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Some recent studies have addressed a class of human-machine coordination employing "virtual fixtures," which are computer-generated walls or guides presented through haptic devices for assisting precise path tracing and for preventing the entry to specified regions. This paper presents the concept and control algorithms of a new class of virtual fixtures that is based on simulated plasticity. The plasticity-based virtual fixtures act as hard walls as long as the user's force is smaller than a predetermined yield force, but the user can deviate from the fixtures by intentionally producing a force larger than the yield force. As a characteristic of plasticity, the proposed virtual fixtures do not store elastic energy; the reaction force from the fixture almost always opposes the user's motion to decelerate the motion. Thus, the plasticity-based virtual fixtures are expected to be useful in some applications where safety is an utmost priority. This paper presents control algorithms for realizing the concept of plasticity-based virtual fixtures, addressing technical challenges in treating discontinuous nature of plasticity in discrete-time systems. The algorithms were demonstrated through experiments using impedance-type and admittance-type haptic devices. [ABSTRACT FROM AUTHOR]

Contact and deformation modeling for interactive environments has seen many applications, from surgical simulation and training, to virtual prototyping, to teleoperation, etc., where both visual feedback and haptic feedback are needed. High-quality feedback demands a high level of physical realism as well as a high update rate in rendering, which are often conflicting requirements. In this paper, we present a unique approach to modeling force and deformation between a rigid body and an elastic object under complex contacts, which achieves a good compromise of reasonable physical realism and real-time update rate (at least 1 kHz). We simulate contact forces based on a nonlinear physical model. We further introduce a novel approximation of material deformation suitable for interactive environments based on applying Bernoulli-Euler bending beam theory to the simulation of elastic shape deformation. Our approach is able to simulate the contact forces exerted upon the rigid body (that can be virtually held by a user via a haptic device) not only when it forms one or more than one contact with the elastic object, but also when it moves compliantly on the surface of the elastic object, taking friction into account. Our approach is also able to simulate the global and local shape deformation of the elastic object due to contact. All the simulations can be performed in a combined update rate of over 1 kHz, which we demonstrate in several examples. [ABSTRACT FROM PUBLISHER]

Modeling of friction force is cumbersome because of its discontinuity at zero velocity. This paper presents a set of discrete-time friction models for the purpose of haptic rendering and virtual environment construction. These models allow friction to be treated as an admittance-type or impedance-type element of a virtual environment. They are derived from implicit Euler integration of Coulomb-like discontinuous friction and linear mass-spring-damper dynamics, and have closed-form expressions. They include rate-dependent friction laws, and their extension to multidimensional cases is easy in most practical cases. The validity of the models is demonstrated through numerical examples and implementation experiments. [ABSTRACT FROM AUTHOR]

This paper presents a modular algorithm for six-degree-of-freedom (6-DOF) haptic rendering. The algorithm is aimed to provide transparent manipulation of rigid models with a high polygon count. On the one hand, enabling a stable display is simplified by exploiting the concept of virtual coupling and employing passive implicit integration methods for the simulation of the virtual tool. On the other hand, transparency is enhanced by maximizing the update rate of the simulation of the virtual tool, and thereby the coupling impedance, and allowing for stable simulation with small mass values. The combination of a linearized contact model that frees the simulation from the computational bottleneck of collision detection, with penalty-based collision response well suited for fixed time-stepping, guarantees that the motion of the virtual tool is simulated at the same high rate as the synthesis of feedback force and torque. Moreover, sensation-pre- serving multiresolution collision detection ensures a fast update of the linearized contact model in complex contact scenarios, and a novel contact clustering technique alleviates possible instability problems induced by penalty-based collision response. [ABSTRACT FROM AUTHOR]

A new minimum-distance tracking algorithm is presented for moving convex bodies represented using tiled-together parametric surface patches. The algorithm is formulated by differentiating the geometric minimization problem with respect to time. This produces a hybrid dynamical system that incorporates dependence on rigid body motion, surface shape, and surface boundary interconnectedness. The minimum distance between a pair of previously identified closest features is found by feedback stabilizing the dynamical equations and numerically solving the resulting closed-loop system equations. Maintenance of the minimum distance and the associated closest points during motion is achieved through the action of a feedforward controller and a switching algorithm. The feedforward controller simultaneously accounts for surface shape and motion while the switching controller triggers updates to the extremal feature pair when extremal points on one body cross between Voronoi regions of the other body. In contrast to previously available minimum distance determination algorithms, attractive properties of the new algorithm include a means of determining the highest gain K that maintains stability under a given discretization scheme and a large and easily characterized bat of attraction of the stabilized closest points. These properties may be used to achieve higher computational efficiency. Simulation results are presented for various planar and spatial systems composed of a body and point or composed of two bodies. [ABSTRACT FROM AUTHOR]