Surgical Robotic Manipulator Based on Local Magnetic Actuation1

Abstract

Magnetic coupling is a strategy to transmit actuation forces across a physical barrier. This approach can be applied to remotely control and manipulate robotic instruments in minimally invasive surgery (MIS) [1]. Interrupting the mechanical continuity of such system by having surgical instruments and laparoscopic camera magnetically coupled across the abdominal wall greatly enhances both the workspace of operation and triangulation without the need for multiple abdominal incisions [2]. On the other hand, continuum robots are able to provide a large amount of mechanical power to accomplish surgical tasks [3]. Focusing on the typical surgical task of suturing a tissue, 1 N of force in any direction and 180 deg per second rotational speed must be achieved throughout a 50 × 50 × 50 mm3 workspace [3].In Ref. [4], the authors introduced the concept of local magnetic actuation (LMA), where mechanical power is transmitted across the patient abdomen by specific magnetic couplings to drive the degrees of freedom (DOF) of the robotic surgical instrument. This approach removes the need for electromagnetic motors on board and wired connections.The LMA-based surgical retractor presented in Ref. [5] combines two pairs of magnets, one providing anchoring and the other transferring motion to the internal mechanism actuating a single DOF. This study shows the feasibility for the LMA approach to transfer a relevant amount of mechanical power to produce forces of up to 5 N.Previous papers, such as Ref. [6], have proposed the use of cable-driven mechanism in surgical applications. Major advantages of cable-actuation are the light weight, small size, transmission of force to hard-to-reach location, and high bending radii.The design presented in this paper aims to develop a surgical manipulator for MIS able to perform surgical tasks combining mechanical power transmission based on LMA and cable-driven actuation of a novel design of spherical parallel wrist.This robotic manipulator features an LMA-actuated 4DOF cable-driven spherical wrist, which is schematically represented in Fig. 1(a) and referred to as multiDOF–LMA. The final prototype has a diameter less than 15 mm allowing it to enter from a standard 15-mm trocar for MIS. The multiDOF–LMA design has three actuation units (AcU) and an anchoring unit (AnU). Each AcU provides the mechanical power to actuate 1DOF of the wrist through a pair of antagonistic cable drive. The AnU provides for the gross positioning, support, and through its ability to translate, also provides the actuation of the tilt angle (θ1) DOF of the multiDOF–LMA.The AcU consists of a couple of diametrically magnetized magnets—the external driving magnet (EDM) and the internal driven magnet (IDM)—designed to transmit mechanical power from the external motor to the mechanism embedded inside each of the transmission modules (TM) 1–3. The gear transmission inside the TM amplifies the torque delivered by the IDM to the antagonistic-cables attachment. Each TM is equipped with a planetary gear train (1:16 gear ratio), a set of spur gears (1:14 gear ratio), and a cable reel (2.5 mm radius). The two antagonistic-cables lines are connected with the reel and rolled-up by lengths S1, S2, and S3, respectively, for each actuated DOF of the spherical wrist. Each TM is magnetically anchored against the abdominal wall by magnetic coupling with the correspondent EDM; also, each TM is connected to the manipulator’s link 1 through flexible pipes hosting the pair of antagonistic cables.The AnU consists of a pair of axial magnetized permanent magnets. The external anchoring magnets (EAMs) are connected to each other by motorized linear slide. The EAMs are magnetically coupled with the internal anchoring magnets generating the forces to support the multiDOF–LMA during operation by offering two points of contact with the abdominal wall. For a typical abdominal surgery procedure, we considered a toroidal workspace with a height of 30 mm and a diameter o