Table of Content

25 September 2016, Volume 27 Issue 18

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Study on Tool Profile Design of Screw Compressor Rotors Based on Life-cycle

He Xueming , Chen Zehua, Wu Meiping, Zhang Rong

2016, 27(18):  2415-2423. 

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In the rough milling process, the allowance differences of screw rotor blades at different positions were huge. There were the problems of uneven blade wears, and the machining precision and efficiency of the rotors were dropped. As a result, an algorithm of blade life-cycle was introduced to the cutting tool designs and a new design method was proposed. The numbers of serious worn blades were increased to make the blade life-cycle stay the same. Finally, the arc profile of screw rotors was put as research object. The cutting tools of screw rotors were designed and manufactured. The processing experiments of rotor were established through the cooperation with Wuxi compressor Co. Ltd. The machined surface roughness of multi-blade rough milling cutter of screw rotors is as Ra=12.5μm, which coincides with roughing machining standard of screw rotors. The interval of cutter blade replacement is extended twice. The experiments show that this design method has a better rationality.

Workspace Algorithm of Cable-driven Serial and Parallel Manipulators Based on Convex Set Theory

Dong Xiaodong, Duan Qingjuan, Ma Biao, Duan Xuechao

2016, 27(18):  2424-2429,2436. 

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In order to solve the wrench feasible workspace of n-degrees-of-freedom serial and parallel manipulators driven by m cables, a non-iterative algorithm was proposed based on covex set theory. The properties of Minkowski Sum was introduced to construct the cable wrench set, and a non-iterative mathematical method was presented to verify if the wrench set fully included the external wrench set. Firstly, all boundary hyperplanes of convex set would be found by determining initial hyperplane. The projected boundary positions were determined according to the offset distance of the initial hyperplane. Then the explicit expression of the wrench equilibrium was deduced, and the wrench feasible workspace of cable-driven manipulator was obtained by using numerical analysis. The results demonstrate the effectiveness of the wrench feasible workspace analysis method based on convex set theory.

An One-step Reliability Analysis Method with Random and Dependent Interval Variables

Pan Baisong, Xie Shaojun, Jiang Lizheng

2016, 27(18):  2430-2436. 

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Random variables and dependent interval variables often coexisted, and this made the reliability analysis problem into a double-loop optimization problem and reduces the efficiency of the reliability analysis. So an one-step reliability analysis method was proposed. Specifically, the double-loop optimization problem where the dependent interval variables were modelled by the ellipsoid model, was decoupled into a simple one-step problem by using the HDMR. Based on the proposed sampling strategy, a quadratic polynomial was applied to approximate each of the HDMR expression, making the implicit one-step problem into the explicit one. The example results show that the proposed method has good efficiency and accuracy, and may calculate the reliability results with good accuracy at a little cost of calling the origin limit-state function.

Analysis of Orifice Area of Slide Valve with Sinking Grooves

Zhang Lijie, Wang Lihang, Wang Shuai, Li Dexin

2016, 27(18):  2437-2442. 

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Multiple valve with its high degree of integration was widely used in the field of engineering machinery, where the valve port form possessed a very important impact on flow control characteristics. Aiming at the cylindrical and conical valve orifice of the spool valve with grooves on the valve body, and based on the structural characteristics and pressure distribution and velocity changes of the internal flow field, and with the equivalent orifice area theory, the calculation equations of orifice area of the cylindrical and conical valve orifice were proposed and analyzed. The results were corrected by the flow field simulation, and the accuracy of the results was verified by experiments. The study results have some reference values for the design and performance prediction of the hydraulic master valve.

Prediction Model and Experimental Study of Subsurface Damage Depths in Grinding  for K9 Glasses

Zhang Feihu, Li Chen, Zhao Hang, Leng Bing

2016, 27(18):  2442-2446. 

