PERCROScuola Superiore S. Anna1 Exeter September 26-27 2005 HAPTEX 4 nd Technical Meeting Architectural Design of the Haptex System F. Salsedo, M. Fontana,

PERCRO Scuola Superiore S. Anna 1

Exeter – September 26-27 2005

HAPTEXHAPTEX44ndnd Technical Meeting Technical Meeting

Architectural Design of the Haptex SystemF. Salsedo, M. Fontana, F. Tarri, E. Ruffaldi, M. Bergamasco

N. Magnenat-Thalmann, P. Volino, U. Bonanni

A. Brady, I. Summers, J. Qu

D. Allerkamp, G. Böttcher, F.-E. Wolter

M. Makinen, H. Meinander


ContributorsContributors

Responsible: PERCRO

F.Salsedo, M.Fontana, F. Tarri, E.Ruffaldi

Contributors:

MIRALab

N. Magnenat-Thalmann, P. Volino, U. Bonanni

UNEXE

A. Brady, I. Summers, J. Qu

UHAN

D. Allerkamp, G. Böttcher, F.-E. Wolter

SWL

M. Makinen, H. Meinander


OverviewOverview

•Introduction

•Background

•Definition of the scenario

•Architectures of HAPTEX: Gen. Considerations

•Architecture of HAPTEX System

•Conclusions


• Objective:The main objective of the HAPTEX project is the realization of a VR system the allows the assessment of the Fabric Hand of a cloth or a garment, i.e. its overall quality as perceived by the humans through their tactile sensors in response to actions like touching, squeezing, rubbing, or otherwise handling a fabric

• Foreseen Applications:One possible application of the final system is in the online market of textiles

• Technical Challenge:The big challenge is to identify suitable implementations able to render in real-time the mechanical behaviour of the fabric using appropriate physically based models that have to be simplified enough to be run in real-time but not too much to affect the realism of the rendering.

IntroductionIntroduction


BackgroundBackground•Application SoA: Only two other research projects have the same objective of simulating both the visual and tactile components of fabrics.

HAPTIC SIMULATION OF FABRIC HAND Prof. M.Govindaraj of the School of Textiles and Materials Technology, Philadelphia University.

At present the system allows only rubbing of a virtual fabric laid down on a plain surface with one finger.

• Architecture SoA: The time requirements for the visual and haptic rendering of the virtual fabric are very similar to those relating to the simulation surgery procedures. A huge amount of researches has been carried out in this field.

• Refresh Rate: 20-30Hz for Visual and 300-1000Hz for haptic

• Possible Models (Physical Based): Particles or FEM

• Simplifications: Linear Behavior, Off-line precalculation, Multi-Resolution-Multi-Rate etc.

The SoA analysis has been extended also in the field of non-real time rendering of cloth animation.

Used Physical based models: Particle and Hybrid (Particle FEM) Models


Definition of the scenarioDefinition of the scenarioIn order to steer the research and development activities to a clear focus, it has been decided to set, since the beginning of the project, the most demanding scenario that the HAPTEX system would be able to simulate

• Rectangular sample of fabric fixed on one of its edges

•The physical interaction takes place with two fingers (thumb and index)

•The user can touch squeeze and stretch the piece of fabric


Architecture of HAPTEX :Architecture of HAPTEX :General considerationsGeneral considerations

• No-Offline pre-calculations: The physical interaction with the fingertips can occur in every part of the cloth, so it does not make sense to conceive a mesh with a statically predefined resolution (offline pre-calculation are not allowed);

• Managing Two Finger Interaction: The interaction occurs through two independent fingertips: they can be overlapped or separate;

• Simulation of Local deformation of fingertips: To make the simulation realistic, it is important to render also the local deformation of the fingertips: especially when overlapped;

• Large Deformations/Displacements: The curvature as well as the deformation of the fabric in the proximity of the fingertip can be very high;

• Stick & Slip simulation: The fabric can slip with respect to the surface of the fingertip if the local tangential force exceeds the static friction threshold, that in turn depends on the pressure normal to the contact surface;

• Contact Operating Conditions: The stimulation of the mechanoreceptors of the skin depends on the local fine characteristics of the fabric but also on the operating conditions (relative velocity and pressure).


Dual-Layer Dual-Rate Architecture:

The physical engine is composed by two layers: a Large Scale Model (LSM) running at 20-30Hz, and a Small Scale Model, running at 300-1000 Hz. The two models are linked through a Norton Equivalent Impedance.LSM:

Is a coarse model of the whole piece of fabric running at 20-30Hz. It is responsible of providing the fabric geometry to the visualization system. Built with a Large Scale Properties Database

SSM:

Is a fine model of the area of the fabric located in the proximity of the user fingertips positions. It is responsible of providing of the needed data for the generation of the haptic and tactile stimulus. Built with the Small Scale Properties Database

20-30Hz 300-1000Hz

Architecture of HAPTEX Architecture of HAPTEX


Architecture of HAPTEX system Architecture of HAPTEX system


ConclusionsConclusionsChallenging Issues:•The requirements relating to the real-time rendering are very strict especially for what concerns the haptic feedback;

• Non-Linear Models have to be used since large displacements/deformations have to be simulated (geometry non-linearities)

• High spatial resolution is required due to rapidly changing mechanical variables in proximity of the contacts with the fingertips;

• From the hardware point of view, an integrated kinesthetic plus tactile stimulator device has to be developed allowing at least 2 points interaction.

A dual thread architecture has been selected complying with the two different time constraints of the Visual and Haptic rendering.

Two mechanically linked models of the fabric have been used having different spatial resolution in order to distribute the computational burden.

The development of this project is still in a very early stage and the details of the various software and hardware components will be defined in the future.


Thank youThank youfor your for your attentionattention

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PERCROScuola Superiore S. Anna1 Exeter September 26-27 2005 HAPTEX 4 nd Technical Meeting Architectural Design of the Haptex System F. Salsedo, M. Fontana,