ObjectiveTo 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.MethodsFirstly, 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.ResultsThe 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.
Shifting industry attitudes to gender diversity are reflected in the coverage of two of the sector’s longest-running publications: The Engineer (launched in 1856) and Machinery (launched in 1912).
ObjectiveIn order to improve the pose accuracy of the 2PSR-PUU parallel machine tool with large swing angle characteristics, related research was conducted on the 2PSR-PUU parallel machine tool as the object.MethodsFirstly, the closed-loop vector method was used to solve the forward and inverse kinematics of the parallel robot. Secondly, an error model for parallel robots was established using partial differential theory, and a quantitative analysis was conducted on the relation between error parameters and the pose accuracy of the moving platform. The error compensation model of the parallel machine tool was established, and the improved particle swarm optimization algorithm was introduced to perform optimization solution of the error compensation function. Finally, simulation analysis of the error model for the parallel robot was carried out in Matlab.ResultsThe simulation and test results show that after error compensation of the parallel machine tool, the order of error of each pose parameter is effectively improved. The maximum error values of the moving platform in the x and z axes and the angle of freedom direction in the φ direction are reduced from 1.614 mm, 1.612 mm, and 0.468° to 0.001 99 mm, 0.001 50 mm, and 0.001 1°, respectively. Moreover, the peak in the pose error curve before and after compensation is improved, proving that the error compensation algorithm can effectively improve the motion stability and pose accuracy of the 2PSR-PUU parallel machine tool.
ObjectiveA multi-dimensional improvement strategy was proposed to address the defects of the traditional A* algorithm in path planning of orthogonal snake-like robots, including large search range, excessive redundant corners and insufficient path smoothness, so as to generate planned paths adapted to the winding motion characteristics of snake-like robots.MethodsFirstly, a weight coefficient was added to improve the heuristic function, realizing controllable adjustment of the algorithm’s search range and improving search efficiency. Secondly, the redundant corner optimization method under the same cost was adopted to effectively reduce the number of redundant corners in the path. Then, the gradient descent method was introduced to generate the basic path suitable for the winding motion of snake-like robots. Finally, the lowess locally weighted regression smoothing method was used to re-smooth the path to further improve path smoothness. A co-simulation model was built using Adams software and Matlab software, and co-simulation tests were carried out on variable-amplitude paths and turning paths.ResultsThe results show that the snake-like robot can achieve smooth amplitude switching from 0.982 3 to 0.576 3 with a turning angle of approximately 45°, and can complete two stable turning transformations in opposite directions. The rationality of the improved A* algorithm is verified, which provides a reference for motion path planning of snake-like robots.
ObjectiveAiming at the tracking and capturing challenges of non-cooperative space targets characterized by unpredictable motions and irregular geometries, which frequently cause rigid manipulators to slip, a novel biomimetic coupled space capture gripper featuring a large workspace, low requirement for relative positioning precision, and high modularity was developed based on the evolutionary predation enveloping strategy of the basket star.MethodsFirstly, the finger structure was synthesized using a crossed four-bar linkage as the core modular cell with serially connected knuckles, into which a synchronized master-branch steering transmission scheme was embedded to execute coordinated single-actuation multi-joint linkage motions. Secondly, the spatial kinematics of a single finger were derived through the closed-loop vector loop-closure technique, and the multi-body coordinate transformations were solved via the Denavit-Hartenberg parameter method. Thirdly, singularity configurations inside and along the boundary of the operational zone were identified via the determinant of the system Jacobian matrix. Furthermore, the workspace boundaries under distinct structural designs were calculated using an analytical boundary-stitching methodology integrated with the Gauss area formulation. Finally, a physical prototype was fabricated utilizing photosensitive resin 3D printing and validated through macroscopic cage-enveloping grasping sweeps on an automated motor-driven evaluation platform.ResultsKinematic evaluations and laboratory tests demonstrate that the single-actuator symmetric pushrod mechanism effectively governs the five-finger synchronized closure trajectories. The parameterized sweeps indicate that optimization of link proportions substantially expands the peripheral reachability boundaries. The fabricated prototype successfully accomplishes form-closed self-adaptive captures on both rigid irregular polyhedrons and complex soft targets, confirming the high reliability and control simplicity of the biomimetic layout for orbital maintenance and debris removal missions.
