Research on tool wear detection based on machine vision in end milling process

This paper suggests a novel technique for the tool wear measurement based on machine vision. Tool images are captured between cutting operations using a machine vision system. The gray value difference threshold is determined from the tool image itself and the reference line is found to locate the tool in the image. The edges of the tool wear region are extracted by column scanning. A method of continuity testing is used to find the correct edge position in each wear column. To achieve a more accurate result, the sub-pixel edge detection technology is adopted to extract the edges. Finaly, the tool wear parameters can be obtained after rebuilding the top edge of the wear region and determining the bottom edge of the wear region. The measurement results gotten by the proposed method are compared with those gotten by measuring directly with a microscope. The proposed scheme is shown to be reliable and effective for the automated tool wear measurement.     

Weld line transverse energy density distribution measurement in laser transmission welding of thermoplastics

While laser beam profiling techniques are available for the measurement of a laser beam power profile, such techniques are difficult or impossible to use in order to characterize the power profile of the beam which has passed through the light-scattering semi-crystalline polymer (such as nylon). This paper presents a technique for measuring the scattering of the laser beam caused by the laser-transparent part in laser transmission welding. The technique is easy to implement and does not require specialized or expensive equipment. It relies on measurements of line widths for a sequence of lines left on the polymer surface by a rapidly moving laser beam at progressively increasing powers. The line width and power information is then used to obtain the distribution of the laser energy across the weld line. An application for a case of a high-power diode laser and (glass-reinforced and natural) polyamide 6 is presented.     

板料变形的投影栅三维快速测量技术研究

目前, 国内外研究的物体形面光学三维测量系统, 多用于静态物体的三维测量, 测量时间较长。本文研究了一种投影栅三维形面快速测量系统, 可应用于处于动态状态的物体的三维测量。文中介绍了其原理、相展开以及双CCD相位周期匹配等关键技术, 并且应用该系统对汽车侧围板变形进行测量。精度验证表明, 系统在测量范围内误差为10μm量级, 可用于工业快速测量领域。     

3D tool wear measurement and visualisation using stereo imaging

Tool wear detection has traditionally restricted itself to 2D study and measurement. A new technique for the measurement and visualisation of tool wear pattern has been presented in this paper. This method provides visualisation of the tool wear geometry using a pair of stereo images and generates the volume of crater wear as a new parameter for inspection. The results demonstrate that the volume of crater wear can be effectively used to characterise the tool wear. The average depth of the tool wear and surface area of the crater are also obtained as parameters for measurement. The technique provides a fast and a possible on-line method of tool wear analysis and measurement.     

基于激光三角法的自由曲面零件测量

针对超细长螺旋曲面工件廓形误差脱机测量所用测量设备不能满足工件长度和工件稳定旋转等方面要求的难题,提出了一种基于激光三角法的自由曲面零件测量系统,该系统通过利用机床对工件的定位、夹紧、支撑以及有关运动和控制机构,增配激光检测系统,增配运动部件实现的。构建完成了在机激光检测硬件技术平台;通过对采集所得的点云数据进行分析处理,绘制出被测工件的截面廓形。结果表明:该系统提高了检测的效率和准确性,提高了细长螺旋曲面零件的精度,从而实现了螺旋曲面廓形的精确测量。     

基于面结构光投影法的刀具轮廓尺寸非接触测量技术研究

针对刀具的几何形状和轮廓尺寸对刀具的使用寿命和产品的加工质量有直接影响,提出采用面结构光投影法对刀具轮廓尺寸进行非接触测量,该方法不仅可以准确获得刀具轮廓的深度信息,同时能直观反映出刀具表面本身有无缺陷。文中开展了面结构光投影法的测量原理、测量系统的数学模型以及刀具点云拼接方法的研究,给出了刀具转台坐标系与摄像机成像坐标系间的转换关系。以通用的麻花钻头为例进行实际测量,实验结果表明:该方法可以很好地获取钻头的几何形状及轮廓尺寸,其测量误差在0.07 mm左右,可行性较高。     

Application of statistical filtering for optical detection of tool wear

The application of automated tool condition monitoring systems is very important for unmanned machining systems. Tool wear monitoring is a key factor for optimization of the cutting processes. Basically, tool wear monitoring systems can be subdivided into two classes: direct and indirect. Currently direct tool wear monitoring systems are most frequently based on machine vision by camera. Several approaches have been studied for tool wear detection by means of tool images, and an innovative statistical filter proved to be very efficient for worn area detection. A new approach has been implemented and tested in order to develop an automatic system for tool wear measurement. This new approach is described in this paper and the main topics related to tool wear monitoring using wear images have been discussed.     

