Design And Experimental Study Of Active-passive Compound Adjustment Mechanism For NOTES Robot

Compared with open surgery and traditional laparoscopic minimally invasive surgery,natural orifice transluminal endoscopic surgery(NOTES)has the advantages of non-invasive surface,good cosmetic effect,short recovery time and so on.However,the use of soft instruments has led to problems such as the rising difficulty of surgical operations for surgeons.With only a single operation channel,most of the existing instruments used for NOTES are poor in flexibility.What’s more,the digestive tract approach is complicated and lengthy,which result to the difficulty of instrument introduction.Due to lack of passive adjustment arm,most current NOTES instruments exist the problem with twisting and inaccurate positioning.With limited adjustment range,parts of the instrument with passive arm cannot cover most surgical positions.Aimed at the above problems,this article proposed a design of active-passive compound adjustment mechanism.The specific content is as follows:Firstly,a new design method of the mechanism with remote center of motion that based on curved linkages is proposed.The mechanism designed by this method is used as the passive adjustment arm of which the design process and mathematical constraints are given in this article.Secondly,an active-passive compound instrument arm with 20 mm out diameter and two operation channel base on continuum mechanism is designed.The end of instrument arm is composed by two 80 mm long active continuum segment.The article has compared the open-loop tendon transmission with close-loop tendon transmission and the design of the porotype based on tendon-sheath mechanism is finally completed.Then,the relationship between actuation space-virtual joint space mapping relationships of active continuum segment is analyzed.According the mapping relationship and the construction of the joint itself,the configuration parameters of active joint are optimized to reduce the difference of a pair of antagonist tendons.Based on screw theory,the kinematics model of the active continuum segments is analyzed.According to the kinematics,the transformation matrix and velocity Jacobian matrix of the end of instrument arm are given.In addition,the wire-driven continuum robot is greatly affected by external loads and the analysis of its static model is necessary.The article gives the static model of single active continuum segment based on holisticisolated method.Finally,relevant experimental research is carried out to test the designed instrument arm prototype and theoretical model.The experiments show that the rotation angle of single active continuum segment joint reaches the design goal of 90 ° and the minimum bending radius is 20 mm,which meets the needs of physiological parameters.The hysteresis error was tested experimentally,with an average value of 3.5 mm.Besides,according to the results of experiments,the average error of kinematics model was 3.7mm and the repeat positioning accuracy was 0.88 mm on average.Finally,the minimum load capacity of the instrument arm designed in this paper is tested to 1 N,which verifies the feasibility of its support cavity to provide operating space for surgical instruments.