Dynamic Characteristics Of Rolling Motion For A Dual Hemisphere Capsule Robot

The wireless capsule endoscope has been widely used due to its advantages of low risk,small trauma,convenience and speed.With the development of wireless endoscopes,capsule endoscopy robots with active movement capabilities have become an inevitable trend in clinical medical examinations.The wireless capsule endoscope that has been put into use is only suitable for the inspection of small intestine lesions,and the research of the capsule endoscope robot that can work in ample environments such as stomach and colon is still difficult to achieve.The dual hemispherical capsule robot proposed and developed by this research group uses a three-axis Helmholtz coil as the driving source to drive,realizes the arbitrary adjustment of the direction of the rotating magnetic field,and solves the problem of the inseparable control of attitude adjustment and movement.The applicability in ample environments such as the colon is enhanced.However,the dynamic system of the capsule robot's active rolling motion is more complicated,and the stability control of the robot is also facing greater challenges.In order to ensure that the robot can adjust the speed in real time as needed,realize stable and accurate position control in ample environment,and at the same time explore the influence of the rotating magnetic field strength,rotation speed and other parameters on the dynamic performance of the capsule rolling,this thesis focuses on the dynamic characteristics and stability of the active mode of the dual-hemisphere robot.First of all,this thesis studies the motion characteristics of the capsule robot.The dynamic model of the capsule robot driven by the rotating magnetic field is established by the theorem of momentum.By analyzing the dynamic characteristics of the robot model,the change curves of the rotation angle and the slip angle are obtained.According to the principle of active rolling motion,the kinematics equation of the robot is established;the magnetic torque and friction torque of the robot are analyzed,the dynamic model of the robot in the rolling mode is established,using the Lagrangian dynamic modeling method and the rotation transformation between the coordinate systems.The rolling dynamics model provides a theoretical basis for subsequent analysis.Then,the dynamic model in the form of high-order nonlinear differential equations under the rolling motion of the capsule robot is simplified,and linearized in the neighborhood of the equilibrium point of the nonlinear system to replace the original system,using the interval state transition matrix approximation algorithm obtains the numerical solution of the approximate system,and analyzes its dynamic characteristics.And the eigenvalue of the state transition matrix is used as the characteristic index to judge the stability of the system,and the influence of each magnetic field parameter on the dynamic stability of the system is analyzed,and the critical and optimal control parameters for stable rolling are determined.This provides a theoretical basis for the robot control strategy.Finally,an attitude angle measuring device is developed based on the principle of laser measurement.The robot attitude offset angle is figured out on the basis of the maximum offset between the axis trajectory and the reference line.The results of experiments have proved that the magnetic field parameters have an impact on the robot stability.The correctness and feasibility of the control parameter conditions obtained by theoretical analysis are confirmed.