Research On Force Measurement Technology Based On Model In Minimally Invasive Surgery Robot

Minimally invasive surgical robot system can not only expand the ability of surgeons in minimally invasive surgery, but can increase the precision of surgical operation, flexibility and vision. Force and haptic feedback plays a very important role in minimally invasive surgery. It can enable the surgeon to feel organic tissue hardness, measure tissue properties, evaluate anatomical structures, and allows him/her to commit appropriate force control actions for safe tissue manipulation. Currently commercially available robot systems lack force and tactile feedback, the main reason is that it is difficult for the special environment of minimally invasive surgery to acquire the force and torque information between end-effector and the environment. According to the above-mentioned problem, force measurement technology based on dynamic model is proposed to extract the interaction force between the surgical instruments and the environment without force and torque sensors. It provides a basis theory for the implementation of force sensing and force feedback in minimally invasive surgical robot. The following aspects in the dissertation have been achieved:1. The design requirements of MicroHand A system are proposed according to minimally invasive abdominal surgery and the components and functions of the system are introduced in detail. Half-loop tendon-driven method based on the kinematics of tendon-driven manipulator is put forward. The relationship equation between motor angular displacement and joint angle can be directly written by half-loop tendon-driven method. The kinematics of master manipulator and slave manipulator are analyzed by screw theory and the mapping relationship among the Cartesian space, joint space and motor-driven space is established. Space and body Jacobian matrixes of the master and the slave manipulators are derived. Those laid the foundation of realizing intuitive motion control under kinematically dissimilar master-slave manipulators and force measurement technology based on model.2. The complete dynamic model of the general open-loop chain manipulator and the tendon-driven manipulator including motor rotor dynamics and joint friction are modelled by Lagrangian method. Force measurement model based on dynamic model between end effector and environment is derived to acquire force and torque information without force and torque sensors.3. The whole dynamic model for active part of the MicroHand A system with the remote center of motion and the tendon-driven surgical instruments is established by product of exponentials formula and Lagrangian method. The joint friction, rotor dynamics and coupling of tendon-driven joint are taken into account in the model. The dynamic model is linearly parameterized and the dynamic parameters are experimentally identified using least squares method, which provides a strong guarantee for the realization of force measurement technology based on model.4. The hardware architecture and the software algorithms of master-slave control system are designed for the MicroHand A system. Intuitive motion control and motion scaling control are accomplished to solve absonant hand-eye coordination, kinematic dissimilarity and workspace mismatch of master-slave manipulators. The dynamics model of a simplified master-slave teleoperation system with one degree of freedom is derived to accomplish bilateral motion and force feedback control. The teleoperation system can be presented by a two-port network theory. The necessary and sufficient conditions for absolute stability are derived and the stability and the transparency of the system are qualitatively analyzed.5. Force measurement based on model experiments and position tracking experiments are carried out. Force measurement experiments include the force measurement accuracy experiments based on dynamic model and the interaction force measurement experiments between the surgical instrument and the environment under different experimental tasks such as knot tying and suturing. Position tracking experiment between the desired trajectory commanded by the master manipulator and the actual trajectory of the slave manipulator is carried out. The correctness and the technical feasibility of force measurement principle are validated.