Jose San Martin

Soft finger tactile rendering for wearable haptics

This paper introduces a tactile rendering algorithm for wearable cutaneous devices that stimulate the skin through local contact surface modulation. The first step in the algorithm simulates contact between a skin model and virtual objects, and computes the contact surface to be rendered. The accuracy of this surface is maximized by simulating soft skin with its characteristic nonlinear behavior. The second step takes the desired contact surface as input, and computes the device configuration by solving an optimization problem, i.e., minimizing the deviation between the contact surface in the virtual environment and the contact surface rendered by the device. The method is implemented on a thimble-like wearable device.

Optimization-Based Wearable Tactile Rendering

Novel wearable tactile interfaces offer the possibility to simulate tactile interactions with virtual environments directly on our skin. But, unlike kinesthetic interfaces, for which haptic rendering is a well explored problem, they pose new questions about the formulation of the rendering problem. In this work, we propose a formulation of tactile rendering as an optimization problem, which is general for a large family of tactile interfaces. Based on an accurate simulation of contact between a finger model and the virtual environment, we pose tactile rendering as the optimization of the device configuration, such that the contact surface between the device and the actual finger matches as close as possible the contact surface in the virtual environment. We describe the optimization formulation in general terms, and we also demonstrate its implementation on a thimble-like wearable device. We validate the tactile rendering formulation by analyzing its force error, and we show that it outperforms other approaches.

Volume haptic rendering with dynamically extracted isosurface

Haptic interfaces offer an intuitive way to interact with and manipulate 3D data, and may simplify the interpretation of visual information. This work proposes an algorithm to provide haptic feedback directly from volumetric data sets, as an aid to regular visualization. The haptic rendering algorithm lets the user perceive isosurfaces in the volumetric data, and it relies on several design features that ensure a robust and efficient rendering. Robustness is derived from existing proxy-based methods. The presented algorithm adds a novel continuous collision detection based on dynamic extraction of isosurfaces in tetrahedral meshes in order to avoid fall-through of surfaces. The isosurface is extracted dynamically in a local manner, hence there is no need to construct and store the full isosurface, thereby reducing both computational cost and storage at the same time. Isosurfaces are defined by interpolating a density field on tetrahedral meshes. The use of tetrahedral meshes guarantees continuity and watertightness of the isosurface, and it also enables smooth transitions between isosurface values.

Measurement of suitability of a haptic device in a virtual reality system

In the context of the optimization of the mechanical platform of a virtual reality system involving a haptic device, this paper introduces two tools in order to help the designer for obtaining the best positioning of the device respect to the application workspace. With this purpose we have defined a measure called Average Volumetric Manipulability, of how the application workspace fits in with the volume where haptic device provides its best performance. Also, we have defined other measure called Useful Manipulability which takes in account the frequency with which each zone of the application workspace is visited during the simulation process. The practical use of these measures is demonstrated using them during the design and development of a real application.

A study of the Manipulability of the PHANToM OMNI Haptic Interface

In order to perform the assembly of a haptic device in the set of a simulator, we have to check that it operates in its optimal workspace. In general it will depend on the required functionality. One of the characteristics that define the performance of a haptic device is the manipulability. In this paper we are going to accomplish a kinematics study of the device PHANToM OMNi. This study will produce as result the calculation of a map, in which to each of the points of the workspace, we assign a value of manipulability. In this way it is obtained a drawing that identifies the best zones of functioning of the device and therefore those in which we wish that our manipulator preferably works as a design criteria.

A New Approach to Automatic Segmentation of Bone in Medical Magnetic Resonance Imaging

This paper presents the modelling and segmentation with correction of inhomogeneity in magnetic resonance imaging of shoulder. For that purpose a new heuristic is proposed using a morphological method and a pyramidal Gaussian decomposition (Discrete Gabor Transform). After the application of these filters, an automatic segmentation of a bone is possible despite of other semiautomatic methods present in the literature.

Haptically Assisted Connection Procedure for the Reconstruction of Dendritic Spines

Dendritic spines are thin protrusions that cover the dendritic surface of numerous neurons in the brain and whose function seems to play a key role in neural circuits. The correct segmentation of those structures is difficult due to their small size and the resulting spines can appear incomplete. This paper presents a four-step procedure for the complete reconstruction of dendritic spines. The haptically driven procedure is intended to work as an image processing stage before the automatic segmentation step giving the final representation of the dendritic spines. The procedure is designed to allow both the navigation and the volume image editing to be carried out using a haptic device. A use case employing our procedure together with a commercial software package for the segmentation stage is illustrated. Finally, the haptic editing is evaluated in two experiments; the first experiment concerns the benefits of the force feedback and the second checks the suitability of the use of a haptic device as input. In both cases, the results shows that the procedure improves the editing accuracy.

A Study of the Attenuation in the Properties of Haptic Devices at the Limit of the Workspace

In the context of the optimization in virtual reality systems involving a haptic device, this paper introduces a correction in the formula that defined the performance of the device near the boundary of its workspace. We introduce too corrections to an index based on the Manipulability which takes in account the frequency with which each zone of the application workspace is visited during the simulation process, in order to help the designer for obtaining the best positioning of the device respect to the virtual environment. We demonstrate the new formula studying three different tasks to be accomplished. Finally we look for this best positioning analyzing not only the displacement but the different orientations we can introduce in the virtual environment in order to take advantage of the best zones of the workspace in terms of Manipulability.

Optimal Design of a Haptic Device for a Particular Task in a Virtual Environment

When we create an environment of virtual reality based training that integrates one or several haptic devices sometimes the first choice to make is the device to use. This paper introduces an algorithm that allows us, for a particular task to be simulated in a virtual environment, to find key data for the design of appropriate haptic device, or to select the clues in order to get optimum performance for that environment and that particular task.

Study of optimal behavior in complex virtual training systems

In previous works we have studied the behavior of simple training systems integrated by a haptic device basing on criteria derived from Manipulability concept. The study of complex systems needs to re-define the criteria of optimal design for these systems. It is necessary to analyze how the workspace of two different haptics, simultaneously on the same model, limits the movement of each other. Results of the new proposed measures are used on Insight ARTHRO VR training system. The Minimally Invasive Surgery (MIS) techniques use miniature cameras with microscopes, fiber-optic flashlights and high definition monitors. The camera and the instruments are inserted through small incisions on the skin called portals. The trainer uses two PHANToM OMNi haptic devices, one representing the camera and other the surgical instrumental.