最新刊期
卷 47 ， 期 3 ， 2023
- 摘要：Parameter sensitivity values of natural frequency of the two branch herringbone gear drive system commonly used in a high-power ship are calculated,and the influence of structural parameters such as meshing stiffness,moment of inertia and manufacturing error on natural frequency of the transmission system is obtained. The torsional dynamic model of the branched drive is established, the vibration mode characteristics of the branched drive are verified by finite element analysis, the parameter sensitivity expression under multi-excitation is deduced by the mode method, and it is applied to the stability analysis of the two-branched herringbone gear drive system. Then, according to the sensitivity value calculated theoretically and the actual working conditions, by optimizing the structure of the transmission system, the modified scheme obtained by this method significantly improves the vibration resistance of the gear train, and through an example, it is found that the key parameters obtained by this analysis method have obvious effect on anti-vibration and noise reduction of the system. This analysis method can also be used in vibration and noise reduction design of other types of branch drives.关键词：Two branch herringbone gear transmission;Sensitivity;Natural frequency;Structural optimization
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发布时间：2023-03-29 - 摘要：Involute tooth profile contains a lot of waviness information. Digging and expanding the application of waviness information to establish its relationship with gear transmission performance has important engineering value. Studying the construction principle of equation of the involute with waviness is to fit the waviness curve based on the measured teeth surfaces data. The involute tooth profiles with different sine waviness are constructed. Based on the meshing principle, the correlation of wavelength, amplitude, phase of waviness and transmission error is analyzed in the time domain and frequency domain, and verified by actual tooth surface data. The finite element model of involute tooth surface with waviness is established, and the correlation between wavelength, amplitude, phase of waviness and contact stress in gear transmission is simulated and analyzed. The gear transmission error test is carried out to verify the correctness of the calculation of transmission error. The results show that the fluctuation amplitude of transmission error is sensitive to the amplitude change of tooth profile waviness; the periodicity of tooth profile waviness is related to the order component of transmission error; with the increase of the number of waviness fluctuation periods, the order amplitude of the corresponding multiple of the number of teeth increases significantly; the magnitude of tooth surface contact stress is mainly affected by the amplitude of profile waviness. Thus the waviness information of gear measurement results between macro and micro quantities is extended and applied, and the research provides a basis for predicting transmission performance based on waviness information.关键词：Waviness in involute;Transmission error;Contact analysis;Finite element model
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发布时间：2023-03-29 - 摘要：In response to the shortcomings such as the degradation of transmission performance of magneto-rheological fluid at high temperature, an alternating transmission method of shape memory alloy and magneto-rheological fluid is proposed. Based on the thermodynamic effect of the shape memory alloy, the relationship between the squeezing pressure of the spring and the temperature is derived, and the correctness of the equation is verified by experiment; the finite element analysis of the magnetic field of the transmission device is carried out, and the magnetic field distribution along the radial direction of the working gap is derived; based on the thermal driving characteristics of the shape memory alloy spring, the relationship between the friction torque and the squeezing pressure, the structure size and other parameters is established. The results show that the squeezing force generated by the shape memory alloy spring increases with the increase of temperature; when the temperature is lower than 40 ℃, the torque is mainly transferred by the magneto-rheological fluid, reaching 9.14 N·m; when the temperature is between 40 ℃ and 60 ℃, the torque is transferred by the magneto-rheological fluid and the shape memory alloy together, reaching 13.24 N·m; when the temperature is higher than 60 ℃, the torque is mainly transferred by the shape memory alloy, reaching 9.40 N·m. As the temperature rises, the shape memory alloy can transmit torque instead of the magneto-rheological fluid, and the device can sense the temperature change to realize the alternating transmission.关键词：Shape memory alloy;Magneto-rheological fluid;Torque;Alternating transmission
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发布时间：2023-03-29 - 摘要：When the gears work under high-speed and heavy-load conditions, the effects of friction and wear cannot be ignored. The gear modification can reduce gear wear and surface temperature, and has a significant effect on improving the anti-scuffing ability of gears. Thus, the heat distortion and modification of gears are studied. Based on the basic theories of gear meshing principle and gear modifying principle, the following studies have been made: a parametric model of gear thermo-mechanical coupling is established using the finite element simulation software; the steady-state heat balance equations for each face of the gear teeth are determined, and the finite element simulation software is used to automatically impose convection boundary conditions and frictional heat fluxes on each point of the gears. By solving the temperature field of the gear, the influence of gear tooth temperature change on gear deformation is analyzed, and gear modification technology is studied. The calculation formulas of elastic deformation, thermal deformation and thermo-mechanical coupling deformation are derived. The results show that the modification can reduce the gear temperature and improve the scuffing strength of the gear.关键词：Gear transmission;Thermo-mechanical coupling;Tooth profile modification;Thermal deformation
