最新刊期
卷 47 ， 期 11 ， 2023
- 摘要：In order to study the influence of tooth root cracks on the fatigue life of case-hardened gears, taking an involute case-hardened gear as the research object, the mechanism of the tooth root fatigue crack growth is analyzed based on the fracture mechanics method and fatigue crack growth theory. The residual life analysis model of the tooth root crack propagation for case-hardened gears is established, considering the influence of load, initial crack size and initial crack location, etc. The evolution of stress intensity factor and crack propagation mechanism at different root crack propagation stages is studied. According to the bending fatigue test data of an involute case-hardened gear pair, the calculation model is analyzed and verified, and the accuracy of the model is proved. The results indicate that, compared with type Ⅱ and type Ⅲ, type Ⅰ stress intensity factor is the highest, which gradually decreases from the tooth surface to the direction of crack depth. With the increase of factors such as load, crack length, crack width, and initial crack distance from the center position of the tooth width, the residual life of crack propagation decreases accordingly.关键词：Case-hardened gear;Root crack;Stress intensity factor;Residual life
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发布时间：2023-12-01 - 摘要：A proportional plus derivative (PD) adaptive tracking control strategy based on neural sliding mode is proposed for the interference of unknown factors in the mathematical model of four-wheel omnidirectional robots. Firstly, the dynamics model of the robot is analyzed. Secondly, the backstepping trajectory tracking controller is used to obtain the virtual velocity, and the PD controller is designed based on the error between the virtual input and the actual input. Then, the neural network is used to approximate the uncertainty in the dynamics model, and the stability of the system is proved by the Lyapunov theorem. Simulation and experimental results show that the control strategy is effective.关键词：Trajectory tracking;Omnidirectional mobile robot;Neural network adaptive control;PD control
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发布时间：2023-12-01 - 摘要：In order to accurately study the temperature field distribution during the long-term sliding friction process of the limited slip clutch, Fluent software is used to solve the flow field velocity distribution of the friction pair under different working conditions to obtain the average convective heat transfer coefficient and calculate the cooling power of the lubricating oil. A dynamic heat flow distribution temperature prediction model is established with the constraint of continuous friction contact surface temperature by the heat balance method, and a long-time sliding friction test is designed to verify the analysis results. The results show that under the condition of the constant heat flow input, there is a temperature difference between the steel disc and the friction plate, which increases with time, the temperature prediction results are higher than the experimental values, and the maximum deviation is 22.2 K. The predicted deviation of the dynamic heat flow distribution temperature model is within 8.1 K. The input heat power at each position on the surface of the steel disc sheet decreases with time and tends to a fixed value. The equilibrium temperature is distributed in a parabola along the radial direction and reaches a peak at the place between the mid and the outer diameter.关键词：Limited slip clutch;Dynamic heat flow distribution;Convective heat transfer;Temperature field
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发布时间：2023-12-01 - 摘要：For the trajectory tracking control problem of the omnidirectional mobile platform of Mecanum wheels, a strategy of double closed-loop control with model predictive control (MPC) and differential forward proportional plus integral plus derivative (PID) is proposed. The attitude control loop and velocity control loop are designed based on the kinematics characteristics of Mecanum wheels. The linear error model of the Mecanum wheels chassis is established by the attitude control loop, the quadratic objective function is designed, and the problem of path following is transformed into predictive control for the nonlinear model. In the velocity control loop, the differential forward PID controller is used to avoid the high-frequency disturbance to the system caused by frequent step changes of the input quantity, accelerate the convergence of the angular velocity of the Mecanum wheels, and enhance the stability of the system. Simulation experiments demonstrate that the controller designed in this study has better convergence speed and tracking accuracy than the commonly used trajectory algorithm, and it can provide good robustness to control the mobile platform of Mecanum wheels.关键词：Mecanum wheel;Trajectory tracking;Linear error model;Model predictive control;Differential forward PID
