Table of Content

25 August 2019, Volume 30 Issue 16

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Analysis of Vibration Suppression Effectiveness on Frames of Water-cooled Chillers

YAO Yuhui1;DING Liang2;WANG Xiaojian1;LI Zhishen1;LI Hongguang1

2019, 30(16):  1891-1895. 

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A vibration suspend frame was designed according to the structural characteristics of the chiller,and the natural frequencies and modes were calculated by ANSYS software.An evaluation method for vibration suppression effectiveness on the chiller frames  was presented using FRF.The FRF was obtained through simulation method by ANSYS software,and the feasibility of the method was verified by experiments.The results show that the designed frame has an obvious vibration suppression effectiveness,and the FRF method may effectively evaluate the vibration suppression effectiveness of the units or components.

Influences of Workpiece Masses and Positions on Measurement Errors for Single-plane Vertical Dynamic Balancing Machines

WANG Qiuxiao;WANG Dequan;TAN Jian ;FU Xiaoyan;ZHANG Guangyan

2019, 30(16):  1896-1903. 

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Aiming at the large measurement errors of permanent calibration single-plane vertical dynamic balancing machines under different workpiece masses or heights, a method for analyzing the error sources was proposed by using torsion effects of swing frame. The swing frame system was processed as a 2 DOFs system, and the kinematical equations of the swing frame structure were established based on theoretical mechanics. The position formula of system vibration centers was derived, and the influences of rotation speeds, workpiece positions and masses on the vibration center positions were analyzed. The formula of torsional stiffness of spring plate around the vibration center was deduced, and the relationship between torsional stiffness and vibration center position was analyzed.The torsion effect law which changed with workpiece masses and positions was verified from experiments, and the correctness of torsional stiffness formula of spring plate was proved.The permanent calibration errors were analyzed.The maximum error rate is of 34.41%.It reveals the irrationality of permanent calibration method and provides a reference for optimizing measurement methods.

Thermodynamic Entropy Characteristics Analysis and Life Prediction Model of Metal Low Cycle Fatigue Processes

ZHU Darong1,2;XU Dejun1,2;LIU Tao1,2;WANG Fangbin1,2;CHU Zhutao1,2

2019, 30(16):  1904-1910. 

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Q235 steel samples were selected to carry out low-cycle fatigue tests.The thermodynamic entropy generation rate and cumulative entropy production characteristics of low-cycle fatigue processes  were analyzed under different loading conditions such as loading amplitude and loading frequency.Results show that the entropy generation rate increases with the increase of the loads and it is approximately constant under the same loads.The accumulation of thermodynamic entropy during low cycle fatigue is a quasi-linear accumulation process.The final FFE value of the material increases with the decrease of the load amplitudes,but has no obvious relationship with the loading frequency. Then,a low-cycle fatigue life prediction model was established based on thermodynamic entropy,which may be used in real-time evaluation of fatigue damages of metal component.

Optimization of Hydraulic Brake Piston Springbacks in Rapid Compression Machines

HAN Yiyong1,2;SHANG Yibao1;LIAO Shengyou2;LUO Haofeng2;CHEN Weifeng2;PAN Jiaying1;WEI Haiqiao1

2019, 30(16):  1911-1915. 

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In order to solve the common problems of piston springbacks in rapid compression machines using pneumatic drive and hydraulic brake,the structure optimization design of a high-pressure drive system and hydraulic buffer system for a rapid compression machine were studied herein.The results show that increasing the number of exhaust ports,which may reduce the resistances of power pistons and improve deflation processs of drive cylinder piston-sides, will be able to alleviate the piston springback to some extent.Meanwhile,the rapid establishment and release of oil in the driven sides of hydraulic buffer system are the crux of the piston springbacks.The structure optimization of hydraulic brake pistons and the adjustment of oil drain holes,which improve the adaptability of hydraulic brake pistons to various experimental conditions,may fundamentally solve the springback problems of hydraulic brake pistons in rapid compression machines.

Evolutionary Design of Mechanism Kinematics Chain of Genetic Programming

HUA Ertian1,2;ZHOU Meng1;LI Shenghui1;LU Hao1

2019, 30(16):  1916-1924. 

