Table of Content

25 October 2022, Volume 33 Issue 20

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Topological Structure Synthesis and Optimization of 1T2R Parallel Mechanisms

WANG Manxin, LI Lanbin, LI Zhengliang, LIU Haitao, HUANG Tian

2022, 33(20):  2395-2402.  DOI: 10.3969/j.issn.1004-132X.2022.20.001

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The topological structure synthesis and optimization of 1T2R parallel mechanisms was studied herein. Applying the composition principles and constraint characteristics of planar mechanisms, the topological structure of 1T2R parallel mechanisms was regarded as consisting of a 1T1R planar parallel kinematic chain connected in series with a revolute joint and two spatial unconstrained active limbs. Then the topological structure optimization and performance verification of 1T2R parallel mechanisms were carried out by comprehensively considering the criteria such as appropriateness of mechanisms pose capability, rationality of branch-chain structure mechanics, reconfigurability of robot module, simplicity of position inverse solution, and compactness of moving platform structure,etc. Then, a new five-degree-of-freedom hybrid robot module that may inherit the advantages of Tricept robots was proposed. The module has exactly the same kinematics performance as Tricept robots, and most of the components may be interchanged with Tricept robots.

Research on Dynamics of Magnetic Bearing Rotor Drop on Back-up Bearings

WANG Junshui, JIA Xiangyu, ZHANG Kai, XU Yang

2022, 33(20):  2403-2413，2419.  DOI: 10.3969/j.issn.1004-132X.2022.20.002

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The studies of the nonlinear dynamics of the protective bearing-rotor system in the past 30 years were reviewed. Firstly，  The development history of the local collision model was sorted out. the development of the system structure model from the two aspects of the rotor and the back-up bearing was summarized， and the characteristics of each model were given . Secondly， the main reason for back-up bearing—rotor system damage—backward whirl was analyzed. Then the relationship between the drop response results and the system structure and parameters was expoualded from three aspects of rotor structure， bearing structure and bearing parameters. Finally， some general guidelines for the design and selection of back-up bearings structure and parameters were summarized， and some issues which was worth further study were pointed out. 

Design of High Precision Apertures Driven by a Single Phase Piezoelectric Motor

CAO Teng, LI Xiaoniu, WANG Boquan, WEN Zhiyi, WU Dawei

2022, 33(20):  2414-2419.  DOI: 10.3969/j.issn.1004-132X.2022.20.003

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To meet the requirements of miniaturization, lightweight and precision of space optical instruments, an aperture driven by single-phase piezoelectric motor was designed. The whole structure of the apertures was designed to realize the integration of structure and function. Then, piezoelectric stators with high strength and power density were designed by using piezoelectric ceramics and carbon fiber composite materials. The dynamics characteristics of laminated piezoelectric stators were analyzed by COMSOL finite element software, and the modal frequency consistency was adjusted. The structure optimization and interference mode separation design of the moving rings of diaphragm were also completed. According to the design scheme, the prototype of piezoelectric apertures was manufactured. The mass is only 49 g, aperture range is in 0.5~35 mm.The experimental results show that the full opening and closing time of the apertures are as 89 ms and 92.4 ms respectively,and the minimum angular resolution is as 4×10-5 rad. This study simplifies the composition and control of the diaphragm, making it more compact in structures and smaller in weight while ensuring accuracy. 

Modeling and Experimental Validation of Lubrication Characteristics of Spherical Valve-plate Pairs with Conical Cylinder Block

