Table of Content

10 September 2017, Volume 28 Issue 17

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Expressing Method for an Independent Link Group Parameter Matrix

LU Wenjuan1,2;LIU Ruonan1,2;ZHANG Lijie1,2;ZHANG Yitong1,2

2017, 28(17):  2017-2023. 

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The different types of constraints among the link groups in parallel mechanisms led to the independent and mixed parameters in part of link group parameter vectors, which made the number and engendered nature of DOFs(degree of freedoms) of output components along with the intuitiveness of judging overconstraints in the mechanisms worse. To construct the parameter vectors which only included independent motion parameters, dependent parameters in vectors such as “angular motion parameters”, “non-derivative line motion parameters” and “derivative line motion parameters” were discussed. Meanwhile based on the screw theory, the relevance of screw system was deduced to obtain the linear independent basic screw system which was equivalent into the matrix of link group parameters. Independent matrix of link group parameters was constructed. Furthermore the rule named “the validity of vertical component” was proposed. Finally based on a new mobility formula—GOM, combined with the rules mentioned above, the DOFs of several kinds of typical mechanisms were analysed. The applications of the theories presented before and herein were verified in the following parts: determination of independent matrix for link group parameters, calculations of the mobility and mobility property of output components, and determination of overconstraints.

Multi-objective Optimization of Threaded Connection on Tension Rods for a Uniform Load Distribution between Teeth

LIN Xiezhao;WANG Fuzhen

2017, 28(17):  2024-2028. 

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For improving the serving life of the threaded connection, an elastic-plastic contact finite element method was used for analyzing the stress distribution of the connecting threads. After that, the parametric modeling technique was used for establishing the multi-objective optimization model where the load distribution uniform and the stress peak values were considered. This model was then solved by the radial basis function (RBF) neural network method and the elitist non-dominated sorting GA (NSGA-Ⅱ).The numerical results indicate that compare with the original design, the non-uniform rates of load distribution between the teeth in the optimized design are reduced by 13.6%, and the maximum of equivalent stresses is dropped by 6.9%, and the peak values of the first principal stress are cut down by 11.5%.

Mechanics Characteristics Analysis of Wheel/Rail Impact Induced by Wheel Flats Based on SIMPACK

QIN Yudong;HU Ming;YANG Liuqing;ZHOU Xun

2017, 28(17):  2029-2035,2042. 

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In order to study the dynamics issues of high-speed train wheels with multiple flats, a dynamics model of CRH2 EMU and wheel flat model was developed. The simulation method that changed wheel radius to simulate wheel flats was applied. By analyzing the wheel-rail impact response caused by single flat and two flats, the effects of wheel/rail impact caused by the changes of flat lengths, train speeds and phase angles of multiple flats were determined, and the wheel flat limit was determined under CRH2 EMU safely running. These provide a basis for safe running of high-speed trains.

Analysis on Dynamic Characteristics of Air Bearing over Bit Pattern Media in Hard Disk Drives

YANG Lihua1,2;YANG Kai1;XU Haoliang1;YU Lie1

2017, 28(17):  2036-2042. 

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With the assumption of small perturbation, this paper applied the partial derivative method to solve the compressible gas-lubricated dynamic Reynolds equation in the complex domain. This method might be used to calculate air-film dynamic stiffnesses and dampings of hard disk drives with arbitrary surface topography of disks. The dynamic stiffness and damping coefficients of air bearing over bit pattern media were calculated. Moreover, the effects of bit height of cylindrical and cuboidal bit pattern media on the dynamic coefficients were studied and also the dynamic performances of two types of bit pattern media were compared. The results indicate that the dynamic stiffness and damping coefficients of air bearing over bit pattern media largely decrease compared with those over smooth disk. With the increasing of bit height, the dynamic coefficients gradually reduce. Compared with cylindrical bit pattern media, the gas bearing over cuboidal bit pattern media has larger dynamic stiffnesses and dampings. These results may provide important theoretical reference for the designs of bit pattern media.

Research on Two-phase Flow Mechanics Properties of Hydro-pneumatic Suspensions Considering Physical Property Varieties

DENG Peiyao 1;GU Zhengqi1,2;ZHANG Sha1;MA Xiaokui1

2017, 28(17):  2043-2048,2055. 

