on laparoscopic robot design and validation

Integrated Computer-Aided Engineering 10 (2003) 211–229 211IOS Press

On laparoscopic robot design and validation

Victor F. Munoz∗, J. Fernandez-Lozano, J. Gomez-de-Gabriel, I. Garcıa-Morales, R. Molina Mesa andC. Perez-del-PulgarInstituto Andaluz de Automatica Avanzada y Robotica, Universidad de Malaga, Malaga, Spain

Abstract. This paper presents a robotic assistant for helping surgeons in minimally invasive surgery. The system provides thedirect control of the camera positioning inside the abdominal cavity, including teleoperation capabilities. This prototype does notrequire any modification of a standard operating room for its installation and its application in surgical procedures. The insertionpoint of the laparoscopic camera constitutes the most important kinematic constraint in laparoscopic techniques. In the proposeddesign, this has been solved with a passive wrist. A three active degrees of freedom manipulator positions the wrist. In orderto demonstrate the robot suitability to develop the tasks it has been designed for, a design validation has been performed. Thisvalidation consists of simulations based on the configuration space concept. Finally, trials with alive animals have been carriedout in an experimental operating theatre.

1. Introduction

During the last years, a new field has attracted the in-terest of robotic researchers. Minimally invasive tech-niques, such as laparoscopy, have grown as a very suit-able domain for robotic systems. Laparoscopic tech-niques involve the use of long stem instruments throughsmall incisions in the abdominal wall of the patient. Aspecial camera, whose optic penetrates as well into theabdomen, helps the surgeon to manoeuvre the instru-ments in order to explore the anatomical structures andtheir pathologies [15]. Thus, the surgeon only uses thevisual feedback information provided by the cameraattached to the optic.

Currently, the usual procedureconsists in holding thecamera by an assistant while the surgeon manoeuvresthe surgical tools inside the patient abdomen. This factrequires a high coordination between them. However,in some procedures the surgeon needs more than twoinstruments at the same time, and a second surgeon, incharge of the camera and a surgical tool, is necessary.

Since these procedures can last up to two (or evenmore) hours, the camera image can suffer a significant

∗Corresponding author: Victor F. Munoz, Instituto de AutomaticaAvanzada y Robotica, Universidad de Malaga, Severo Ochoa, 4.Parque Tecnologico de Andalucıa, Malaga, Spain. Tel.: +34 952 131406; Fax: +34 952 13 7203; E-mail: [email protected].

loss of stability due to the tiredness of the surgeonwho moves the camera. Focusing the point of interestcan also become a difficult task. In this scenery, arobotic aid, being able to move the laparoscopic camera(allowing him or her to use both hands in the surgicalprocedure itself), would become a very helpful tool inthe operating room. A robotic camera could improvecoordination and efficiency, and release the assistant orthe second surgeon (the one who moves the camera) tohelp the main surgeon,or to carry out another procedurein a different operating room.

A review of the literature can show different waysof facing the development of a laparoscopic assistant.In 1995 Taylor et al. [16] proposed a complete system,including a manipulator, a special end-effector to carrythe laparoscopic camera and a new control strategy. Inthis design, as in most of the robot manipulators, the ori-entation of the camera through the incision was decou-pled of its positioning. The interface was based on aninstrument-mounted joystick, since voice-recognitionsystem were not very capable at that moment.

Green, at SRI International [8], developed a differentconcept. The target of this system was to explore thepossibility of a telesurgery scheme, not only suitablefor minimally invasive surgery but also to open surgeryas well. This telesurgery concept was later enhancedand taken to a commercial stage by Intuitive Surgical’sDa Vinci system [9].

ISSN 1069-2509/03/$8.00 2003 – IOS Press. All rights reserved

212 V.F. Munoz et al. / On laparoscopic robot design and validation

The HISAR system [6] presented a new configura-tion of the manipulator. The proposed one was a 7degrees of freedom (dof) robot mounted on the ceiling.Two of the orientation axes were passive, to grant freecompliance with the entry port. Since this point actsas a fulcrum, it is necessary to have an accurate knowl-edge of its position to move the camera with precision.In order to achieve this, a geometrical re-estimationprocedure of the pivoting point is proposed.

