Research On Driving Performance Of Petal-shaped Capsule Robot When Swimming Off-center In Pipe

Capsule robots are new means of diagnosing of human gastrointestinal disease.With themushroom growth of computer and sensor technology,capsule robots have been further researched and developed to achieve active control and safe driving,which can improve diagnosis accuracy and reduce operative risk.Clinical application of capsule robot is of great value to modern medical industry.The environment of human gastrointestinal tract is curved and complex,capsule robots will swim in the bottom of pipe under gravity and damage the tract.For increasing the trafficability and guarantee the safety of driving in complex environment,in this paper,a petal-shaped capsule robot with self-centering ability in pipe filled with viscous fluid is proposed.This new profile robot can achieve suspension swimming at a certain distance deviated from the center of pipe after start-up.Then the off-center swimming performance of petal-shaped capsule robot is analysed.First,structure feature of the petal-shaped capsule robot is introduced.the robot consists of four eccentric tiles covered with spiral ribs.Convergent wedge-like gaps form between the surface of the tiles and the inner wall of the pipe,which generates multiple wedge effects and increases the hydrodynamic pressure.Magnetic driven mechanism is summarized,which drives the robot to move along any desired direction by the space universal rotating magnetic field to adapt to complex environment of human gastrointestinal tract.Then,the driving performance of petal-shaped capsule is analysed from two aspects:start-up characteristic and stable swimming performance.A fluid film thickness model and a fluid dynamics pressure model are established when the robot swims off-center inside the pipe fully filled with viscous fluid under gravity.Then a suspended dynamical equation in vertical direction is derived.The research and experiment has shown that petal-shaped capsule robot possesses self-centering characteristic,suspends rapidly after start-up and swims at a certain distance off-center in pipe.This robot has achieved non-contact driving and improved the trafficability in complex environment owing to the start-up characteristic.Regarding theory of Couette flow and Newton inner friction law as theoretical basis,axial and circumferential force balance equation of the robot swimming off-center in pipe are established.The stable swimming velocity and the liquid torque are considered as the indexesto evaluate stable swimming performance.Research shows that petal-shaped capsule robot has good stable swimming performance: faster stable swimming velocity and lower liquid torque.The analysis of the influence on driving performance is conducted with respect to eccentricity of the petal shape,driving frequency,fluid viscosity and so on,aiming to use reasonable parameters to improve the diagnostic efficiency,weaken the distorting effect on gastrointestinal tract and reduce the power consumption of generating magnetic field,which can ensure the safety of driving.Finally,four profile capsule robots with different eccentricity are manufactured,and the correctness of theoretical model has been verified by the experiment of driving different robot in transparent pipe filled with silicone oil.In addition,the experiments in vitro pig intestines were carried out to demonstrate the driving feasibility of petal-shaped capsule robot in unstructured environment,which lays foundation for driving and clinical application of complex gastrointestinal environment.