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In order to study the mechanics properties of a hydro-pneumatic suspension accurately, the influences of the gas dissolving and the density variety of oil on the mechanics properties of hydro-pneumatic due to the high pressure was taken into account. Using the UDF, on the one side, the mass source was added to the model of volume of fluid(VOF), and on the other side, the variety of the density of oil was defined with the varieties of pressures, then a hydro-pneumatic two-phase flow accurate model was established to analyze the mechanics properties of the hydro-pneumatic suspensions. And the vehicle random road experiments were conducted. The acceleration signals of the hydro-pneumatic suspension's fulcrums up and down were monitored. Based on the experimental data,the hydro-pneumatic suspension virtual experimental platform was established to verified the accuracy of the accurate two-phase flow model. The results show that the accuracy of the accurate model is improved by 10% compare to the original one.

Dynamic Characteristics of 2D Electro-hydraulic Proportional Directional Valves with a Ball-screw Type Axial Compression-torsion Coupling

ZUO Qiang1;LU Qianqian1,2;LI Sheng2;XING Tong2;RUAN Jian2

2017, 28(17):  2049-2055. 

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A ball-screw type axial compression-torsion coupling was proposed herein. This design achieved an output force amplifications for about 20 times, which effectively overcome the disadvantages of small flows of proportional directional valves caused by proportional solenoid magnetic saturation. The coupling connected 2D directional valves and proportional electromagnets by compression-torsion  amplification drive technology. The electromagnetic forces were transformed into the pressure differences from both ends of the spools, which was sufficiently capable of overcoming the frictional forces, clamping forces and nonlinear hydrodynamic forces etc. The pressure distribution and flow field distribution from the main valve P-A and the pilot stage, the steady-state fluid force were simulated and analyzed. Theoretical and experimental studies show that the compression-torsion coupling effectively enlarges the electromagnetic forces. The step response of the valves is about 0.35s, and the frequency characteristics at -90° is about 4Hz at a flow rate of about 210L/min. The step characteristics is not improved obviously by superposing dithering, but the latter may effectively satisfy the following features between the spool displacement and the electromagnet displacement.

Finite Frequency Domain Weighting Switching Control of an Electro-hydraulic Position Control System

CHEN Gang1,2;CAO Sai2;WANG Yiqun1,2;ZHAO Tuanmin3

2017, 28(17):  2056-2061. 

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The mechanism of the double-order state feedback (DOSF) control system that had static errors was analyzed. A three-order state feedback (TOSF) controller without static errors was designed. To overcome the high order of TOSF control systems, a finite frequency domain weighting switching algorithm was adopted to realize TOSF-DOSF dual-controller switching control. The algorithm might reduce the sensitivity of control action on weighting coefficient changing. Simulations show that the static errors of electro-hydraulic position servo DOSF control system are positive correlation with load elastic stiffnesses and TOSF control system may eliminate static errors in conformity with dynamic performances. Experiments show that the system with TOSF-DOSF dual-controller finite frequency domain weighting switching control has good dynamic and static performances. It has smaller switching impacts compared with threshold switching.

Consideration on Operation, Management and Development of State Key Laboratories in Mechanical Engineering Fields

SONG Jianli1;QIAO Yali1;WANG Guobiao2

2017, 28(17):  2062-2068. 

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State key laboratories in the field of mechanical engineering (SKL-ME) oriented on the frontiers of the discipline, serving the major national demands，making efforts to improve the innovation abilities and research levels, and remarkable research fruits were obtained. Through 30 years constructions and developments, a large number of high-level scientific talents was aggregated and cultivated, and SKL-MEs become important bases of conducting high-level academic communications and corporations. Centered on the orientations and research directions, team constructions and talent cultivations, academic communications and international cooperations, opening-sharing and system construction and so on, combining the evaluation conditions of 2013 and example instances, existing problems in the operations and managements of SKL-MEs were analyzed, and the suggestions on the future development were also proposed.

Constraint Tolerance Optimization Design Based on Performance Deviation

GUO Yingfu1;LUO Yanwang1;ZHAO Yanming2;HE Hongxi1;TAN Huajiang1

2017, 28(17):  2069-2074. 

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Based on the actual production processes, there were many factors that affected the processing costs, it was difficult to use a unified mathematical model to accurately describe all types of processing costs-tolerance relationships, the product processing costs and the quality loss costs were regared  as targets, the product tolerance optimization model was established and with the restriction of product performance deviation and economic machining precision. GA was used to solve them, and finally a type of automotive air conditioning compressor was to be an example to verify the validity of the model.

Research on Speed Regulation Performance of Self-excited Electromagnetic Eddy Current Couplings

MEI Xinxin;YE Lezhi;LI Desheng;LIU Yupeng

2017, 28(17):  2074-2079. 

