06710147

IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 19, NO. 6, DECEMBER 2014 1821

Array of Robots Augmenting the Kinematicsof Endocavitary Surgery

Giuseppe Tortora, Member, IEEE, Paolo Dario, Fellow, IEEE, and Arianna Menciassi, Member, IEEE

Abstract—Minimally invasive surgery (MIS) has been intro-duced in the last decades with the goal of making scarless surgeryfeasible. In general, an MIS approach allows concrete benefits interms of reduced trauma, quicker recovery times, and improvedcosmetics. On the other hand, in its current state, MIS introducesmore difficulties for surgeons, due to its intrinsic complexity. Thisissue has inspired the major technological challenge of designingminiaturized robots able to completely enter the body and to per-form surgical procedures under intuitive teleoperation. The dreamof achieving a completely minimally invasive therapeutic proce-dure, while offering the typical advantages of traditional opensurgery, has brought to the complete elimination of external in-cisions by gaining access to the peritoneal cavity through a naturalorifice. These scarless procedures are known as Natural OrificeTransluminal Endoscopic Surgery (NOTES) interventions. In thispaper, novel approaches to NOTES instruments and platforms arepresented, in which modular robots measuring 12 mm in diam-eter with basic functionalities (manipulation, cutting, vision, andretraction) and multiple degrees of freedom are deployed inside ahuman phantom and anchored on a supporting frame for the stableexecution of tasks. This paper illustrates the general concept, noveldesign guidelines for the modular robots, and two robotic unitssuccessfully assembled and tested with ten users, in order to assessthe capabilities of the system in pick and place experiments andcutting tasks. Experiments for the assessing force and accuracy aredescribed as well.

Index Terms—Endocavitary surgery, modular robot, NaturalOrifice Transluminal Endoscopic Surgery (NOTES).

I. INTRODUCTION

S INCE their introduction in medical practice, robotic sys-tems have been continuously improved, with the final aim

of allowing noninvasive surgical procedures and improving ben-efits for patients, in terms of lower number and size of incisions,less complications, and shorter recovery time. The increasingrequest to reduce the invasiveness of surgical procedures is fol-lowed by the technological challenge of giving the surgeon ad-vanced capabilities in terms of dexterity, applied forces, andview of the surgical scenario with respect to traditional laparo-scopic surgery. The first generation of existing medical robots,

Manuscript received July 1, 2013; revised October 10, 2013 and Decem-ber 20, 2013; accepted December 20, 2013. Date of publication January 13,2014; date of current version June 13, 2014. Recommended by Technical EditorF. Carpi. This work was supported by the ARAKNES FP7 European Project224565 (http://www.araknes.org).

The authors are with the BioRobotics Institute, Scuola SuperioreSant’Anna, 56127 Pisa, Italy (e-mail: [email protected]; [email protected];[email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TMECH.2013.2296531

where the da Vinci Surgical System (Intuitive Surgical, Sun-nyvale, CA, USA) is the most common example [1], aims toprovide a robotic substitute for holding traditional laparoscopictools inside the patient through standard trocars. The surgeoncan control the robotic arms from a dedicated console by lookingat a 3-D video streaming of the operative site. The da Vinci sys-tem is an advanced, commercially successful telerobotic systemfor minimally invasive surgery (MIS) and is nowadays installedworldwide. On the other hand, the da Vinci robot still requiresthe same number of incisions as in traditional laparoscopy, thusresulting in a similar level of invasiveness. Other surgical sys-tems exploiting the same telerobotic concept have been devel-oped worldwide, such as more compact and versatile systemsfor robotic laparoscopy [2], [3].

A further step from a medical viewpoint has been takenwith the introduction of new surgical approaches: single-portlaparoscopy (SPL) and single-incision laparoscopic surgery(SILS), based upon which multiple tools can be inserted througha single incision generally made at the umbilicus. SPL andSILS have inspired new solutions, such as an articulated roboticarm for bimanual interventions based on internal motors [4], arobotic system for SPL from Intuitive Surgical [5], or snake-likerobotic systems for single-port entry [6], [7].