A different approach consists in a modificationof a standard industrial manipulator. For instance,Hurteau [11] proposed a system based on an industrialmanipulator, modified by means of an universal jointbetween the end-effector and the camera holder. Thesystem of the Universitat Politecnica de Catalunya [1]goes a step beyond and shows a motion control systemable of moving the camera following the movementsof the instruments. This system is based on a SCARAindustrial manipulator modified with an universal jointin the end effector. An extension of this device permitsto clear space near the stretcher since the robot doesnot need to be placed right beside it. The control ofthe camera is achieved through a computer vision sys-tem that tracks special marks on the instruments. In afurther development, a specific robot was designed [2].

The Computer Motion AESOP [17] is a commercialsystem intended to move the camera according to thecommands of the surgeon, first through a pedal andafter through a speech recognition system. It is a 4 dofrobot arm attached to the stretcher, and presents an end-effector with three axes (two passive and one active).Many surgical procedures have been completed usingthis system, and it has received the FDA-approval.

Another commercial device is the EndoAssist [3]by EndoSista. The orientation is obtained thanks toa remote centre of rotation scheme. The robot has tobe placed over the patient in such a way that its centreof rotation coincides exactly with the insertion point.Though it is a commercial system, not much data hasbeen released.

This paper deals with the principles and considera-tions prior to the development of a laparoscopic robot,called WLR, as a part of the whole ERM system. Sec-tion 2 states the requirements to design such a system.Section 3 describes the several types of kinematic con-strains that the manipulator has to comply with. Sec-tion 4 faces the design according to the previous prin-ciples. Section 5 presents a kinematic validation ofa manipulator design. Section 6 introduces the maincharacteristics of the ERM system. Finally, Sections 7and 8 are devoted to the experiments and conclusions.

2. Requirements for a laparoscopic manipulator

Laparoscopic techniques involve the use of speciallong stem instruments through small incisions in theabdominal wall of the patient. A special camera, whoseoptic penetrates as well into the abdomen, helps thesurgeons to manoeuvre the instruments in order to com-plete the procedure [15]. The entry points of the instru-ments in the abdomen only allow them four degrees offreedom: two rotations around the entry point,one rota-tion around the tool axis and one displacement through-out this axis. The characteristics of these degrees offreedom imply the following drawbacks:

1. Inversion of the movement. The entry point actslike a fulcrum in such a way that the camera pivotsaround it (except in movements of penetration orextraction). Thus, when the surgeon moves thehand to the right, it is translated in a left movementof the tool tip.

2. Scaling. The tool amplifies or attenuates the sur-geon’s movement depending on the penetration:a value over a threshold produces an amplifica-tion, whereas a value below it causes the oppositeeffect. The applied efforts are also scaled.

3. Loss of touch. The tissue texture and the efforts,which gives a useful information to the surgeon inopen surgery procedures, are transmitted poorlyin laparoscopic techniques. Moreover, the ful-crum effect and the trocar friction adds errors tothe little information the surgeon gets.

In a laparoscopic procedure different instruments areused, and must be manoeuvred coordinately with thecamera movements. In general, the main surgeon han-dles the tools while an assistant moves the camera. Thiscooperation between both presents three fundamentalproblems:

1. The surgeon must inform the assistant whateverhe wants in every instant. So, problems derivedfrom the verbal communication appears, and theassistant could misunderstand the surgeon orders.

2. As the camera is held by the assistant, the imageis not totally stable, and it is affected by his/herstrength of wrist. This effect rises during thesurgical procedure.

3. The assistant works in an uncomfortable positionto move the camera accurately, specially whenthe fatigue appears. This makes the camera to rubtissues, soiling itself and obliging the assistantto extract and clean it. This problem increasesthe procedure duration, and so the risks for thepatient.

V.F. Munoz et al. / On laparoscopic robot design and validation 213

To solve or to attenuate some of these problems, theuse of manipulator robots has been suggested. Themain purpose of the proposed system is to help surgeonsby moving the camera through their commands. Noinstruments are intended to be robotized at this stage. Asurgical robot has to accomplish a set of requirementsfor its successful integration in a laparoscopicoperatingtheatre. According with the scenery where it has towork, a set of requirements has been defined:

1. To allow the accomplishment of habitual laparo-scopic techniques. In other words, it should belocated in different modes according to the pro-cedure necessities, and it should have the samecapacity to move the camera as a human assistant.

