Abstract:[Significance]The helicopter transmission system is the key source of cabin noise,which significantly affects the flight quality and ride comfort.A systematic review of its vibration and noise suppression technologies can provide a technical basis and practical guidance for engineering design,system integration and domestic substitution.Research progress of vibration and noise suppression technologies for helicopter transmission systems at home and abroad was reviewed.[Analysis]Passive vibration suppression techniques(including structural optimization,damping,absorption,and isolation)and active vibration suppression techniques(covering actuators and active control algorithms)were elucidated.The research status of vibration suppression technology for transmission systems of special configurations of helicopters with high-speed flight characteristics,such as coaxial reverse twin rotor helicopters and tilt rotor helicopters,were summarized.At the same time,the vibration reduction mechanism of new transmission components such as magnetic gears,ceramic bearings,composite shafts,and casings was explored,as well as the research progress of revolutionary electric drive technologies such as electric tail rotor and fully electric drive.Finally,based on the current research status in China,suggestions were proposed for multidimensional optimization of active vibration suppression technology,technological innovation to promote the upgrading of new transmission components,and the development of new energy helicopters,in order to enhance the international competitiveness of China's helicopters.

Abstract:[Objective]Aerospace gears have strict requirements for surface integrity.Ultrasonic vibration-assisted grinding(UVAG)can enhance the residual compressive stress and fatigue resistance of gear surfaces,but the thermal-mechanical-microplastic coupling mechanism remains to be further clarified.Therefore,a crystal plasticity finite element model(CPFEM)considering both ultrasonic vibration and thermal-mechanical coupling was established to predict the residual stress on the gear surface and reveal the ultrasonic control mechanism.[Methods]A gear surface following coordinate system and grinding contact geometry were constructed,and models for friction attenuation,tangential grinding force,and transient heat flow under UVAG conditions were derived.The ultrasonic softening term and temperature softening term were introduced into the CPFEM,and the material parameters of 12Cr2Ni4A alloy steel were calibrated to establish a surface/depth dual-scale polycrystalline model.Simulations under different grinding parameters and conditions were conducted in the Abaqus-UMAT framework.An UVAG test platform was built,and the grinding temperature rise was verified by embedded thermocouples.The residual stress on the gear surface and at different depths was measured by the X-ray diffraction(XRD)layer-by-layer peeling method to validate the model.[Results]Under the reference condition,the model predicts a peak residual compressive stress of approximately-369 MPa on the gear surface and about-50 MPa at 100 μm,with a deviation from the XRD measurement of no more than 20%.Under different conditions,the average verification error of the surface is approximately 21%,and the trend of the simulated values is consistent with the test values.Compared with conventional grinding,the peak residual compressive stress under UVAG conditions increases by 20%-30%,and the effective depth of action increases by about 50%.The results show that UVAG can reduce the average Taylor factor and increase the slip activity by suppressing frictional heating and promoting multi-slip coordination and dislocation proliferation,thereby reconstructing the cross-scale stress field.The established model can be used for residual stress prediction and process parameter optimization of UVAG in aerospace gears.

Abstract:[Objective]Aiming at the problem that the gear transmission system of aero-engines is prone to traveling wave resonance under complex operating conditions,which further restricts high-reliability lightweight design,the vibration avoidance optimization of gear web structure was carried out.[Methods]Firstly,a surrogate model for gear modal frequencies was constructed based on Kriging interpolation method and Bayesian hyperparameter optimization to replace high-cost numerical analysis and efficiently predict the influence of structural parameters on natural frequencies.Secondly,a multi-objective optimization mathematical model was established with web thickness ratio and rim ratio as design variables,aiming at minimizing system mass and maximizing comprehensive mesh stiffness.Thirdly,the surrogate model was embedded into the non-dominated sorting genetic algorithm Ⅲ framework,and multiple constraints including resonance speed margin were imposed to conduct multi-objective iterative optimization.Finally,the technique for order preference by similarity to ideal solution was adopted to comprehensively evaluate the Pareto front solutions and select the optimal structural scheme.[Results]The results show that the coefficients of determination(R2)of the established surrogate model for the first three nodal diameter natural frequencies of gears reach 96.8%,94.7%,and 98.8%,respectively,and the prediction accuracy meets the requirements of engineering design.After optimization,the resonance points of six gears with traveling wave resonance risks under continuous and high-speed operating conditions are all effectively avoided.Compared with the initial design scheme,the total mass of the gear set is reduced by 14.4%,and the contact and bending fatigue safety factors of each gear still meet the strength standards of greater than 1.25 and 1.5,respectively,which provides a reference for the lightweight design of aviation gear transmission structures.

