Showing papers by "Oussama Khatib published in 2003"

Interactive rendering of deformable objects based on a filling sphere modeling approach

Abstract: Mass-spring systems have widely and effectively been used for modeling in real-time deformable objects. Easier to implement and faster than finite elements, these systems, on the other side, suffer from several drawbacks when coming to render physically believable behaviors. Neither isotropic or anisotropic materials can be controlled easily and the large number of springs and mass points composing the model makes it fastidious to define parameters to control elongation, flexion and torsion at a macroscopic level. Another weakness is that most of the materials found in nature maintain a constant or quasi-constant volume during deformations; unfortunately, mass-spring models do not have this property. In this paper, we extend the current state-of-the-art in soft tissue simulation by introducing a six-degree of freedom macroscopic elastic sphere described by mass, inertia and volumetric properties. Spheres are placed along the medial axis transform of the object whose centers are connected by a skeleton composed of a set of three-dimensional elastic links. Spheres represent internal mass, volume and control the global deformation of the object. The surface is modeled by setting point masses on the mesh nodes and damped springs on the mesh edges. These nodes are connected to the skeleton by individual elastic links, which control volume conservation and transfer forces between the surface and volumetric model. Using this framework we also present an efficient method to approximate collision detection between multiple bodies in real-time.

Real-time adaptive control for haptic manipulation with Active Observers

Abstract: The paper discusses compliant motion control using Active Observers (AOBs) applied in robotic manipulators. Stochastic estimation strategies for haptic manipulation are introduced. Stability and robustness analysis is made as a function of stiffness mismatches. Real time adaptation is discussed.

Dynamic loading criteria in actuator selection for desired dynamic performance

Abstract: This article presents two methods for selecting actuators based on the dynamic loading criteria which yield a manipulator with a desired level of dynamic performance. Here, dynamic performance is measured in terms of a robot's acceleration and force capabilities, which describe its ability to accelerate the end-effector and to apply forces to the environment, given the limitations on its actuator torques. The Dynamic Capability Equations are used to model the relationship between actuator torque capacities and the acceleration and force capabilities, because they treat linear and angular quantities in a consistent and physically meaningful way. This article discusses actuator selection for a single configuration, as well as for multiple configurations.

Actuation Methods For Human-Centered Robotics and Associated Control Challenges

Abstract: In recent years, many successful robotic manipulator designs have been introduced. However, there remains the challenge of designing a manipulator that possesses the inherent safety characteristics necessary for human-centered robotics. In this paper, we describe recent developments in low impedance actuation that have allowed for improvements in the safety characteristics of human-centered manipulators. In addition, the control challenges unique to the use of low impedance actuation are discussed along with possible control strategies for their successful implementation.

Beyond the Looking Glass : The Haptic Exploration of Virtual Environments

Abstract: The visual quality, complexity and fidelity of virtual environments displayable on modern computer systems continues to grow unabated. A barrier exists, however, between these worlds and our own, leaving them presently out of reach. This thesis examines two technologies, haptic rendering and dynamic simulation, that help to break the barriers between these worlds by allowing direct “hands-on” interaction with physically intuitive virtual environments. Haptic systems allow users to receive and transmit information by touch. Through a force-reflecting mechanical device, users experience the illusion of contact with a real body. A novel representative model is created to allow the robust display of an object given its geometry and surface characteristics. This model attempts to, whenever possible, take advantage of representations that are common in graphics display, including geometry, shading and texture. The algorithms which comprise this model enable realistic contact with arbitrarily complex virtual objects. The advantage of being able to touch virtual objects would be of limited value, however, if the objects did not react in a physically intuitive manner. Objects cannot be described solely in terms of their geometric properties; they must also mimic physical characteristics such as mass, inertia and non-penetration. In the second part of the thesis a framework to efficiently resolve collision and contact constraints between different complex multi-body articulated systems is developed. This framework simplifies the resulting equations by breaking the space of motions between components effected by the collision and those that do not. The models developed for this framework also highlight many of the attributes common to simulation, robotic control and dynamic modeling. This thesis presents results incorporating both haptics and dynamic simulation for tasks in a variety of disciplines. Whether for training; research, education or entertainment, the technologies described help add tangible value to the virtual experience.

Non-redundant robotic manipulator acceleration capability and the actuation efficiency measure

Abstract: This article presents a performance measure, the actuation efficiency, which describes the imbalance between the end-effector accelerations achievable in different directions of non-redundant robotic manipulators. A key feature of the proposed measure is that in its development the unitary differences between linear and angular accelerations are treated in a physically meaningful manner. The measure also indicates oversized actuators, since this contributes to the imbalance in achievable accelerations. The development of this measure is based on the formulation of the Dynamic Capability Hypersurface. The shape of this hypersurface is a weak indicator of the level of imbalance in achievable end-effector accelerations.

Real-Time Adaptive Control for Haptic Manipulation with Active 0 bservers

Abstract: The paper discusses compliant motion control using Active Observers (AOBs) applied in robotic manip ulators. Stochastic estimation strategies for haptic manipulation are introduced. Stability and robustness analysis is made BS a function of stiffness mismatches. Real time adaptation is discussed.