The stabilization of the position of the body of walking machinesLa stabilisation de la position du corps d'une machine marchante

This paper shows that in the task of the maintenance of constant orientation of the body of a walking robot the determination of the actual position of the body, i.e. absolute altitudes of its points and remoteness from the supporting surface, is the most complicated problem. Two possible systems of measurement and stabilization of the position by the height of the body of the walking mechanism are compared, i.e. a system of adaptation automatically adjusting the length of the supporting leg to the roughness of the terrain, and the system of the maintenance of constant remoteness of the body from the terrain. The inefficiency of a solitary application of any described system is revealed and the possibility of an accumulation of errors of the position of the body by the walking on the soft terrain is shown. Possible approaches for raising the quality of stabilization of the body by the walking are evaluated.     

Numerical study on the dynamics of an electrical discharge generated vapor bubble in EDM with different shapes of the tool and the workpiece

In this paper, the effect of the shapes of the tool and the workpiece on the dynamic behavior of an electrical discharge generated vapor bubble in the process of EDM (Electrical Discharge Machining) is investigated. The boundary integral equation method is employed for numerical simulation of the problem. Results show that in the case of the concave tool and workpiece the lifetime of the electrical discharge generated vapor bubble is longer than the case of the flat tool and workpiece. By increasing the concavity of the shapes of the tool and the workpiece, the lifetime of the bubble increases. Results also show that in the case of the convex tool and workpiece, the lifetime of the electrical discharge generated vapor bubble is shorter than the lifetime of the bubble in the case of the flat tool and workpiece. In this case also, by increasing the convexity of the shapes of the tool and the workpiece, the lifetime of the bubble decreases. Numerical results show that in the case of the concave tool and workpiece the rate of pressure drop on the surface of the workpiece is higher than the rate of pressure drop on the workpiece in the cases of the flat and convex tool and workpiece. The high rate of pressure drop on the surface of the workpiece leads to the ejection of more molten material from the crater and consequently leads to more material removal rate.     

新型十字摆盘驱动式水液压轴向柱塞泵阀配流系统设计

针对一种新型十字摆盘驱动式水液压轴向柱塞泵的配流阀系统结构参数与泵转速、柱塞直径不匹配导致的容积效率不足的问题,搭建了该新型泵的ADAMS-AMESim固液耦合仿真模型。在额定转速下,分析了配流阀阀芯质量、弹簧刚度、弹簧预紧力、阀芯球面直径对其容积效率的影响,并对其配流系统进行优化设计。结果表明:新型泵的容积效率随着配流阀弹簧刚度、预紧力的增加而增加,随着配流阀阀芯质量、阀芯球面直径的增加而减少,且吸液阀结构参数的变化对容积效率影响大于排液阀。因此,在设计新型泵的配流阀时可适当提高阀芯复位弹簧刚度和预紧力,适当减小阀芯质量和阀芯球面直径,以提高新型泵的容积效率。     

Synchronization of two non-identical coupled exciters in a non-resonant vibrating system of plane motion

In the average method of modified small parameters, the synchronization of two coupled exciters is converted to a problem on the existence and stability of zero solutions for the average differential equations of small parameters over the average period of two exciters. To implement frequency capture, the torque of frequency capture should be greater than or equal to the absolute value of the difference between the residual electromagnetic torques of the two motors. Because each exciter is involved in the motion of the vibrating system it has excited, its relative moment of inertia is reduced. The reduction is proportional to half its coefficient of cosine effect of phase angles (CCEPA). Because one of the exciters is involved in the motion excited by the other, a coupled moment of inertia exists for the two exciters. The stability of the synchronization of the two exciters is affected by the reduction of their relative moments of inertia and their moment of coupling inertia. For the synchronization to be stable, two conditions must be satisfied: (1) the non-dimensional relative moments of inertia of the two exciters are all greater than zero, and (2) four times the product of their non-dimensional relative moments is greater than the square of the coefficient of coupled cosine effect (CCCPA). The stability of synchronization depends solely on the ratios of the masses of the two exciters to the mass of the vibrating system and the ratio of the distance between one exciter and the centroid of the rigid frame to the equivalent rotating radius of the vibrating system about its centroid of the rigid frame, and is independent of the parameters of the two induction motors.     

