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Now showing items 17 - 32 of 53

  • Kinematic Modeling of a Combined System of Multiple Mecanum-Wheeled Robots with Velocity Compensation

    Li, Yunwang   Ge, Shirong   Dai, Sumei   Zhao, Lala   Yan, Xucong   Zheng, Yuwei   Shi, Yong  

    In industry, combination configurations composed of multiple Mecanum-wheeled mobile robots are adopted to transport large-scale objects. In this paper, a kinematic model with velocity compensation of the combined mobile system is created, aimed to provide a theoretical kinematic basis for accurate motion control. Motion simulations of a single four-Mecanum-wheeled virtual robot prototype on RecurDyn and motion tests of a robot physical prototype are carried out, and the motions of a variety of combined mobile configurations are also simulated. Motion simulation and test results prove that the kinematic models of single- and multiple-robot combination systems are correct, and the inverse kinematic correction model with velocity compensation matrix is feasible. Through simulations or experiments, the velocity compensation coefficients of the robots can be measured and the velocity compensation matrix can be created. This modified inverse kinematic model can effectively reduce the errors of robot motion caused by wheel slippage and improve the motion accuracy of the mobile robot system.
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  • Frictional Properties and Mechanisms of an Organic-Metal Brake Pair Braking Repeatedly in Magnetic Field

    Bao, Jiusheng   Lu, Lijian   Yin, Yan   Ge, Shirong   Liu, Tonggang   Liu, Yang  

    With the aim to investigate repeated braking of organic-metal brake pairs, tribological and scanning electron microscopy (SEM) experiments were performed to reveal the influence of a magnetic field on the tribological performance of brakes. A nonasbestos copper-based brake pad and gray cast iron brake disc were selected as the brake pair. The X-DM pad-on-disc friction tester was improved to set up a tribological tester under a magnetic field. The worn surfaces were observed by SEM to reveal the friction mechanisms. It was found that a magnetic field can ameliorate the dynamic friction and wear. In addition, the global mean friction coefficient increases and the wear resistance of brake materials improves. A magnetic field promotes surface oxidation and aggravates the surface heat emission condition. As a result, the mean temperature on the friction surface increases obviously. An appropriate magnetic field can improve the dynamic temperature rise and decrease the global temperature rise on the friction surface. It is considered that a magnetic field has important influences on tribological performance in repeated braking. Therefore, this research could provide theoretical references for studying the tribological performance in repeated braking and/or under a magnetic field.
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  • A study on drum cutting properties with full-scale experiments and numerical simulations

    Li, Xuefeng   Wang, Shibo   Ge, Shirong   Malekian, Reza   Li, Zhixiong   Li, Yifei  

    In order to investigate the properties of cutting loads on shearer drum, a series of full-scale shearer drum cutting tests were conducted in the National Energy Coal Mining Machinery Equipment Research and Design Center of China. The pick forces and the torque acting on the drum were measured and recorded under different cutting conditions by the strain sensors that were embedded in the cutting picks. Besides, an attempt was made to simulate the shearer drum cutting process. For this purpose, a computer program named Particle Flow Code in three dimensions (PFC3D) based on discrete element method (DEM) was used. The rock sample was models by graded particle assemblies and the micro-properties were calibrated by modeling the uniaxial compressive strength tests. The cutting process for the front and back drums with different traction speeds were simulated with this model. The torque of drums and forces of each pick were obtained during the simulation. Reasonable agreement and significant correlations were found between experiment and numerical simulation in terms of cutting forces of picks and the mean torque of the drums. The specific energy increased with the increase of traction speed in experiments, which was reproduced well in numerical simulation. Moreover, according to the analysis in frequency domain, the vibration of drum torque consists of components with multiple frequencies below 50 Hz, which is observed in both experiment and simulation. Therefore, numerical simulation by PFC3D is an easier, faster and reasonable method in the prediction of drum cutting load and design of shearer drum.
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  • Dynamic torsional characteristics of mine hoisting rope and its internal spiral components

    Zhang, Jun   Wang, Dagang   Zhang, Dekun   Ge, Shirong   Wang, Dao'ai  

    Dynamic torsional characteristics of mine hoisting rope and its internal spiral components were investigated in the present study. Theoretical models of tensions of rope segments at distinct locations were presented to obtain dynamic rope tensions. Theoretical models of torque, unit torsion angle, torsion angle, twisting parameters, and torsional stress were introduced to investigate dynamic torsional characteristics of hoisting rope and its internal spiral components under tension. Rope tests were conducted in order to validate dynamic torsional properties of the rope under fluctuation tensions. The results show three-stage fluctuating trends of rope tension and torque. An increase of hoisting time induces a decreased torsion angle of the rope, fluctuating upward trends of unit torsion angles of the rope, spiral strands and steel wires, respectively, fluctuating increases in lay angles of the spiral strand and steel wires, respectively, and the fluctuating decreased lay length of the spiral strand. An increase of the distance between rope segment and friction pulley tangent causes a decrease at first and then an increase in the unit torsion angle in cases of the rope, spiral strands and steel wires, an increase at first and then a decrease in the rope torsion angle, increased lay angle and decreased lay length of the spiral strand, a decrease at first and then an increase in the torsional stress of steel wire in every layer of the spiral strand.
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  • Increasing the wear resistance of UHMWPE acetabular cups by adding natural biocompatible particles

