john lloyd

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Lund University

University of California, San Diego

Náyade Sharon

Universidad Pedagogica Nacional

Swedish Defence Research Agency

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Papers by john lloyd

Programming contact tasks using a reality-based virtual environment integrated with vision

IEEE Transactions on Robotics and Automation, 1999

We present an integrated system in which an operator uses a simulated environment to program part... more We present an integrated system in which an operator uses a simulated environment to program part-mating and contact tasks. Generation of models within this virtual environment is facilitated using a fast, occlusion-tolerant, 3D grey-scale vision system which can recognize and accurately locate objects within the work site. A major goal of this work is to make robotic programming easy and intuitive for untrained users working with standard desktop hardware. Simulation can help accomplish this, offering the ease-of-use benefits of "programming by demonstration", coupled with the ability to create a programmer-friendly virtual environment. Within a simulated environment, it is also straightforward to track and interpret an operator's actions. The simulator models objects as polyhedra and implements full 3D contact dynamics, making is easy to place and manipulate objects using input from a simple 2D mouse. When a manipulation task is completed, local planning techniques are used to turn the virtual environment's motion sequence history into a set of robot motion commands capable of realizing the prescribed task.

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Removing the singularities of serial manipulators by transforming the workspace

Proceedings. 1998 IEEE International Conference on Robotics and Automation (Cat. No.98CH36146)

A new method of handling the kinematic singularities of serial robotic manipulators is proposed. ... more 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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Teaching health economics to medical personnel from developing nations

Health Manpower Management, 1996

Outlines the author’s experiences and the lessons learnt from work in the field of management tra... more Outlines the author’s experiences and the lessons learnt from work in the field of management training for doctors and other medical personnel. Explains the policy of using a dual approach: economic concepts and ideas in practical situations. States that by adopting this participative, problem‐solving approach and involving the discipline of economics in tandem with other skills and subjects, it addresses some of the issues which medical personnel face in their places of work.

The legacy of a superpower

The Economics of Transition, 1997

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Kinematics of common industrial robots

Robotics and Autonomous Systems, 1988

An approach to finding the solution equations for simple manipulators is described which enhances... more An approach to finding the solution equations for simple manipulators is described which enhances the well known method of Paul, Renaud, and Stevenson, by explicitly making use of known decouplings in the manipulator kinematics. This reduces the set of acceptable equations from which we obtain relationships for the joint variables. For analyzing the Jacobian, such decoupling is also useful since it manifests itself as a block of zeros, which makes inversion much easier. This zero lock can be used to obtain a concise representation for the forward and inverse Jacobian computations. The decoupling also simplifies the calculations sufficiently to allow us to make good use of a symbolic algebra program (MACSYMA) in obtaining our results. Techniques for using MACSYMA in this way are described. Examples are given for several industrial manipulators.

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$Research paper thumbnail of Revisiting the concept of talar shift in ankle fractures$

Revisiting the concept of talar shift in ankle fractures

Foot & ankle international, 2006

In 1976, Ramsey and Hamilton published a classic experiment investigating the biomechanical effec... more In 1976, Ramsey and Hamilton published a classic experiment investigating the biomechanical effects of talar shift in a simple ankle fracture model. Their finding was that 1 mm of talar shift resulted in a 42% decrease in tibiotalar contact surface area. Based on this conclusion, 1 mm of talar shift became the recognized indication for operative fixation. Twelve cadaver ankles were dissected and the distal tibia coated with carbon powder. A 70-kg load was applied to the distal tibia that resulted in transference of the carbon onto the talus. The contact surface area was determined at 0, 1, 2, 4 and 6 mm of talar shift using spacers fixed in the medial gutter. Tracing paper was used to mark the outline of the contact area and measured using graph paper. Our results were similar to Ramsey and Hamilton's original experiment. One millimeter of lateral talar shift resulted in 40% loss of contact surface area compared with 42% in the original experiment. A large variance was seen in t...