基于柔性动力学的辊道窑烧结过程匣钵运动特性分析

盛装锂电正极材料的匣钵在辊道窑烧结过程中极易出现异常横向运动,为此基于柔性动力学分析辊道柔性对传动过程匣钵运动特性的影响。首先,基于柔性动力学建立匣钵-辊道传动动力学简化模型,分析辊棒弹性变形及传送时匣钵运动特性,并通过实验验证了模型的有效性;其次,建立相应的匣钵-辊道刚体动力学模型,通过对比分析刚性和柔性两种辊棒传送条件下匣钵运动特性的变化以及不同辊棒挠度下匣钵横向运动的变化,揭示辊道柔性对匣钵运动特性的影响。在此基础上,对原有辊棒进行了改进并开展实验验证改进方案的效果。结果表明:由于弹性变形的影响,匣钵在前行的同时,匣钵之间间隙出现了明显向外扩张趋势,而当辊棒呈现刚性时匣钵则几乎无外扩现象;辊棒挠度对横向运动有重要影响,在辊棒挠度从0到2 mm区间变化时,其匣钵扩展间隙随挠度增加而呈增大趋势,而当辊棒挠度超过2 mm后,匣钵扩展间隙随挠度增加反而呈减小趋势。改进实验效果表明,适当增大辊棒刚度可显著减轻匣钵异常横向运动现象。     

柴油机微粒捕捉器电加热再生控制系统及控制策略的研究

柴油机微粒捕捉器热再生系统实用化的关键在于对过滤体的可靠再生,而过滤体的可靠再生则取决于对再生过程的有效控制。根据开发的柴油机排气微粒捕捉器电加热再生系统实用化的需要,提出了利用排气气流对过滤体再生过程进行控制的思想,分析了影响微粒捕捉器电加热再生过程的各种因素。在此基础上,进行了微粒捕捉器电加热再生控制系统设计,确定了再生系统的控制策略。     

管片拼装机回转系统齿轮啮合动力学分析

为了研究管片拼装机回转系统齿轮啮合的动力学特性,以管片拼装机小齿轮-大齿圈的传动系统为研究对象,采用集中参数法建立了考虑齿面摩擦的六自由度直齿轮动力学模型,依据管片拼装机实际工况参数,利用Runge-Kutta方法分析了管片拼装机回转系统在空载和负载两种工况下小齿轮和大齿圈的振动位移情况,对管片拼装机回转系统进行了振动测试,验证了模型及求解的正确性,并提出了可以通过增大管片拼装机回转系统刚度来减小振动的方法。研究结果对管片拼装机回转系统的减振和降噪处理,以及提高管片拼装机回转系统的精度有重要的理论和实用价值。     

刀面粗糙度及刀刃锯齿状态对已加工表面质量的影响

为研究刀面粗糙度及刀刃锯齿状态对已加工表面质量的影响,特别采用不同刀面粗糙度和刀刃锯齿状态的硬质合金刀具进行薄切削铝合金的对比试验。试验表明:刀具各刀面粗糙度对已加工表面粗糙度和加工硬化有较大影响,刀面粗糙度增大,已加工表面粗糙度和加工硬化随之增大;刀刃锯齿状态对巳加工表面质量的影响程度可用锯齿影响系数来表征,随着锯齿影响系数的增大,巳加工表面粗糙度和加工硬化程度也增大。     

哈佛大学监事会章程的调整与变革

监事会章程是哈佛大学章程体系的重要组成部分.1781～1869年间,哈佛大学监事会章程进行了一系列修订和变革,扩大了监事会的自主权力,调整了监事会成员的选举制度和办法,加强了对宗教人士和政府官员作为监事会成员的限制,增加了校友等校外人士.监事会成员结构呈现出多元化、世俗化趋势.通过考察哈佛大学监事会成员结构的变化以及校友、教师等世俗力量的加强对哈佛大学发展所产生的影响,发现大学章程在大学治理结构中具有重要的地位和作用.     

