基于3D打印并联机器人机构的工作空间分析

以一种新型三自由度并联机构3-HSS为研究对象,对该机构进行运动学逆解分析,推导出该并联机构的运动学逆解方程,并求解了并联机构的雅可比矩阵,采用Gosselin几何法编程对该并联机器人的工作空间和边界进行研究,得到比较规则的工作空间,且该构型并联机构的工作空间连续,无空洞,并呈现一定的对称性。该研究能够满足当前3D打印技术的设计需求,并为并联机构进一步优化研究提供了理论依据。     

基于灵巧特性的三平动并联机构的尺度综合研究

考虑机构的灵巧性提出一种新型3-PUU并联机器人,对该并联机构进行运动学分析,得到了3-PUU并联机器人的运动学反解,在此基础上,建立了并联机构的雅可比矩阵;引入运动灵巧性指标。对该并联机器人的运动灵巧性进行了尺度综合分析,为并联机构的构型设计和进一步提供了依据。研究结果表明,该种机器人具有较好的实际应用前景。     

五自由度混联机构型综合的研究

提出了一种系统有效的混联机器人构型综合的新方法和单并联、多并联混联机构的概念及表示方法。根据螺旋理论构造了单开链五自由度串联机构;基于自由度分配原理,分析了可能出现的五自由度混联机构具体类型;将并联机构视为一个复合运动单元构型到串联机构中,替代串联机构中运动基相同且连续的若干运动单元,获得五自由度混联机器人构型;通过运动螺旋的线性组合来生成其他混联机构,并通过实例验证了该构型的正确性。分析表明该机构兼具串联机构和并联机构的优点。     

柔性并联机器人的研究进展

根据掌握的大量文献资料,对柔性并联机器人的构型、机构性能、运动学、动力学和控制策略等几个领域的主要研究成果进行了系统总结。指出了在柔性并联机器人动力学建模和控制研究中应解决的主要问题,以明确进行研究的方向。文章对柔性并联机器人的系统分析和控制研究等的进一步开展,具有一定的参考价值。     

空间3-RPC柔顺并联机构拓扑优化设计

为了获得空间柔顺并联机构构型,基于传统并联机构的设计原型,采用拓扑优化理论对空间并联机构进行拓扑优化设计。首先,以空间3-RPC并联机构为研究对象,建立机构的微运动学矢量连续映射Jacobian矩阵。然后,建立空间3-RPC柔顺并联机构的拓扑优化SIMP模型,运用优化准则算法(Optimization Criterion)对所建立的SIMP模型求解。最后,运用曲线拟合方法对拓扑后的构型轮廓进行拟合修正,采用Solid Works软件建立其拟合修正后的模型,进而通过Hyper Works有限元软件对机构进行静力学分析。仿真结果表明:与同构型的传统并联机构相比,拓扑优化后的空间柔顺并联机构具有相同的微动特性,因而验证了空间并联机构的拓扑优化设计方法的有效性。     

一种靠内力提高并联机构精度的方法的研究

工作空间小、实际可达精度和刚性低是影响并联机床实用化的主要原因,冗余的方法常被采用来消除并联机构的奇异、改善动力学性能,实现跨构型空间.文章提出了靠冗余内力提高并联机构实际精度的方法,设计了一种2DOF驱动冗余验证机构,推导了位置及速度协调条件,设计了力控制系统,试验表明该方法可以有效提高并联机构精度,该研究为改善并联机构运动精度提供了理论及试验基础.     

