China Mechanical Engineering

Analysis on Instantaneous Contact Thermal Characteristics of Reducing Mechanisms for Precision Ball Transmissions

SUN Pengfei, AN Zijun, LIU Xianghui

2017, 28(09): 1009-1015.

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Based on the Hertz contact theory, a tooth surface contact model was established forward to analyze the instantaneous contact areas and thermal characteristics of reducing mechanisms for precision ball transmissions. The contact patches among the balls and tooth surfaces of cycloidal groove were analyzed, then the effects of the input shaft speeds and loads on the thermal characteristics of reducing mechanisms were investigated. Instantaneous heat generation rates and instantaneous frictional temperature rises among the balls and tooth surfaces were obtained. The results indicate that the instantaneous contact areas among the balls and tooth surfaces of cycloid groove is a time-varying contact ellipse. The input shaft speeds and loads have visible influences on instantaneous heat generation rates and frictional temperature rises, but the influences of speeds are greater. Instantaneous friction temperature rises are monotonically increasing with the increased speeds under the general speed conditions, but in the low speeds, temperature rises are monotonically decreased and then monotonically increased. The results of the study provide a good foundation for three dimensional thermal mechanical coupling analyses of precision ball transmissions.

X-Y Micropositioning Piezostage Design with Large Workspace Density

CAO Ruimin, HAO Lina, GAO Jinhai

2017, 28(09): 1016-1020,1028.

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Aiming at the problems of small microstage workspace density, a kind of 2-DOF symmetrical parallel microstage was put forward herein. First, the main deformation factors were analyzed in the displacement amplifier; second, the stiffnesses of circular flexible hinge, parallel plate flexible hinge and corner-filleted flexible hinge were calculated; third, the energy method and the displacement matrix were utilized to get the output force formula of parallelogram displacement amplifier, displacement formula of the stage movement; finally，the variables of microstage were optimized and the optimal results were verified through the simulations and experiments. Results show that the workspace and workspace density may reach to 143.7μm×142.1μm and 2.521μm2/mm2 respectively，thus it may realize a higher workspace density.

One Dimensional Oblique Ultrasonic Vibration Assisted Grinding for Rolling Bearing Steels and Experimental Validation

WANG Yan, WANG Shuai, LIU Jianguo, LI Delin

2017, 28(09): 1021-1028.

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Previous studies about one dimensional ultrasonic vibration assisted grinding were limited to fixed directions of ultrasonic vibration such as one dimensional axial or tangential vibration. A novel process of oblique ultrasonic vibration assisted grinding was presented. The motion paths of abrasive particles in oblique ultrasonic vibration assisted grinding were simulated in MATLAB. A dynamics model of experimental ultrasonic vibration system was established. Experimental devices of oblique ultrasonic vibration assisted grinding were designed through modal analysis of ultrasonic workbench. Grinding forces and surface roughnesses in grinding rolling bearing steels were studied at different directions of ultrasonic vibrations. The regulation of grinding forces and surface roughnesses with the direction of ultrasonic vibration was studied. Experimental results show that the best surface quality may be obtained when the angle of ultrasonic vibration is as 67.5° and grinding forces are also decreased. Results of orthogonal experiments demonstrate that ultrasonic vibration angle of 67.5°, wheel speed of 20m/s, workpiece speed of 0.5m/min, grinding depth of 4μm are the optimum parameters to obtain the best surface quality of workpiece， and the speed of workpiece has the most important impacts on the surface quality of workpiece.

Analyses for Influences of Magnetization State on Magnetomechanical Coupling Relationship

DUAN Zhenxia, REN Shangkun, ZHAO Zhenyan, ZU Ruili

2017, 28(09): 1029-1034.

