Properties of compatibilized nylon 6/ABS polymer blends

Nylon 6/poly(acrylonitrile-butadiene-styrene)(ABS) blends were prepared in the molten state by a twin-screw extruder. Maleic anhydride-grafted polypropylene (MAP) and solid epoxy resin (bisphenol type-A) were used as compatibilizers for these blends. The effects of compatibilizer addition to the blends were studied via tensile, torque, impact properties and morphology tests. The results showed that the additions of epoxy and MA copolymer to nylon 6/ABS blends enhanced the compatibility between nylon 6 and ABS, and this lead to improvement of mechanical properties of their blends and in a size decrease of the ABS domains.

Electrostatic-field-induced chain alignment of liquid crystalline copolyether TPP thin films

A liquid crystalline (LC) copolyether has been synthesized from 1-(4-hydroxy-4'-biphenyl)-2-(4-hydroxyphenyl)propane with 1,7-dibromoheptane and 1,11-dibromoundecane with a 50/50 (both in %) equal composition of the 7- and 11-methylene monomers [coTPP-7/11(5/5)]. A mono-domain with a homeotropic alignment can be induced by a thin film surface in the LC phase. When an electrostatic field is applied to the surface-induced mono-domains parallel to the thin film surface normal, the molecular alignment undergoes a change from the homeotropic to uniaxial homogeneous arrangement. However, when the field is applied to a direction perpendicular to the thin film surface normal. the molecular alignment is about 10 degrees -tilt with respect to the homeotropic alignment toward the a*-axis. This is because the permanent dipole moment of the copolyether is not right vertical to the molecular direction. The calculation of molecular dipoles indicates that the permanent dipole moment of this copolyether is about 70 degrees away from the molecular axis, which leads to a negative dielectric anisotropy. It is speculated that the 10 degrees- rather than 20 degrees -tilt is due to a balance between the alignment induced by the electrostatic field and the surface. In the electrostatic field, molecules are subjected to a torque tau, which is determined by the permanent dipole moment P and the electrostatic field E: tau = P x E. The molecular realignment in both parallel and perpendicular directions to the thin film surface normal is determined by satisfying the condition of tau = P x E = 0. (C) 2001 Elsevier Science Ltd. All rights reserved.

MORPHOLOGY AND DYNAMIC-MECHANICAL PROPERTIES OF NYLON 66/POLY(ETHER IMIDE) BLENDS

The morphology and dynamic mechanical properties of blends of poly(ether imide) (PEI) and nylon 66 over the full composition range have been investigated. Torque changes during mixing were also measured. Lower torque values than those calculated by the log-additivity rule were obtained, resulting from the slip at the interface due to low interaction between the components. The particle size of the dispersed phase and morphology of the blends were examined by scanning electron microscopy. The composition of each phase was calculated. The blends of PEI and nylon 66 showed phase-separated structures with small spherical domains of 0.3 similar to 0.7 mu m. The glass transition temperatures (T(g)s) of the blends were shifted inward, compared with those of the homopolymers, which implied that the blends were partially miscible over a range of compositions. T-g1, corresponding to PEI-rich phase, was less affected by composition than T-g2, corresponding to nylon 66-rich phase. This indicated that the fraction of PEI mixed into nylon 66-rich phase increased with decreasing PEI content and that nylon 66 was rarely mixed into the PEI-rich phase. The effect of composition on the secondary relaxations was examined. Both T-beta, corresponding to the motion of amide groups in nylon 66, and T-gamma, corresponding to that of ether groups in PEI, were shifted to higher temperature, probably because of the formation of intermolecular interactions between the components.

CHARACTERIZATION OF BLENDS OF POLYPROPYLENE WITH A SEMIRIGID LIQUID-CRYSTAL COPOLYESTER

Blends with a liquid-crystal polymers (LCP) as one component show, in general, very interesting properties. Reduction of shear visocity and improvement of mechanical properties are very remarkable. High melting temperatures and high costs of the LCP limit the use of these blends. A new class of thermotropic LCPs with flexible spaces, with relatively low melting temperatures, can overcome the first problem. In this work, rheological and mechanical properties of blends of polypropylene with low contents of this LCP are presented. Torque during extrusion and viscosity decrease with LCP content. Elastic modulus is remarkably increased when the LCP phase is oriented.

一种用于异步电机效率优化的混合搜索方法

针对异步电机效率优化问题,提出了一种混合搜索方法。该方法起始于模糊自适应搜索,然后切换至黄金分割法以获取确定收敛速度。这样的搜索步骤能够降低转矩波动,避免在最优点附近发生振荡。利用一个包含铁损和机械损耗的异步电机模型,对该方法进行了矢量控制下的性能验证。仿真结果验证了该方法的有效性。

输电线巡检机器人越障机理与试验

分析超高压输电线路架空地线上的障碍物类型以及跨越这些障碍的过程。可以发现,巡检机器人采用双臂交替跨越障碍,越障过程简单。但是由于受巡检机器人自身重力偏矩的影响和手臂长度尺寸的限制,当单臂悬架在架空地线上时,导致巡检机器人本体倾斜,另一手臂完成脱线和上线任务变得十分困难,有时甚至造成越障失败。为了解决上述问题,提出质量调节的控制方法。该方法通过调节巡检机器人的质心,使巡检机器人的本体保持水平状态。为了验证质量调节控制方法的正确性,采用Lagrange方法建立巡检机器人动力学模型,通过仿真试验、实验室模拟实际架空地线试验以及超高压实际现场试验说明了提出方法的可行性。

