  Manual oropharyngeal (OP) swab sampling is an intensive and risky task. In
this article, a novel OP swab sampling device of low cost and high compliance
is designed by combining the visuo-tactile sensor and the pneumatic
actuator-based gripper. Here, a concave visuo-tactile sensor called CoTac is
first proposed to address the problems of high cost and poor reliability of
traditional multi-axis force sensors. Besides, by imitating the doctor's
fingers, a soft pneumatic actuator with a rigid skeleton structure is designed,
which is demonstrated to be reliable and safe via finite element modeling and
experiments. Furthermore, we propose a sampling method that adopts a compliant
control algorithm based on the adaptive virtual force to enhance the safety and
compliance of the swab sampling process. The effectiveness of the device has
been verified through sampling experiments as well as in vivo tests, indicating
great application potential. The cost of the device is around 30 US dollars and
the total weight of the functional part is less than 0.1 kg, allowing the
device to be rapidly deployed on various robotic arms. Videos, hardware, and
source code are available at: https://sites.google.com/view/swab-sampling/.
