Research On A Capsule Micro-Robot With Radial Clearance Self-Compensation Function

Minimally invasively interventional therapy accomplished by micro robot inside human body can reduce healing time and alleviate patients' sufferings, thus minimally invasive or noninvasive treatment is becoming a research hotspot both at home and abroad.This paper proposed a capsule micro robot with the function of self-compensation for radial clearance, by our discovery on the "critical gap" phenomenon with the spiral-type capsule micro robot inside pipe with liquid, aiming at enhancing its swimming capacity significantly and remedying the defect of the micro robot by automatic radial clearance compensation.Firstly, the structure of the micro-robot with function of self-compensation for radial clearance is designed. The technical precept is proposed in which the main body of the capsule micro robot is composed of four counterweight copper tiles with spiral blades connected to each radial synchronized extending mechanisms encapsulated with a rubber sleeve. The driving principle is that: as the effect of magnetism-machine coupling, the inner actuator rotates synchronously with the outer actuator which has the same magnetic poles structure as the inner one; as the micro-robot rotating, the spiral blades on the copper blocks generate fluid dynamic pressure, which pushes the micro robot to move; meanwhile, centrifugal force generated by the copper blocks push the rubber sleeve to expand radially, and the clearance between the surface of the micro-robot and the pipe wall reduces, the fluid dynamic pressure and the thrust increase.Based on Navier-Stokes equation and Reynolds equation, the mathematical model of the micro-robot swimming in fluid is established firstly. The process of the expansion of the micro-robot is analyzed, and the dynamic balance equation of the radial clearance compensation is established, further the motion equation of the micro-robot with function of self-compensation for radial clearance is established and the dynamic characteristics is computed and simulated. The motion equation of the micro-robot swimming in flexible and elastic pipe is established, and the characteristics of the micro-robot are computed and simulated, and the effect of the flexible and elastic wall is analyzed. The effects of the micro robot's parameters and the thickness of the rubber sleeve to the swimming speed of the micro robot are analyzed. Prototype of the micro-robot with radial clearance compensation is fabricated, experiments both in pmma pipe and pig intestine are conducted. Theoretical calculation and experiments show that the micro-robot with function of self-compensation for radial clearance can compensate the clearance between the micro-robot and pipe wall effectively, resulting in enhancement of motion efficiency.