Table of Content

25 September 2019, Volume 30 Issue 18

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Yield Strength Testing Method of Ferromagnetic Materials Based on Pulsed Eddy Current

LI Kaiyu;GAO Wenjuan;WANG Ping;ZHANG Yanyan;HANG Cheng

2019, 30(18):  2143-2149. 

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Yield strength detection of ferromagnetic materials in iron and steel industries relied on loss detection, which greatly increased the cost of testing. So, a multi-feature fusion method for yield strength pulsed eddy current testing of ferromagnetic materials was proposed herein. Firstly, the time domain characteristics and frequency domain characteristics of pulsed eddy current response signals were extracted. And then, a neural network model for establishing the yield strength of each signal characteristic and material was established. Finally, the neural network model was used to predict the yield strength of the materials. As a non-destructive testing method, the method may achieve prediction errors less than 5%.

Lubrication Analysis of Plain Journal Bearings Considering Axial Motion of Journal

LI Biao1;SUN Jun2;ZHU Shaoyu2;FU Yangyang2;MIAO Enming3;LI Yunqiang4;ZHU Guixiang4

2019, 30(18):  2150-2155,2163. 

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Taking shaft-journal bearing systems as research object, a hydrodynamic lubrication model was established considering axial motions and misalignments of journals, and Reynolds equations were solved by finite difference method. The influences of axial motions of the journal on the lubrication performance of journal bearings were analyzed under the conditions of different journal tilt angle, rotating velocities,  eccentricities, and bearing clearances. Results show that the axial motion of journal has significant influences on lubrication characteristics of misaligned journal bearings, and the tilt angle and rotating velocity of journals have direct relationship with the influence degree of axial motion of journal on the bearing performance. Bigger tilt angle of journal has greater effect of axial motion on the lubrication performance of journal bearings. Lower rotating velocity of journal has more significant influences of axial motion. Smaller bearing clearance has greater effect of axial motion.

Aeroengine Rotor Fault Diagnosis Based on Fourier Decomposition Method

LIU Yang;LIU Xiaobo;LIANG Shan

2019, 30(18):  2156-2163. 

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Aiming at the problems that the traditional time-frequency analysis method might not effectively extract rotor fault feature informations, a fault diagnosis method was proposed based on FDM for rotor rubbing. Firstly, frequency modulation and amplitude modulation simulation signals were constructed. The signal decomposition results of methods such as EEMD, VMD, and FDM were contrastively analyzed. The FDM may achieve complete decomposition of the simulated signals, and get a high time-frequency resolution. Finally, the FDM was used to analyze the fault sample data of the single-point on casing and whole-cycle on rotor rubbing tests of the collected rotor tester. Comparing the periodic power spectrum density estimation and fault feature extraction results of different algorithm fault signal decomposition results, the method proposed herein has higher diagnostic reliability, and effectively solves the rotor fault diagnosis problems.

Mass Metric Method and Its Correction of Grinding Medium Filling Rates for  Vibrating Mill

CHENG Min1,2; LIU Baoguo1;LIU Yanxu1

2019, 30(18):  2164-2171. 

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Relative density coefficient considering the shape and size of grinding medium was introduced to modify the mass metric method of grinding medium filling rates. Hexagonal arrangement characteristics of cylindrical grinding medium in grinding cylinder were obtained by means of geometric close-packed drawing method, and the basic calculation formula of the relative density coefficient of grinding medium was given. Then, the discriminative conditions for continuous filling of grinding medium in wall gaps of the grinding cylinder were derived. Triangle area was used to approximately replace the total area of grinding medium in the gaps of the grinding cylinder, and the modified formula for calculating the density relative coefficient was obtained. Errors between the calculated results of theoretical formulas and the experimental results of geometric close-packing drawing are less than 5%. The limiting value of the modified formula for the relative density coefficient of spherical grinding medium is as 0.625 2, which is close to the experimental result 0.61. The calculating results of application examples show that it is necessary to modify the mass metric method of grinding medium filling rates.

