Table of Content

10 March 2018, Volume 29 Issue 05

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Fault Diagnosis of Electro Hydraulic Servo Valves Based on GA+LM Algorithm Optimized BP Neural Networks

QUAN Lingxiao1, 2;GUO Hai Xin1,3;SHENG Shiwei3;LI Lei1

2018, 29(05):  505-510. 

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The BP neural network had some shortcomings, such as the learning speed was very slow, easy to fall into local minima, and was sensitive to initial parameters. To improve the precision and speed of fault diagnosis of electro hydraulic servo valves, a new combination optimization method was proposed. GA was used to optimize the initial weights and thresholds of the neural network to improve the training speed and to reduce the BP neural network's sensitivity to initial parameters. And LM algorithm was used to train accurately and search for the global optimal solution in the local solution space. In the premise of preserving the mapping ability of the BP neural network, the method may improve the learning speed and accuracy of the networks, and thus the efficiency and accuracy of fault diagnosis of electro hydraulic servo valves may be greatly improved. At last, the MOOG D761-2716A servo valve's diagnosis results were given, which explained the practicality and efficiency of this method.

A Calculation Method of Car Body in White's Static Stiffness Based on Modal Theory

ZHANG Wentao1;WANG Zhenhu2;FANG Xiangdong3;YANG Xuyue1;LI Luoxing2;WANG Wanlin2

2018, 29(05):  511-518. 

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The mathematical relationship of simple rectangular frames between flexible modes and static stiffness were generalized to car body in white based on the modal theory in linear systems, and the specific mathematical expressions for stiffness calculation were derived. The modal method which obtained static stiffness by extracting each modal parameters with FEA was described, instead of the previous methods of calculating static stiffness based on the compliance matrix theory and large tests. The results show that, the differences of static stiffness values calculated by two methods respectively are less than 10%, which illustrates that the global static compliance of the car body may be expressed by the sum of all modal compliance contributions, and this calculation method has high precision, so it may provide a reference for target setting of low order modes and stiffness properties. Furthermore, the modal compliance contributions may be an important basis for modal identification. Finally, comparing the finite element calculation results and static stiffness test ones, the errors are less than 8%, especially the torsional stiffness calculation errors are less than 3%, which are calculated by the modal method. So it illustrates that the FEA is reliable.

Optimal Design of Vortex Flow Non-contact Pneumatic Gripper Structures

LI Jianfeng1;LI Guoping1;LU Bo2;LIANG Dongtai1

2018, 29(05):  519-525. 

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In order to improve the absorption capability of the single air-inlet non-contact pneumatic grippers and make the pneumatic gripper structures processing more convenient, based on the features of flow field characteristics of pneumatic grippers and the theory of 3D printing, an advanced swirling flow pneumatic gripper design proposal was developed. Aiming at improving the absorption capability of pneumatic grippers, the model of pneumatic gripper cavities was well designed through simulation analysis of non-contact pneumatic gripper's operational principles and flow field characteristics of pneumatic grippers. The claw structure model was built with 3D rapid prototyping technology and was developed with the simulation calculation design. Experimental results show that the negative pressures by improved pneumatic gripper cavities are twice as high as before.Also, the absorption capability increaseds by 57 %. With respect to the processing of pneumatic grippers, compared with traditional machining technology, 3D printing technology is more convenient and the complicated inner parts of pneumatic gripper cavities may be produced more easily.

Analyses on Flow Characteristics and Bearing Performances of Aerostatic Gas Bearings with Pocketed-orifice Type Restrictor Working in Vacuum Conditions

LI Yuntang;WANG Jun;WAN Xin;WU Jintian;LI Xiaolu

2018, 29(05):  526-530,543. 

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The flow characteristics inside aerostatic thrust bearings with pocketed-orifice type restrictors were analyzed for the bearings working in vacuum conditions. In the analysis, transition flows were ignored and the viscous and molecular flows were considered only to simply the calculation. And the critical radius and critical pressures of viscous flows transition to molecular flows were obtained according to the basic flow equations. Moreover, the errors of calculation formula and results presented by other scholars were corrected. Further, the following issues were studied: relationship between the critical radius and critical pressure; influences of gas channels, air chamber pressures and air chamber sizes on the critical radius and critical pressures; constraints of molecular diameters and masses, temperature to air chamber pressures; factors for improving bearing performances. The results are helpful to performance calculations and design parameter optimizations for aerostatic thrust bearings working in vacuum conditions.

Static Stiffness Property Analyses of a Novel PRRR+PURU+S Spherical Parallel Humanoid Robotic Ankle Mechanism

ZHOU Yulin1;YANG Long1, 2;XIAO Chao1

2018, 29(05):  531-538. 

