A calibration method for misaligned scanner geometry in cone-beam computed tomography

Computed tomography (CT) images often suffer from artifacts caused by misaligned scanner geometry of CT system. Calibration and correction must be done before image reconstruction. A method for calibration of misaligned scanner geometry in cone-beam CT with single-circle orbit is proposed. In this method, a four-point phantom is used to estimate a set of parameters that describe the geometry of a cone-beam CT system. It requires only one projection of the phantom, instead of several projections at multi-angles. An analytical formula is derived, which avoids falling into local minimum. In addition, there is no restriction on any one of the geometric parameters. The simulated results are illustrated. It is proved that this method is applicable and efficient for misaligned scanner.     

扇束等距CT极坐标反投影重建算法的速度优化

为提高扇束滤波反投影(FBP)算法重建CT图像的速度,提出了利用正余弦函数性质对极坐标反投影算法进行优化的快速重建方法。首先将扇束等距CT扫描得到的投影数据进行加权,卷积滤波处理;其次将预处理后的投影数据运用正余弦函数性质进行极坐标反投影重建。试验结果表明,与传统的卷积反投影重建算法相比,该方法可以将重建速度提高4倍以上,而且重建质量与传统卷积反投影相当。这种算法也适应于多层螺旋三维重建,并且可以推广到三维锥束重建。     

Cooperative data fusion of transmission and surface scan for improving limited-angle computed tomography reconstruction

Limited-angle computed tomography allows faster inspection during production, but the reconstruction from limited-angle transmission data is an underdetermined problem which cannot be solved without any prior knowledge of the sample. In this paper, surface data from an optical scan is selected as prior information due to its high accuracy and availability. To incorporate this information, we have developed a new cooperative data fusion model in the compressed sensing framework. The model has been applied to numerical and experimental data and solved with a tailored algorithm. We demonstrate the benefit of the data fusion model and prove the robustness of the algorithm. The results from this study indicate that the data fusion process combines features resolved by both modalities and gives a significant increase in image quality. These improvements enable metrological measurements that are impossible with data acquired with any single modality.     

An improved genetic algorithm for planar and spatial straightness error evaluation

The measurement data obtained from the Coordinate Measuring Machines (CMMs) have to be further processed and analyzed to evaluate the form errors of manufactured components. An improved genetic algorithm (GA) is proposed to implement the minimum zone evaluation of planar and spatial straightness errors simultaneously. The algorithm employs the generation alternation model based Minimal Generation Gap (MGP) and blend crossover operators (BLX-α). Compared to traditional GAs, it is efficient and robust. Then, the objective function calculation approaches of planar and spatial straightness error are developed, which directly originate from the definition of minimum zone solution and conform to the ISO standard. Finally, the experimental results evaluated by different methods confirm the effectiveness of the proposed GA. Compared to conventional evaluation methods; it has the advantages of algorithm simplicity and good flexibility. Also it is a unified approach for other form error evaluations and is well suited for the form error evaluation on CMMs.     

基于快速成型的颅骨断层影像模型重建的探讨

对于内外结构复杂的实物原型,难以采用传统的测量方法如三坐标测量机(CMM)、激光扫描等手段获取内外表面完整的点云数据,以逆求实物原型的CAD模型。基于此种问题,介绍了CT(ComputedTomography)辅助快速成型技术。以最新的16排螺旋CT机测量设备及由Materialise公司开发的三维重构软件M im ics为手段,运用图像图形处理中的边缘检测、阈值分割、边界细化、矢量化及格式转换等算法与技术,获取实物内外表面轮廓矢量数据,并将其输入UG软件,逆求出实物原型的CAD模型。将三维几何模型输入快速成型机加工,为将快速成型技术应用到医学领域提供了一定的基础。     

Microwave complex permeability of planar anisotropy carbonyl-iron particles

Planar anisotropy carbonyl-iron (PACI) particles were prepared from sphere-shaped carbonyl-iron (SSCI) materials by a simple ball milling technique. The frequency-dependent complex permeability of paraffin composites with 50% volume concentration of particles has been investigated in 0.1-18 GHz frequency range. The as-milled PACI composites show a dramatic enhancement of complex permeability and a higher resonance frequency compared with SSCI composite. This is due to the PACI particles, which have an easy magnetization plane and a thickness smaller than their skin depth, suppressing the eddy current effects. Furthermore, the complex permeability is further improved after the PACI composite was rotationally orientated in an external magnetic field. The real permeability of oriented PACI composite reaches a large value of approximate 10.5 at 0.1 GHz, and the resonance frequency shifts to a higher frequency range.     

