Study Of Control Algorithm Of Shape Memory Alloy Based Free Inflatable Rectal Expansion Device

Transanal endoscopic microsurgery (TEM) is a minimal invasive surgical technique which incorporates a device to access the rectum and allows the surgeon to operate on problems in rectum through anus without having to make an incision through the abdomen. In the original design of TEM, the rectum is expanded using CO₂ insufflation to expose the lesion. However, the use of CO₂ insufflation for rectum expansion to expose the lesion with high operation requirement might bring the potential risks of contamination of the peritoneal cavity. The main problems of TEM system are associated with CO₂ insufflation. So the implementation of rectum expansion at atmospheric pressure has become a research hotspot and several expansion methods using the no CO₂ insufflation have been reported by various research groups. These new designs only allow small expansion of the rectum and involve the manual control which might not be very sensitive and could bring the potential risk of perforating the rectal wall. Ni-Ti shape memory alloy (SMA) is not only in the nature of unique memory effect and super elasticity, but also owns excellent mechanical properties, corrosion resistance and biocompatibility. So Ni-Ti SMA with high flexibility and controllability has become the most promising construction material for smart actuators in diverse applications, and it is widely used in the fields including medical, aeronautics and astronautics, machinery and electronics, especially in development of new medical device. But Ni-Ti SMA exhibits nonlinear hysteresis characteristics, and these characteristics can influence control accuracy and cause system instability. Therefore, to achieve the precise control of shape memory alloy is the most important factor to apply it to expansion device for transanal endoscopic microsurgery.In order to eliminate the effects of hysteresis behavior, the usual method is to establish the mathematical model and to construct the corresponding inverse model to realize hysteresis compensation. The most common used model is Preisach hysteresis model and its modified model. Aiming at the problems of expansion method and SMA hysteresis behavior, a pilot SMA-based expansion device for transanal endoscopic microsurgery is designed. In order to perform the lesion exposing safely, reliably, and fully, the optimal expansion is realized using automatic control algorithm, and an improved KP hysteresis model is proposed which use the modified KP operator, and its corresponding inverse model is applied to adaptive hysteresis control. The control scheme is established after studying of SMA hysteresis behavior. The two main components of are hardware unit and control algorithm unit, and the control algorithm is the core of the system. The control algorithm is implemented using Matlab/Simulink. The model and its corresponding inverse model are programmed as several functions in the computer language C, and then transferred to the S-functions compatible by the use of its S-Function Builder. All the S-functions are connected to the hardware using Real-Time Windows Target mode in the Simulink environment. The performance of hardware circuit which can meet the requirements of SMA heating well is tested on the preliminary experimental platform. The experiments not only demonstrate the drive system and control method can work in controlling the expansion device robustly and accurately, but also verify the feasibility and validity of the scheme applying shape memory alloy in expansion device for transanal endoscopic microsurgery.This proposed control scheme is established based on summarizing the achievement and the shortage of the former control scheme techniques. It can be a universal scheme to be applied to other SMA-based study. The modified hysteresis model and the proposed control scheme can be considered important improvements in SMA control field which have great theoretical significance and application significance.