Table of Content

25 September 2020, Volume 31 Issue 18

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Influences of Splicing Characteristics of Cover Panel Moulds on Milling Vibrations with Ball End Tools

WU Shi；ZHU Meiwen；ZHANG Tianyuan；LIU Xianli； LI Chuandong

2020, 31(18):  2143-2152.  DOI: 10.3969/j.issn.1004-132X.2020.18.001

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In order to analyze the influences of the curved surface splicing characteristics on vibrations, an undistorted chip thickness model was established considering splicing characteristics and surface characteristics. Based on the undistorted chip thicknesses in the splicing areas of curved surfaces, a milling dynamics model was established considering the change of time delay. Through the numerical calculations, the influences of impact vibrations during the splicing seams, tool axial position angles and splicing seam widths on milling vibrations were analyzed comprehensively. Finally, based on the curved surface splicing milling experiments of hardened steels, the accuracy of milling vibration prediction model was verified considering the splicing surface characteristics. At the same time, the corresponding vibration acceleration signal amplitudes and fractal dimensions were calculated based on the milling vibrations under different splicing characteristics. The results show that the nonlinear characteristics of milling vibrations are weaken by the splicing characteristics of hardened steel surfaces, and vibration energy is concentrated in a certain frequency band. According to this situation, the optimal processing parameters may be analyzed under different splicing characteristics.

Suitability about FEM Standard on AS/RS with Monte-Carlo Simulation

ZHAO Ning1；LUO Xinzhen1；LI Wenying1；YUAN Zhaoyun2

2020, 31(18):  2153-2160.  DOI: 10.3969/j.issn.1004-132X.2020.18.002

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FEM9.851 standard was a method for calculating warehouse productivity when planning an AS/RS. It was applicable to the input/output(I/O) points in different positions of the AS/RS, covering two fixed I/O point positions and four varying I/O point positions. A parametric AS/RS discrete event simulation model was established. Monte-Carlo simulation experiments were performed on the six I/O point positions in FEM9.851 standard to analyze the applicability. The experimental

results show that FEM9.851 standard calculation results are in good agreement with the simulation results when the I/O points are located on the lower left side , one on the left and another on right lower sides, and the I/O points are in the same position and change in the horizontal or vertical directions. However, when the inbound and outbound positions are different, one of which is fixed on the lower left side and another is changed in the vertical direction, FEM9.851 standard shows a small amount of inapplicability.

Nonlinear Topology Optimization of Continuum Structures Based on HCA Algorithm

WANG Guan1；ZHANG Qian2；KOU Linyuan1；LIU Zhiwen3；LI Shikang3

2020, 31(18):  2161-2173.  DOI: 10.3969/j.issn.1004-132X.2020.18.003

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A HCA algorithm without gradient was used. The topology optimization was realized by coupling the CA rules with the LS-DYNA solver, the non-convergence problems such as numerical oscillation and catastrophe in the iteration processes were solved under the conditions of small deformation with material nonlinearity. By introducing volume constraint function and constantly updating the target values of strain energy density, the masses of the optimized structure might converge to the target masses accurately, the purposes of topology optimization results to the size optimization of structures were realized. The research results show that nonlinear analysis is very important for structural optimization design in practical engineering. The HCA topological ptimization algorithm combined with LS-DYNA solver is efficient and reliable for solving nonlinear problems, which may effectively overcome the singular solutions and the checkerboard problem. The HCA method has a practical value for engineering applications.

Analysis of Anti-eccentric Load Characteristics of Hydraulic Cylinder Hydrostatic Supports

SHAO Junpeng；XU Longfei；SUN Guitao

2020, 31(18):  2174-2180.  DOI: 10.3969/j.issn.1004-132X.2020.18.004

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The anti-eccentric load characteristics of the hydrostatic supports of the hydraulic cylinders were studied, the lubrication performance and leakage characteristics of the hydrostatic support hydraulic cylinders were analyzed, the pressure field characteristics of the oil films were simulated by using FLUENT software, and the anti-eccentric load characteristics of the hydrostatic supports of the hydraulic cylinders were analyzed. The oil film characteristics of the rectangular and I-shaped oil chambers of the hydrostatic bearing guide sleeves were analyzed and compared.  The relationship among velocity, eccentricities, inlet flows of the hydraulic cylinders and bearing capacities, leakages and lubrications of the hydrostatic bearing guide sleeves were studied. An experimental platform was built to measure the eccentricity distance of the piston rod by using eddy current sensor, and the anti-eccentric load performance with hydrostatically supported hydraulic cylinders and without hydrostatically supported hydraulic cylinder was compared.