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The influences of magnetization state on magnetomechanical coupling relationship were analyzed both at the micro level and at the macro level. From the microscopic perspective, under different magnetization states, the changing rules were analyzed,that the domain structure of ferromagnetic components was subjected to applied stresses was analyzed. From the macroscopic perspective, based on approaching principle, the process which a applied stress made the initial magnetization state approached nonhysteresis magnetization state constantly was explained, where the closed direction is determined by the sizes of differences between nonhysteresis magnetization and initial magnetization. If the differences are greater than zero, the magnetization will increase with stress increasing, and if the differences is less than zero, the situation is versa, but nonhysteresis magnetization will change momently with the changes of stresses. Finally, in order to further verify theoretical analysis experimentally, a static load tensile test was applied to Q235 steel with three different magnetization states, the experimental results are consistent with theoretical analyses.

Optimization Design of Electromagnetic-driving Schemes of a Cold Gas Micro-thruster

ZHANG Xi, GUO Jiali, ZHANG Xinbin, WANG Yue

2017, 28(09): 1034-1038.

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Evaluation indicators of electromagnetic-driving project for solenoid-based cold gas micro-thruster were discussed. CAE analysis and comprehensive evaluation method were used to optimize the solenoid design for a cold gas micro-thruster. At first, a dynamic simulation model which could match the test data well was built to establish the solenoid design matrix. Then, the optimal design was acquired by using the combination assigning method. The test results of the prototype by using the excellent scheme are proved to be accord with the expectations.

Theoretical Analyses and Experiments of Micromachined Graphite Rotor Based on Diamagnetic Levitation

SU YufengYE ZhitongZHANG Kun

2017, 28(09): 1039-1043.

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A diamagnetic levitation structure consisted of NdFeB permanent magnets and a highly oriented pyrolytic graphite rotor was studied herein. The rotor was designed as a disc with four identical blades. The gravity of the rotor was equal to the diamagnetic force from the permanent magnets, leading to the stable levitation and consistent rotation of the rotor under external driving torques. The levitation height of the rotor was simulated to be 130μm in the finite element analysis software, which matched well with the experimental results, and the simulation errors are as 1.5%. In order to introduce a driving torque, needle nozzle was adopted to produce tangential airflow to the blade of the rotor. The relationship between the rotor rotation speed and the flow rate of the airflow was investigated and analyzed, and the maximum speed of the rotor could reach 500r/min. The diamagnetic structures possess potentials in the applications of non-contact microsensors and micromotors.

Simulation on Parameter Matching Based on Multi Control Strategies of Oil-hydraulic Hybrid Excavator

TAN Xianwen, FANG Jinhui, FEI Shuhui, JIN Yuefeng

2017, 28(09): 1043-1049.

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In order to improve the energy saving effectiveness on an oil-hydraulic hybrid excavator, the parameter matching was studied based on multi control strategies of the auxiliary power systems. According to the driving structures, working principles and load characteristics, four kinds of control strategies were proposed including stabilizing engine operating points with constant displacement release, stabilizing engine operating points with constant torque release, stabilizing main pump operating points with constant displacement release, stabilizing main pump operating point with constant torque release. Then a mathematical model of the system main components was established. Compared the energy saving effectiveness of the four control strategies through simulations and analyses, coming to a conclusion that energy saving effectiveness of stabilizing main pump operating points with constant displacement release is optimal, and according to this fact, the auxiliary motor parameters are determined. Simulation results show that, compared with the original system, the hybrid system's fuel saving rate has increased by 9.8%, and work efficiency has increased by 9.72%.

Research on Dynamic Characteristics of Multi-wedge Journal Bearing Based on Fluid-structure Coupling

LI QiangZHANG ShuoMA LongXU WeiweiZHENG Shuiying

2017, 28(09): 1050-1055,1117.

