| Capsule robot can be widely used in modern biomedical engineering.The swallowable capsule robots capable of traveling actively inside the gastrointestinal(GI)tract will play important roles such as diagnosis,drug delivery,and even surgical operation,acquiring images by vision system or wireless transmission device and then transmitting them using wireless transmission equipment.So far,there exists problems with low hydrodynamic pressure,slow swimming speed,apparent distorted effect and poor active steering performance.For this situation,in order to improve aforementioned comprehensive driving performance of capsule robot,the hydromechanics,magnetic driving mechanics,steering dynamics and driving control strategy,etc.of the novel capsule robot is studied.The experimental verification is conducted.The main contents of the paper are listed as follows.Based on the physical feature of the human gastrointestinal tract,an innovative high performance petal-shaped capsule robot with high fluid dynamic pressure,fast swimming speed and low fluid resistance torsion moment is proposed,and a fluid resistance torsion moment-weaken effect is discovered.The capsule robot that utilized the effect is composed of four petal-shaped tiles,NdFeB permanent magnet as the inner actuator,anterior end cover,rear end cover and sleeve.The fluid resistance torsion moment-weaken effect has a good effect on fluid dynamic pressure and swimming speed,and could decrease fluid distorting effect on the GI tract,the developed fluid film isolates the robot from the GI tract and achieves full suspension of the robot,and the energy consumption is reduced.The comprehensive driving performance is significantly enhanced.An innovative method employing critical coupling magnetic moment of high performance petal-shaped capsule robot for indirectly detecting the fluid resistance torsion moment and slip angle computing is proposed,and the slip angle with respect to magnetic field frequency is derived.First,the swimming speed of the fluid outside the robot is analyzed,the model of fluid dynamic pressure is established and the fluid dynamic pressure distribution rule is derived.The pressure gradient,fluid dynamic pressure and the fluid resistance torsion moment of petal-shaped and cylindrical capsule robot are analyzed contrastively.Second,compensate the driving currents for achieving a uniform magnetic vector.Last,by gradually reducing the driving current and magnetic moment until the lost step phenomenon occurs.According to the equilibrium relationship between the coupling magnetic moment and fluid resistance torsion moment,online detection of the fluid resistance torsion moment and compute of the slip angle are realized.A magnetic navigation planning method of optimal orientation for universal magnetic spin vector is proposed.According to the geometric condition of the capsule robot in spatial curve environment,the relationship between commutation angle and spatial slip angle are obtained.For realizing fast and contact-free steering swimming,a multiple objective optimization method to optimize the steering driving angle is employed based on two evaluation indexes including the average steering speed and the average steering trajectory deviation first,achieving the initial optimal orientation of a universal magnetic spin vector.On this base,the model of the spatial magnetic moment of spatial universal rotating magnetic vector is established.The relationship among the steering spatial magnetic moment,commutation angle,plane slip angle and spatial slip angle is revealed.And then,a main target method for optimizing its final orientation,which is used for fine adjustment,is employed under the constrains of the magnetic moments to further reduce robotic magnetic vibration.Finally,the critical coupling magnetic moment and slip angle computing in curve environment is proposed,realizing the detecting for the fluid resistance torsion moment in spatial curve environment.The dynamic characteristic of viscoelastic intestine model is analyzed,the fluid film thickness equation of the deformation for the intestine is derived,and the model of fluid dynamic pressure in viscoelastic intestine is established.The steering dynamics model of robot within bend environment is built.First,the steering stability region of capsule robot is determined and the relationship between the steering stability and slip angle is derived.Under different nonlinear system parameters,the capsule robot is able to converge to stable focus or periodic oscillation.Second,the steering fluid moment model in enclosed fluid environment is established.The impact of slip angle on steering stability of the robot is analyzed,revealing the robot is in the motion of convergent spiral,which is a stable spiral swing motion.The high performance petal-shaped capsule robot experiment platform is built to testify the comprehensive driving performance.First,the pressure and fluid torsion moment are verified by experiment.Then,the critical coupling magnetic moment method is verified and the twist impact on the GI tract by the petal-shaped capsule robot is analyzed.After that,high definition camera is utilized to record the trajectory of the capsule robot to derive the motion state.The offset distance between the axis of the robot and the tangent line of the curved pipe before and after optimization is analyzed.Therefore,the magnetic navigation planning method for determining the orientation of universal magnetic spin vector is verified.The steering dynamics model is verified by the high definition camera to record the laser projection trajectory when the robot steering to detect the size of the envelope circle as the attitude angles vary with the parameters.Finally,the relationship among the fluid resistance torsion moment,clearances and magnetic field frequencies is analyzed and the full suspension swimming characteristic of the robot is verified.Through experiments and comparison with steering swimming in the acute angle pipe,right angle pipe and arc pipe,it is shown that the robot has good driving capability. |
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