    Ge, Shirong   Wang, Shibo   Huang, Xiaolong  

    Ultra-high molecular weight polyethylene (UHMWPE) is a kind of biomaterial applied as the acetabular cup in artificial hip joints. However, wear debris generation of UHMWPE materials after their replacements in human body has been proved to induce aseptic loosening and osteolysis, which is the main cause of long-term failure of total hip joints composed of UHMWPE and hard femoral balls. in this paper, natural coral (NC) particles in the size within 50 mu m were applied as reinforcement fillers into UHMWPE to increase the wear resistance of UHMWPE composites as artificial acetabular cups. The micro-hardness and scratch resistance of UHMWPE/NC composites were studied. A hip joint wear simulator was operated to investigate the wear behavior of UHMWPE/NC composites against CoCrMo balls, the wear tests were lubricated by 25% bovine serum solutions. The wear mass loss and wear debris distribution through one million test cycles were examined in the paper. It is shown that the adding of NC particles in UHMWPE resulted in the enhancement of micro-hardness and scratching resistance of the UHMWPE/NC composites. The micro-hardness of UHMWPE/NC composites increased with natural coral contents in the linear relationship. The scratch coefficients of UHMWPE/NC composites increased in contents range of 10 wt% NC particles, the scratch depth decreased with the increasing NC contents. The wear resistance of UHMWPE/NC composites increased with the increasing contents of natural coral particles. It was found that the relation of wear mass loss of UHMWPE acetabular cup to the micro-hardness followed a negative power law. The wear mechanism of UHMWPE/NC composites was mainly controlled by adhesive wear. The NC contents in UHMWPE changed the severity of adhesive wear. The investigation of UHMWPE wear debris revealed that adding of NC particles in UHMWPE resulted in variations of size distribution of UHMWPE wear debris. Because micro-hardness of natural coral materials was much lower compared to CoCrMo alloy, few metal debris from CoCrMo ball were captured in the filter paper. (C) 2009 Elsevier B.V. All rights reserved.
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  • Hydrogenated diamond-like carbon film deposited on UHMWPE by RF-PECVD

    Shi, Xingling   Wang, Qingliang   Xu, Lingli   Ge, Shirong   Wang, Chao  

    In this work, investigations were conducted to analyze the properties of diamond-like carbon (DLC) film deposited on ultra-high molecular weight polyethylene (UHMWPE) by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) at a low temperature of 50 degrees C. Composition and structure of the films were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Hardness and wettability of the film were tested. Tribological characterizations were carried out on a universal micro-tribometer, and reciprocating friction against ZrO(2) ball was adopted with 25% bovine serum as lubrication. Results show that DLC film was successfully deposited on UHMWPE surface by RF-PECVD and the sp(3) content was about 20% in the film. The film increased the macrohardness of the substrate by about 42% and the wettability was improved too. Tribology test showed a higher friction coefficient but a much smaller wear volume after the deposition due to the surface roughening and strengthening. (C) 2009 Elsevier B. V. All rights reserved.
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  • Biodegradation behavior and tribological properties of ultrahigh molecular weight polyethylene stabilized with alpha-tocopherol

    Kang, Xueqin   Yao, Chi   Ge, Shirong  

    Purpose This paper aims to investigate the effect of simulated body fluid (SBF) on biodegradation and tribological properties of ultrahigh molecular weight polyethylene (UHMWPE) and UHMWPE stabilized with alpha-tocopherol. Design/methodology/approach The samples of UHMWPE and UHMWPE stabilized with alpha-tocopherol were prepared by a hot-pressing method, and then immersed in SBF for one year. Tribological test was performed on a UMT-2 tribometer. Findings The crystallinity and tribological properties increased slightly after UHMWPE stabilized with alpha-tocopherol, whereas the O/C ration decreased slightly. The crystallinity and O/C ratio increased after all samples immersed in SBF for one year. This resulted in the deterioration of tribological properties and the wear mechanism change. The tribological properties change was smaller in UHMWPE stabilized with alpha-tocopherol than that in UHMWPE, because the oxidation resistance of UHMWPE was increased by alpha-tocopherol. Originality/value The results of the experimental studies demonstrated and compared the biodegradation behavior and tribological properties of UHMWPE, UHMWPE stabilized with alpha-tocopherol, and after they immersed in SBF for one year.
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  • Finite element analysis of hoisting rope and fretting wear evolution and fatigue life estimation of steel wires

