弧面分度凸轮机构的固有频率分析

以弧面分度凸轮机构为对象,建立了考虑其输入/输出轴的扭转、弯曲刚度及凸轮曲面与滚子间接触刚度等多种因素的动力学模型,在此基础上,重点分析接触刚度、凸轮与分度盘滚子啮合个数的变化、运动规律对系统固有频率的影响。实验结果表明,所建立的动力学模型具有较高的计算精度。     

Natural frequency and mode shape analysis of structures with uncertainty

Two methods called random factor method (RFM) and interval factor method (IFM) for the natural frequency and mode shape analysis of truss structures with uncertain parameters are presented in this paper. Using the RFM, the structural physical parameters and geometry can be considered as random variables. The structural stiffness and mass matrices can then, respectively, be described by the product of two parts corresponding to the random factors and the deterministic matrix. The structural natural frequencies, mode shapes and random response can be expressed as the function of the random factors. By means of the random variable's algebra synthesis method, the computational expressions for the mean value and standard deviation of natural frequencies and mode shapes are derived from the Rayleigh quotient. Using the IFM, the structural parameters can be considered as interval variables and the computational expressions for the lower and upper bounds of the natural frequency and mode shape are derived by means of the interval operations. The effect of uncertainty of individual structural parameters on structural dynamic characteristics, and the comparison of structural natural frequency and mode shape using the RFM and IFM are demonstrated by truss structures.     

高频半导体激光器的驱动设计及稳定性分析

通过系统地分析影响LD稳定性的主要因素,设计出了计算机实时检测反馈、闭环控制、脉冲稳流的高频LD驱动电源。采用抑制浪涌,减小纹波以及加入延时和软启动电路等多项安全设计及措施确保LD工作的安全性。并且采用半导体制冷片,结合计算机实时检测电路对LD工作温度进行精确控制。初步测量得到LD激光稳定输出功率150 W,温度稳定电路的控温精度达到0.2 ℃,激光频宽为6 GHz的实验结果。     

不同连接形式桁架结构的有限元分析

1问题的提出 工程结构桁架铰接、铆接与焊接这3种不同连接形式如图1所示。 假设一平面桁架,该桁架节点编号、杆件编号及约束条件如图2所示,各杆均为圆形截面,直径为10mm,长为200mm,在节点2作用一大小为1000N的向下集中力。对此桁架各节点处分别为铰接、铆接与焊接这3种不同连接形式时进行有限元分析。     

Performance measurement analysis of various cone flow meters with various beta edge types and flow field parameters

The beta edge, as one part of the cone element in cone flow meters, has several types. Cone flow meters with different beta edges have different applications and measurement performance. The sharp angle, corner cut and arc are the most common forms of beta edges used in cone flow meters. Their structures are analyzed without changing other parameters. Through theoretical analysis of their hydromechanics, a conclusion can be drawn that the discharge coefficient linearity error and permanent pressure loss in cone flow meters can be predicted based on the consistency in the recirculation quantity and the dissipation function value. The research objects are cone flow meters with different beta edge forms whose inner tube diameter is 100 mm and whose β values are 0.45, 0.55 and 0.65. The cone wake flow field characteristics were obtained and analyzed using the CFD method. Different beta edges cause different changes to the recirculation quantity and the dissipation in the cone wake flow region. Based on the theoretical prediction, the corner cut beta edge has the best discharge coefficient linearity error and relatively small permanent pressure loss. The accuracy of this prediction was experimentally verified. The experimental results demonstrate that the sharp-angle beta edge achieves the best performance in mechanical processing consistency, while the arc beta edge is the worst.     

Three degrees of freedom stability analysis in the milling with bull-nosed end mills

Automated packaging is becoming more and more interesting for production sites. However, in many companies, the packaging process can only handle a limited amount of products. Most of the time for new products, the packaging system needs to be modified. One of the main components in an automated packaging process is the grasping of the objects that need to be packed. For different products, mostly a different gripping system is required. In this paper, solutions from a research project are presented which enables the flexible grasping of different products. These solutions include flexible pose recognition for different objects, path planning for the recognized objects and finally, a prototypical design for a flexible gripper, which enables handling of various objects of different weight and size.     

Discharge coefficient for vertical sluice gate under submerged condition using contraction and energy loss coefficients

A novel method is suggested for the determination of flow discharge in vertical sluice gates with considerably small bias. First, in order to derive an equation for the discharge coefficient, energy-momentum equations are implemented to define the physical realization of the phenomenon. Afterward, the discharge coefficient is presented in terms of contraction and energy loss coefficients. Subsequently, discharge coefficient, contraction, and energy loss coefficients were determined through an implicit optimization technique on the data. Data analysis illustrated that there is a meaningful power relationship between the contraction and energy loss coefficients. Thereafter, dimensional analysis is performed and an explicit best-fit regression equation is developed for defining the energy loss coefficient. The obtained equations for contraction and energy loss coefficients were then used in the computation of the discharge coefficient and determination of the flow discharge in the vertical sluice gate. The performance of the developed approach is validated against the selected benchmarks existing in the literature.     

