Research On Mechanism Design And Safety Control Of Endoscopic Sinus Surgery Assistant Robot

Endoscopic sinus surgery is an effective method for the treatment of nasal cavity and sinus inflammation and thorough removal of nasal cavity and sinus lesions.Endoscopic sinus surgery has a high risk because of the complex anatomical structure,narrow surgical area and paranasal sinus adjacent to the orbital cavity and cranium.Traditional endoscopic sinus surgery is usually performed by surgeons with left-handed nasal endoscope and right-handed surgical instruments.Because the surgical channel is narrow and slender,the endoscope reaches the surgical area heavily relies on the surgeon's experience.The surgeon's hands are prone to fatigue and shaking due to long-time operation,which causes misoperation.In addition,for some complicated operations,the assistant surgeon is required to assist to hold the endoscope and the chief surgeon is to operate with both hands.Operations between surgeons are easy to interfere,and coordination is difficult.Introducing a robot to assist the surgeon to hold the endoscope,acting as the surgeon's third hand,can combine the outstanding advantages of the robot with the surgeon's experience,so that the surgeon can change the one-hand operation to two-hand operation,the stability of operation can be enhanced and the quality and safety of the operation can be improved.In this dissertation,mechanism design and safety control of the endoscopic sinus surgery assistant robot are studied.The auto-tracking endoscopic sinus surgery assistant robot system is proposed,and the key scientific issues such as the robot's mechanism design,motion planning and constraints,safety control are studied.This research has laid a solid foundation for the early clinical application of endoscopic sinus surgery assistant robot.In this dissertation,by analyzing the typical endoscopic sinus surgery procedure,the workspace characteristics of the endoscope and the requirements of the intraoperative robot placement,the scheme of the robot is proposed,which is suitable for the narrow space of the nasal cavity.For the robot end-effector mechanism,the scheme based on RCM(remote center of motion)mechanism is proposed.Furthermore,a type synthesis method of RCM mechanism based on coupled motion is proposed and a new family RCM mechanism is obtained.By comparing and analyzing the typical robot positioning mechanism,the positioning arm scheme based on PRR(prismatic-revolute-revolute)structure is determined.By integrating the RCM mechanism and the PRR positioning mechanism,the endoscopic sinus surgery assistant robot system is detailed designed and implemented.In order to ensure the safety of the surgical operation,the motion of the robot during surgery is planned.Firstly,through the analysis of the endoscope tip trajectory during surgery,the motion planning requirements of each motion stage are obtained.Then,based on the patient's CT medical image sequences,the spatial model of patient's nasal tissue and the point cloud model of patient's nasal boundary are established.Based on the obtained boundary point cloud model,a search map is built.The A-star search algorithm is introduced to search the intraoperative endoscopic motion path,and the endoscope safe motion path from the nasal entrance point to the surgical area is obtained.Finally,a virtual nasal endoscopy system is constructed based on the three-dimensional reconstruction model of the nasal cavity,and a virtual nasal endoscopy experiment is performed on the planned surgical path to verify the effectiveness of the robot motion planning.For the safety of robot-assisted endoscopic sinu surgery,the virtual fixture is introduced to study the motion constraint of the robot.Firstly,by analyzing the existing virtual fixture types and their action mechanism,combined with the characteristics of endoscope motion in endoscopic sinus surgery,several typical virtual fixtures suitable for endoscopic sinus surgery are proposed,which are guiding virtual fixture based on spatial polynomial curve,forbidden regions virtual fixture based on hyperboloid,and forbidden regions virtual fixture based on nasal sinus anatomy.Then,considering that a single virtual fixture is difficult to meet the requirement of diverse constraints during surgery,a composite virtual fixture is constructed based on the basic virtual fixture geometry,and overall robot motion constraint scheme based on the nasal sinus anatomy is obtained,then the whole surgical process constraints in endoscopic sinus surgery is realized.Finally,the experiment studies are carried out,with and without constraints of virtual fixtures,and the effectiveness of the virtual fixtures is verified.Based on the analysis of robot-assisted endoscopic sinus surgery procedure,three control modes of robot during surgery and its motion control method are proposed.For the free drag mode,a human-robot cooperative control method based on admittance control is proposed.For the constrained drag mode,the human-robot cooperative control method based on virtual fixture is proposed.For the automatic tracking mode,the navigation-based auto-tracking safety control method is proposed;while the surgeon is operating the surgical instrument with both hands,the endoscope at the end of robot automatically tracks the surgical instrument to provide the surgeon with a real-time surgical field of view.Finally,combining the above three control modes,the overall framework of intraoperative human-robot cooperation safety control is proposed,and the whole surgery process safety control is realized.A robot-assisted endoscopic sinus surgery experimental platform is built based on the robot,control system hardware and software,navigation system and high-imitation human head model.Through robot-assisted endoscopic nasal examination surgery and robot-assisted maxillary sinus surgery,the robot's motion planning method,virtual restraint effect,human-robot cooperative control method and navigation-based auto-tracking safety control method were verified.The experiment results show that the robot system of this dissertation can assist the surgeon to hold the nasal endoscope and act as the surgeon's third hand,so that the surgeon can change the one-hand operation to two-hand operation and assist the surgeon to complete the surgery.