关键词： Robust control  

摘要： The paper highlights the potentials of using a feedforward model based Active Force Control (AFC) as a disturbance rejection scheme in the motion control of a mobile manipulator (MM). The AFC part creates a force or torque feedback within the dynamic system to allow for the compensation of the sudden disturbance introduced into the system prior to relaying the signal to the conventional outerloop position controller employing a resolved acceleration control (RAC) configuration, thereby increasing the robustness of the MM system. The proposed AFC-based model also shows a faster computational performance by manipulating the estimated inertia matrix (IN) of the system instead of considering the entire system dynamic model. A feedforward element in the form of a simplified model of the dynamic system is implemented to complement the IN for a better trajectory tracking performance of the system. The simulation was performed and the results were compared with the computed torque control (CTC) with RAC scheme to benchmark the performance and robustness of the AFC-based counterpart. The MM consists of a skid steering four wheel nonholonomic mobile platform with a three degree-of-freedom (DOF) articulated manipulator attached on top. With the proposed controller incorporated into the system, the tracking performance of the MM is considerably enhanced with increased workspace capacity and better operation dexterity.

关键词： Nd16Fe76B8 alloy   Gas-solid reactions   Phase transitions   Kinetics   Mossbauer spectroscopy  

摘要： The process of mechanically activated disproportionation by ball milling in hydrogen and subsequent desorption-recombination has been proved to be a promising method to produce nanocrystalline NdFeB-type magnets. Aiming to install higher magnetic properties of NdFeB-type magnet, it is crucial to select properly and optimize the desorption-recombination processing temperature and time to achieve a fully recombined microstructure with homogeneous nano-sized Nd2Fe14B grains. Thus, the desorption-recombination kinetics of the as-disproportionated Nd16Fe76B8 (atomic ratio) alloy during vacuum annealing was experimentally investigated using Mossbauer effect, X-ray diffraction and transmission electron microscopy. The effect of processing time and temperature on the desorption-recombination kinetics to form Nd2Fe14B was elucidated and the underlying mechanisms were discussed by referring to the thermal energy input intensity and the Gibbs free energy change for the reaction. The optimum magnetic properties were achieved by vacuum annealing at 780 degrees C for 30 min due to a fully recombination microstructure with uniform grains of 50-55 nm in average size. Furthermore, by applying chemical equation for Mossbauer spectra, the transformed fraction of Nd2Fe14B phase during desorption-recombination process was determined, which increased as f = 1-exp(-kt(n)) with n falling in the range of 0.91-0.97. The kinetic equation, the rate constant, the reaction order exponent, and the activation energy for the desorption-recombination reaction to form Nd2Fe14B during vacuum annealing were obtained by fitting the experimental data with the JMAK theory, and thus the kinetics of desorption-recombination can be quantified and evaluated. (C) 2013 Elsevier B.V. All rights reserved.

关键词： 机械系统   摩擦动力   新进展  

摘要： 摩擦是一种十分普遍的自然现象,并且广泛应用于机械系统中。如何充分利用并且扩大摩擦的功能,并且同时减少摩擦带来的不利影响,是研究摩擦动力学研究的重大意义之一。本文论述了集中摩擦力的特性,介绍了几种常见的摩擦模型以及摩擦系统自激振动,并且阐述了制动噪声形成的机理,简要分析了机械系统摩擦动力最新研究进展。

关键词： 动力车间   检修管理   安全效益   分级管理  

摘要： 为提高设备检修效率,减少检修成本,提高检修质量,对当前本单位机械动力设备检修存在的问题,从设备检修管理、安全效益角度出发,做一个系统的反思,并探究设备检修管理的理念及方式方法,采取多种措施切实提高检修管理水平和检修质量。

关键词： 灰色GM（1   ,   1）模型   BP神经网络   农业机械总动力  

摘要： 本文在灰色GM(1,1)模型基础上,利用BP神经网络修正残差,建立灰色BP神经网络组合预测模型,对农业机械总动力进行预测。此组合模型既克服了数据的非线性关系及随机波动大对预测精度的影响,也增强了预测的自适应性。进而,以郑州市农业机械总动力作为实例进行预测,结果证明了该组合模型的优势,为农业机械总动力预测提供参考依据。

关键词： 机械扰动   富营养化   溶解氧   推动力   数值模拟  

摘要： 选取3种结构相似、倾角和盘面比不同的机械扰动桨叶,安装在3个体积、初始状态相同的试验水池中,在相同的工况下研究其溶氧量和动力学情况。经过47 d后,试验水池的溶氧量相对稳定,稳定后的表层溶氧量平均为6.4、7.1、9.6 mg/L,底层溶氧量平均为6.2、6.9、9.5 mg/L;空白水池的表层和底层溶氧量为5.6、5.3 mg/L。应用Fluent软件对水体运动状态进行数值模拟,并用流速仪进行验证。结果表明,溶解氧的推动力来源于富氧水和贫氧水的相互交换,交换速度越快的桨叶获得的溶解氧越多。

关键词： 储氢合金   活化   动力学   机械合金化  

摘要： 为了研究压力和温度对Mg2Ni储氢合金动力学性能的影响以及吸氢反应机理,采用机械合金化的方法制备了Mg2Ni储氢合金。利用P-C-T测试仪进行活化并测试其吸氢动力学特性,并在实验的基础上结合3种常用的动力学模型分析了Mg2Ni合金吸氢反应的控速步骤。结果表明:Mg2Ni合金在673K、7.4MPa条件下活化3次就能够基本活化完全,吸收1mol氢气所需活化能为43.47kJ;温度对其动力学性能影响不明显,相反压力的影响比较大,吸氢反应速率和吸氢量都随压力的升高而增加;实验结果与JDM和JMA动力学模型比较吻合;金属氢化物形核长大与氢原子在产物层中的扩散过程是Mg2Ni合金吸氢反应的混合控速步骤。

关键词： 混合动力技术   北京理工大学   动力方案   分流式   院长   学院   车辆   机械  

摘要： 节能和减排是当前汽车技术面临的两个主要问题。由于纯电动车的发展存在固有的制约性问题，近年来混合动力技术作为一种主导的发展技术，在各个国家都得到了很好地发展和推动。长安、比亚迪、奇瑞及北京现代等汽车厂商都开发出了混合动力乘用车，而且准备上市。中国政府也出台了很多鼓励纯电动汽车和混合动力汽车走向市场的政策，把新能源汽车产业作为新型战略型产业来推动。

关键词： 胶原纤维   分子动力学模拟   点突变   成骨不全症   机械性能  

摘要： 现代人对胶原机械性能和结构的理解程度，对于生物医学材料以及纳米技术的应用至关重要。而且，点突变与许多胶原类疾病有关，其中包括成骨不全症（OI）。我们进行一系列传统研究以及能够操纵原子的分子动力学模拟，以便检测点突变对于胶原纤维结构和机械性能的影响，包括甘氨酸到丙氨酸、天冬氨酸、半胱氨酸和丝氨酸的突变以及羟脯氨酸到精氨酸、天冬酰胺、谷酰胺和赖氨酸的突变。研究发现，所有点突变均能分散胶原纤维的结构，并降低其强度，从而影响纤维的层堆积。相对于羟脯氨酸突变（wT〉Arg〉Glu〉Asn〉Lys），甘氨酸突变（wT〉Ala〉ser〉cys〉Asp）对纤维的机械强度的影响更为有害。甘氨酸突变的临床表现与通过分子模拟预言纤维可拉伸强度降低的趋势相一致。大体上，胶原纤维机械性能的降低能够预言点突变的临床表现。