Abstract:[Objective]During the grinding of helical gears with helical crowning,tooth flank twist defects frequently occur,which degrade tooth flank accuracy and transmission performance.Accordingly,an anti-twist grinding method using variable-lead worm grinding wheels was proposed for helical gears with helical crowning.[Methods]Firstly,the instantaneous contact lines between the worm grinding wheel and the helical gear were calculated based on their meshing relation,and the tooth flank inclination deviation and tooth flank twist at different tooth width positions were obtained.Secondly,a variable-lead dressing motion model between the dressing roller and the compensation section of the worm grinding wheel was established according to the calculated twist values at three measurement positions.Finally,the calculation algorithm of tooth flank twist and the dressing motion algorithm of the roller were integrated into the numerical control system to develop a numerical control dressing program for variable-lead worm grinding wheels.[Results]The results show that after twist compensation,the twist of the left and right tooth flanks is reduced by 93.6%and 81.4%,respectively,which verifies the effectiveness of the proposed twist compensation algorithm.

Abstract:[Significance]Oriented to the supporting and mounting struts of helicopter final drive,the technical development status of periodic and intelligent struts was explored based on the evolution trend of strut structure.[Analysis]Firstly,the layout configurations for mounting and supporting of the helicopter final drive was introduced.Secondly,the structural characteristics and applicable scopes of each mounting and supporting layout were summarized and analyzed.Finally,combined with typical aircraft cases,the application status of various mounting and supporting layouts in conventional single-rotor helicopters and coaxial twin-rotor helicopters was concluded.[Prospect]It is proposed that the collaborative optimization of lightweight materials and intelligent algorithms will serve as a vital approach to improve the dynamic performance of support systems in the future.

Abstract:[Objective]15Cr14Co12Mo5Ni alloy is a new type of low-carbon high-alloy steel featuring high strength,high temperature resistance and excellent wear resistance,which is widely adopted in high-end fields such as aerospace and automotive transmissions.Magnetic particle inspection plays a vital role in quality inspection of components made from this alloy.However,the occurrence of short rod-shaped magnetic traces frequently interferes with inspection results.Investigating the formation mechanism of short rod-shaped magnetic traces and analyzing their correlations with the internal microstructure,carbide distribution and forging process of the alloy can provide basis for optimizing forging procedures,controlling grain size,restraining excessive development of dislocation slip bands and reducing interference from magnetic traces.[Methods]Specimens with and without magnetic traces on the shaft bore of alloy gears were selected.Combined with magnetic particle inspection,scanning electron microscopy,metallographic observation and energy dispersive spectroscopy analysis,comparative research on morphological characteristics of magnetic traces,carbide compositions and grain structure differences was carried out from both macroscopic and microscopic perspectives.[Results]Macroscopic and microscopic analyses reveal that the formation of short rod-shaped magnetic traces is closely associated with the clustered distribution of Cr-Mo carbides inside the alloy.Such carbides generate magnetic leakage fields by altering local magnetic permeability,leading to the accumulation of magnetic particles.Further research clarifies the microstructure evolution chain for short rod-shaped magnetic traces,which can be summarized as:coarse grains → dislocation slip bands → Cr/Mo enrichment → directional precipitation along interfaces →carbide banding → magnetic permeability gradient → short rod-shaped magnetic traces.