Tribological Properties of FeS/iron-based Bearing Materials by High Energy Ball Milling-Powder Metallurgy Method

ZHANG Kaiyuan;YIN Yanguo;ZHANG Guotao;XIE Zhiyuan;CHEN Qi

2019, 30(18):  2172-2178. 

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With Fe, C and FeS as raw materials, FeS/iron-based bearing materials were prepared by high energy ball milling technology and powder metallurgy. The microstructure of the materials was studied and the friction and wear properties of the materials were investigated. The results show that the high energy ball milling processes may improve the distribution uniformity of FeS particles and the interface bonding with the matrix. The mechanics properties of the materials are higher than those of the non ball milling materials. The FeS belongs to the solid lubricant and has good oil storage characteristics. Under oil lubrication, the transfer of FeS to the friction surface is easy to form a liquid solid lubricating film, which plays a good antifriction and viscosity reduction. The 8% FeS ball milling iron-based bearing materials have better friction reducing wear resistance and higher load capacity.

Defect Detection Method of Linear Guide Surfaces Based on HSI Color Space

ZHOU Youhang;MA Zhuxi;SHI Xuanwei;KONG Tuo

2019, 30(18):  2179-2184. 

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In order to solve the problems that tiny defects of linear guide surfaces were not accurately detected due to the effects of background texture, a visual detection method was proposed for surface defects of linear guides in HSI color space. Firstly, the images of the surfaces were converted from RGB space to HSI space for obtaining the components of hue,saturation and brightness. Then, the dimensions of images were reduced, which was based on the cumulative contribution rate of PCA, and a mixed gray model was established by the low-dimension images.After that，the corresponding weighting coefficients were optimized by PSO algorithm, and finally, the defects were segmented by threshold. The results of experiments and calculations show that the proposed method may accurately detect 4 types of defects compared with the extraction method in RGB space.

Modeling and Optimization Experimental Research of Conversion Rates in Chemical Mechanical Dry Lapping

YUAN Julong1;WANG Jie1,2;LYU Binghai1;HUANG Sheng1;ZHANG Taojie1;HANG Wei1

2019, 30(18):  2185-2190,2197. 

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The maximum removal rate of chemical mechanical dry lapping was produced when the balance between the chemical solid-state reaction and mechanical action was achieved. The mathematic model of solid-state conversion rate was established to comprehensively analyze the influencing factors. 4 main parameters were selected from the influencing factors to carry out the experimental research on the lapping of sapphire with fixed SiO2 abrasive tools. The experimental results show that the 4 parameters ranked from high to low according to the significant degree of influence are the abrasive tool rotation speed, load, abrasive particle size, and the percentage of abrasive to the binder. The optimum parameter combination of chemical and mechanical action within the scope of research is that abrasive particle size is as 45 μm, percentage of abrasive to the binder is as 30%, load is as 0.6 MPa, and abrasive tool rotation speed is as 150 r/min.

A Fourier Descriptor Based Approach to Integrated Type and Dimensional Synthesis of CSM

ZHU Liuxian1，2;LYU Hao1 ;HAN Yuanfei1;ZHAO Ping3;LI Xiangyun1

2019, 30(18):  2191-2197. 

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With the aid of Fourier transform, a  novel approach to integrated type and dimensional synthesis of CSM was proposed herein.Through the harmonic analysis of point trajectories from the given task motions,the simplest trajectory which contains the minimum number of harmonic components was identified.Then,characteristic informations of those harmonics such as number of terms,magnitude and frequency were used to determine the topological features and dimensional parameters of CSM,thus effectively solving the motion synthesis problems of CSM.Finally,examples were given to demonstrate the validity of the proposed method.

Effects on Radius of Curvature of Load Pad on Position Errors of Force Transducer

LIANG Wei1,2;YANG Xiaoxiang1,3;WANG Xiurong2;YAO Jinhui2

2019, 30(18):  2198-2206. 

