Collaborative Robot Arm Inserting Nasopharyngeal Swabs with Admittance Control

TL;DR

The paper tackles autonomous nasopharyngeal swab insertion using a standard rigid collaborative robot arm by applying admittance (force-feedback) control to regulate contact forces and enhance safety. It introduces a low-cost force-sensing end-effector mounted on a Panda arm, along with a force-filter, waypoint-generated trajectory, torque-control law, and a termination observer, validated on a 3D-printed nasal cavity phantom. Experimental results compare force-feedback against a baseline position controller, reporting higher insertion success and reduced sustained forces with force feedback, though outcomes vary with initial misalignment and safety considerations. The work demonstrates the feasibility of repurposing common collaborative robots for sensitive close-contact medical tasks and outlines pathways toward full automation, vision-guided initiation, and handling head motion in clinical settings.

Abstract

The nasopharyngeal (NP) swab sample test, commonly used to detect COVID-19 and other respiratory illnesses, involves moving a swab through the nasal cavity to collect samples from the nasopharynx. While typically this is done by human healthcare workers, there is a significant societal interest to enable robots to do this test to reduce exposure to patients and to free up human resources. The task is challenging from the robotics perspective because of the dexterity and safety requirements. While other works have implemented specific hardware solutions, our research differentiates itself by using a ubiquitous rigid robotic arm. This work presents a case study where we investigate the strengths and challenges using compliant control system to accomplish NP swab tests with such a robotic configuration. To accomplish this, we designed a force sensing end-effector that integrates with the proposed torque controlled compliant control loop. We then conducted experiments where the robot inserted NP swabs into a 3D printed nasal cavity phantom. Ultimately, we found that the compliant control system outperformed a basic position controller and shows promise for human use. However, further efforts are needed to ensure the initial alignment with the nostril and to address head motion.

Figures (9)

• Figure 1: Nasal cavity apparatus arranged next to the Franka Emika Robot arm with the proposed force sensing swab end-effector attached. Two GoPro cameras are used to observe the outcome of the insertions and are not part of the control loop.
• Figure 2: Observed noisy task-space force measurements when using the FR internal torque sensors. This demonstrates the necessity of designing an end-effector with an external loadcell that is sensitive enough to observe forces transmitted by the swab.
• Figure 3: Components of the custom end-effector. Left: Wheatstone bridge amplifier and digital conversion circuit. Right: the tri-axial loadcell interfaced with its housing and swab mount. Note that the red stripes on the swab are labelled to gauge distance in experiments, but do not have any functional purpose related to the controller.
• Figure 4: Nasal cavity phantom used for validation experiments. The red line highlights the path to reach the nasopharynx from the nostril.
• Figure 5: Block diagram for the proposed NP swab insertion system.