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Due to the complex structures of a permanent magnet eddy current coupling, this paper presented a novel structure of self-excited electromagnetic eddy current couplings, which combined the technology of excitation power generation and eddy current drive. The generating characteristics and the drive characteristics were studied on the self-excited electromagnetic eddy current couplings by establishing the finite element numerical model of the electromagnetic fields for excitation power generation and eddy current drive. The influences of rotational speed differences, conductor layers and air gap lengths on the driving torque were analyzed, then draw a conclusion that when the materials with high conductivity are used for the conductor layers, a larger torque at a low rotational speed differences may be obtained; when the thicknesses of copper layers increase from 1mm to 9mm, the driving torque increases first and then decreases, and the maximum of the driving torque is reached at thickness of 5mm. The driving torque reduces along with the increments of the air gap lengths.

State Recognition of Milling Tool Wears Based on Harmonic Wavelet Packet and BSA Optimization LS-SVM

DONG Caiyun1;ZHANG Chaoyong1;MENG Leilei1;XIAO Pengfei1;LUO Min2;LIN Wenwen3

2017, 28(17):  2080-2089,2108. 

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Aiming at the problems of milling tool wear state recognitions, a state recognition method was proposed based on harmonic wavelet packet and LS-SVM. To overcome the band overlapping problems in traditional wavelet packet decompositions, the milling force signal energies of each bands were extracted in different wear states by harmonic wavelet packet, which were brought in multi-class LS-SVM classifier after normalizing, then the classification recognition of different cutting tool states was achieved. BSA was proposed to search the optimal values of the kernel functional parameters and error penalty factors which affected the precision of the LS-SVM significantly. Experimental results show that harmonic wavelet packet is more effective and feasible than wavelet packet, and the proposed milling tool wear recognition method has higher accuracy.

Adaptive Distribution of Inspection Points for Free-form Curved Surfaces Based on Real-time Reconstruction

LIU Hongjun;YE Wenjing;JI Li

2017, 28(17):  2090-2014. 

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Based on the drawbacks of large calculations and poor applicabilities of existing adaptive algorithms, a real-time reconstruction method of inspection points was proposed to guide the coordinate measuring machine to increase points automatically according to the characteristics of surfaces. In inspection processes, existing inspection points were judged not to satisfy the precision by B-spline lines and surfaces, both sides curvature radius of two inspection points were used to calucate the extract locations of increased inspection points, and surfaces were refitted including new points until accord accuracy requirements. Surface part was taken as an example, supplemented by computer visual graphics to certify the algorithm. The results show that inspections with reconstruction may meet the requirements of accuracy, reduce the calculation amounts to a large extent than that by adaptive algorithm in engineering, and may improve efficiency of inspection surfaces effectively.

Infrared Image Enhancement Algorithm for Hot Forgings Based on Wavelet Transform and Bicubic Interpolation

ZHANG Yucun1;ZHANG Xiying1;FU Xianbin2;ZHANG Guiru3;XU Fei1

2017, 28(17):  2095-2099. 

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A new image resolution enhancement technique was presented based on wavelet transform and bicubic interpolation, which used discrete wavelet to decompose the original images into different subbands, and then the original images and these subbands were bicubic interpolated. Meanwhile, an intermediate stage for estimating the high-frequency subbands was proposed in image processing, the differences among the low low(LL) subband images and the low-resolution input images wers extracted and this difference image(high-frequency components) was used in the intermediate processes to correct the estimated high-frequency components such as low high(LH), high low(HL) and high high(HH). At last, all these images were combined by using inverse wavelet transform. This method may effectively eliminate image noises and improve the image detail informations, and may preserve more edge informations and obtain a sharper image. The processing results of infrared images from main pipeline forgings of nuclear power and small hot forgings show that the superiority of the proposed algorithm on improving the quality of infrared images compared with the conventional image enhancement methods.

Theoretical Research of Vibration Modes for Double-helical Star Gear Transmission Systems

HAO Lifeng;WANG Sanmin;WANG Feiming

2017, 28(17):  2100-2108. 

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Dynamics model and dynamics equations with coupled bent-torsional-axial of a double-helical star gear transmission system was established based on the lumped mass method. The double-helical gears were treated as two helical gears with opposite spiral angle connected by massless spring which had the bending, torsion and axial stiffnesses. The natural cyclic frequencies and vibration modes of the system were calculated. The structure of the vibration modes were well-defined, where the special structure resulted from the cyclic symmetry of the star herringbone gears. Vibration modes were classified into four categories and the multiplicities and numbers of the eigenvalue were analyzed. The results show that the double-helical star gear transmission system has four typical vibration modes: axial-rotational coupled vibration mode (multiplicity r=1), star gear mode (multiplicity r=N-3, N>3), center component translational vibration mode (multiplicity r=2), star gear and center gear coupled mode (multiplicity r=2).