Review on Research Status of Positioning Accuracy Reliability of Industrial Robots

WU Jinhui1,2；TAO Yourui1,2

2020, 31(18):  2180-2188.  DOI: 10.3969/j.issn.1004-132X.2020.18.005

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The positioning accuracy of industrial robots seriously affected the accuracy level and quality consistency of the auxiliary manufacturing products. The positioning accuracy reliability and positioning error compensation of industrial robots became the focus of academia and industry. The development status of positioning accuracy reliability and positioning error compensation of industrial robots were analyzed and discussed. The main research methods and focus problems in this field were summarized. Finally, the development directions of this field were prospected.

Asymmetric Inertia Driving System for In-pipe Robots and Its Dynamics Characteristics

LIU Dawei1，2；LIU Jiajia1

2020, 31(18):  2189-2195，2205.  DOI: 10.3969/j.issn.1004-132X.2020.18.006

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An asymmetric inertia driving robot composed of noncircular gears and double-shaft rotating masses was presented for the bad in-pipe environments. The inertia driving mechanism of the robots was illuminated in an isotropic dry friction condition. The effects of the eccentricity, the order of noncircular gears and the phase angles between the noncircular gears and the rotating masses on the inertia forces were discussed, a generation principle of asymmetric inertia forces suitable for isotropic friction environments was obtained. The dynamics models of the robots in the horizontal and inclined pipes were solved through numerical method. The variations of the system parameters on the average movement velocities of the robots were analyzed. The results show that as the mass ratio of robots to the rotating mass and the obliquity of pipes (in uphill state of the robots) increases, the movement velocities of the robots reduce; with the increasing of the angular velocities of motors, eccentric ratios of the noncircular gears, the turning radii of the rotating masses and the supporting forces from the pipes, the movement velocities of the robots first increase and then decrease.

Analysis of Output Characteristics for Small Horizontal Axis Variable Eccentricity Wind Turbines

BAO Daorina；LIU Xujiang；WANG Xiaoxue；WANG Shuailong；LIU Jiawen

2020, 31(18):  2196-2205.  DOI: 10.3969/j.issn.1004-132X.2020.18.007

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Due to limitations of mechanical strength and the generator capacity, the output power values of small wind turbines would continue to rise when the rated wind speed was exceeded, therefore, it was necessary to take effective measures to control the output powers. A horizontal axis variable eccentricity wind turbine with power regulation function was designed. And the numerical simulation of flow fields and wind tunnel tests of a single 1.5 kW variable eccentricity wind turbine prototype were carried out. The results show that with the increasing of eccentricity, the maximum pressures of the inner and outer surfaces of the wind wheels are concentrated on one side, the speed loss degree at the rear of the wind turbines is gradually reduced. When the rated wind speed of 12 m/s is exceeded, the wind turbine with left and right eccentricity may reduce the output power values. When the wind speed is as 15 m/s, the eccentricity is as 75 mm, the minimum output power values corresponding to the left and right eccentricity are as 1 353 W and 1 539 W respectively, and the regulatory errors are as 9.8% and 2.6% respectively. The above results fully verify the feasibility of variable eccentricity wind turbine power control, and also may provide theoretical and experimental basis for the design of wind electromechanical control systems.

Lightweight Optimization Design of Commercial Vehicle Frames Combined by Steel and Aluminum Materials under Multiple Working Conditions

ZHANG Kaicheng；LI Shunming；SUN Mingjie

2020, 31(18):  2206-2211，2219.  DOI: 10.3969/j.issn.1004-132X.2020.18.008

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In order to find effective lightweight schemes for commercial vehicles, the frame of a heavy commercial vehicle was taken as the research object, the finite element model was established and the free modal analysis and the static analysis of four typical working conditions were carried out. The frame optimization model was established by using the multidisciplinary optimization software HyperStudy, and the dimensions and materials of the frame were optimized simultaneously under four typical working conditions. The results show that the designed frame combined by steel and aluminum materials may effectively reduce the mass by 5.6% under certain strength and modal performance conditions.