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发布时间：2023-03-29 - 摘要：In order to study the nonlinear dynamic characteristics of the curve-face gear transmission system and the influence of parameters on the dynamic characteristics of the system, a nonlinear dynamic model of the curve-face gear system is established. The dimensionless meshing frequency is selected as the control parameter, and the bifurcation diagram, phase diagram, time history diagram and Poincaré diagram are analyzed. The mapping graph is used to study the dynamic characteristics of the system. The results show that the system changes from the non-impact state to the unilateral impact state by jumping bifurcation, and then leads to chaotic motion by continuous doubling bifurcation. When the comprehensive transmission error is increased or the torque is reduced, the non-impact state region of the system shrinks gradually, and the jumping bifurcation value and doubling bifurcation advance, which make the system jump ahead of time. The mode of transition from non-shock to unilateral shock changes, the subharmonic motion region expands gradually and moves forward, the types of motion increase, the number of motion cycles increases, the chaotic motion region expands gradually, and the stability of the system decreases.关键词：Periodic motion;Bifurcation;Chaos
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发布时间：2023-03-29
Theory·Research
- 摘要：Based on the potential energy method, an algorithm for modifying the meshing stiffness of helical gears is proposed. This method considers the real machining of the tooth root transition curve, which is a trajectory line formed by the tip angle of the tooth when the tool rolls into motion, and the starting point of the involute is the intersection of the tooth root transition curve and the involute. When calculating the stiffness, the tooth root transition curve equation from the root of the tooth to the starting point of the involute is used for the calculation, and the involute equation from the starting point of the involute to the top of the tooth is used in the calculation. The meshing stiffness calculated by this method is closer to the reality. Compared with the finite element method, the accuracy of the modified algorithm is verified and the calculation accuracy of the helical gear meshing stiffness is improved. Based on this method, the influence of involute shape, meshing position and contact ratio on the meshing stiffness and transmission error of helical gears is analyzed. The research results show that when the pressure angle increases, the radius of curvature of involute will increase. Thus the transverse stiffness of gears is improved. At the same time, the transverse contact ratio will firstly increase and then decrease. Under the influence of transverse stiffness and transverse contact ratio, the variation trend of average meshing stiffness is the same as that of transverse contact ratio; when the meshing position is closer to the node, the meshing stiffness will increase; an increased total contact ratio will make the average stiffness increase, and the transmission error (TE) decrease as a whole. However, when the contact ratio is close to the odd multiple of 0.5, the TE peak-to-peak value will reach a maximum value.关键词：Tooth root transition curve;Potential energy method;Helical gear;Meshing stiffness;Contact ratio
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发布时间：2023-03-29 - 摘要：In order to improve the comfort and stability of the separable nursing bed-chair, a new type of eight-bar back lifting mechanism with single degree of freedom is designed. Firstly, combining with ergonomics and taking back slip and slip speed as parameters, it is verified that the back lifting motion of the combined lumbar-back backing plate is more comfortable than that of the traditional single-plate backing plate. Secondly, the kinematics model of the backing mechanism is established, and the parametric model of the mechanism is established in Adams software. Based on this model, the sensitivity of each component to the change of maximum angular acceleration of backing plate during backing process is analyzed, and the key dimensions of the mechanism are optimized with the goal that the maximum angular acceleration of backing plate is the minimum. Furthermore, according to the optimized result, the 3D model of the mechanism is built using the SolidWorks, and the rationality of the mechanism strength is verified by the joint simulation of Adams and Workbench. Finally, a prototype is built to verify the feasibility of the mechanism.关键词：Back lifting mechanism;Eight-bar mechanism;Parameter optimization;Adams software;Finite element analysis
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发布时间：2023-03-29 - 摘要：A X-wing flapping-wing mechanism with wings flapping symmetrically is designed. The crank slider mechanism is adopted to convert the circular motion of the crank into the linear reciprocating motion of the straight shaft, and the straight shaft drives the wings on both sides through the rocker to realize the symmetric flapping of the wings. A prototype of the flapping-wing mechanism is made, and the motion test of the flapping-wing mechanism is carried out using an optical motion capture system and a wind tunnel. The reliability of the flapping-wing mechanism is analyzed from the flapping angle amplitude, the flapping frequency, the lift generated, and the operating condition of the motor. Through comparative experiments, a set of suitable flapping angle amplitudes and wing surface areas are determined, so that the flapping-wing mechanism could generate 12.9 g of lift, and it is verified that the clap-fling mechanism could effectively improve the lift of the flapping-wing mechanism.关键词：Flapping-wing mechanism;X-wing;Crank slider mechanism;Motion test;Parameter optimization
