The deformation control problem arises in applications where a mechanical system needs to actively modify the shape of a soft object. This problem is needed in surgical robotics to automate delicate procedures with soft tissues, e.g. suturing and needle insertion, in food industry to automate the shaping of food materials such as dough, or in textile industry to automate the folding and positioning of extensible fabrics, to name a few cases. However, despite the recent progress in physically interactive and soft robotics, the active deformation of compliant objects remains an open research problem with many economically important applications. One of the main issues that complicates the implementation of these types of tasks is the difficulty to identify the deformation properties of soft materials. / The aim of this thesis is to provide model-free solutions to this challenging control design problem. For that, new adaptive methods to servo-control unknown elastic deformations are presented. First, this thesis proposes a kinematic controller that estimates the deformation Jacobian matrix in real-time, hence, avoids the identification of the object’s deformation model. This method computes the unknown matrix based on measurements of the deformation flow and the velocity input to the manipulator; the matrix is then used to map the deformation control action into end-effector velocities. Next, this thesis presents a conceptually different adaptive control approach that does not require to numerically estimate the deformation Jacobian matrix or to numerically compute the optical flow. However, to compute the velocity control input, offline testing deformations must be performed. In this method, the deformation control action is mapped to end-effector velocities by an adaptively varying transposed matrix, thus no matrix inversion is required. / This thesis also tackles the simultaneous vision-based control of multiple elastic deformations. This method incorporates the attitude of a fully-constrained gripper and the measurements from multiple vision sensors into the Jacobian estimation algorithm; by doing this, the number of controllable deformation degrees-of-freedom is increased. Additionally, this thesis addresses the vision-based deformation problem but with torque-controlled manipulators. The presented adaptive method exploits the passivity properties of the system and computes the controller with the online estimated Jacobian matrix. Finally, this thesis formulates the deformation control problem but in terms of force sensory feedback, in other words, the control objective is the regulation of the applied force onto the elastic object; the presented energy shaping controller preserves in closed-loop the Hamiltonian structure of the dynamical system. / The originality of this work lies in the uncalibrated nature of the control methods, i.e. none of the proposed controllers require the identification of the object’s deformation/stiffness model and the camera’s parameters. This uncalibrated feature allows to control on-the-fly elastic deformations of unknown compliant objects. It must be remarked that for each of the control methods, its stability is analysed with Lyapunov theory, and its performance is experimentally verified with robot manipulators. / Navarro Alarcon, David. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 123-132).

We simulate the behavior of a steel ball bearing as it impacts a rigid foundation by solving a discretized version of the dynamic equations of linearized elasticity for a homogeneous, isotropic material. Space is discretized using the finite element method and time is discretized using the implicit trapezoidal method. Impact with a fixed foundation is incorporated into the model using a complementarity condition. This ensures that we have normal forces acting on the bearing only when and where the bearing is in contact with the foundation. After discretization in space, this condition becomes a linear complementarity problem which is solved using an iterative method for solving LCPs that is similar to the Gauss-Seidel method for solving linear systems. The LCP is solved at each time step to determine the normal forces due to contact. By assuming cylindrical symmetry, we are able to simulate the impact of a three-dimensional ball using only two spatial coordinates and two-dimensional finite elements. This decreases the computational cost of a highly refined three-dimensional simulation dramatically. Using this model, we investigate the deformations that occur during and after contact. We hypothesized that dropping a steel ball from even a small height causes plastic deformation. We tested this hypothesis using our model by computing the state of stress inside the ball at various times during the simulation. By comparing the computed maximum shear stress to the yield strength of the material, we can determine if the threshold for plastic deformation is reached. We found that with an impact speed of 2 m/s the stresses induced in the ball are large enough to cause plastic deformation. Because plastic deformation requires energy and is irreversible, it is an important consideration when investigating how high the ball will bounce after contact. To quantify the energy loss due to plastic deformation, we propose a theoretical model capable of describing plastic deformation.

