Desktop haptic virtual assembly using physically-based part modeling

This research investigates the feasibility of using a desktop haptic virtual environment as a design tool for evaluating assembly operations. Bringing virtual reality characteristics to the desktop, such as stereo vision, further promotes the use of this technology into the every day engineering design process. In creating such a system, the affordability and availablity of hardware/software tools is taken into consideration. The resulting application combines several software packages including VR Juggler, ODE (Open Dynamics Engine)/OPAL (Open Physic Abstraction Layer), OpenHaptics, and OpenGL/GLM/GLUT libraries to explore the benefits and limitations of combining haptics with physically-based modeling. The equipment used to display stereo graphics includes a Stereographies Emitter, Crystal Eyes shutter glasses, and a high refresh rate CRT Monitor. One or two-handed force feedback is obtained from various PHANTOM haptic devices from SensAble Technologies. The application\u27s ability to handle complex part interactions is tested using two different computer systems which approximate the higher and lower end of a typical engineer\u27s workstation. Different test scenarios are analyzed and results presented with regards to collision detection and physical response accuracies

Haptic Rendering of Interacting Dynamic Deformable Objects Simulated in Real-Time at Different Frequencies

International audienceThe dynamic response of deformable bodies varies significantly in dependence on mechanical properties of the objects: while the dynamics of a stiff and light object (e. g. wire or needle) involves high-frequency phenomena such as vibrations, much lower frequencies are sufficient for capturing dynamic response of an object composed of a soft tissue. Yet, when simulating mechanical interactions between soft and stiff deformable models, a single time-step is usually employed to compute the time integration of dynamics of both objects. However, this can be a serious issue when haptic rendering of complex scenes composed of various bodies is considered. In this paper, we present a novel method allowing for dynamic simulation of a scene composed of colliding objects modelled at different frequencies: typically, the dynamics of soft objects are calculated at frequency about 50 Hz, while the dynamics of stiff object is modeled at 1 kHz, being directly connected to the computation of haptic force feedback. The collision response is performed at both low and high frequencies employing data structures which describe the actual constraints and are shared between the high and low frequency loops. During the simulation, the realistic behaviour of the objects according to the mechanical principles (such as non-interpenetration and action-reaction principle) is guaranteed. Examples showing the scenes involving different bodies in interaction are given, demonstrating the benefits of the proposed method

Haptic Rendering of Hyperelastic Models with Friction

International audience— This paper presents an original method for inter-actions' haptic rendering when treating hyperelastic materials. Such simulations are known to be difficult due to the non-linear behavior of hyperelastic bodies; furthermore, haptic constraints enjoin contact forces to be refreshed at least at 1000 updates per second. To enforce the stability of simulations of generic objects of any range of stiffness, this method relies on implicit time integration. Soft tissues dynamics is simulated in real time (20 to 100 Hz) using the Multiplicative Jacobian Energy Decomposition (MJED) method. An asynchronous preconditioner, updated at low rates (1 to 10 Hz), is used to obtain a close approximation of the mechanical coupling of interactions. Finally, the contact problem is linearized and, using a specific-loop, it is updated at typical haptic rates (around 1000 Hz) allowing this way new simulations of prompt stiff-contacts and providing a continuous haptic feedback as well

The NifTK software platform for image-guided interventions: platform overview and NiftyLink messaging

PURPOSE: To perform research in image-guided interventions, researchers need a wide variety of software components, and assembling these components into a flexible and reliable system can be a challenging task. In this paper, the NifTK software platform is presented. A key focus has been high-performance streaming of stereo laparoscopic video data, ultrasound data and tracking data simultaneously. METHODS: A new messaging library called NiftyLink is introduced that uses the OpenIGTLink protocol and provides the user with easy-to-use asynchronous two-way messaging, high reliability and comprehensive error reporting. A small suite of applications called NiftyGuide has been developed, containing lightweight applications for grabbing data, currently from position trackers and ultrasound scanners. These applications use NiftyLink to stream data into NiftyIGI, which is a workstation-based application, built on top of MITK, for visualisation and user interaction. Design decisions, performance characteristics and initial applications are described in detail. NiftyLink was tested for latency when transmitting images, tracking data, and interleaved imaging and tracking data. RESULTS: NiftyLink can transmit tracking data at 1,024 frames per second (fps) with latency of 0.31 milliseconds, and 512 KB images with latency of 6.06 milliseconds at 32 fps. NiftyIGI was tested, receiving stereo high-definition laparoscopic video at 30 fps, tracking data from 4 rigid bodies at 20-30 fps and ultrasound data at 20 fps with rendering refresh rates between 2 and 20 Hz with no loss of user interaction. CONCLUSION: These packages form part of the NifTK platform and have proven to be successful in a variety of image-guided surgery projects. Code and documentation for the NifTK platform are available from http://www.niftk.org . NiftyLink is provided open-source under a BSD license and available from http://github.com/NifTK/NiftyLink. The code for this paper is tagged IJCARS-2014

