Special Issue on Virtual Reality Application in Product Development

Guest Editorial for the Special Issue on Virtual Reality Application in Product Development

NURBS-Based Geometry for Integrated Structural Analysis

This grant was initiated in April 1993 and completed in September 1996. The primary goal of the project was to exploit the emerging defacto CAD standard of Non- Uniform Rational B-spline (NURBS) based curve and surface geometry to integrate and streamline the process of turbomachinery structural analysis. We focused our efforts on critical geometric modeling challenges typically posed by the requirements of structural analysts. We developed a suite of software tools that facilitate pre- and post-processing of NURBS-based turbomachinery blade models for finite element structural analyses. We also developed tools to facilitate the modeling of blades in their manufactured (or cold) state based on nominal operating shape and conditions. All of the software developed in the course of this research is written in the C++ language using the Iris Inventor 3D graphical interface tool-kit from Silicon Graphics. In addition to enhanced modularity, improved maintainability, and efficient prototype development, this design facilitates the re-use of code developed for other NASA projects and provides a uniform and professional 'look and feel' for all applications developed by the Iowa State Team

NC Milling Error Assessment and Tool Path Correction

A system of algorithms is presented for material removal simulation, dimensional error assessment and automated correction of Þve-axis numerically controlled (NC) milling tool paths. The methods are based on a spatial partitioning technique which incorporates incremental proximity calculations between milled and design surfaces. Hence, in addition to real-time animated Þve-axis milling simulation, milling errors are measured and displayed simultaneously. Using intermediate error assessment results, a reduction of intersection volume algorithm is developed to eliminate gouges on the workpiece via tool path correction. Finally, the view dependency typical of previous spatial partitioning-based NC simulation methods is overcome by a contour display technique which generates parallel planar contours to represent the workpiece, thus enabling dynamic viewing transformations without reconstruction of the entire data structure

Computational Geometry for Optimal Workpiece Orientation

Workpiece orientation is formulated as an optimal design problem based on a discrete approximation of design surface geometry, the kinematic capabilities of the process machine tool, and processing cost. The primary process application addressed is three-and four-axis numerically controlled (NC) milling, although the techniques presented may be applied to machines with more general articulation. Recent developments in applied spherical geometry are employed to formulate a constrained problem, and furthermore, a nonlinear optimization problem. For three-axis milling applications, a weight is assigned to each surface normal of the discrete model corresponding to the actual area it represents. Workpiece/machine orientation is optimized such that the angle between the weighted normals and the milling tool axis is minimized. This formulation is augmented, for four-axis milling, to incorporate limitations of the rotational degree of freedom, into the optimization formulation. The influence of tool geometry is also discussed and incorporated within constrained orientation algorithm

Sensor Augmented Virtual Reality Based Teleoperation Using Mixed Autonomy

A multimodal teleoperation interface is introduced, featuring an integrated virtual reality (VR) based simulation augmented by sensors and image processing capabilities onboard the remotely operated vehicle. The proposed virtual reality interface fuses an existing VR model with live video feed and prediction states, thereby creating a multimodal control interface. VR addresses the typical limitations of video based teleoperation caused by signal lag and limited field of view, allowing the operator to navigate in a continuous fashion. The vehicle incorporates an onboard computer and a stereo vision system to facilitate obstacle detection. A vehicle adaptation system with a priori risk maps and a real-state tracking system enable temporary autonomous operation of the vehicle for local navigation around obstacles and automatic re-establishment of the vehicle’s teleoperated state. The system provides real time update of the virtual environment based on anomalies encountered by the vehicle. The VR based multimodal teleoperation interface is expected to be more adaptable and intuitive when compared with other interfaces