[Objective]Aiming at the demand for high reduction ratio,high rigidity and high power density in precision transmission,a double-branch zero-backlash toroidal worm helical gear mechanism was proposed.Tooth surface topology modification was adopted to improve the comprehensive curvature and load-bearing capacity of transmission pairs,and solve the problems of large backlash and insufficient dynamic stability in traditional worm helical gear transmission.[Methods]Firstly,a precise three-dimensional model of the reducer was established,and the finite element method was used to compare the equivalent stress and displacement distribution of the tooth surface before and after modification to determine the optimal topology modification parameters.Secondly,multi-body dynamic simulation was carried out using Adams software to analyze the dynamic response characteristics of the system under different rotational speeds and load conditions.Finally,a closed power flow reducer test bench was built,and vibration signals were collected through acceleration sensors to verify the dynamic performance of the double-branch mechanism.[Results]The results show that the bidirectional topology modification of tooth profile and helix can reduce the equivalent contact stress of the tooth surface by 18.2%,the strain by 24.5%,and the tooth root bending stress by 26.2%.The double-branch mechanism can significantly suppress the vibration response of the system,and the overall vibration acceleration amplitude is reduced by 25.09%compared with the single-branch mechanism.The test data have high consistency with the simulation results,which can provide a reference for the design of high-performance precision transmission devices.
ObjectiveThis study aims to investigate the coupling effect between inner and outer defects on fatigue crack initiation in high-speed train axles to ensure operational safety.MethodsFirstly, a multi-crystal finite element model was established at the mesoscopic scale based on crystal plasticity theory. Secondly, tensile and impact tests were conducted, and finite element simulations were utilized to analyze the stress field and structural deformation around these defects. Finally, the crack initiation location was predicted based on the characteristics of stress distribution and plastic strain energy density.ResultsThe findings indicate that the interaction between the two defects strengthens as the inner defect approaches the outer defect, significantly promoting crack initiation. Conversely, when the inner inclusion is located at the center of the model, the interaction is minimized, and external defects become the primary drivers of crack initiation.
ObjectiveTo address the challenge of accurately extracting weak fault features of rolling bearings under strong background noise, a novel fault feature extraction method integrating improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN), variational mode extraction (VME), and multipoint optimal minimum entropy deconvolution adjusted (MOMEDA) was proposed. The aim is to enhance the identification accuracy of weak fault characteristics.MethodsFirstly, with minimum envelope entropy as the objective, the crested porcupine optimizer (CPO) algorithm was employed to optimize the white noise amplitude weight and the number of added noise ensembles for ICEEMDAN. The original vibration signal was decomposed, and the optimal intrinsic mode function (IMF) was selected based on the maximum envelope spectrum peak factor. Secondly, guided by minimum envelope entropy, CPO optimized the balancing parameter and center frequency of VME to extract the frequency band containing the most critical fault information from the optimal IMF. Then, targeting the maximum envelope spectrum peak factor, CPO optimized the filter length and fault pulse period for MOMEDA to enhance the fault features of the extracted signal. Finally, envelope demodulation analysis was performed on the enhanced signal to extract fault characteristic frequencies.ResultsValidated by a public dataset, the proposed method clearly extracted the inner race fault frequency (162.185 2 Hz) of the rolling bearing and its multiples, with interference frequencies effectively suppressed in the envelope spectrum. The outer race fault characteristic frequency (107.364 3 Hz) is also accurately identified. Compared to using ICEEMDAN or VME alone, this method more effectively highlights fault-induced impulses, significantly improves the signal-to-noise ratio, and provides a reliable basis for accurate fault type identification.
ObjectiveIn order to clarify the resonance characteristics, dynamic load, and even load laws of the NASA LCTR2 project composite planetary gear variable speed transmission system in high and low speed gears, and to make up for the existing research deficiencies in the coupling analysis of the dynamic characteristics of dual gear planetary transmission, relevant research was carried out to meet the dynamic performance evaluation requirements of the system.MethodsFirstly, a multi-degree-of-freedom translational-torsional dynamic model was established using the lumped mass method. Secondly, dynamic equations were derived and solved via Matlab/Simulink software to obtain response data. Thirdly, natural modes were calculated, and the accuracy of the model was verified by modal tests with a modal assurance criterion value ≥ 0.7. Finally, comprehensive meshing errors were introduced to analyze the effects of input speed and load torque on dynamic load and load sharing coefficients.ResultsThe natural frequencies and resonance speeds for the low-speed gear (231.7-10 723.9 Hz) and high-speed gear (556.8-10 723.1 Hz) were identified. Both dynamic load and load-sharing coefficients increase with the increase of the input speed, with the high-speed gear's dynamic load coefficient being more speed-sensitive. Conversely, both coefficients decrease as the load torque increases, particularly for the internal meshing dynamic load coefficient. Reducing input speed and increasing load torque appropriately can improve the system's dynamic characteristics.