Desarrollo de un sistema de teleodontología para adultos mayores en el contexto de la pandemia de COVID-19: integración de modelos de diagnóstico 3D en una plataforma web

Objective: To recognize the usefulness of incorporating Three-Dimensional models of standardized humans in electronic health records, in the context of the development of a teledentistry web platform designed for the attention of the elderly population in COVID-19 pandemic context. Material and Methods: A teledentistry web platform designed with different modules for clinical records. Through a new user-computer interface with a standardized virtual 3D phantom, an extraoral physical examination, an intraoral examination section was modeled. A label-associated marker is allowed to record descriptive aspects of the findings. A 3D odontogram represents multiple patient’s conditions for each of the 32 dental positions. Results: From a total of 135 patients registered on the platform, 51 markers and 33 photographs associated with the surface of the virtual 3D phantoms were recorded. For the Location parameter: Hard palate 27.6%, inserted gingiva 15.7%, tongue 15.6%. For the Type of lesion parameter (according to the information entered in the pathology selector): unidentified 35.3%, sub-prosthetic stomatitis 23.5%, irritative fibroma 9.8%. Through the registration of the exact location of the finding in the virtual phantom by a 3D marker, the 3D modeling of the oral pathologies contributed to a better diagnosis, improving the remote communication between the attending dentist and specialists. Conclusion:  The combination of the 3D modeling and anatomical-referencing in a teledentistry platform can become a powerful tool for the dental practice, due to their utility and specificity.Objetivo: Reconocer la utilidad de incorporar modelos tridimensionales de humanos estandarizados en registros electrónicos de salud, en el contexto del desarrollo de una plataforma web de teleodontología diseñada para la atención de la población adulta mayor en contexto de pandemia por COVID-19. Material y Métodos:  Una plataforma web de teleodontología diseñada con diferentes módulos para historias clínicas. A través de una nueva interfaz usuario-computadora con un fantoma 3D virtual estandarizado, se modeló un examen físico extraoral, una sección de examen intraoral. Se permite un marcador asociado a la etiqueta para registrar aspectos descriptivos de los hallazgos. Un odontograma 3D representa múltiples condiciones del paciente para cada una de las 32 posiciones dentales.Resultados: De un total de 135 pacientes registrados en la plataforma, se registraron 51 marcadores y 33 fotografías asociadas a la superficie de los fantomas virtuales 3D. Para el parámetro Ubicación: Paladar duro 27,6%, encía insertada 15,7%, lengua 15,6%. Para el parámetro Tipo de lesión (según la información ingresada en el selector de patología): no identificado 35,3%, estomatitis subprotésica 23,5%, fibroma irritativo 9,8%. A través del registro de la ubicación exacta del hallazgo en el fantoma virtual mediante un marcador 3D, el modelado 3D de las patologías orales contribuyó a un mejor diagnóstico, mejorando la comunicación remota entre el odontólogo tratante y los especialistas. Conclusión: La combinación del modelado 3D y la referenciación anatómica en una plataforma de teleodontología puede convertirse en una poderosa herramienta para la práctica odontológica, debido a su utilidad y especificidad

Discrete ordinates CT organ dose simulator (DOCTORS)

Computed tomography (CT) has become pervasive in medical diagnostics as improved imaging techniques and processing algorithms provide higher quality information to doctors. However, the exponentially increasing usage of CT has raised concerns regarding long term low-dose radiological risks. Currently, the dose to patients is computed using Monte Carlo methods and experimental tests. In other areas of radiation transport, deterministic codes have been shown to be much faster than Monte Carlo codes. Currently, no deterministic methodology exists to automatically generate a spatially distributed dose profile from a CT voxel phantom. This work proposes a new code, Discrete Ordinate CT Organ Dose Simulator (DOCTORS) which utilizes a GPU accelerated raytracer and discrete ordinate solver to compute photon flux in the patient. The flux is then converted to dose. The DOCTORS code was benchmarked against MCNP6 and found to have good qualitative agreement using both a water phantom and a realistic patient phantom. DOCTORS was also found to be much faster than MCNP6; MCNP takes hours to compute flux profiles that take less than a minute using DOCTORS. A GPU algorithm was implemented that speeds up the DOCTORS code by a factor of up to nearly 40 for large problems. GPU acceleration was found to benefit smaller problems much less. Speedup was seen in both single precision and double precision problems --Abstract, page iii

Delivering computationally-intensive digital patient applications to the clinic: An exemplar solution to predict femoral bone strength from CT data