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Colloidal macroions are known to interact very strongly with oppositely charged polyionic hydrogels. Sometimes this results in a non-uniform distribution of the macroions within the gel, a phenomenon that is not fully understood. This thesis is a summary of four papers on the development of a theory of the thermodynamics of macroions interacting with hydrogels, aimed at explaining the phenomenon of core/shell separation in spherical gels. It is the first theory of such interactions to use a rigorous approach to whole-gel mechanics, in which the elastic interplay between different parts of the gel is treated explicitly. The thesis shows that conventional theories of elasticity, earlier used on gels in pure solvent, can be generalised to apply also to gels in complex fluids, and that the general features of the phase behaviour are the same if mapped to corresponding system variables. It is found that the emergence of shells is due to attractions between macroions in the gel, mediated by polyions. Since the shell state is unfavourable from the perspective of the shell itself, being deformed from its preferred state, there will be a hysteresis between the uptake and the release of the macroion, like already known to occur with the uptake and release of pure solvent. Due to the elastic interplay, growth of the shell makes further growth progressively more favourable. Thus, unless there is a limited amount of macroions available the system will not reach equilibrium until complete phase transition has taken place. If the amount is limited the core/shell separation can be in equilibrium, so the volume of the solution that the gel is in contact with plays a very important part in determining the thermodynamic resting point of the system. The ability of a macroion/hydrogel to phase separate thus depends on the molecular properties whereas the ultimate fate of such a separation depends on the proportions in number between the ingoing components.

Thesis (Ph. D.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xiv, 224 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 149-155).

Thesis (M. Sc.)--University of Hong Kong, 1960. / Type-written copy. Includes bibliographical references.

Thesis--Ph. D., University of Hong Kong. / Offset from typescript.

Thesis (M.S. in Physics)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Young W. Kwon, James H. Luscombe. Includes bibliographical references (p. 29-31). Also available online.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: homogenization; calculus of variations. Includes bibliographical references (p. 21).

This thesis considers the modelling of two and three dimensional molecular networks with a view to being able to predict how the geometry of a network will affect the elastic constants and specifically the Poisson's ratios of the network. Materials with negative Poisson's ratios have much better engineering properties then those with positive Poisson's ratios. Theory states that a network polymer, with negative Poisson's ratios at a molecular level, would have much better properties than most materials with negative Poisson's ratios made to date. Molecular modelling has been used to examine the elastic constants of those two and three dimensional network polymers which are most likely to be synthesised in the near future. Such networks have been predicted to have either large positive or large negative Poisson's ratios depending on the molecular arrangement of the network. Poisson's ratios varying between 0.96 and -0.86 for the three dimensional cases and between -0.9 and 1.26 for the two dimensional cases have been calculated. Young's moduli in the order of 1 GPa have been observed for the three dimensional networks as compared to Young's moduli in the order of 20 - 400 kPa which have been experimentally measured for foam materials. Comparison with local density functional calculations for two 2-D networks with the molecular modelling have confirmed the negative Poisson's ratio in these networks and shown that it is not a function of the molecular modelling packages or force field used. The off-axis properties for both the two and three dimensional networks have been calculated. These show that whilst the networks with a positive Poisson's ratio in the principal axis directions always have a positive Poisson's ratio, those networks with a negative Poisson's ratio in the principal axis directions have off-axis Poisson's ratios that vary between large and positive and large and negative. In general the networks with positive Poisson's ratios are much more isotropic than those with negative Poisson's ratios. Analytical models which model the networks using simple beam theory have been produced for various two and three dimensional networks. These models can be used to predict the elastic constants of a network without the need to do time consumingmolecular modelling calculations to a first approximation. Comparison of the molecular models and analytical models has led to the development a library of force constants for two dimensional networks which can be used to more accurately predict the elastic constants of a network based on a knowledge of the geometry of the network and the constituent `sub-units' from which it is made