Using Rigid and Soft Grippers for Assistive Robotic Tasks

Abstract

For robot arms to perform everyday tasks in unstructured environments, these robots must be able to manipulate a diverse range of objects. Today's robots often grasp objects with either soft grippers or rigid end-effectors. However, purely rigid or purely soft grippers have fundamental limitations: soft grippers struggle with irregular, heavy objects, while rigid grippers often cannot grasp small, numerous items. Combining the capabilities of rigid and soft grippers while equipped to the end effector of a robot arm could provide a larger range of capabilities for everyday tasks. For millions of adults with mobility limitations, eating meals is a daily challenge. A variety of robotic systems have been developed to address this societal need. These robots serve as a proxy for the human's arm: the user inputs the food they want to eat, and the robot autonomously picks up that food and brings it to the user's mouth. Unfortunately, end user adoption of robot-assisted feeding is limited, in part because existing devices are unable to seamlessly grasp, manipulate, and feed diverse foods. Recent works seek to address this issue by creating new algorithms for food acquisition and bite transfer. In parallel to these algorithmic developments, however, we hypothesize that mechanical intelligence will make it fundamentally easier for robot arms to feed humans. In this paper we therefore introduce two end effector designs. One of which is called the RISO, a mechanics and controls approach for unifying traditional RIgid end effectors with a novel class of SOft adhesives. When grasping an object, RISOs can use either the rigid end effector (pinching the item between non-deformable fingers) and/or the soft materials (attaching and releasing items with switchable adhesives). This enhances manipulation capabilities by combining and decoupling rigid and soft mechanisms. The second end effector design we propose is the Kiri-Spoon, a soft utensil specifically designed for robot-assisted feeding. Kiri-Spoon consists of a spoon-shaped kirigami structure: when actuated, the kirigami sheet deforms into a bowl of increasing curvature. Robot arms equipped with Kiri-Spoon can leverage the kirigami structure to wrap-around morsels during acquisition, contain those items as the robot moves, and then compliantly release the food into the user's mouth. Overall, Kiri-Spoon combines the familiar and comfortable shape of a standard, rigid spoon with the increased capabilities of soft robotic grippers. In this paper, we go on to outline the process used to develop these end effector designs. In addition, we show the experimental and user study results obtained suggest these grippers could improve the current capabilities of robot arms in assisting humans and performing everyday tasks.