YE Shaogan, LAI Weiqun, HOU Liang, BU Xiangjian

2022, 33(20):  2420-2428，2436.  DOI: 10.3969/j.issn.1004-132X.2022.20.004

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The lubrication characteristics of oil film of valve-plate pairs were of great significance for reliable operations of axial piston pumps. A simulation model was developed for oil film lubrication characteristics of spherical valve-plate pairs with conical cylinder block， and the effectiveness of the model was validated using experimental tests. First， the forces acting on conical cylinder blocks were analyzed， and the forces acting on cylinder blocks generated by piston-slipper assemblies were obtained by analyzing the kinematics and dynamics of piston-slipper assemblies. Second， the oil film carrying forces were obtained by analyzing the thickness and pressure distributions of oil films in spherical valve-plate pairs. Third， the oil films were discretized using finite volume method， and the oil film lubrication characteristics of spherical valve-plate pairs and the equation of motion of conical cylinder blocks were numerically solved using Newton iterative method. Last， the high-pressure steady-state tests and the surface profile scanning tests were performed， the morphologies of spherical valve plates with different steady-state test durations were obtained， the spherical valve-plate wear profile and the simulated oil film thickness and pressure distributions were compared. Results show that the simulated thick oil film area is in consistence with spherical valve-plate main wear areas， indicating that the oil film lubrication model of spherical valve-plate pairs with conical cylinder block is effective. 

Design of Variable-diameter Flexible Walking Wheels Based on Two-bar Three-cable Tensegrity Structure

SUN Jianwei, LUAN Yipeng

2022, 33(20):  2429-2436.  DOI: 10.3969/j.issn.1004-132X.2022.20.005

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In order to take the advantages of fast moving speed of wheeled robots and strong maneuverability of legged robots, a new tensegrity variable-diameter walking wheel that might switch between wheeled and legged was proposed. A new type of tensegrity structure was proposed by equivalent replacement of tensile and compression members in the two-bar, three-cable plane tensegrity structure. Then, the basic unit structures, unit connection methods and optimum numbers of wheel hubs of the tensegrity variable-diameter walking wheels were given. In order to overcome the disadvantages of poor rigidity caused by multiple degrees of freedom,the method of degree of freedom constraint and equivalent integrated of elastic components of the wheels were given. Therefore, the tensegrity variable-diameter walking wheels have convenient assembly, stable movement and loadable supports. Combining with the principles of minimum potential energy and the kinematics analysis of the tensegrity units of tensegrity variable-diameter walking wheels, the structural parameters and the spreading ratio of tensegrity variable-diameter walking wheels were obtained.The implementations of each functions of the tensegrity variable diameter walking wheels were verified through experiments.

Asymptotic Prescribed Performance Tracking Control of Electro-hydraulic Servo Systems under Matched and Unmatched Disturbances

DONG Zhenle, YANG Yinghao, YAO Jianyong, ZHANG Zheng, LI Geqiang, WANG Shuai

2022, 33(20):  2437-2443.  DOI: 10.3969/j.issn.1004-132X.2022.20.006

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For the coexistence of matched and unmatached disturbances in electro-hydraulic servo systems, a new high-precision motion tracking strategy was proposed, where the needs of transient and steady-state performance were all taken into account. A valve-controlled electro-hydraulic position servo system was chosen as the example, the nonlinear mathematical model including matched and unmatched disturbances was established, prescribed performance function was defined to plan the control errors, and the planned conversion errors were used for backstepping design, while a new continuous asymptotic control technology was integrated to deal with the matched and unmatched disturbances based on the estimation of disturbance upper bound. Finally, the pre-designable transient performance and asymptotic steady-state performance were obtained, and the stability proof was derived via Lyapunov analysis. Tracking experiments under two position commands show that compared with PID and feedback linearization control, tracking accuracy in the initial stages is improved by over 22.9%. Compared with the controller only containing prescribed performance function, tracking accuracy in the steady-states is further improved by over 42.9%.

