Complete Autonomous Robotic Nasopharyngeal Swab System with Evaluation on a Stochastically Moving Phantom Head

TL;DR

This work addresses autonomous nasopharyngeal swabbing by deploying a dual-arm robotic system that performs pre-contact alignment via a modified visual servo and a compliant velocity-based contact phase. It introduces a nonlinear trajectory optimization to reach the nasopharynx, a force-aware control law with dynamically tunable gains, and a fuzzy nasopharynx observer to determine when sampling occurs, all validated against a moving phantom head. A stochastic head-motion model based on a modified Ornstein–Uhlenbeck process and extensive experiments quantify the trade-offs between controller gains, head motion, and phantoms, highlighting configurations (notably D2.0 and S1.5) that balance speed, safety, and accuracy. The results support the system’s safety, robustness, and potential for human trials, while outlining avenues to further improve oscillation handling, latency, and integration of additional sensory cues.

Abstract

The application of autonomous robotics to close-contact healthcare tasks has a clear role for the future due to its potential to reduce infection risks to staff and improve clinical efficiency. Nasopharyngeal (NP) swab sample collection for diagnosing upper-respiratory illnesses is one type of close contact task that is interesting for robotics due to the dexterity requirements and the unobservability of the nasal cavity. We propose a control system that performs the test using a collaborative manipulator arm with an instrumented end-effector to take visual and force measurements, under the scenario that the patient is unrestrained and the tools are general enough to be applied to other close contact tasks. The system employs a visual servo controller to align the swab with the nostrils. A compliant joint velocity controller inserts the swab along a trajectory optimized through a simulation environment, that also reacts to measured forces applied to the swab. Additional subsystems include a fuzzy logic system for detecting when the swab reaches the nasopharynx and a method for detaching the swab and aborting the procedure if safety criteria is violated. The system is evaluated using a second robotic arm that holds a nasal cavity phantom and simulates the natural head motions that could occur during the procedure. Through extensive experiments, we identify controller configurations capable of effectively performing the NP swab test even with significant head motion, which demonstrates the safety and reliability of the system.

Figures (26)

• Figure 1: Figure showing the setup between the two robotic arms. One arm performs the NP swab test using the instrumented end-effector, while the second arm holds the nasal cavity phantom and simulates head motion.
• Figure 2: Top: Image showing the instrumented swab end-effector, which features a tri-axial loadcell, an RGB-D camera, and a electromagnet system to attach and detach the NP swab. Bottom: supporting electronics for controlling power to the electromagnet and ADC circuitry to measure forces on the loadcell.
• Figure 3: Diagram of the stages and proposed system for a robot executing the NP swab test. The test is divided into a pre-contact phase and a contact-phase. The pre-contact phase is responsible for aligning the swab next to the nose using visual information. A sentry stage locates the face within the arm's workspace and moves to a closer joint configuration, while the nostril approach phase uses visual servo to place the swab next to the nostril. The contact phase has an insertion stage that moves the swab through the nasal cavity, the sample collection stage that holds and rotates the swab at the nasopharynx, and an extraction phase where the swab is removed from the nasal cavity.
• Figure 4: Visualization of the pose estimation system adapted for the phantom fixture. The location of at least three of the fiducials leads to the identification of the nostril pose (red-green-blue axes).
• Figure 5: Sequence of the optimized trajectory as it travels through the nasal cavity volume. Notice how this trajectory begins at an incline angle and then rotates shortly after entering to point at the nasopharynx.