Research On Guiding Device For Catheter Used In Invasive Surgery

In minimally invasive surgery, catheter was used to perform operation. However, conventional method of catheterization has many disadvantages, such as difficult guiding, steep demand for manipulative skill and injuring blood vessels. For a better catheterization, a kind of active catheter actuated by shape memory alloy (SMA) was developed in this paper.It composes of a bias spring in the center and three SMA actuators distributed. In order to achieve a large bending angle meanwhile not to increase the outer diameter too much, the catheter consists of several bending units. When the SMA actuator is heated by an electrical current above a certain transition temperature, it shrinks and bends the active catheter. The bending direction is determined by behaviors of two adjacent SMA actuators. Only depending on the bias spring, the active catheter can't resume to linear state, and time for resuming is too much. Therefore, it should bend in the reverse direction.Static structural characteristic of the active catheter was mainly based on hypothesis that deflection curve of the axis is circular arc. But method based on large deflection theory was proposed in this paper. Accordingly, output force and displacement of each SMA actuator under anticipative attitude was obtained as well as accurate coordinate of the center of the joint and deflection curve equation of the axis of the active catheter. Two methods were compared with the finite element method and experiment. It proved that method based on large deflection was reasonable and effective. It can provide initial parameters for the design of SMA actuator.Relation between temperature and output force displacement is determined by constitutive relation of SMA. Pulse current was used to control SMA actuator. Speed of heating, time of cooling and heat preservation was obtained. According to tendency that electric resistance of SMA varies with temperature, heating process was divided to four stages during which different duty cycle was used. Thus, a quick response can be obtained. SMA actuator becomes more operative in the transform temperature range and degradation caused by overheating can be avoided. Performance of SMA actuator was also tested, and active catheter was...