Mona Mühlich

Abstract

This paper aims to define the influencing design criteria for compliant folding mechanisms with pneumatically actuated hinges consisting of fiber-reinforced plastic (FRP). Through simulation and physical testing, the influence of stiffness, hinge width as well as variation of the stiffness, in the flaps without changing the stiffness in the hinge zone, was evaluated. Within a finite element model software, a workflow was developed for simulations, in order to infer mathematical models for the prediction of mechanical properties and the deformation behavior as a function of the aforementioned parameters. In conclusion, the bending angle increases with decreasing material stiffness and with increasing hinge width, while it is not affected by the flap stiffness itself. The defined workflow builds a basis for the development of a predictive model for the deformation behavior of FRPs.

Abstract

This paper presents the development of an actively controlled shape changing surface-like structure, where geometric adaptivity is utilised by local elastic deformation on the component level. Besides the physical development of a proof of concept demonstrator, the research proposes a digital form-driving process, a computational workflow which allows the design and fast simulation of the shape changing structure, as well as the digital control of the actuation on the component level. The proposed material system consists of an initially flat surface, which is tessellated into single components based on a hexagonal grid. Each cell is comprised of a three-layer system, where a pneumatic cushion is placed in the middle of two bending active plates with strategic cut outs 1. In this way, each cell can be pneumatically actuated and therefore elastically deformed. The induced bending in the outer plates leads to a controlled change of area – the cells shrink or expand. By controlling this local behaviour within the global arrangement according to principle geometric rules 2 it is possible to achieve a controlled shape change from an initially flat surface to an anticlastic or synclastic geometric configuration. To design, simulate and control the shape change, the authors propose a digital form driving process. Here, the cells are abstracted and simplified into polygons, which can shrink and expand within a given range, according to the proposed physical system. This allows for the fast simulation of different actuation patterns and resulting geometric changes. The abstract values of shrinkage or expansion of each cell can be translated into pressure values and are used to control the pneumatic actuators in the physical demonstrator (figure 1).