Design Principles for Robust Grasping in Unstructured Environments

Grasping in unstructured environments is one of the most challenging issues currently facing robotics. The inherent uncertainty about the properties of the target object and its surroundings makes the use of traditional robot hands, which typically involve complex mechanisms, sensing suites, and control, difficult and impractical. In this dissertation I investigate how the challenges associated with grasping under uncertainty can be addressed by careful mechanical design of robot hands. In particular, I examine the role of three characteristics of hand design as they affect performance: passive mechanical compliance, adaptability (or underactuation), and durability. I present design optimization studies in which the kinematic structure, compliance configuration, and joint coupling are varied in order to determine the effect on the allowable error in positioning that results in a successful grasp, while keeping contact forces low. I then describe the manufacture of a prototype hand created using a particularly durable process called polymer-based Shape Deposition Manufacturing (SDM). This process allows fragile sensing and actuation components to be embedded in tough polymers, as well as the creation of heterogeneous parts, eliminating the need for fasteners and seams that are often the cause of failure. Finally, I present experimental work in which the effectiveness of the prototype hand was tested in real, unstructured tasks. The results show that the grasping system, even with three positioning degrees of freedom and extremely simple hand control, can grasp a wide range of target objects in the presence of large positioning errors.