Researches On The Key Technologies Of A Diameter-variable Crawler-type Micro-robot For Colon Exploration

As one of the possible alternatives to the traditional colonoscopy,micro-robot is promising to enable a screening of colon diseases.Under supports of the project of National Natural Science Foundation of China(No.61803347),this dissertation focuses on the research of the key technologies of a diameter-variable crawler-type micro-robot for colon exploration.The key technologies involve the compatibility between the robot and the complex colonic environment,and design of the locomotion mechanism.The research on the compatibility between the robot and the complex colonic environment aims to provide theoretical basis for the optimization of robot design and motion control,mainly including the following two aspects:1.Modeling the slippery characteristics of the colon: An experiment device are built for measuring the friction coefficient between the internal surface of colon and three commonly-used materials(silica gel pattern crawler belt,white photosensitive resins and transparent photosensitive resins)under different contact pressure,hoop strain ratio and relative motion speed.Based on the experimental data,the causes of the influence of three factors on the friction coefficient are analyzed,and a fitting model is established to predict the friction coefficient.Using the friction coefficient model,the kinematic model of a crawler-type robot in colon is established.The correctness of the kinematic model is verified by testing the pulling force produced by three crawler-type robots with different diameters in different colon.2.A method for sensing the geometric parameter of colon based on the diameter-variable mechanism and thin-film pressure sensor is proposed.By installing thin-film pressure sensors on the tips of the expanding mechanism,the contractile forces of intestines in different expanded radius can be measured.And based on the pressure data and a sensing model taking constitutive equation as the core,the initial radius and thickness of intestines can be sensed.An experimental platform is set up to verify the proposed method in several ex-vivo pig intestines,and the results show that: the intestinal geometric parameters can be sensed out within 15 s,and the sensing errors of the intestinal radius and thickness are in the ranges of[0.084 mm,0.239 mm] and [0.186 mm,0.339 mm],respectively.Based on the research result above,a locomotion mechanism is designed: The robot,measuring Φ35.0mm×40.9mm,is composed of a variable diameter mechanism and three crawler mechanisms.With the help of the variable diameter mechanism,the robot can actively change its diameter in a large range from 35.0mm to 85.2mm,for expanding intestinal folds and stopping at any location in the colon.The three crawler mechanisms are fixed at the expanding tips of the diameter-variable mechanism and are in contact with the colon lumen,for enabling the robot to locomotion quickly.In addition,a thin-film pressure sensor is installed between each crawler mechanism and the expanding tip of the diameter-variable mechanism,for detecting the contact pressure between the crawler belts and colon.The robot performance is evaluated in several rigid pipes having different diameters,as well as in an ex-vivo colon.It was observed that the robot can actively change its diameter to adapt to the situated environment,based on the detected contact pressure;and the realized velocities were6.25cm/s,3.69cm/s and 1.77cm/s in the horizontal pipe,vertical pipe and ex-vivo colon,respectively.These results manifest that the robot is promising for colon exploration.