非接触激光圆度仪的研制

本文介绍一种非接触式检测大型回转体件圆度误差的激光圆度仪工作原理及总体构成、并通过实验予以验证。该仪器采用激光狭缝扫描原理和光电传感技术, 通过电子学单片机技术进行误差分离及数据处理, 从而实现圆度误差测量     

一起低温液体贮槽制造过程爆裂事故分析

通过一起固定式低温绝热液体贮槽夹层气压试验时内壳发生失稳变形 ,导致外壳爆裂的事故原因分析 ,证明此类容器在制造过程应严格控制内壳的成型尺寸和焊缝残余应力 ,并加强对夹层气压试验、抽真空检漏的工艺程序监控。     

The influences of textural parameters of grains on the LCPC abrasivity of coarse-grained igneous rocks

Rock abrasivity causes the tool wear in rock excavation or drilling. The understanding of wear mechanism is important for the cost estimation and planning of projects. In this study, the effects of textural properties of grains such as aspect ratio, roundness, and diameter on the LCPC abrasivity coefficient (LAC) were investigated for coarse-grained igneous rocks. First, the LAC was correlated to the abrasive mineral content (AMC) and a good correlation was found between the two parameters. Then, the LAC was correlated to the AMC multiplied by the textural properties of grains, respectively. Compared to the correlation coefficient of the relation between the LAC and the AMC, the correlation coefficient was increased by including the textural properties of grains to the correlation. A combined parameter called shape and size coefficient (SSC) was defined in order to see the combined effect of the textural properties of grains on the LAC. The correlation coefficient of the relation between the LAC and the AMC multiplied by the SSC is very strong and fairly higher than that of the previous correlations derived. It can be concluded that the textural properties of loosened materials have a strong influence on the tool wear.     

Forgery detection for perforated number in security document by analysing the perforated holes

The perforated number is an important anti-counterfeiting technique widely used in recent years in security document for protecting document number from being forged. However, forgery detection of perforated number is still made by means of manual inspection, which is not only time-consuming but also error-prone. In this paper, we propose an automatic method for verifying the authenticity of perforated number by analysing the shape of the perforated holes and their alignments in horizontal and vertical direction. First, the image with perforated number is captured by the 10–20× optical zoom, and then the perforated holes are segmented by the maximum between-cluster variance. Second, each perforated hole is labelled by the connected component analysis and then fitted as a circle using the least-squares method for determining the parameters of each hole. Lastly, we propose two criteria to verify the authenticity of the perforated number. One is the new defined roundness measurement called local feature, which is denoted by computing the distance between the contour of the perforated hole and its fitted circle. The other is the measurement of the alignments of all perforated holes in horizontal and vertical direction, which is called global feature. The alignments are determined by means of K-means clustering method. The experimental results show that the proposed method has the correct detection rate over 92%, which means the proposed method is an effective method for recognising the authenticity of the perforated number for security document.     

Factors affecting wheel collapse in grinding

An investigation was made into the phenomenon of wheel collapse, where power increases steadily with attritious wear until a critical value is reached, upon which power drops rapidly to a steady-state value and the wheel loses its roundness. Causes and mechanisms were investigated, along with the relationships between amount of material removed at collapse, power at collapse, post-collapse steady-state power, cooling, wheel self-sharpening, and G-ratio. Examples from laboratory tests and production tests are used. Practical recommendations are given for delaying or eliminating collapse.     