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发布时间：2023-12-01 - 摘要：In order to more reasonably simulate the force and force transmission characteristics of the main shaft of a wind turbine, and to find out the influencing factors of the fatigue strength of the main shaft, the nonlinear contact element is used to simulate the roller of the main bearing and correctly simulate the self-aligning effect of the main bearing. The interference contact model between the main shaft and the inner ring of the main bearing of a wind turbine is established. Based on the equivalent time series load spectrum and Miner's fatigue damage criterion, the effects of the size of the interference between the inner ring of the main shaft and the main-bearing, the size of the inner bore of the spindle, the surface roughness, the friction coefficient of the contact surface and the tensile and yield strength of the material on the fatigue strength properties of the spindle are studied and analyzed. The research results have certain guiding significance for engineering practice and production, and lay a foundation for further lightweight design of spindles.关键词：Wind turbine;Main shaft;Nonlinear contact;Fatigue strength
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发布时间：2023-12-01 - 摘要：To improve the meshing performance of harmonic reducers and the working performance of robots, a novel tooth profile design method for harmonic gears based on the improved kinematics and transient dynamics is proposed. Firstly, based on the characteristics of common tangent double arc tooth profile and S-type tooth profile, a new flexible tooth profile is proposed, which is the combination of S-type tooth profile and common tangent double arc tooth profile. Secondly, the tooth profile of the steel gear is calculated based on the improved kinematics method. Finally, the meshing backlash between the different tooth profiles and the stress of flexsplines without considering plastic deformation are analyzed based on the transient dynamics method. Through comparative analysis, it is found that the new tooth profile without considering plastic deformation has smaller meshing backlash and equivalent stress, the minimum meshing backlash is only 0.003 6 mm, the maximum equivalent stress under the given load condition is only 1 211.6 MPa, which are significantly lower than those of the double circular arc tooth profile flexspline, the S-shaped tooth profile flexspline, and the common tangent double circular arc tooth profile. The novel tooth profile design method can effectively improve the transmission performance of harmonic gears, which lays a theoretical foundation for the design of high-performance harmonic gears.关键词：Harmonic gear;Improved kinematics;Transient dynamics;Novel tooth profile design;Meshing performance
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发布时间：2023-12-01
Theory·Research
- 摘要：Aiming at the main problems existing in the jumping robot, combined with the galago senegalensis monkey's characteristics of small sizes, stable and explosive jumping, a kind of galago senegalensis monkey single leg jumping robot is proposed in this study, and its main structure and control system are designed. Based on the principle of the Stephenson's six-bar linkage, a planar eight-bar linkage for the leg of simulating galago senegalensis monkey robot is designed, and its trajectory is optimized to obtain the bar length parameters with the best jumping ability. The three directions of the robot's jumping are controlled and adjusted, and the double closed-loop feedback control system is used to ensure the stability of the robot's attitude when taking off, soaring in the air, and landing on the ground. Finally, the physical verification model of the robot is established. The total weight is only 395.5 g, and the overall height is 250 mm. The experimental results show that the simulating single leg robot can achieve continuous and stable jumping, the highest jumping speed can reach 20 m/s, and the response time at a jumping height of 100 mm is 0.1 s.关键词：Galago senegalensis monkey;Single-leg jumping robot;Planar eight-bar linkage;Structure design;Attitude control
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发布时间：2023-12-01 - 摘要：At present, there are two ways to design the rotor profile of a twin screw compressor: forward design and reverse design. In the forward design, the first step is to obtain a certain profile of one rotor (female rotor generally). The next is to solve the profile of the other rotor (male rotor generally) based on the law of meshing and the method of coordinate transformation. Further, the meshing line is achieved. In the reverse design, we should obtain the meshing line firstly and then the profiles of rotors are obtained based on the method of coordinate transformation and the law of meshing. This study conducts a research on the forward design of twin screw compressor based on comprehensive performance and tries to deduce a method of automatic optimization. The procedures are as follows: dividing the profiles of rotors into sections, solving the expression of each section, achieving the nodes of each section, making sure the adjustment range of control points of the rotor profile and proceeding the automatic optimization based on comprehensive performance. By comparison, the sealing property of rotor profiles has been improved by automatic optimization.关键词：Forward design;Comprehensive performance;Automatic optimization;Sealing property