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A new mesh movement approach used for multi-wedge journal bearings was proposed, and the unsteady flow fields were calculated under arbitrary perturbations of journal (free oscillation motions, plus excitation motions, and eccentric whirls). A coupling calculation between the oil film in multi-wedge journal bearings and rotor dynamics was realized by transferring data between two domains. When the journals freely oscillated, excited by pulses, and eccentrically whirled, the influences of bearing installation angle on the dynamic characteristics of multi-wedge journal bearing were discussed. The calculation results indicate that the multi-wedge journal bearings have small damping and poor stability when the bearing installation angles are changed in the ranges of 20°~40°, and the multi-wedge journal bearings have large damping and good stability when the bearing installation angles are changed in the ranges of 100°~120°. Moreover, with the increase of the bearing numbers, the installation angle has less effects on the stability.

Intelligent Fault Diagnosis for Gears Based on Deep Learning Feature Extraction and Particle Swarm Optimization SVM State Identification

SHI PeimingLIANG KaiZHAO NaAN Shujun

2017, 28(09): 1056-1061,1068.

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For the fault diagnosis of gears, using statistical methods for feature extraction, deep learning neural network (DNN), particle swarm optimization algorithm and SVM technology, a novel intelligent diagnosis model was proposed, which combined the deep learning feature extraction and particle swarm optimization SVM state identification. The model combined the frequency domain features which were extracted by deep learning adaptively and the time domain features which were extracted by mathematical statistics method to form a combined feature vectors, then using particle swarm optimization SVM to diagnose the feature vectors. This model provides reliable identification of intermediate shaft gears of different types of faults in the fault diagnoses of gear transmission system test bench, and the satisfactory diagnostic results are obtained. The application results also verify the effectiveness of the adaptive extraction of spectral features based on deep learning.

On-line Monitoring of Pick's Wear Degrees Based on BP Neural Network

ZHANG Qiang, LIU Zhiheng, WANG Haijian, HUANG Chuanhui, Nguyen Viet Tuyen

2017, 28(09): 1062-1068.

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In order to realize the real-time monitoring degrees of pick wear in cutting processes, based on BP neural network a method was proposed for detection of multi-feature signal fusion. By extracting different wear degrees pick signals,such as three direction vibration signals, infrared temperature signals and current signals during the cutting processes, A database of multi-feature signal samples of different pick wear degree was established, the BP neural network was learned and trained by using the multi characteristic pick wear degress signal samples, and the pick wear a recognition model for pick wear degress was established to achieve online monitoring and recognition.The results show that: Based on the BP neural network, the network discrimination results of monitoring system for the degree of pick wear is consistent with the actual wear degree category of the test samples, the establishment of BP neural network system may accurately monitor and identify the type of wear degrees.

GVMD and Its Applications in Composite Fault Diagnosis for Gearboxes

YANG Yu, LUO Peng, CHENG Junsheng

2017, 28(09): 1069-1073.

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According to the defects of the VMD that its penalty parameters and number of components were based on the prior knowledges in the processes of the actual applications, based on the VMD an improved method, namely, the GVMD was proposed herein. This method held the potentials to overcome the deciencies of VMD, and it might reduce the subjective influences on the decomposition results. By decomposing the signal into non recursive and variational modal, the method might effectively separate the harmonic frequency components that were similar to each other and had good robustness. It was applied in the composite fault diagnosis of the gearboxex, and the simulation results and test verify the validity of this method.

Algorithm of Separation Edge Extraction of Aerospace Electrical Connector in High-speed Photography

HONG TaoZHAO Dianyun

2017, 28(09): 1074-1078.

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In order to accurately measure the space electric connector of the separation distance, for further study of its separation characteristics, a high-speed photography environment oriented electrical connector on the edge of the separation extraction method was presented herein. Mainly through the algorithm divided the region of interest area selected for measuring positions, after processing through the filter, wavelet transform to enhance image edge of weak signals, and then through the two adaptive threshold segmentation of image, and by using SUSAN operator for edge detection, and then the edge was extracted, the accurate edge informations were obtained.

Dynamic Simulation Analysis and Optimization of Low-voltage Switches

Tan Wei, Zha Hailin, Xiao Xing

2017, 28(09): 1079-1085.