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发布时间：2023-03-29 - 摘要：The shape of wave generator directly affects the mechanical characteristics of the flexspline. Flexspline is the weakest part of harmonic drivers. In order to improve its life, the design of a cam wave generator based on a conical curve combination is introduced. The combined curve cam is composed of a parabola, a connecting arc and an eccentric arc; the smooth transition between the parabola, the connecting arc and the eccentric arc is taken as the constraint conditions. The influence degree of each parameter on the maximum equivalent stress of the flexspline is calculated and analyzed by orthogonal experiment, and the curve parameters of each section of the combined curve cam wave generator are determined. The transient dynamic analysis of the flexspline under the action of standard elliptic cam and combined curve cam is carried out using the finite element software, and the fatigue life of the flexspline is studied using the transient dynamic analysis results based on the nCode-Designlife software. The results show that the maximum equivalent stress of the flexspline is lower than that of the standard ellipse cam wave generator, under the action of combined curve cam wave generator, the stress at the front and back ends of the tooth ring in the meshing area of the flexspline is obviously reduced, the stress distribution is more uniform, and the fatigue life is also improved.关键词：Combined curve cam wave generator;Conic curve;Orthogonal test;Flexspline stress;Fatigue life
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发布时间：2023-03-29 - 摘要：In order to ensure the effectiveness and safety of ankle rehabilitation training, an ankle rehabilitation mechanism based on the 3-UPRU/S parallel configuration and its foot fixation and quick release components are designed, and its motion performance and training planning are investigated. A virtual model of the rehabilitation mechanism is established using Adams software. Taking into account the influence of the non-coincidence between the physiological center of the rotation of the ankle joint and the center of the rotation of the mechanism, the virtual model of the ankle is introduced and the S-shaped and T-shaped angular velocity curves are optimized using angular velocity planning to obtain a better training plan. The displacement data of each actuator of the mechanism is obtained by inverse kinematic simulation, and the drive function of each actuator is determined using spline fitting. The actual working angle and training plan are verified by means of a principle prototype test. The results show that the optimized mechanism can increase the training time at constant speed by approximately 12% and reduce the angular velocity fluctuations by approximately 47% in one cycle, indicating that the training plan can improve the effectiveness and safety of the ankle rehabilitation.关键词：Ankle joint;Rehabilitation mechanism;Inverse kinematics;Adams software;Training planning;Spline fitting
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发布时间：2023-03-29
Design· Calculation
- 摘要：Aiming at the difficulty of analyzing the meshing contact characteristics of gear transmission system under the big data formed by multiple working conditions and uncertain parameters, a meshing contact characteristics analysis method of gear transmission system based on data mining technology is proposed. Based on the principle of multi-dimensional Gaussian distribution and the finite element model of gear transmission system, the meshing contact characteristic data set of the system is constructed. The correlation between system parameters and meshing contact characteristics is analyzed using the maximum information coefficient, which provides a candidate feature subset for the prediction model. Then, the prediction model of meshing contact characteristics of the system is established using support vector machine and random forest algorithm, which realizes the efficient prediction of meshing contact characteristics of the system. The results show that the prediction error of the prediction model based on support vector machine is the smallest, and the average absolute percentage error is 3.87%, which is far less than the theoretical calculation error. Under the optimal feature subset, the prediction error index of contact characteristics of the prediction model based on support vector machine decreases significantly, and its average absolute percentage error reaches 3.03%, which is 21.71% lower than the prediction error of contact characteristics before optimization. These have verified the accuracy and effectiveness of the proposed method.关键词：Gear transmission system;Meshing contact characteristics;Maximum information coefficient;Data mining;Prediction model
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发布时间：2023-03-29 - 摘要：The rack and pinion of the three gorges ship lift is a low speed and heavy load open gear transmission with hard tooth surface. Once the lubrication is poor, it is easy to cause damage such as tooth surface scuffing, which will affect the operation safety and reliability of the ship lift. This study is based on the actual operation data of the three gorges ship lift, and the lubrication of racks and pinions under various typical service conditions is systematically analyzed using the oil film thickness criterion. The relationship between the false water depth and the film thickness ratio in the ship compartment is deduced and the film thickness ratio of the lubrication state of the most dangerous meshing point under typical false water depth is calculated when the ship compartment is under constant speed. The worst lubrication condition of the rack and pinion is determined when the ship compartment is ascending and descending with variable speeds, and the relationship between the water depth in the ship compartment and the lubrication condition under variable speed typical operating conditions is analyzed. The position where the scuffing damage is more likely to occur is further determined. The results show that, when the ship lift is running at a constant speed, the lubrication state of the rack and pinion is the best under the optimum water depth in the ship compartment, and the film thickness ratio of the deviation from the optimal water level decreases with the power function