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A new mechanism and the original mechanism of regenerative kinematics chain method had the same number of components and kinematic pairs.Genetic programming was proposed to replace the number synthesis, the generalization and embodiment processes of the regenerative motion chain method were retained, the essential components of original mechanism were analyzed and deter-mined, which ensured that the new mechanism satisfied the functional properties of the original mechanism, realized the evolutionary design of different number of components and kinematic pairs of the new mechanism and the original mechanism.The fitness evaluation function was designed based on the contents of information axiom of axiomatic design.The total number of components and the number of multiple auxiliary bars were used as the fitness measure factors, and a feasible solution with the smallest amount of information was obtained.The experimental results show the effectiveness of evolutionary design method of the mechanism kinematic chain based on genetic programming.

A Hybrid PECT/EMAT NDT Based on Wavelet Analysis

TIAN Mingming1;XIE Shejuan1,2; HAN Jie3,4;LI Peng2;PEI Cuixiang1;CHEN Zhenmao1

2019, 30(16):  1925-1930. 

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To effectively utilize pulse eddy current signal parts in electromagnetic acoustic signals and complement the advantages of EMAT and PECT method in detection, a new hybrid NDT method of PECT/EMAT was proposed based on wavelet analysis. The effectiveness of the proposed method was verified by the numerical simulations and experiments.

Shear Buckling Analysis and Optimization of Composite Laminates Using Perturbation GDQ Method

SUN Shiping;ZHANG Bing;HU Zheng

2019, 30(16):  1931-1939,1949. 

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There was poor accuracy, calculation oscillation and non|convergence for the cases of shear buckling responses of composite laminates by using GDQ method. The example study found that the problems came from the singular load matrix, therefore, the perturbation GDQ method was proposed to realize the stable and efficient solution of shear buckling problems for composite laminates, by disturbing the main diagonal weight coefficients to improve the singularity of the load matrix. Numerical examples demonstrate the validity of the perturbed GDQ method. The stacking sequence of composite laminates including shear loads was optimized combined perturbation GDQ method with the direct search simulated annealing algorithm. The results show that the ply numbers and lay forms of composite laminates have little effects on the optimum ply under shear loads, and optimized layup angle tends to 60° with the increasing of  aspect ratio. Under combined loads of shear and axial compression, the relatively small shear forces may improve the buckling behavior of laminates, while the optimized buckling performances are gradually reduced and the optimum ply is converged to the ply of shear loads with the increasing of shear forces. The results provide a reference for the shear buckling performance design of composite laminates.

Dynamics Response of Wind Turbine Towers under Seismic and Multi Wind Conditions

ZOU Jinhua1;YANG Yang1;LI Chun1,2;WANG Yuanbo1;LIU Zhongsheng1

2019, 30(16):  1940-1949. 

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In order to estimate the dynamics responses of large-scale wind turbines under the conditions of unsteady turbulent winds coupled with different degree of,NREL 5 MW prototype wind turbine was selected as the research object. Soil-structure interaction was taken in account based on Wolf theory, while aerodynamic forces were calculated via generalized dynamic wake and blade element momentum corrected by Prandtl theory. Based on the data interface of FAST, the seismic load computation module was compiled, while the coupling simulation model for turbulent winds and earthquakes was established. The wind turbine tower dynamics response under 150 working conditions including 5 wind speeds and 30 seismic accelerations was calculated. The results show that the tower top displacement is affected significantly by earthquakes under rated wind speeds. Under low wind speeds, tower acceleration is affected greatly by the earthquake conditions. High speed turbulent winds will exacerbate tower shear forces and bending moment responses. With the combinations of turbulent winds and earthquakes, the critical peak ground acceleration(PGA) of tower top displacement, tower top shear forces, tower base shear forces and tower base bending moments increase first and then decrease with the increasing of wind speeds. When wind speeds are high, the critical PGA of tower top acceleration increases with the increasing of wind speeds.

Analysis for Failures of CNC Machine Tools Based on Meta-action Chain Methodology

ZHANG Genbao;WANG Yang

2019, 30(16):  1950-1958,1966. 