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A novel PRRR+PURU+S spherical parallel humanoid robotic ankle mechanism with a 8 order statically indeterminate mechanism was proposed, and the calculations of its stiffness were conducted. Firstly, by means of small deformation superposition principle, the relationship between the angle displacements of moving platform and linear displacements of spherical point and the forces acted on the components were derived out. Then, based on the results of static analyses including the relational equations between applied forces and the forces acted on the components, the relationship between the applied forces, the line displacements and the angle displacements of the mechanism were set up. Finally, the static stiffness matrix was obtained. The six principal stiffnesses of the mechanism and the corresponding directions were achieved by the orthogonal transformation. The results show that the torsion stiffness and the line deformation stiffness are all increased compared to the UP+R ankle mechanism, and the line deformation stiffness sharply increased. The stiffness of the novel ankle mechanism basically achieve to balance.

Experimental Study on Variable Mass Negative Stiffness Dynamic Vibration Absorbers

LIU Gang;ZHENG Dasheng;DING Zhiyu;YAO Hongliang

2018, 29(05):  538-543. 

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Aiming at the defects of narrow band of traditional dynamic vibration absorbers, a new type of variable mass negative stiffness dynamic vibration absorber was presented, so that the vibration absorber might have a good low-frequency efficiency. Firstly, the dynamic equation of the variable mass negative stiffness vibration absorber was established and the operating principles of the absorber were analyzed. Secondly, the variable mass negative stiffness vibration absorber experimental table was built, while the PID control program was compiled. The performance of the new dynamic vibration absorbers in vibration reduction on a primary system was studied via dynamic simulation and some experiments. The results show that, the designed vibration absorbers may be continuously adjusted and the effective frequency band of the designed vibration absorbers were widened by 17.3% compared with the traditional vibration absorbers.

Research on Large Capacity Coupling Design Task Planning Based on Cluster Analysis

TIAN Qihua;MEI Yueyuan;DU Yixian;Zhou Xiangman

2018, 29(05):  544-551. 

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For large capacity coupled design tasks, using serial execution model would lead long development cycles and large planning scheme numbers of the design projects. The feasibility of using cluster analysis to shorten the coupling task execution cycles and reduce the planning scheme numbers was expounded by comparing the characteristics of cluster analysis objects and coupled design tasks. A new solving method of task planning for large capacity coupled designs was proposed based on cluster analysis, and the optimal execution orders and the shortest execution times for coupling design tasks were obtained. Taking the development of a manipulator as an example, the validity of this method was proved.

Engine Fault Diagnosis Based on Tensor Tucker Decomposition

XU Xiaowei1,2;SHEN Qi1;YAN Yunbing1,2;WU Qiang1;ZHANG Nan1

2018, 29(05):  552-557. 

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The traditional engine fault diagnosis method based on vector mode to extract data features was a method which might lose the structure informations of the data and damage the correlation between the data. To solve this problem, the paper presented a method to extract engine data features in tensor mode, and the engine state samples of the three order tensor form of the “signal class×crank angle×rotation rate” were constructed.Based on alternating projection theory, the HOSVD-HOOI tensor Tucker decomposition of the simultaneous solution algorithm was used to extract data features.The data were processed without feature extractions and with the method based on the tensor Tucker decomposition respectively,and the experimental data were processed under three kinds of state of normal operation, single cylinder misfire and shaft misalignment .The parameters of the classification model was optimized by using the grid parameter optimization method, genetic algorithm and particle swarm optimization respectively.Then the prediction accuracy and model learning time were compared and analyzed as evaluating indicator.The experimental results show that the prediction accuracy of engine data feature extraction and diagnosis method based on tensor Tucker decomposition is higher, and the learning time of classification model is shorter.

A New Method for Determining Equivalent Diameters of Milling Cutters

ZHU Jianmin;LI Yao;HE Dandan;TIAN Fengqing;LI Xiaoru

2018, 29(05):  558-564. 

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In order to determine the equivalent diameters of milling cutters, an equivalent model of milling cutters was established, which was divided into tool holder and cutter teeth, then based on structural analysis and results calculated theoretically, the target function of optimizing cutter teeth equivalent diameters was established, and cutter tooth's equivalent diameters were determined using genetic algorithm. Taking several two fluted milling cutters, three fluted ones and four fluted ones with different parameters as the study objects, adopting the proposed method to determine their teeth's equivalent diameters, which were used to calculate their tool point frequency response functions respectively, and comparing the tool point frequency response functions calculated by the proposed method with ones calculated by equivalent mass method and experimental results. It is shown that the proposed method has higher calculation accuracy and better adaptation.

