Design of modular in vivo robots for precision tasks in minimally invasive surgery

Natural Orifice Transluminal Endoscopic Surgery (NOTES) is the next step in Minimally Invasive Surgery (MIS) that aims to provide incision-less surgery performed through natural orifices. This application is driven by patients for its prospective surplus values, such as no visible scarring, less recovery time, and less physical discomfort, compared to traditional minimally invasive procedures. In this framework, flexible endoscopy is expanding its role from diagnostics and simple therapeutics, to advanced surgical techniques applicable to disease of the gastrointestinal tract and peritoneal structures. However, conventional tools provide limited tissue manipulation in NOTES, because of the constrained directionality of force application and actuation. Furthermore, endoscopes have a constrained field of the view that is difficult to position and properly orient for the surgical team. In a prospective complete intracavitary approach, the employment of an array of micro-robots whose tasks differ from unit to unit, is supposed to overcome present drawbacks in NOTES procedures. The modular in vivo robots designed and analised in this thesis could represent a significant progress in the development of the next generation minimally invasive surgical equipment. The conception of robotic units started from scratch and its development has been carried on with a single design with slight modifications for several robotic modules. These modules are 11 mm in diameter and of an average link lenght of about 35 mm. Essential robotic units are an image acquisition robot and a robot for precision manipulation tasks; thus, the first robot design consist of a single module, three-DOFs (roll pitch yaw) camera robot, and the second consists of a bimodular, seven-DOFs (roll pitch yaw roll pitch yaw tool) manipulator robot. Namiki BrushLess Direct Current (BLDC) micro motors are used because their dimensions, 4 mm of diameter, and output torque, 1.5 or 5.7 Nmm, meet the robots actuation specifications. Reduction ratios of Namiki motors are chosen according to the required mechanism range of forces; thus, 1:79 Namiki motors are considered for the camera robot, whose task is to rapidly move in its workspace, and 1:337 Namiki motors are considered for the manipulator robot, whose task is to interact with the environment and to develop a minimum force of 0.5 N at the end-effector. The camera robot end-effector can reach any orientation in the space. However, due to its limited three DOFs the end-effector position is dependant on its orientation, as it should be expected from a robot with less than 6 DOFs in a 3D framework. The manipulator robot end-effector has a much larger workspace; this is due both for its extended number of DOFs, and for its higher links length. It can reach any position and orientation in the 3D framework, being only limited by joints parameters range and links lenght. The Jacobian matrix is used to compute robots differential kinematics and statics. This analisys illustrates how high velocities are available at the end-effector of both robots, due to faster motors in the camera robot case, and to longer links in the manipulator robot case. Considering robots dimensions and subsequent actuators power, maximum forces at the end-effector are about 1 N; thus, designed robotic units have not to be considered as a generic surgical tool. Instead, they have to be considered as small force--high precision robotic instruments, to be used for tasks where repeatability and accuracy are more important than high forces. There are two major advantages that make our robots a prospective progress in the development of NOTES equipment. Firstly, our robotic modules have an extremely thin diameter: considering the 11 mm diameter, no other surgical robot as succeded in taking so many degrees of freedom completely inside the patient yet. Secondy, from the kinematic analisys, the employment of an array of in vivo robotic units overcome conventional tools drawbacks, both providing precise tissue manipulation in NOTES, because of the unconstrained directionality of force application and unconstrained field of the view