Design Method And Experimental Study Of The Stiffness-switchable Instrument For Natural Orifice Transluminal Endoscopic Surgery

With technical innovation and the development of minimally invasive surgery concept,based on the traditional multi-port and single-port laparoscopic minimally invasive surgeries,researchers have further proposed the Natural Orifice Transluminal Endoscopic Surgery(NOTES)that leaves no scar on body surface.Although with more ideal operation results,NOTES has increased operational difficulty,and the existing surgical instruments fail to fulfill the operational requirements.After analyzing the operating environment of NOTES and its requirements for surgical instruments,this thesis proposes innovative resolutions to solve critical problems of instrument design.The main achievements are as follows.Starting from the configuration analysis,surgical instruments are divided into rigid,flexible,rigid-flexible coupling and stiffness-swithable types.For the instruments of different types,this paper proposes the RCM mechanism kinematic algorithm suitable for rigid surgical instruments outside the body,and the constant curvature and non-constant curvature kinematic algorithm suitable for soft instruments inside the body,providing theoretical support for the mechanism design and motion control of surgical instruments.Focusing on the requirement of NOTES instruments for stiffness-swithable characteristic,we propose three implementation schemes based on liquid metal,braiding structure and SMP material,respectively.The rigid-flexible transformation mechanisms of the three types are studied carefully,and their control systems are designed.The two indicators of stiffness conversion ratio and time are put forward for the evaluation of these innovative surgical instruments.In the meantime,the feasibly of using braiding structure as the lesion extraction instrument in the natural orifice environment is verified.To meet the needs of pricise operation,we also study the tendon-driven system adopted by NOTES instruments,verify the influence law of structural factors and physical characteristics on stress relaxation of the driving tendon,study the friction and elastic deformation problems of tendon-sheath transmission,and propose an error composition algorism suitable for the situation of long-distance transmission.Guided by the above theories,we develop a kind of tendon-driven NOTES instrument,whose motion accuracy is calibrated by utilizing an image-based non-contact testing method,and verify the proposed theories in the meantime.Against the lack of force sensing in the natural orifice environment,we propose a mapping model from planar two-dimensional image to spatial six-dimensional force feedback,and establish a motion model from image processing algorism to spatial position and a physical model from structural design to stiffness matrix,respectively.In the meanwhile,we build a small sized force sensing module with the proposed models,whose six-axis precision is measured through calibration experiments,thus proposing a solution to the force sensing in the natural orifice environment.Based on the above studies,the detailed design and system integration of various parts of the NOTES instrument are made.The novel instrument consists of multiple kinds of operating tools.Meanwhile,some functional,in vitro and animal experiments are carried out step by step,to make comprehensive assessment of the system from practical effects,and the results show that the developed surgical instrument is able to satisfy requirements of NOTES.