双臂式空间机械臂捕捉目标问题

基于动量守恒关系,分析了空间机械臂抓取目标过程中的碰撞问题.针对单臂式系统提出了直臂抓取与广义直臂抓取构型,并将后者推广到双臂式空间机械臂系统.利用广义直臂抓取方法得到的空间机械臂构型,可有效减少碰撞作用对于空间机械臂系统角冲量、基座姿态的影响,保证了系统的稳定性,克服了控制算法中存在的构件转角和执行机构力矩限制问题.仿真证明了方法的有效性。

野外地面移动机器人系统设计与实现

本文针对机器人在野外地形环境下的高机动性要求,设计开发了减震机构,针对机器人轮-腿复合结构和驱动冗余特点,提出并开发了面向高速行进的牵引力控制算法和面向越障的构型控制算法,通过与环境建模技术结合,实现了机器人的遥控、自主导航、自主越障等功能,构成了机器人的分层式控制系统。

一种适用于多指灵巧手的机电一体化驱动器概念

本文提出了一种机电一体化驱动器的概念,这种驱动器能够将电机的旋转运动转换为直线运动,并在不外加力和力矩传感器的基础上利用运动转换副上产生的微应变来估算电机的输出力矩和驱动器末端的牵引力信息。利用高精度、高灵敏度并带有温度和噪声补偿电路的应变片来测量微应变,以取得稳定而可靠的测量结果。应变片直接贴在驱动器的主体结构表面可以最小化尺寸,而且可以实现机电一体化而不是机械-电子集成系统。仿真实验表明,这种方法和传统的电流估算法相比,可以减少由于噪音和波动带来的电流信号误差,得到更加精确的信息,并且(与加入力或者力矩传感器相比)能够有效缩小外型尺寸,同时去除不必要的机械与电子接口,因此增加了系统的鲁棒性。

仿人机器人腰部机构的动力学建模、控制与仿真

本文介绍的仿人机器人具有差动腰部机构,它除了受自身的动力学影响以外,还受到手臂和车体运动以及外力、外力矩等对腰部机构关节力矩的影响。笔者利用高效牛顿-欧拉算法完成了仿人机器人的整体建模;在不考虑各关节间耦合运动的情况下,对整体动力学模型进行适当简化,得到了腰部机构的动力学模型。简化后的动力学模型既反映了机器人车体、腰部及双臂的动力学关系,又大大地减小了计算量,易于实现基于动力学的控制算法。基于动力学模型,给出了腰部机构PD伺服轨迹跟踪控制算法,并结合计算力矩方法用于补偿腰部机构两关节受到的力矩扰动。仿真分析表明,该控制方法可以明显提高腰部机构的位置跟踪精度,并提高仿人机器人的整体作业精度。

地面移动机器人越障动力学建模与分析

对采用轮—腿—履带复合型移动机构的地面移动机器人进行了研究,首先分别描述了机器人采用腿—履带、轮—腿—履带两种方式的越障过程,进而对腿—履带复合越障过程进行了动力学建模,分析了电机驱动力矩与机器人速度及障碍物高度等之间的关系,为确定机器人的复杂环境适应能力提供理论依据.

一种Stewart结构六维力/力矩传感器参数辨识研究

介绍了一种大量程Stewart结构六维力/力矩传感器系统.建立了传感器力/力矩测量数学模型,构建了基于运动学逆解的优化目标函数.提出了一种新的参数标定法,称作分支轮换标定法.基于所研发的六维力/力矩传感器系统进行了实验研究,实验结果表明分支轮换法可以有效地辨识出传感器的结构参数,提高了测量精度.该方法可用于类似结构的六维力/力矩传感器参数标定.

轮式移动仿人机器人的动力学建模与分析

利用高效迭代牛顿-欧拉方法对一个21自由度的轮式移动仿人机器人进行了整体动力学建模,该模型虽然维数较高,但消除了分块建模中需要对模块之间相互作用力进行建模的难点问题,并且由于机器人双臂的对称结构,当合理规划双臂运动时,动力学模型将得到部分简化。本文还对某关节运动时在各个关节所产生的力或力矩进行了仿真分析。解析及仿真结果表明,合理规划上臂各关节的协调运动,将极大地削弱车体及腰部各关节所受的力或力矩扰动,为基于动力学的机器人运动控制以及稳定性分析提供理论依据。

基于多种群遗传算法的波能装置的优化设计及分析

作为可再生能源,波浪能的吸收和利用一直是国内外热点研究内容之一。本文提出一种新的基于惯性摆结构的波浪能吸收转换方法,对这种结构在波浪力作用下的频域响应进行了分析,建立了其最优化能量获取模型,提出采用多种群遗传算法对其结构进行优化设计,并针对系统所受波浪力(矩)随载体半径改变而改变,且求取困难的问题,采用最小二乘法对波浪力(矩)与载体半径变化的关系进行了拟和。通过优化结果找出影响结构获取波浪能量的因素,仿真结果表明了方法的先进性,为进一步的应用研究和频域波能获取研究奠定了基础。

输电线巡检机器人行走动力特性与位姿分析

根据跨越超高压输电线路障碍物的类型,提出一种新的双臂自主越障巡检机器人机构。该机器人采用复合轮爪机构在架空地线上连续行走并跨越障碍。由于架空地线呈悬链线状,机器人在连续行走过程中会出现上坡和下坡,对行走动力特性的影响非常明显。在上坡时行走电动机提供驱动力矩,在下坡时行走电动机提供制动力矩,以保持匀速巡线。详细分析了机器人在架空地线上行走时所处的加速、匀速、减速和停止的各个状态,驱动机器人所需的驱动力矩以及它们与机构参数之间的关系,并应用优化方法给出各个状态电动机驱动力矩最小时,机器人机构参数对应的最优解,为巡检机器人的设计和控制系统方案的确定提供了理论依据。