Design strategies for large range flexure mechanisms

Abstract

The moving parts in a mechanical device often rely on rolling or sliding contacts such as in ball bearings to gain motion. These suffice in many applications, but the friction inherent to their working principle limits their motion repeatability and thereby their precision. Flexure mechanisms are a popular alternative in the field of precision engineering because they gain motion by elastic deformation of slender segments such as thin spring steel plates, resulting in a highly repeatable motion due to the absence of friction and play. Furthermore, they are lubricant-free and do not generate particles, which makes them suitable for applications in space, astronomy, the semiconductor industry, and healthcare. A drawback of flexure mechanisms is their limited range of motion compared to their build volume, which results in voluminous designs and which limits their application field. Their range is limited by material stress but also because at large displacements the stiffness in their support directions decreases significantly, and their actuation effort increases at large deflections, resulting in high energy consumption and heat generation. Increasing the motion range would highly benefit the field of precision engineering and could also lead to innovations in healthcare or space. The motivation for this thesis is the observation that the vast majority of flexure mechanisms consist of initially straight and stress-free flexures. Recent developments in fabrication methods such as the additive manufacturing of steel are providing the possibility to create more complex shapes, which could improve the range of motion of flexure mechanisms. The objective of this thesis is to provide design strategies to increase the motion range of flexure mechanisms. The thesis consists of two parts, of which the first (chapters 2-4) focuses on a new method to design stressed and curved flexures. The second part (chapters 5 and 6) further develops a recent strategy to increase the range of motion using torsion reinforcement structures.