Design, manufacture and evaluation of a new and simple mechanism for transmission of power between intersecting shafts up to 135 degrees (Persian Joint)

This paper introduces a new mechanism which is designed for the transmission of power between two intersecting shafts. The mechanism consists of one drive shaft and one driven shaft, six guide arms, and three connecting arms. The intersecting angle between the input shaft and the output shaft can be varied up to 135° while the velocity ratio between the two shafts remains constant. The research also includes a kinematic analysis and a simulation using Visual NASTRAN, Autodesk Inventor Dynamic and COSMOS Motion. The softwares showed that this mechanism can transmit constant velocity ratios at all angles between two shafts. By comparing the graphs of analytical analysis and simulation analysis, validity of equations was proved. Finally, by fabrication and evaluation of the mechanism it was shown that this mechanism can transmit constant velocity practically.     

Quantitative analysis of microstructure refinement in ultrafine-grained strips of Al6063 fabricated using large strain extrusion machining

Abstract

In present research work, ultrafine-grained strips of Al-6063 alloy were fabricated using hybrid extrusion machining technique known as “large strain extrusion machining (LSEM).” Fabrication of strips was done using the customized HSS tools of different rake angles varying from 0° to 10° under different machining conditions. Microstructural and mechanical characterizations of these strips were done to ascertain the effect of different parameters on their properties. From the results of hardness measurement of strips, it was concluded that hardness of the strips increased by 34–97% of the base material as of the refinement of grain size occurred. Surface lay was improved by 30% with higher cutting velocity and rake angle. Crystallite size was found to decrease with increase in the rate of strain. The shear strain was increased as chip compression ratio increased and rake angle decreased. Fabrication ability of strips increased due to increase in strain hardening exponent and it may result in the large scope of their applications. Nano-hardness of the strips was found to be more than bulk alloy. These above said results showed that ultrafine strips fabricated using LSEM process can become a good choice for future material fabrication.     

采用微分法确定曲柄滑块机构最大行程速比系数

曲柄滑块机构,瞬间传动角愈大,其运动性能愈好;单向工作的曲柄滑块机构,行程速比系数愈大,急回特性愈强,工作效率愈高.采用微分法,以机构允许的最小传动角[γ]为设计依据,以机构行程速比系数为函数,对设计变量求导联立,导出机构能够实现最大行程速比系数kmax的函数表达式,绘制出函数曲线,并得出结论:机构最大行程速比系数k一只与许用传动角[γ]有关,且随着[γ]增大而减小.     

基于特征提取与识别两阶段的汽车电机轴承故障诊断

针对特征提取和故障识别这两个轴承故障诊断的关键环节,提出一种汽车电机轴承故障诊断新方法。该方法在特征提取环节:提出了将LCD分解和符号熵(SE)相结合的特征提取方法;在故障识别环节为提高果蝇算法(FOA)对相关向量机(RVM)参数的寻优能力,在FOA算法中增加了向"历史"学习的策略,提出具有历史学习能力的果蝇算法(HSAFOA),有效地提升了RVM的分类性能。汽车电机轴承不同类型、不同程度故障诊断实例表明,LCD符号熵可有效对故障进行表征,而HSAFOA算法则提升了RVM的识别效果,相比于其他一些方法更有优势。     

Upper Bound Analysis of Turning Using Sharp Corner Tools

A generalized upper bound model of turning operations using flat-faced sharp corner tools with both the side and end cutting edges engaged in cutting is described. The projection of the uncut chip area on the rake face plane is divided into a few regions separated by lines parallel to the chip flow direction at transition points. The area of each of these regions is transformed to the area of the corresponding regions of the shear surface using the ratio of the shear speed to the chip speed. Summing up the area of these regions, the total shear surface area is obtained. The tool-chip contact length at vertices is obtained from the length along the shear surface using the similarity between orthogonal and oblique cutting in the “equivalent” plane (the plane formed by the cutting velocity and chip velocity). Knowing the tool-chip contact length, the friction area is calculated. The chip flow angle and chip speed are obtained by minimizing the cutting power with respect to both these variables. Comparison of the chip flow angle predicted by the current model with the chip flow angle measured by direct high speed photography of the chip motion over the tool rake face shows good correlation between the two for various tool geometries and cutting conditions. The shape of the shear surface and the chip cross section predicted by the model are also presented.     

离心式水泵冲击损失的计算与分析

以降低叶轮进口冲击损失为目标,对进口边为径向和轴向两种情况下的叶轮进口条件进行了优化,得到了相应的进口直径计算公式。分析了离心泵叶轮进口冲击损失的形成机理,计算并分析了冲击损失随流量和冲角变化的关系。基于此研究分析了流量和进口冲角对冲击损失的影响,得出了进口冲击损失值在设计和非设计流量下的变化趋势,为泵产品的性能预测提供了理论和技术支持。     

圆柱分度凸轮单侧面加工及误差计算方法研究

应用空间啮合原理和旋转变换矩阵理论，推导了圆锥滚子从动件圆柱分度凸轮的理论工作廓面方程及单侧面加工凸轮实际工作廓面方程；廓面采取单侧面加工时，给出了刀具误差对凸轮廓面法向误差影响的精确计算方法和近似计算方法，解决了空间凸轮廓面误差计算的难题，进一步完善了圆柱分度凸轮机构的设计和制造理论。     

大转角柔性铰链的结构设计及转动刚度研究

为满足航天可展结构需要,提出了一种大转角柔性铰链,其转动角度可达180°。借助几何运动学理论,进行了大转角柔性铰链的结构设计;并对柔性体的尺寸、啮合曲面轮廓、转动刚度、储存能量等关键问题进行了理论分析。得出了柔性体最小长度、厚度与柔性体转动时的最小弯曲半径之间的关系;给出了啮合面的轮廓计算、铰链的转动刚度、柔性铰链储存能量的计算解析表达式。这一柔性铰链的提出及关键问题的解决为相关领域的研究应用提供了重要的参考。     

Entropy generation from hydrogen production of catalytic partial oxidation of methane with excess enthalpy recovery

Catalytic partial oxidation of methane (CPOM) is an important route for producing hydrogen and it is featured by autothermal reaction. To recognize the reaction characteristics of CPOM, H₂ production and entropy generation from CPOM in Swiss-roll reactors are studied numerically. The considered parameters affecting the performance of CPOM include the excess enthalpy recovery, gas hourly space velocity (GHSV), number of turns and atomic O/C ratio. The impact of chemical reactions, heat transfer and friction on entropy generation is also analyzed. The results indicate that preheating reactants through waste heat recovery as well as increasing GHSV or number of turns is conducive to enhancing H₂ yield, whereas the maximum H₂ yield develops at O/C = 1.2. A higher H₂ yield is always accompanied by a higher value of entropy generation, and chemical reactions are the main source of entropy generation, especially from steam methane reforming. In contrast, viscous dissipation almost plays no part on entropy generation, compared to heat transfer and chemical reactions. From the analysis of entropy generation, detailed mechanisms of H₂ production from CPOM can be figured out.