# Development of Robot-Assisted Untact Swab Sampling System for Upper Respiratory Disease
## 2 Materials and Methods  
### Slave System  
The slave system is composed of a sample collecting robot (slave robot) and a robot base. The motions necessary for NP swab insertion seem relatively simple compared to those of other surgical procedures. However, the kinematic structure should be designed to move the swab in multiple degrees of freedom so that the position and orientation of the swab can be adapted for each patient. We apply a parallel kinematic manipulator (PKM) in the slave robot. In comparison to a serial robotic arm, a PKM is generally known to have a limited workspace and complex singularity behavior; however, others of its features, such as a higher payload-to-weight ratio, greater stiffness, greater accuracy, and higher speed, are attractive for the design of a small and robust positioning mechanism [15; 16]. Specifically, a rotary Stewart platform is applied for the slave robot. This platform has six servo motors with forearms and rods connected by ball bearings. The six rods support a top plate, onto which a swab insertion unit is fixed. A disposable NP swab is installed in a swab holder and inserted into the swab insertion unit. The swab insertion unit then moves the swab holder back and forth with respect to the patient through the hole in the base frame. This hole is designed to be 120 mm in diameter to cover the human facial area for NP swab sampling. We establish an elliptic workspace with diameters of 60 mm \(\times\) 80 mm around both nostrils. The swab insertion unit can insert the NP swab up to a depth of 150 mm, considering the depth of the posterior nasopharynx from the nostrils. The slave robot is also equipped with a camera with a wide-angle lens to transfer images of the patient's face to the master site in real time. The slave robot is fixed to the robot base. The robot base is placed next to the subject such that the slave robot is located in front of the patient's face, as shown in Figure 1. To maintain distance from the slave robot to the patient's face and ensure that the face is located in the center of the slave robot, a head & chin rest is mounted on the robot base, as shown in Figure 1a,b. The patients will voluntarily place their face to the head & chin rest. If the patients feel inconvenience during the swab insertion, they can pull their head back. As shown in Figure 2, the swab insertion unit of the slave robot is implemented by means of a double roller mechanism. To push and pull the swab, a double roller structure is adopted rather than a linear actuator by ball screw. This can prevent the further advance of the swab due to slippage if the swab holder impacts the target with a force greater than the friction force between the rollers and the rod of the swab holder. The friction force can be adjusted by modifying the gap between two rollers as the value of \"d\" in Figure 2a. Currently, the swab insertion unit of the slave robot can apply a maximum force of 0.9 kg\(\cdot\)f to the swab holder, as measured in experiments. Two servo motors face each other and rotate in the same direction at up to 106 RPM. Since the roller diameter is 22 mm, the maximum speed of the linear motion of the swab holder is approximately 122 mm/s. During swab insertion, whether the tip of the swab has penetrated sufficiently to touch the target area (Nasopharynx wall for NP swap sampling) is the most important criterion to determine the success or failure of sample collection. The camera on the slave robot allows the length of swab insertion to be visually checked; however, in general, the specimen collection with NP swabs is done by the swab insertion along the nasal passage to the nasopharynx until resistance is felt [17]. Therefore, not only visual monitoring of the swab displacement to estimate the insertion depth but also additional information such as the resistance force exerted at the tip of the swab are used to confirm whether it is touching the target area.