Analysis of Magnetic Field of Double-Excitation Modulation AFMPMG Based on Subdomain Method

GE Yanjun, LIU Fang, WANG Daming, MA Xueqi, YU Han

2022, 33(20):  2444-2449,2458.  DOI: 10.3969/j.issn.1004-132X.2022.20.007

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AFMPMGs had serious axial and tangential leakages and low torque density. Based on AFMPMG, an external magnetic ring was introduced to make it a dual-excitation modulation AFMPMG(DEM-AFMPMG) structure. As the DEM-AFMPMG low-speed permanent magnet rotor was clamped between the inner and outer magnetizing rings, the axial and tangential leakage flux of the AFMPMG could be converted into useful harmonics, which increased the output torque and torque density of the DEM-AFMPMG. Although the 3D finite element method taken into account the magnetic leakages at the end of permanent magnet gears and had the advantage of high calculation accuracy, it also maked the occupancy of computer resources too high and the optimization period of structural parameters too long. A mathematical and physical model for calculating DEM-AFMPMG air gap magnetic field and electromagnetic torque was proposed herein based on subdomain method. This method could equate the 3D model to the 2D model, but all factors of the 3D model were included, so that the calculation accuracy was equivalented to that of the 3D finite element. The calculation examples show that the calculation accuracy based on subdomain method is equal to that of 3D finite element method(the calculation errors of air gap magnetic density and electromagnetic torque are less than 5% and the calculation errors of torque density are less than 1.5%), but the calculation speed of subdomain method is faster and it is easy to realize computer programming, which facilitates the analysis and optimization of structural parameters of DEM-AFMPMG. 

Effects of Cryogenic Treatment on Cutting Performance of PCBN Tools

YU Liang, ZHENG Guangming, YANG Xianhai, CHENG Xiang, CHANG Kaishuo, LI Xuewei

2022, 33(20):  2450-2458.  DOI: 10.3969/j.issn.1004-132X.2022.20.008

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Aiming at the problems of PCBN tool serious wear and short cutting life were prominent in hard cutting, the cryogenic PCBN tools and the high speed hard turning AISI 4340 steel tests were carried out to study the effects of cryogenic treatment on the surface integrity (including microstructure, roughness, microhardness and residual stress) and cutting performances of PCBN tools, and the method of improving PCBN tool wear resistance and tool life was explored. The results show that the defects such as shrinkage cavity and porosity on the surface of the tools are significantly reduced or even disappeared, and the surface morphology is improved after cryogenic treatment. However, the surface roughness of the tools is improved. The surface microhardness and residual stress of the tools are increased. The influences of surface morphology and surface residual stress on tool life are great, followed by surface microhardness, and the surface roughness has little effects on tool life. The treated tool adhesion and oxidation wear are reduced, and the maximum tool life may be increased by 24.78%. It may be seen that cryogenic treatment may effectively improve the surface integrity of PCBN tools, so as to improve the tool life. 

Research on Cutting Mechanism of A-WEDM of Single-crystal Silicons

JIA Zhen, LI Shujuan, MA Gaoling, SHAO Wei, QIAO Chang, ZHANG Chen

2022, 33(20):  2459-2467,2475.  DOI: 10.3969/j.issn.1004-132X.2022.20.009

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Aiming at the problems that the micro-cutting mechanism of A-WEDM was not clear. Single-crystal silicons were used as the processing objects herein. The maximum discharge gap was measured by designing a circuit. The material removal mechanism of A-WEDM was studied by collecting and analyzing the discharge waveform, observing the surface topography of the workpieces, and comparing the height of the abrasive grain and the discharge gap. The effects of 4 factors(pulse width, duty cycle, feed speed and wire speed) on the material removal rate and surface roughness were investigated. The experimental results show that the maximum discharge gap is as 57 μm, i.e., in the initial stage of machining, discharge corrosion first occurs. When the machining is in stable stages, within each pulse width, the materials are removed under the coupling effects of discharge corrosion and diamond particle grinding. In each pulse interval, the discharge corrosion effect stops and the diamond particle grinding action still exists, thereby removing parts of the recast layer and craters.