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发布时间：2023-12-01 - 摘要：At present, the demand for heavy-duty hydraulic automatic transmission in engineering machinery and other equipment is increasing. As one of the core components of such kind of transmission, the design of hydraulic torque converters requires better accuracy and efficiency. Due to the difference of scale and torque, the design method of common torque converters is no longer applicable. The torque converter parametric design process is separated from the 3D software model generation process currently, which prolongs the design cycle. Therefore, this study presents a parametric design method for torque converters of the heavy-duty hydraulic automatic transmission and develops the parametric design software. Firstly, the geometric model of torus is established by constructing the middle streamline by two elliptical arcs, the camber line is designed with the quartic B-spline curve, and a method of controlling the shape of the camber line through the two-level inlet and outlet angles and vertex coordinates is proposed. The connection is established between the blade camber line shape control method and the curve control points, and the constraint conditions of camber line control parameters are designed. The automatic design program of torque converters is developed based on the NX Open software, and the central scheduling data processing framework is established with parameter rationality checking as the constraints. The instance results show that the design method can make the torque converter get reasonable shape quickly.关键词：Hydraulic torque converter;Parametric design;B-spline curve;NX secondary development
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发布时间：2023-12-01 - 摘要：Aiming at the problems of single flapping wing movement mode and low flight flexibility and stability of flapping-wing aircraft, a single-drive multi-mode flapping-wing aircraft based on the space linkage mechanism is designed. The kinematic model of the flapping-wing aircraft is established, and the driving mechanism is analyzed by Matlab and Adams co-simulation, and the kinematic characteristics of the flapping-wing aircraft is obtained by comparison. The aerodynamic model of a single-drive multi-mode flapping-wing aircraft is established. The windward resistance with periodic variation is applied to the wing, and the dynamic characteristics of the flapping-wing aircraft are analyzed. Through the kinematic and aerodynamic coupling analysis of the combined mechanism, the coupling dynamic characteristics of the flapping-wing aircraft are obtained, which provides a research basis for the flight control and performance improvement of the flapping-wing aircraft in the future.关键词：Flapping-wing aircraft;Multiple flight mode;Space mechanism;Motion analysis;Coupling dynamic analysis
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发布时间：2023-12-01 - 摘要：A method for designing tooth surface of spiral bevel gears based on quantitative mismatch modification is proposed in this study. Firstly, the mathematical relationship between modification quantity, modification coefficient and structural parameters of tooth surface is revealed. Then a target tooth surface oriented by mesh performance is established according to conjugate tooth surface and second-order modification surface. The tooth surface deviation correction model between target tooth surface and theory tooth surface is constructed, and the corrections of machine setting parameters are calculated. A numerical example is taken to verify, the corresponding modification coefficients are calculated quickly according to modification quantity, and the problem of blind selection of modification coefficients is solved. The experimental results are consistent with the theoretical analysis, and the mesh performance is improved. Experiments verify the effectiveness of the proposed method, and the method is also suitable for tooth surface modification of other gears.关键词：Spiral bevel gear;Quantitative mismatch modification;Machining parameters correction;Experimental verification
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发布时间：2023-12-01 - 摘要：According to the parameters and geometric dimensions of the gear, the parametric equations of the transition curve and involute line of the root cutting gear are established based on the principle of machining the gear with the generating method, the tooth shape diagram of the root cutting gear is accurately drawn, and the minimum chord tooth thickness and maximum root cutting radius are accurately calculated with the Matlab software. It provides a reliable basis for establishing the finite element model of the root cutting gear, quantifying the relationship between the bending fatigue strength and the displacement coefficient of the root cutting gear, determining the best displacement coefficient of the root cutting gear, and studying the feasibility of the use of the root cutting gear in the industrial production.关键词：Root cutting gear;Transition curve;Extended involute line;Equidistant curve
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发布时间：2023-12-01
Design· Calculation
