Design of a Breakaway Utensil Attachment for Enhanced Safety in Robot-Assisted Feeding

TL;DR

The paper tackles safety in robot-assisted feeding by introducing a passive mechanical fail-safe: a breakaway utensil attachment that detaches under excessive force. It combines design optimization with FEA to create a U-shaped slot-based mechanism, fabricated via 3D printing, and validated through a drop-test rig that characterizes breakaway forces. The key result is a configurable attachment whose slot depth $d$ and wall loops $w$ set the break force, achieving $F_{impact}=65N$ with $d=1mm$ and $w=3$, while illustrating how to tailor safety to user needs with alternative settings. This approach complements software-based safety by providing a physical safety layer that is robust to unforeseen interactions, advancing safer robot-assisted feeding.

Abstract

Robot-assisted feeding systems enhance the independence of individuals with motor impairments and alleviate caregiver burden. While existing systems predominantly rely on software-based safety features to mitigate risks during unforeseen collisions, this study explores the use of a mechanical fail-safe to improve safety. We designed a breakaway utensil attachment that decouples forces exerted by the robot on the user when excessive forces occur. Finite element analysis (FEA) simulations were performed to predict failure points under various loading conditions, followed by experimental validation using 3D-printed attachments with variations in slot depth and wall loops. To facilitate testing, a drop test rig was developed and validated. Our results demonstrated a consistent failure point at the slot of the attachment, with a slot depth of 1 mm and three wall loops achieving failure at the target force of 65 N. Additionally, the parameters can be tailored to customize the breakaway force based on user-specific factors, such as comfort and pain tolerance. CAD files and utensil assembly instructions can be found here: https://tinyurl.com/rfa-utensil-attachment

Figures (7)

• Figure 1: Utensil attachment with a mechanical failsafe (a) Components of our proposed utensil attachment (b) Utensil attachment grasped by a two-finger gripper
• Figure 2: Utensil attachment designs -- (a) L-shaped design with notches at both corners (b) U-shaped design with a slot in the horizontal section
• Figure 3: Finite element analysis (FEA) on the L-shaped (left)o and U-shaped (right) design. (Top) FEA where the spoon end is fixed and (bottom) FEA where the opposite end is fixed.
• Figure 4: 3D printing orientations -- (a) Visualization of two 3D printing orientations in the Bambu slicer: the left corresponds to (b), and the right corresponds to (c). (b) Print orientation with layer lines perpendicular to the breaking line for strength, resulting in an unclean break (c) Print orientation with layer lines parallel to the breaking line, producing a clean break
• Figure 5: Drop test rig