Realization of a demonstrator slave for robotic minimally invasive surgery

Abstract

Robots for Minimally Invasive Surgery (MIS) can improve the surgeon’s work conditions with respect to conventional MIS and to enable MIS with more complex procedures. This requires to provide the surgeon with tactile feedback to feel forces executed on e.g. tissue and sutures, which is partially lost in conventional MIS. Additionally use of a robot should improve the approach possibilities of a target organ by means of instrument degrees of freedom (DoFs) and of the entry points with a compact set-up. These requirements add to the requirements set by the most common commercially available system, the da Vinci which are: (i) dexterity, (ii) natural hand-eye coordination, (iii) a comfortable body posture, (iv) intuitive utilization, and (v) a stereoscopic ’3D’ view of the operation site. The purpose of Sofie (Surgeon’s operating force-feedback interface Eindhoven) is to evaluate the possible benefit of force-feedback and the approach of both patient and target organ. Sofie integrates master, slave, electronic hardware and control. This thesis focusses on the design and realization of a technology demonstrator of the Slave. To provide good accuracy and valuable force-feedback, good dynamic behavior and limited hysteresis are required. To this end the Slave includes (i) a relatively short force-path between its instrument-tips and between tip and patient, and (ii) a passive instrument-support by means of a remote kinematically fixed point of rotation. The incision tissue does not support the instrument. The Slave is connected directly to the table. It provides a 20 DoF highly adaptable stiff frame (pre-surgical set-up) with a short force-path between the instrumenttips and between instrument-tip and patient. During surgery this frame supports three 4 DoF manipulators, two for exchangeable 4 DoF instruments and one for an endoscope. The pre-surgical set-up of the Slave consists of a 5 DoF platform-adjustment with a platform. This platform can hold three 5 DoF manipulator-adjustments in line-up. The set-up is compact to avoid interference with the team, entirely mechanical and allows fast manual adjustment and fixation of the joints. It provides a stiff frame during surgery. A weight-compensation mechanism for the platformadjustment has been proposed. Measurements indicate all natural frequencies are above 25 Hz. The manipulator moves the instrument in 4 DoFs (??, , ?? and Z). Each manipulator passively supports its instrument with a parallelogram mechanism, providing a kinematically fixed point of rotation. Two manipulators have been designed in consecutive order. The first manipulator drives with a worm-wormwheel, the second design uses a ball-screw drive. This ball-screw drive reduces friction, which is preferred for next generations of the manipulator, since the worm-wormwheel drive shows a relatively low coherence at low frequencies. The compact ??Zmanipulator moves the instrument in ?? by rotating a drum. Friction wheels in the drum provide Z. Eventually, the drum will be removable from the manipulator for sterilization. This layout of the manipulator results in a small motion-envelope and least obstructs the team at the table. Force sensors measuring forces executed with the instrument, are integrated in the manipulator instead of at the instrument tip, to avoid all risks of electrical signals being introduced into the patient. Measurements indicate the separate sensors function properly. Integrated in the manipulator the sensors provide a good indication of the force but do suffer from some hysteresis which might be caused by moving wires. The instrument as realized consists of a drive-box, an instrument-tube and a 4 DoF tip. It provides the surgeon with three DoFs additional to the gripper of conventional MIS instruments. These DoFs include two lateral rotations (pitch and pivot) to improve the approach possibilities and the roll DoF will contribute in stitching. Pitch and roll are driven by means of bevelgears, driven with concentric tubes. Cables drive the pivot and close DoFs of the gripper. The transmissions are backdriveable for safety. Theoretical torques that can be achieved with this instrument approximate the requirements closely. Further research needs to reveal the torques achieved in practice and whether the requirements obtained from literature actually are required for these 4 DoF instruments. Force-sensors are proposed and can be integrated. Sofie currently consists of a master prototype with two 5 DoF haptic interfaces, the Slave and an electronic hardware cabinet. The surgeon uses the haptic interfaces of the Master to manipulate the manipulators and instruments of the Slave, while the actuated DoFs of the Master provide the surgeon with force-feedback. This project resulted in a demonstrator of the slave with force sensors incorporated, compact for easy approach of the patient and additional DoFs to increase approach possibilities of the target organ. This slave and master provide a good starting point to implement haptic controllers. These additional features may ultimately benefit both surgeon and patient.