A Pivot-Based Kirigami Utensil for Hand-Held and Robot-Assisted Feeding

TL;DR

A re-designed kiri-spoon that can be leveraged as either a hand-held utensil or a robot-mounted attachment, and characterized the amount of force required to open or close the kiri-spoon, and shows how designers can modify this force through kinematic or material changes.

Abstract

Eating is a daily challenge for over 60 million adults with essential tremors and other mobility limitations. For these users, traditional utensils like forks or spoons are difficult to manipulate -- resulting in accidental spills and restricting the types of food that can be consumed. Prior work has developed rigid, hand-held utensils that often fail to secure food, as well as soft, shape-changing utensils made strictly for robot-assisted feeding. To assist a broader range of users, we introduce a re-designed kiri-spoon that can be leveraged as either a hand-held utensil or a robot-mounted attachment. Our key idea -- developed in collaboration with stakeholders -- is a pivot-based design. With this design the kiri-spoon behaves like a pair of pliers: users squeeze the handles to change the shape of the utensil and enclose food morsels. In practice, users can apply this kiri-spoon as either a spoon (that scoops food) or as a fork (that pinches food); when the handles are closed, the utensil wraps around the morsel and prevents it from accidentally falling. We characterize the amount of force required to open or close the kiri-spoon, and show how designers can modify this force through kinematic or material changes. A highlight of our design is its accessibility: the hand-held version consists of just four 3D printed parts that snap together. By adding a servo motor, we can extend this same kinematic structure to robot-assisted feeding. Across our user studies, adults with disabilities and elderly adults with Parkinson's reported that the kiri-spoon better met their needs and provided a more effective means of spill prevention than existing alternatives. See a video of our kiri-spoon here: https://youtu.be/FFIomm5RL98

Figures (7)

• Figure 1: By using a pivot design similar to pliers, we enable hand-held and robot-mounted kiri-spoons. Rotating the pivot causes the kirigami mesh to extend, changing its shape from a flat sheet to an ellipsoid enclosure. The kirigami enclosure prevents accidental spills. a) Hand-held kiri-spoon. b-c) User squeezing the kiri-spoon to acquire cereal from a bowl. d) Robot-mounted kiri-spoon. e) Robot arm leveraging the kiri-spoon to grasp foods.
• Figure 2: Assembling a hand-held kiri-spoon. (a) The handles can be snapped together by aligning the two bumps. (b) The kirigami mesh is then attached by pushing its side holes onto their respective pegs. (c) A band is wrapped around the posts. This optional band acts as a spring to open the mesh when the squeezing force is removed. (d) The completed assembly.
• Figure 3: Schematic of the applied forces, moments, and generated displacements. (a) The forces of the kirigami and band are applied horizontally to their respective pegs, while the squeezing force is applied perpendicular to the handle. (b) The blue lines represent the moment arms and similar triangles utilized in Equation (\ref{['eq:K2']}). The central vertical line represents the line of symmetry for the full kiri-spoon assembly.
• Figure 4: Results from Section \ref{['sec:mechanics']} used to model the kirigami mesh. (Left) Force vs. Displacement from real-world experiments and ANSYS simulations. Each separate graph represents a change in the kirigami sheet's parameters. From top to bottom, the sheet is increasing in size from $1\times$ to $1.5\times$. From left to right, the sheet is increasing in material stiffness, ranging from a Shore hardness of $85$A to $95$A. (Right) Force vs. Young's modulus times displacement. Here we group all nine experimental plots on a single graph, and show that (a) we can approximate the kirigami mesh as a spring, and (b) the spring constant is of the form $K_K E$. A line of best fit is overlaid to highlight the kirigami stiffness factor $K_K$ from our model.
• Figure 5: Setup for our preliminary study with university students without mobility limitations. (Left) In the Manual phase participants completed two tasks using hand-held utensils: transferring food from a bowl to a pitcher, and eating food from the bowl. (Right) In the Robotic phase we mounted the utensil to the end-effector of a UR5 robot arm. Using a combination of teleoperation and programmed motions, participants controlled the robot to eat cereal from a bowl. We compared our pivot-based kiri-spoon to a Liftware utensil in both phases.