Abstract:[Objective]The encased differential planetary gear train of a coaxial helicopter consists of numerous components with varying failure probabilities.Identifying weak components and potential failure modes is critical for implementing targeted measures,such as structural optimization or material substitution,to enhance the system's service life and reliability.[Methods]Firstly,a comprehensive risk assessment model was developed by integrating fuzzy set theory with the technique for order preference by similarity to ideal solution(TOPSIS).Secondly,trapezoidal fuzzy numbers were utilized to construct a robust fuzzy evaluation matrix,and a hybrid weighting scheme combining the analytic hierarchy process(AHP)and the entropy weight method was implemented to determine objective and subjective index weights.Finally,an expert scoring framework was established,and a ranking index was calculated for each component to prioritize failure risks.[Results]The analysis results demonstrate that among the gear components,the sun gear of the differential stage exhibits the highest risk index,identifying it as the weakest part of the system.The primary failure modes are determined to be tooth surface wear and tooth root cracks.The evaluation results provide clear technical guidance for the structural optimization and material replacement of this gear train.

Abstract:[Objective]To meet the high-quality and high-efficiency manufacturing requirements of spur gears for aviation equipment,conventional single-degree-of-freedom forming processes such as die forging and extrusion suffer from insufficient tooth profile filling and excessive forming load when fabricating aviation spur gears.A novel multi-degree-of-freedom forming concept for aviation spur gears was innovatively proposed.By applying continuous local multi-degree-of-freedom loading via rolling dies,the metal flow capacity was improved and forming load was reduced.Meanwhile,the grain structure of gears was refined,and continuously distributed metal flow lines along the tooth profile were generated,which further enhances gear strength and extends fatigue life,thus provides a new technical route for manufacturing aviation spur gears with high strength,high toughness and long service life.[Methods]Firstly,finite element simulation was adopted to investigate the influence law of blank shape on tooth profile filling performance and forming load,based on which an optimized blank design method was proposed.Secondly,the laws of tooth profile filling,distribution and evolution of equivalent strain,as well as the evolution of metal flow lines during forming were revealed.Finally,multi-degree-of-freedom near-net-shape forming process test for aviation spur gears was carried out according to finite element simulation results.Grain size and metal flow line inspections were conducted on test specimens to verify the validity of the above finite element model and simulation results.[Results]The results indicate that the frustum-shaped blank can effectively improve tooth profile filling and reduce forming load,and aviation spur gear specimens with fully filled tooth profiles are ultimately obtained.Moreover,the multi-degree-of-freedom forming method introduces severe plastic deformation in the tooth profile region,which not only significantly refines gear grains,but also produces continuous metal flow lines following the tooth contour.Accordingly,the multi-degree-of-freedom near-net-shape forming technology enables high-performance manufacturing of aviation spur gears.

Abstract:[Objective]Shot peening can significantly improve the fatigue resistance of gears by introducing residual compressive stress into the gear surface layer.In existing numerical simulations of shot peening,the tooth surface is mostly simplified as a local plane,and the effect of tooth profile curvature is not fully considered.To reveal the influence mechanism of tooth profile curvature on residual stress distribution,a shot peening simulation model of helical gears considering tooth profile characteristics was established,and the distribution law of residual stress at key positions of the tooth surface was investigated.[Methods]Firstly,an explicit dynamic simulation model of shot peening was constructed based on the Johnson-Cook constitutive model with the aid of Abaqus software,and a calculation method for coverage under different incident angles was proposed.The accuracy of the model was verified by comparison with test results from prior studies,providing reliable support for subsequent analysis.Secondly,calculation methods for normal curvature,shot incident angle and velocity at the addendum circle,pitch circle,common tangent line and transition surface center of helical gears were derived,and the tooth profile characteristic parameters of each position were clarified.Then,single shot peening simulation was carried out to analyze the influence law of concave and convex tooth surface curvature on the residual stress field.Finally,multiple sets of secondary shot peening process schemes were designed to explore the regulatory effects of shot diameter and peening velocity on residual stress distribution.[Results]The results show that both the surface residual compressive stress and the maximum residual compressive stress present a decreasing trend during the transition of the tooth surface from concave to convex.The surface residual compressive stress,maximum residual compressive stress and depth of the residual stress layer at the transition surface center all reach the maximum values on the whole tooth surface.Secondary shot peening can effectively increase the maximum residual compressive stress,and increasing the shot incident velocity of secondary shot peening is the core strengthening measure,which can provide reference for the optimization of helical gear shot peening processes.

