Design Of Capsule Robot Drive System Based On Rectangular Helmholtz Coils

One of the features of modern medical surgical operation is minimally invasive treatment.Although the existing surgical navigation system development has been relatively mature in all aspects,the problems encountered by surgeons during the actual operation are not well solved.Wireless capsule endoscope is a miniature medical instrument for inspection of gastrointestinal tract non-invasively.Wireless capsule endoscopy is a new technique that allows complete exploration of the small bowel without external wires.Its role has been analyzed in many small bowel diseases such as obscure gastrointestinal bleeding and gastrointestinal polyposis syndromes with promising results.This paper surveys the actuation and localization method of the wireless capsule endoscopy in terms of frontier research and prototypes in labs worldwide.Challenges facing us in designing and manufacturing active wireless capsule endoscopes are outlined,together with potential methods to tackle them.Magnetically manipulated untethered magnetic robot shows great potential to control inspection and surgical tools working effectively inside the gastrointestinal tract.To enable the effective manipulation of the micro-robot in the confined and complex environment,real-time position and orientation information of the robot must be obtained as an important sensory feedback.Usually,a magnetic tracking method is used to provide the pose information.However,due to the magnetic disturbance from the external actuation field,a traditional magnetic tracking method cannot work simultaneously with the magnetic manipulation system.In this abstract,a real-time wireless tracking and actuation strategy for magnetic robot is proposed to realize a closed-loop control of the magnetically manipulated untethered robot.The proposed approach is shown in Fig.1.Four rectangular coils are used to generate a rotating external magnetic field to control the movement of the magnet,which is inside the pipe.The magnet is then rolling to move under the external magnetic field with the help of friction force.A magnetic sensor array is placed under the pipe to track the magnet in real-time.The reason to use rectangular coils instead of Helmholtz coils is to enlarge the working space of the tracking system.The magneti c field model of the proposed coils can be derived based on Biot-Savart Law.With the propose coil setup and the derived magnetic field model,we can generate the desired magnetic field and the gradient field by using optimization method.Therefore,a more flexible control strategy can be achieved.To overcome the disadvantage of magnetic disturbance between the actuation system and the tracking system,we proposed a superposition principle based simultaneous tracking and actuation method.The magnetic field value that measured from the magnetic sensor array is the sum of the field from the magnet and the magnetic coils.Therefore,during each magnetic positioning,we first measure the current that fed to each coil,and then calculate the magnetic field distribution of the magnetic actuation system coils.The field from the coils is then subtracted from the sensing filed from the sensors.As a result,the field from the magnet is obtained and the position and orientation of the robot can then be estimated using an optimization algorithm.With the help of the real-time positioning result,accurate feedback control of the magnetic robot can be achieved.