Although these solutions are attracting increasing interest to-ward MIS and robotics potential [8], an important breakthroughin medical perspective is represented by the introduction of Nat-ural Orifice Transluminal Endoscopic Surgery (NOTES) whichaims to conduct surgery by entering narrow body natural ac-cesses with long and slender tools. Several modified endoscopeshave been studied for NOTES [9]–[12]. Since the operation dis-tal point might be quite far from the proximal insertion point,stability at the end-effector level can be a problem [13]. Onthe other hand, continuum robots take advantage of a highlyredundant kinematic structure for accomplishing surgical tasksremotely from the insertion point [14]–[16].

Another approach to NOTES relies on delivering all therobotic modules inside the abdomen for accomplishing specificsurgical tasks [17]–[20]. A modular approach has been pro-posed as well [21] in which small-scaled robotic modules areingested and assembled to form an articulated structure in thestomach. Despite their functionalities, they still lack robustnessand stability in the working environment, and they are generallyaffected by low dexterity and limited functionalities of the sin-gle robotic tool, which usually cannot be interchanged duringthe surgical procedure.

In order to overcome these limitations, we propose a modularmagnetic platform for NOTES procedures composed of severaldedicated robotic tools with the possibility of being docked and

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1822 IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 19, NO. 6, DECEMBER 2014

Fig. 1. Schematic representation of the array of robots within the abdominalcavity.

docked from an anchoring frame when needed. This paper stemsfrom the idea to transfer the abilities of bimanual laparoscopicsurgery to the endocavitary surgical approach, in order to reduceoperative trauma and enhance the therapeutic outcome of certainMIS procedures. An array of robotic multi-degrees-of-freedom(DOF), able to perform basic tasks in endocavitary procedures,is presented. The general approach of the array of robots de-signed to perform NOTES procedures is shown in Fig. 1, inwhich the platform is introduced from the mouth, then along theesophagus, and finally it crosses the stomach wall thus reachingthe abdominal cavity. The design concept of the novel roboticunits used for manipulation and cutting, performance analysis,and final experiments are described to assess the capability ofthe proposed NOTES platform.

II. MATERIAL AND METHODS

A. Medical Rationale

The role of modern medical practice is moving closer andcloser to the concept of prevention, with a view to fighting dis-eases at their early stage and enabling a truly minimally invasivesurgical approach, when needed. Early diagnoses allow diseasesto be treated therapeutically and surgically with lower risk andhigher chances of success. The concept we propose is based onmodular robotic units that aim to provide current NOTES withsmaller and less complicated devices capable of performing ba-sic surgical tasks where low forces and small workspace arerequired. Larger operative areas may thus be addressed since itis possible to reposition the platform intraoperatively (see theexternal handles in Fig. 1).

From a medical viewpoint, the following aspects were con-sidered during the system design:

1) Size constraints are essential for NOTES robotic modules.The robotic modules should be as small and compact aspossible. The maximum allowed diameter and rigid lengthof the platform components are limited by the fact thatthey are inserted through the esophagus and due to theirencumbrance in the abdominal cavity. The esophageal ac-cess port we considered in this paper is a 17-mm internaldiameter overtube (Guardus, US endoscopy, Mentor, OH,USA).

2) A natural access, such as the mouth, should be accessedby all the platform components. Since there are manylimitations as to the application of wireless devices insurgery, and due to safety reasons also, only thin wiresfor powering, imaging, and functional needs should beleft back in the access port. After insertion, each moduleshould be able to be fixed in a convenient position andchanged as needed during the surgical procedure. This willallow additional assistive tools (i.e., a flexible endoscopeas shown in Fig. 1) to be inserted when needed;

3) The delivery of many tools inside the human body, ratherthan a single one, allows surgeons to have the right toolthey need during the surgical procedure. Tool interchange-ability during the procedure is essential.

4) The platform components should be able to perform atleast basic tasks, such as vision, manipulation, and cutting.

In laparoscopic procedures, typical applied forces are in therange of 5–10 N and typical speeds reach 360◦/s [22]. Forcesand speeds in these ranges are difficult to be matched by minia-ture devices, but design flexibility in terms of intraoperativerepositioning of the platform thanks to magnetic anchoring candramatically assist in surgical tasks. In addition, high forces(e.g., for pure retraction tasks) can be generated as well by themagnetic coupling itself or by the assistive endoscope ratherthan by the single miniature robots. On the other hand, therobotic units can still perform other useful and basic tasks, suchas inserting a probe in a soft tissue which requires about only0.45 N [23].

