Author name cluster

John E. Lloyd

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

8 papers

1 author row

ICRA Conference 2005 Conference Paper

Fast Implementation of Lemke's Algorithm for Rigid Body Contact Simulation

John E. Lloyd

We present a fast method for solving rigid body contact problems with friction, based on optimizations incorporated into Lemke’s algorithm for solving linear complementarity problems. These optimizations improve computation time in general and reduce the expected solution complexity from O(n 3 ) to nearly O(nm + m 3 ), where n and m are the number of contacts and rigid bodies. For a fixed number of bodies the expected complexity is therefore close to O(n). Our method also improves numerical robustness, and removes the need to explicitly compute the large matrices associated with rigid body contact problems.

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ICRA Conference 2001 Conference Paper

Robotic Mapping of Friction and Roughness for Reality-based Modeling

John E. Lloyd
Dinesh K. Pai

This paper discusses the robotic acquisition and characterization of surface friction and roughness for real-world objects. Our motivation is the construction of detailed "reality-based" models for existing objects that can be used in haptic displays and other applications involving simulation. A key challenge addressed in this paper is the acquisition of these surface properties on real objects with nontrivial shape, and registration of these properties with respect to geometric models of the shape. We show how Coulomb friction may be effectively estimated in the presence of variations in surface normal. We also show how to estimate a stochastic process model of surface roughness. Finally, we demonstrate the robotic mapping of surface friction over an entire object, using the UBC Active Measurement Facility (ACME).

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ICRA Conference 1998 Conference Paper

Generating Robust Trajectories in the Presence of Ordinary and Linear-Self-Motion Singularities

John E. Lloyd
Vincent Hayward

An algorithm is presented which computes feasible manipulator trajectories along fixed paths in the presence of kinematic singularities. The resulting trajectories are close to minimum time, given an inverse kinematic solution for the path and bounds on joint velocities and accelerations. The algorithm has complexity O(M log M), with respect to the number of joint coordinates M, and works using "coordinate pivoting", in which the path timing is generated locally with respect to whichever joint coordinate is changing the fastest. This allows the handling of singularities, including linear self-motions (e. g. , wrist singularities), where the path speed is zero but other joint velocities are non-zero. Examples involving the PUMA manipulator are shown.

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ICRA Conference 1998 Conference Paper

Removing the Singularities of Serial Manipulators by Transforming the Workspace

John E. Lloyd

A new method of handling the kinematic singularities of serial robotic manipulators is proposed. The idea is to transform the manipulator's workspace W into a desingularized workspace W*. Robotic motions can then be planned anywhere in W*, subject to limits on spatial velocity and acceleration, and the resulting joint velocities and accelerations will be well-behaved and bounded. W* differs from W only near a singularity surface, where a deformation is applied in the direction normal to the surface. While the technique does not handle self-motion singularities and may not be practical in some cases, it is very easy to implement for certain manipulators, such as the PUMA, which is studied in the paper. When applicable, the method offers various advantages when compared with other methods of singularity control.

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ICRA Conference 1997 Conference Paper

Model-based telerobotics with vision

John E. Lloyd
Jeffrey S. Beis
Dinesh K. Pai
David G. Lowe

We describe an implemented model-based telerobotic system designed to investigate assembly and other tasks involving contact and manipulation of known objects. Key features of our system include ease of maintaining a world model at the operator site and a task-centric operator interface. Our system incorporates gray-scale model-based vision to assist in building and maintaining the local model. The local model is used to provide a task-centric operator interface, emphasizing the natural and direct manipulation of objects, with the robot's presence indicated in a more abstract fashion. The operator interface is designed to work with widely available and inexpensive desktop computers with low DOF input devices (such as a mouse). We also describe experimental results to date, which include performing assembly-like tasks over the Internet.

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ICRA Conference 1996 Conference Paper

A discrete algorithm for fixed-path trajectory generation at kinematic singularities

John E. Lloyd
Vincent Hayward

An algorithm is presented for computing the necessary time-scaling to allow a non-redundant manipulator to follow a fixed Cartesian path containing kinematic singularities. The resulting trajectory is close to minimum-time, subject to bounds on joint velocities and accelerations. The algorithm assigns a series of knot points along the path, increasing the knot density in the vicinity of singularities. Appropriate path velocities are then computed for each knot point. Two experiments involving the PUMA manipulator are shown.

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ICRA Conference 1996 Conference Paper

Using Puiseux series to control non-redundant robots at singularities

John E. Lloyd

It is shown that the joint solution for a nonredundant robot following a piecewise analytic path can be expressed at kinematic singularities using a fractional power series (or Puiseux series). This is of use because the derivatives of such joint solutions often become infinite at singularities, making it difficult to track the path without incurring very large joint velocities and accelerations. Puiseux series provide a way to smoothly reparameterize the joint solution at singularities, which can be applied to path timing and perhaps other aspects of robot control.

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ICRA Conference 1991 Conference Paper

Real-time trajectory generation using blend functions

John E. Lloyd
Vincent Hayward

A techniques for transitioning between path segments that is tolerant to dynamic changes arising from sensor inputs is described. The main idea is to blend the segments together in a way that does not require advance knowledge of the paths. It is also possible to decompose the transition into an action which brings to rest the motion along the final path. By adjusting the timing of these two components, one may control the shape of the transition, in both time and space, so as to satisfy different task constraints. >

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