Abstract:[Objective]The time-varying mesh stiffness of gears is influenced by multiple coupled factors,including initial parameters,assembly errors,overlap ratio,wear,and thermo-mechanical coupling effects.To address the ambiguity in applicability boundaries caused by the diversity of existing numerical calculation methods,several typical numerical approaches were systematically elaborated and compared based on the fundamental calculation principles of gear mesh stiffness.[Methods]Firstly,a parametric model was established using cylindrical spur gear pairs as the research object.Secondly,a finite element model was constructed based on the parametric model.Thirdly,employing modular object-oriented programming approaches,the selected typical numerical calculation methods(ISO 6336-1:2019 standard,Ishikawa method,Weber method,and potential energy method)were programmatically implemented.Finally,the finite element model was solved and numerical calculations were performed for each method,followed by comprehensive comparative analysis from multiple perspectives including time-varying mesh stiffness variation patterns,single tooth stiffness,compliance components,average mesh stiffness,and average single tooth stiffness.[Results]The study reveals that the ISO 6336-1:2019 standard demonstrates strong engineering applicability but fails to construct a time-varying model.The analytical method and finite element method share similar mechanical principles,yet their relative error reaches 14%due to model simplification and theoretical discrepancies.The compliance calculated by the analytical method exhibits a nonlinear increasing trend from the tooth root to the tip,aligning with mesh deformation patterns and validating its modeling rationality.However,model modifications are required for complex gears or special operating conditions to enhance adaptability.The potential energy method,which accounts for coupled tooth-body deformation,achieves a computational efficiency significantly higher than the finite element method while maintaining an error margin within 1%.This comparative study clarifies the distinctions and commonalities among algorithms,providing guidance for method selection and the development of high-precision,high-efficiency gear stiffness calculation models.

Abstract:[Objective]To address the low prediction accuracy and parameter optimization difficulties of tooth surface roughness for spiral bevel gears,and overcome the limitations of traditional methods in handling complex nonlinear relationships and multivariate coupling effects,machine learning models were adopted to predict the tooth surface roughness of spiral bevel gears.[Methods]Firstly,based on the grinding test dataset of spiral bevel gears,three machine learning algorithms including decision tree(DT),support vector regression(SVR)and artificial neural network(ANN)were used to establish roughness prediction models for the convex and concave tooth surfaces,and the prediction performance of the three models was compared.Secondly,multiple linear regression was applied to derive a calculation formula for tooth surface roughness incorporating machining parameters of spiral bevel gears.Finally,Shapley additive explanations(SHAP)were employed to quantify the contribution of each input feature to the predicted roughness,providing references for the application of machine learning in high-performance gear manufacturing.[Results]The results show that the DT model suffers from underfitting and the SVR model suffers from overfitting,both yielding poor prediction performance.The ANN model achieves excellent data fitting and accurate roughness prediction at the cost of relatively slow computation speed.Its mean relative errors for predicting convex and concave surface roughness reach 3.5%and 6.09%,respectively.The influence degree of each machining input parameter on tooth surface roughness,sorted from highest to lowest,is grinding speed,grinding depth and generating speed.

Abstract:[Significance]Aiming at the strict requirements for lubrication performance of face gear transmission in helicopter transmission systems,as well as the problems that the analysis system of tooth surface contact-lubrication coupling characteristics in existing research needs to be improved and the engineering application technical path is not clear,the research progress of face gear lubrication technology was systematically sorted out,and the core technical direction and development trend were clarified.[Analysis]Firstly,the research context of face gear lubrication technology for helicopter transmission scenarios was sorted out,and the core research boundary of this field was defined;secondly,the core technology of tooth surface contact characteristic analysis of face gear was disassembled to provide key input parameters for lubrication characteristic analysis;thirdly,the analysis methods and research results of tooth surface lubrication characteristics of face gears were summarized to clarify the key influencing factors of lubrication performance;finally,combined with the engineering requirements of helicopter transmission,the future key development directions of this field were prospected.

