## 4 Application of the Balancing Arm  
Image guided navigation systems have been popular for microsurgery. There are already many commercial products and navigation software packages for research and clinical applications. There are also many surgical procedures that use the technology. Current surgical navigation systems provide an operator with the positional data of the organs and the surgical tool inside the human body, but such information cannot prevent mistakes in operation. The otologic surgical robot using the proposed stackable mechanism employs five magnetic brakes in order to prevent mistakes. The magnetic brakes are operated when the surgical tool reaches the safety margin set by the operator so that any mistakes in surgery can be prevented. Figure 17 shows five magnetic brakes mounted on a revolute joint. Three magnetic brakes act as a brake on the stackable arm, and two magnetic brakes act as a brake on the surgical tool's revolution. The developed otologic surgical robot was applied to a mastoidectomy, which is a surgical procedure that removes the infected portion of a mastoid bone. A mastoidectomy is a common procedure to access the inner ear area. Figure 18 shows the process of a mastoidectomy. Figure 16: Box plot of the EMG data in the case of the zigzag motion: (**a**) Average RMS of the EMG sensor at the M. biceps brachii and the (**b**) average RMS of the EMG sensor at the M. flexor carpi radialis. Figure 17: Magnetic brakes. Figure 19 shows the system configuration of the otologic surgical robot system. This system consists of a surgical robot (spring balancing type), image-guided navigation software, and an optical tracker. In order to localize the positions and orientations of the surgical drill and the phantom, two probes are employed. The navigation system is an important component of the robotic system. Some of the important organs inside the temporal bone (such as the facial nerves and carotid artery) are invisible during surgery. Thus, an image-guided navigation and warning system is necessary to help novice surgeons avoid damaging important organs inside the temporal bone. In order to integrate the navigation system with the robotic system, the patient coordinates must be registered to the CT image coordinates. The registration is done in order to find the corresponding points in the preoperative CT image data and the points on the patient's anatomy on the operating table. Figure 20 shows the coordinate transformation between the CT image coordinates and the optical tracker coordinates. The feature point is \(p_{n}\), and \({}^{I}_{O}T\) is the homogenous transformation matrix that relates the optical tracker (i.e., patient) coordinate system to the image coordinate system. Six feature points were used for registration. In order to display the position of the robot in the 3D image coordinates, registration of the robot coordinates into the image coordinates was conducted. This enabled the surgeon to ensure that the drilling did not damage important organs inside the temporal bone during operation. Furthermore, using the warning algorithm, safety problems can also be handled. Figure 19: System configuration. Figure 18: Mastoidectomy. The surgeon can monitor a target lesion, the relevant organs, and the surgical drill in real-time using the image-guided navigation system. Figure 21 shows the navigation software, including the warning algorithm. The warning algorithm helps the surgeon prevent the surgical drill burr from entering critical organs. A 3D model of the target organ was made using the CT data of a patient, and a 3-step virtual wall was formed around the target organ. The virtual wall of each step was generated at a certain distance from the surface of the target organ. The distance of each virtual wall can be modified by an operator. If the drill burr reaches the virtual wall, the warning algorithm is activated by flickering the navigation view with a warning sound.