| Natural orifice transluminal endoscopic surgery(NOTES)novelly takes a body orifice as its operation channel.It strives for the smallest cut and the least tissue damage,thus having a better treatment effect.A slender,flexible surgical instrument is adopted to pass through the tortuous human body orifice in the operation.However,the low stiffness makes the instrument show low efficiency in shape locking and force transmission,thus causing problems in force capability and manipulation accuracy.In addition,the multiple functions to be integrated with including cutting,hemostasis and lighting make it difficult to reduce the radial size of the instrument.As a result,it is easy to cause tissue damage and increase patient discomfort during insertion and withdrawal via the narrow orifice.Using a tubular manipulator with a tunable diameter and variable stiffness as an assistant device is an efficient solution to the problem.The flexible,small-diameter state of the manipulator can facilitate its insertion and withdrawal,while the rigid,largediameter state can provide a path that is rigid and large enough to guide and support the following instrument.Up to now,a variety of tunable stiffness mechanisms have been proposed and applied in manipulator design,involving wire tensioning,phase change material,granular jamming,negative pressure friction,etc.,which have achieved good tunable stiffness results.However,these manipulators have a non-tunable profile,which only satisfy the requirement for stiffness.They only solve the problem of stiffness,and the size interference during entering and leaving the human body is still unsolved.To solve the problems in stiffness and size simultaneously,in this dissertation,a braided tube with great radial deployability is adopted as the basis to design the manipulator.A tunable stiffness method based on negative pressure as well as a bidirectional tunable diameter actuation design have been proposed.Considering the potential failure modes of the proposed manipulator,mechanical behaviors of the braided skeleton,the tunable stiffness and the tunable diameter of the manipulator have been systematically analyzed.Finally,based on the analytical results,design rule and workflow of the manipulator have been proposed,and prototype fabrication and demonstration experiment have been carried out.The main contents of this dissertation are as follows:Mechanical characteristics of the braided tube have been analyzed for the application as manipulator skeleton.Deployability in radial direction of the tube under constraints of geometry and actuation force is firstly analyzed,and the equation to estimate the researchable diameter range has been derived.Bending collapse behavior is studied next,and it is found that the braiding angle and the fiber number are the key parameters affecting the collapse behavior.It further declares that a bending angle less than 48.5 degree can guarantee an intact profile.Longitudinal stiffness is finally tested,and a new braiding configuration with a hybrid braiding angle has been proposed.Due to the interference between the braiding fibers,the longitudinal stiffness has been increased by 57.1% times compared with that of a normal one,allowing a better profile stability under longitudinal load.A tunable-stiffness mechanism based on the braided tube and the negative pressure has been proposed and analyzed.Sealing membranes are dressed which cover both the inner and outer surfaces of the braided tube and form a sealed cavity.Negative pressure is applied to the membranes to restrict the relative sliding between the braiding fibers and the membranes and limit their deformations,thereby enhancing the overall stiffness.Experimental results show that the bending stiffness and the radial stiffness are respectively increased to 6.85 times and 3.90 times as those in the flexible state.A theoretical fiber-membrane interaction model and the numerical simulation models have been established,with which the stiffness enhancing mechanism is further declared.It finds that frictional condition and membrane stiffness are the most efficient in tuning the stiffening capability.A bi-directional tunable-diameter method based on shape memory material has been proposed and analyzed.The skeleton deploys to the memorized shape and presents a large-diameter profile at electrical heating.When cooled it folds to a slim configuration under the compression of rubber bands.Experimental results show that it can achieve a diameter range up to 1.46 times within a response time of 20 seconds.Based on the spring theory,a mechanical model of the interaction between the components of the skeleton has been established,which theoretically determines the tunable diameter range.Based on heat-transfer analysis,heat-response behavior of the manipulator has been analyzed.It finds a preheating to 37 degrees Celsius can reduce the response time to be less than 10 seconds.A prototype system is fabricated and put in a demonstration experiment.Design rules are firstly summarized,following which a prototype together with a control system is established.The workflow of the manipulator has been proposed,which integrates the tunable stiffness and tunable diameter mechanisms,making the manipulator still function at no electric current.A demonstration test has also been carried out,which simulates the operation processes of the manipulator in vitro,which involving insertion,deploying,stiffening,shape-locking,returning flexible and withdrawal.Together with the comparison of diameter and stiffness ranges between the prototype and the commercial endoscopes,it verifies the feasibility of the designed manipulator.This dissertation designs,analyzes and fabricates a deployable tunable-stiffness manipulator based on a braided tube.The tunable-stiffness mechanism and tunablediameter actuation method are revealed,and the feasibility and efficiency of the manipulator are verified.The work provides a new idea for solving the problems of stiffness and size of flexible surgical instruments. |
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