Design and Applications of Generalized Eccentric Noncircular Gears

YE Jun1,2;CHEN Jianneng1,3;ZHAO Xiong1,3;SUN Xincheng2;XIA Xudong1,3;GAO Qifeng2

2018, 29(05):  565-571,578. 

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In order to improve the eccentric noncircular gear design flexibility to meet the requirements of more transmission characteristics, the generalized eccentric noncircular gear pitch curves were constructed based on the derivation of the tangent polar coordinates of eccentric curves. In order to facilitate the machining and design of this kind of noncircular gears, the convexity of the curves of the gears was deduced and the arc length formula was derived. This new generalized eccentric noncircular gear was used to drive the transverse seal mechanisms of horizontal pillow packing machines, which may meet the requirements better of horizontal sealing processes compared with conventional eccentric noncircular gears.

Design and Dynamics Model Simulation of Vehicle Semi-active Occupant Restraint Protection Systems

CHENG Wenming1,2;LI Xianghu1;XIN Yong1;XIANG Zhongke2

2018, 29(05):  572-578. 

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A semi-active vehicle occupant protection system was designed to estimate the possibilities of car collisions according to reaction time allowance. Based on different possibilities of collisions the situations would be classified into corresponding risk levels so as to alert the driver to avoid dangers, otherwise, passive protection system will be aroused in advance. The software of MADYMO was used to establish the simulation model of automobile front collisions, which was verified by tests. The designed seat belt preload device and the seat cushion obliquity adjusting device were simulated, and then compared with the simulation results of traditional passive actuating mechanisms. The results indicate that, compared with the traditional passive protection systems where gunpowder preloaded and the angle of seat cushion obliquity unchanged, semi-active occupant protection system may achieve seat belt preload and seat cushion tilt adjustment in advance, the head and hip trauma injury decline slightly, but the peak values of the neck bending moments, the chest accelerations and chest compressions decrease respectively by 20.6%,14.6%,15.6%. And the semi-active restraint system may effectively reduce occupants' injury.

Adaptive Sliding Mode Path Tracking Control of Agricultural Wheeled Mobile Robots

LI Taochang

2018, 29(05):  579-584,590. 

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An adaptive sliding mode control method was proposed based on non-time reference, aiming at the path tracking problems of agricultural wheeled mobile robots with uncertain disturbances. First of all, an appropriate non-time reference was selected and then a relative kinematics model was established to cater to designing path tracking controllers of mobile robots. The model got rid of the influences of time and speed. Secondly, the classic exponential reaching law was modified and a new fast reaching law was constructed. Subsequently, the RBF neural network was introduced to estimate the uncertain disturbances, and then an adaptive sliding mode control method was proposed based on the new reaching law. The performance of the control method was demonstrated by theoretical analyses and proofs. By utilizing the proposed method, path tracking performance is improved and chattering phenomena is eliminated when the wheeled mobile robots suffer from the uncertain disturbances. Finally, the effectiveness and superiority was verified by a series of simulation experiments.

Fault Diagnosis for Rolling Bearings Based on Synchrosqueezing Wavelet Transform

LIU Yiya1,2;LI Ke1,2;CHEN Peng3

2018, 29(05):  585-590. 

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In order to overcome the difficulties of feature extraction of non-stationary faulty signals in rolling bearing fault diagnosis, this paper proposed a fault feature extraction method by using the synchrosqueezing wavelet transform (SWT). Firstly, the measured vibration signals were processed with the continuous wavelet transform (CWT), and the wavelet transform coefficients were subjected to synchrosqueezing transform (SST). Moreover, an adaptive threshold denoising technology was presented to cancel noises of the SST coefficients, and the effective signal data near the center of the frequency were extracted by integrating. Finally, the signal reconstruction was carried out by utilizing the extracted effective signals. The simulation and the equipment tests were designed to verify the effectiveness proposed methods herein. The test results show that SWT has a high signal extraction accuracy and noise reduction capability. SWT also has higher time-frequency resolution, which may convert the fault signals into high-resolution time-frequency spectrum and make up for the lacks of CWT.

Shearer's Helical Drum Multi-objective Optimization Design Based on GA

ZHAO Lijuan;FAN Jiayi

2018, 29(05):  591-596. 