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A prediction model of sub surface damage depths for K9 glass was established based on the principles of the indentation tests. In order to obtain the unknown parameters, the grinding tests for K9 glass were carried out. The values of surface roughness were measured by laser scanning confocal microscope, and the morphology of surface and sub surface damage layers was detected by scanning electron microscopy (SEM). The influence laws of process parameters on the surface roughness value, the workpiece surfaces and depths of sub surface damage were analyzed. The influence laws of process parameters on the normal grinding force were analyzed, and the empirical formula for the normal grinding force was established by using multiple linear regression fitting according to the experimental data. Furthermore, the unknown parameters were obtained.  The prediction values are consistent with the experimental data, which indicates that the prediction values are reliable.

Fuzzy Robust H∞ Control and Flexible Vibration Optimal Control for Free-floating Flexible Space Manipulator

Zhang Lijiao, Chen Li

2016, 27(18):  2447-2452. 

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The trajectory tracking and vibration suppression control for free-floating flexible space manipulator with disturbance were discussed. With the momentum conservation relations, system dynamics model was set up by the Lagrange method. Using the two-time scale decomposition of singular perturbation method, and the system was decomposed into a slow subsystem which was described joint trajectory tracking and a fast subsystem which was described the vibration of flexible manipulator. Then a composite controller consisting of a slow control component and a fast control component was proposed. For the slow subsystem, adaptive fuzzy H∞ control algorithm was designed, the fuzzy logic system was used to approximate the system uncertainty, and a robust H∞ control was used to overcome the fuzzy approximation errors and eliminate the influences of the external disturbance on the output tracking errors. For the fast subsystem, optimal linear quadratic regulator(LQR) was designed to damp out the vibration of the flexible links. Based on Lyapunov stability theory, it is proved that this algorithm can ensure the control system is asymptotically stable. Numerical simulation results illustrate that the proposed controller is reliable and effective, this control scheme makes the tracking errors of the system and the flexible vibrations quickly convergence.

Research on High Efficiency EDM Process of Integral Bling with Grouped Electrodes

Zhou Xujiao, Zhao Jianshe, Chu Huisheng, Chen Yang

2016, 27(18):  2453-2457,2466. 

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To improve the overall efficiency of EDM process for integral bling,a new process of simultaneously machining several tunnels with grouped electrode was presented based on the structure of a typical bling. Key technologies were discussed in detail, which included the electrode shape design, feed motion and movement track generation. The processing plan was verified by the technological test, and a qualified test sample was machined successfully. The results show that grouped electrodes can increase the utilization of pulse and shorten the manufacturing cycle in EDM process.

Simulation Method of Variable Stiffness and Damping Load Characteristics on Hydraulic Drive Unit of a Quadruped Robot

Yu Bin, Ba Kaixian, Wang Pei, Wu Liujie, Kong Xiangdong,

2016, 27(18):  2458-2466. 

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The position control system mathematic and simulation model of HDU was established by the mechanism modeling method. A variable load stiffness and load damping characteristics simulation method was derived through the position control loop as controller inner loop, considering the dynamic characteristics of the stiffness and the load damping under different environment structures. The simulation model for load characteristics was established. Then, the experimental test of simulation method was conducted on the HDU performance test platform. During the test, the stiffness, under the ramp-step and sinusoidal load force, and the characteristics of load with varied damping were researched. The research results indicate that the method designed herein may well simulate the variations of load stiffnesses, the variations of load dampings and even the coinstantaneous variations of load stiffness and load damping characteristics.

Applications of Mathematical Morphology Method to Fault Feature Extraction of Rolling Bearings Based on Minimum Entropy Deconvolution

Gong Tingkai, Yuan Xiaohui, Wang Xiyang

2016, 27(18):  2467-2471. 

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Aiming at the extractions of fault features of rolling bearings under the strong noise background, a novel method, called mathematical morphology based on minimum entropy deconvolution (MMBMED) was proposed herein. In this method, MED was first introduced to enhance the impact behaviors of the signals. And the fault characteristics of defective bearings were extracted by MM method, where the DIF filter with catching the bidirectional pulses was adopted as morphological operator, and kurtosis was employed as the criterion to the length selection of structural elements. The effectiveness of the new method was validated by both of simulation signals and vibration signals of rolling bearings with the outer and inner race faults. Finally, the results disclose that MED is effective to increase signal kurtosis and to strengthen the impulsive characteristics.