- 摘要：In this study, a simulation model of the two-stage helical gear pair-rotor-bearing of the main reducer is developed by Adams software. The simulation results show that the noise mainly comes from the resonance of the system and the contribution of the high-speed gear pair is large when the speed is in the range of 0~3 000 r/min. Furthermore, the vibration test of the main reducer and the real vehicle noise test are also conducted. The test results show that the noise of the main reducer increases obviously when the input speed is 2 138.67 r/min, and the corresponding meshing frequency of the gear pair is 605.96 Hz, verifying the simulation results. Finally, the effect of bearing stiffness on the resonance speed distribution is studied, and the optimization measures of the structural stiffness of the system are proposed. After optimization, the vibration amplitude decreases significantly when the speed is in the range of 1 400~2 200 r/min, and the resonance speed shifts to a higher speed. The relative errors between the test results and simulation analysis results are less than 5%, which verifies the Adams simulation results and the optimization measures, and provides some reference for shortening the development cycle of the electric drive axle main reducer and saving research and development costs.关键词：Electric drive axle;Gear-rotor-bearing system;Resonance characteristics;Road test
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发布时间：2023-12-01 - 摘要：A simplified three-dimensional brake model with crater structure is established by using the finite element software Abaqus, and the influence of the depth, diameters, degrees and types of craters on the temperature and stress of the brake disc is investigated by combining the thermal coupling theory and the orthogonal test method. On this basis, the temperature and stress fields of brake discs with different non-smooth surface forms are analyzed, and the influence of temperature with radius on non-smooth discs with different braking initial speeds and pressures during emergency braking is investigated under the optimal combination. The results show that the square pit brake disc with the pit depth of 5 mm, the diameter of 8 mm and the 20° interval between adjacent pits in the circumferential direction has the smallest temperature and stress by the orthogonal test method, which is the optimal combination. Among them, the square pit brake disc has the best heat dissipation performance. With the increase of the initial speed and pressure of braking, the temperature of this brake disc surface gradually increases, the highest temperatures of the brake disc all appeares in the brake disc radius of 136 mm.关键词：Orthotropic anisotropic;Non-smooth brake disc;Thermodynamic coupling;Dissipation performance
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发布时间：2023-12-01 - 摘要：To deal with the phenomenon of partial load of the hybrid transmission gear pair in the actual working process and to solve the eccentric load problems of a hybrid light transmission gear pair, the gear analysis software Romax is used for 3D modeling of the meshing helical gears; one gear pair is simulated and analyzed under the commonly used operating conditions of the hybrid transmission set for operation, and the second-generation genetic algorithm is used for gear modification. The modification results show that the transmission error value, contact load and maximum contact stress of the gear pair are reduced under different working conditions, the offset load of the gear face is improved, and the meshing performance and life of the gear pair are improved, which provides some reference for the modification of the hybrid transmission gear.关键词：Gear modification;Romax software;Hybrid electric power;Meshing of gears;Transmission error
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发布时间：2023-12-01 - 摘要：Aiming at the problem of gear interference in the meshing transmission process of the double circular arc flexspline of the harmonic reducer in the actual working condition, based on the finite element method of tooth surface contact analysis between the flexspline and the circular spline, the flexspline tooth is modified by a two-stage helix modification method, and then the comprehensive performance of the prototype is tested. The results show that the maximum contact stress of the modified flexspline to the tooth surface of the circular spline is 72 MPa, which is 368 MPa less than that before the modification, and the contact stress of the other positions of the modified flexspline is slightly higher than that before the modification, which not only effectively avoids the problem of gear interference, but also improves the meshing transmission performance of the harmonic reducer. The comparative test of the prototype also verifies that the transmission performance of the harmonic reducer after the modification of the flexspline is better than that before the modification. This work is useful for the analysis on the dynamic transmission characteristics of the harmonic reducer.关键词：Harmonic reducer;Double circular arc flexspline;Helix modification;Simulation analysis;Test verification