并联机构造型设计研究

从并联机构的造型与功能、结构的关系入手，阐述了并联机构造型设计的方法，并对并联机构的控制面板设计进行研究。     

并联机器人的研究进展与现状(连载)

并联机器人是20世纪80年代新兴起的先进技术，是一类全新的机器人。引起了国际学者的广泛关注。论文根据掌握的大量并联机器人文献，对其构型、运动学、动力学、机构性能和控制策略等几个领域的主要研究成果进行了系统总结，并指出了尚未解决的一些主要问题。     

一种三自由度弱耦合并联机构运动学分析

提出一种PRR+2-PRRU型两平移一转动并联机构,并研究其运动学特性.根据方位特征集理论分析并联机构的POC集、自由度和耦合度等机构拓扑特性;该机构耦合度为1,其构型为弱耦合设计.运用解析法进行位置分析,并通过MATLAB验证位置求解的正确性.在位置分析的基础上,分析了机构工作空间,并求解机构运动Jacobian矩阵...     

空间三转动并联机构工作空间和刚度分析

针对数控回转台的实际运动需求,以三自由度并联构型3-PUS-RU为研究对象,利用封闭矢量法建立位置逆解方程和并联机构的雅可比矩阵。引入并联机构的工作空间和刚度性能指标,并绘制机构的工作空间和机构守恒协调刚度在工作空间中的分布图谱。结果表明,由于机构的对称性,使得工作空间和刚度性能仍出现对称分布,工作区域尽量选取刚度值大的位置。对该3-PUS-RU并联构型工作空间和守恒协调刚度性能进行研究,其研究结果对并联机构的设计具有一定的指导作用。     

RHEOLOGY FEATURE OF SIMPLE METAL MELT

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Microstructures and Mechanical Properties of a Newly Developed Austenitic Heat Resistant Steel

The effect of heat treatment on the microstructures and mechanical properties of a newly developed austenitic heat resistant steel(named as T8 alloy) for ultra-supercritical applications have been studied. Results show that the main phases in the alloy after solution treatment are γ and primary MX. Subsequent aging treatment causes the precipitation of M_(23)C_6 carbides along the grain boundaries and a small number of nanoscale MX inside the grains. In addition, with increasing the aging temperature and time, the morphology of M_(23)C_6 carbides changes from semi-continuous chain to continuous network.Compared with a commercial HR3C alloy, T8 alloy has comparable tensile strength, but higher stress rupture strength. The dominant cracking mechanism of the alloy during tensile test at room temperature is transgranular, while at high temperature, intergranular cracking becomes the main cracking mode, which may be caused by the precipitation of continuous M_(23)C_6 carbides along the grain boundaries. Typical intergranular cracking is the dominant cracking mode of the alloy at all stress rupture tests.     

The 15th Global Foundry Sourcing Conference 2014held in Qingdao China

Organized by Suppliers China Co., Ltd and co-organized by the National Technical Committee 54 on Foundry of Standardization Administration of China, the 15th Global Foundry Sourcing Conference 2014 （hereinafter referred to as FSC 2014） was successfully held on Sep. 23rd in Grand Regency Hotel, Qingdao. More than 500 delegates from home and abroad attended this conference, including over 130 purchasers from 20 countries and 380 domestic and foreign suppliers.     

LASER CLADDED TiCN COATINGS ON THE SURFACE OF TITANIUM

Laser cladded coatings of TiCN were produced on the surface of titanium. To obtain the optimal techniques, several conditions were tested by varying the laser scanning rate. The choice of shielding gas was also studied. The cladded coatings were then evaluated from the surface mechanics point of view based on their microhardness. The microstructure of some interesting samples was investigated by optical micrographs (OM). The results showed that under the condition of fixed pulse frequency and pulse width, the laser scanning rate and the shielding gas are the main factors influencing the components of coatings. TiCN coatings were decompounded and oxidized during the cladding process in the condition of no shielding gas of N2. X-ray diffraction results indicated that the composite coatings composed of TiCN, TiC, Ti2N, and TiO2 were produced using appropriate techniques. The results indicated that the best condition in terms of the surface microhardness is obtained when the scanning rate is 1.5mm / s, the pulse frequency is 15Hz, the pulse width is 3.0ms, and N2 is chosen as the shielding gas. The microhardness of the composite coatings is about 1331kg · mm - 2, which is about 4 times that of the substrate. The optical micrographs indicated that the cladding zone is made up of TiCN, TiO2, and some interdendritic Ti, but the diffusion zone mainly consists of the dendrites phase, and the cladded depth is about 80m, which is more than 2 times that of the laser nitrided sample. There were no microcracks or air bubbles in the cladded sample, which was cladded using the above optimal techniques.     