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To analyze running faults of CNC machine tools, meta-action chain methodology was proposed to establish the model between macro system reliability and micro failure cause of meta-actions. Taking the wear failure of worm gear as an example, the relationship between microscopic failure causes and probability of occurrence of faults was analyzed. Reliability curves of the whole system were calculated by integrating reliability curves of failure bottom events of all meta-actions. The system structure informations, system operation informations, microscopic failure cause informations, and macro reliability model were all integrated into the meta-action chain methodology.The examples show that the proposed meta-action chain model may fully reflect the state transition of each components in a CNC machine tool when the whole system implements each function, thus eliminating the uncertainty in traditional reliability modeling and is good for accurately analyzing all the fault modes of the mechatronic systems.

Subsurface Crystal Structural Evolution Mechanism of Single Crystal Coppers during Nano-indentation

WANG Quanlong1;ZHANG Chaofeng1;WU Meiping1,2;CHEN Jiaxuan3

2019, 30(16):  1959-1966. 

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To investigate the subsurface crystal structure evolution mechanism of single crystal coppers in nano-indentation,molecular dynamics method was used to construct the simulation model of nano-indentation and realize the simulation of nano-indentation processes.The improved center symmetry method was used to analyze the dislocation nucleation processes and defect evolution mechanism of single crystal copper specimens.It is found that the dislocation defect nuclear is under the indenter,extend along the {1 1 1} slipping system to the internal of specimens,and the stacking faults are formed.The atomic steps are remained on the surfaces of specimens,and typical defects exist in subsurface damage layers of the specimens,such as V-shaped dislocation.Aiming at recognizing crystal structural status of the dislocation nucleation areas and dislocation extension areas of the specimens,the spherical harmonic function method was used to analyze the simulation results.The analysis results show that the material crystal structure is arranged from FCC(face-centered cubic) to HCP(hexagonal close-packed) and ICO(icosahedron) structure which are more closely in dislocation nucleation areas,and the crystal structure is arranged from FCC to DFCC(deformed face-centered cubic) structure in dislocation extension areas.

Dynamics Parameter Identification and Control of a Spherical 2-DOF Redundant Driven Parallel Robot System

LI Yongquan1,2;WU Pengtao1,2;ZHANG Yang1,2 ;ZHANG Lijie2,3

2019, 30(16):  1967-1975. 

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A spherical 2-DOF redundant drive parallel robot driven by servo motor was the research object.Firstly,the inertia parameter identification model of the mechanisms was established,and the inertial parameter identification trajectory was programmed.Secondly,the friction parameter identification model of the mechanism pairs and the friction parameter identification model of the driving system were established,and their identification principles were analyzed respectively.The trajectory of friction parameter identification was also programmed.Thirdly,through the identification experiments,the mechanism inertia parameters,the mechanism rotation pair friction parameters and the driving system friction parameter identification results were obtained,the original mechanism parameters were modified by the identification results,a more accurate robot system dynamics model was obtained,and the identification results were validated by the trajectory test experiments.Finally,a feed forward control strategy was developed based on the dynamics model of the robot system and compared with the traditional mechanism kinematics closed-loop control strategy.The feasibility of this control strategy was proved.

Multi-objective Optimization Design of Support Cylinders for Excavation and Anchor Combined Units

XIE Miao;LI Xiaojing

2019, 30(16):  1976-1981. 

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An excavation and anchor combined unit for comprehensive roadway was developed.The influences of support cylinder stiffness on frequency responses were investigated by parametric modeling method for improving the safety and stability of excavation and anchor combined units.The optimization analysis was conducted, which took the stiffness of each supporting cylinder as the design variable and the maximum displacement amplitude least and the maximum stress amplitude least of the structure as the optimum objective function.The stiffness of the supporting cylinders was optimized and the optimum stiffness of each springs was determined.The simulation results were verified by experiments.The results show that after optimization,the maximum response stress ratio of the three axial directions of the model decreases 96.72%,95.87% and 96.65% respectively than that before optimization.The maximum displacement response of the optimized model is slightly larger in the Z axis than that before optimization,but the X and Y axes decrease 98.17% and 74.61% respectively.The maximum natural frequency errors between the experimental results and the simulation ones are as 86%,and the variation rules of frequency response curve are basically the same,which proves the effectiveness of the optimal design.

A Method for Analyzing Error Characteristics of Lower-mobility Parallel Mechanisms

ZENG Daxing;FAN Mingzhou;ZHANG Qingwu;WANG Juanjuan;YANG Yandong;HOU Yulei

2019, 30(16):  1982-1988,2002. 

