Philip C. Igwe

Developing alternative design concepts in VR environments using volumetric self-organizing feature maps

The conceptual design process has not benefited from conventional computer-aided design (CAD) technology to the same degree as embodiment design because the creative activities associated with developing and communicating alternative solutions, with minimal detail, is far less formulaic in its implementation. Any CAD system that seeks to support and enhance conceptual design must, therefore, enable natural and haptic modes of human–computer interaction. A computational framework for economically representing deformable solid objects for conceptual design is described in this paper. The physics-based deformation model consists of a set of point masses, connected by a series of springs and dampers, which undergo movement through the influence of external and internal forces. The location of each mass point corresponds to a node on a 3D mesh defined by a volumetric self-organizing feature map (VSOFM). A reference mesh is first created by fitting the exterior nodes of the VSOFM to sampled data from the surface of a primitive shape, such as a cube, and then redistributing the interior nodes to reflect evenly spaced hexahedral elements. Material properties are introduced to the mesh by assigning a mass value to individual nodes and spring coefficients to the nodal connections. Several illustrations involving the redesign of an ergonomic writing pen is used to demonstrate how the proposed virtual reality-based modeling system will permit the industrial designer to interactively change the shape and function of a design concept.

3D Object Reconstruction Using Geometric Computing

Fragmented objects are encountered in a variety of diverse engineering and scientific fields including industrial inspection, customized medical prosthesis design, forensic science, paleontology, and archaeology. The arbitrarily broken pieces must be reassembled and new material often added to complete the process of shape reconstruction. To prevent physical damage of the pieces during reconstruction and enhance shape visualization scientists have begun to exploit 3D data acquisition and graphical modeling tools. An algorithm for enabling free-form shape reconstruction from digitized data of fragmented pieces is described in this paper. The method exploits the topological structure and learning algorithm of a 3D self-organizing feature map (SOFM). The lattice of the SOFM is a spherical mesh that maintains the relative connectivity of the neighboring nodes as it transforms under external forces. The weight nodes of the lattice represent vertices of the constituent elements in the facetted surface model. The technique is illustrated by reconstructing two clay objects with closed geometries from several fragmented parts

Self-Organizing Feature Map (SOFM) based Deformable CAD Models

An adaptive modeling approach that uses a self-organizing feature map (SOFM) to create deformable hexahedral meshes for interactive geometric modeling is presented in this paper. The technique uses the nodes of a three-dimensional SOFM to represent discrete point masses that comprise a solid object. Although the geometry of the resultant mass-spring mesh will change under the influence of inputs applied through a haptic tool and interface, the relative connectivity of neighboring nodes in the time-varying mesh are maintained under the external and internal forces. The initial mesh can either be retrieved from a library of primitive shapes, or created by automatically fitting the topology preserving SOFM to selected surface points. The designer reshapes the virtual object by applying external forces and pressure to the initial mesh. The accuracy of the system depends on the mathematical equations used in formulating the model behavior. The model behavior can be altered by changing the material properties in the underlying mathematical equation. Examples of shape deformation are provided to illustrate the concepts introduced.

Modeling Deformable Objects for Computer-Aided Sculpting (CAS)Modeling Deformable Objects for Computer-Aided Sculpting (CAS)

Software tools for modeling complex freeform objects require the designer to use sophisticated procedures and complex protocols that do not inherently support the creative design process. Typical tasks include tedious control point manipulation and manual surface patch stitching operations. An interactive computer-aided sculpting (CAS) framework based upon deformable geometric models is described in this paper. The technique exploits the topology and learning algorithm of a self-organizing feature map (SOFM) to generate an adaptive volumetric mesh comprised of hexahedral elements. The pre-ordered lattice of the SOFM maintains the relative connectivity of neighbouring nodes in the mesh as it transforms under external and internal forces. Prior to virtual sculpting, the shape primitive is either retrieved from the object database or created by fitting a deformable mesh to representative surface points. Material and dynamic properties are incorporated into the deformable solid model by treating the surface and interior nodes as point masses connected with a network of springs. Illustrations are provided to demonstrate the virtual sculpting framework

Shape Morphing and Reconstruction Using A Self-Organizing Feature Map

The shape reconstruction process has remained an active research area in archaeology, paleontology, forensics, cultural heritage restoration and art conservation. In all these cases, the reconstruction process is tedious and time consuming. Aside from collecting several randomly mixed fragments, the fragments also have to be glued together. A stable and efficient algorithm for computer aided reconstruction of fragmented models is introduced in this paper. This novel approach is based on the morphing technique using the deformable self organizing feature map (SOFM). The SOFM is a skeletal framework for modeling surfaces that dynamically change shape. The lattice of the SOFM is a spherical map that maintains the relative connectivity of the neighboring nodes as it transforms under external and internal forces. The digitized fragments are assigned weight vectors and morphed into the weight vectors of the original model. The technique is illustrated by reconstructing the geometry of a complete vase from the surface data acquired from several fragmented pieces.

Microgripper design based on the photothermal bending effect of optical fibers

A micromanipulator based on the photo-thermal bending effect experienced by a beveled optical fiber is described in this paper. The micromanipulator design incorporates four fingers, two bendable fibers for actively grasping small objects and two stationary fibers to provide structural support while holding the object. Each finger is a 1mm diameter acrylic optic fiber with a 25mm beveled edge near the tip. The beveled edge is coated with a thin layer of black paint where the thickness has a measurable impact on the amount of tip deflection. A light beam, from a 150W halogen illuminator, is directed into the fixed end of the sculpted optic fiber causing the tip at the free end to deflect by approximately 50 microns. Several experiments are conducted to demonstrate that this simple microgripper is able to grasp, hold, and release a variety of small metal screws and ball bearings. Finite element analysis is used to further investigate the physical properties of the optical actuator. The theoretical deflections are slightly greater than the experimentally observed values. The FEM analysis is also used to estimate the maximum force (~ 0.7mN) generated at the actuator tip during deflection.