Study On The Steering Robot For Catheters Used For Minimal Invasive Surgery

In recent years, minimal invasive surgery (MIS) is getting greater attention in vascular surgeries. The technique allows reducing patient pain and lower potential sequelae. Catheter is one of the MIS tools used in intravascular surgeries. Catheter is a long, narrow tube that is inserted from the groin to the heart or from the arm to the head via blood vessels depending on the surgeon's skill and experience. To operate intravascular surgical devices such as a catheter inside the blood vessels is very difficult because of the complexity and narrowness of blood vessels. In particular, physicians manually rotate, push and pull one end of the catheter outside the body. This kind of manual operations are not only somewhat crude, but also inefficient. Twists initiated outside the body yield much smaller movements at the wire's tip several feet away. Moreover, this difficulty causes not only an extension of operating time, but also the fatigue of operators and patients.In order to solve the disadvantages existed in vascular invasive surgery, we put forward to use a micro steering robot to lead the catheters in the vascular invasive surgery, and the related technology were developed. In this paper, around the structure and control system design of the steering robot, mechanics characteristic of the shape memory alloy (SMA) coil spring actuators, design calculation theory of the steering robot, kinematics of the steering robot for catheter, prototype development and simulated vascular invasive surgery, and other key techniques, a series of research were developed in depth, and a steering robot used for minimally invasive surgery was developed successfully.Firstly, structure and control system of the steering robot were designed. According to the characteristics of the minimally invasive vascular operation, the design goals of the steering robot were analyzed in detail. The structure project of the steering robot was designed. Then the resistance feedback control system of catheter steering robot based on PIC16F877 chip was developed, and the resistance feedback control program was developed with modular idea.Secondly, mechanical properties of the SMA spring actuator were discussed. The SMA phase transition constitutive relation applied to shear deformation was obtained through the amended Brinson static stretching phase transition constitutive model. Combined with the formula of the general spring theory, the formula of the SMA spring thermodynamic property was derived, further it was analyzed through the experiment and simulation. Finally, the dimension calculation formulas of the SMA helical spring were deduced.Thirdly, the design calculation theory of the steering robot for catheters was investigated. According to the current situation that there is not systemic design calculation method for the catheter steering robot, the calculation methods of dimension parameters of cylinder helical spring skeleton, the output force and the output displacement of the SMA actuator under the known bending angle of the catheter steering robot, and the axis curve shape of the one segment catheter steering robot were deduced. Ultimately, a set of systemic design calculation method for the catheter steering robot was established.Fourthly, kinematics of the steering robot was analyzed in consideration of the characteristics of the steering robot that has no clear joints and links. In this paper, the axis bending shape of one segment steering robot was investigated, and kinematics of the SMA actuators was analyzed. The D-H method was used to analyze the planar kinematics of one segment steering robot, and the spatial kinematics of one segment steering robot with a connective part was analyzed. According to the multi-segments characteristics, the whole steering robot's kinematics was analyzed. Utilize this kinematics model, we can obtain the kinematics of the catheter steering robot included any segments very easily.Finally, a prototype was developed and a series of invasive surgeries were simulated. By the design calculation method, a prototype of catheter steering robot was developed. A series of test change direction capability and the relationship between bending angle and PWM duty cycle were carried out. In the human chest vessels model, the simulant invasive surgeries through the aortic arch into the left vertebral artery and right common carotid artery were accomplished respectively in the direction of the steering robot.