B. System Overview

Following the aforementioned medical guidelines, the plat-form we propose is based on modular robotic units that can beinserted through an esophageal access port and assembled ona dedicated anchoring frame by using an assistive endoscope.The robotic units which are considered essential during a typicalsurgical procedure are the following: a manipulator, an electro-cutter, a tissue retraction device, and a camera.

The full insertion procedure and positioning of the endocav-itary platform consist of the following four steps.

1) Insertion of the Access Port: The insertion of the accessport prepares the insertion of the platform components into theabdominal cavity. This is a standard procedure for NOTES, andit is essential to prevent damage to the esophageal walls due tothe introduction of the robotic modules.

2) Insertion and Positioning of an Anchoring Frame: Theanchoring frame is a three-segments supporting frame that isused during the procedure to provide stability to the roboticunits. The frame is inserted in a straight configuration and thenit recovers its original triangular shape thanks to shape memoryalloys springs placed between the frame segments, as describedin [24]. The anchoring frame can be moved intraoperatively,thus allowing the platform to rely on an enhanced workspace.

3) Insertion and Deployment of the Robotic Units: Therobotic units are inserted through the port. This makes it possibleto insert as many robotic units as needed by the specific surgicalprocedure (i.e., different graspers, loops, electro-cutters, etc.).

TORTORA et al.: ARRAY OF ROBOTS AUGMENTING THE KINEMATICS OF ENDOCAVITARY SURGERY 1823

Fig. 2. Schematics of consecutive phases of the platform insertion through theesophageal access port; the encumbrances of the modules is represented.

An assistive endoscope is used to dock the modules to the spe-cific docking site on the anchoring frame.

4) Activation of the System: Once the system is positioned,the surgeon can remotely perform basic procedures by actingon the robot controllers.

III. ARRAY OF ROBOTS

The concept of an “array of robots” was carried on by keepingin mind a single common design (with slight modifications)aimed at developing different robotic units for the performanceof dedicated tasks in NOTES. The first proposed design wasused for a camera robot, as described in [25]. In this paper,additional robotic units, such as retraction, manipulator, andelectro-cutting robots, were developed starting from a similarconcept of basic module.

In Section III-A, details on the design of the basic moduleas a unit for assembling the electro-cutter robot (see SectionIII-B) are given, slight variations needed for the realization ofthe manipulator robot are described in Section III-C. For thesake of clarity and in order to give an overview of the wholearray of robots integrated together, a description of previouslydeveloped robotic units (i.e., the camera and retraction robots)is given in Sections III-D and III-E.

A. Basic Module

The final aim is to provide small and simple robotic toolsto be used in NOTES, depending on the specific tasks to beperformed, as in traditional surgery. One of the limits of currentrobotics for NOTES is that it is impossible to easily change thedesired tool. For this purpose, the array of robots was designedby keeping in mind the modularity approach and the possibilityof easily assembling new tools depending on the specific surgicalneeds. The surgeon can select the desired robotic tools duringthe preoperative phase; basic and advanced robotic units willbe assembled and prepared by medical assistants to be usedintraoperatively.

Based on these requirements, a cylindrical basic module wasdesigned with 2-DOFs and with the possibility of assemblingmore modules/tools together. Based on medical guidelines, thebasic module diameter is 12 mm, which is compatible with inser-tion in the access port partially taken from the anchoring framepowering, and allows use of a flexible endoscope through theaccess port [26]. Fig. 2 shows the consecutive phases of platform

Fig. 3. Top: detail of the pitch and roll mechanisms of the basic module with2 DOFs; bottom: manufactured module.

insertion with a clear representation of the encumbrances of allthe platform components, that set the mechanical constraintsfor the overall design. At the beginning of the procedure, theesophageal access port is inserted (I). After the insertion of theanchoring frame (II), that takes almost completely the sectionof the access port, only communication and powering wires re-main to take a small area of the access port (III). The insertionof the robotic units is always possible (IV). Afterward, the flex-ible endoscope can be used as assistive tool in order to positionand dock the robotic modules for a complete deployment of theplatform (V).

