## 4 Discussion
This means that there was no difference in the accuracy of the kinds of tools when either the robot or the person was operating. We recognized that the instrument was detecting the surface of the mandible model and made it work accordingly, so both 6 mm and 20 mm discs should work with the same program, and the accuracy with the different kinds of instruments should not be significantly different. However, comparing the robotic and manual surgeries, there were significant differences in many categories. The error was calculated by dividing by the absolute mean value and the RMS. The accuracy of a measurement system is the degree of closeness of a quantity to true value. The precision of a measurement system, related to reproducibility and repeatability, is the degree to which repeated measurements under unchanged conditions show the same results. Considering these metrics, robotic surgery was better than manual surgery for the position and length errors in both accuracy and precision. The position error is an indicator of how accurately the end effector of the robot is located and the length error is an indicator of how accurately the end effector of the robot has moved during osteotomy of the model. Thus, obviously the robot can be positioned and moved more accurately and precisely than a person's hand. In the angle error, there was a different result. The absolute mean value of angle error was not significantly different between robotic and manual surgery, but the RMS of the angle error was significantly different between the groups. There was no difference in accuracy between the two groups in adjusting the angles to position the instruments. In this study, only the angle of 90\({}^{\circ}\) was used for the osteotomy design. The 90\({}^{\circ}\) angle can be measured relatively accurately by the human naked eye. Therefore, there seems to be no difference in accuracy between the two groups. If we designed it at an arbitrary angle, such as 30\({}^{\circ}\), 45\({}^{\circ}\) or 60\({}^{\circ}\) rather than 90\({}^{\circ}\), the results might have been different. In regard to precision, the robot was better than humans for positioning at the designated angle. However, the depth error has the opposite results. The manual surgery had more accurate and precise results than the robotic surgery for the depth error, which was the largest of all the errors in our results. The depth control of the disc was the most difficult osteotomy type performed in this study. In the future, we need an algorithm that can feed back the resistance of the robot while it performs osteotomy in order to achieve more accurate depth control. Safety is one of the most important issues, and our robot has several integrated safety features. One of them is protection of the patient and the surgeon against a patient's unexpected movement. When the robot is touched by external force more than 15 N in the surgical field, it automatically stops moving. As an amount of external force, we can modify the threshold of unpredicted external force. The ergonomic aspects of the robot guidance were assessed and confirmed under optimal conditions. The robot arm osteotomy was compact enough to allow two surgeons to operate comfortably. In the future, the robot will be able to play the role of one surgeon in the operating room. Since a force of up to 15 N can be applied to the fissure bur (2 mm width and 15 mm length) connected to the robot arm, a pressure of up to 500 kPa can be applied to the bone. When this mechanical impact is applied to the bone, it can affect the interaction between the cell and the extracellular matrix [18]. Since this can affect bone healing, it will be important to control the robot arm carefully so that minimal pressure can be applied to reduce this bias. Future research should be focused on the improvement of the real-time interaction between the end-effect of the robot and the target patient.