Design and control of a laparoscopic surgery device

This thesis focuses on grasping mechanism in laparoscopic surgery where an excessive grasper force can lead to an unnecessary harm to tissue. The dynamics of grasping mechanism of a conventional laparoscopic grasper is investigated analytically and experimentally. Relative error values are obtained up to %13. In this design a Nickel-Titanium based shape memory alloy actuator is used. Shape memory alloys (SMAs) are alloys, which can remember their original shape. In this thesis, SMA wire that is provided from Dynalloy, is used. This actuator is composed of a shape memory alloy wire and a linear antogonistic spring. The actuator is integrated to laparoscopic tool, instead of the conventional tool's shaft. Unlike conventional laparoscopic tools which are generally based on lever mechanism or other mechanical simple machine mechanisms, SMA actuated devices reduces surgeon's hand fatigue and by achieving this, it improves surgeon's comfort during operation due to electrical actuation system compared to manual mechanical actuation. Considering the small incisions up to 15 mm, the tool's shaft diameter must be no larger than 15 mm. Actuation mechanism is based on SMA wire which must be no longer than 300 mm. The tool's handle must be ergonomic. Due to containing electrical parts, the tool must not shock the patient and the surgeon. Additionally, voltage and current level must be as minimum as possible in electronic parts. These will lead to a surgical tool with lower power usage and lower harm risk. The grasper force is controlled through the actuator by different controllers where structure of the controller effects are examined. Force control of shape memory alloy actuator allows a force limit. This means grasper force can be controlled with no harm on the tissue. This actuator is controlling the grasping force with a PID and a SMC controller. Closed-loop dynamics of the grasper mechanism is achieved with %3.34 overshoot and zero steady state error with SMC controller. Cooling procedure is applied to actuator where the response time of the actuator greatly improves, steady-state error goes to zero.