Orienting Deformable Polygonal Parts without Sensors

Parts orienting is an important part of automated manufacturing. Sensorless manipulation has proven to be a useful paradigm in addressing parts orienting, and the manipulation of deformable objects is a growing area of interest. Until now, these areas have remained separate because existing orienting approaches utilize forces that if applied to deformable parts violate the assumptions used by existing algorithms, and could potentially break the part. We introduce a new algorithm and manipulator actions that, when provided with the geometric description and a deformation model of choice for the part, exploits the deformation and generates a Plan that consists of the shortest sequence of manipulator actions guaranteed to orient the part up to symmetry from any unknown initial orientation and pose. Additionally, the algorithm estimates whether a given manipulator is sufficiently precise to perform the actions which guarantee the final orientation. This is dictated by the particular part geometry, deformation model, and the manipulator action path planner which contains simple end-effector constraints and any standard motion planner. We illustrate the success of the algorithm with multiple parts through 192 trials of experiments that were performed with low-precision robot manipulators and six parts made of four types of materials. The experimental trials resulted in 154 successes, which show the feasibility of deformable parts orienting. The analysis of the failures showed that for success the assumptions of zero friction are essential for this work, increased manipulator precision would be beneficial but not necessary, and a simple deformation model can be sufficient. Finally, we note that the algorithm has applications to truly sensorless manipulation of non-deformable parts

VISIO-HAPTIC DEFORMABLE MODEL FOR HAPTIC DOMINANT PALPATION SIMULATOR

Vision and haptic are two most important modalities in a medical simulation. While visual cues assist one to see his actions when performing a medical procedure, haptic cues enable feeling the object being manipulated during the interaction. Despite their importance in a computer simulation, the combination of both modalities has not been adequately assessed, especially that in a haptic dominant environment. Thus, resulting in poor emphasis in resource allocation management in terms of effort spent in rendering the two modalities for simulators with realistic real-time interactions. Addressing this problem requires an investigation on whether a single modality (haptic) or a combination of both visual and haptic could be better for learning skills in a haptic dominant environment such as in a palpation simulator. However, before such an investigation could take place one main technical implementation issue in visio-haptic rendering needs to be addresse

Variational methods for modeling and simulation of tool-tissue interaction

Ph.DDOCTOR OF PHILOSOPH

Thermal-mechanical response modelling and thermal damage prediction of soft tissues during thermal ablation

During thermal ablation, target soft tissue responses both thermally and mechanically simultaneously. However, current thermal ablation treatment mainly relies on the quantitative temperature indication to evaluate tissue behaviours and control the delivered thermal energy, which is ineffective and inaccurate. Based on these, our research study focuses on: bioheat transfer theory, linear and nonlinear elasticity of soft tissues at varied temperatures, as well as thermal damage prediction theory, and the whole program was developed in Netbeans IDE 8.1. The main contributions of our research work lie in the following aspects: Firstly, considering a situation where soft tissue’s mechanical deformation during thermal ablation is only caused by thermal loading, it is reasonable to assume that the generated strain value is within the linear range of stress-strain relationship characterisation which is also thermal stable (nearly temperature independent). Therefore, we propose our first model by integrating the heating process with thermally-induced mechanical deformations of soft tissues for simulation and analysis of the thermal ablation process. This method combines classical Fourier based bioheat transfer and constitutive elastic mechanics derived from the method of multiplicative decomposition of thermal mechanical deformation gradient, as well as non-rigid motion dynamics. The 3D governing equations are discretised spatially using finite difference scheme and temporally using implicit time integration scheme and the obtained linear system of equations are subsequently solved using a Gauss-Seidel iterative solver. Simulation implement based on proposed method can serve as a visible assistance for relevant surgeons on analysing soft tissue’s behaviours from both thermal and mechanical deformation fields rather than from just determined temperature distribution. Secondly, we present a method to characterize soft tissue thermal damage by taking into account of thermal mechanical interactions during thermal ablation, concerning stored energy by both thermal and mechanical effects can affect the energy barrier for macromolecular transitions, leading to further or the reverse damage to treated biological tissues. To do this, traditional tissue damage model of Arrhenius integration is improved by including the thermally and mechanically induced strain energy term. Simulations and comparison analysis based on different types of soft tissues are also performed to study its influences. Our findings may provide more reliable guidelines for relevant surgeons to control the tissue damage zone during thermal ablation practice. Thirdly, thermal relaxation time used to describe heating process in homogeneous substance is usually referred to as the characteristic time in non-homogeneous biological materials, which is needed to accumulate enough energy to transfer to the nearest point. Such non-Fourier thermal behaviour has also been experimentally observed in biological tissues. Our second model is presented by integrating non-Fourier bioheat transfer and constitutive elastic mechanics derived from the method of multiplicative decomposition of thermal mechanical deformation gradient, as well as non-rigid motion of dynamics to predict and analyse thermal distribution, thermal-induced mechanical deformation and tissue damage under purely thermal loads. The simulation performances are compared between two numerical methods: Finite Difference Method and Finite Element Method, from perspectives of accuracy and computing efficiency, and also against available existed experimental data and other commercialized analysis tools. Finally, our research moves on to nonlinear range characterization of tissue deformation under combined thermal and mechanical loads. Basically, the contribution of our proposed nonlinear thermal mechanical model is by extending the finite strain framework of Neo-Hookean energy function to the heating process of soft tissues during thermal ablation. Meanwhile, our nonlinear thermal mechanical model also considers the effect of collagen fibre bundles as embedded in many biological tissues. Separating free energy density modelling into isotropic and anisotropic parts, it is assumed that the anisotropy is due to the collagen fibre bundles behaviour, while the ground substance, behaves in an isotropic manner can be modelled using selected nonlinear biomaterial model. The necessary ingredients for the finite element method implementation including: weak form and time integration are also included in this chapter. Keywords: Thermal ablation, soft tissue, non-Fourier bioheat transfer, thermal mechanical deformation, anisotropic nonlinear, tissue damage