Abstract:[Objective]The primary failure modes of aviation spiral bevel gears include tooth surface scuffing,wear,and scoring.Current evaluation methods for these failures neglect the influence of surface integrity parameters,making it difficult to accurately assess the correlation between the appearance of scuffing and the actual degree of damage.This study was conducted to establish a clear relation between surface integrity parameters and the extent of tooth surface damage.[Methods]Taking a pair of aviation main reducer spiral bevel gears as the research object,the evolution of its surface integrity parameters—surface roughness,residual stress,and surface layer crystal structure—was systematically measured and analyzed pre-and post-scuffing.Specifically,the surface morphology skewness and kernel average misorientation maps at various depths were employed to quantitatively characterize the scuffing topography and the micro-plastic strain state.Based on the numerical changes in these integrity parameters,the actual damage state of the tooth flank was analyzed,leading to the proposal of a new concept and a precise evaluation method for a phenomenon termed"running-in scuffing".[Results]For the specific aviation spiral bevel gears studied,significant contact stress and high sliding velocity during test runs lead to tooth surface scuffing.The surface integrity parameters after scuffing are characterized by a decrease in surface roughness,a surface skewness approaching zero,an increase in residual compressive stress,and grain refinement.This type of scuffing is defined as"running-in scuffing",and it is proposed that gears exhibiting these characteristics can continue in service and should not be classified as failed.This research provides a new perspective on the classification and evaluation of gear tooth scuffing and offers a reference for troubleshooting scuffing faults in aviation gears.

Abstract:Robot dexterous hand can mimic human movements to realize multiple tasks in complex scenar-ios,which is a key technology for developing intelligent humanoid robots.Focusing on the research history of ro-botic dexterity,the current research status of multi-fingered dexterity was elaborated,and the evolution process and research progress of dexterity were analyzed.The classification and characteristics of dexterous hands were discussed in terms of the number of degrees of freedom,drive mode,mechanical transmission mode and sensing technology,and the future development trend of dexterous hands was envisioned.

Abstract:In order to solve the problems such as low efficiency,route redundancy and insufficient smooth-ness of the traditional probabilistic roadmap method(PRM),an improved PRM was proposed for obstacle avoid-ance path planning of manipulators.Sobol sequence sampling method was used to improve the connectivity of probabilistic road map and the success rate of the algorithm.Redundant node pruning and progressive route pruning based on dichotomous interpolation were adopted to make the path more approximate to the optimal so-lution.Finally,the path was smoothed by using the quintic polynomial interpolation method to make the motion of the manipulator more stable and smoother.The simulation results show that the improved PRM can improve the success rate of path planning,optimize the path,reduce the number of nodes and path length,and the manip-ulator is more uniform and smoother.The experiment proves that the method can effectively and reasonably real-ize the obstacle avoidance and path planning of the manipulator.

Abstract:As a core component of mechanical equipment,the health status of gear transmission devices is related to various aspects of industrial production.Therefore,the health status monitoring and fault diagnosis of gear transmission devices are of great significance.Firstly,a thorough analysis of the advantages and feasibility of the fault diagnosis based on acoustic signals was conducted,and the process and methods of the fault diagno-sis based on acoustic signals were combed.Then,the principle,advantages,limitations and application effect of the acoustic signal denoising,feature extraction and machine learning application methods respectively were ex-pounded and summarized.Finally,the research hotspots and difficulties of the fault diagnosis based on acoustic signals in the field of rotating machinery were pointed out,and prospects for future research directions in the ar-ea were made.

Abstract:To address the problems of long planning time and poor operability of pick-and-place(PAP)movement of a mobile manipulator in an indoor environment,an enhanced regular A* algorithm was proposed to determine the optimal docking position and perform system motion planning,using manipulator operability as the evaluation criterion.Firstly,on the basis of conventional A* algorithm,eight search directions were simpli-fied to five to improve the search efficiency.At the same time,a new heuristic search function was designed,and Floyd algorithm was introduced into the A* algorithm to increase the smoothness of the path.The simulation re-sults show that the running time of the improved A* algorithm is shortened by 59.1%,the path length was re-duced by 3.5%,and the number of search nodes is reduced by 41.6%.Secondly,according to the reachable workspace and Jacobian matrix of the manipulator,the maneuverability of the mobile manipulator in different po-sitions near the target object to be PAP was evaluated,and the docking position was optimized to improve the maneuverability of the PAP movement.Finally,a mobile manipulator system consisting of a DIY six-degree-of-freedom(DOF)manipulator and Turtlebot2 mobile platform was employed to conduct comprehensive motion planning experiments in indoor environment,which verifies the effectiveness and reliability of the proposed method.

