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1.
Rapid prototyping (RP) provides an effective method for model verification and product development collaboration. A challenging research issue in RP is how to shorten the build time and improve the surface accuracy especially for complex product models. In this paper, systematic adaptive algorithms and strategies have been developed to address the challenge. A slicing algorithm has been first developed for directly slicing a Computer-Aided Design (CAD) model as a number of RP layers. Closed Non-Uniform Rational B-Spline (NURBS) curves have been introduced to represent the contours of the layers to maintain the surface accuracy of the CAD model. Based on it, a mixed and adaptive tool-path generation algorithm, which is aimed to optimize both the surface quality and fabrication efficiency in RP, has been then developed. The algorithm can generate contour tool-paths for the boundary of each RP sliced layer to reduce the surface errors of the model, and zigzag tool-paths for the internal area of the layer to speed up fabrication. In addition, based on developed build time analysis mathematical models, adaptive strategies have been devised to generate variable speeds for contour tool-paths to address the geometric characteristics in each layer to reduce build time, and to identify the best slope degree of zigzag tool-paths to further minimize the build time. In the end, case studies of complex product models have been used to validate and showcase the performance of the developed algorithms in terms of processing effectiveness and surface accuracy.  相似文献   

2.
Die-cavity pocketing via cutting simulation   总被引:9,自引:0,他引:9  
For die-cavity pocketing, the cavity volume is sliced into a number of cutting-layers by horizontal cutting-planes, and each layer is pocket-machined using the contour-parallel offset method in which the tool-paths are obtained by repeatedly offsetting the boundary-pocketing curve. The major challenges in die-cavity pocketing include: 1) finding a method for obtaining the boundary-pocketing curve, 2) generating evenly spaced contour-parallel offset toolpaths, 3) detecting and removing uncut-regions, and 4) estimating chip-loads for an adaptive feed control. No systematic solution for these problems has been offered in the literature, except the curve offsetting methods for computing contour-parallel offset curves. Presented in the article is a straightforward approach to die-cavity pocketing, in which all the four challenges are handled successfully by using the existing cutting-simulation methods.  相似文献   

3.
In this study, a method for generation of sectional contour curves directly from cloud point data is given. This method computes contour curves for rapid prototyping model generation via adaptive slicing, data points reducing and B-spline curve fitting. In this approach, first a cloud point data set is segmented along the component building direction to a number of layers. The points are projected to the mid-plane of the layer to form a 2-dimensional (2D) band of scattered points. These points are then utilized to construct a boundary curve. A number of points are picked up along the band and a B-spline curve is fitted. Then points are selected on the B-spline curve based on its discrete curvature. These are the points used as centers for generation of circles with a user-define radius to capture a piece of the scattered band. The geometric center of the points lying within these circles is treated as a control point for a B-spline curve fitting that represents a boundary contour curve. The advantage of this method is simplicity and insensitivity to common small inaccuracies. Two experimental results are included to demonstrate the effectiveness and applicability of the proposed method.  相似文献   

4.
Tool-path generation from measured data   总被引:4,自引:0,他引:4  
Presented in the paper is a procedure through which 3-axis NC tool-paths (for roughing and finishing) can be directly generated from measured data (a set of point sequence curves). The rough machining is performed by machining volumes of material in a slice-by-slice manner. To generate the roughing tool-path, it is essential to extract the machining regions (contour curves and their inclusion relationships) from each slice. For the machining region extraction, we employ the boundary extraction algorithm suggested by Park and Choi (Comput.-Aided Des. 33 (2001) 571). By making use of the boundary extraction algorithm, it is possible to extract the machining regions with O(n) time complexity, where n is the number of runs. The finishing tool-path can be obtained by defining a series of curves on the CL (cutter location) surface. However, calculating the CL-surface of the measured data involves time-consuming computations, such as swept volume modeling of an inverse tool and Boolean operations between polygonal volumes. To avoid these computational difficulties, we develop an algorithm to calculate the finishing tool-path based on well-known 2D geometric algorithms, such as 2D curve offsetting and polygonal chain intersection algorithms.  相似文献   

5.
STL rapid prototyping bio-CAD model for CT medical image segmentation   总被引:1,自引:0,他引:1  
This paper presents a simple process to construct 3D rapid prototyping (RP) physical models for computer tomography (CT) medical images segmentation. The use of stereolithography (STL) triangular meshes as a basis for RP construction facilitates the simplification of the process of converting CT images to an RP model. This is achieved by constructing the STL triangular meshes directly from data points without having to draw the curve model first. The grey prediction algorithm is used to sort contour point data in each layer of the medical image. The contour difference detection operation is used to sequence the points for each layer. The 3D STL meshes are then constructed by this proposed layer-by-layer sequence meshes algorithm to build the STL file. Once this STL file is saved, a 3D physical model of the medical image can be fabricated by RP manufacturing, and its virtual reality model can also be presented for visualization. CT images of a human skull and femur bone were used as the case studies for the construction of the 3D solid model with medical images. The STL models generated using this new methodology were compared to commercial computer-aided design (CAD) models. The results of this comparative analysis show that this new methodology is statistically comparable to that of the CAD software. The results of this research are therefore clinically reliable in reconstructing 3D bio-CAD models for CT medical images.  相似文献   