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Load eccentricity and contact stress of load pads with different contact forms were compared. 9 pieces of load pads with different structures were designed and tested.The experimental results show that the position errors of the sphere-plane contact are smaller than that of sphere-sphere point contact.Load eccentricities with sphere-sphere uniform contact and sphere-plane contact are similar. The sphere-sphere point contact and the sphere-sphere uniform contact are suitable for the situations when the angle of adjustment is small.The sphere-plane contact and the sphere-sphere uniform contact with small radius are used if the angle of adjustment is large.

Tribological Behavior of DLC Films under Water Environment

GUO Feifei1;JIN Shoufeng1;QIN Liguo2;DONG Guangneng2

2019, 30(18):  2206-2210. 

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Tribological behavior of the DLC films was analyzed systematically, which were deposited on the polished surfaces of CoCrMo alloy with respect to the CoCrMo under the lubrication of aqueous solution. Results show that the average friction coefficient is about 0.10 under bovine serum albumin (BSA) solution lubrication with different concentrations,and the smallest wear loss of CoCrMo pin is about 1.69×10-5 mm3. In the same conditions, the wear loss of CoCrMo pins under the lubrication of physiological saline solution is 1.38×10-5 mm3. The DLC transfer layer exists on the wear scar lubricated with physiological saline solution. It indicates that the formation of DLC transfer layer is inhibited by the adsorption of bovine serum albumin protein layer. The formation of transfer layer has undergone the processes of wear debris adhesion, continuous transferring, and partial delamination.

Dynamics Analysis of Spindle-bearing Systems on Spiral Bevel Gear Cutting Machines

WANG Zhiyong;DU Weitao

2019, 30(18):  2211-2216,2223. 

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Tool spindle systems of spiral bevel gear milling machines often produced chatters in machining processes, which affectsed the quality of workpieces. According to the lumped mass method, an equivalent dynamics model of tool spindle systems was established. Stiffness matrix of spindle rotor was obtained by using Timoshenko beam theory analysis. Based on mechanics analysis of tapered roller bearings, formulas for calculating the axial stiffness and radial stiffness of the bearings under axial preload were established. A dynamics model of tool spindle systems constructed by numerical analysis method was verified by force hammer excitation experiments. The comparison results show that the dynamics model may effectively reflect the dynamics characteristics of tool spindle systems.

Temperature Field Analysis of Hysteresis Heat of Squeezing and Rotating Rubber Rollers

CHU Hongyan1，2;XU Kangjian1，2;SUN Dongming1，2;CAI Ligang1，2

2019, 30(18):  2217-2223. 

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In order to study the effects of hysteresis heat generation on nonlinear viscoelastic behaviors of rubber materials,a pair of squeezing and rolling steel-rubber roller was studied. Firstly, the decoupling method was adopted for the first transient mechanics field analysis, and then the heat generation rates of the nodes were calculated by the losses. Finally, the late heat generation was used as the internal heat sources for thermal analysis to obtain the steady-state temperature field distribution. The results show that the temperature rises of hysteresis of rubber roller are as 6~13 ℃. Along the circumferential direction, the highest temperature appears on both ends. Along the radial direction, the highest temperature appears on the center. The simulation results are consistent with the experimental ones which pro ides the feasibility of the analysis method, and the hysteresis heat generation is the main heat-producing factor in the movement processes.

Acceleration Saturation Performance Optimization Method of Direct Feed Drive Systems Using Hybrid PLS Regression and PSO

LIN Xiankun1,2;ZHANG Liming1

2019, 30(18):  2224-2230. 

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For the purpose of enhancing the driving performances of linear motor feed drive systems, an optimization method of acceleration saturation was investigated for the systems. After the analyses of influence factors of acceleration saturation performances in direct feed drive processes,an optimization method was presented based on hybrid PLS regression and PSO.Orthogonal experimental design method was used to assign experimental servo parameters.The motion time and speeds of the feed drive systems were measured by laser interferometer to establish a sample database.An acceleration saturation performance model was founded based on PLS.The servo parameters for acceleration saturation performance optimization were identified by PSO.An experimental platform was set up and the random experiments with 200 group data were run.Results show that the hybrid servo parameters have better acceleration saturation performance which is 68% higher than the average values of the sample groups.