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In the optimum design of low-voltage switches, it was necessary to analyze the dynamic behaviors. The bounces caused by impact contacts in the mechanical system would lead to arc ablations, and directly a effect the electrical lifetimes of the switches. With virtual prototyping technologies to do the dynamic simulations for the closing processes of the switches, the dynamic behaviors of the mechanical system and the changes of the contact status were investigated. The simulation model was verified by comparing with the bounce time tests of the switch closing processes, and the bounce positions were the same as the arc ablation positions of the test samples. The influences of the design parameters on the contact bounce of the switches were investigated through the orthogonal test of the simulation model, and the optimization method was designed and verified by the test samples.

Influences of Work Roll Horizontal Displacements on Shape in Small Four High Rolling Mills

BAI Zhenhua, LIU Yaxing, QIAN Cheng, LI Boyang, Du Jiangcheng, Li Jianzhong

2017, 28(09): 1085-1091.

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In view of the fact that the work roll “long diameter ratio” was larger and the absolute value of the roll diameter was small, it was easy to produce the horizontal displacements of the work roll along the rolling direction for the small four roll mills, the shape calculation model might not meet the accurate calculations and predictions of the exit shapes. Thus, a shape model of the four high rolling mill was established, which considered the horizontal displacements of the work rolls and combined the equipment and processing characteristics of the four high rolling mills.Then it might be tested the accuracy of the results by comparing the shapes. On the basis of the shape model, the laws of horizontal displacements of work rolls, the effects of horizontal displacements of work rolls on the exit shapes and the effects of bending roll forces on the shape control under considerations of the horizontal displacements of the work rolls were analyzed in detail. The model was applied to 650 reversible four high rolling mill in a steel mill and the “effect analysis software of work roll horizontal displacement of 650 reversible four high rolling mill” was compiled, which effectively solved the existing problems of the shape calculation errors and the accurate calculations and predictions of the exit shapes are realized.

Multiaxial Fatigue Test of Aeronautical Aluminum Alloy 2A12 and Research on Stress Criterion Life Predictive Model

CHEN Yajun, LIU Bo, LIU Chenchen, ZHOU Jian

2017, 28(09): 1092-1096,1100.

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Based on multiaxial fatigue failures, compound fatigue tests of stress-amplitude ratio, tension-torsion phase and average stress variables were carried out on 2A12 aluminum alloy. With the discussions of 3 common multiaxial fatigue life predictive models of stress criterion which included Lee criterion, Carpinteri criterion and Sines criterion, a modified model was built on the basis of Carpinteri criterion considering effects of both stress-amplitude ratio and tension-torsion phase. The comparison between predicted life and experimental life under different conditions shows that Lee criterion's predictive results are too over-estimated for the above experiments. Without consideration of stress-amplitude ratio and tension-torsion phase, the predicted life of Carpinteri criterion and Sines criterion have large errors compared with the experimental life. The new modified stress criterion life predictive model may give results that 90 percent of life prediction data will be in the 2 times error band with different conditions.

Research on Preventing Weld Cold Crack of 40Cr by Impact Revolution Curved Rod

ZHANG Yong, SUN Linlin, QI Xiuling

2017, 28(09): 1097-1100.

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Weld cold cracks of 40Cr under the conditions of strong constraint degrees were controlled by the method of welding with impact revolution. In order to increase the plastic deformations of the action zones, the geometrical shapes of the impacting rod were designed to curved shapes. The residual stresses of the workpieces with and without the impact revolution effect were measured. The distances between the welding torch and impacting rod were as 80mm, 100mm and 110mm respectively. The residual stresses at the joints were measured by small hole method. The experimental results show that the residual stress may be reduced by the method. The new method may prove the possibility on preventing weld cold cracks by reducing residual stresses.

