Design and Analysis of a Bimanual Multifunctional Robot for NOTES1

摘要

Natural orifice transluminal endoscopic surgery (NOTES) has gained attention for its potential benefits, including short recovery time, no skin incision, and lower anesthesia requirement [1]. However, constrained by limited workspace, visual triangulation, lack of dexterous tools, and tool-changing, its clinical application and development are inhibited [2]. Current research [3] pursues dual articulated instruments to increase the available tool dexterity. However, to the best of our knowledge, none of the existing solutions addresses the issue of multitasking and tool-changing functionality.We have designed a bimanual NOTES robot with tool-changing capability. It is driven by a snakelike mechanism to traverse a natural orifice [4]. This paper presents the structure of the bimanual robot and analysis of its kinematics and force transmission. Preliminary tests demonstrate its functionality and capability.As shown in Fig. 1, the system consists of two arms with multiple-instrument end effectors and a snakelike drive mechanism actuated by four motors via cables. The details of the snakelike drive mechanism and the robot reconfiguration operation sequence have been presented in Ref. [4]. This paper describes the structure of the bimanual arm and the multifunctional manipulator. Workspace is analyzed to check the robotic functionality and dexterity, and the force transmission is analyzed to demonstrate its capability. Two experiments are done to verify the basic robotic functionality and capability.As shown in Fig. 2, the multifunctional manipulator consists of a tool tip container containing up to three different tool tips: a lead screw transmission and two motors for actuation. One motor rotates the tool container for tool-changing and instrument locking, and another motor actuates the lead screw transmission for instrument advancing and operation. This actuation method is inherited from our previous prototype [5]. In the new prototype, a “wrist roll” degree-of-freedom (DOF) actuated by a brushed DC motor is added to enhance the dexterity; nevertheless, the size of the manipulator is smaller than that of the previous prototype due to appropriate motor selection and well-arranged placement of the components. A keyway is created between the tool tips and the tool container, and a weak hook-and-loop fastener is attached at the bottom of the container. This guarantees the tool tips to be advanced accurately during tool-changing and keeps the tool tips stable after tool-changing (so that they do not slide freely when not engaged on the lead screw).As can be seen in Fig. 3, the robot has a bimanual structure. Each arm has 3DOFs to provide full dexterity. The right arm has a multifunctional manipulator with a rolling DOF. The left arm, usually applied for retraction, has a fixed grasper manipulator. In the middle of the shoulder, there is a docking port which is used to connect the robot with the snakelike mechanism. These components are kept at or below 24 mm in diameter. In the shoulder, a Faulhaber 1024 brushed DC motor with a 1024:1 ratio gearhead is installed for each arm. On each elbow, a Faulhaber 1512 brushed DC motor with a 324:1 ratio gearhead is installed. To increase the elbow torque, a second 81:16 gear stage is added. The robot is wrapped with plastic film (biaxially oriented polypropylene) to keep it free of bodily fluids during operation.The Denavit–Hartenberg (DH) convention [6] is used to obtain the kinematic transforms and hence the workspace. As the two arms have the same structure, we will focus on analyzing only the right arm. The global origin is set in the middle of the shoulder link, and the subsequent reference frames are shown in Fig. 4. Table 1 summarizes the DH parameters, including the joint variables θ1,2,3.With −45 deg ≤ θ1 ≤ 45 deg, 0 ≤ θ2 ≤ 90 deg, 0 ≤ θ3 ≤ 120 deg, l1 = 54 mm, l2 = 56 mm, and l3 = 108 mm, we can get a shell-like workspace with about 30 mm average thickness, as shown in Fig. 5. The work