Miniature gripping device Filippo Morra, Rezia Molfino, Francesco Cepolina Dipartimento di Meccanica e Costruzione delle Macchine Via All’Opera Pia 15 A - 16145 Genova, Italy E-mail: filippomorra@fastwebnet.it, cepolina@dimec.unige.it Abstract Teleoperation is a relatively old practice; recently new fields of intervention are born where the slave arms need to have small dimensions and high dexterity; examples are pipes inspection, rescue missions, planets exploration, minimally invasive surgery. The object of the paper is to describe the design of a miniature gripper suitable for laparoscopic operations. First some possible solutions are analyzed and compared. Then the detail design of the preferred embodiment is described; a physical mock-up has been used to check the tool performance. Advantages and drawbacks of the system have been pointed out. Finally some possible system implementations are suggested. 1 Introduction Scientific communities, Universities and some of the most important research laboratories believe that medical robotics is a key field of research. Different applications exist: from eye surgery, to abdominal surgery, to prostheses and colonoscopies. Long since that robotic systems are used inside surgery rooms for minimally invasive robotic surgery (MIRS) operations. The task of the robot is not to replace the surgeon, but to support him with a set of instruments that simplify the procedures and to reduce the patient trauma. One of the main drawbacks of these instruments is their limited number of DoF. For this reason today new robots able to guarantee more dexterity and workspace are under study; the final goal is to provide to surgeons, during MIRS, the same movement freedom typical of classic “open” surgery. MIRS instruments, like grippers and scissors, need to be as compact as possible. The arm and the end effector actuation should be decoupled to simplify the control; to achieve this task, the actuator is positioned close to the instrument. As a further constraint, in case of grippers, the actuator should be able to exert the forces of several tens of Newtons. The scope of the article is to propose some innovative MIRS grippers. 2 Proposed solutions One of the most difficult operations, due to the lack of dexterity of conventional systems, is suturing with needle and wire; the arms with grippers have to mime the movements of the surgeon fingers. The main specifications for the proposed gripper are: 40 N grasping force, 10 mm external diameter, about 25 mm length, possibility to work in an humid environment, high reliability and body compatibility. We have chosen to reject the cable actuation, despite it is widely used in the surgical field, for two reasons; it is difficult to embed the cables inside a poli-articulated miniature arm. Besides the cable actuation, high grasping force, can affect the global rigidity of the arm [1] [2]. Three types of actuators have been considered: electric motors, hydraulic pistons and shape memory alloys (SMA). 2.1 Electric motors solution Initially it has been chosen to drive the gripper with classic electric mini-motors; the motors (fig. 1, part 1) are coupled with planetary reducers (fig. 1, part 2) to increase the torque. Conic gears (fig. 1, part 3) transfer the motion to the jaws (fig. 1, part 4). A detail view of the jaw is reported in the figure 1; the actuation of both the jaws has the same schema. The two conic gears, mounted on the shaft, are idle; while the shaft is fixed, the gears can rotate. Figure 1. Gripper actuated by electric motors I The jaws can be independently actuated; this embodiment, having two DoF, allows the jaws to close along the axis of the device or at any other angular position. A similar independent jaws closure can be found in the patent from Intuitive (patent WO0059384) [3]. This solution has been discarded because the motion is reversible; a force applied on the jaws can rotate the Morra Filippo, Molfino rezia, Francesco Cepolina, “Miniature gripping device”, in Proc. of IEEE International Conference on Intelligent Manipulation and Grasping IMG 04, Genova, Italy, 1-2 July 2004