2. It should involve an improvement of the laparo-scopic technique. It means that it should solve orattenuate some of the problems of laparoscopictechniques.

3. Easy integration in a conventional laparoscopicoperating room. Needing special installations orcares is not advisable.

4. To be multipurpose, if possible, so that it takespart in several kinds of procedures. It allows anincrease of the features of the system improvingits amortization.

5. It must work safely and the risk of damages to thepatient or to the surgical team must be minimized,even in a wrong use of the system.

These desired characteristics for a robot assistant inlaparoscopic procedures can be translated in a set ofspecifications that helps to define its design. Theserequirements will also permit a first validation of theproposed design. Thus, a laparoscopic robot shouldcomply with the following points:

1. Positioning independent of the operating table, insuch a way that it could be located in differentplaces around the surgical field relative to theapplied procedure.

2. Multiple workspace configurations to perform thesystem positioning with respect to the operatingtable and the rest of the surgical equipment.

3. Enough workspace without interfering with thesurgeon or the rest of the surgical team.

4. It should not be bulky.5. Minimum number of degrees of freedom and ac-

tuators.6. Compatible with the constraints that the laparo-

scopic technique requires (kinematic constraintsof the surgical tool insertion point).

7. Easy procedure conversion to either open surgeryor conventional laparoscopic surgery (i. e. with-out robot).

8. Ability to work with the available equipmentin a conventional laparoscopic operating theatre,without any new system such as compressed airor trifasic electric supply.

9. Autoclavable and easy cleaning.10. Regarding the operation, the attention needed by

the surgeon should be minimum.11. It should be safe for the patient as well as for the

medical team.

Requirements 1 to 6 affect in a special way to thekinematic design of the robot. However, all the specifi-cations must be taken into account in every stage of thedesign. For instance, a favourable kinematic structurecould present dangerous movements for the staff evenif the surgical tool is operated safely inside the patientbody.

3. The task model

In order to develop a robotic system that handles asurgical tool, the way a human uses it must be studied.In this case, the tool is a laparoscopic camera. Nev-ertheless, most of the general conclusions can also beapplied to other surgical instruments. Therefore, a taskmodel has been established.

Two reference systems have been defined, one in theentry point{F}, and the other one in the camera{C}(Fig. 1). The camera position and orientation is de-fined through the transformation. This transformationis composed by a rotation and a displacement, as it canbe observed in the following equation:

FTC =[FRC FPC

0 1

]

whereFRC is defined by the ZYZ Euler angles:

FRC = Rz(ϕ) ·RY ′(θ) ·RZ′′(ψ)

The orientation can be decomposed in three angles:

– ϕ, aroundZ axis of the{F} system, in such a waythat theX ′ axis of the rotated{C} system pointsto the working area.

– θ, aroundY ′ axis of the rotated{C} system, insuch a way that theZ ′′ of the transformated{C}system (and therefore the optic of the camera) ispointed to the target zone.

– ψ, aroundZ ′′ axis of the resultant{C} system ofthe latter transformation.


Fig. 1. Axes assignment for camera position and orientation.

When the three angles are null, the system{C}matches to the{F} one.

In the proposed system, only zero degree optics havebeen considered. Thus the{C} system is linked tothe camera and not to the optic. This model couldbe applied to optics with angle if the reference systemwere linked to the optic. In this case, theψ angle wouldbe a latter rotation to get the desired image.

The characteristics of the laparoscopic camera move-ment are defined by two main factors: insertion pointand orientation.

3.1. Insertion point

The entry point to the patient abdomen imposes a setof constraints to the laparoscopic tool movement, in-cluding the camera. It prevents the lateral displacementso that the available degrees of freedom are reduced tofour: three rotations and one translation (Fig. 2). Twoof these rotations pivot around the entry point of thecamera according to two perpendicular axes, both con-tained in the same plane as the patient abdomen. Thethird one turns around the camera longitudinal axis, andthe last degree of freedom is a longitudinal displace-ment along the latter axis.

