable for the solid-liquid suspension process.

This study examined the drag reduction properties of cylindrical flows across various asymmetric notched structures through numerical simulation and particle image velocimetry. The focus was on investigating the influence of the number of asymmetric grooves on the drag characteristics, including the mean drag, spectral characteristics, time-averaged streamlines, separation point prediction, time-averaged pressure, wake vortex strength, Reynolds stress, and turbulent kinetic energy. The results showed that the presence of asymmetric grooves significantly influenced these flow parameters. Notably, the improvement was optimal in the four-groove configuration, evidenced by the lowest mean drag coefficient (0.804), vortex shedding frequency (2.74 Hz), recirculation area length (1.208D), and pressure difference across the cylinder (81.76). Moreover, this configuration resulted in the weakest trailing vortex, a 45% reduction in the maximum Reynolds stress (0.011), and a 40.5% decrease in the maximum turbulent kinetic energy (0.05). Thus, the presence of asymmetric grooves had a significant positive effect on the cylindrical flow properties, though the degree of improvement decreased with further increase in the number of grooves.

The diffusion porous media combustion is one possible way to eliminate the drawbacks of the existing combustion systems. Inverse diffusion flame (IDF) has features of both premixed and non-premixed flames. To integrate the advantages of porous media combustion with IDF, inverse diffusion porous (IDP) medium burner is tested for change in flame morphology and emissions at different equivalence ratio (ɸ). The porous media located at the exit of IDF burner has potential to deliver minimum flame length with low emissions. Flame appearance, flame height, flame zones etc. and emissions are experimentally investigated. Methane is used as fuel. Visible flame height is captured digitally and evaluated using ImageJ software. Central plane flame temperature is measured experimentally. CO and NOX emissions are recorded with Testo-340 flue gas analyser. The use of porous media at flame base is beneficiary in terms of achieving better air-fuel mixing and radial diffusion of air-fuel mixture. This reduces flame height with porous medium at all range of ɸ. Increase in ɸ reduces CO and enhances NOX emissions. Porous media reduces CO by 75 % and NOX by 60 %. Inverse diffusion porous medium burner emits lowest emissions in rich conditions.