薄膜蒸发器转子系统固有频率及稳态不平衡响应分析

薄膜蒸发器转子系统中的不平衡力易导致转子振幅加大,从而加剧刮板磨损,导致刮板失效.采用VB对ANSYS进行二次开发,对薄膜蒸发器转子系统进行模态分析,并对转子某些位置上的不平衡量进行了稳态不平衡响应分析,初步实现了薄膜蒸发器转子动力学分析,为薄膜蒸发器设计及安全运行提供依据.     

Timoshenko beam-based stability and natural frequency analysis for heavy load mechanical spindles

The heavy load mechanical spindle is an important functional component in a 5-axis computer numerical control (CNC) machine tool, which is used to process large and complex free-form surfaces. It is necessary to obtain the natural frequency and analyze the spindle stability for improving the machining precision. In this paper, Timoshenko beam theory is introduced to model the mechanical spindle shaft, where the centrifugal force and gyroscopic effects are considered. Stability of the heavy load mechanical spindle shaft is analyzed, and the buckling load of the spindle shaft is obtained under different rotational speeds. The natural frequency of spindle is investigated in a freedom and restraint state, respectively. Comparing the proposed method with the simplified hollow cylinder and shaft prototype in the freedom state, the results show that they are highly correlated with experimental results. For the restraint state, the axial load, rotational speed, gyroscopic effect, and centrifugal force are discussed, and all of these parameters affect the natural frequency. The proposed modeling approach can be used for spindle design and optimization in a given machining process and can be easily extended to other spindle design.     

3-dimensional microscope analysis of bone and tooth surface modifications: comparisons of fossil specimens and replicas

Cut-marks on fossil bones and teeth are an important source of evidence in the reconstruction of ancient butchery practices. The analysis of butchery marks has allowed archaeologists to interpret aspects of past subsistence strategies and the behavior of early humans. Recent advances in optical scanning microscopy allow detailed measurements of cut-mark morphology to be undertaken. An example of this technology is the Alicona 3D InfiniteFocus imaging microscope, which has been applied recently to the study of surface modifications on bones and teeth. Three-dimensional models generated by the Alicona microscope have been used to identify cross-sectional features of experimental cut-marks that are characteristic for specific cutting actions (e.g., slicing, chopping, scraping) and different tool types (e.g., metal versus stone tools). More recently, this technology has been applied successfully to the analysis of ～500,000 year-old cut-marked animal bones from Boxgrove (U.K.), as well as cannibalized 14,700 cal BP year-old human bones from Gough's Cave (U.K.). This article describes molding methods used to replicate fragile prehistoric bones and teeth, where image quality was adversely affected by specimen translucency and reflectivity. Alicona images generated from molds and casts are often of better quality than those of the original specimen.     

Influence of tooth profile and oil formulation on gear power loss

Nowadays power losses are a main concern in transmission systems and the friction between gear teeth during the meshing cycle is one of the main sources. The friction losses reduction is mandatory to promote lower energy consumption, lower operating temperatures, lower oil oxidation and lower risk of failures.In this study the power losses reduction is obtained using two different approaches: using lower modulus helical gears and significant positive profiles shifts and using gear oil formulations with different base oils.The adopted geometries proved to reduce the power losses considerably, promoting a reduction of oil operating temperature up to 20 K.     

天然牙釉质/纯钛摩擦磨损行为的研究

对天然牙釉质与TA2纯钛球组成的摩擦副进行了实验研究，结合显微分析，研究了牙釉质的摩擦磨损行为。结果表明牙冠外层釉质的摩擦学特性与釉质的基本结构釉柱的排列方向密切相关，釉质在He面上的耐磨性明显优于垂直方向。     

Finite element analysis of head-neck kinematics under simulated rear impact at different accelerations

The information on the variation of ligament strains over time after rear impact has been seldom investigated. In the current study, a detailed three-dimensional C0-C7 finite element model of the whole head-neck complex developed previously was modified to include T1 vertebra. Rear impact of half sine-pulses with peak values of 3.5g, 5g, 6.5g and 8g respectively were applied to the inferior surface of the T1 vertebral body to validate the simulated variations of the intervertebral segmental rotations and to investigate the ligament tensions of the cervical spine under different levels of accelerations. The simulated kinematics of the head-neck complex showed relatively good agreement with the experimental data with most of the predicted peak values falling within one standard deviation of the experimental data. Under rear impact, the whole C0-T1 structure formed an S-shaped curvature with flexion at the upper levels and extension at the lower levels at early stage after impact, during which the lower cervical levels might experience hyperextensions. The predicted high resultant strain of the capsular ligaments, even at low impact acceleration compared with other ligament groups, suggests their susceptibility to injury. The peak impact acceleration has a significant effect on the potential injury of ligaments. Under higher accelerations, most ligaments will reach failure strain in a much shorter time immediately after impact.     