These four cartesian degrees of freedom are also re-stricted. The first two are limited according to the na-ture of the surgical technique and, mainly, to the pa-tient characteristics. The tools penetrates into the pa-tient body through the trocar, which is inserted in the

abdomen approximately at 45◦. The instrument move-ments involve forcing the elasticity of the abdominaltissues, which are a composition of four types: skin,fat, muscle and soft tissues. This elements have a lim-ited elasticity and it depends on the corpulence of thepatient. The thinner the abdominal wall, the less effortsare applied on the patient. Certain authors [4] report amaximum deflection angle with respect to the tool axisat +75◦/−75◦ (Fig. 3). According to the task model,this limit can be set by a range of the angleθ:

105◦ � θ � 255◦

The third rotational degree of freedom is related tothe camera orientation and is detailed in the next sec-tion. The last degree of freedom is a displacementalong the camera axis, called penetration. The maxi-mum penetration that can be reached is determined bythe maximum instrument length and the external trocarlength. The former is the segment length that can beinserted into the abdomen, that is to say, the distancealong the optic from its tip until the position where itsdiameter cannot be introduced into the trocar. Regard-ing the trocar length out of the patient, it is a variablemagnitude as well as the total size of the trocar is.

According to the task model, the penetration restric-tion can be expressed as follows:

LET � p � LLap

where:

– LET is the external trocar length.


Fig. 2. The mobility of the laparoscopic tools is restricted to 4 cartesian degrees of freedom.

Fig. 3. Lateral view of the laparoscopic tool workspace.

– p = |FPC | is the distance from the origin of thesystem{C} to the origin of the system{F}.

– LLap is the length of the laparoscopic, in otherwords, the distance from the optic tip to the originof the system{C}.

3.2. Orientation

The camera orientation is fundamental in a laparo-scopic procedure since the monitor image depends onit. In particular, a rotation along the longitudinal axiswill produce the same rotation in the image.

The proper laparoscopic camera movement consistsof parallel translations to the generatrixes of an in-verted cone trunk. In such a way, the upper side ofthe camera always points to the vertical axis of theabove-mentioned cone. Different positions of the cam-

era are shown in Fig. 4, where the internal and externalworkspaces are represented. The camera cannot be lo-cated in any position in the external workspace, but itsupper side must be always pointing to the inside. Thismovement causes a rotation in the monitor image, butthis rotation is easily assumed by the surgeon, since theimage that he perceives is the same image he would seeif he was placed instead of the camera position (Fig. 5).

According to the task model, this orientation con-straint is expressed asψ = 0.

4. Kinematic design

4.1. Orientation

As in general robotics, in laparoscopic applicationsthe problem of orientation and the problem of position-ing are usually decoupled. It allows to resolve bothquestions through the inverse kinematic model. Also,the design and the construction of the robot mechanicalstructure are facilitated.

In laparoscopic applications, the orientation must beachieved complying with the task constraints. The toolthe robot moves can be modified only by means ofthree rotations around the entry point. This impliesthat any design that tries to separate the problem oforientation and the problem of positioning will onlyachieve it relatively, because any change in the wristorientation must involve a displacement too, unless itis located indeed in the entry point. This is not possiblebecause the tool is inserted in the abdomen through arigid trocar. Moreover, a piece of the tool must stayoutside. Nevertheless, there are three ways to obtain theproper laparoscopic tool orientation while complyingwith the kinematic constrains of the insertion point:


Fig. 4. Laparoscopic movement. For the workspace of the optic tip defined by the task being executed, the outer laparoscopic tip has a specificworkspace where it must move with certain orientation.

Fig. 5. Image rotation shown in the monitor during the laparoscopic camera movement.

– Remote centre-of-motion. The kinematic struc-ture of the robot is designed in such a way that itforces the end effector to rotate around a centre ofmotion. Since this one is not located at any ma-nipulator joint axis, it is denominated remote cen-tre. This concept can be achieved by several ways.One possibility consists in using curved rails and

to move the instrument along them. Another wayis to make the mechanism with spherical links be-tween consecutive joints of a standard manipula-tor. Maybe the most common option is a four barlinkage. Combining two of this structures, the tworotations contained in the same plane as the ab-dominal wall are obtained. The main disadvantage


of this strategy is the final volume of the mechan-ical structure. It is used by Intuitive Surgical’s DaVinci [9,12].

