A Conceptual Framework to Support Natural Interaction for Virtual Assembly Tasks

Over the years, various approaches have been investigated to support natural human interaction with CAD models in an immersive virtual environment. The motivation for this avenue of research stems from the desire to provide a method where users can manipulate and assemble digital product models as if they were manipulating actual models. The ultimate goal is to produce an immersive environment where design and manufacturing decisions which involve human interaction can be made using only digital CAD models, thus avoiding the need to create costly preproduction physical prototypes. This paper presents a framework to approach the development of virtual assembly applications. The framework is based on a Two Phase model where the assembly task is divided into a free movement phase and a fine positioning phase. Each phase can be implemented using independent techniques; however, the algorithms needed to interface between the two techniques are critical to the success of the method. The paper presents a summary of three virtual assembly techniques and places them within the framework of the Two Phase model. Finally, the conclusions call for the continued development of a testbed to compare virtual assembly methods

Mesh Reduction Using an Angle Criterion Approach

Surface polygonization is the process by which a representative polygonal mesh of a surface is constructed for rendering or analysis purposes. This work presents a new surface polygonization algorithm specifically tailored to be applied to a large class of models which are created with parametric surfaces having triangular meshes. This method has particular application in the area of building virtual environments from computer-aided-design (CAD) models. The algorithm is based on an edge reduction scheme that collapses two vertices of a given triangular polygon edge onto one new vertex. A two step approach is implemented consisting of boundary edge reduction followed by interior edge reduction. A maximum optimization is used to determine the location of the new vertex. The criterion that is used to control how well the approximate surface represents the actual surface is based on examining the angle between surface normals. The advantage of this approach is that the surface discretization is a function of two, user-controlled variables, a boundary edge angle error and a surface edge angle error. The method presented here differs from existing methods in that it takes advantage of the fact that for many models, the exact surface representation of the model is known before the polygonization is attempted. Because the precise surface definition is known, a maximum optimization procedure, that uses the surface information, can be used to locate the new vertex. The algorithm attempts to overcome the deficiencies in existing techniques while minimizing the number of triangular polygons required to represent a surface and still maintaining surface integrity in the rendered model. This paper presents the algorithm and testing results

Spatial Mechanism Design in Virtual Reality With Networking

Mechanisms are used in many devices to move a rigid body through a finite sequence of prescribed locations. The most commonly used mechanisms are four-bar planar mechanisms that move an object in one plane in space. Spatial mechanisms allow motion in three-dimensions (3D), however, to date they are rarely implemented in industry in great part due to the inherent visualization and design challenges involved. Nevertheless, they do provide promise as a practical solution to spatial motion generation and therefore remain an active area of research. Spatial 4C mechanisms are two degree-of-freedom kinematic closed-chains consisting of four rigid links simply connected in series by cylindrical (C) joints. A cylindrical joint is a two degree-of-freedom joint, which allows translation and rotation about a line in space. This paper describes a synthesis process for the design of 4C spatial mechanisms in a virtual environment. Virtual reality allows the user to view and interact with digital models in a more intuitive way than using the traditional human-computer interface (HCI). The software developed as part of this research also allows multiple users to network and share the designed mechanism. Networking tools have the potential to greatly enhance communication between members of the design team at different industrial sites and therefore reduce design costs. This software presents the first effort to provide a three-dimensional digital design environment for the design of spatial 4C mechanisms

A Virtual Reality Environment for Synthesizing Spherical Four-bar Mechanisms

This paper describes the development of a virtual reality environment which facilitates the design of spherical four-bar mechanisms. A short discussion of spherical mechanism design theory and computer-aided mechanism design is followed by a description of the virtual environment and the development and operation of the SphereVR program. The virtual environment allows the user to naturally interact with the input data and specify the design parameters while operating in a three-dimensional environment. We see this development as a logical extension of existing graphics-based spatial design software. The need for a three-dimensional design space is driven by the difficulty in specifying design inputs and constraints for a spatial problem using a two-dimensional interface. In addition, once the mechanism has been created, the virtual environment provides the opportunity for the user to visually verify that the mechanism will perform the desired three-dimensional motion