The overall length of the module in Fig. 2 is 42.5 mm for atotal weight of 8 g including motors (4-mm diameter brushlessmotors by Namiki Jewels, Tokyo, Japan) and electronics. Themanufacturing processes involved a microcomputer-numerical-control machine Kern Hspc, a Sarix Micro Sink EDM, anda Sodick AP 200 L wire electrical discharge machine. Analuminum alloy was used as the manufacturing material. Thebasic module was designed including an internal channel to en-able powering when active tools (e.g., electro-cutters and activegraspers) are used as end-effectors. The two sides of the basicmodule were kept free for embedding the electronics, while thelink embeds two rotational motors and respective mechanisms.Each module includes a pitch and roll DOF. The basic moduleand the embedded mechanisms for pitch and roll, together withthe manufactured prototype before the final assembly, are shownin Fig. 3.

The position of the motors strongly influences the mechan-ical design. Moreover, a 2-mm central channel is left free forthe inclusion of additional functional elements, such as wiresor cables for different tools. The design of the mechanisms forthe pitch DOF consists of a worm meshed with a helical gear,resulting in a 0.028 transmission ratio (i.e., the output speeddivided by the input speed). This mechanism is used to trans-mit motion between the axis of the motor and the orthogonalpitch joint axis. Due to the high reduction ratio, the systemis nonbackdrivable. This can be considered an advantage, be-cause the force can be maintained without providing energyduring static procedures (e.g., for keeping a tissue steady in a de-sired position). Safety is guaranteed by the module dimensions:in any possible pitch rotation, the maximum diameter of the


Fig. 4. Assembling of two basic modules (left) and prototype of poweringconnection between modules (right).

projection of the single module on the transversal plane of therobot (plane XY as in Fig. 5) is less than 16 mm, thus allowing asafe extraction in case of failure after disassembling the roboticunit in single modules with the aid of the flexible endoscope.The rotational joint is located on the opposite end of the mod-ule. This involves two spur gears as a reduction stage, and arotating output shaft supported by a ball bearing. In particular,the spur gear is manufactured preserving the aforementionedcentral channel. The transmission ratio of this mechanism is0.43. Regarding the range of motion, the maximum bending forthe pitch is ±180◦, essential to preserve the widest workspacepossible; the roll can rotate indefinitely in both directions, sincethere are no physical constraints between the modules.

Thanks to the cylindrical shape of the basic module and thecoupling between mating ends, connection between modules ortools is easy, thus allowing the assembly of different miniaturerobots by simply attaching two modules, as shown in Fig. 4(Left), as detailed in Section IV. It is worth noting that eachmodule is functionally self-consistent and integrated with actu-ators, mechanisms, and electronics.

A commercial six-axis load cell (Nano17, ATI, IndustrialAutomation, Apex, NC, USA) having a resolution of 3.18 mNhas been used for characterizing the basic module mechanisms,including the motor, in terms of an output torque. The maximummeasured output torques considering mechanism efficiencieswere 51.2 N·mm for the worm/helical gear and 10.15 N·mm forthe spur gears, from which the tip forces of the robots, relyingon the same mechanisms, are derived.

B. Electro-Cutter Robot

The electro-cutter robot is obtained by assembling two basicmodules and integrating a commercial tip as a tool.

The design of the basic module results in a roll as last DOF ofthe kinematic chain for the electro-cutter robot, as representedin Fig. 5.

Although this DOF is not used in this specific case, becauseof the needle-shaped tip of the electro-cutter (i.e., there is noneed to change the orientation of the axis), it will be very usefulwhen a grasper will be integrated on the robot tip for performingsuturing tasks. The overall dimensions of the electro-cutter robotare 12 mm in diameter and 85 mm in length. Thanks to theperformance of the basic module, these robotic units can achievea wide range of motion. J1 and J3 sweep ±180◦ while J2 and J4

Fig. 5. Arrangement of the DOFs and joints in the electro-cutter robot.

Fig. 6. Assembled electro-cutter robot with an integrated control board; in theinset, a detail of the distal module.

do not have limits in rotation. The assembled robot is shown inFig. 6.

The force available on the tip, due solely to the activationof J1 and considering the total robot length, is 0.65 N, that isa value compatible with the execution of dedicated tasks (i.e.,cutting of tissue samples) in endocavitary surgery [23]. The totalweight that can be manipulated is thus 65 g, which is up to fourtimes the robot weight (i.e., 16 g). A maximum speed of 90◦/sfor the pitch and of 190◦/s for the roll can be obtained for eachjoint.