落地铣镗床主轴箱平衡补偿系统故障诊断与维修

针对落地铣镗床主轴箱平衡补偿系统故障诊断问题,首先通过主轴箱受力分析,获得滑枕伸出前、后钢丝绳受力变化规律,结合平衡补偿系统液压原理,分析得出钢丝绳前吊点液压平衡缸动作逻辑,为PLC程序逻辑修改提供依据;然后开展滑枕伸出直线度检测试验,得到不同伸出量对应的液压平衡缸电液比例阀控制电压,从而确定PLC程序非线性控制电压;...     

变焦系统中可调光焦度器件初值分析

为了实现变焦系统中可调光焦度器件初值分析，对可调光焦度器件的变焦系统进行了像差分析。根据变焦系统的光束孔径角和成像物高等特征参数确定系统初级像差，并以像差独立性的原理分析共轴可调光焦度器件变焦系统。采用薄透镜像差理论分析形状参数与变焦系统放大率的关系，应用球差和彗差最小值对可调光焦度变焦系统初值进行确定。结果表明，采用变焦系统放大率与形状参数的计算方法可满足变焦系统中可调光焦度器件初值的确定要求，并具有简单、快速、可靠等特点，为进一步计算机校正变焦系统像差提供了参考。     

旁通泄漏与摆动式叶片马达最低稳定角速度的关系

摆动式叶片马达的内泄漏量直接影响其输出角速度大小;文章建立了带有旁路泄漏通道摆动马达的传递函数;在系统传递函数建立过程中,以马达工作腔输入流量为输入,马达输出角速度为输出,考虑旁通泄漏模型以及马达摩擦力矩模型,推导出马达最低稳定速度的表达式;通过分析旁路泄漏通道的参数对于马达最低稳定运行速度的影响,从而给出马达最低稳定速度与马达内泄漏、旁路泄漏通道参数之间的关系,并提出了马达最低稳定速度对应输入流量的计算方法。     

截割头几何因素影响下的巷道表面形貌特征与建模

考虑到纵轴式掘进机截割头运动轨迹直接影响巷道成形表面形貌特征，分析了截割头截割巷道得到的巷道外轮廓的创成机理，运用机器人运动学分析方法确定掘进机截割头在巷道空间坐标系内的坐标，构建截割头截割巷道外轮廓的数学模型；通过数值计算分析截割进给量、截割角度、截割头形状、截割头半径及截割头锥角等参数对截割表面形貌特征的影响规律。研究结果表明：“球冠+圆柱”式截割头截割得到的巷道表面最不平整，“球冠+圆锥+圆柱”式截割头截割得到的巷道表面最为平整；随着截割升降角度和截割进给量的减小、截割头球冠半径和截割头圆锥角的增大，截割得到的巷道平整度提高；截割升降角度越大，越需要对巷道平整度进行精确控制。     

A mechanism of lubricant trapping in slow speed compression

A mechanism for the trapping of liquid lubricant in compressive metal forming is suggested. The basis of this mechanism is the interaction of elastic deformation of the tool and the hydrodynamic behaviour of the lubricant. A computer simulation of the process of slow speed compression of a cylindrical rigid-plastic billet between semi-infinite elastic tools with films of lubricant illustrates the validity of the proposed mechanism. From the result of the simulation together with dimensional analysis, the thickness of the trapped lubricant film is determined as a function of the lubricant viscosity, the elastic constant of the tool, the speed of compression and the radius of the billet.     