A Resistance-Inductance Debris Sensor Based on Microfluidic Fabrication

SHI Haotian, ZHANG Hongpeng, XIE Yucai, SUN Yuqing

2022, 33(20):  2468-2475.  DOI: 10.3969/j.issn.1004-132X.2022.20.010

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A microfluidic-based sensor which might detect resistance and inductance parameters was fabricated to achieve high-precision measurement of metal debris in oil. The characteristics of magnetization and eddy current effects of metal particles in harmonic magnetic field were obtained by simulation, and the voltage and frequency characteristics of resistance and inductance detections were also studied by experiments. High-frequency excitation might enhance the eddy current effects inside metal particles, and excitation voltages had little effects on the detection results of sensors. The results show that inductance parameter has stronger detection ability for ferromagnetic metals, and resistance parameter has stronger detection ability for non-ferromagnetic metals. At 2.0 V, 2.0 MHz excitation, the sensor may effectively identify 60 μm diameter copper particles and 16 μm diameter iron particles by comparing and analyzing resistance and inductance detection results. The method of detecting non-ferromagnetic metal debris based on coil resistance parameters provides a new way to enhance the comprehensive performance of debris sensors.

Applications of Adaptive Bandwidth Kernel Density Estimation in Recognition of Poor Quality Monitoring Data of Rotating Machinery

NI Zexing, WANG Xiufeng, XU Bo, LI Rui

2022, 33(20):  2476-2482.  DOI: 10.3969/j.issn.1004-132X.2022.20.011

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The abnormal operating environments, human factor interference and acquisition equipment failures might cause abnormal values or missing data irrelevant to the equipment health status in monitoring data of rotating machinery, resulting in misjudgment of mechanical health status and improper formulation of maintenance strategy. Therefore, an identification method of inferior monitoring data was proposed based on adaptive bandwidth kernel density estimation. Firstly, the zero drift and local noise were “impacted” by integrating the collected data in frequency domain and the kurtosis index after integration was calculated. Then the local mean error was used to adaptively select the Gaussian kernel bandwidth, the probability density function of kurtosis index was obtained, and the boundary of 95% confidence interval was used as the identification threshold of inferior data. Finally, the extraction method was verified by the whole life data of axle durability monitoring. The results show that compared with the fixed bandwidth and the kernel density estimation method based on quadtree segmentation algorithm, the proposed method has better recognition effectiveness on poor quality monitoring data.

Application of MMD in Gear Fault Feature Extraction under Variable Rotating Speed Working Conditions

ZHANG Kang, TIAN Zeyu, CHEN Xiangmin, LIAO Lida, WU Jiateng

2022, 33(20):  2483-2491.  DOI: 10.3969/j.issn.1004-132X.2022.20.012

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 Under variable working conditions, the components of gear fault vibration signals had complex time-frequency characteristics that crossing multiple time scales or overlapping time-frequency domains. The traditional decomposition method could not decompose this kind of signals based on local time-scale characteristics. A new MMD method was introduced. The MMD method innovatively regarded the mono-component signals as a linear combination of eigenvectors with different weight coefficients. By iteratively optimizing the weight coefficients, the corresponding component signals were obtained. The problems that large amount of data reduced the decomposition efficiency when MMD analyzed the actual vibration signals with high sampling rate was solved. And the MMD method was applied to analyse gear fault vibration signals under variable rotating speed working conditions.The results show that the method may effectively decompose to the overlapping fault component signals in time-frequency domain, and has obvious advantages compare to the traditional method based on time-scale characteristics.Combined with order analysis, the gear fault feature information may be extracted clearly and accurately.

Research on Adaptive Cutting Control Strategy of Roadheader Cutting Arms

WANG Dongjie, WANG Pengjiang, LI Yue, GUO Mingze, ZHENG Weixiong, SHEN Yang, WU Miao