Bearing Remaining Life Prediction Based on Full Convolutional Layer Neural Networks

ZHANG Jidong;ZOU Yisheng;DENG Jialin;ZHANG Xiaolu

2019, 30(18):  2231-2235. 

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Traditional method of data-driven bearing remaining life prediction was based on knowledge and experience, and the degradation index was established manually which was time-consuming and labor-intensive. Therefore, the convolutional neural network (CNN) was used to perform feature self-learning and remaining life prediction. All connected layers in the traditional CNN were replaced with convolutional layers and pooling layers to reduce the training parameters of the neural network. Weighted average method was used to denoise the prediction results. Dataset of the accelerated life test of the bearings shows the effectiveness of the proposed method.

Stability Prediction in CNC Pocket Milling Processes

LYU Shujie;LI Haolin

2019, 30(18):  2236-2241. 

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Chatter happened due to the changes of engagement conditions with milling cutter entering into the corners along the tool path in pocket milling processes. In view of that situation, on the basis of semi-discrete method for predicting the stability of milling with tool-workpiece engagement, the changes of tool-workpiece engagement information caused by the milling path in CNC pocket milling processes were combined, and a method for predicting the stability of pocket milling was proposed according to the given milling path. Experiments indicate that the method may successfully predict the milling stability in the processes of CNC pocket milling.

A Method of Image Perspective Distortion Correction in Ball Pose Detections

LIU Jian;WANG Yuanyuan

2019, 30(18):  2242-2249,2256. 

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Aiming at the problems of image foreshortening effects in ball pose visual detections,a correction method of image perspective distortions in ball pose detections was proposed.Based on the camera imaging model,the characteristics and causes of perspective distortions were analyzed.According to the spherical feature model,camera calibration technology and principles of reverse perspective transformation,an image correction model of perspective distortions was constructed to correct the perspective distortions of the balls arbitrary pose images.The experimental results show that the average absolute errors of detecting ball pose less than 60mm in diameter by using this method is less than 0.6°.And this method is applicable to other visual measurements of spheres.

A Method for Fitting Pose of Cabins through Measured Key Features

CHEN Dong;LI Shiqi;WANG Junfeng;FENG Yi;HE Wang

2019, 30(18):  2250-2256. 

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Due to the limitations of processes and performances of producs,the reference points for measuring cabin poses could not be made on the cabins beforehand.Therefore,a method of pose estimation by measuring and fitting the key characteristics of cabins was presented.First,according to the structural features of cabins,the key characteristics which met the assembly precision requirements were selected and measured by laser tracker.The gross error point data of the key characteristics were removed by using 2σ criterion method to improve the problems of poor fault tolerance of least-squares method based on classical surveying adjustment theory.Then the processed data of key characteristics were adopted to fit the origin and the unit vectors of each axis of cabin coordinate system.Finally,parameters of cabin poses were obtained.Simulation results show that the improved least-squares method is helpful to obtain higher precision in fitting cabin poses.The proposed method is practical and universal, which may meet the requirements of the pose estimation of cabins and provide a reference for pose estimation of other rigid bodies.

Gait Planning Strategy for a New Type of Wheel-legged Robot

LIU Jicheng;JI Hongchao

2019, 30(18):  2257-2262. 

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A new type of structure of wheel-leg robot was designed. The wheel-legged robot might work in the amphibious environment for the drive system in the closed structure and switch the wheel gait and leg gait without redundant structure easily. According to the method of model control, the foot trajectory generation method was used for the wheel-legged structure to raelize the robot to follow the trajectory in leg gait. The prototype robot was used to prove that the foot trajectory generation method may work in experiments.