Linear stability analysis of hydrodynamic journal bearings under micropolar lubrication

The dynamic characteristics of hydrodynamic journal bearings lubricated with micropolar fluids are presented. The modified Reynolds equation is obtained using the micropolar lubrication theory. Applying the first order perturbation of the film thickness and steady state film pressure, the dynamic characteristics in terms of the components of stiffness and damping coefficients, critical mass parameter and whirl ratio are obtained with respect to the micropolar property for varying eccentricity ratios and slenderness ratios. The results show that micropolar fluid exhibits better stability in comparison with Newtonian fluid.     

不同外载作用下特殊螺纹油管接头应力有限元分析

为确保足够的连接强度,联接入井的特殊螺纹接头密封面、扭矩台肩处的密封副必须保持合理的应力水平。文中以某特殊螺纹接头为例,通过ANSYS有限元软件进行应力分析,得到了内压、轴向力及复合载荷等不同载荷作用下油管接头的应力分布规律。结论表明:内压与轴向拉力复合作用时,随着轴向拉力的增大,最大等效应力点由密封面逐渐向大端螺纹处转移;复合载荷作用下,该特殊螺纹接头两端仍有较大的应力集中现象,存在应力不均问题,应该进一步优化设计螺纹参数。     

Time–frequency analysis of friction-induced vibration under reciprocating sliding conditions

A time–frequency analysis can give an overall view of the behaviour of friction-induced vibration. In this paper, short-time Fourier transform (STFT), Wigner–Ville distribution (WVD), Choi–Williams distribution (CWD) and Zhao–Atlas–Marks distribution (ZAMD) are applied to analyze time–frequency characteristics of friction-induced vibration. The result shows that there is always a frequency change in the time–frequency presentation of vibration in the location where the vibration is bounded. The frequency changes in time–frequency presentations are associated with nonlinearity of vibration systems. The nonlinearity may be counted as the evidence to support the consideration that friction-induced vibrations are bounded by limit cycles due to the system nonlinearity. Based on the time–frequency presentations of vibrations, it may be concluded that the friction vibration system is generally a linear system in the phase of vibration initiation but is a nonlinear system in the phases of vibration being bounded and disappearance.     

不同支承条件下梁结构弯曲振动的固有特性

根据梁模型端部的四种不同支承条件,将梁模型区分为一般支承梁、弹性支承梁、约束简支梁和约束悬臂梁四种,分别由各自的边界条件和梁弯曲振动模态函数的一般表达式推导出了这四种不同支承条件下梁模型弯曲振动的模态函数及其频率方程,计算得到了四种支承条件下梁模型的前两阶振动模态,具体分析了支承刚度对其特征值的影响.根据该方法,可以得出任意约束刚度下梁弯曲振动的任一模态及其特征值,其结果可以直接用于工程设计与分析.对于各种支承条件下的弹性约束刚度,根据梁的实际支承情况合理选取.     

渐开线谐波齿轮空间齿廓设计及仿真分析

针对杯形柔轮在波发生器作用下的锥度变形特征造成垂直于回转轴的横截面内中面变形曲线差异的问题,设计刚轮空间齿廓以提高谐波齿轮的啮合性能。基于杯形柔轮的空间变性特征,将刚轮空间齿廓设计转化为垂直于轴线的多个横截面内的平面齿廓设计。设计了与变形后的柔轮齿廓实现空间啮合的刚轮空间齿廓设计方法,及其啮合齿面间的侧隙计算方法。基于多个平面内的共轭齿廓,利用放样算法生成空间齿廓,并进行干涉检查和侧隙结果验证。验证表明:空间齿廓能增大啮合区间和齿廓接触面积;采用两截面直引导线的放样方法生成的空间齿廓与多个截面内设计的共轭齿廓差别不大,可以满足一般精度的谐波齿廓传动的设计要求。     

电力液压推动器结构与性能比较

电力液压推动器主要是作为块式、盘式制动器的驱动装置,广泛地应用于起重机等各种机器和机构的机械制动。若通过电器控制和杠杆机构使其实现顶压、往复、摇摆、圆周等运动形式,还可派上更多的用场。我国现产的电力液压推动器,除了本世纪60年代上海起重电器厂推出的YT1型双推杆系列产品,80年代中期原焦作制动器厂还引起了原西德EMC公司的Ed型单推杆系列产品,与此同时,我国各制动器生产厂家也先后推出了YT２、YT３、YT４、YT５、YT６等各型单推杆系列产品。1996年,我国在已有的YT１型双推杆及Ed型等各单推杆系列产品基础上,经…     

Design and stability analysis of impedance controller for bilateral teleoperation under a time delay

A new impedance controller is proposed for bilateral teleoperation under a time delay. The proposed controller does not need to measure or estimate the time delay in the communication channel using the force loop-back. In designing a stable impedance controller, absolute stability is used as a stability analysis tool, which results in a less conservative controller than the passivity concept. Moreover, in order to remove the conservatism associated with the assumption of infinite port impedances, the boundaries of human and environment impedance are set to finite values. Based on this, this paper proposes a parameter design procedure for stable impedance controllers. The validity of the proposed control scheme is demonstrated by experiments with a 1-dof master/slave system.