高温合金闭式叶轮的工业CT检测

高温合金闭式叶轮为多层、薄壁、曲面流道的内腔与较大直径轴颈相连的整体复杂结构,使用透照电压不高于450kV的传统X射线照相方法对其进行检测时,存在X射线无法穿透叶轮厚大区域以及无法实现缺陷定位的问题,为此采用高能X射线工业计算机断层扫描(CT)方法对其进行检测。为了验证CT检测方法的缺陷检出能力,在高温合金闭式叶轮上加工已知尺寸的人工孔并进行检测,证明可检出φ0.5mm的孔。最后,对闭式叶轮的实际缺陷进行检测,可实现其内部气孔、缩孔等缺陷的检测和定位。     

Automatic fabrication for bridged laminated object manufacturing (LOM) process

Laminated object manufacturing (LOM) is one of the most popular rapid prototyping (RP) techniques in terms of speed and cost effectiveness. Despite the advantages of the LOM process, some problems are yet to be overcome. One of the major difficulties encountered in the current LOM practice is the metallic part cannot be fabricated. Focusing on the drawback inhered in LOM, a new Bridge-LOM process and its associated building algorithm are proposed in this paper. The process starts with the construction of the bridge structures to link a stack of 2D geometry contours to the outer frame based on the proposed bridge building algorithm. Afterwards, laser is directed to cut along the contours, and then the upper pressing head is pushed down and the layers are bonded. Spraying adhesive on the top of bonded layers follows this. The procedures of cutting, bonding and adhesive spraying are repeated until the complete part is produced. The proposed Bridge-LOM process has overcome two problems, support and position. Regarding the function of position, in order to ensure the proper bonding treatment, as well as holding a precise position between layers, the processes from cutting to bonding in the process should maintain the same X–Y position. Therefore, worries of not having a fixed positioning would then be eliminated. Regarding the function of support, bridge has taken the place of the supporting function of waste material in the current LOM process. The metallic part can be built directly based on the efficiency of on-line waste material removal in the process. From the experiments, it is verified that the proposed Bridge-LOM process and its associated building algorithm not only save laser-cutting time, the time on waste material removal is also reduced significantly. Furthermore, the metallic part and mold can be fabricated and their performances are investigated.     

Computed tomography with image intensifier: potential use for nondestructive testing and imaging of small objects

An image intensifier based computed tomography scanner and a tube source of X-rays are used for nondestructive evaluation, imaging of small objects for archaeological studies and conservation of works of art and micro analysis of soft materials. It consists of a charge coupled device (CCD) camera and an acquisition board. The CCD camera and the acquisition board allow image processing, filtration and restoration. The object is irradiated by an X-ray tube with a conical collimator and rotated on 180°. Projections are obtained at various angles as cross sectional image slices. A reconstruction program written in pascal is able to give the reconstruction matrix of the linear attenuation coefficients, simulates the matrix and related tomography. The flux emitted by the tube is filtered using the appropriate filters at the chosen optimum energy and reasonable monochromacy is achieved for all the images. Although X-ray imaging is a potential tool for strongly attenuating materials, the images of weakly attenuating materials provide new information to know about their structure and also the foreign body for the image reconstruction at an optimum value. The image of the plastic material which contains the internal defect is studied thoroughly at the optimum value in order to image the small objects for nondestructive testing, archaeological studies and conservation of works of art. The images are analysed using the profile data showing the internal defect of the object to obtain information at the optimum value. At the optimum value and with the aid of the tomographic image, the size and location of the defect could be ascertained.     

TIG焊快速制造金属体性能优化研究

介绍了TIG焊快速制造金属体成形过程及特点,通过对金属体各层金相组织特点及形成原理的分析,提出了一种基于红外测温仪TIG焊快速制造神经网络-PID温度控制系统,并介绍了该系统的结构组成及工作流程.试验证明,该系统的使用结合表面金属无丝焊热理,能有效地提高整体金属体的性能.     

Improvement of image characteristics in high-voltage computed tomography (CT) by applying a compressed-sensing (CS)-based image deblurring scheme

We have established a high-voltage computed tomography (CT) system with a 1–3 MV LINAC x-ray generator for industrial nondestructive testing. However, reconstructed CT images are typically blurred, limiting its image performance, mainly due to the finite focal spot size of the x-ray source, aspects inherent to detector such as the detector pixel size and the detector resolution, and the reconstruction procedure as well. Thus the recovery of the reconstructed CT images from their degraded version is essential for improving the image characteristics. In this work, we investigated the compressed-sensing (CS)-based deconvolution scheme for more accurate image deblurring in CT. We implemented the proposed image deblurring algorithm for CT and performed a systematic simulation and experiment to demonstrate its viability. Our results indicate that the proposed deblurring scheme appears to be effective for the blurring problems in CT and is applicable to improve its present image characteristics.     

一种车载X射线工业CT系统

为满足小批量、多规格、不可拆解、存放地域分散、运输成本高、难于集中检测的特殊工件的个性化无损检测需求,研制了一种车载X射线工业CT系统.该系统采用组合式的模块化结构.X射线源系统、探测采集传输系统、工件夹持系统、控制系统等独立组成模块,通过优化集成在一专用方舱内部,既可以通过载运车辆实现公路机动,也可与载运车辆一起实现...     

