In this paper, we present a haptic painting system which provides users an easy way to accurately add color on the mesh models. Unlike some of previously published methods which require texture mapping or point resampling, our system is totally mesh-based. Since a local dynamic subdivision algorithm has been developed in our method, the quality of painting can be less dependent on the original mesh density so that fine details can also be created in sparse models. Sample studies have shown that the visual painting results on mesh models are good enough for early industrial design of multi-materials (or multi-colors) parts where frequent and easy changes of painting are required. Our approach can also provide useful information in mesh editing like smoothing and cutting, which makes the system possible to be further developed into a 3D interactive design tool for parts made of multi-materials that are normally manufactured by multi-shot molding processes.
Clamshell casting is a popular manufacturing technique where liquid is poured into a mold or cast and the cast is removed once the liquid has hardened. The term clamshell refers to the way in which the cast is removed. The two cast parts are removed by rotation through a hinge much like a clamshell. Given an object, modeled by a polyhedron P of arbitrary genus with combinatorial complexity n , we determine when the surface of the polyhedron can be decomposed into two parts s.t. each part can be rotated around a line in space without colliding with each other or intersecting the interior. Such a line is a valid casting line. Specifically, we solve the following problems: (1) Given a line l in space, we determine in ( )O n time whether l is a valid casting line for P . If degeneracies are present, such as a reflex edge or face of P is perpendicular to l , the running time increases slightly to ( log ) O n n . (2) In 4 ( ( )) α O n n time, where ( ) α n is the inverse Ackermann function, we report all combinatorially distinct valid casting lines. The running time is 4 ( log ) O n n in the presence of degeneracies. All of the running times are shown to be almost optimal.
Multi-material products are getting increasingly popular in recent years. Yet no systems have been developed to support the design of such products. In this article, a haptic-based method for designing multi-material products is proposed. The proposed method consists of three main parts: haptic painting/marking, boundary smoothing/fitting, and volume decomposition. A prototype system based on the three parts has been implemented using a haptic input device. The haptic device provides an intuitive user interface for quick volume mark-up in a multi-material product by direct mesh painting. Each painted region represents a material volume whose boundary can be automatically traced. The boundary points are then used as control points for Catmull-Rom spline fitting. To constrain a spline to the original mesh surface, the spline is projected onto the mesh. Now, using the boundary splines, volume decomposition can be done automatically when needed. Each decomposed volume can be assigned a different material or colour. The numerous iterations of volume mark-up and decomposition in the early stage of multimaterial product design can now be made easy and effective using the proposed method.
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