Considering the structure of the electro-cutter robot andthe Denavit–Hartenberg (DH) representation, the reachableworkspace is represented as in Fig 7.

Accuracy measurements within the robot workspace havebeen performed in order to estimate the overall system accuracy.The robot has been controlled to follow three 20-mm straighttrajectories on xy, xz, and yz planes within the robot workspace,automatically generated by the PC in a teleoperated fashion. Theposition of the end-effector has been tracked by an electromag-netic localizer (Aurora Electromagnetic Measurement System,NDI, Waterloo, ON, Canada). Results of accuracy measure-ments in terms of root mean squares (RMS) with respect tothe planned trajectory are reported in Table I. For every dataacquisition, the trajectories have been repeated five times forimproving statistics. The maximum absolute errors are 1.64,


Fig. 7. Graphical representation of the workspace of the electro-cutter robot,units in millimeters (top left: XY; top right: ZX; bottom right: ZY; bottom right:3-D).

TABLE IACCURACY EXPRESSED IN TERMS OF RMS ALONG 20-mm STRAIGHT

TRAJECTORIES ON XY, XZ, AND YZ PLANES

1.87, and 2.57 mm on x, y, and z paths, respectively. This re-sult is essentially due to the lack of motor encoders and to themodality used by the software to predict the robot position thatcould be improved by new software algorithms. These resultsalso include backlash effect. Additional efforts will be devotedto backlash reduction during robots assembly.

C. Manipulator Robot

The manipulator robot is slightly different from the electro-cutter robot.

Specifically, the manipulator robot was used to provide theplatform with an actuated tool for grasping. The kinematic chainof this robot, shown in Fig. 8, includes an active end-effector.The roll of the end-effector is not possible for this robot, be-cause the motor activating the roll in the previous robot is nowdevoted to activating the grasper. The overall dimensions of themanipulator robot are 12 mm in diameter and 95 mm in length,with a total weight of 22.5 g. The force available at the tip thanksto the action of J1 is 0.65 N.

D. The Retraction Robot

Another essential module to be used in surgical proceduresis the retraction robot. The design of this unit was inspired by aprevious work [25] and was optimized by including the supportfor a magnet used to anchor the robot to the abdominal wall.

Fig. 8. Arrangement of the DOFs and joints in the manipulator robot.

In this way, the retraction robot can be used as an independentrobotic tool when needed. The retraction robot has a diameterof 12 mm and a total length of 52 mm, including the support forthe magnet, and a weight of 12 g.

Since the main goal of retraction tasks is to retract tissueand allow the manipulation of the underlying tissues by anotherrobotic unit, we made the technical choice to integrate two mo-tors into the robot for a pitch DOF and for the opening/closingmechanisms of the gripper, in order to keep the module shorterand maximize the retraction force. The workspace is 1-D, sincethe only task consists of pulling the retracted tissue toward theabdominal wall in order to expose the target site. The motionrange of the pitch DOF is ±180◦, while the maximum pullingand grasping forces are 1.53 and 5.3 N, respectively. The re-traction robot reachable workspace can be enhanced thanks tothe motion of the external magnetic handle. In fact, thanks tothe magnetic link, the retraction robot relies on three additionalexternal DOFs for the correct positioning of the robot in theabdomen. In addition, the handle can be pushed against theinsufflated abdomen for the approximation of the target tissuewith the robot. The retraction robot and anchoring frame ex-ternal handles can be used without problems on the abdomensince they are embedded in soft cases that limit magnetic in-terferences. In a real scenario, it is supposed that both handlesare maintained in position by medical assistants, who move thehandles according to surgeon’s indications.

E. Camera Robot

The camera robot consists of a 2-DOFs robotic unit, con-ceived to enable workspace vision during NOTES. The camerarobot is based on a roll/pitch module linked to a passive sup-port for holding the vision system. An additional viewpoint isconstantly provided by the flexible endoscope if needed.

The vision system was integrated in the distal part of thecamera robot. It includes a camera and a source of illumination in


order to optimize the lighting conditions in a dark environment,such as the abdominal cavity.