    Wang, Dagang   Zhang, Dekun   Wang, Songquan   Ge, Shirong  

    This paper is concerned with the finite element analysis of hoisting rope and three-layered strand for the exploration of fretting fatigue parameters and stress distributions on the cross-section. Also, the Archard's wear law based evolution of fretting wear depth of wires crossed at different angles and implications to fatigue life estimations of fretted wires were presented. The results show that different wires in the rope or strand and distinct material models in the analyses both induce different stress distributions and fretting fatigue parameters. The predicted fretting wear depths of wires show good agreement with experimental results. (C) 2012 Elsevier Ltd. All rights reserved.
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  • Modeling of Human Lower Limb and Technical Analysis of Athlete's High Leg Lift

    Han, Shuyang   Ge, Shirong   Liu, Hongtao  

    The appearance of human motion capture system enables the analysis of human motion. In this paper, the athlete's high leg lift exercise is studied. The motion was sampled through NDI motion capture system, and the data was imported into Visual 3D software to establish a lower limb model and to execute the simulation and analysis. The high leg lift exercise is partitioned into 6 stages, and it is found that there is a difference of 20 degrees in the maximum knee flexion angle between the dominant and non-dominant limb. Simultaneously, a multi-rigid-body was build to carry out the dynamic analysis. The flight height is linear with the square of angular acceleration of the non-supporting leg, and the thrust force changes with the angular velocity of the non-supporting leg in a parabolic line law. In conclusion, the human motion analysis technology helps the athletes to make the exercise scientific and efficient.
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  • Contact damage failure analyses of fretting wear behavior of the metal stem titanium alloy-bone cement interface.

    Zhang, Lanfeng   Ge, Shirong   Liu, Hongtao   Wang, Qingliang   Wang, Liping   Xian, Cory J  

    Although cemented titanium alloy is not favored currently in the Western world for its poor clinical and radiography outcomes, its lower modulus of elasticity and good biocompatibility are instrumental for its ability supporting and transforming physical load, and it is more suitable for usage in Chinese and Japanese populations due to their lower body weights and unique femoral characteristics. Through various friction tests of different cycles, loads and conditions and by examining fretting hysteresis loops, fatigue process curves and wear surfaces, the current study investigated fretting wear characteristics and wear mechanism of titanium alloy stem-bone cement interface. It was found that the combination of loads and displacement affected the wear quantity. Friction coefficient, which was in an inverse relationship to load under the same amplitude, was proportional to amplitudes under the same load. Additionally, calf serum was found to both lubricate and erode the wear interface. Moreover, cement fatigue contact areas appeared black/oxidative in dry and gruel in 25% calf serum. Fatigue scratches were detected within contact areas, and wear scars were found on cement and titanium surfaces, which were concave-shaped and ring concave/ convex-shaped, respectively. The coupling of thermoplastic effect and minimal torque damage has been proposed to be the major reason of contact damage. These data will be important for further studies analyzing metal-cement interface failure performance and solving interface friction and wear debris production issues. Copyright =C2=A9 2015 Elsevier Ltd. All rights reserved.
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  • Dynamic contact and slip characteristics of bent hoisting rope in coal mine

    Zhang, Jun   Wang, Dagang   Zhang, Dekun   Ge, Shirong   Araujo, Jose Alexander  

    Dynamic contact and slip characteristics of bent hoisting rope in coal mine were investigated in this study. Dynamic tensions of hoisting rope bending around friction lining at distinct arc locations were obtained employing hoisting dynamics and friction transmission theories. The finite element model of contacting bent rope and friction lining was established to explore dynamic contact characteristics and relative slip amplitudes between the rope and friction lining, and between contacting strands in the rope, respectively. The results show that dynamic tensions of bent rope at distinct arc locations are related to slip and inactive slip states of rope segments. Higher stress concentrations are present at contacting locations between adjacent strands and between the rope and friction lining at every central angle at any lifting time. An increase of central angle phi causes overall increased equivalent von Mises stress distributions on the rope cross-section and near contacting locations within the slip angle between the rope and friction lining as compared to constant equivalent stress distributions within the inactive slip angle. Relative slips are induced by differences between tensions of bent rope segment at both sides within the slip angle as compared to no relative slip within the inactive slip angle, which is the same in cases of contacting rope and friction lining, and neighboring strands.
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  • Tactile perception of skin:research on late positive component of event-related potentials evoked by friction

    Tang, Wei   Lu, Xiangyong   Chen, Si   Ge, Shirong   Jing, Xianghong   Wang, Xiaoyu   Liu, Rui   Zhu, Hua  

