Automatic Detection of the Optimal Ejecting Direction Based on a Discrete Gauss Map

Masatomo Inui,Nobuyuki Umezu,Hidekazu Kamei (사)한국CDE학회 2013 한국CAD/CAM학회 국제학술발표 논문집 Vol.2010 No.8

In this paper, the authors propose a system for assisting mold designers of plastic parts. Plastic parts are usually produced by the injection molding. In this method, the formed part must be removed from the mold core in a single ejecting direction. With a CAD model of a part, the system automatically determines the optimal ejecting direction of the part with the minimum undercuts. Two methods are introduced for improving the performance and the accuracy of the authors’ prior system. New point distribution method for the discrete Gauss map is adopted which is based on the architectural geodesic dome concept. Hierarchical structure is also introduced in the point distribution, a higher level “rough” Gauss map with sparse point distribution and another lower level “fine” Gauss map with much dense point distribution. By using this discrete Gauss map representation, a new algorithm is developed for computing the optimal ejecting direction. An experimental system is implemented and computational experiments are performed. Our system needs less than 30 seconds for determining the optimal ejecting direction of a CAD model with more than 1 million polygons.

Automatic detection of the optimal ejecting direction based on a discrete Gauss map

Inui, Masatomo,Kamei, Hidekazu,Umezu, Nobuyuki Society for Computational Design and Engineering 2014 Journal of computational design and engineering Vol.1 No.1

In this paper, the authors propose a system for assisting mold designers of plastic parts. With a CAD model of a part, the system automatically determines the optimal ejecting direction of the part with minimum undercuts. Since plastic parts are generally very thin, many rib features are placed on the inner side of the part to give sufficient structural strength. Our system extracts the rib features from the CAD model of the part, and determines the possible ejecting directions based on the geometric properties of the features. The system then selects the optimal direction with minimum undercuts. Possible ejecting directions are represented as discrete points on a Gauss map. Our new point distribution method for the Gauss map is based on the concept of the architectural geodesic dome. A hierarchical structure is also introduced in the point distribution, with a higher level "rough" Gauss map with rather sparse point distribution and another lower level "fine" Gauss map with much denser point distribution. A system is implemented and computational experiments are performed. Our system requires less than 10 seconds to determine the optimal ejecting direction of a CAD model with more than 1 million polygons.

Visualizing sphere-contacting areas on automobile parts for ECE inspection

Inui, Masatomo,Umezun, Nobuyuki,Kitamura, Yuuki Society for Computational Design and Engineering 2015 Journal of computational design and engineering Vol.2 No.1

To satisfy safety regulations of Economic Commission for Europe (ECE), the surface regions of automobile parts must have a sufficient degree of roundness if there is any chance that they could contact a sphere of 50.0 mm radius (exterior parts) or 82.5 mm radius (interior parts). In this paper, a new offset-based method is developed to automatically detect the possible sphere-contacting shape of such parts. A polyhedral model that precisely approximates the part shape is given as input, and the offset shape of the model is obtained as the Boolean union of the expanded shapes of all surface triangles. We adopt a triple-dexel representation of the 3D model to enable stable and precise Boolean union computations. To accelerate the dexel operations in these Boolean computations, a new parallel processing method with a pseudo-list structure and axis-aligned bounding box is developed. The possible sphere-contacting shape of the part surface is then extracted from the offset shape as a set of points or a set of polygons.

Thickness and clearance visualization based on distance field of 3D objects

Inui, Masatomo,Umezun, Nobuyuki,Wakasaki, Kazuma,Sato, Shunsuke Society for Computational Design and Engineering 2015 Journal of computational design and engineering Vol.2 No.3

This paper proposes a novel method for visualizing the thickness and clearance of 3D objects in a polyhedral representation. The proposed method uses the distance field of the objects in the visualization. A parallel algorithm is developed for constructing the distance field of polyhedral objects using the GPU. The distance between a voxel and the surface polygons of the model is computed many times in the distance field construction. Similar sets of polygons are usually selected as close polygons for close voxels. By using this spatial coherence, a parallel algorithm is designed to compute the distances between a cluster of close voxels and the polygons selected by the culling operation so that the fast shared memory mechanism of the GPU can be fully utilized. The thickness/clearance of the objects is visualized by distributing points on the visible surfaces of the objects and painting them with a unique color corresponding to the thickness/clearance values at those points. A modified ray casting method is developed for computing the thickness/clearance using the distance field of the objects. A system based on these algorithms can compute the distance field of complex objects within a few minutes for most cases. After the distance field construction, thickness/clearance visualization at a near interactive rate is achieved.

Visualization of potential sink marks using thickness analysis of finely tessellated solid model

Masatomo Inui,Shunsuke Onishi,Nobuyuki Umezu 한국CDE학회 2018 Journal of computational design and engineering Vol.5 No.4

Sink marks are unwanted shallow depressions on the molded plastic surface caused by localized shrink-age during the hardening process of injection molding. Sink marks appearing in the exterior impair the aesthetic quality of the product. In this study, a novel method for extracting potential sink marks that can occur on the part surface is proposed. The thicker portion of the part shrinks with a greater amount than that of the thinner portion. This difference in the shrinkage amount is the main cause of the sink mark. In the plastic part design practice, engineers often check the thickness distribution to predict potential sink marks in the part surface. Our method can be considered as an automated technique of such manual inspection task. A polyhedral solid model of the part with sufficiently small triangles of nearly the same size is prepared. The amount of shrinkage at each polygon is estimated based on its thickness and the shrinkage ratio of the part. The developed algorithm extracts the potential sink marks by analyzing the shrinkage distribution on the part surface.

2D wavelet transform data compression with error level guarantee for Z-map models

Nobuyuki Umezu,Keisuke Yokota,Masatomo Inui 한국CDE학회 2017 Journal of computational design and engineering Vol.4 No.3

Most of workpiece shapes in NC milling simulations are in Z-map representations that require a very large amount of data to precisely hold a high resolution model. An irreversible compression algorithm for Z-map models using a two-dimensional Haar wavelet transform is proposed to resolve this tight memory situation for an ordinary PC. A shape model is first transformed by using Haar wavelet to build a wavelet synopsis tree while the maximum errors caused by virtually truncating high-frequency components are simultaneously calculated. The total amount of the shape data can be reduced by truncating particular sections of the wavelet components that satisfy the error threshold given by the user. Our algorithm guarantees that any error due to its irreversible compression processes is smaller than the specified level measured against the original model. A series of experiments were conducted using an Apple iMac with a 3.2 GHz CPU and 8 GB of memory. The experiments were performed with 16 sample shape models on 512?512 to 8192?8192 grids to evaluate the compression efficiency of the proposed method. Experimental results confirmed that our compression algorithm requires approximately 20–30 ms for 512?512 models and 7 s for 8192?8192 models under a maximum error level of 10? 10?6 m (a typical criteria for NC milling simulations). The compressed binaries outputted by the proposed method are generally 25–35% smaller than the baseline results by gzip, one of common reversible compression libraries, while these two methods require almost the same level of computational costs.