Design and Braking Performance Analysis of Hydrodynamic Retarders with Vertical Blade Structure

ZHUANG Xinghan；LI Desheng；YE Lezhi；GUO Wenguang；GAO Zhiwei

2020, 31(18):  2212-2219.  DOI: 10.3969/j.issn.1004-132X.2020.18.009

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Aiming at the complex manufacturing processes of the traditional hydraulic retarder structures such as axial inclined blade, closed torus, inlet and outlet channel, a new retarder structure with vertical blade and dual torus was proposed, which greatly simplified the manufacturing processes. By establishing the mathematical model and using computational fluid dynamics technology, the change rules of retarder braking torques were obtained and verified by bench test. The results show that: the change rules of the braking torques of the novel retarders are basically the same as that of the traditional retarders, the braking torques of the novel retarders reach 1 490 N·m at 1 750 r/min, and the change rules are similar to the calculation. The relative errors are less than 12%, which confirmes the reliability of the calculation. In conclusion, the braking performance of this retarder basically satisfies with the vehicle requirements for braking torque and braking stability.

Optimization of Buffer Allocations in Hybrid Production Lines Based on Availability Evaluation

LIU Xuemei；LIU Tao；GUO Huan

2020, 31(18):  2220-2230.  DOI: 10.3969/j.issn.1004-132X.2020.18.010

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In order to quickly and efficiently allocate buffer capacity and improve the availability and throughput of the hybrid production lines, a buffer allocation method was proposed based on availability evaluation. Considering the characteristics of the hybrid production lines and analyzing the transition rules between the machine states and the buffer states, the availability of the equivalent machine was obtained through the equivalent processing of the buffer. The mathematical model of the relationship between the availability and buffer capacity of the hybrid production lines was established by using UGF method. Aiming at the maximum availability of the whole line, the optimal buffer allocation strategy was obtained by using GA. Buffer optimization allocation results of multiple production lines indicate that the buffer allocation method based on availability evaluation may significantly reduce the average numbers of work-in-process in the production lines while effectively solving the buffer allocation problem.

Spindle System Digital Twin for Dynamics Characteristic Monitoring

TAN Yang1；ZHANG Yu2；LIU Libing1；YANG Zeqing1

2020, 31(18):  2231-2238，2246.  DOI: 10.3969/j.issn.1004-132X.2020.18.011

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Dynamics characteristics of spindle systems were reconstructed with the changes of spindle speeds and boundary conditions in milling processes, so that the traditional hammer impact experimental modal analysis-driven method was failed to reflect the physical reality. In view of this problem, a five-dimensional model of spindle systems digital twin for dynamics characteristic monitoring was established, the modeling method and operation mechanism were discussed, and the dynamics characteristic monitoring service of spindle system driven by spindle system digital twin was elaborated and it was applied to the dynamics monitoring of spindle systems in milling machining centers. The experimental results show that the model utilizes the interactive fusion of the physical entity and the virtual entity of the spindle systems to accurately obtain the dynamics characteristics of the spindle systems in milling processes through monitoring services, which makes design improvement, operation optimization, fault diagnosis and accurate maintenance of spindle systems possible.

