| Wireless capsule endoscope (WCE) has shown its great advantages in detecting diseases of gastrointestinal tract, especially for small intestine. But traditional WCEs move passively by peristalsis and gravity in gastrointestinal tract. Active control of WCE can decrease the omission factor and improve the detection efficiency, in addition, it can realize biopsy, drug delivery, and minimally invasive surgery in the future clinical application. Electrical stimulation, biomimetic robot, and magnetic control are the current main active control methods for use in WCE. Magnetic control method has been widely studied due to its no need of energy and wireless control, etc. In this thesis, we propose rotating an external permanent magnet to drive the synchronous rotation of magnetic spiral-type WCE, taking into consideration the advantages of current magnetic drive method and Helmholtz coils method. Compared with current magnetic control methods, this method can overcome the problems existing in the current methods, such as complex equipments, small control region, and great damage to intestinal tract. An active control system based on rotational permanent magnet has been developed.The principle of active control of WCE and the several current active control methods are analyzed, such as electrical stimulation, biomimetic robot, and magnetic control. The advantages and disadvantages of them are compared with each other. The magnetic drive method and Helmholtz coils method are discussed deeply, and the method rotational permanent magnet controls the magnetic spiral-type WCE, is proposed based on the two methods. The principle of actively controlling magnetic spiral-type WCE by rotational permanent magnet is analyzed. The model of the suspension "synchronous" rotation control between rotational permanent magnet and magnetic spiral-type WCE is analyzed, so are the calculation method, calculation process and boundary conditions of the permanent magnet field of this method. The detailed control scheme of this method is introduced. Control distance and estimation method of the friction torque from gut of this method are analyzed, respectively.The static magnetic simulations, concerning this active control method in Ansoft Maxwell, are analyzed. The simulations are mainly focused on the magnetic force and torque between external permanent magnet (square shape and cylindrical shape) and the magnetic shell on the surface of magnetic spiral-type WCE. The minimum and maximum control distances of this active control method can be calculated by the simulation results. The setups of the static magnetic simulations, including model establishment, material distribution, meshing, load apply, post-processing and parameter sweep, is described in detail. The simulation results of magnetic force and torque are obtained by which the minimum and maximum control distances of the active control method are analyzed.The design and fabrication of the active control system based on rotational permanent magnet are described in detail, the fabricated equipments mainly consist of handheld permanent magnet control actuator, adjustable bracket, and magnetic spiral-type WCE.Active control experiments on magnetic spiral-type WCE have been carried out in ex-vivo pocine small intestine by utilizing the active control system based on rotational permanent magnet. To verity the different control performances to magnetic spiral-type WCE provided by the permanent magnet control actuator, different cases have been studied and they are the case of with or without bracket, different shape and different magnetism of external permanent magnets, different intestinal fillers, and different spiral number, respectively. In the experiments, the corresponding minimum and maximum control distances were measured, so was the velocity of magnetic spiral-type WCE. Meanwhile, stability performance of magnetic spiral-type WCE was recorded during its motion. The friction torque of magnetic spiral-type WCE from intestinal wall was estimated by experimental results.It has been verified that this control method is feasible and effective by the experiments conducted in fresh ex-vivo pocine small intestine by utilizing the active control system based on rotational permanent magnet. Experimental results show that the active control system is easy to operate with good control performance. The maximum control velocity of this active control system can reach 27.17 mm/s. And the maximum control distance of this active control system can reach 253.3 mm which is comparable to the thickness of an adult's chest, in addition, it means that the system is of great potential to be used in future clinical application. The system is also fairly stable in control process. Compared with the traditional Helmholtz coil method, the method proposed here have greater advantages, for it has higher control velocity, broader control range, no electromagnetic radiation, lower limitation in control space, lower equipment cost, and simpler operation. |
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