Rounding and stability in centreless grinding

The paper presents a method for selecting grinding conditions and assists researchers to understand the complex dynamics of centreless grinding. It overcomes the problem of deriving dynamic stability charts for particular geometries and difficulty of interpreting such charts to adjust work speed to overcome lobing problems. Classic dynamic stability charts cannot assess stability levels in proximity to integer lobes, a particular problem for centreless grinding. The paper overcomes these problems employing a simply calculated new dynamic stability parameter A_dyn. The new parameter A_dyn simplifies the optimisation of grinding variables including set-up geometry and work speed in relation to resonant frequency. It is difficult to interpret relative dynamic stability of centreless grinding by classical methods for different set-ups, work speeds and numbers of lobes. A new method is employed in this paper based on the well-established Nyquist stability criterion. The dynamic stability parameter A_dyn is based on the real part of the characteristic equation. It is easily computed and presented on a single chart for particular work speed, resonant frequency and for a wide range of numbers of lobes. The method clearly shows the effect on rounding strength both for stable and unstable conditions. Most authors computing dynamic stability charts have ignored positive down boundaries and negative up boundaries showing a lack of a comprehensive treatment for a situation that conflicts with recommendations for conventional positive up boundaries. The new method simplifies this problem.Small differences in set-up geometry and work speed selection can be easily assessed. The new method can be used as a diagnostic tool for adjusting grinding conditions to overcome roundness problems. The user is not constrained by a historic set-up range since there are practical situations where other set-ups are preferred such as small tangent angles for large and heavy work-pieces, and even negative tangent angle for some types of centreless machine.Previous research is reviewed to provide an understanding of the need for a new approach to stability. Practical implications are explained for selection of grinding conditions. The method is supported by reference to experimental results.     

A Spindleless Instrument for the Roundness Measurement of Precision Spheres

This paper presents an automated instrument for high-precision roundness measurement of spheres. Instead of a rotating spindle, the surface of the sphere itself is used as a geometrical reference. The measurement method is based on the well-established three-point method. In our design, two points are realized as mechanical contacting points and one as a capacitive gauge that directly faces the surface of the sphere. By this simple design—without any moving parts involved in the probing process—we measured the roundness of 1-inch steel spheres with nanometer resolution. After a short introduction into the basic mathematics of the three-point method, the design of the instrument is presented, including the automation of the measuring process and the means used to minimize environmental effects in an industrial environment. Results are presented that prove the outstanding repeatability and accuracy of the instrument. In a comparison with conventional methods, the advantages and limitation of the method are discussed.     

Influence of contact loss between workpiece and grinding wheel on the roundness errors in centreless grinding

The objective of this paper is the study of certain non-linear phenomena in the centreless grinding process and their effect on roundness quality. These phenomena arise as a consequence of contact loss between workpiece and grinding wheel. A simplified analysis of the problem is carried out to determine the main parameters involved. A qualitative assessment of the effect of these parameters is undertaken by means of a time simulation based on a non-linear bi-dimensional model of the centreless grinding process. Two situations are analysed: the steady process, and the transient spark-out process. The results, which are generalised in graphics form provide an estimation of roundness errors resulting from working under linearly unstable conditions. Finally, a correlation between theoretical and experimental results is presented.     

基于机器视觉的机油冷却管圆度检测与分拣研究

针对机油冷却管生产过程中,管口的圆度误差主要是人工测量导致的,且检测效率低,无法实时检测的问题,基于视觉检测提出一种机油冷却管口圆度检测与分拣方法。构建机器人SR7CL的运动学模型,利用ADAMS和MATLAB对其运动学和动力学进行仿真,验证模型的正确性,以保证抓取的准确性。以机油冷却管为抓取对象,通过自适应阈值分割,突出管口特征;利用Canny算法提取出边缘信息,通过最小二乘法检测圆度误差,并根据圆度误差对冷却管进行分拣。结果表明：所提方法提高了检测的质量和效率,解决了实时性的问题。     

高精度无心磨削圆度保证和成圆过程解析

为了对无心磨削的圆度误差进行研究,讨论了影响高精度无心磨削过程的关键因素,包括稳定性、磨削参数、砂轮和导轮,给出了改进圆度误差的措施。在时域内对无心磨削成圆过程进行了解析。在解析研究中考虑了成圆过程的非线性环节,通过工件的轮廓和工件与砂轮、托板和导轮之间的作用研究工件的成圆过程。实验结果和理论结果的对比显示,解析模型可以对成圆过程进行准确预测。