螺旋式泵效环结构参数对泵送性能的影响

为研究机械密封用螺旋式泵效环的结构参数对其泵送性能的影响,利用Fluent对不同结构参数的螺旋式泵效环内部流场进行数值模拟,使用模拟得到的泵效环内部流场的压力计算出泵效环的扬程,并获取流量-扬程性能曲线,分析不同结构参数对螺旋式泵效环的流量-扬程关系的影响。结果表明:螺旋槽轴向槽宽、泵效环外径与过渡座内径之间的间隙对泵送性能影响明显,增加螺旋槽轴向槽宽,扬程先增加后减小,增加泵效环外径与过渡座内径之间的间隙,扬程明显减小;泵效环螺纹头数、螺旋槽槽深、螺旋槽螺旋长度对泵送性能也有一定的影响,增加螺纹头数,扬程先增加后减小,增加螺旋槽槽深和螺旋槽螺旋长度,扬程均增加。     

Method for Determination of the Inertia Characteristics of Bodies

A method for determination of the mass, of the coordinates of the center of mass, and of the tensor of body inertia was developed. The peculiarity of this method is that we have set for the body under study the rotation and finite fixed linear and angular displacements. The response of the dynamic system of the measuring bench to the changes in the location of the masses of the body and of the test load on a rotating platform contains all the information on the inertia characteristics of the body.     

丝杠冷滚打变形力影响因素研究

为研究丝杠冷滚打成形过程中滚打轮半径、滚打轮圆角半径和打入量与变形力之间的关系,在丝杠冷滚打成形原理的基础上建立了有限元仿真模型。通过仿真获得单次滚打以及多次滚打成形过程中,变形力随滚打轮半径、滚打轮圆角半径和打入量的变化规律;设计了正交试验,研究打入量、滚打轴转速、滚打轮厚度及工件转速4个因素对变形力的影响规律。在自行设计的冷滚打成形丝杠设备上进行实验,测得变形力的变化趋势与仿真结果基本一致,验证了有限元仿真模型的正确性。     

五轴电火花机床加工空间斜孔的电极定位参数研究

空间斜孔的加工实质上是电火花机床电极沿孔的轴线的运动。对于由3个坐标轴旋转变换得到的空间斜孔,可通过五轴电火花机床沿3个坐标轴方向上的平移运动和绕两个坐标轴方向的旋转运动,使机床电极轴线与空间斜孔轴线重合,为此需要求解加工空间斜孔的电极定位参数。分析了通过坐标系旋转平移变换得到空间斜孔轴线的过程。根据空间斜孔的空间角度和几何参数求解空间斜孔轴线矢量的坐标变换矩阵,以建立空间斜孔轴线的矢量模型。得到了五轴数控电火花机床加工空间斜孔的电极摆角和电极定位坐标,使电极轴线与空间斜孔轴线重合。并制作了根据空间斜孔几何参数自动求解数控电火花机床的电极摆角和电极坐标的计算软件。     

轻量化高精度反射面天线保型设计与动静态特性分析

为满足某型号工程的测控需求,设计了一种新型轻量化高精度反射面天线,满足天线系统高精度、轻量化、过顶跟踪的要求。基于三自由度调整方法和天线反射体轻量化技术,采用面板整体互连的结构保型设计方案,有效减轻了天线反射体的整体质量,达到了较高的天线主面再装精度。基于ANSYS有限元分析软件,对天线反射体进行静力特性分析、面形精度分析、安全性校核,结果表明在典型俯仰角下,天线主面精度及承载能力满足要求。通过动态特性分析,得到了天线反射体的各阶固有频率和振型。经过天线主面精度测试和系统指标实测,确认天线的各项指标满足要求,并且可以实现对低轨卫星的稳定跟踪。     

敷设阻尼薄板隔声性能的测试与计算分析

首先,采用脉冲响应衰减法测试了敷设阻尼薄板的阻尼损耗因子,分析了阻尼敷设比例及薄板的悬挂状态对薄板阻尼损耗因子的影响;其次,在混响-全消室中测试了敷设阻尼薄板的隔声量,比较了不同阻尼敷设比例薄板的测试结果;最后,建立了敷设阻尼薄板隔声量计算分析模型,隔声量计算值与试验值吻合较好,验证了计算模型的有效性。研究了敷设阻尼材料厚度与敷设比例对薄板结构隔声性能的影响,综合考虑轻量化和隔声性能,分析了阻尼材料厚度与敷设比例对薄板降噪效率的影响,并以降噪效率最大为目标进行了薄板隔声特性的优化。