In this paper, a standard 2-D camera was integrated to provideon board platform vision. The camera (Misumi Electronics Cor-poration, New Taipei City, Taiwan) is characterized by a framerate of 30 frames/s and a resolution of 320 × 240 pixels. It is10 mm in length and 8.6 mm in diameter, and power consump-tion is 110 mA @ 3.3 V. These features are compatible with theapplication in terms of frame rate and resolution (they are suf-ficient for the proposed tasks), dimensions (the camera can beeasily integrated in the robotic module), and power supply andconsumption (there are no critical energy constraints becausethe camera is wire-supplied from an external power source at3.3 V). The camera was chosen because it is easily availableoff-the-shelf. Appropriate lighting conditions were guaranteedby a printed circuit board integrating four white LEDs by NichiaCorporation.

F. Anchoring Frame and Docking System

A triangle-shaped anchoring frame was used to support thearray of robotic modules in a stable position inside the abdomen.This device is described in detail in [24]. It is magnetically an-chored to the abdominal wall by means of an external magnetichandle. In particular, the anchoring frame has a three-segmentsnake-like structure that allows insertion through the esophagealaccess port. Once inside the abdomen, the anchoring frame re-covers its triangular shape thanks to the action of shape memoryalloy springs positioned on the vertexes of the structure. Theanchoring frame is equipped with three docking systems for po-sitioning the robotic units. The robotic modules can be dockedand undocked during surgical procedures depending on medicalneeds, thus enabling the platform to change tools. This is crucialduring medical procedures and is usually a main limitation forresearch-level surgical robots. A dedicated reversible mecha-nism has been implemented for the docking and undocking ofthe robotic modules [27]. In this paper, a modified mock-up ofthe anchoring frame was used, in order to integrate additionalelements (in particular the control board for communication be-tween modules). The role of the anchoring frame is twofold:providing stability to the entire platform, and being the cen-tral node of communication between the robots, as explained inSection IV.

IV. CONTROL AND DRIVING ELECTRONICS

The robotic units are designed to integrate mechanisms, elec-tronics, and miniature motors.

A wireless microcontroller (CC2430, Texas Instruments, Dal-las, TX, USA) together with the motor drivers was embeddedon a dedicated electronic board having dimensions of 10.8 mmin diameter and 2.3 mm in thickness. Each board can controlup to two brushless motors and provide wireless communica-tion. The main advantage of using custom boards is that thereare no power limitations with respect to commercial controllers,thus allowing us to get better performance from the motors interms of an output torque. All the embedded boards can be

Fig. 9. Top: assembled platform with integration of the control board on theanchoring frame; in the inset, detail of the control board; Bottom: schematicsof the overall platform architecture showing the communication links betweencomponents.

powered through dedicated electrodes positioned on the mod-ules, as shown in Fig. 4 (Left).

An intraabdominal wireless network is set up for communica-tion between the platform components (i.e., the anchoring frameand the robotic units), by exploiting a ZigBee “star” architecture.The central node (i.e., the master) of the network is the boardintegrated in the anchoring frame, while the other nodes areconstituted by the boards integrated in the robotic units. Thus,the electronic boards provide both low-level motor control andmanage network wireless communication between the activeelements of the system. On the other hand, the central node pro-vides robust and stable internal–external cabled communication.This is a clear advantage of the proposed system, which relieson wireless communication between modules (enabling the toolto change intraoperatively) and at the same time prevents dis-turbances in wireless transmission through human tissues. Anoverview of the platform with the integrated master board andschematics of the system architecture are reported in Fig. 9.

Embedded electronics successfully solves the problem ofwireless/wired communication. However, a major drawbackof the 4-mm Namiki motor is the lack of embedded encodersthat makes the implementation of position control difficult. Al-though this is advisable for controlling the robotic units beforeapplication in real surgery, in a way it can be considered a consol-idated methodology that we will implement as soon as miniatur-ized encoders will be available. We explored a control strategybased on the prediction of the robot position directly through the


TABLE IIDENAVIT–HARTEMBERG PARAMETERS OF THE 4-DOFS ROBOTS

embedded microcontroller, as proposed in [28]. Sensorless po-sition control, based on this approach, was implemented on anexternal control unit (i.e., a PC), communicating via serial portwith the master network node. A two-channel joystick (CyborgRumble Pad, Saitek, Torrance, CA, USA) was used for con-trolling both robots, while a dedicated controller was used formoving the camera robot. The new position retrieved from thejoystick interface results in a new position for the joints, whichare calculated by implementing inverse kinematic algorithmson the basis of the robot DH parameters reported in Table II.However, after a short operating time, the position errors of thepredictive algorithm were too high to guarantee robust controlof the robot. For this reason, an open-loop control was preferredin order to demonstrate the performance of the robotic platformas is. This was suitable to show the feasibility of the roboticplatform and to perform the experimental session described inthe following section.

