Utilizing manufacturing-induced stresses for obtaining non-monostable compliant mechanisms

Abstract

A broad range of bistable, multi-stable and neutrally stable compliant mechanisms have been developed over the years. These non-monostable systems show great potential for deployment in e.g. the medical, the manufacturing and the precision industry. Often the presence of prestress is a requirement for obtaining non-monostability within the realm of compliant mechanisms. This prestress is for example a strict necessity for neutrally stable behaviour, but also various types of bistable systems need it for correct operation. Systematic methods to induce prestress to these mechanisms do not yet exist. Currently, the application of prestress is most often achieved by manual assembly steps. The manual nature of these assembly steps poses problems onto the dimensional scalability, the production scalability and the design freedom of these mechanisms. In this research the possibilities of imposing prestress onto compliant mechanisms during their fabrication, solely by utilizing inherent features of the manufacturing method, are explored. With such a technique at hand, an accurate, scalable and tailorable method for prestressing is obtained. In this work the fused filament fabrication technique is used to create PLA monostable compliant mechanisms. By making use of the heat-induced shrinkage property of PLA, a distributed and variable material shrinkage field can be acquired. By the virtue of this variable shrinkage, elements within the system can selectively be prestressed. Results show that the mechanical stability behaviour of a demonstrator mechanism can permanently be changed from monostable to bistable. The influence of various design parameters on the shrinkage yield and the force-delivering potential of PLA is examined to tailor and maximize both factors. The result of this work provides the onset for the further creation of multi and neutrally stable compliant mechanisms in a systematic way.