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发布时间：2023-12-01 - 摘要：In view of the failure problem of sun gear splines in fan gearboxes, through the analysis of the chemical composition, microstructure, microfracture and mechanical properties of the failure spline, the cause of the spline wear is found out. The results show that there are more rods, unequal axes or islands of the undissolved ferrite in the metallographic structure of inter mediate shaft（IMS） sun gear motor side splines, which reduces the wear resistance of the material. The failure of sun gear splines is mainly caused by low tooth surface hardness. At the same time, due to the comprehensive action of fatigue wear, chemical corrosion, abrasive wear and other wear mechanisms, serious tooth surface wear occurs, resulting in a decrease of the bearing capacity of IMS sun gear motor side splines. The force transmission is not smooth, and the vibration is aggravated during operation, resulting in the failure of the gearbox. The test results can provide some theoretical guidance for the fault detection and diagnosis of wind power gearboxes.关键词：Wind motor gearbox;Sun gear spline;Failure;Microfracture;Wear
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发布时间：2023-12-01 - 摘要：The research on electric drive wheel technology is an important direction of the research on the new energy drive system in the future. With the increasing requirements of the electric drive wheel on the speed, the oil churning power loss has become a non-negligible part, even up to 50%-80% of the total power loss. The existing calculation method of churning loss mainly adopts simple empirical formula, which cannot be applied to complex planetary gear transmission. The splash lubrication of the two-stage planetary gear drive is simulated by computational fluid dynamics (CFD) software and C language user defined function (UDF), and the visualization of oil gas two-phase transient flow field is realized; by extracting the surface pressure and the viscous force, the churning loss of the sun gears, planet gears and planet carriers are obtained; the simulation and analysis of the 25 working conditions show that the churning loss varies with the immersion depth and speed; the results show that the oil churning power loss increases with the oil immersion depth and the speed, and there is no obvious inflection point. To achieve the minimum oil stirring loss, the minimum oil immersion depth should be taken on the premise of ensuring full lubrication.关键词：Planetary gear;Oil churning loss;CFD;Fluid field transient visualization;UDF;Joint simulation
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发布时间：2023-12-01 - 摘要：In order to meet the motion requirements of the elbow joint of the rehabilitation robot, a double-node symmetrical spiral corrugated elastic element is applied to the series elastic actuator (SEA), and the energy storage ratio is used as the optimization standard. Under the premise of the same quality,the maximum energy storage ratio can be achieved, which can better absorb the vibration of the mechanical arm and ensure the safety of the patient. Firstly, the three-dimensional modeling of the SEA is carried out. Then the torque spring is simulated and analyzed by using the finite element software, and the safety factor of the elastic unit is 2.37. Finally, the real object is processed. The experiment shows that the energy storage ratio can reach 9.63 J/kg, the measured stiffness kr is 264.04 N
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发布时间：2023-12-01
Test·Analysis
- 摘要：A method for modifying the outer cam of sprags is proposed, the calculation method of the force of sprags in the overrunning and the engagement condition is studied, and the influence of different modification curves on the contact performance of sprags is analyzed. The results show that the modification of the outer cam of sprags can reduce the contact stress of the sprag clutch wedge in the overrunning condition without affecting the engagement performance, which is helpful to reduce the overrunning wear of sprags.关键词：Sprag clutch;Outer cam modification;Contact performance
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发布时间：2023-12-01 - 摘要：In order to improve the cavitation performance under high-speed for external gear pumps, a comprehensive compensation method with the small backlash, innovative annulus relief-groove and increasing inlet oil-pressure is proposed. Based on all derived models of the trapped-oil expansion-process interval, trapped-oil volume change rate, compensation flow rate for the expanded trapped-oil, relief areas and trapped-oil pressures differently under large backlash or small backlash, the minimum trapped-oil pressures under conventional rectangular relief-groove and innovative annular relief-groove are compared with an example. All results show that the maximum trapped-oil expansion rate and the expansion interval under the large backlash are only 18.3% of those of the small backlash; the maximum relief-area of the trapped-oil in the large backlash is only 7.9% of that in the small backlash due to different relief-groove space; the cavitation phenomenon is more serious; the ripple range of the trapped-oil pressure in the large backlash is 1.93 times than that in the small backlash, etc. It is concluded that the cavitation phenomenon of the high speed gear pump can be effectively alleviated by the comprehensive compensation method with the small backlash, innovative annular relief-groove and increasing inlet oil-pressure.关键词：High-speed gear pump;No cavitation phenomenon;Trapped-oil pressure;Expansion-process;Small backlash;Relief-groove;Inlet oil-pressure