ObjectiveEffective lubrication is one of the most efficient methods for reducing friction and minimizing wear on metal component surfaces in mechanical motion pairs. To address the rapid friction and wear failure of the planetary gear shaft in differential assemblies, the anti-wear and friction-reduction effects of fullerene C60 nano-carbon sphere lubricant on planetary gear shafts were investigated.MethodsFirstly, friction and wear tests were conducted under the action of fullerene C60 lubricant to analyze the influence of C60 nano-carbon sphere concentration on the friction coefficient and wear scar surface morphology. Secondly, a differential assembly fatigue life test bench was utilized to perform fatigue wear tests on the differential planetary gear shaft, observing the friction-reducing effects of C60 nano-carbon spheres on the gear shaft.ResultsThe analysis results demonstrate that the average friction coefficient under the action of fullerene C60 nano-carbon sphere lubricant is as low as 0.080 1, representing a 71.1% reduction compared to the base lubricant. Furthermore, the wear amounts on both ends of the planetary gear shaft pins decrease by approximately 60%.
ObjectiveTo analyze the meshing performance of the face gear pair, a method for calculating the meshing area of the face gear tooth surface was proposed. Based on this, the influence of misalignment on the meshing area was revealed.MethodsFirstly, a meshing coordinate system for the face gear pair was established, and the tooth surface equation for the face gear was derived based on the gear meshing principle. Secondly, a contact analysis model for the face gear pair was developed, and a meshing area calculation model for the face gear pair was derived using numerical integration and curve interpolation. Then, the influence of axis offset error, axis angle error, and axis alignment error on the meshing area of the face gear pair was analyzed. Finally, the correctness of the meshing area calculation method and the influence of misalignment was verified through the finite element method.ResultsThe results show that the misalignment has an impact on the meshing contact area, and the influence law is related to the offset direction of the contact trajectory. Among these error types, the axis angle error has the greatest impact on the meshing contact area, followed by the axis offset error, and the axis alignment error has the least impact.
ObjectiveAiming at the problem that the four-point support transmission chain of wind turbines is designed as pure torsion while ignoring bending moment transmission, the load-bearing mechanism of hydraulic elastic supports and the law of additional bending moment transmission caused by system micro-deformation were thoroughly explored to provide a reference for the design optimization of transmission components.MethodsFirstly, the stiffness composition and bending moment transmission mechanism of hydraulic elastic supports were analyzed, and the superposition characteristics of bending-torsion coupling were clarified to lay a foundation for modeling. Secondly, a transmission dynamic model was established using SIMPACK software, and a calculation method for equivalent torsional stiffness was proposed to achieve decoupling of vertical and torsional stiffness, ensuring model authenticity. Thirdly, bending-torsion coupling tests were carried out on a 6-degree-of-freedom test bench, and load data at the hub center and gearbox input end were obtained by applying loads under different working conditions using the control variable method. Finally, the simulation and test results were compared, the causes of deviations were analyzed and the model was corrected to verify the reliability of the method.ResultsThe results show that the simulation and test results are highly consistent in both the trend and quantification of bending moment transmission. The maximum deviation of the bending moment at the gearbox input end is no more than 7.71%. Part of the hub center bending moment is transmitted to the gearbox, with the transmission ratio less than 3% in the heavy load range and less than 4% in the light load range. The results have practical guiding significance for the design of relevant drivetrain components.
ObjectiveAiming at the problem that wind power bearings are interfered by nonlinear factors and non-Gaussian noise during the monitoring process, and the degradation showing stage characteristics, a model combining adaptive particle filtering with a multi-stage nonlinear Wiener process was constructed.MethodsFirstly, the Wiener process was introduced into the state-space model of particle filtering to enhance the nonlinear expression ability of the model. Meanwhile, the sampling process was adjusted using an adaptive sampling strategy to effectively avoid particle degradation, thus improving the accuracy of the state estimation and correcting the bearing degradation index. Secondly, a degradation model of bearings was established based on the multi-stage nonlinear Wiener process, and the drift coefficients were randomized by taking into account the variability of different individual bearings. The segmentation points of the degradation stages of bearings were determined by the cumulative sum algorithm, and the model parameters were estimated using the maximum likelihood estimation algorithm. Finally, verification and analysis were conducted on the test bench data and the monitoring data of the free-end bearings of the wind turbine, and the remaining life prediction results obtained by the proposed method were compared with those obtained from the degradation index without filtering correction.ResultsThe results show that the proposed method has higher prediction accuracy.
