Research On Pantograph Haptic Device And Application In Master-Slave Orthopedic Surgery

With the consistent development of medical, image, robotics and computer technologies, the research on teleoperation surgical robots have become one of the most interesting areas in the robotics community. By introducing teleoperation in orthopedic surgery, it can protect surgeons from suffering X-ray, relieve them work load and improve the accuracy of bone-setting operation. The haptic device is the key equipment of the master-slave manipulation and the interface between surgeons and robots, with which they control the slave manipulators to realize their intent of operation and to receive the acting force feedbacked from remote region on realtime. The haptic devices are very important influence on the system manipulability, force fidelity and stability. A high-performance haptic device ensures high efficiency and quality of the operation task. Therefore, the development of the haptic device and the theoretical research on force reflection are of great meaningful in enhancing naturalization and efficency of the human-machine interface.The work of this thesis is sponsored by National High Technology and Development Program(863) projects. A pantograph type parallel haptic device is presented and manufactured. Through bars and joints reasonably rearranged, all the motors are fixed on the base plate, which greatly decreases the moving inertia. The active bars are actuated by the motors directly, which reduces the clearance, and increase rigidity, and consequentially leads to a better dynamic performance. Compared with the prototype of pantograph parallel mechanisms, the architecture of the haptic device is special. D-H method is utilized to analyze the forward kinematics problem. For this architecture, two steps are required: First, to solve the nonlinear equations in order to obtain the revolute angle of the joints attached to the top plate by the numeric approach. And second, by obtaining the transformation matrix between the plate and the reference coordinate system, to get the relationship of input and output. The inverse kinematic problem is relatively simple to parallel mechanism, but it also has multi-solution problem. Aiming at multi-solution problem, a new type of subproblem is presented and the solutions are derived. By the screw and exponential product methods, the inverse kinematic problems are solved and the conditions with multi-solutions are given in geometrically also. And the Jacobian matrix is obtained by the concepts of the twist and reciprocal screw. For the specific hybrid architecture of the haptic presented in this dissertation, the dynamic model is obtained by the Kane method. The vector differentiation method is utilized to derive the velocity and acceleration mapping matrices between the top plate and bars. Considered the masses and inertias of the components, the mapping equation between actuating torques and the top plate motion is established and validated through ADAMS simulation.A novel position-orientation-coupled workspace called position workspace with specified orientation capability requirement is presented by using modified Euler angles. When using the normal Jacobian matrix to analyze the dexterity values in certain posture, an inhomogeneity trend will be occured. To overcome this problem, a normalized method based on three-point-velocity of the top plate is presented. After the normalization, the mechanism dimensional parameters are optimized with the maximizing global dexterity as the objective, and the volume of the new workspace and the mechanism as the constraint codition.The control system which composed of motion control units, measuring units and safety units is constructed. Since the accurate model of the operator is difficult to established, an adaptive controller integrated with velocity close-loop is presented. It is theoretically proved that during the operation, even if the contract rigidity is time-varying, the system can still achieve asymptote stability and good force tracing.The orthopedic surgery system is then established. By analyzing the characteristics of operation, the teleoperation control strategy is determined. With the experiments of free motion, bone-setting with animal and corpse, the tracing ability and operation effectiveness and system performance are testified. The experiment results show that, by using the control strategy presented in this dissertation, the teleoperation system with the haptic device is suitable and feasible. It can really enhance the performance of operation.