V. EXPERIMENTS

The aim of the experimental session was twofold:1) to assess the feasibility of the insertion procedure of the

array of robots based on the sequence described in SectionII-B;

2) to determine the robot capabilities to perform simple tasks(i.e., pick and place, surgical cutting).

These experiments were performed to assess the system tech-nical capabilities. Medical assessment will be performed as afuture work.

The procedure regarding the insertion and positioning of thearray of robots is described in Section V-A. Pick and placetests on different users and cutting experiments are subsequentlygiven in Section V-B and V-C, respectively.

A. Insertion and positioning of the Array of Robots

The complete platform was tested in a phantom abdominalcavity to assess overall compatibility of the platform with theesophageal access port. In particular, in this paper, the steps de-scribed in Section II-B were performed for all robotic modulesto show the feasibility of the procedure. Once the access port hasbeen inserted, a user with nonmedical experience performed theinsertion of the robots in about 15 s for each unit. Afterward, thedocking of the camera robot using the assistive endoscope wasperformed in less than 4 min and 30 s. The medical procedure

Fig. 10. Assembled NOTES platform in a human abdomen simulator.

will be assessed during future in vivo evaluation with medicalstaff. In addition, the retraction module was inserted and an-chored to the abdominal wall through magnetic coupling. Theoverview of the deployed array of robots in a human abdomensimulator is shown in Fig. 10.

B. Pick and Place Experiments

The bimanual miniature robotic platform was tested for pickand place experiments. These experiments were performed ona group of people with technical skills in robotics. In particu-lar, ten engineers (five males, five females) performed pick andplace exercises. The experiments were designed to assess thefunctionalities of the overall system in its current implementa-tion. The users performed the exercises by using the joystickand controlling the manipulator and electro-cutter robot, underdirect visual feedback from the operative environment. Duringthese experiments, the tip of the electro-cutter was replaced witha metallic hook, since there was no need for electro-cutting.

The first exercise consisted in a peg-transfer setup, accordingto SAGES manual skills tests [29]. However, since only onemanipulator robot was available, the users were asked to performthe following tasks using a single peg:

1) Task 1: pick the peg from one position of the pegboardusing the manipulator robot;

2) Task 2: place the grasped peg in a different position of thepegboard using the manipulator robot;

3) Task 3: hit the peg just released using the electro-cutterrobot.

The time spent for each task was recorded to report the pre-liminary results for the pick and place experiments with thecurrent control implementation. The experiment was repeateduntil all the tasks were completed without losing the peg. Eachtime the peg was lost during the experimental tasks (i.e., whenit was placed outside the robot workspace or when it fell), afailure event was recorded. A summary of the experimental ses-sion, including the time for performing the single tasks per userand the number of failures, is reported in Table III. A snapshotduring the pick and place experiment is reported in Fig. 11.

C. Tissue Cutting

Tissue cutting experiment has been performed with thetwofold aim of proving the interaction capability of the two


TABLE IIIPICK AND PLACE EXPERIMENTS

Fig. 11. Miniature robots during pick and place experiments.

Fig. 12. Miniature robots performing tissue cutting in consecutive snapshots.

arms in a real exercise and for demonstrating the compatibilitybetween the commercial cutting tip and the wireless communi-cation during cutting. A tissue sample was positioned within therobot workspace to be manipulated and cut. The tissue samplehad the following dimensions: 80 mm (length), 60 mm (width)and 4 mm (thickness). The tip of the electro-cutter robot wasconnected through an electric cable to the external commercialunit (Erbe, Tubingen, Germany). The user was able to controlactivation of the electro-cutter by using a foot-pedal and controlthe miniature robots by using the joystick. A snapshot of thetissue cutting experiment is shown in Fig. 12. Tissue cuttingwas performed in 2.5 min without any technical problem. Thistask was performed to qualitatively demonstrate the feasibilityof tissue cutting rather than providing a statistical analysis.