一种点位式三维坐标视觉测量系统

利用摄像机测量方向和激光测距仪测距精度较高的优势,提出了一种基于摄像机和激光测距仪的点位式视觉三维坐标测量系统,给出了系统的组成和测量原理,建立了系统模型,推导出了被测点三维坐标的求解公式,并对系统测量的稳定性进行了实验测试。结果表明,本系统的测量精度较高,且系统模型及其求解都比较简单。     

Fabrication of concave micro lens array using laser patterning and isotropic etching

Micro lens arrays are widely used in optical communication and laser-fiber coupling applications. In this paper, a technique to fabricate concave micro lens arrays on glass substrate using a third harmonic Nd:YAG laser direct patterning and followed by chemical wet isotropic etching is presented. The patterning process was done on gold film, which was coated on a glass substrate by using a NC controlled laser ablation tool paths. The glass substrate is then etched by using hydrofluoric acid (HF) solutions whereby the exposed area will be dissolved away by chemical reaction with HF. The type of etching process is an isotropic etching which the etching rate is equal at all direction thus produce hemispherical concave profile on glass. The optimum laser patterning parameters is obtained and the effect of different types of HF solutions on etching efficiency is studied. The surface morphology, 2D and 3D profiles are also measured. Various micro lens diameters are fabricated with different values of lens sag.     

轮对轮缘磨耗非接触测量的现场标定方法

摄像机标定方法的选择和标定精度直接影响着轮对动态视觉测量系统的精度.本文利用二元二次多项式变形技术,提出了一种轮对外形尺寸非接触测量的现场标定方法.首先根据现场实际测量环境的要求,利用平面靶标标定装置,确定高分辨率面阵CCD和激光线光源的位置,然后采集平面靶标图像,获取关键控制点物像坐标,最后利用非线性畸变模型求解出标定参数.实验结果表明,该方法标定过程操作简单,标定精度高,测试数据满足车辆段现场动态检测的要求.     

Progressive cutting tool wear detection from machined surface images using Voronoi tessellation method

Tool condition monitoring by machine vision approach has been gaining popularity day by day since it is a low cost and flexible method. In this paper, a tool condition monitoring technique by analysing turned surface images has been presented. The aim of this work is to apply an image texture analysis technique on turned surface images for quantitative assessment of cutting tool flank wear, progressively. A novel method by the concept of Voronoi tessellation has been applied in this study to analyse the surface texture of machined surface after the creation of Voronoi diagram. Two texture features, namely, number of polygons with zero cross moment and total void area of Voronoi diagram of machined surface images have been extracted. A correlation study between measured flank wear and extracted texture features has been done for depicting the tool flank wear. It has been found that number of polygons with zero cross moment has better linear relationship with tool flank wear than that of total void area.     

三维拼缝激光焊接的变形动态补偿

针对三维拼缝激光焊接过程中的变形扰动,为实现三维轨迹的精确跟踪,需要在焊接过程中进行拼缝轨迹实时测量和动态补偿.在五轴联动数控焊接机床上,利用激光视觉传感器实现三维拼缝焊接过程的实时测量,获取拼缝轨迹的偏差信息,将偏差信息从测量坐标系转化到T件坐标系,实时补偿各运动轴的进给量,从而实现三维拼缝曲线焊接过程的动态补偿;分...     

An experimental and numerical study on the face milling of Ti-6Al-4V alloy: Tool performance and surface integrity

This paper is concerned with the experimental and numerical study of face milling of Ti-6Al-4 V titanium alloy. Machining is carried out by uncoated carbide cutters in the presence of an abundant supply of coolant. Experimental analysis is conducted by focusing on the measurement of specific cutting energy, surface integrity and tool performance. The experimental analysis is supplemented by simulations from a 3D finite element model (FEM) of face milling simulation where needed. A tool wear model parameterized from FEM predictions of the tool-chip interface temperature, contact stress and chip velocity is presented. Tool wear patterns are described in terms of various cutting conditions and the influence of tool wear on surface integrity is investigated. Tool wear predictions based on the 3D FEM simulation show good agreement with experimental tool wear measurements. The highest cutting speed realized for the cutting tool material is 182.9 m/min (600 sfpm). Good surface integrity in terms of favorable residual stress and surface finish is achieved under the machining conditions used with limited tool wear. Residual stresses imparted to the machined surface are shown to be compressive.     

单目视觉的大型零件三维测量方法

以单目视觉为基础,构建一种便携、大量程的在线测量曲面重构系统。当辅助靶标上的刚体测量头与曲面待测点垂直接触时,测头上的开关同步控制摄像机来获取靶标标志点的特征图像信息,进而由计算机进行图像处理得到各标志点的像面坐标,最后再经过坐标转换即可得到被测物体的三维坐标。通过对系统进行标定,提高了测量精度;通过摄像机的转站实现了最优视点规划分析,提高测量范围和自动化程度;另外,对系统测量不确定度进行论并提出了改进措施。     

Characterization of wear damage in coatings by optical profilometry

The accurate determination of the volume loss of plasma- sprayed coatings submitted to abrasive and erosive wear and the visualization of wear track or crater profiles are of major concern when ranking coatings, developing wear- resistant coatings, or identifying the mechanism responsible for failure. The determination of the volume loss by liquid displacement measurements is impractical when the size of coated pieces is large and the volume loss is small. For evaluating coating damage and directly measuring the volume loss, a three- dimensional surface mapping method is proposed. The three- dimensional image of the worn surface is obtained by a laser triangulation method. The experimental setup is basically composed of an illuminating source and a detecting device. The light source is focused on the sample surface, and the reflected light is then collected on a network of charge couple detectors linked to a computer. Because the spot location on the network is a direct function of the measured height, a three- dimensional image can be obtained after scanning the entire damaged surface so that the volume loss can be calculated easily. Intensity- coded depth images of the worn surface and computerized cross sections of the damaged area can also be obtained. Inspection of coatings damaged by abrasion wear or slurry erosion by optical profilometry reveals that the volume loss measurements by this technique are very accurate as opposed to the volume measured by liquid displacement methods or calculated from weight loss measurements. Moreover, intensity- coded depth images of worn surfaces and computerized cross sections of damaged areas provide relevant information about the coating performance or defects resulting from the deposition process.     