Study on Effects of Sampling Frequency on Performance of EEMD

Chen Huanguo, Chen Pei, Chen Wenhua, Cai Li, Shen Jianyang, Wu Jianwei, Wu Mingjian,

2016, 27(18):  2472-2476. 

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This paper revised the definition of residual energy according to the characteristics of EEMD firstly, and then investigated the effects of sampling frequency on the EEMD by analyzing the misalignment errors, residual energy, successive and orthogonality of intrinsic mode functions(IMFs). The analysis results show that the value of misalignment errors decreases with the raise of sampling frequency while the other three parameters periodic change approximately. Based on this rule, a selection principle of sampling frequency was obtained. Simulation example shows that the sampling frequency must be controlled in the range of 10.3 to 11 times of the maximum of the signal frequencies.

Research on 3D Reconstruction of Retina Based on Monocular Vision

Wang Yuliang, Liu Fei, Shen Jianxin, Liu Xianxi

2016, 27(18):  2477-2481. 

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In order to obtain high accuracy and good visualization in the diagnosis of retinal diseases, a new algorithm for 3D reconstruction was proposed based on monocular vision. Through two pieces of preprocessing image feature points extraction the algorithm was used to determine the matching relationship between pairs of points and RANSAC algorithm was adopted to remove the false matching points to obtain the feature point to improve the accuracy, the feature points matching of multiple images were obtained by using the method of chain registration. According to the corresponding relationship among the feature points in different images, the relative position of the camera in space was determined by using the method of 4 pass bundle adjustment, PMVS algorithm was used to achieve three-dimensional reconstruction of the retina. Experimental results show that the algorithm has good robustness and stability, may better realize the three-dimensional reconstruction of the retina.

Dynamic Reliability Assessment Method Based on POMDP for Electromechanical Equipment

Zhang Hongqi, Shao Xiaodong, Hu Xiangtao

2016, 27(18):  2482-2486,2493. 

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This paper focused on the operation and maintenance problems of electromechanical equipment, and proposed a new approach to assess the reliability and formulate the maintenance strategies based on POMDP theory. In the new approach, the dynamic reliability of electromechanical equipment was considered as an uncertain state which might be estimated by the monitoring informations (such as noise, pressure, temperature, vibration, et al.) according to POMDP theory. Furthermore, the influences of different maintenance strategies on reliability level of electromechanical equipment were investigated, and a dynamic reliability model was developed based on state transition. In order to plan the optimal maintenance strategy, an evaluation function was defined by minimizing the maintenance costs and the lost of faults. The experimental results confirm that the new approach based on POMDP is reasonable for electromechanical equipment, and possesses application and dissemination values.

Analysis and Evaluation of Measurement Uncertainty Sources for Parasitic Time Grating Sensors

Yang Hongtao, Zhang Liusha, Fei Yetai, Peng Donglin

2016, 27(18):  2487-2493. 

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In order to conduct systemic analyses of the error and uncertainty sources of parasitic time grating sensors, and to improve the measuring accuracy, a 84-level parasitic time grating was used as the research object to establish the uncertainty evaluation system which met the international GUM standard. The angle calculation formula was analyzed according to its measurement principles, and the uncertainty sources were divided into four categories which included errors of interpolation pulses, quantization errors of interpolation pulse signals, periodic errors of traveling wave signals and environmental errors. The theoretical transfer relationship among different uncertainty components were used to deduce the formula for the calculation of the synthetic measurement uncertainty according to the modern uncertainty theory. The experimental platform was built to measure the specific values of the uncertainty components by using the oscilloscope measurement result evaluation. And the synthetic measurement uncertainty of the parasitic time grating sensors was calculated by using the above specific value of the uncertainty components which was compared with the actual sensor measurement errors of the whole circumference. It may be seen that the uncertainty evaluation results by using the above built uncertainty evaluation method are consistent with the actual sensor errors. Therefore, it may be used in the practical evaluation of the parasitic time grating sensors.

