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.

This paper presents a manufacturing method for a zero-stiffness compliant mechanism to be used as a flexible head support. The manufactured design consists of two curved, thin-walled U-beams made of high strength steel. The beams are prestressed in opposite directions to obtain zero torsional stiffness so that rotation of the head is allowed. The presented manufacturing method for the beams consists of three different steps; (1)Production of a straight U-beam using a saw mill, (2)Bending the U-beam with a bending tool based on press die forming, (3)Heat treatment to increase the strength of the profile.
C75 high strength steel is used for the production of the beams. The straight U-beams with a wall thickness of 0.4 mm were produced within an accuracy of 0.03 mm. The formed U-beams in step 2 approximately follow the desired curve with a maximum lateral error of 1mm which is deemed sufficient for this application. Finally, the beams were strengthened using a standard quenching and tempering heat treatment which increased the yield strength with a factor of 4 up to 1650 MPa. A prototype was made which consists of a 3D printed lower and upper base, as well as two prestressed curved U-beams produced with the presented manufacturing method. The performance of the compliant mechanism design with the produced beams is analysed in terms of the moment-angle curve. Prestressing reduced the maximum moment between -60 and 60 degrees with a factor of about 60 to 0.015 Nm.