Non-polyhedral Objects Research Articles

Physically accurate haptic rendering with dynamic effects

We focus on the realism/transparency aspect of haptic rendering. We introduce a novel approach that enables physically correct and accurate simulation of contact wrench W/sub c/ for general rigid objects in real time, taking into account not only friction and gravity but also dynamic effects. Our method for contact force and moment simulation builds on the real-time identification of geometrically valid contact states despite digital errors. Our approach applies to general rigid bodies including both polyhedral and nonpolyhedral objects. For nonpolyhedral, curved objects, we build our contact state representation and contact force/moment model directly on the smooth and accurate representation of the object surfaces. Our approach's key idea is to solve for the contact force and moment analytically based on not only the contact configuration, but also the real-time identification of the exact type of the corresponding contact state, the type of instantaneous motion of the held object prior to reaching the contact configuration.

Global Three-Dimensional Surface Reconstruction from Occluding Contours

This paper considers the problem of 3D surface reconstruction of nonpolyhedral objects through a series of images taken by a moving camera. We propose a new direct method of surface reconstruction which is based on 3D regularized uniform bicubic B-spline surface patches. This reconstruction is achieved by observing the motion of occluding contours where the view lines graze the surface. It is shown that such a reconstruction of 3D surface is possible when the motion of the camera is known, with the exception of those fully concave parts where no view line can be tangential to the surface. Once a set of overlapping B-spline surface patches which constitute the 3D surface of an object are recontructed, our developed method can fuse them efficiently to obtain a global surface. This is based on 3D triangular mesh and regularized uniform bicubic B-spline surface interpolation. This method differs from some of the previous works: First, it considers the problem of regularization on the 3D surface instead of smoothing the contours in the 2D image. Second, we propose a global surface recovery from small local patches. Previous authors have been content only with the recovery of some local properties of the surface such as 3D shape position and surface curvature estimation. Experimental results are presented for both synthetic and real data.

Kinematic Models for Model-Based Compliant Motion in the Presence of Uncertainty

This article presents a systematic and fully general model- based approach to compliant robot motion, taking into account uncertainties in the geometry of the manipulated object and the environment with which it is in contact. The emphasis is not on control but on modeling, instantaneous motion specification, and on-line uncertainty identification. The presented models are intuitive and yet sufficiently flexible to deal with multiple and time-varying motion constraints between nonpolyhedral objects. The description of the interaction between the manipulated object and its environment starts from first- and second-order approximations of the objects' geometry at the contact points. From these geometric descriptions, the manipulated object's motion freedom—and its dual, the set of possible reaction forces—is modeled up to second order (i.e., accelerations) using the similarity with the kinematics of manipulators. Geometric uncertainties of the manipulated object and the environment, also up to second order (i.e., curvature), are integrated into these kinematic models. The on-line identification of uncertainties is based on the measured motion and/or the reaction forces. Two basic con cepts underlie the identification approach: consistency and reciprocity. These concepts give rise to linear identification equations in the uncertainty parameters by applying them to the first-order series expansions of the mathematical representa tions of the motion constraints. Both approaches are shown to be equivalent. The theoretical developments are illustrated by real-world experiments: the motion specification of a complex three-point contact situation between a cylindrical peg and the corre sponding chamferless hole; and force-controlled 2D contour tracking of an unknown object, with recursive identification of the curvature. Redundancy resolution and robot calibration are suggested as other potential applications.