Lucio Flavio Campanile

The Belt-Rib Concept: A Structronic Approach to Variable Camber

The belt-rib concept for lifting surfaces with variable camber evolved at DLR recently as one of the most promising solutions for the adaptive wing. With the belt-rib idea the adaptive wing issue is approached in a new way: instead of a “mechatronic” solution with hinges or linear bearings a “structronic” solution is chosen, where distributed flexibility allows the desired shape changes. The resulting system is not only easier to maintain due to the absence of wear, but also is structurally more reliable and substantially lighter. The new concept evolves from the classical wing structure. The classical rib, which is in charge of the wing section’s stiffness, is replaced by a “belt rib,” which allows camber changes within given limits while leaving the remaining in-plane stiffness properties of the section widely unchanged. The evolution of the belt-rib concept was accompanied by experimental tests on different prototypes. After a first development stage, in which mainly the system’s shape adaptability and the overall stiffness properties were investigated, further steps followed, focused on manufacturing, weight optimization and strength aspects. Recent developments dealt with the construction of a model with solid-state hinges, realized as hybrid glass fiber-carbon-fiber reinforced composite structure. The model is actuated mechanically by cables, which can be replaced by multifunctional actuators—like shape memory wires—in the future. The paper opens with an introduction about shape control of aerospace structures and variable camber in particular, in which the major advantages of a “structronic” approach with respect to classical solutions are discussed. Then the fundamentals of the belt-rib concept are sketched, with some significant results of the feasibility proof phase, followed by the description of the last developments. The conclusion summarizes the potential of a structronic approach to shape control with an outline of possible future work.

Initial Thoughts on Weight Penalty Effects in Shape-adaptable Systems

If a structural system has to be subjected to high loads and large geometry changes, according to the state of the art, articulated systems with discrete actuators are used, with the articulated systems consisting of stiff members connected by hinges. As an alternative, smart structures technologies can supply solutions based on the deliberate use of structural flexibility and on distributed actuation. In order to assess the advantages, which can be expected from such solutions, a thorough comparison must be made between the properties of compliant mechanisms and the conventional ones. A crucial aspect of this comparison, on which this contribution is focused, is the impact on the system’s structural weight. The first part of the paper deals with the relevance of weight penalty effects in shape-adaptable systems, with a special focus on airfoil shape control. A quantitative analysis of weight penalty effects in pin-jointed articulated structures follows. The criterion on which this analysis is based allows a characterization of general validity, not restricted to a particular example, and can be applied to other mechanisms or hinge architectures, providing a sound way of assessing the lightweight potential of a given concept and allowing a consistent comparison between different design philosophies. An extension to weight penalty effects in compliant systems shows a higher degree of complexity and could not be addressed in the same detail in this study. Anyway, some peculiar aspects are discussed in the final part of the paper, which can serve as a basis for future developments in this sense. In particular, the dependence of weight penalty effects on the system’s range of motion as well as on the load-dependence of the mechanism’s kinematics is addressed. Even if the presented results can be of direct significance to the designer of conventional articulated mechanisms, the primary relevance of this work is to be seen in the long term. Its main target is to provide a basis for the analysis of the potential offered by the compliant mechanisms and smart materials for the realization of light shape-adaptable structures and to give an impulse to research efforts aiming at developing suitable optimization procedures as well as formulating proper design rules for such kind of systems.

Parallel Robots with Adaptronic Components

Performance in high-speed mechanisms can be increased by means of a lightweight design. But, quite often, the resulting structures have the drawback of being susceptible to vibrations. This can be overcome by applying a smart-structures technology. In this work, an application to parallel mechanisms is presented, in which undesired vibrations are reduced by integrated piezoceramic (PZT) actuators and sensors, which are driven by a proper control system. As a basis for the development of suitable control laws, a proper simulation approach is to be used which is capable to model the mechanism’s dynamic behavior correctly, taking into account large motions. The multibody approach fulfills these requisites. The paper deals with the development of a fast C++-coded S-function in MATLAB/SIMULINK for a “five revolute joint” mechanism chosen as a test platform. This routine incorporates a multibody model with changing states. The flexibility of the bodies is taken into account in a modal form. The corresponding parameters are read from data files which can be generated by suitable preprocessors of proprietary multibody software packages like SIMPACK. The created model is compared with an equivalent SIMPACK-model and an interpolation-based control strategy is discussed.

The fish-mouth actuator: Design issues and test results

The so-called “fish-mouth actuator”, developed at DLR in the framework of the Adaptive Wing project (ADIF), is a compact hybrid actuator based on the interaction of a shape memory material and a composite flexible mechanism. The actuator offers a high effective strain (ratio between actuator’s stroke and mounting dimension in the activation direction) and is therefore particularly interesting for the shape control of thin surfaces. In the ADIF project, the actuator development was focused on the realization of a wind-tunnel model for an adaptive wing with transonic bump. The actuator is designed and tested for a maximum stroke of 2 mm and a maximum force of 200 N. Its thickness (in activation direction) amounts to about 8 mm. If used with a feedback control system, it can reach a displacement precision of less than 1 mm. More than 400 single actuators were built and tested; 84 of them were integrated in the final system. In this paper, several design issues are discussed that are typical for such fully coupled hybrid systems. The design analysis and procedure used for the actuator development is described and a choice of experimental results is shown and discussed. The reported design philosophy and the related discussion include many concepts and solutions of general relevance which can be adopted for the development of similar hybrid actuators in the future.