VISIO-HAPTIC DEFORMABLE MODEL FOR HAPTIC DOMINANT PALPATION SIMULATOR

Vision and haptic are two most important modalities in a medical simulation. While visual cues assist one to see his actions when performing a medical procedure, haptic cues enable feeling the object being manipulated during the interaction. Despite their importance in a computer simulation, the combination of both modalities has not been adequately assessed, especially that in a haptic dominant environment. Thus, resulting in poor emphasis in resource allocation management in terms of effort spent in rendering the two modalities for simulators with realistic real-time interactions. Addressing this problem requires an investigation on whether a single modality (haptic) or a combination of both visual and haptic could be better for learning skills in a haptic dominant environment such as in a palpation simulator. However, before such an investigation could take place one main technical implementation issue in visio-haptic rendering needs to be addresse

Differential equation-based shape interpolation for surface blending and facial blendshapes.

Differential equation-based shape interpolation has been widely applied in geometric modelling and computer animation. It has the advantages of physics-based, good realism, easy obtaining of high- order continuity, strong ability in describing complicated shapes, and small data of geometric models. Among various applications of differential equation-based shape interpolation, surface blending and facial blendshapes are two active and important topics. Differential equation-based surface blending can be time-independent and time-dependent. Existing differential equation-based surface blending only tackles time-dependen

Simulación dinámica y deformaciones de superfícies paramétricas

Se desarrolla un modelo basado en NURBS, BSplines4D, de representación de superficies parametrizadas en 4D. El objetivo es la representación y simulación dinámica de superficies deformables basadas en el modelo; se realiza un estudio de las ecuaciones del movimiento, asociando un funcional de energía para medir la deformación de objetos, realizando un estudio riguroso sobre los métodos de integración y de discretización, tanto temporal como espacial, determinando su adecuación para resolver el sistema de ecuaciones diferenciales generado. El movimiento y la simulación de la deformación se realizan exclusivamente usando los puntos de control 4D, obteniendo una eficiencia numérica y computacional excelentes. La determinación del modelo BSplines4D se realiza tras un estudio pormenorizado de los modelos existentes. También se ha utilizado para desarrollar un modelo, N-Scodef, de deformaciones de formas libres (FFD), utilizando deformaciones geométricas basadas en restricciones. Se han establecido las condiciones para aplicar restricciones con trayectorias no rectilíneas, representadas por curvas B-Spline 4D. La deformación se adapta de forma precisa a la forma descrita por las curvasEs desenvolupa un model basat en NURBS, Bsplines4D, de representació de superfícies parametritzades en 4D. L'objectiu és la representació i simulació dinàmica de superfícies deformables basades en el model; es realitza un estudi de les equacions del moviment, associant un funcional d'energia per mesurar la deformació d'objectes, realitzant un estudi rigorós sobre els mètodes d'integració i discretització, tant temporal com espacial, determinant la seva adequació per resoldre el sistema d'equacions diferencials generat. El moviment i la simulació de la deformació es realitzen exclusivament utilitzant els punts de control 4D, obtenint una eficiència numèrica i computacional excel·lents. La determinació del model Bsplines4D es realitza després d'un estudi detallat dels models existents. També s'ha utilitzat per desenvolupar un model, N-Scodef, de deformacions de formes lliures (FFD), utilitzant deformacions geomètriques basades en restriccions. S'han establert les condicions per aplicar restriccions amb trajectòries no rectilínies, representades per corbes B-Spline 4D. La deformació s'adapta de forma precisa a la forma descrita per les corbesBsplines4D, a NURBS based model, is presented. The model allows the representation of 4D parameterized surfaces. The objective is the representation and dynamic simulation of deformable surfaces based on this model; a study of the movement equations has been made, associating to them an energy functional to measure the objects' deformation. A rigorous study on the integration and discretization, both temporal and spatial, is made to evaluate its suitability to solve the system of differential equations generated. The movement and simulation of the deformation is performed only using the 4D control points. An excellent numeric and computational efficiency is achieved. The Bsplines4D model is obtained after a detailed study on the existent models. The model has been also used to develop a free-form deformable (FFD) model, N-Scodef, using geometric constraint-based deformations. The conditions to apply constraints with non rectilinear trajectories, based on 4D B-Spline curves, have been established. The deformations fit precisely to the curves form