ObjectiveThe influence of the geometric difference of opposite tooth flanks on the contact line length and meshing performance of traction helical gear pairs for rail transit trains was analyzed to reveal the formation mechanism of the transmission performance difference of traction gearboxes during the train’s upward and downward travel, and make up for the deficiency that the geometric difference of opposite tooth flanks of helical gears is not considered in existing studies.MethodsFirstly, the geometric difference angle of opposite tooth flanks was defined, and its calculation formula was derived to provide a parameter basis for the quantitative analysis of the tooth back contact line length. Secondly, combined with the characteristics of the tooth back contact surface and the geometric difference of opposite tooth flanks, a calculation formula for the tooth back contact line length was established to explore the coupling influence law of the geometric difference of opposite tooth flanks and backlash on it. Then, a multi-state meshing dynamic model of helical gear pairs considering the geometric difference of opposite tooth flanks was constructed, and the dimensionless normalization of the model was completed. Finally, the dynamic characteristic analysis of the system was carried out through numerical calculation to clarify the system motion characteristics under different meshing frequencies.ResultsThe results show that the geometric difference of opposite tooth flanks leads to an obvious phase difference between the contact line lengths of the tooth flank and the tooth back, and the influence of backlash on the tooth back contact line length increases with the increase of the backlash value; when the dimensionless meshing frequency ω<0.33, the system maintains a stable single-period motion without tooth disengagement; when 0.33≤ω≤0.37, the system presents a short-term tooth back contact phenomenon; with the increase of meshing frequency, the tooth back contact phenomenon disappears completely, and the system presents tooth surface collision and tooth disengagement. The geometric difference of opposite tooth flanks has a significant influence on the dynamic characteristics of helical gear pairs with frequent reversing, and the relevant analysis results can provide a reference for the design and optimization of traction helical gear pairs for rail transit trains.
ObjectiveThe 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.MethodsFirstly, 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.ResultsThe 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.
[Objective]Splines are important connectors in aviation power transmission systems,and are affected by manufacturing errors,assembly errors or working loads,and often occur in parallel misalignment,angular misalignment and comprehensive misalignment,which affects the meshing length and bearing capacity of each tooth of the spline.In order to improve the stability of the transmission system and reduce the failure rate of aviation splines,the dynamic meshing stiffness characteristics of misaligned splines was analyzed.[Methods]Firstly,the concept of spline meshing length was introduced and equated to the waist length of the equivalent trapezoidal cross-section for sliced single spline teeth,whereby the meshing stiffness of a single spline tooth was acquired.Secondly,a dynamic model for the aviation spline-rotor system was established to solve the time-varying meshing length of splines.Finally,the slicing method was combined with the Ishikawa method to obtain the meshing stiffness of single spline teeth under various misalignment conditions,and the dynamic responses of the system were solved accordingly.[Results]The results show that the change amplitude of spline single-tooth meshing stiffness and the dynamic response of the rotor system increase when the static parallel dislocation and static angular dislocation amount are increased.When the static parallel dislocation amount remains unchanged,and the static angular dislocation amount changes,the change of spline meshing stiffness and the dynamic response of the rotor system is not obvious.When the static angular dislocation amount remains unchanged,the static parallel dislocation amount increases,the spline meshing stiffness and the dynamic response of the rotor system change significantly.