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发布时间：2023-12-01 - 摘要：Although pure time-domain features have the advantages of fast extraction speed and clear physical meaning, the diagnostic accuracy is slightly inferior to other methods. To solve this problem, a new bearing feature extraction method based on the time subsequence (BOTS) is proposed, which combines word package model and time subsequence. First, the sliding window is used to slide in the vibration signal to obtain multiple continuous and non-stationary time series, which are regarded as a document. For each time series, multiple continuous subsequences of fixed length are randomly intercepted to obtain the time-domain or frequency-domain characteristics of subsequences. Then, the random forest algorithm is used to count the class votes of all subsequences in each time series, and a dictionary is constructed based on the class votes. Finally, the dictionary is used as a new feature and input into the random forest classifier for training and learning. A variety of experiments are carried out using the bearing data provided by the SQI-MFS experimental platform of Wuxi Innovation Center of SIEMENS China Research Institute, Southeast University and Institute of Mechanical Failure Prevention Technology. The experiments show that the features extracted by BOTS+ wavelet packet energy method have higher recognition.关键词：Rolling bearing;Fault diagnosis;Feature extraction;Fault status identification
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发布时间：2023-12-01 - 摘要：In order to analyze the influence of the climbing posture on the motion characteristics and stability of the ladder climbing wheelchair, a concept of the forward ladder climbing wheelchair is put forward. The structure of the ladder wheelchair is designed and the kinematic model of the ladder wheelchair is established. The motion characteristics of the forward ladder wheelchair are analyzed by simulation, and the stability of its operation is verified. By introducing the parameters of the change of the center of gravity of the wheelchair, the quantitative analysis equation of the tilting stability of the forward ladder climbing wheelchair is established, and the stability change of the wheelchair during the ladder climbing process is obtained. The results show that the stability and the ladder wheelchair stance advance the ladder wheelchair stability to a range from 0.26 to 0.74, the minimum value is increased by 136.36%, and the maximum value is increased by 100%. The prototype is made and the experiment is carried out to verify the feasibility and effectiveness of the forward ladder climbing wheelchair.关键词：Ladder climbing wheelchair;Structure design;Kinematics;Stability
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发布时间：2023-12-01
Development·Application
- 摘要：Due to its unique wearing comfort, operational flexibility and human-machine cooperation, the supernumerary robotic limb has a wide range of applications, such as medical rehabilitation, the aerospace, industrial production and building decoration, etc. This study analyzes the research status and development trend of supernumerary robotic limb at home and abroad, and reviews the design of the external limb structure, motion modeling, human-machine information interaction and coordination control. Meanwhile, the advantages and disadvantages of rigid external limb and flexible external limb are analyzed, the core and key of the motion modeling of the external limb are illustrated, and the technical challenges of human-machine interaction and optimal cooperative control are revealed. Finally, the main research points of the supernumerary robotic limb are summarized, and its future development direction and trend are prospected.关键词：Supernumerary robotic limb;Wearable robot;Human-machine cooperation;Motion modeling;Auxiliary operation
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发布时间：2023-12-01 - 摘要：Non-circular gear transmission is a new type of mechanical transmission mechanism relative to circular gear transmission, which can realize special movement, improve mechanism performance and improve mechanism motion conditions. With the improvement of non-circular gear transmission design ability and the increase of application scope, the research on non-circular gear transmission is increasing. This study introduces the current research status of non-circular gear transmission applications, summarizes the research progress of non-circular gear transmission design and analysis, discusses the methods and strategies for manufacturing non-circular gear drives, summarizes the problems faced by the current development of non-circular gear transmission, and looks forward to the research directions of non-circular gear transmission in applications, design and analysis, and processing and manufacturing.关键词：Non-circular gear transmission;Application;Design and analysis;Manufacture
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发布时间：2023-12-01
Review
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