Background and objective:Whilst fragility hip fractures commonly affect elderly people, often causing permanent disability or death, they are rarely addressed in advance through preventive techniques. Quantification of bone strength can help to identify subjects at risk, thus reducing the incidence of fractures in the population. In recent years, researchers have shown that finite element models (FEMs) of the hip joint, derived from computed tomography (CT) images, can predict bone strength more accurately than other techniques currently used in the clinic. The specialised hardware and trained personnel required to perform such analyses, however, limits the widespread adoption of FEMs in clinical contexts. In this manuscript we present CT2S (Computed Tomography To Strength), a system developed in collaboration between The University of Sheffield and Sheffield Teaching Hospitals, designed to streamline access to this complex workflow for clinical end-users. Methods:The system relies on XNAT and makes use of custom apps based on open source software. Available through a website, it allows doctors in the healthcare environment to benefit from FE based bone strength estimation without being exposed to the technical aspects, which are concealed behind a user-friendly interface. Clinicians request the analysis of CT scans of a patient through the website. Using XNAT functionality, the anonymised images are automatically transferred to the University research facility, where an operator processes them and estimates the bone strength through FEM using a combination of open source and commercial software. Following the analysis, the doctor is provided with the results in a structured report. Results:The platform, currently available for research purposes, has been deployed and fully tested in Sheffield, UK. The entire analysis requires processing times ranging from 3.5 to 8 h, depending on the available computational power. Conclusions:The short processing time makes the system compatible with current clinical workflows. The use of open source software and the accurate description of the workflow given here facilitates the deployment in other centres

Discrete Differential Geometry of Thin Materials for Computational Mechanics

Instead of applying numerical methods directly to governing equations, another approach to computation is to discretize the geometric structure specific to the problem first, and then compute with the discrete geometry. This structure-respecting discrete-differential-geometric (DDG) approach often leads to new algorithms that more accurately track the physically behavior of the system with less computational effort. Thin objects, such as pieces of cloth, paper, sheet metal, freeform masonry, and steel-glass structures are particularly rich in geometric structure and so are well-suited for DDG. I show how understanding the geometry of time integration and contact leads to new algorithms, with strong correctness guarantees, for simulating thin elastic objects in contact; how the performance of these algorithms can be dramatically improved without harming the geometric structure, and thus the guarantees, of the original formulation; how the geometry of static equilibrium can be used to efficiently solve design problems related to masonry or glass buildings; and how discrete developable surfaces can be used to model thin sheets undergoing isometric deformation

Unstructured grid algorithms for two- and three-dimensional flows on parallel computers

The Navier-Stokes equations are solved numerically for two-and three-dimensional viscous laminar flows. The domain is discretized using triangular control volumes in two dimensions and tetrahedra in three dimensions, using existing grid generators. The flow solvers are implemented on a variety of computers, including distributed memory parallel computers;A finite-volume approach is used to discretize the governing flow equations in conservation law form using conserved variables. A cell centered approach is used where the unknowns are computed at the center of each control volume. Both explicit and implicit solution strategies are pursued. In the two-dimensional version of the algorithm an explicit upwind scheme as well as a central-difference scheme with added artificial dissipation is used. The upwind scheme implemented in two dimensions is the advection upstream splitting method. Time-derivative preconditioning using primitive and conserved variables is applied to the two-dimensional flow solver. Time-derivative preconditioning is used to enhance the low Mach number rate of convergence. A multistage Runge-Kutta scheme is used to advance the solution in time;In the three-dimensional version of the algorithm, an implicit upwind scheme is used. For the implicit scheme, an approximate flux Jacobian is used on the left hand side to reduce the computational effort and a Roe flux difference splitting is used on the right hand side. The gradients in the control volume need to be computed so the upwind scheme is second order accurate;The gradients in each cell are computed based on the values of the flow variables at the vertices of the grid. The values at the vertices of the grid are obtained by inverse distance weighting all the cell-centered values of the control volumes surrounding each vertex. For the implicit scheme, a block Gauss-Seidel solver is used to solve the resulting sparse matrix. The correctness of the solution strategies is determined by comparing the calculated solutions to data available in the literature;The schemes are implemented on parallel distributed memory computers. The parallelism exploited is coarse grained. The discretized solution domain is partitioned such that each processing unit is allocated a part of the domain. The processing units perform the solution of the Navier-Stokes equations independently from each other on different parts of the grid and with different data. Communication between processors is needed to properly model the domain;Numerical results for two-dimensional flows are obtained for a developing channel flow, a sudden expansion flow, a driven cavity flow with and without heat transfer and the flow over on obstruction in a channel. Three-dimensional flows computed are a developing straight channel flow of constant cross section, a driven cavity flow, and a developing curved channel flow. Good agreement of the computed results with data available in the literature is found