A foldable arm is one of the practical applications of folding. It can help mobile robots and unmanned aerial vehicles (UAVs) overcome access issues by allowing them to reach into confined spaces. The origami-inspired design enables a foldable structure to be lightweight, compact, and scalable while maintaining its kinematic behavior. However, the lack of structural stiffness has been a major limitation in the practical use of origami-inspired designs. Resolving this obstacle without losing the inherent advantages of origami is a challenge. We propose a solution by implementing a simple stiffening mechanism that uses an origami principle of perpendicular folding. The simplicity of the stiffening mechanism enables an actuation system to drive shape and stiffness changes with only a single electric motor. Our results show that this design was effective for a foldable arm and allowed a UAV to perform a variety of tasks in a confined space.

An origami-inspired, self-locking robotic arm that can be folded flat.

Solar sail technology—A state of the art review

From stadium covers to solar sails, we rely on deployability for the design of large-scale structures that can quickly compress to a fraction of their size1–4. Historically, two main strategies have been used to design deployable systems. The first and most frequently used approach involves mechanisms comprising interconnected bar elements, which can synchronously expand and retract5–7, occasionally locking in place through bistable elements8,9. The second strategy makes use of inflatable membranes that morph into target shapes by means of a single pressure input10–12. Neither strategy, however, can be readily used to provide an enclosed domain that is able to lock in place after deployment: the integration of a protective covering in linkage-based constructions is challenging and pneumatic systems require a constant applied pressure to keep their expanded shape13–15. Here we draw inspiration from origami—the Japanese art of paper folding—to design rigid-walled deployable structures that are multistable and inflatable. Guided by geometric analyses and experiments, we create a library of bistable origami shapes that can be deployed through a single fluidic pressure input. We then combine these units to build functional structures at the metre scale, such as arches and emergency shelters, providing a direct route for building large-scale inflatable systems that lock in place after deployment and offer a robust enclosure through their stiff faces. Origami-inspired multistable structures that can be inflated from flat to three dimensions have been designed; a library of foldable shapes is created and then combined to build metre-scale functional structures.

Multistable inflatable origami structures at the metre scale.

Large-scale deployable solar panels are crucial for certain engineering applications. However, a complex network of actuators and power supplies are usually required to achieve deployment, and can be prone to failure. The single-degree-of-freedom design proposed here embeds shape-memory polymers within an elastic origami substrate, to achieve self-deployment through temperature change. The unexpected bifurcation during folding is studied by examining strain energy as a function of dihedral angle. By optimizing the geometry, tenfold self-deployment is achieved in under one minute. The results could benefit space exploration, as well as solar power generation in inaccessible areas.

https://link.aps.org/pdf/10.1103/PhysRevApplied.11.064069

Autonomous Deployment of a Solar Panel Using Elastic Origami and Distributed Shape-Memory-Polymer Actuators

Morphology plays an important role in behavioral and locomotion strategies of living and artificial systems. There is biological evidence that adaptive morphological changes can not only extend dynamic performances by reducing tradeoffs during locomotion but also provide new functionalities. In this article, we show that adaptive morphology is an emerging design principle in robotics that benefits from a new generation of soft, variable-stiffness, and functional materials and structures. When moving within a given environment or when transitioning between different substrates, adaptive morphology allows accommodation of opposing dynamic requirements (e.g., maneuverability, stability, efficiency, and speed). Adaptive morphology is also a viable solution to endow robots with additional functionalities, such as transportability, protection, and variable gearing. We identify important research and technological questions, such as variable-stiffness structures, in silico design tools, and adaptive control systems to fully leverage adaptive morphology in robotic systems.

Adaptive Morphology: A Design Principle for Multimodal and Multifunctional Robots

The main focus of this paper is the detailed introduction of the oom deployment concept implemented for the German eployable membrane technology demonstrator Gossamer-1. The technology aims for solar sailing, thin-film photovoltaic and drag augmentation as possible use cases.
Therefore, the main functional and geometrical requirements for the mechanisms are derived from the mission design and the global sail deployment concept which are both introduced in detail. The regarding mechanism design is explained on concept level and illustrated with evaluating tests of the engineering model. Finally, an outlook on the future of the project, including the current design status of the engineering qualification model, is given.

The Design and Test of the GOSSAMER-1 Boom Deployment Mechanisms Engineering Model

One of the key challenges for small satellites is packaging and reliable deployment of structural booms and arrays used for power, communication, and scientific instruments. The lack of reliable and efficient boom and membrane deployment concepts for small satellites is addressed in this work through a collaborative project 
between NASA and DLR. The paper provides a state of the art overview on existing spacecraft deployable appendages, the special requirements for small satellites, and initial concepts for deployable booms and arrays needed for various small satellite applications. The goal is to enhance deployable boom predictability and ground testability, develop designs that are tolerant of manufacturing imperfections, and incorporate simple and reliable deployment systems.

/pdf/advanced-deployable-structural-systems-for-small-satellites-4pg66bm6k9.pdf

Advanced Deployable Structural Systems for Small Satellites

Industrial robots play an important role in automation technology. A further increase of productivity is desired, especially in the field of handling and assembly, the domain of industrial robots. Parallel robots demonstrated their potential in applications with needs for high-dynamic trajectories in the recent years. Within the scope of the Collaborative Research Center (SFB 562)--`Robotic Systems for Handling and Assembly' the German Aerospace Center (DLR) and the Technical University of Braunschweig investigate smart-structures technology for parallel robots. In this paper the results of the main topics new active components, Finite-Element based elastic position dependent modeling and vibration control are summarized. The latest parallel robot called is equipped with new active rods. The design as well as the dimensioning of the rod with surface mounted piezo patch actuators is described. For trajectory based robot control, rigid body models are required. In parallel robots with vibration reduction a coupled approach is necessary in which elastic and rigid body equations are combined. The derivation of the equations for parallel robot is presented. Finally, the implemented vibration control is explained. In a position-dependent approach several robust controllers are switched to gain optimal control performance. A stability proof for the switching process is derived.

Smart-Structures Technology for Parallel Robots

Since 2011 DLR is preparing 3 orbit demonstrations of deployment and operation of a solar sail. For this mission bundle a new deployment control mechanism for DLR’s tubular CFRP shell booms has been developed that is applicable to all 3 evolution steps of the GOSSAMER—Road Map. According to the mission goal of GOSSAMER-1 and its addressed deployed sail size of 5 × 5 m2, a down scaled configuration of the booms and an adapted deployment mechanism are currently under development. The paper introduces the boom and its deployment mechanism concepts and describes and concludes tests and simulations that have been performed to proof the mechanical performance of the deployed booms.

Design and Sizing of the GOSSAMER Boom Deployment Concept

The paper at hand provides an overview of the gossamer solar sail technology developed by DLR since the 1990s. Boom and foil structures, including deployment mechanisms, with a focus on solar sail applications were developed. The technology was subject to extensive on ground qualification testing. The qualification included vibration testing, fast decompression, centrifuge tests and laboratory deployment. In addition metalized films were subject to degradation testing employing DLR’s complex irradiation facility.

Marco Straubel

Papers

The Design and Test of the GOSSAMER-1 Boom Deployment Mechanisms Engineering Model

Advanced Deployable Structural Systems for Small Satellites

Smart-Structures Technology for Parallel Robots

Design and Sizing of the GOSSAMER Boom Deployment Concept

Large lightweight deployable structures for planetary defence: solar sail propulsion, solar concentrator payloads, large-scale photovoltaic power