| Robot-assisted minimally invasive surgery is a cross-fusion of robotics and medical disciplines.It combines the advantages of robotics and minimally invasive surgery,not only possessing the advantages of precise surgical positioning,high operation accuracy,small patient's trauma,and quick postoperative recovery,but also reducing the number of medical workers and the doctor's fatigue.Therefore,it has received widespread attention and is developing rapidly.However,the current surgical robot system still has many parts to be improved in the development process.Among them,surgical instruments' operational flexibility,motion control accuracy,and whether they have the capability of external force sensing are related to the quality of surgery.This dissertation focuses on the motion estimation method of end joints and the external force sensing method for the cable-driven surgical instruments,mainly including the motion decoupling of end joints,high-precision motion estimation method,indirect force estimation method without sensors at the joints,and the direct force sensing method with integrating force sensors into the end forceps.The research process involves lots of detailed theoretical modeling,simulation analysis,and experimental verifications.The specific contents are listed as follow:Firstly,the universal bedside robotic arm developed in the laboratory,and used in the robot system for laparoscopic surgeries,is introduced and analyzed.Then,the MD-H method is adopted to model the kinematics of the bedside robotic arm without considering the overall rotational and translational movement freedom of the surgical instrument,and the simulation verification is also completed.By analyzing the coupling effect of end joints' motion of the 3degrees of freedom(3-DOF)flexible cable-driven surgical instrument,a symmetrical wrist mechanism and parallel and symmetrical layout of the winding track of flexible cables is proposed.Then,a new type of surgical instrument driven by flexible wire cables is designed,which can realize the movement decoupling of the end joints on the mechanical mechanism.Through mathematical modeling and simulation analysis of forced deformation of the cable driving the end operating forceps,the correctness of the designed surgical instrument is verified.Through the kinematics modeling and simulation verifications of the surgical instrument,the operability of the single joint motion of the designed surgical instrument is proved,which provides a basis for the high-precision motion estimation of the end joints.Secondly,for the situation that a position sensor to collect accurate position information cannot be installed at the end joints of the flexible cable-driven surgical instrument,a new motor-spring bidirectional drivable mechanism scheme is proposed by analyzing the working principle of the flexible cable-driven end joints.In this scheme,the return spring can keep the flexible cable in the tension state at all times,eliminating the mechanical assembly clearance.By approximating the flexible cable as a "mass-spring-damper" model,a nonlinear dynamic model considering factors such as cable deformation,damping and system friction is established.The joint angle identification and motion estimation are carried out by using the least square method(LSM),and the installation scheme of the displacement sensor at the motor drive side is determined.Then,the system's state equation is established,and the motion error compensation model is integrated into the traditional UKF algorithm to obtain the improved UKF model motion estimation method,which achieves high-precision motion estimation of the end joints.The high-precision motion estimation performance of the proposed method is verified by the motion estimation experiments under the condition of no load and with load.Thirdly,by using the estimated value of the end joint rotation angle as feedback information,the closed-loop motion control of the end joint is studied.Based on the measurement information of the flexible cable's displacement sensor at the system's drive end,the displacement estimation model of the flexible cable at the reset end is established by performing many identification experiments with using the least square method.Based on the measurement information at the drive and reset ends and the estimation information at the reset end for the flexible cables,two kinds of tension estimation models of cables are established for the external load force and no external load force at the tip of the end forceps.Aiming at the situation that force sensors cannot be installed at the end joints of surgical instruments for external force sensing,an indirect estimation method of external force based on the tension estimation model of flexible cables is proposed.The correctness and feasibility of the proposed external force estimation method are verified by many static and dynamic loading experiments.Finally,with integrating force sensors on the end forceps for direct external force sensing as the research goal,a double "E-beam" vertical staggered configuration of the elastic body structure is proposed.The elastic body has the characteristics of two-dimensional force decoupling,and it has an integrated configuration design with the base body of the forceps.Furthermore,the elastic body is arranged on the two graspers in the form of 90° rotation angle around the axis.Then,the deformation simulation analysis of the operating forceps is carried out by using ANSYS,and the installation position and arrangement form of strain gauges as sensing elements are determined.Based on the force-strain simulation model of the double graspers,a three-dimensional operating force decoupling algorithm is proposed.The verifications of external force direct sensing are carried out through simulation,and experiments of static and dynamic external force loadings.The experimental results prove the feasibility of the proposed external force sensing method with integrating force sensors into surgical forceps,and the grasping force and the three-dimensional operating force can achieve good sensing accuracy. |
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