VI. DISCUSSION AND CONCLUSION

In this paper, an array of different robots integrated in a mul-tifunctional platform for application in NOTES has been pre-sented. The system offers the possibility of performing proce-dures intraabdominally, by setting up a surgical room in the pa-tient’s abdomen. In particular, the whole platform is composedof an anchoring frame able to support two miniature robots formanipulation and cutting, and a robotic camera enabling visionof the operative scene. In addition, a retraction robot can bepositioned in the abdomen for tissue retraction tasks. The con-cept of modularity adopted in the design allows the modules tobe interchanged during the surgical procedure, thanks to imple-mentation of an intraabdominal wireless network. Each roboticunit communicates via wireless with the anchoring frame, whichmanages overall communication and is interfaced via wires withthe external control unit, overcoming the current limitations ofa full wireless approach.

The complete platform was successfully inserted in a phantomabdominal cavity to assess the platform’s overall compatibilitywith the esophageal access port. As additional outcome, themeasured time from the insertion of the camera robot to thefinal docking was 4 min and 34 s. A maximum tip force of0.65 N has been measured for the robots, with an accuracyexpressed in terms of RMS of ± 0.39, ± 0.67, 0.67 mm on x-,y-, and z-axes, respectively, measured on straight trajectories.

Pick and place experiments were performed by ten users toassess the overall performance on a bench test. Manipulationand tissue cutting tasks have also been demonstrated.

Results showed that pick and place can be performed in amean time of 160.5 s with a minimum execution time 55 s with-out any training session. In addition, tissue cutting (2-cm long)was performed in 2.5 min to prove the interaction capabilitybetween the two arms in a real exercise. These figures can beconsidered successful results, if considering that the joystick in-tuitiveness is intrinsically limited for controlling multiple DOFs.Intuitive multiple-DOFs haptic interfaces will be implementedon the master side as a future step.

In conclusion, this paper has demonstrated the possibility ofusing an array of robots for performing basic tasks in NOTESprocedures. Once the platform will be finalized (in particular interms of sealing with respect to biological fluids), ex vivo andin vivo experimental sessions involving medical experts will beperformed.

ACKNOWLEDGMENT

The authors wish to thank the colleagues of the BioRoboticsInstitute for the precious support and A. Dimitracopoulos forhaving inspired this paper.

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Giuseppe Tortora (S’09–M’13) was born in Iser-nia, Italy, in 1983. He received the M.S. degree inbiomedical engineering from the University of Pisa,Pisa, Italy, 2008, and the Ph.D. degree in bioroboticsfrom the BioRobotics Institute, Scuola SuperioreSant’Anna, Pisa, Italy, in 2012.

In April 2007, he joined the Scuola SuperioreSant’Anna, focusing his activity on medical roboticsand biomechatronic systems. He spent a period as aVisiting Researcher at the Imperial College Londonand Carnegie Mellon University in 2011. His main

research interests are in the field of biorobotics and minimally invasive roboticsurgery.

Paolo Dario (F’02) received the Master’s degree inmechanical engineering from the University of Pisa,Pisa, Italy, in 1977.

He is currently a Professor of biomedical roboticsat the Scuola Superiore Sant’Anna, Pisa, Italy, wherehe supervises a team of about 150 young researchers.His main research interest is biorobotics, includingmechatronic and robotic systems for rehabilitation,prosthetics, surgery, and microendoscopy. He is theauthor of more than 160 ISI journal papers, manyinternational patents, and several book chapters on

medical robotics.Mr. Dario received the Joseph Engelberger Award as a Pioneer of Biomedical

Robotics.

Arianna Menciassi (M’00) received the Master’s de-gree in physics (Hons.) from the University of Pisa,Pisa, Italy, in 1995, and the Ph.D. degree from theScuola Superiore Sant’Anna (SSSA), Pisa, Italy, in1999.

She is currently an Associate Professor of biomed-ical robotics at SSSA. Her main research interests arein the fields of biomedical micro- and nano-roboticsfor the development of innovative devices for surgery,therapy, and diagnostics. She is the coauthor of morethan 150 international papers, about 100 in ISI jour-

nals, and five book chapters on medical devices and microtechnologies.

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