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Screw theory was applied to analyze the screw system of both parallel mechanism and each branch. From the controllable and uncontrollable degree of freedom, a general analytical method (freedom analyzing method) was proposed for analyzing the error characteristics of lower-mobility parallel mechanisms by virtual kinematic pairs. The method was unnecessary to establish static error model and might be used independently to analyze the effects of specific errors on the outputs of the moving platform. Then by taking 3-CUR parallel mechanism as an example,error characteristics were analyzed and obtained in this way. Vector method was used to set up the error model of 3-CUR mechanism and proved the regularity by simulation. The prototype was designed and machined in terms of the regularity and the prototype tests validated the correctness of the freedom analyzing method.

FOPID Improved ADRC in AC Servo Systems

WANG Ronglin1;LU Baochun1;HOU Runmin1;GAO Qiang1;ZHANG Wei2;ZHU Yun3;DAI Lian3

2019, 30(16):  1989-1995. 

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Aiming at the complicated nonlinear problems such as frictions,moments of inertia,variable loads and internal and external disturbances under different working conditions in AC servo systems of rocket launchers driven by PMSM, considering the strong internal and external interference resistances of ADRC and the excellent dynamic performance characteristics of FOPID control,an improved auto disturbance rejection controller optimized by FOPID controller(FOPID-IADRC) was designed herein.In order to achieve good dynamic performances and reduce the parameters' calculations,the non-linear state error feedback was substituted by FOPID controller.PSO algorithm was adopted to realize real-time self-tune of 5 parameters of FOPID controller.The simulation and semi-physical bench test results show that the control strategy may effectively resist position disturbances,and has good dynamic performances and strong anti-interference ability.

Design and Analysis of a New 5-DOF Hybrid Robot Considering Workspace and Force Transmission Efficiency

XU Yundou1,2;XU Zhenghe1;YANG Fan1;ZHAO Yun1;MEI Youen1;ZHOU Yulin1,2;YAO Jiantao1,2;ZHAO Yongsheng1,2

2019, 30(16):  1996-2002. 

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A novel 5-DOF hybrid robot with the structure of R(2RPR)R/SP+RR was proposed,and the performances were analyzed.The size optimizations were carried out according to the performance indexes in both workspaces and force transmission efficiencies,and the key design dimensions were obtained.On the basis of above,the structural design and stiffness analysis of the hybrid robot were conducted.The results of stiffness were compared with other similar typical robots.The workspace of the hybrid robot was analyzed,and finally a method for workspace search was put forward to analyze whether the workspace met the exceptations under different arrangements.

Research on Large-capacity and Long-distance SAW Tags

JIA Hao1;CHEN Zhijun1;XU Hailin2;LI Yafei1

2019, 30(16):  2003-2009. 

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Based on the pulse amplitude and pulse position coding, a phase stepping pulse position coding scheme was designed,and the time slots and phases were extracted by digital quadrature demodulation method. The coding capacity is close to 3 million,which may meet the needs of most applications.The relationships between echo amplitudes and reflectivity of reflectors of single-channel and dual-channel SAW tags were compared through theoretical derivation and simulation analyses.The results show that for the two type of tags with the same number of reflective gratings,the dual-channel tags may select a higher reflectivity of the reflective grating,thus having a farther recognition distance.The corresponding SAW tags were actually fabricated and tested.The test results verify the large-capacity and long-distance characteristics of the dual-channel tags with phase stepping pulse position coding.

Method and Mechanism of Spiral Unfolding Whole Surfaces of Steel Balls by Orthogonal Clamping

PU Haiming1,2;WANG Zhe1;KANG Yihua1

2019, 30(16):  2010-2013. 

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Firstly,movement conditions of unfolding the whole surfaces of steel balls were analyzed.According to kinematics theory, a mathematical model on spiral line unfolding movement of steel balls was established and the unfolding trajectory equation was solved by coordinate transformations.The processes of unfolding the whole surfaces of steel balls were analyzed by MATLAB simulation,and the factors affecting trajectory density of the unfolding movements were discussed.Finally,a kind of orthogonal clamping and spiral unfolding mechanism of steel balls was designed.It is successfully applied to automatic ultrasonic testing equipment of steel balls.