Examining the misalignment of a linear guideway pair on a feed drive system under different ball screw preload levels with a cost-effective MEMS vibration sensing system

This paper presents an innovative and cost-effective scheme for examining on line the degree of misalignment of a pair of linear guideway rails in a feed drive system. Prototype MEMS-based vibration detection modules were constructed and installed on the ball screw nut and linear guideway block. The ball screw preload was adjusted with four settings by changing ball sizes in this feed drive system. For each preload setting, a linear guideway rail was adjusted using feeler gauges to produce 11 misalignment statuses. The y-axis deviation caused by misalignment along the feed direction (x-axis) was measured with a dial gauge. For each preload and misalignment setting, the vibration signal was ascertained from the installed detection modules while the work table was driven by the controller. By analyzing the vibration signals from the detection module on the linear guideway block, we found that the characteristic frequency in a specific spectrum band could be used as a misalignment index. The characteristic frequencies exhibited a descending trend when the deviation was less than 40 μm and an increasing trend when the deviation was 40–120 μm. These findings demonstrate the feasibility of using cost-effective sensing units to examine the parallelism or distinguish the deviation between the linear guideway rails without disassembling the work table. This could be valuable for machine intelligence applications in the automation industry.     

Effect of a preload force on anchor system frequency

The interrelationship between preload forces and natural frequencies of anchors was obtained from the structure of an anchor and its mechanical characteristics. We established a numerical model for the dynamic analysis of a bolt support system taking into consideration the working surroundings of the anchor. The natural frequency distribution of the system under various preload forces of the anchor was analyzed with ANSYS. Our results show that each order of the system frequency varied with an increase in preload forces. A single order frequency decreased with an increase in the preload force. A preload force affected low-order frequencies more than high-order frequencies. We obtained a functional relationship by fitting preload forces and fundamental frequencies, which was in agreement with our theoretical considerations. This study provides theoretical support for the detection of preload forces.     

Effects of sustained axial load and cooling phase on post-fire behaviour of reinforced concrete stub columns

In this paper is presented an experimental investigation of the effects of preload and cooling phase on the residual strength, stiffness and ductility of reinforced concrete stub columns which were heated and cooled down to room temperature under sustained axial load. Reinforced concrete stub columns were axially loaded and heated to designed temperatures in a specially built electrical furnace. After the specimens cooled down to ambient temperature with the axial loads kept constant, the stub columns were loaded to failure. The sustained preload led to significant residual deformations of reinforced concrete stub columns during the cooling phase. The test results showed that the mechanical behaviour of the fire-damaged reinforced concrete stub columns with preload was remarkably different from those without preload. The sustained axial loads resulted in obviously increased strength and stiffness during the loading phase, but reduced stiffness and deteriorated ductility in the unloading phase. Based on the test results, it is recommended that the effects of sustained axial loads during the fire and cooling phase should be taken into consideration in assessing the fire-damaged reinforced concrete columns.     

大型油罐软弱地基充水预压加固试验沉降监测

结合很多工程项目的实践经验，对大型油罐软弱地基充水预压加固试验的沉降监测作专题简述。分析了软弱地基、大型油罐给沉降监测带来的特定条件；阐述了其所表现的主要特点；介绍了所采取的有针对性的有关措施。并提出所采用的精度指标确定方法。     

高速切削机床主轴轴承的研究与发展

基于高速切削中高速机床主轴用轴承的运动机理，本文着重从润滑、密封、预紧等方面阐述了滚动轴承的研究与发展，并明确了其与工程应用的关系。     

Improved 2D mass-spring-damper model with unstructured triangular meshes

In this paper, we investigate both the visual realism and the physical accuracy of the 2D mass-spring-damper (MSD) model with general unstructured triangular meshes for the simulation of rigid cloth. For visual realism, the model should, at a minimum, bend smoothly under pure bending load conditions. For physical accuracy, it should bend approximately the same amount and shape as dictated by continuum mechanics. By matching the 2D MSD model with an elastic plate, we obtain a series of constraints on the parameters of the model. We find that for a 2D unstructured MSD model, it is necessary to apply preloads on the springs for accurate modeling of bending resistance. By simultaneously applying the constraints for both visual realism and physical accuracy, we can optimize the parameters of the model to enhance its fidelity. The simulation shows that the deformation of the optimized MSD model with preload is very close to the result obtained by the finite element method (FEM) under either point load condition or pressure load condition. With a much smaller computational burden compared with FEM, the optimized MSD model is especially suitable for real time haptic applications.     

高速机床主轴－轴承系统动态性能研究

为研究主轴－轴承系统的动态性能,以某型号精密卧式加工中心主轴系统为研究对象,通过偏心质量激励法测得主轴支承轴承刚度,采用Timoshenko梁单元对主轴进行有限元建模,系统地分析了主轴离心效应、轴承预紧力对于主轴动态性能的影响,并进行了实验验证。结果表明：提高预紧力可有效增加主轴轴承刚度,提高主轴动态性能。同时证明采用有限元法计算主轴轴承的刚度是一种行之有效的方法。     

高速双螺母滚珠丝杠副轴向接触刚度研究

对双螺母预紧的滚珠丝杠副进行了接触受力分析,推导出接触变形的公式,建立了滚珠丝杠副的轴向刚度计算公式。研究分析了影响滚珠丝杠副轴向刚度的几个主要因素,包括预紧力、螺旋升角、接触角等,给出了这几个因素与滚珠丝杠副轴向刚度对应的关系曲线,为新型高速滚珠丝杠的合理设计提供了理论基础。     

主减速器总成主动齿轮内、外调整垫片在线测选系统

提出一种主减速器总成主动齿轮内、外调整垫片测选系统,其技术特征为应用相对测量原理,建立数学模型,在线采集主减速器壳体、主动齿轮及内、外轴承与刚性隔套之间距尺寸数据,准确快捷测选出内、外调整垫片值。     

轴承预紧对机床主轴刚度的影响

阐明了用有限元法分析计算机床主轴组件刚度的步骤和方法,并对主轴刚度进行计算,讨论不同预紧条件下,轴承刚度对主轴性能的影响;并探讨轴承预紧后,增大预紧量对主轴刚度的影响。结果表明:支承轴承预紧的增大使主轴弯曲刚度增幅最大为22%,而对固有频率的影响不明显。