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发布时间：2023-03-29 - 摘要：In order to evaluate the gearbox condition based on dynamic response, a helical gearbox test platform is built in the present work to test and analyze diverse physical parameters, including rotational speed, dynamic transmission error, axis orbit, vibration acceleration, sound pressure and load torque. By adjusting the working condition (shaft speed and load torque) of the gearbox, the assembly accuracy among the components of the gearbox is assessed, and the correlation between different physical parameters is revealed. The results show that the input shaft is misaligned with the motor shaft, and the output shaft suffers the dynamic unbalance; the peak-to-peak value of transmission error is positively correlated with rotational speed, and has a significant correlation with the root mean square value of acceleration and the peak-to-peak value of radial component of the output axis runout at different speeds.关键词：Helical gearbox;Multi-parameter test;Dynamic performance;Angle domain;Correlation
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发布时间：2023-03-29 - 摘要：Microstructure and mechanical properties of the failure flexspline and the Japanese flexspline for harmonic reducers and fracture reason are analyzed by quantitative of microstructure, determination of mechanical properties and fracture analysis. The result shows that the microstructure of the flexspline of the failed harmonic reducer is the same as that of Japan, both of which are tempered troostite. The average grain size of the failure flexspline is 8.2 μm, which is 1.5 μm higher than that of the Japanese flexspline. The microstructure of the failure and Japanese flexible bearings is tempered martensite. The average grain size of failure flexible bearings is 13.1 μm, which is 6.9 μm higher than that of the Japanese flexible bearings. The fracture morphology of the flexspline presents brittle fracture characteristics without obvious crack source. The fracture of flexible bearings shows obvious fracture trend. There are obvious crack trends in the fracture of flexible bearing. The crack source is pinpointed at the region where large agglomerative inclusions are observed. The poor purity of flexible bearing and the coarse microstructure with poor ability to hinder crack propagation are the main causes of premature failures of domestic harmonic reducers.关键词：Flexspline;Flexible bearing;Grain size;Inclusion
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发布时间：2023-03-29
Test·Analysis
- 摘要：In the field of gear fault diagnosis, it is of great significance to effectively diagnose early wear faults of gears. However, early wear fault has weak characteristics and is difficult to diagnose. Thus, a gear early wear fault diagnosis model based on the sparse attention mechanism is proposed to solve this problem. This model uses a new sparse attention mechanism combined with a convolution neural network to improve the traditional sectional attention mechanism and locate the specific fault frequency. The gearbox fault simulation test data is used for test verification. Compared with other diagnosis methods, this new method can achieve a more accurate and comprehensive diagnosis, reduce analysis cost and obtain sensitive fault characteristic frequency under the same sample condition and calculation cost. The conclusion of this method can provide data support for gear maintenance.关键词：Gear wear;Fault diagnosis;Convolution neural network;Attention mechanism
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发布时间：2023-03-29 - 摘要：Data-driven fault diagnosis methods have been widely used in the field of fault diagnosis of rotating machinery components. However, most of the current research methods mainly rely on a large amount of data generated by fixed-length data segmentation. The segmented data is usually a short-period small segment signal, and the actual long-period redundant signal cannot be directly used as a test sample for fault identification. In view of the above shortcomings, a new fault diagnosis method based on data probability density and one-dimensional convolutional neural network (DPD-1DCNN) is proposed. It has two characteristics: ①the density feature of the extracted signal resists the redundancy of the data; ②adapt redundant signals of different lengths as input to the diagnostic model. The method is verified on the planetary gearbox fault data generated by the DDS test bench, which not only ensures high diagnostic accuracy, but also enhances the adaptability of the diagnostic model.关键词：Planetary gearbox;Data probability density;1DCNN;Fault diagnosis
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发布时间：2023-03-29 - 摘要：A kind of RV-like reducer is proposed. Taking the reducer as a model and according to its structural principle, the single-loop XP system type is derived. Based on the single-loop XP system, the reducer speed, the torque and the power matrix are established and the reducer input and output power matrix is obtained; the power flow direction of each component is analyzed, the power flow direction is mapped to the single-loop XP system, and the reducer power flow model is established; a conclusion has been drawn that the RV reducer has no internal circulation power and the overall transmission efficiency of the reducer is relatively high. The transmission efficiency of the reducer is calculated as an example and the overall transmission efficiency can theoretically reach 0.821 0.关键词：RV-like reducer;Single-loop XP system;Power flow;Transmission efficiency
