Page 68 - Demo

Chapter 466robotic control and simulation. It provides hardware abstraction, device drivers, and libraries. The image pipeline repository is used to convert the image data from the video camera to the ROS framework. For controlling the KUKA, the iiwa stack repository is used which contains high level commands to collaborate with the robot through the ROS framework[10]. A custom ROS driver was written to read out the serial data from the FT- sensor and enable its usage in the ROS environment.To enable the clinician to freely move the forceps, the robot mode is switched to a passive mode (impedance control). Impedance control enables a dynamic collaboration between the clinician and the robot. In this mode, all 7 joints are acting as separate spring-damper systems. The stiffness and damping constants can be tuned by the user for each individual joint. High values will result in rigid joint motion, whereas lower values will result in more compliant/floating motion. To prevent joints drifting into joint limits and to facilitate the clinician during the experiments, joints numbers a2 and a5 are set to a higher stiffness and damping value compared to the other joints (Fig. 1). It results in a more compliant motion of the dental forceps.Both the FT-sensor and robot need to be calibrated before each experiment to register the position and orientation of the teeth. The robot is used for calibration of the position and orientation of the teeth. Because of the orientation difference of the upper and lower jaw (vertical/horizontal), two calibration tools were necessary. A lower incisor dental forceps is used for calibration in the lower jaw, due to the 90-degree angle and its straight design. For the upper jaw, a straight dental elevator (Usto-Lux, Ustomed, Germany) is used for calibration. The calibration is done by touching the center of the crown holding the tool in line with the z-axis of the tooth (see Fig. 5). The tool’s position and orientation was then registered using the graphical user interface (see below, Section II-E). By combining the exact position of the holding device (using the scale provided on the setup’s frame) and the positional information of the robot, a mathematical conversion can be made to determine the position and orientation of the teeth. Because the teeth in the upper jaw are positioned horizontally and the teeth in the lower jaw are positioned vertically, the z-axis of the teeth in the upper jaw is oriented along the x-axis of the robot’s world frame, as opposed to the lower jaw in which the z-axis is aligned with the z-axis of the robot’s world frame. Therefore, teeth in the upper jaw need a different transformation to the world frame than teeth in the lower jaw. The calibration method, as described above, enables the forces, torques and rotations of all teeth in both upper and lower jaw to be expressed in exactly the same reference frame, easing data analysis.Tom van Riet.indd 66 26-10-2023 11:59