Research On Semi-Autonomous Colonoscopic Robot System

Due to environmental pollution, changes in the diets and mental stress, many people suffer from intestinal diseases. These diseases include inflammatory bowel diseases, intestinal tumor and intestinal cancers. As a direct tool, the colonoscope is a reliable and thus important for diagnosis and treatment of intestinal diseases. However, only a very short distal tip of the colonoscope can be controlled to bend actively, the bend of other sections is realized passively by the pressure between the tube and the colon wall. Consequently, the colonoscope usually changes the bending shape of colon and thus causes the patient a great deal of pain and taking a risk of perforation.Aimed at the disadvantages of traditional colonoscope, a novel semi-autonomous colonoscopic robot is presented in this paper. The robot consists of 5 continuum sections which is inspired by snake, elephant trunk or octopus tentacle, and has a total of 10 degrees of freedom (DOF). The robot moves in colon tract with a kind of semi-automous mode: it moves forward by the control of manipulator, and bends actively and compliantly according to the bending model of adult colon and the feedback of pressure sensors. The research of this paper includes bionic structure design and kinematics analysis of colonoscopic robot, trafficability analysis and compliance control in the unconstructed environment of colon tract.Based on the analysis of the anatomical characteristics of human colon and the bionic principle of continuum robot, a colonoscopic robot with multi-sections continuum structure is proposed. The robot is composed of five sections, each has two DOF and driven by cables. As the standard D-H method can't be used to realize the kinematics analysis of continuum robot, a kinematics analysis method which is concise and real-time is presented. The relationship among drive space, section space and operation space of single section and multi-sections is studied respectively, and then validated by simulation. The structure design and kinematics analysis laid the foundation for trafficability analysis and adaptability analysis in the unconstructed environment of colon tract.According to the anatomical characteristics of human colon, the bend model of adult colon is constructed which is concise and without loss of generality. Aimed at the multi-section continuum structure of colonoscopic robot, a semi-autonomous control strategy for the motion of colonoscopic robot in the unconstructed environment of colon tract is proposed. The implementation of control strategy in the two-dimensional colon model which includes sigmoid flexure and descending colon and the three-dimensional colon model which includes transverse colon is studied respectively, and validated by simulation.The biomechanical property of human colon tissue is analyzed, and the safety threshold of pressure between the colonoscopic robot and colon tract is derived. These studies provide a basis for the compliance control of colonoscopic robot in colon tract. A pressure sensor which is used to measure the pressure between the colonoscopic robot and colon tract is designed and the mechanical characteristics is analyzed. Aimed at the adaptability of colonoscopic robot in the unstructured environment of colon tract, a compliance control method is proposed based on the biomechanical property of colon tissue. This method avoids computing the complicated dynamics of colonoscopic robot and thus features high real-time and feasibility.Finally, the prototype experiment system of semi-autonomous colonoscopic robot is built. The hardware and software of distribute control system for colonoscopic robot are introduced. The bending experiments of single section and multi-sections are carried out respectively, which validate the kinematics of continuum robot. In order to test the effectiveness of semi-autonomous control strategy for the motion of colonoscopic robot in colon tract, the trafficability experiment in rigid colon model is performed. The result of compliance control experiment in medical colon model shows that the pressure between colonoscopic robot and colon tract is within the threshold, which validates the effectiveness of the compliance control method in the unstructured environment of colon tract.