Experimental Ressearch on Mechanics Properties of Composite Pre-tightened Teeth Connection Based on Length Changes of Steel Teeth

SUN Jian, LIU Yawen, GAO Yifeng, ZHAO Qilin, QI Liang

2017, 28(09): 1101-1105,1111.

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The CFRP pre-tightening teeth connector were investigated by changing the length of steel teeth, and the failure modes and the ultimate load of the specimens were tested. In addition, the critical tooth lengths of bending shear deformations were put out through deducing equations and theoretical analyses. The research shows that the specimens have three failure modes when the lengths of steel teeth were changed. It may effect the ultimate bearing capacity of single tooth when the length of steel tooth is small .However, the influences tend to be stable when the steel tooth achieves a certain length. Critical tooth length may be calculated and the result is just the designed length of the steel tooth.

Study on Steering Geometry of Racing Cars with Consideration of Tire Cornering Characteristics

CHAI Tian, LI Fan, LEI Fei, LIU Jie, ZENG Xia , TANG Yingshi,

2017, 28(09): 1106-1111.

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For improving the tire lateral resultant forces and lateral accelerations of racing cars, a steering geometry was proposed considering the effects of tire cornering characteristics. The instantaneous center of steering was defined by analyzing the impacts of tire slip angles, and a 3-DOF full vehicle model containing tire model was developed for steering simulation. The steering geometry was obtained via optimization of maximizing lateral resultant forces of tires by IP-GA. Simulations and tests were conducted to validate the theoretical basis of the present steering geometry. The results indicate that the maximum lateral resultant force is raised under the design using the present steering geometry compared with Ackerman steering geometry. Thus the steering performance within extreme condition could be improved.

Energy Management of a 4WD Hybrid Electric Vehicle Based on ECMS

SI Yuan, QIAN Lijun, QIU Lihong, LI Hao

2017, 28(09): 1112-1117.

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An ECMS optimized by GA was presented for a 4WD hybrid electric vehicle (HEV). According to the characteristics of the 4WD HEV, a dynamics model of the vehicles was established and the energy optimization management strategy was designed on the basis of ECMS. For further improvement of fuel economy of the 4WD HEV, key parameters of ECMS was optimized by GA. Hardware-in-the-loop (HIL) simulation results validate that the ECMS optimized by GA may realize the energy optimization management of the 4WD HEV and the average fuel economy under typical driving conditions is 8.94% better than that of the rule-based energy management strategy and also improves by 2.68% compared with the original ECMS without parameter optimization.

Research Status and Perspectives of ELID Grinding Fluid

WU Qiaoping1,2; WANG Yu1;QU Wei1;DENG Zhaohui1,2

2017, 28(09): 1118-1125.

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As a low cost and high efficiency ultra-precision processing method, ELID mirror grinding technology played an important role in the field of modern mechanical manufacturing. The formation rate, compactness, adhesion and insulation of the oxide layer were decided by the composition and ratio of grinding fluid, which was the key technology in ELID grinding processes. This paper mainly introduced the composition of ELID grinding fluids, the influences of grinding fluids on the oxide layers and the improvements of ELID grinding fluids, and the next step of the research of ELID grinding fluids was prospected.

Research Status and Development Tendency of Wind Turbine Reliability

LI Yao1;ZHU Caichao1;TAO Youchuan2;SONG Chaosheng1;TAN Jianjun1

2017, 28(09): 1125-1133.

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The failure modes and research progresses of reliability for wind turbines at home and broad were analyzed. The failure modes, failure reasons and detection methods of key components in the wind turbines were summarized. Also, the frequently used methods of reliability analysis and research status of wind turbine reliability were analyzed. Then research focuses, research methods and measures to improve wind turbine reliability were presented. Combining with the engineering requirements and research status, the development tendency of wind turbine reliability was analyzed and the flowchart to investigate the smart health management technology of wind turbines was proposed. It is of great significance to reduce the costs of operations and maintenances and to improve the safety of wind turbines.

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