2022, 33(20):  2492-2501.  DOI: 10.3969/j.issn.1004-132X.2022.20.013

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Aiming at the problems of low intelligent cutting degree of underground roadheaders, and the swing speed of cutting arms might not be adjusted adaptively according to the hardness of coals and rocks, an adaptive cutting control strategy of roadheader cutting arms was proposed based on multiple sensor information. On the basis of the currents of the cutting motor, the pressures of the driving cylinder of the cutting arms and the vibration accelerations of the cutting arms, the signal recognizer of the cutting loads was designed by using RBF neural network, which provided an accurate basis for the swing speed control of the cutting arms. Aiming at the complex and time-varying swing speed control system of cutting arms, based on genetic algorithm optimization， a fuzzy PID intelligent controller was designed to realize the efficient control of swing speed of cutting arms. The mathematical model of cutting arms of roadheaders was established, and the adaptive cutting simulation control system of cutting arms was built in MATLAB/Simulink. The simulation results show that the control system has fast response speed and high control precision. An airborne adaptive cutting control system of roadheaders was built based on the software of B&R Automation Studio. The simulation cutting experiments were carried out with EBZ135 roadheader in the simulated roadway of Shijiazhuang Coal Mining Machinery Co., Ltd. the experimental results show that the proposed control strategy may realize the efficient adaptive control of the swing speed of cutting arms according to the changes of cutting loads.

Shakedown　Analysis and Optimization of Airtight Cabin Used in Spacecrafts

WANG Xin, CHEN Geng, LIU Feng, YU Chenfan, ZHANG Lele,

2022, 33(20):  2502-2508.  DOI: 10.3969/j.issn.1004-132X.2022.20.014

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As the main metal components of return-type spacecraft, the integrally stiffened structure of airtight cabins was subjected to complex loads and had to meet high reliability requirements, therefore it was not easy to achieve structure optimization. Since the traditional design method with elastic limit as the core was difficult to achieve structural weight reduction effectively with the premise of ensuring strength, a structural design and optimization method of airtight cabins was proposed based on shakedown theory. Parametric modeling method of Abaqus was used to perform a batch shakedown analysis of the model with different combinations of parameters.After calculated the load factor from each samples and performed very detailed parameter sensitivity analyses, the strength-to-weight relationship of each configuration was integrated into account and a more efficient design solution was given. Results show that, using shakedown analysis in airtight cabins, the load-carrying capacity may be improved by optimizing structural dimensions, while keeping the weight unchanged.

Effects of Pantograph Subsidence on Its Aerodynamic and Acoustic Behaviors

QIN Deng, DAI Zhiyuan, ZHOU Ning, LI Tian

2022, 33(20):  2509-2519.  DOI: 10.3969/j.issn.1004-132X.2022.20.015

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In order to study the effects of pantograph subsidence on its aerodynamic and acoustic behaviors, a high-speed pantograph calculation model was established considering installation platform. Based on the theory of computational fluid dynamics and acoustic analogy, the aerodynamic and acoustic behaviors of the pantograph were numerically simulated. The subsidence heights of the pantograph were as 100, 200, 300, 400 and 500 mm respectively. The rationality of the numerical calculation method was verified by wind tunnel tests. The results show that with the increasing of the subsidence height of the pantograph installation platform, the positive pressures on the windward surface of the insulator and the base decrease, and the aerodynamic resistance of the pantograph decreases. The aerodynamic resistance of the installation platform increases first and then decreases. By optimizing the transition angles of the cavity, the aerodynamic resistance of the installation platform may be significantly reduced. When the subsidence height of the installation platform is as 300 mm and the inclination of the cavity is as 30°, the aerodynamic resistance of the pantograph in the knuckle-downstream direction/knuckle-upstream direction is reduced by 2.0% and 1.8% respectively. At the same time, the resistance of the whole train is reduced by 1.4% and 1.1% respectively. The pantograph aerodynamic noise has obvious dominant frequency characteristics, the main frequency is about 330 Hz, and the energy is mainly concentrated in the range of 400~2500 Hz. Due to the subsidence of the installation platform, the velocity of the fluid around the insulator and the base is reduced, and the surface acoustic power of the insulator and the base is significantly reduced. When the subsidence height of the installation platform is as 300 mm, the maximum sound pressure level of the far-field aerodynamic noise of the pantograph is reduced by 2.02 dBA, and the average sound pressure level is reduced by 1.31 dBA. The subsidence of the pantograph may improve the aerodynamic and acoustic performance.