Research On The Stability And Analytical Solution Of The Dual Hemisphere Capsule Robot During Posture Adjustment

As a new interventional detection device for human gastrointestinal diseases,capsule robot has been used widely.It overcome disadvantages of the traditional gastrointestinal detection methods such as missing regions of interest,hard to control,and discomfort to patients.The dual hemisphere capsule robot(DHCR)developed in this paper is driven by wireless magnetic field,which realizes the separation of attitude and position control.It also has the advantages such as simple structure,convenient operation and precise control,and it is believed that more attractive applications of DHCR will be realized.However,the DHCR shows complex nonlinear dynamic characteristics,and if the control parameters are not suitable,the DHCR will be unstable,which hinders the clinical application of the DHCR.Therefore,this paper focuses on the nonlinear dynamics of the DHCR in passive mode,and studies on the stability of the attitude adjustment process and controllable conditions of the DHCR.First of all,this paper proposes a dimension reduction method of the universal magnetic spin vector(UMSV)and the coupling magnetic torque equation expressed using reduced-dimensional UMSV,which corrects the problem of the current mathematical model in the description of the UMSV rotation.New equations greatly simplify the expression of the UMSV and magnetic torque,and provides convenient conditions for further study of complex nonlinear problems in the posture adjustment process.Secondly,by re-selecting the reference coordinate system,this paper converts the absolute attitude angles of the DHCR in space into relative attitude angles to the magnetic field,which further simplifies the dynamic equations,and reveals unified dynamic characteristics of the posture adjustment process in different orientations.Furthermore,based on the theory of nonlinear dynamics,the possibility of the DHCR gets stable at the target orientation is proved.The theoretical derivation proves that the target orientation is a fixed point in the DHCR non-linear dynamic system.The stability of the nonlinear system depends on the stability of the approximate linear system(AIS)near the fixed point.Then,the interval state transition matrix approximation algorithm is used to study the stability of the AIS under different control parameters.The influence of each control parameter on the stability of the DHCR is analyzed,and the critical stability control line and controllable conditions of the DHCR are further obtained.The power series algorithm was used to solve the AIS within a small attitude angle range.The time domain series analytical solution and the inter-cell approximate solution of the attitude angles were obtained.Simulation in Matlab shows that the analytical solution is accurate,and the approximate solution has high fitting accuracy.Finally,this paper uses a new posture simulation device to verify the influence of various control parameters on the stability of the DHCR during actual control process through experiments.The final results are consistent with the theoretical analysis results,which proves the accuracy of the theoretical research method,and the controllable conditions obtained by calculation can ensure the smooth operation of the DHCR.The theoretical research provides a basis for the stable control of DHCR.