Design and Analysis of a Rotary-type Robot Flexible Joint

Shi Yanlei, Zhang Minglu, Zhang Xiaojun, Bai Feng

2016, 27(18):  2494-2500. 

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According to the researches of the mechanism of flexibility of human knee joint, the animal musculo-tendinous tissue was modeled to design a suitable motor-driven rotary-type robot flexible joint. Then, comparative mechanism characteristics of the rotary type and linear type SEA(series elastic actuator) were analyzed, a flexible output mechanism with eight interaction compression spring was proposed as the core of the compliant joint, and based on this structure the relationship among joint structure parameters and output stiffness was calculated. To achieve the joint modularity, versatile, lighter and more compact, motor, reducer and flexible output mechanism centrally were installed in joints. Software simulation and tests on a prototype joint show that this joint has impact property and flexible output capacity and may be applied to various robots with respect to its structure design and functions.

Green Mastication Parameter Modeling of Open Mill and Multi-objective Optimization

Zhang Liang, Wang Qidong, Zhu Lihong, Hu Jinfang

2016, 27(18):  2500-2506. 

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Through the analyses of the efficiency and energy consumption of the mastication processes of an open mill, the Mooney viscosity objective function and carbon emissions objective function were established. Considering the actual constraints in the processes of open mill performance and mastication parameters, a multi-objective optimization model and a dimensionless single objective model were established, which took the open mill linear speed of roller, roller spacing and roller ratio as the variables, the minimum Mooney viscosity and the lowest carbon emission as the optimization objectives. An improved genetic algorithm was used to solve the optimization model. An experimental case was performed to verify the effectiveness and accuracy of the optimization model, and the mastication parameter optimization results and the sensitivity of optimization variables were analyzed.

Influences of Cutting Tool Load on Impedance Characteristics of Honeycomb Composite Material Ultrasonic Cutting Acoustic System

Ji Huawei, Yu Wenze, Hu Xiaoping, Yu Baohua

2016, 27(18):  2507-2512. 

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The impedance characteristics of a honeycomb composite material ultrasonic cutting acoustic system varied with the cutting tool load. By combing piezoelectric transducer with horn, a hybrid design equation of the acoustic system was put forward based on four-terminal network, and the relationship between load and the impedance characteristics of acoustic system was obtained. The modal analysis and the harmonic response analysis to the acoustic system were carried on by using of the finite element software and the impedance, resonant frequency and output amplitude of the acoustic system were measured by the impedance analyzer and laser displacement sensor. Simulation and experimental results show that the impedance of the acoustic system is increased, and the resonance frequency decreases with the increase of the tool load, but the output amplitudes among theoretical analysis, simulation and experiment are different, which is due to the amplification of the tool. The study has a guiding significance for the design and applications of honeycomb composite material ultrasonic cutting acoustic system.

Nonlinear Vibration Characteristics of Strip Mill Influenced by Horizontal Vibration of Rolled Piece

Liu Bin, Jiang Jiahao, Liu Fei, Liu Haoran, Li Peng

2016, 27(18):  2513-2520. 

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Based on the Roberts friction factor formula and the Hill rolling force formula, a kind of dynamic rolling force model was established. The model might characterize different friction states. On the basis of further consideration of the interaction between the structure of rolling mill vibrations and rolled piece vibrations, a coupling vibration model of rolled piece-roll was proposed. According to the Lagrange principle of generalized dissipation, a dynamic equilibrium equation was established respectively both of in rolling direction and in vertical direction. Then by using the method of multiple scales, the amplitude-frequency characteristic equation of the system was solved. The law of mill vibration influenced by different internal nonlinear parameters and external excitations was analyzed. Research results show that when rolled piece is slided, the coupling system is far more sensitive to the change of internal nonlinear parameters and external excitation than static state. If the coupling cube nonlinear parameters are reasonable, the occurance of system unstable vibration may be controlled in a small frequency range, which may weaken the impacts from rolled piece-roll coupling system on the vibration of strip mill.

Research on energy-saving EDM Pulse Power Supply

Huang Ruining, Li Yi, Liu Xiaofei

2016, 27(18):  2520-2523. 

