Research On Transient Characteristics Of A Capsule Robot Based On Orthogonal Transformation Operation

By the electromagnetic coupling between the permanent magnet embedded in the petal-shaped capsule robot and the spatial universal rotating magnetic field,magnetic actuated capsule robot can realize the accurate locomotion and posture adjustment inside non-structural ample environment such as human gastrointestinal tract,achieving high-efficiency,safe and noninvasive diagnosis for zones which are difficult to be checked.Capsule robot possesses a promising clinical application prospect,and it has become a research hotspot for domestic and foreign scholars in the recent years.Our research group has proposed a new control approach,which uses a spatial universal rotating magnetic vector generated by tri-axial Helmholtz coils to actuates the petal-shaped capsule robot to move,steer or adjust its posture inside diagnostic environments such as gastrointestinal tract.In order to improve the accuracy of steering magnetic navigation and the stability of manipulation,this paper has done some research on the self-centering characteristics of the capsule robot,while theoretically and experimentally investigated the transient error problems and transient error suppression methods concerned with the spatial universal rotating magnetic vector.Firstly,based on the orthogonal transformation operation and superposition theorem of the spatial universal rotating magnetic vector,the causes of the transient errors including transient orientation error and transient magnitude error have been analyzed,it has been concluded that when the current control parameters are changed abruptly,the current transient phenomena would occur in the circuit system,causing the complete transient response in the spatial uniform magnetic field and generating new transient decaying magnetic components.Thus,it would reduce the control accuracy and the motion stability of the capsule robot.Then,the magnetic field complete response models has been derived respectively when the orientation angle of the magnetic vector is change abruptly and the current amplitude is changed abruptly.The end track of the actual rotating magnetic vector has been analyzed based on the the coordinate rotation transformation and the differential geometry,by which it has been found that the end track of the actual magnetic vector is a spatial spiral line when the orientation angle is changed abruptly,and it is a planar spiral line lying in the rotating plane when the current amplitude is changed abruptly.Based on these analyses,the transient orientation error model and the initial transient relative magnitude error model of the actual rotating magnetic vector have been established respectively.In the case when the orientation angle is changed abruptly,two approaches including graphical method and analytical method have been proposed to figure out the optimal switching moment,and a comprehensive double transient error suppression method based on selecting this optimal moment has been proposed;in the case when the current amplitude is changed abruptly,a comprehensive double transient error suppression method based on reducing the amplitude of current amplitude change has also been proposed.Finally,two experiments has been conducted to testify the validity of these two kinds of proposed comprehensive double transient error suppression methods,the results proves that these two error suppression methods can suppress the transient magnitude error to some extent while eliminating the transient orientation error radically,thus effectively improving the control accuracy and motion stability of the capsule robot when it is moving,steering or adjusting its posture in curving environments such as human gastrointestinal track,and it lays a solid foundation for achieving noninvasive diagnosis and high-efficiency control of the petal-shaped capsule robot.