Holistic design and implementation of pressure actuated cellular structures

Abstract

Providing the possibility to develop energy-efficient, lightweight adaptive components, Pressure-Actuated Cellular Structures (PACS) are primarily conceived for aeronautics applications. The realization of shape-variable flaps and even airfoils provides the potential to safe weight, increase aerodynamic efficiency and enhance agility. The herein presented holistic design process points out and describes the necessary steps for designing a real-life PACS structure, from the computation of truss geometry to the manufacturing and assembly. The already published methods for the form finding of PACS are adjusted and extended for the exemplary application of a variable-camber wing. The transfer of the form-finding truss model to a cross-sectional design is discussed. The end cap and sealing concept is described together with the implementation of the integral fluid flow. Conceptual limitations due to the manufacturing and assembly processes are discussed. The method's efficiency is evaluated by Finite Element Method (FEM). In order to verify the underlying methods and summarize the presented work a modular real-life demonstrator is experimentally characterized and validates the numerical investigations. [-] Reduction factor for seal design Figure 1: Venus flytrap, Dionaea muscipula (top left; photography by J. W. Webb); Microscope slide of Venus flytrap (top right; Copyright Carolina Biological Supply Company); Reproduction of the biological model by PACS (bottom) Various concepts for adaptive structures are inspired by this working principle. Ranzani et al. [3] developed a medical soft manipulator for minimally invasive surgery. Further soft robot concepts for gripping tools and robotic movement are realized by Ilievski et al. [4] and Guiducci et al. [5]. Zhang et al. [6], [7] theoretically investigate a three-dimensional approach that utilizes closed liquid cell materials for shape-changing structures. Two-dimensional approaches are examined by Lv et al. [8], [9] and Luo Q. et al. [10]. The concept of Pressure-Actuated Cellular Structures (PACS) differs from the above morphing structures as it bases on the optimization of discrete cell sides instead of the voids between them. It share most of their advantages with the pressure-adaptive honeycombs (PAH), which are extensively investigated by Vos et al. [11] and Barrett et al. [12] and patented in [13] and [14]. The idea of PACS utilizes the mechanisms of the Venus flytrap for technical use. It provides the possibility to specify arbitrary single-curved structures that deform stepless between predefined states of shape and allow to specifically manipulating its pressuredependent stiffness. First investigated theoretically by Pagitz et al. [15], a single row PACS demonstrator was subsequently realized by Gramüller et al. [16]. The lower depiction of Figure 1 shows the exemplary imitation of the Venus flytrap with a simplified illustration of a PACS with rigid cell sides and flexible hinges. One arm of this double row structure is realized in the ongoing work of Gramülle...

Mechanical Metamaterials and Their Engineering Applications

“…Stacked cellular origami consisting of tubular channels could exhibit increasing stiffness by pressurizing it as well. Pressurizing the channels would result in a fold that maximizes the enclosed volume, thus any deformations that result in reduced volume would be resisted by pressure …”

Pneumatic Coiling Actuator Inspired by the Awns of Erodium cicutarium

“…For example, the trap closing motion in Venus flytrap ( Dionaea muscipula ) is rapid enough to capture agile insect prey like the fruit flies, which are then digested as nutrition supplement (Forterre et al, 2005 ; Skotheim and Mahadevan, 2005 ). The Venus flytrap gains its speed from actively changing the turgor pressure in its motor cells and exploiting an embedded snap-through instability, and it has inspired many robotic grippers (Kim et al, 2014 ; Zhang et al, 2016 ; Wani et al, 2017 ) and adaptive cellular structures (Gramüller et al, 2015 ; Li and Wang, 2015b ). On the other end of the speed spectrum is the pinecone opening motion.…”

Development and Testing of Woven FRP Flexure Hinges for Pressure-Actuated Cellular Structures with Regard to Morphing Wing Applications

“…For all of these subsystems, conceptual solutions are developed and presented in detail in previous publications [21][22][23][24][25]. The holistic design approach is illustrated in Figure 7.…”

“…The biomimetic approach of PACS was first investigated by Pagitz et al with regard to technical applications and translated into a two-dimensional concept [20]. Gramüller et al further developed the theoretical concept to technical maturity and were able to demonstrate the outstanding flexibility of such structures to achieve arbitrary form functions [21,22]. The design methodology is based on an optimization algorithm developing a two-dimensional truss structure.…”