扇束CT重建图像的几何伪影分析

实际工业CT系统在机械安装时很难满足经典CT图像重建公式所要求的几何对准关系。当不满足该几何对准关系时，利用经典CT重建公式重建的图像将出现几何伪影，从而影响对CT图像的判读。针对扇束CT扫描系统，研究了几何参数误差对一根细丝断层图像的影响，导出了描述细丝断层图像伪影形态的包络线方程，并基于包络线给出了几何伪影的形态分类、演化规律和性质，同时给出了几何参数误差的调整方法。     

A new dual driver planar eddy current probe with dynamically controlled induction pattern

A new planar eddy current probe design is presented. This new concept is capable of dynamically modify the induced eddy currents pattern in accordance with the operational non-destructive testing parameters. The probe is composed by two orthogonally positioned driver traces and a set of sensing coils on each quadrant between the traces. Eddy currents result from the magnetic field contribution of the two driver traces and can be modified by changing the relative amplitude and phase of the currents flowing in the driver traces. Finite Element Modeling was used to simulate the eddy currents patterns and to predict the probe response to defects with different orientations. Experimental validation was carried using a prototype of the probe and artificial defects showing very good agreement with the Finite Element Modeling.     

Estimation and correction method for the two-dimensional positionerrors of a planar XY stage based on motion error measurements

This paper describes an estimation and correction method for the two-dimensional (2D) position errors of a planar XY stage that is driven along the Y-axis by two linear motors. The 2D position errors of the stage were estimated and corrected based on measured motion errors from a conventional laser interferometer system. To compensate for the planar XY stage 2D position errors, corrections were introduced for the yaw, perpendicular, straightness and 1D position errors along each axis, which are predominantly caused by linear scale, yaw, and pitching motion errors. The effect of the motion error corrections was evaluated by diagonal measurements based on the ISO230-6 standard and six different 1D position error measurements along the X and Y-axes. By applying error motion corrections, the diagonal systematic deviation at the center point was improved from 499.7 μm to 1.16 μm, and the estimated maximum 2D position errors were improved to −0.263 and 0.530 μm in the X and Y directions, respectively. The diagonal systematic deviation at a corner point was 1.23 μm and the estimated maximum difference between the corner and center points improved from −2.603 and 2.603 μm to −0.05 and 0.12 μm in the X and Y directions respectively.     

Quantification of surface roughness of parts processed by laminated object manufacturing

Additive manufacturing (AM) technology is essentially performed using a layered manufacturing (LM) process. Because more complex 3D physical models can be efficiently fabricated without geometric limitation by the technology, a remarkable reduction in production life cycle has been achieved. However, due to the LM process, a deterioration of the surface quality of the parts processed by AM may occasionally occur, which is the primary reason that the surface problem has been a key issue in AM. In this paper, a methodology is proposed to quantify the surface roughness of the parts processed by laminated object manufacturing (LOM), which is a typical technology in AM. The surface profiles of the parts were investigated, a schematic was constructed by considering the LOM process factor geometrically, and a theoretical approach to quantify average surface roughness according to surface angle variation is presented. The expressions required for numerical computation were deduced and defined. By comparing the measured data and computed values, the proposed approach was verified. Additionally, the effects of the process variables related to surface quality were evaluated and analyzed.     

An object oriented multi-robotic graphic simulation environment for programming the welding tasks

An object-orlented nudti-robotic graphic slmulatlon environment is described in this paper. Object-orlented programming is used to model the physical objects of the robotic workceU in the form of software objects or classes. The virtual objects are defined to provide the user with a user-frlendly inteoCace including realistic graphic simulation and clarify the software architecture. The programming method of associating the task object with active object effectively increases the software reusability, maintainability and modifiability. Task level programming is also demonstrated through a multi-robot welding task that allows the user to concentrate on the most important aspects of the tasks. The multi-thread programming technique is used to simulate the interaction of multiple tasks. Finally, a virtual test is carried out in the graphic simulation environment to observe design and program errors and fix them before downloadlng the software to the real workcell.     

工业CT技术参数对性能指标的影响——兼谈如何选择工业CT产品

叙述了工业CT技术参数对性能指标的影响，以便读者在选择和购买工业CT设备时，能：恰如其分地提出技术要求，合理地在性能和价格之间取得折中。     

Scatter simulation and correction in computed tomography: A reconstruction-integrated approach modelling the forward projection

Scattered photons lower the quality of the reconstructed images in computed tomography. Additionally to scattering in the scintillator material that lowers the resolution, object-scattered photons cause artefacts due to non-linear absorption and are difficult to simulate. In the context of model-based reconstruction we developed a fast approximation for scattered radiation that is integrated in the forward projection of an iterative polychromatic reconstruction method. We develop the modelling of scattered intensities in an iterative maximum-likelihood reconstruction method, demonstrate a comparison with Monte-Carlo simulated scatter-data and show the result of reconstructed data within the field of industrial non-destructive testing.