    During tactile perception, the electrical system in the brain will respond to the changes in vibration, friction, and surface properties between the perceived surface and human skin. To establish the relationship between tactile perception and friction, 64-channel Neuroscan event-related potential (ERP) system and a three-axis force sensor were used to obtain electroencephalograph (EEG) and friction signals during fingers exploring surfaces. An oddball variation mode was applied to produce the late positive component (LPC) of ERP. Three fabric samples with different friction coefficient were chosen. The results indicate that LPC amplitude is affected by friction. High friction leads to high LPC amplitude. LPC latency is related to difference of friction. Large difference of friction between samples induces small LPC latency. During tactile perception, the applied normal load of male is larger than that of female. Tactile perception is effected by gender. Female has larger LPC latency than male, indicating female are more sensitive to recognize fabrics. This fundamental study could provide theory support to the related researches.
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  • Formation of titanium carbide coating with micro-porous structure

    Luo, Yong   Ge, Shirong   Jin, Zhongmin   Fisher, John  

    Micro-porous titanium carbide coating was successfully synthesized in a vacuum gas carburizing furnace by using a sequential diffusion technology. The composition and structure of the as-synthesized TiC were examined by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and glow discharge mass spectrometry (GDMS), and scanning electron microscopy (SEM). All of the XRD, XPS and GDMS analysis results indicate that carbon atoms effectively diffused into the titanium alloys and formed a uniform acicular TiC coating with micro-porous structure.
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  • Study on Biotribological Behavior of the Combined Joint of CoCrMo and UHMWPE/BHA Composite in a Hip Joint Simulator

    Wang, Qingliang   Liu, Jinlong   Ge, Shirong  

    UHMWPE composites reinforced with Bovine Bone Hydroxyapatite (BHA) in different contents were prepared by heat pressing formation method. A hip joint wear simulator was used to investigate the biotribological behavior of UHMWPE/BHA composite acetabular cups against CoCrMo alloy femoral heads in bovine synovia lubrication at 37 +/- 1 degrees C. It was found that the addition of BHA powder to UHMWPE can improve the hardness and creep modulus of UHMWPE/BHA composites, and decrease their wear rates under bovine synovia lubrication. When the content of BHA filler particles was up to 30 wt%, UHMWPE/BHA composites demonstrated the well design performances of the surface and biotribological properties. Fatigue, ploughing and slight adhesive wear were the main wear mechanisms for UHMWPE and its composites. In addition, the sizes of wear particles became larger with an increase in BHA powder addition. These results suggest that BHA filler is a desirable component to increase the wear resistance of UHMWPE/BHA composites for biomedical applications.
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  • Fretting wear of carburized titanium alloy against ZrO(2) under serum lubrication

    Luo, Yong   Ge, Shirong   Zhang, Dekun   Wang, Qingliang   Liu, Hongtao  

    Fretting wear of carburized titanium alloys was investigated on the universal multifunctional tester (UMT) with the ball-on-fiat fretting style under bovine serum lubrication. The tangential load and friction coefficient during the fretting process were analyzed, and the evolution of fretting log during the fretting process was investigated to understand the wear mechanism of the titanium alloy and carburized titanium alloy. Furthermore, the wear scar was examined using a SEM and three-dimension surface profiler. It was found that the friction coefficient of the titanium alloy increased faster than that of carburized titanium alloy in the first stage under serum lubrication, and then remained steady with a similar value in the second stage. The Ft-D curve indicated that there was wear mechanism transition from gross slip to mixed stick and slip. Finally, it was observed that there was a slight damage of the titanium alloy and carburized titanium alloy showed excellent performance during the fretting wear process under serum lubrication. All of the results suggested that carburized titanium alloy was a potential candidate for the stem material in artificial joints. (C) 2010 Elsevier Ltd. All rights reserved.
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  • Tribological behavior and mechanism of a magnetic conductive brake pair under action of alternating magnetic field

    Bao, Jiusheng   Huang, Shan   Liu, Yang   Ge, Shirong   Yin, Yan   Liu, Tonggang  

    Tribological experiments of a brake pair consisting of magnetic conductive organic friction pad and HT250 disc were conducted on a test bench of disc brake. SEM and EDS were used to reveal influence mechanisms. Results showed that both magnetic induction intensity and frequency have important influences on tribological performance. Friction temperature increases slightly with increasing of magnetic induction intensity. Debris is gradually refined and oxidation reaction becomes intensified, which promotes formation of friction layer on worn surface. Braking torque is then increased and braking process becomes more stable. Friction temperature increases greatly with increasing of magnetic field frequency. Increased magnetic frequency could improve wear resistance, but once frequency reaches a high enough value, dislocations aggregates and wear resistance declines.
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