Fukang Liu 1, Kavya Puthuveetil 2, Akhil Padmanabha 2, Karan Khokar 2, Zeynep Temel 2, Zackory Erickson 2
1 Georgia Institute of Technology, 2 Carnegie Mellon University
IROS 2025 🎉
Robotics presents a promising opportunity for enhancing bathing assistance, potentially to alleviate labor shortages and reduce care costs, while offering consistent and gentle care for individuals with physical disabilities. However, ensuring flexible and efficient cleaning of the human body poses challenges as it involves direct physical contact between the human and the robot, and necessitates simple, safe, and effective control. In this paper, we introduce a soft, expandable robotic manipulator with embedded capacitive proximity sensing arrays, designed for safe and efficient bathing assistance. We conduct a thorough evaluation of our soft manipulator, comparing it with a baseline rigid end effector in a human study involving 12 participants across 96 bathing trails. Our soft manipulator achieves an an average cleaning effectiveness of 88.8% on arms and 81.4% on legs, far exceeding the performance of a state-of-the-art baseline. Participant feedback further validates the manipulator's ability to maintain safety, comfort, and thorough cleaning.
Soft Manipulator (Ours)
The soft manipulator comprises two soft fingers designed to wrap around a human limb
Each finger is tendon-actuated and powered by two Dynamixel XM430-W350-T motors.
Each finger is equipped with four capacitive proximity sensing electrodes: three are located on the back of the finger, and one is placed on the inner surface.
A layer of shape memory foam is added between the soft finger and the washcloth to add compliance and support safe contact with human skin.
Rigid End Effector (Baseline)
The baseline end effector consists of six capacitive electrodes.
The flat tool is also covered with shape memory foam and a washcloth.
Soft Finger Control
The capacitance measured from the electrodes vary based on the distance between the electrode and an external conductive object, such as a human limb. We leverage these measurements to quantify distance and contact between human skin and a washcloth that covers the finger and capacitive electrodes.
Capacitance values increase with the tendon’s displacement, indicating an increasing level of tightness between the soft finger and the limb.
“Full contact” refers to the condition in which the inner surface of the soft finger is in complete contact with the human skin.
As the servos continue to apply tension on the tendon, the soft finger compresses the human skin until it achieves “Tight contact”, at which point the capacitance values stabilize.
Mobile Manipulator Control
During the Approaching phase, the end effector continues to approach the human limb with its fingertips open.
During the Closure phase the two fingers progressively close and surround the human limb for “full contact”.
The system then maintains this “full contact” dynamically.
We conducted a human-robot study involving 12 able-bodied adult participants [2 females, 10 males, age: 26.9 (6.5) mean (SD) years, weight: 73.3 (9.3) kg, height: 176.6 (8.2) cm]. This study was approved by Carnegie Mellon University’s Institutional Review Board under 2022.00000273.
Participants lie on a hospital bed with the head and foot of the bed adjustable for comfort based on individual preferences. A limb holder secures the participant’s limb parallel to the ground plane during the cleaning task, and three cameras are positioned to capture top, side, and bottom views of the participant’s limbs. Prior to cleaning, three rings of shaving cream are applied to the limb that the robot must clean off to demonstrate skin coverage and bathing performance.
Recorded images from all three cameras are used to evaluate the cleaning performance of both the soft and baseline end effectors. An additional phone camera records video throughout the experiment. For each participant and each end effector, the robot conducted 2 bathing attempts for both the arm and the leg, resulting in 8 bathing trials per participant. We randomized ordering between the two end effectors for each participant.
r-arm-2.mp4s-arm-2.mp4
r-leg-2.mp4s-leg-2.mp4
Quantitatively, the soft manipulator (Ours) has consistently better cleaning performance in comparison to the rigid manipulator (Baseline).
The soft manipulator maintains a high cleaning efficiency, irrespective of limb diameter, suggested by best-fit trend lines.
The baseline end effector demonstrates a decrease in bathing performance as the arm diameter increases.
The soft manipulator consistently outperforms the baseline strategy across the range of limb lengths.
After each trial, the participants evaluated their experience using four 7-point Likert scale questions:
‘I felt safe during interaction with the robot’,
‘I felt comfortable with the robot interacting with me’,
‘The robot cleaned off my entire limb’, and
‘The robot cleaned my limb in a reasonable amount of time’.
Following the completion of all trials, participants indicated their preferred manipulator and the reasons for their choice. They selected one or more reasons from a set of the following options:
‘it felt safer’,
‘it was more comfortable’,
‘it cleaned off a larger surface area of my limb’,
‘it took less time to clean my limb’, ‘it is durable’,
‘it fits well’, ‘it is pain free’,
‘it looks good’, or
provide their own reason in a blank space provided.
Participants show a general preference for the soft manipulator across key assessment factors
@article{liu2024skingrip,
title={SkinGrip: An Adaptive Soft Robotic Manipulator with Capacitive Sensing for Whole-Limb Bathing Assistance},
author={Liu, Fukang and Puthuveetil, Kavya and Padmanabha, Akhil and Khokar, Karan and Temel, Zeynep and Erickson, Zackory},
journal={arXiv preprint arXiv:2405.02772},
year={2024}
}