Kinematic isotropic design of laparoscopic surgery robot master and motion scaling for usability improvement

Abstract

The development of surgical robots has brought various advantages over conventional surgical methods. Due to the teleoperation system using the master-slave, the surgeon can maintain a comfortable posture and perform surgery while sitting on the console. In addition, through the application of the motion scale, precise movements beyond the limits of the human body could be performed, and the tremor problem could be solved due to robot technology. However, many surgeons still take physical discomfort as a problem when the master of the surgical robot uses it for a long time and shows high cognitive load due to the occurrence of visual-perceptual mismatch due to the use of the clutch function. In particular, the more novice surgeons, the higher this level of fatigue was. We would like to propose a new RLS master that can solve these problems. In the RLS master design, important design elements are identified, functional requirements are defined, and design directions are presented accordingly. Not only the master function as an input device but also the user's convenience through ergonomic design. By comparing the newly proposed master system with the existing masters and kinematic performance, the strengths and weaknesses are clearly presented. As a motion-scaled teleoperation system requiring a clutch function, the RLS master must have a large workspace and high isotropy characteristics. In addition, in order to reduce the fatigue applied to the surgeon, a design considering ergonomics is required, and it must be designed considering inertia, back-drivability, and friction kinematically. In order to satisfy these characteristics, a hybrid structure different from the existing serial and parallel mechanism and a structure using spherical joints were proposed. A spherical parallel mechanism with 3 degrees of freedom consisting of 2 revolute joints and 1 prismatic joint is responsible for the positioning part. The wrist part is made up of two spherical shells, with a 3-degree of freedom structure and a gripper with 1 degree of freedom. An optimization design was performed considering the reachable workspace of the master manipulator, the workspace of interest in the target operation, and kinematic isotropy characteristics. As a result, the proposed structure showed higher isotropy performance than general serial and parallel structures. We intend to conduct a usability verification experiment on the proposed surgical robot master. First, we define the workspace where the user can comfortably work while sitting on the console as the Ergonomic Comfort Workspace (ECW), and try to find it through user experiments. The workspace required by the master of motion-scaled teleoperation system, not general teleoperation, was found through peg-transfer user experiments. In the surgical robot, it is important for the surgeon to maintain a comfortable posture while sitting on the console. At this time, the workspace mainly used by the user is defined as the Ergonomic Comfort Workspace (ECW), and the ellipsoidal workspace with three axes of 188mm, 192mm, and 245mm respectively am. ECW is proposed as the minimum required workspace in the RLS master design. Second, we investigate how to change the motion scaling factor between master-slave during surgery to improve task performance and reduce user fatigue. In order to increase user convenience, we investigated which method showed the highest performance and the least user fatigue through user experiments under the condition of changing according to various methods, not a constant scaling factor between master-slave. In order to perform a precise technique, ECW applied a scaling factor of a constant value and then increased the scaling factor in proportion to the logistic function according to the distance, which showed the highest performance and required the lowest user cognitive load. Through these results, the design direction of the RLS master could be presented. In addition, the master optimization method from the user's point of view was considered. An adaptive scaling factor strategy for high usability was also presented through comparative experiments. This method is considered suitable for application to RLS as a methodology considering ECW.