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发布时间：2023-03-29 - 摘要：In the current study, a large exposed forged-and-welded gear with a diameter of 7 160 mm is taken as the research object. An integrated computational approach is employed to predict the total welding deformation of the gear during welding process. Based on software MSC. Marc, three typical welded joints are extracted from the large forged-and-welded gear structures, and the inherent deformations of each joint under multi-pass welding conditions, are calculated by the thermo-elastic-plastic finite element method. The inherent deformations of each welded joint are converted into the corresponding inherent strains, and the total welding deformation of the welded gear is calculated using the elastic finite element method based on inherent strain theory. The numerical simulation results show that the radial shrinkage of the large forged-and-welded gear is about 11 mm after welding, and the amount of contraction in the circumference direction is about 3 mm.关键词：Exposed forged-and-welded gear;Multi-pass welding;Welding deformation;Inherent strain;Numerical simulation
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发布时间：2023-03-29
Development·Application
- 摘要：The gearbox is an important component of the system of high-speed trains, which is susceptible to damage and failure due to the long-term high-speed and heavy-load working environment, so it is important to diagnose the faults of high-speed train gearboxes quickly and accurately. Thus, based on analysis of the structure type and common faults of the EMU gearbox, the current application status of the typical technologies such as vibration analysis, noise analysis, temperature field analysis, oil analysis and acoustic emission used for fault diagnosis of the EMU gearbox at home and abroad is explained, the applicability of these technologies is analyzed and key research directions are proposed. The analysis results show that the current multiple fault diagnosis technologies applied in high-speed EMU gearboxes have their own advantages, disadvantages and application occasions. The single diagnosis technology can not accurately diagnose the multi-type failures of the gearbox due to its limitations, and the fusion of multiple techniques based on advanced intelligent algorithms is expected to be one of the research focuses for fault diagnosis in this field in the future.关键词：Railway transportation;EMU gearbox;Detection technology;Review;Fault diagnosis
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发布时间：2023-03-29 - 摘要：The significance of developing upper limb assisted exoskeletons in the current epidemic situation, frequent disasters and shortage of labor resources is briefly described. The development history, classification methods of exoskeletons and the characteristics, applicable groups, application scenarios of upper limb assisted exoskeletons are introduced. The research results and products related to upper limb assisted exoskeletons at home and abroad are reviewed in detail, including their basic structure and evaluation experimental results, and the key technologies are described and analyzed such as the drive and transmission, human motion intention recognition, human-robot coordinated motion involved in human-robot interaction, etc. The existing problems in the current research are summarized and the future development trend of upper limb assisted exoskeletons is prospected.关键词：Upper limb assisted exoskeleton;Evaluation experiment;Human-robot interaction;Human motion intention recognition;Human-robot coordinated motion
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发布时间：2023-03-29 - 摘要：The planetary gear train is an important rotating mechanical component, and its early faults diagnosis is an important means to avoid major accidents. Early faults diagnosis of planetary gear trains is bound to become the focus of scholars. The characteristics of early faults signals of planetary gear trains are analyzed, the research status of the early faults mechanism, signal acquisition methods, faults feature extraction and identification of planetary gear trains are combed, and the main problems in early faults diagnosis are summarized. Some suggestions are put forward, such as the research of early compound faults mechanism based on the dynamic model, the research of early faults signal acquisition method based on the multi-sensor, the research of early faults characteristic index based on multi-domain analysis, the research of early faults diagnosis based on numerical model and so on. It can be used as a reference for further research on early faults diagnosis of planetary gear trains.关键词：Planetary gear train;Early faults;Dynamic modeling;Signal analysis and recognition;Status and development
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发布时间：2023-03-29 - 摘要：On-line real time diagnosis of bearing incipient faults is the intersection of practical engineering application requirements and basic scientific research. It is one of the development directions of bearing fault diagnosis at home and abroad. Firstly, this study analyzes the bearing fault and its evolution process; secondly, according to the needs of bearing incipient fault diagnosis in time, the difficult problems of bearing incipient fault diagnosis are summarized; then, it focuses on the various technologies used in the three crucial links of bearing early fault diagnosis: the weak monitoring signal enhancement technology, the fusion representation technology of monitoring parameters and the early fault intelligent diagnosis technology; finally, the development trend of bearing incipient fault diagnosis technology is summarized and prospected.关键词：Bearing;Minor fault;Incipient fault diagnosis;Blind source separation;Deep transfer learning
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发布时间：2023-03-29
Review
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