| Various academic and commercial projects have investigated applications of grasping from unmanned aerial vehicles (UAVs) and have demonstrated vehicles delivering cargo, grasping and retrieving objects, perching on walls and branches, and manipulating their environment. However, these projects have relied heavily on structuring the interaction task, and have utilized simple single purpose grippers that are only capable of grasping a particular object geometry or type of surface. Therefore, in an effort to broaden the capabilities of UAV based grippers, I have investigated the constraints and limitations that aerial vehicles impose on grasping, and have designed more general purpose robotic hands specifically for them.;In this thesis I begin by describing existing approaches to aerial grasping and how grasping from a UAV differs from more traditional applications involving a fixed robotic arm or large mobile robot. I then present a model of the SDM hand that has been repurposed for aerial grasping and investigate this design's capabilities and how it can be improved. This modeling shows that this hand design is capable of both grasping objects and supporting the vehicle when perching. Parametric analysis also suggests that the spacing between the two proximal finger joints has a significant impact on the hand's grasping performance. I then present the design of a new general purpose gripper intended for aerial grasping that utilizes fingers with prismatic and revolute joints. The initial version of this hand relies on an additional unactuated revolute joint that allows the grasp to adapt to the principal axis of the object regardless of how it is initially positioned in the hand and demonstrates reliable grasping capabilities over a wide range of object geometries. Next, I describe a model of a generalized version of this hand and use it to explore the impact of various design parameters on the hand's grasping performance. The parametric analysis of the design shows the impact that the relative link lengths and joint torques have on the hand's grasp performance and suggests that multilink fingers with longer distal and shorter proximal links are desirable.;I then present a revised hand prototype that incorporates the optimization results and evaluate its capabilities. In comparison to the previous prototype, this final design also includes an additional flexion degree of freedom in each finger and uses optimized link lengths and relative joint torques. It also incorporates between finger adaptability into the actuation which greatly improves its positional error tolerance and minimizes the grasp reaction forces, both of which are design goals for the aerial grasping application. These design choices result in a hand that is capable of grasping objects under high positional uncertainty and at the same time, minimizes reaction forces applied to the vehicle. |
