Research On Errors Of A Universal Magnetic Spin Vector For Magnetic Navigation Of The Capsule Robot

Magnetic actuated capsule robot can not only effectively solve the problem of the energy for the capsule robot driving, but also be used as a driving source for the control of the movement and posture of the capsule robot. What's more, it can realize efficient, noninvasive traversal examination of the human gastrointestinal tract, has a broad clinical application prospect, and become a hot spot of research at home and abroad.Our group has proposed a petal-shaped capsule robot system, in which the petal-shaped capsule robot realize full suspension swimming actuated by a universal uniform magnetic spin vector which is superimposed by manipulating the three-phase sinusoidal currents inside tri-axial orthogonally nested square Helmholtz coils. In order to improve the accuracy of the posture adjustment and steering magnetic navigation of the petal-shaped capsule robot, in this paper, the errors of the spatial universal rotating magnetic vector, which is the driven magnetic vector of the capsule robot, are researched and corrected.Firstly, the causes of the magnetic spin vector errors are analyzed based on the orthogonal superposition theorem of the spatial universal rotating magnetic vector. It is concluded that the mismatches of the structure parameters and phase differences of three Helmholtz coils not only cause the orientation error of the magnetic spin vector, but also change the end track of the magnetic spin vector, that means cause the magnitude error.Then, according to the theorem of curve theory, it is proved that the end track of superimposed magnetic spin vector under the influence of structure parameters and phase differences is still the plane curve. And on this basis, the mathematical models associated with the magnitude error and the orientation error of the universal magnetic spin vector are established. Through the simulation analysis, the variation rules of the magnitude error and the orientation error of the magnetic spin vector are researched.The magnitude error of the magnetic spin vector makes the magnetic moment of the capsule robot fluctuated during the process of rotation, which worse the stability of the capsule robot, even causes the lost step phenomenon, and affects the driving efficiency of the capsule robot. The orientation error of the magnetic spin vector makes the posture control of the capsule robot not accurate, increases the risk of collision between the capsule robot and the gastrointestinal tract during the navigation of the robot, which isn't conducive to complete the diagnosis and treatment of the whole gastrointestinal tract effectively and smoothly.To this end, the double error compensation method includes the current magnitude compensation by three different structural coefficients of tri-axial Helmholtz coils, and the current phase compensation by two relative phase differences under linear polarization, is proposed to correct the errors of the magnetic spin vector.Finally, the feasibility of the double error compensation method proposed in this paper is validated through the experiment. The experimental results show that the orientation accuracy and stability of the magnetic spin vector corrected by the double error compensation method are improved obviously, which ensure the posture control accuracy and steering stability of the capsule robot and lay a solid foundation for the clinical application of capsule robot.