Error Analysis Of A Spatial Universal Rotating Magnetic Vector During Transient Process

Capsule robot is promising in medical field, but active control of the robot has not been realized, which can not satisfy the requirements of diagnosis and treatment. For solving this problem, the technology of spatial universal rotating magnetic field is proposed. A spatial universal rotating magnetic vector is superimposed by feeding three sinusoidal currents to triaxial Helmholtz coils, which has a potential to drive the capsule robot to screw forward inside gastrointestinal tract. However, there is a problem to be tackled which is as follows: when the magnetic vector changes from one orientation to another during steering control on capsule robot, error of the magnetic vector will occurs because of transient phenomenon.For this problem, a transforming time transient suppression method is proposed to reduce transient magnetic vector error. Firstly, in the fixed coordinate system, the full-response current model and the transient magnetic vector model are established; then by coordinate transformation, in the rotating coordinate system, the parametric equation of the transient magnetic vector is derived and the influence on the end track is analyzed. Theoretical research shows that the transforming time and the preceding magnetic vector orientation have much impact on the transformed magnetic vector error, because transient component is closely related to the current phase angle at transforming moment. Thus, controlling transforming time can reduce the transient component. According to different transforming ways, one-by-one transforming method and integral transforming method are proposed. After comparing the transforming period and transient magnetic vector error of the two methods, we obtain that the integral transforming method is better than the one-by-one transforming method. Then error magnitude, orientation error and end track error are researched. And example is presented to analyze the transformed magnetic vector error with integral transforming method and the results have shown that this method can reduce transient magnetic vector error effectively. And at last, experiment is conducted to test it.By solving the transient problem, the driving system is improved and the accuracy and stability of rotating magnetic vector are increased, which is expected to improve the driving performance of the capsule robot in curved environment.