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In order to realize shearer's helical drum optimal comprehensive performances of cutting and loading, the changing of cutting performance indexes and the loading rate changed with the structure and motion parameters were obtained based on the virtual prototype technology and the theory of discrete element. On the basis of mechanical optimization design theory, the performance indexes of evaluation function were established. Helix angle, cutting line spacing, speed and traction speed were selected as design variables, multi-objective optimization model with different performance indexes were established, the optimal structure parameters and motion parameters were obtained by GA. The results show that the biggest drum cutting area increases 247 mm2,specific energy consumption reduces 0.014kW·h/m3, cutting power reduces 10.8 kW, cutting resistance decreases 7085 kN and the loading rate improves 1.7 %, it enhances the comprehensive performance of drum effectively. The research provides the data support of the structure and motion parameters' selection, it has certain engineering application values.

Design Space Differentiation Optimization Method and Its Applications to Vehicle Lightweight Design

LIU Niansi;CAI Yongzhou;GU Jichao;ZHENG Hao

2018, 29(05):  597-601,622. 

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A meta-model based design space differentiation method (DSD) was proposed to improve the performance of traditional region elimination methods. In this method, a gradually reduced important region was constructed using the expensive points and the space to be removed in the region elimination methods was defined as the other regions and would also be searched. When the design spaces were divided, the quadratic function (QF) might be used in the search of the two subregions and several new expensive points would be selected for the updates of the QF meta-model both in the important regions and the other regions. Instead of region elimination, fewer new expensive points would be selected in the other regions, which might avoid the traps of the local minima. It is demonstrated by several benchmark functions, the newly proposed method shows its great performance. Then, the proposed method was applied in vehicle lightweight design problems. With the proposed method, the masses of the rear frame are reduced by 7.67kg, reaches the 10.4% of the systems, and its stiffness is also improved. When compared with previously developed hybrid and adaptive meta-modelling(HAM) method, both the search efficiency and accuracy are noticeably increased.

Rolling Bearing Performance Degradation Assessment Based on FOA-WSVDD

ZHU Shuo;BAI Ruilin;LIU Qinchuan

2018, 29(05):  602-608. 

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A rolling bearing performance degradation assessment method was proposed based on FOA-WSVDD, aiming at the problems that the SVDD algorithm was not sensitive to rolling bearing early faults and difficult to select suitable kernel parameters. The feature vectors of the time and time frequency domains were extracted from bearing fault-free stages and then were selected based on monotonicity. Then, the FOA-WSVDD model was established where the wavelet kernel function was introduced to overcome the problems that the existing kernel function was not sensitive to the early faults of the rolling bearings, and kernel parameters were optimized based on the improved FOA where the ratio of the numbers of support vectors and the total samples was used as fitness function. Finally, feature vectors were input into the WSVDD model, and the bearing performance degradation index was obtained. The experimental results show that the proposed method may accurately predict the bearing early faults, and it is 17 hours earlier than that of the SVDD algorithm which is  based on Gauss kernel function.

Numerical Simulation and Experimental Verification of Energy Absorption Performance of PU Foam Filled CFRP Cone Tubes

GAN Nianfei;WANG Duohua;FENG Yanan;ZHANG Qian

2018, 29(05):  609-615. 

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A new type of CFRP filled with polyurethane (PU) foam was proposed for the vehicle front energy absorbing structures. The mechanical properties of PU foam and CFRP composites were obtained by the material property tests, and the results of quasi-static compression of PU foam filled CFRP were obtained. LS-DYNA was used to simulate the quasi-static collapse of composite materials. The simulation results are in good agreement with the experimental results, which verifies the correctness of the finite element model and the material model of the composite filled structures.The results show that the foam filled CFRP cone tubes have good energy absorption ability, and the filling structure specific energy absorptions are higher than that of the two materials used alone.

Welding Deformations and Stress Simulations Control of Large-scale Complex Structures

OU Daquan1;WANG Fazhan1;ZHAO Shen1;ZHENG Jianxiao1;LIU Taiping2

2018, 29(05):  616-622. 

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Aiming at inefficiency problems of finite element calculations of a large-scale complex structure, this paper put forward piecewise mobile body heat source temperature control algorithm, applied to the hierarchical optimizations of discontinuous welded frames in an excavator, and compared calculation efficiencies of segmented moving temperature control body heat sources and point by point moving double ellipsoid heat sources. The results show that welding residual stresses and angular deformations were minimized by using welding procedures of symmetrical welding and skip sequence welding. The peak drop rates of welding residual stresses on both the left side plates and the right side plates reach to 38.46% and 42.13% respectively. Also the welding residual stresses decrease obviously. Compared with the simulation results of segmented moving temperature controlled body heat sources and point by point moving double ellipsoid heat sources, it is indicated that the two methods have the same trends and the calculation accuracy is close, but the computational efficiency is improved remarkably. The simulation results are compared with the measured results, which verifies the accuracy of the heat source model and the optimumprocess, because the two are highly consistent.