Six-degree-of-freedom Wire Drive Minimally Invasive Surgical Instruments

Minimally invasive surgical instruments are the important part of the minimally invasive surgical robot. Design of mechanical structure will directly affect the performance, and also restrict development and design of other components in the system. Supported by the National Science Foundation of China, the detailed structure design, kinematics analysis, statics analysis, workspace analysis and kinematics simulation were studied in this thesis.Firstly, the minimally invasive surgical instrument has six-degree of freedom (DOF) and includes four parts:driving system, the main connecting rod, actuators and quick-exchange fingers. The six-DOF of the surgical instrument includes shoulder yaw DOF, elbow pitch DOF, wrist pitch DOF, roll DOF, finger yaw DOF and fingers’opening & closing DOF. Roll joint between the wrist joint and finger joint can avoid intervening of the surgical instrument and organ or other instruments. The quick-exchange fingers were designed to achieve the rapid replacing of various kinds of surgical instruments in the process of the operation. Seven-degrees of freedom can be obtained when the surgical instrument is carried on the linear guideway. Therefore, it can not only meet the requirements of workspace and surgical operation, but also effectively avoid the interference with the manipulator of the outside body. Driving system is located at the distal of the surgical instrument and cable-driven mechanism is adopted to achieve small diameter instrument, light weight and long distance transmission. Finally, the stress of surgical instrument’s cables was analyzed and the types of the cables and the motors were determined.Secondly, the D-H method was used to establish the kinematics coordinate frame of the surgical instrument. The forward kinematics of the surgical instrument was calculated and the inverse kinematics was analyzed by analytic method. For a kind of N degrees of freedom robot system driven by 2N steel cables, the loop analysis method was applied. Loop matrix and equivalent radius matrix of motor-driven space can be written out by observing the layout of steel cables. Combined with the traditional robotic kinematics, the complete kinematic mapping relationship model between the motor-driven space and the Cartesian space can be accomplished, which speeds up and simplifies the kinematic modeling and analysis process of steel cable- driven robot. Finally, the Jacobian matrix of the surgical instrument was calculated. The manipulability and dexterity evaluation indexes were analyzed by means of the Jacobian matrix’s singular value.Finally, various aspects of the surgical instrument were analyzed. First of all, to ensure reliable, statics analysis of the key components and the main load-carried parts were performed. The workspace of the surgical instrument was also analyzed, which showed the workspace can meet the operation requirements. Finally, to verify the correctness of the forward and inverse kinematics of the surgical instrument and rationality of structure design, the forward kinematics and inverse kinematics simulations of the surgical instrument were carried out.