1. Introduction

Precise and reliable part manipulation is a critical issue in automated manufacturing. Much of the literature on this topic concerns the use of dexterous manipulators (e.g. [1, 2, 3]), which are currently too expensive for industrial applications. Other papers have addressed the use of more practical hardware, such as parallel-jaw grippers. Typically, though, this research has been limited to approaches that model grasped objects in 2D (e.g. [4, 5, 6, 7, 8, 9]). In these cases, it is presumed that constraining an object's horizontal planar motion is sufficient for successful manipulation.

In recent years, an additional consideration has been increasingly emphasized�that tooling for new components be produced quickly. Agile manufacturing systems must adapt rapidly to respond to changing customer needs [10, 11, 12], and such systems depend on rapid retooling. Using the methodology for rapid gripper customization described here, we propose that this need can be met.

In the approach presented here, we are developing a method to derive and fabricate 3-D custom tooling designs based on CAD descriptions of parts to be grasped or fixtured. Our approach is to exploit the geometric computation capabilities available in modern CAD programs and construct derived designs directly using rapid-prototyping technology. Furthermore, invoking computational geometry tools, it appears feasible to incorporate additional valuable considerations in gripper and fixture designs. For example, grasp precision can be improved through consideration of sliding contact constraints. Also, it is often possible to derive tooling shapes that enable precise grasp or fixturing of multiple, distinctly different part shapes with a single tool. Related, earlier work has focused on the design of fixtures, as computed based on parts' CAD models (e.g., [13, 14, 15, 16]). The design approach taken in this work generally presumes the use of modular elements, which may be as simple as thin posts providing approximately point-contact supports on the object surface. Our approach borrows from the results reported in this earlier work. At the same time, our approach appears to be unique in that it does not presume the use of modular fixture elements. Our computed tooling shapes are described by the surfaces of cavities, where such surfaces can be highly complex, non-analytic, and non-convex. The recent emergence of rapid-prototyping technology has enabled practical fabrication of such detailed and complex tooling surfaces.

Use of rapid prototyping for tooling fabrication is only now becoming a practicality. Initially, rapid prototyping was limited to modeling materials; more recently though, variations on rapid prototyping have enabled the use of structural engineering materials for automated production of functional parts. In the work presented here, we are utilizing a process known as Computer-Aided Manufacturing of Laminated Engineering Materials (CAM-LEM) being developed at Case Western Reserve University [17, 18, 19]. The CAM-LEM system is capable of building parts from a variety of materials, including modeling materials (e.g., paper, cardboard, wax) and engineering materials (e.g., plastics, advanced ceramics, and powdered metals). Using this system, it is possible to fabricate our computed shapes in engineering materials within a matter of hours or minutes. In the following sections, we present our computational approach and our fabrication approach as well as initial results. We also review some of the design variables and opportunities being explored in on-going research.

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