Crashworthiness Design of Bumper Beam Structure with Tailor Rolled Using Nonlinear Topology Optimization Method

YANG Jianglin1;ZHANG Shiyang2

2017, 28(17):  2109-2114. 

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The crashworthiness of automotive bumper beams was designed with the TRB rolling manufacturing processes by nonlinear topology optimization. For shell structures, the nonlinear sensitivity formulas of energy absorbing were given based on the thickness interpolation. The sensitivity was constrained in both of axial and circumferential directions. The utilization of this method optimized the bumper beams under three-point bending conditions and the thickness distributions of bumper beams were determined. Compared with that of the uniform thickness structure, the crashworthiness of varied thickness structures is found to enhance averagely by nearly 30% under the same mass conditions.

Optimization of Disassembly Line Balancing Problems with Setup Times Based on Multi-objective Algorithm and Dynamic Simulation

LI Liuke;ZHANG Zeqiang;HU Yang;ZOU Binsen

2017, 28(17):  2115-2124. 

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In view of the influences of disassembly direction changes on operation times, a multi-objective model of disassembly line balancing problem considering the setup times was established involving  three optimization objectives, i.e. minimizing the disassembly costs, minimizing the invalid work rates and minimizing the non-smooth rates. And a Pareto immune genetic algorithm integrated with the simulation technology was proposed. The proposed algorithm introduced the genetic operator and the immune operator which might avoid the local optimum and ensure the global convergence. The proposed algorithm was applied to a 25-task disassembly case, the results of which indicate the effectiveness of the proposed algorithm by comparing with the other 5 algorithms. Further, the proposed model and the algorithm were applied to design a printer disassembly line. Finally, considering the uncertainty of the disassembly times and failures in the actual disassembly productions, simulation technology was used to analyze and optimize the disassembly line. And the simulation results show that the proposed method may effectively reduce the invalid times caused by waiting and blocking and improve the disassembly efficiency.

Load Analysis and Lightweight Design of Garbage Compression Stations

LI Ang;LIU Chusheng

2017, 28(17):  2124-2130. 

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This paper presented the load distribution of the garbage compression station boxes by the stress-strain tests. The commercial software Hyperstudy was used to simulate the load distribution functions, and the functions which best matched with the experimental results were utilized as the boundary conditions of optimization. Simultaneously, the super element (SE) algorithm was introduced herein to reduce the complex structures, which might greatly improve the computational efficiency. Finally, the effectiveness of SE technology was validated by comparisons of traditional method and SE one.

A Coupling CA Algorithm of Meshless and FEM in Elasticity

CHEN Zeyun;YUAN Weifeng

2017, 28(17):  2131-2135. 

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A CA was developed to combine the advantages of FEM and meshless method which was used to analyze 2-dimensional elastic problems. By the CA, a 2-dimensional domain was discretized into a grid of nodes. These nodes were distributed randomly in the domain and they were divided into the FEM group and the meshless group. In the FEM zone which was mostly defined near the boundaries of the domain, FEM elements were used to establish the relationship between one node and other adjacent nodes. In the meshless zone which was normally away from the boundaries, the adjacent nodes were related by employing the concept of displacement interpolation used in FEM. However, each nodes, wherever they were in the FEM zone or meshless zone, were dealt with under the CA frame, that is, the unknown displacements of each nodes were evaluated by CA algorithm. Unlike FEM, the proposed CA solver worked out the results through automatic evolution, instead of Gaussian elimination or other conventional methods. Based on the current CA algorithm, FEM and meshless may be merged seamlessly. The novelty and the correctness of the current approach were proven by numerical examples.

Generation of Contour Path with Unequal Layer Distances in CNC Incremental Forming

ZHU Hu;WANG Hepo;XING Yufei

2017, 28(17):  2135-2141. 

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Considering the influences of layer distance on forming quality in CNC incremental forming, a method to generate the contour path with unequal layer distance was proposed based on the constant scallop height and surface region with different forming angles. First, the forming paths with constant scallop height were generated. Then, the contour paths were inserted in to the region with large forming angle and large layer distance to optimize the layer distances. Finally, the forming paths were generated, which might meet the requirements of scallop height and reduce the forming forces and the springback deformations. The results of numerical simulations and forming experiments show that the unequal layer distance forming path generated by this method has better uniformity of effective strain, higher forming accuracy and better process quality than that of constant scallop height path.