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The system of a new type of energy-saving pulse power supply which had LCL-T topology circuit was designed. This paper presented the schematic circuit and software design ,and analyzed the power efficiency of major energy-consuming components. The performance and feasibility in machining processes were demonstrated by using the designed pulse power prototype. The experiments show that the designed energy-saving pulse power supply possesses ideal processing effect.

Energy-oriented CNC Milling Process Modelling and Parameter Optimization

Huang Zhengtao, Yang Jie, Zhang Chaoyong, Zhou Zhiheng, Xie Yang, Lin Wenwen

2016, 27(18):  2524-2532. 

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In order to select the appropriate cutting parameters to reduce energy consumption, a stable CNC milling process was modeled and optimized based on energy consumption function. First of all, the input power model of CNC milling system was built by characterizing its components. Then an energy consumption test platform was set up. The function between the input power of CNC milling system and cutting parameters was established through multiple regression, and its accuracy was confirmed by a comparative analysis. After that the specific energy consumption function during stable CNC milling process was figured out from the input power function. GSA was used to optimize the cutting parameters by a model, which regarded the ESEC as goal and the performance of milling machine and surface quality as constraints. Compared with empirical data, it is shown that the optimized cutting parameters will improve the energy efficiency of milling machine significantly and drastically.

Design and Reliability Analysis of Cold Roll-beating Equipment's Spindle Adopted Separate Structure

Li Long, Li Yan, Yao Yuan, Yang Mingshun, Yuan Qilong, Dong Hao

2016, 27(18):  2532-2539. 

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As for the characteristics of spindle impacted with the high frequency on cold roll-beating forming, a separate structure of cold roll-beating equipment's spindle was given by improving the existing spindle structure of cold roll-beating equipment, and the corresponding finite element model was established. The feasibility of this structure was proved with the modal and stress distribution of this structure which were obtained by the method of numerical simulation. Then the spindle used in the C630 lathe for cold roll-beating forming was designed, and the first three modes of this spindle were obtained using LMS system, then comparing the above results with the results of numerical simulation, the validity of the finite element analysis method and results was confirmed. The experiments shaping the copper and 20 steel by the technology of cold roll-beating were carried out on the C630 lathe with the above spindle structure shaping and further prove the feasibility of this separate structure of cold roll-beating equipment's spindle.

Preparation and Performance Analysis of Regenerated Materials for Thermosetting Polyurethane Based on Coupled Thermo-mechanical Model

Wu Zhongwei, Liu Guangfu, Cheng Huanbo

2016, 27(18):  2540-2546. 

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For the cross-linked structure, physical and chemical properties of thermosetting polyurethane, regenerative forming mechanism was studied based on the coupled thermo-mechanical model; the structure and activities of recycling materials were analyzed, micro-structure and properties of regenerated materials were analyzed, and the mechanical strengths of new materials were tested. At last, influence factors and their significance for regeneration effects were discussed and evaluated. Experiments and analyses results show that: the regeneration forming process and methods based on the coupled thermo-mechanical model, greatly improve the recycling rate of waste materials under ensuring mechanical performances of regenerated materials,and realize the recycling of waste thermosetting polyurethane and the products.

Formability of Hot Non-metallic Granule Medium of AA5083 Aluminum Alloy Tube under Various Loading Paths

Chen Xiaohua, Zhao Changcai, Dong Guojiang, Yang Zhuoyun, Cao Miaoyan,

2016, 27(18):  2547-2555. 

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Non-metallic granule (NMG) was used as the pressure-transfer medium and applied to the hot internal high-pressure forming technology on tube herein. The constitutive model of AA5083 sheet was created by the hot uniaxial tensile tests. Based on the numerical simulation of bulging on tube with NMG medium and the forming limit diagram (FLD), the influences of loading paths on the distribution of tube thickness, the contraction length of tube end and the path of principal strain were studied. All the work above were also verified by technological tests in the end. The results show that a reasonable match of initial punch force and axial feeding makes tube form a beneficial wrinkle in bulging region which is helpful in improving the forming limit because the material is gathered in the bulging region beforehand.