ObjectiveAiming at the multi-tooth fracture problem of the high-speed clutch gear on the input shaft of a certain type of plastic extruder, the failure mechanism was explored, the fracture cause was clarified, and a basis was provided for gear structure improvement and service life enhancement.MethodsFirstly, through macroscopic fracture morphology analysis and scanning electron microscope (SEM) characterization, the fatigue steps, fatigue striations on the fracture, and plastic extrusion/slip marks on the tooth surface were observed, and the failure mode was initially determined. Secondly, chemical composition detection and hardness testing were carried out to verify the compliance of the gear material composition, and the hardness of the tooth surface and core was tested to determine whether surface strengthening treatment had been performed. Then, the finite element method was used to establish a gear pair model, and three working conditions (normal fit, non-parallel centerlines, and misaligned centerlines) were simulated to analyze the stress distribution law of the tooth root, with emphasis on quantifying the influence of centerline misalignment on the tooth root stress amplitude. Finally, the bending stiffness check of the shafting was conducted, and the influence of insufficient shaft stiffness on the alignment of the gear pair centerlines was verified by calculating the equivalent diameter, moment of inertia of the shaft, and deflection at the gear.ResultsThe gear failure mode is fatigue fracture, with obvious fatigue striations and fatigue source areas visible on the fracture. Insufficient bending stiffness of the shaft causes the shaft deflection at the gear to exceed the allowable deflection, leading to misalignment of the gear pair centerlines. When the displacement in the Y direction of the translational degree-of-freedom is 0.01 mm, the stress amplitudes at the tooth roots of the internal and external gears reache 62.66 MPa and 62.72 MPa respectively, which accelerate the initiation and propagation of fatigue cracks. No strengthening treatment such as carburizing is performed on the gear surface, which further reduce the fatigue resistance.
ObjectiveRoller enveloping toroidal worm drives are widely used in computer numerical control (CNC) turntables but face challenges such as high error sensitivity and difficult installation. To solve these problems, a non-backlash end-face roller enveloping worm drive pair was proposed, achieving zero backlash by using one side for motion transmission and the other for clearance elimination.MethodsFirstly, based on spatial meshing theory and differential geometry, the mathematical model of the non-backlash end-face roller enveloping worm drive was established. Secondly, mathematical expressions for meshing performance, including the meshing equation, contact lines, tooth surface equations, induced normal curvature, lubrication angle, and relative entrainment velocity, were derived. Finally, the influence of geometric parameters on meshing performance was analyzed using Matlab software.ResultsThe results indicate that the theoretical meshing teeth of the proposed drive pair are 5 pairs, providing high load-carrying capacity. The lubrication angles of three or more pairs of meshing teeth are approximately 85°, indicating excellent lubrication performance. The induced normal curvatures of these teeth are below 0.25 mm-1, suggesting a good fit of the conjugate tooth surfaces. This design provides a reliable basis for the development of high-precision CNC transmission systems.
ObjectiveDue to the complex structure of planetary gearboxes, fault features are difficult to extract, and traditional methods rely heavily on professional expertise. To solve these problems, a fault diagnosis method integrating beluga whale optimization (BWO) algorithm optimized variational mode decomposition (VMD), multi-scale permutation entropy (MPE), and extreme learning machine (ELM) was proposed.MethodsFirstly, the BWO algorithm was employed to optimize the decomposition layers K and penalty factor α of VMD using the minimum envelope entropy as the objective function to achieve adaptive signal decomposition. Secondly, the MPE algorithm was used to compute the non-linear features of the intrinsic mode function (IMF) components, and a feature vector consisting of five time-domain indexes was constructed. Finally, the vectors were fed into the ELM for training and diagnosis. Comparative tests were conducted on a planetary gearbox test bench under four working conditions.ResultsThe testing results show that the overall accuracy of the proposed method reaches 97.92%, which is significantly higher than that of EMD-ELM and optimized VMD-SVM models. The findings verify that the BWO-VMD effectively improves signal de-noising and adaptive decomposition. This research provides a reliable basis for the health monitoring and precision design of planetary gearboxes.
ObjectiveAiming at the main bearing with three-row roller structure for shield tunneling machines, a fatigue life calculation method considering roller profile modification was established to provide guidance for determining the modification method and degree.MethodsFirstly, through geometric analysis, the mathematical relation between roller-raceway contact deformation and the overall axial and radial displacements of the inner ring was established. Based on Palmgren's empirical formula and the force equilibrium equations of the inner ring, a load distribution model was constructed and solved to obtain the load on each roller. Secondly, the rollers were sliced equidistantly along the generatrix direction. An elastic contact model between the modified roller and the raceway was established using finite line contact theory to obtain the contact stress at each slice. Finally, according to ISO/TS 16281 standard, the roller slice loads corresponding to the basic rated dynamic load and the equivalent dynamic load of the ring were calculated respectively to determine the fatigue life of the main bearing.ResultsThe results show that the roller modification convexity significantly affects the fatigue life of the main bearing. With the increase of convexity, the fatigue life increases first and then decreases, indicating the existence of an optimal convexity that maximizes the fatigue life.