Abstract:[Objective]Based on the basic assumption of solving the planar kinematics of wheeled mobile mechanisms,the planar kinematics problem of wheeled mobile robots was studied.[Methods]Firstly,the kinematic solution method for a rigid body pure rolling on a fixed plane curve was analyzed,and the time differentiate expression of arc-coordinate of the contact point which the rigid body pure rolling on the curve during the process was obtained;combined the expression with the example of actuated wheel pure-rolling on the terrain,the coordinate of the contact point was obtained as the drive function which repre-sented the interaction between the actuated wheel and the terrain.Secondly,the coordinate relation between wheel-terrain con-tact point and wheel center was derived through the normal direction wheel radius deviation method,making the wheel center trajectory equation ascertain.Thirdly,the derivation was specialized to six-wheel guide-bar-linkage suspension;to illustrate the development method,the solving process was divided into two parts:the rear wheel leg and the rocker arm front wheel leg;the constraints equations of mobility mechanism,drive function of actuated wheel and wheel center trajectory of passive wheel were combined to form the composite equations of the wheeled mobile robot motion.The kinematic equations of mobile robots were solved by using the Matlab nonlinear equation solving algorithm in an integral definition recursive loop,and completed post-pro-cessing of parameters.Finally,Adams software was used to simulate and verify the theoretical model.[Results]The results show that the modeling and solving process of the planar kinematics model of the wheeled mobile robot composed of the driving wheel driving function,mechanism constraint equation,and wheel center trajectory equation is accurate,and can obtain the mo-tion information of each component of the robot.This method can be summarized as a universal approach for modeling and solv-ing the planar kinematics of wheeled mobile robots.

Abstract:[Objective]The application of deep learning methods in the field of rolling bearing fault diagnosis is very effective,but traditional neural networks cannot extract features at multiple scales due to the use of a single scale convolution kernel,and do not consider the importance of different features in fault diagnosis.Therefore,it is difficult to extract fault features of rolling bearing signals under noise interference.A rolling bearing fault diagnosis method based on parameter-optimized variational mode decomposition(VMD)noise reduction and GoogLeNet network with improved attention mechanism was proposed.[Methods]The local minimal envelope entropy was used as the fitness function,and the sparrow search algorithm(SSA)was used to optimize the VMD parameter combination;the optimized VMD algorithm was used to decompose the bearing vibration signals to obtain several modal components,and the signals were reconstructed by filtering the modal components with rich fault features according to the envelope entropy and kurtosis;the reconstructed signals were used to construct the feature matrix and input into the improved GoogLeNet network to complete the diagnosis.[Results]The test results show that the diagnostic accuracy of the method is 95.5%to 99.8%under different noise backgrounds,which is better than other methods in terms of noise robustness.

Abstract:A light truck 3.5 t parallel shaft electric drive axle was taken as the research object,and the NVH test was carried out to it.In order to find out the main cause of howling and carry out optimization lifting,the method of combining experiment with simulation was adopted.Based on the test results,it is found that the main reason of the howling is the meshing excitation of the first gear of the electric drive axle,and then the rigid-flexible coupling multi-body dynamic simulation model of the electric drive axle was established based on the Romax Designer software.Through the calculation of transmission error and load distribution on the gear surface of the reducer,the vibration response of the shell was obtained.In order to reduce the fluctuation of transmission error of the gear,the micro modification of the reducer gear was carried out by using genetic algorithm,thus the excitation of the electric drive axle caused by the gear meshing was reduced,and the NVH performance of the electric drive axle was further improved.The aim is to provide reference for technical research in this field.