Multi-objective Optimization Design of Low Specific Speed Centrifugal Pumps Based on NSGA-Ⅲ Algorithm

TONG Zheming1；CHEN Yao1；TONG Shuiguang1；YU Yue1；LI Jinfu2；HAO Guoshuai3

2020, 31(18):  2239-2246.  DOI: 10.3969/j.issn.1004-132X.2020.18.012

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In order to improve the hydraulic performance of the IJ125-100-400-00 low specific speed centrifugal pumps, a non-dominated sorting genetic algorithm based on reference point(NSGA-Ⅲ) combined with approximate model and numerical simulation was used to optimize the multi-objective optimization of the blades. According to the hydraulic loss model and sensitivity analysis results, three parameters of impeller exit width, impeller exit diameter and impeller exit angle were selected as design variables. Sixty sets of design schemes were randomly generated by using Latin hypercube sampling, and the numerical simulations were performed for non-simplified models. The external characteristic values were obtained, and an efficient BP neural network approximation model was established. Finally, the NSGA-Ⅲ algorithm was used to optimize the approximate model and the optimal design variable combination was obtained. The results show that the numerical simulation results of the initial model are in good agreement with the measured values. The head absolute errors of the two values under rated conditions are less than 2.14%. The BP neural network has good prediction results. Optimized centrifugal pump hydraulic efficiency is increased by 6.86%, the lift meets the design requirements, and the internal flow field of the pumps is significantly improved.

Decoupling Active Caster Omnidirectional Mobile Robot Tracking Control Considering Slip Interferences

LI Yang1,2，3；LIU Ziming1，2，4；CHEN Qingying1,2，3

2020, 31(18):  2247-2253.  DOI: 10.3969/j.issn.1004-132X.2020.18.013

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A trajectory tracking control method was proposed considering the unknown caster slips for the omnidirectional mobile robot systems based on decoupling active casters. Firstly, the kinematics model of the omnidirectional mobile robot including the caster slip was established, and the sliding parameters were estimated by using the redundant information obtained by the additional sensors. Then the trajectory tracking controller was designed according to the backstepping method. Asymptotic stability of the closed-loop system was guaranteed by Lyapunov theorem. The control parameters were determined according to the pole placement method. Simulation and experimental results verify that the control method may make the omnidirectional mobile robot track the set trajectory stably in the complex indoor environments.

Study on Posture Determination Method for Holes of Rock Drilling Robots with Improved Architecture

YAO Haifeng1；LIU Wei2；ZHENG Xiaowen1；ZHANG Lansheng2；LIU Fuxin2；WU Miao1

2020, 31(18):  2254-2261，2267.  DOI: 10.3969/j.issn.1004-132X.2020.18.014

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An improved rock drilling robot was designed, the wrist was an offset structure with a prismatic link, and the shoulder was the intersecting structure. Two features of the robot were found: one was that the solution for the fifth degree of freedom parameter was equivalent to the solution for the angle between a special line and the normal of a special plane, the other one was that the distance between the intersection point of joint axis 3 and 4 and the origin point was fixed. According to the above two characteristics, the fifth and sixth degree of freedom parameter values might be obtained by iterative search method. A new method for solving robot kinematics was presented, it wasnt necessary to establish the coordinate frames attached to all the links in the calculation processes. The forward solution was carried out in reverse order step by step, and the inverse solution was carried out step by step by returning method. The improved rock drilling robot was machined and assembled, the calculation program was compiled, and the industrial test was completed. The testing results show that the designed rock drilling robot is safe and reliable in operations, fast and accurate in calculations, which solves the problems of long calculation time and insufficient positioning accuracy of the old rock drilling robots, and may provide certain references for the realization of unmanned mining in deep

coal seams.

Study on Extrapolation Method of Load Spectrum with Extremum Exceedances Subjected to GPD

ZHENG Guofeng1,2；ZHU Hongguo1；WU Chenbo1；XIAO Pan1,2

2020, 31(18):  2262-2267.  DOI: 10.3969/j.issn.1004-132X.2020.18.015

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The load spectrum extrapolation method with extremum exceedances subjected to GPD was proposed. The proposed method was applied to the extrapolation of automotive customer typical road load spectrum. And the GPD functions with shape parameters of zero and non-zero were fitted respectively. The influences of distribution functions of different shape parameters on the extrapolation results of load spectrum were compared and analyzed. Load spectrum before and after extrapolation, as well as the acquisition load spectrum, were compared in amplitude domain and frequency domain. The results show that load spectrum extrapolation method by using GPD with zero shape parameter may obtain a conservative result. However, non-zero shape parameter GPD applied in the extrapolation method may get a extrapolate load spectrum with larger amplitude than the acquisition load spectrum.