Mechanics of Multifunctional Skin Structures

Abstract

Robotic structures are typically fabricated using discrete components that serve only a single function, such as carbon fibers or polymer composites for structural reinforcement. The ability to integrate these discrete components into a single structure provide enormous opportunities to enhance the performance of robots by reducing weight and increasing the energy storage/harvesting. We have recently been pursuing the integration of sensors and solar cells into multifunctional “skin” structures. One issue that limits the integration of these components is the effect that that the interaction between them will have on the mechanical behavior, and its subsequent impact on multifunctional performance. To minimize these effects and better understand the mechanics of multifunctional skin structures, we first pursued compliant strain sensors integrated onto the compliant wings of a flapping wing MAV to sense deformations at the wing in real time. These measurements were correlated to the thrust force of the wing. The effects of these compliant strain sensors were also determined by comparing the new thrust measurements with the original wings and with 3D Digital Image Correlation (DIC) measurements. It was determined by SRS analysis that strain sensors tended to be more sensitive to lower integral modes of the flapping frequency than the thrust measurement data, while the DIC measurements correlated more directly with thrust measurements in the time domain. Thus, it would appear that the strain sensor and DIC measurements are sensitive to different aspects of the mechanics of the multifunctional skin structures that can be taken into account when using the strain sensors for real-time sensing and control. In addition to compliant strain sensor integration, flexible Solar Cells (SCs) were also integrated onto the compliant wings. Their ability to harvest energy during flight has the potential to prolong the time of flight for more autonomous operation. The effects of the integrated SCs on the 3D shapes of the compliant wings were also characterized during flapping. The solar cells had a significant effect on the wing shape, increasing the stiffness of the wings and reducing the volume of air that the wings need to capture to generate thrust, particularly at the apex and nadir of the flapping cycle where thrust is generated by blowback. Thus, a multifunctional analysis was developed to account for the tradeoff between the extra power require to generate the necessary thrust for the MAV to stay airborne versus what is gained from integrating the SCs in order to determine how to design the multifunctional skin structures to optimize performance.