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The concept of shape-morphing is to embed control in a design to broaden its band of functionality. Whether it is for cars, planes, buildings, or personal medicine, the goal is to achieve more with less. That is more efficiency, more functions, more force, and more range with less energy, and less weight. The design of these new types of structures is however complex, as all the variables of a system are intertwined. Existing designs are either simple or small to reduce the number of design variables, although this affects the achievable deformation range of a structure. There is a need for a design method that can handle the complexity of the search space of shape-morphing structures without compromising the breadth of their design space or the accuracy of their deformation. This thesis proposes four design methods, one for compliance-controlled shape-morphing and three for actuator-controlled shape-morphing. First, compliance-control is achieved through optimization of the distribution of materials with varying stiffness in a 2D lattice structure. The method is implemented for geometric and material linearity and nonlinearity to observe how the choice of model affects the accuracy of the deformations. The method is verified by optimizing the material distribution for a 2.5D NACA target shape and replicating the results experimentally using multimaterial 3D printing. Then, the modeling and four fabrication methods for soft pneumatic actuators are compared, as they are necessary to experimentally verify the actuator-controlled shape-morphing methods. The final actuator design is adapted to the constraints of soft lithography, the fabrication method that delivers the most robust and predictable actuators of the four. Actuator-control is achieved by optimizing the actuator layout within a lattice structure with the aim of achieving a target deformation. The three methods show how reducing the search and design space of a structure improves the computational efficiency and accuracy for 2D, 2.5D, and 3D deformation. The first method assumes static and kinematic determinacy and small displacements; the second assumes small displacements in overdeterminate structures; the third can achieve large shape changes in overdeterminate structures. All three methods are verified through finite element analysis and experimentally. Finally the implications of the findings related to the four shape-morphing design methods are discussed. The achievable search and design space of each method are compared. The designer is free to chose the method best adapted to their needs, as each one is a compromise of accuracy, range, and computational efficiency. The methods can be employed for different types of actuation, but their application to industrial fields is hindered by the mechanical properties of the material that can currently be 3D printed. The advent of several new manufacturers of compliant and multimaterial 3D printers promises further industrial developments for the field of shape-morphing. |