Development and evaluation of an on-machine optical measurement device

Demand for fabricating micro-features such as fine holes, micro-cavity for injection moulding, and micro-pin using both conventional (turning, milling, etc.) and non-conventional edge detection method (EDM), wire cut EDM, etc.) processes is increasing significantly. To successfully achieve micro-machining, development of a miniature machine tool, process technology, and on-machine measurement is essential. However, in such tool-based micro-machining processes, proper tool shape monitoring, precision processing, and dimensional control require significant attention. Since these are tool-based machining processes, tool shape monitoring and control are also important technologies to be established.In this study, an on-machine measuring device was developed based on non-contact optical method to inspect dimensions of the fabricated tools (e.g. electrodes for EDM) as well as the wear of tools used for the respective processes. The developed inspection system uses a laser light source and a photo-electronic device. To minimize errors due to the change of tool measurement position and the Fresnel diffraction of laser light, an edge detection algorithm using a linear discrimination function is proposed in this study. Furthermore, an intensity measuring method was added for specimen with a smaller diameter. The experimental results show that the developed on-machine optical inspection system has the accuracy and stability to effectively monitor the fine dimensions of tools and their wear.     

An evaluation of surface asperity profile changes in truncation processes using optical interferometric microscope

The truncation process as running-in wear was applied to evaluate surface asperity changes as removal at the top of its asperity profile. The measurement was done using an optical interferometric microscope. Whole surface profile was measured by the microscope supported by the stitching technique. The specimen was relocated on the microscope utilizing Hirth coupling as a hardware technique. Data obtained from a truncated specimen were precisely relocated to the original untruncated specimen by computer software in three dimensions. Then the profile change was obtained by deducting truncated data from the original data. The profile change was calculated as removed volume. The volume changes are plotted against a sliding length. As the software relocation technique needs the unchanged profile of a valley part, the evaluation is limited to where the truncation height is higher than −1.28 sigma (the standard deviation of untruncated original profile height). The present research can detect very little volume change that cannot be measured by other conventional methods, such as the gravimetric method. The advantages of the present method are as follows. It is possible to compare the truncated surface profile with the original untruncated surface profile in three dimensions. Thus, the inclination of the truncation surface can be evaluated and any other local changes can also be assessed. From this information the profiles of truncated surfaces will be linked to functions, and new parameters for truncation profile will be presented.     

焊缝轮廓线激光检测系统开发及算法实现

目前焊缝表面检测主要依靠肉眼观察和简单测量实现,其科学性、精确性受到检验人员主观因素的影响。线激光扫描方法是工业应用中比较先进的非接触轮廓检测方法。通过线激光扫描,利用激光三角测量法可以得到物体轮廓,进而得到物体的形貌信息。基于上述技术,开发了一套焊缝轮廓线激光检测系统,系统由半导体线激光器、CMOS工业相机、LabVIEW虚拟仪器软件平台组成。基于LabVIEW编写了包括图像采集、图像处理与焊缝轮廓计算的系统,能够得到较为准确的焊缝表面轮廓信息。     

An improved cutting force and surface topography prediction model in end milling

During the milling operation, the cutting forces will induce vibration on the cutting tool, the workpiece, and the fixtures, which will affect the surface integrity of the final part and consequently the product's quality. In this paper, a generic and improved model is introduced to simultaneously predict the conventional cutting forces along with 3D surface topography during side milling operation. The model incorporates the effects of tool runout, tool deflection, system dynamics, flank face wear, and the tool tilting on the surface roughness. An improved technique to calculate the instantaneous chip thickness is also presented. The model predictions on cutting forces and surface roughness and topography agreed well with experimental results.     

Development of in situ measurement system for welding deformation using digital cameras

Abstract

A three-dimensional (3D) deformation (in plane and out of plane deformations) measurement method is developed using digital cameras, which require no special equipment. This method is a non-contact method, and it can sequentially measure over the entire photographed image. Furthermore, since image analysis is based on the technique of image matching, the method is applicable even when the deformation to be measured is large. In addition, since it is possible to use all pixels as measuring points, the number of available measuring points at one time is the same as the number of effective pixels of the camera. In this study, the proposed method is applied to the sequential measurement of displacement under strong lighting levels in arc welding. Through the comparison of the results measured by a 3D shape measurement system (LAT-3D) using a laser displacement gauge and digital caliper, the quantitative validity of the proposed method is also verified.