6.
In this paper, an automatic grid generator based on STL models is proposed. The staircase boundary treatment is implemented to handle irregular geometries and the computation domain is discretized using a regular Cartesian grid. Using the grid generator, staircase grids that are suitable for fast and accurate finite difference analysis could be generated. Employing the slicing algorithm in RP technologies [1], the STL models are sliced with a set of parallel planes to generate 2D slices after the STL files obtained from a CAD system undergo topology reconstruction. To decrease the staircase error (increase accuracy) and enhance working efficiency, the cross-section at the middle of the layer is taken to represent the cross-section of whole layer. The scan line filling technique of computer graphics [2] is used to achieve grid generation after slicing. Finally, we demonstrate an application of the introduced method to generate staircase grids, which allows successful FDM simulation in the field of explosion. The example shows that the automatic grid generator based on STL models is fast and gives simulation results that are in agreement with practical observations.  相似文献   

7.
Error-based segmentation of cloud data for direct rapid prototyping   总被引:1,自引:0,他引:1  
This paper proposes an error-based segmentation approach for direct rapid prototyping (RP) of random cloud data. The objective is to fully integrate reverse engineering and RP for rapid product development. By constructing an intermediate point-based curve model (IPCM), a layer-based RP model is directly generated from the cloud data and served as the input to the RP machine for fabrication. In this process, neither a surface model nor an STL file is generated. This is accomplished via three steps. First, the cloud data is adaptively subdivided into a set of regions according to a given subdivision error, and the data in each region is compressed by keeping the feature points (FPs) within the user-defined shape tolerance using a digital image based reduction method. Second, based on the FPs of each region, an IPCM is constructed, and RP layer contours are then directly extracted from the models. Finally, the RP layer contours are faired with a discrete curvature based fairing method and subsequently closed to generate the final layer-based RP model. This RP model can be directly submitted to the RP machine for prototype manufacturing. Two case studies are presented to illustrate the efficacy of the approach.  相似文献   

8.
Modelling cloud data using an adaptive slicing approach   总被引:2,自引:0,他引:2  
In reverse engineering, the conventional surface modelling from point cloud data is time-consuming and requires expert modelling skills. One of the innovative modelling methods is to directly slice the point cloud along a direction and generate a layer-based model, which can be used directly for fabrication using rapid prototyping (RP) techniques. However, the main challenge is that the thickness of each layer must be carefully controlled so that each layer will yield the same shape error, which is within the given tolerance bound. In this paper, an adaptive slicing method for modelling point cloud data is presented. It seeks to generate a direct RP model with minimum number of layers based on a given shape error. The method employs an iterative approach to find the maximum allowable thickness for each layer. Issues including multiple loop segmentation in layers, profile curve generation, and data filtering, are discussed. The efficacy of the algorithm is demonstrated by case studies.  相似文献   

9.
In additive manufacturing (AM) process, the manufacturing attributes are highly dependent upon the execution of hierarchical plan. Among them, material deposition plan can frequently interrupt the AM process due to tool-path changes, tool start-stop and non-deposition time, which can be challenging during free-form part fabrication. In this paper, the layer geometries for both model and support structure are analyzed to identify the features that create change in deposition modality. First, the overhanging points on the part surface are identified using the normal vector direction of the model surface. A k-th nearest point algorithm is implemented to generate the 3d boundary support contour which is used to construct the support structure. Both model and support structures are sliced and contours are evaluated. The layer contour, plurality, concavity, number of contours, geometric shape, size and interior islands are considered to generate an AM deposition model. The proposed model is solved for minimizing the change in deposition modality by maximizing the continuity and connectivity in the material deposition plan. Both continuity and connectivity algorithms are implemented for model and support structure for free-form object. The proposed algorithm provides the optimum deposition direction that results in minimum number of tool-path segments and their connectivity while minimizing contour plurality effect. This information is stored as a generic digital file format named Part Attributable Motion (PAM). A common application program interface (API) platform is also proposed in this paper, which can access the PAM and generate machine readable file for different existing 3D printers. The proposed research is implemented on three free-form objects with complex geometry and parts are fabricated. Also, the build time is evaluated and the results are compared with the available 3d printing software.  相似文献   

10.
翁桂荣  何志勇 《软件学报》2019,30(12):3892-3906
几何主动轮廓模型的缺点是对初始轮廓位置特别敏感,基于距离规则水平集(DRLSE)模型的初始轮廓曲线必须设置在目标边界的内部或者外部.基于边缘的自适应水平集(ALSE)模型,提出了一种提高初始轮廓鲁棒性的方法.但两种模型均容易出现陷入虚假边界、从弱边缘处泄露以及抗噪声能力差等问题.设计了一个结合自适应符号函数和自适应边缘指示函数的模型,使得主动轮廓演化能根据自适应符号函数的方向从初始轮廓开始自动进行膨胀及收缩,很好地改善了水平集对初始轮廓敏感的缺点,提高了鲁棒性,同时解决了水平集对收敛速度慢以及易从弱边缘处泄露的问题.此外,为了使得模型演化更加稳定,提出了一个新的距离规则项.实验结果表明:自适应符号函数的主动轮廓模型不仅可以提高分割质量,缩短图像分割时间,同时提高了对初始轮廓的鲁棒性.  相似文献   

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