Microstructure and Mechanical Properties of X80 Pipeline Steel Joints by Friction Stir Welding Under Various Cooling Conditions

X80 pipeline steel plates were friction stir welded(FSW) under air, water, liquid CO_2 + water, and liquid CO_2 cooling conditions, producing defect-free welds. The microstructural evolution and mechanical properties of these FSW joints were studied. Coarse granular bainite was observed in the nugget zone(NZ) under air cooling, and lath bainite and lath martensite increased signifi cantly as the cooling medium temperature reduced. In particular, under the liquid CO_2 cooling condition, a dual phase structure of lath martensite and fi ne ferrite appeared in the NZ. Compared to the case under air cooling, a strong shear texture was identifi ed in the NZs under other rapid cooling conditions, because the partial deformation at elevated temperature was retained through higher cooling rates. Under liquid CO_2 cooling, the highest transverse tensile strength and elongation of the joint reached 92% and 82% of those of the basal metal(BM), respectively, due to the weak tempering softening. A maximum impact energy of up to 93% of that of the BM was obtained in the NZ under liquid CO_2 cooling, which was attributed to the operation of the dual phase of lath martensite and fi ne ferrite.     

INDUSTRY NEWS

China Securities News reported on March 21, 2014： Guangdong Hongtu Wuhan Die Casting Co., Ltd. （Wuhan Hongtu）, a wholly owned subsidiary of Guangdong Hongtu Technology （Holdings） Co., Ltd., held a groundbreaking ceremony recently. With the registered capital of 50 million Yuan, Wuhan Hongtu has a total land area of 100,000 square meters and a plant construction area of 72,000 square meters. It is expected to have a production capacity of about 30,000 tonnes of aluminum castings annually after it is put into production.     

STUDY ON PROPERTIES OF PULSE ELECTRODEPOSITED RE-Ni-W-P-SiC COMPOSITE COATINGS

The effects of pulse frequency f and duty cycle r on the deposition rate, composition, morphology, and hardness of pulse electrodeposited RE （rare earth）-Ni-W-P-SiC composite coatings have been studied. The results indicate that pulse current can improve the deposition rate of RE-Ni-W-P-SiC composite coatings; W, P, and SiC contents in the coating decrease with the increase of pulse frequency and reach the lowest value at f = 33Hz, whereas the RE content in the composite coatings increases with the increase of pulse frequency. SiC content decreases with the increase of duty cycle, W content reaches the lowest value, and P content reaches the highest value at r = 0.4; pulse current and RE can lead to smaller size of the crystalline grains; however, the effects of different pulse frequency and duty cycle on the morphologies of RE-Ni-W-P-SiC composite coatings are not obvious. The hardness of RE-Ni-W-P-SiC composite coatings is the highest when the duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz. At the same pulse frequency, the hardness of RE-Ni-W-P-SiC composite coatings at r= 0.8 is higher than that at r= 0.6.     

GROWTH MORPHOLOGIES OF A BINARY ALLOY WITH LOW ANISOTROPY IN DIRECTIONAL SOLIDIFICATION

Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.     

RELATIONSHIP BETWEEN J-INTEGRAL AND FRACTURE SURFACE AVERAGE PROFILE

To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture surfaces for determining the fracture toughness parameters of J-integral for plain strain was proposed The principle of the fracture-surface topography analysis （FRASTA） was used. In FRASTA, the fracture surfaces were scanned by laser microscope and the elevation data was recorded for analysis. The relationship between J-integral and fracture surface average profile for plain strain was deduced. It was also verified that the J-integral determined by the novel method and by the compliance method matches each other well.