3-RPS并联机构奇异位形分析

文章提出用螺旋理论的方法来构造包括结构奇异和约束奇异信息的雅可比矩阵,应用这种方法针对6PM2机床的3-RPS并联机构奇异位形进行分析.提出的分析方法可以为并联机构的机构设计和控制提供理论依据.     

一种组合并联机构的运动学分析及刚度分析

以一种新型的可实现3-PUU机构和3-UPU机构的组合并联机构为对象,对该机构在可实现两种并联机构的情况下分别进行机构自由度分析、运动学分析,得出机构的运动学正逆解以及雅克比矩阵,根据所求出的雅克比矩阵进一步对机构进行机构刚度分析,并用MATLAB软件求解刚度值,绘制出在给定的位姿时上下平台的相关结构参数对整体刚度值的影响曲线图,为此组合并联机构的进一步分析提供了理论分析的依据,对组合并联机构的设计具有一定指导作用。     

四自由度部分解耦并联机构运动学和性能分析

针对并联机构强耦合性导致的运动学分析复杂、控制难度大、工作空间小等问题,设计了一种新型四自由度并联机构。采用螺旋理论分析了机构的运动特性,得知该机构具有两转动两移动自由度,可由4个移动副驱动;建立了机构的位置数学模型,得到了位置反解表达式,分析了运动部分解耦特性;对机构进行了速度分析,推导了速度雅可比矩阵;基于雅可比矩阵对机构进行了奇异分析,得到了机构的奇异位形;分析了机构的条件数指标,通过添加冗余驱动分支消除了奇异位形,提升了机构的条件数性能,并验证了该机构具有较大的工作空间。     

两种具有弧形移动副的3-RPS并联机构运动学分析

提出两种3-RPS并联机构,其分支运动链均由一个转动副R、一个弧形移动副P和一个球铰S构成。第一种并联机构的驱动副轴线共线,第二种的驱动副轴线相互平行。运用螺旋理论,对这两种并联机构的自由度、位置反解、传动效率系数进行分析。第一种并联机构动平台的转动中心为弧形连杆的中心,动平台绕Z轴的旋转相对其他两个方向的旋转具有解耦性;第二种并联机构动平台的转动中心是各支链球铰中心与弧形连杆中心连线的3条直线的交点,此交点随动平台的位姿变化而变化;此外,它们的传递效率系数与支链球铰的移动方向有密切关系。     

基于遗传算法的3-DOF并联机床机构的结构参数优化

建立了3-P-(2U-2S)并联机床机构的反解方程,求解得到机床的工作空间。通过雅克比矩阵条件数的计算,得到并联机床机构的运动特性条件指标。以工作空间与全局条件指标(GCI)作为评价指标,应用BP网络算法和遗传算法对机床机构尺寸参数半径R与杆长L进行了综合优化。结果表明优化后的综合性能得到了提高。     

3-UPU冗余驱动并联机构的冗余支链优选及仿真

由于当前3-UPU冗余驱动并联机构存在奇异缺陷,造成冗余支链选择方法可靠性低、刚度分布不均.提出一种新的3-UPU冗余驱动并联机构冗余支链优选方法.设计了3-UPU冗余驱动并联机构和自由度要求.将运动平台位姿参数看作变量,求出3-UPU冗余驱动并联机构的力矩阵和力矩矩阵.获取3-UPU冗余驱动并联机构输入,通过位置方程求出驱动螺旋参数和非冗余支链的驱动螺旋,提升可靠性.计算冗余驱动螺旋的参数,获取条件数机构的相关信息,确定刚度矩阵的力矩阵和力矩矩阵,利用灵巧度与刚度获取条件数和刚度最佳的冗余支链,解决刚度分布不均的问题.实验结果表明:所提方法可靠性高、刚度分布均匀.     

3-UPU冗余驱动并联机构的冗余支链优选及仿真（英文）

由于当前3-UPU冗余驱动并联机构存在奇异缺陷,造成冗余支链选择方法可靠性低、刚度分布不均。提出一种新的3-UPU冗余驱动并联机构冗余支链优选方法。设计了3-UPU冗余驱动并联机构和自由度要求。将运动平台位姿参数看作变量,求出3-UPU冗余驱动并联机构的力矩阵和力矩矩阵。获取3-UPU冗余驱动并联机构输入,通过位置方程求出驱动螺旋参数和非冗余支链的驱动螺旋,提升可靠性。计算冗余驱动螺旋的参数,获取条件数机构的相关信息,确定刚度矩阵的力矩阵和力矩矩阵,利用灵巧度与刚度获取条件数和刚度最佳的冗余支链,解决刚度分布不均的问题。实验结果表明:所提方法可靠性高、刚度分布均匀。     

含两个冗余驱动并联机床的灵巧度分析

以两个冗余驱动的并联机床为研究对象,建立机床的运动学模型,得到机床的雅克比矩阵,并对机床进行灵巧度分析。利用雅克比矩阵建立了3个影响机床灵巧度的指标,即可操控性、条件数和最小奇异值,通过这3个灵巧度指标定义了综合灵巧度系数这个评价指标。最后采用MATLAB进行仿真分析,得到不同位置的灵巧度分布情况,为机床的优化和轨迹规划奠定了一定的理论基础。     

4 UPU并联机构奇异研究与工作空间分析

基于螺旋理论,分析了一种4-UPU并联机构的运动性质,利用Kutzbach-Grübler公式计算了机构的自由度。根据机构运动副的布置方式,选取4个移动副作为输入。建立机构的位置关系方程,采用雅克比代数法判断奇异性;根据约束条件和位置关系方程,得到了机构在定姿态且非奇异条件下的工作空间。计算结果表明,机构的奇异位形与姿态角和平台结构参数有关;在非奇异条件下,机构的工作空间不连续,存在"空洞",工作空间范围与姿态角关系显著。     

基于灵巧度3-RCR并联机器人机构的结构参数优化

对新型三平移3-RCR并联机构的位置解、雅克比条件数进行了求解分析;基于3-RCR并联机构的全域条件数,以灵巧度作为优化目标,利用遗传算法对其结构参数进行优化研究,运用MATLAB软件编程得到了该并联机构的灵巧度图谱,为该类并联机构的进一步研究和应用提供了参考.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.