Design of a constant moment crease for use in neutrally stable origami

Abstract

The goal of this thesis is to look into the possibilities of making origami neutrally stable. This is wanted because the inherent stiffness of origami mechanisms introduces unwanted artifacts such as a higher actuation force, and the mechanism not following the theoretical kinematics. By making an origami mechanism neutrally stable the inherent stiffness of the pattern can be removed, and with that the unwanted artifacts as well. Two different strategies are explored, both a form of static balancing. With static balancing, two elements are balanced against each other. In the origami application, this means that two creases are balanced against each other. For the first strategy, a negative stiffness crease is combined with a positive stiffness crease. And for the second strategy two equal but opposite constant moment creases are balanced. To achieve this a negative stiffness, or constant moment crease needs to be designed. For the negative stiffness crease, a design was made where a flat sheet with a slot in the middle was prestressed into a saddle form. This showed bi-stable behavior, and with that negative stiffness. The range of negative stiffness was too short to be relevant for origami. And the prestressing proved hard to model. For the constant moment crease, a convex crease was designed, which did not need to be prestressed. This was easier to model, and three different geometries were found that showed a constant moment. By optimizing these geometries a constant moment over a range of 80 degrees was found. To check if the model is correct, a prototype experiment was performed. The optimized geometry was 3D printed and tested under the same boundary conditions that were present in the model. The results of the prototype experiment matched the results of the model, thereby validating it.