– Active control of the pivoting point. The inser-tion point constraints are imposed by means of therobot joints control. That is, transforming me-chanical constraints to software constraints. Thispossibility only makes sense if the robot has morethan four degrees of freedom, so it is not a wayto minimize the number of actuators in a surgicalrobot.

– Passive joints. The tool orientation is controlledthrough the positioning of the external tip. Viapassive joints, the carried tool complies with theentry point constraints. In fact, the own patientbody imposes the movement limitations. In addi-tion to this security advantage, others can be enu-merated:

1. The required actuators are as much in numberas the degrees of freedom.

2. The resulting system dimensions are reducedin comparison with the robots based on remotecentre-of-motion.

3. The robot will not mechanically force the pa-tient’s tissues at the direction of the passivedegrees of freedom.

One of its disadvantages can be a less ability for theorientation control, but it can be eliminated through aproper design of the manipulatorand its motion control.

There are multiple possibilities in number and con-figuration for passive joints. The following are the mostlogical ones: to set out the axes according to the de-grees of freedom in the abdominal wall (Figs 6a and 6b,the latter adopted by Computer Motion’s AESOP [17]);or to arrange the passive axes in such a way that thecamera movements that a human carries out, are repro-duced (two passive joints in a perpendicular plane tothe abdominal wall, see Figs 7a and 7b).

The two configurations that allow a conical cameramovement are similar in a kinematic way. Both con-figurations present a singularity at axis−Z. Since theincision is always made in angle, this problem doesnot appear actually. In addition to its easy design andconstruction, configuration c) shows another importantadvantage. Whereas the other passive wrists need thatthe orientation of its origin is ensured, in this one, thefirst passive axis disposition eliminates this restriction.It allows to simplify the design of the rest of the robot,because only a proper positioning of the wrist must beachieved. No actuated axes are thus required to obtain

the desired orientation, and they are only used to solvethe position problem. Therefore, it has been adopted inthe WLR (Wireless Laparoscopic Robot) robot whosedescription is detailed later.

4.2. Positioning

The specifications 1 to 8 exposed in Section 2 con-cern the surgical robot positioning. Also, the systemshould be a statically balanced mechanism; in otherwords, the performance of the motors is not needed formaintaining the robot in a certain position.

Requirements 5 and 6 set the number of degrees offreedom to the minimum, that is, three, due to the cho-sen passive wrist. Requirements 1, 7 and 8 eliminatethe mechanisms mounted in the ground or clamped tothe operating table, because they force modifying theoperating room, and they make difficult to withdraw therobot of the surgical field in case of a conversion of theprocedure to open surgery or conventional laparoscopicsurgery (i.e., without robots).

Thus, there are several possibilities, presented inFig. 8. The configuration chosen for the WLR robotpositioning is the showed in Fig. 8c.

The last point to define is the length of the elements.The length of the two elements of the RR manipulatorhave been computed by studying the most unfavourablecase of the camera workspace outside of the abdomi-nal cavity when the optic is inserted through the trocar.Figure 9 shows the outside limits of the camera posi-tion, defined by a minimal insertion length of the opticthrough the trocar with the maximal deflection angle of75◦. Therefore, the cartesian workspace of the camerais defined as an inverted cone with a base radius of a. Ifwe assume a camera optic length of 360 mm from thedistal end (d) to the camera holder grasping point (g),the value of the arm elements length (L1, L2) is com-puted from expressionL1 · L2 = 278750 mm2. Thisequation has been obtained considering that the armshould reach any point of a 550 mm-size square, whichcontains the base of the inverted cone. If we chooseto have both elements with the same length, which hasbeen our selection in order to make easier storage andoperation, we come to an element length defined by:L1 = L2

∼= 530 mm.The prismatic degree of freedom must supply a ver-

tical displacement equal to the depth of a human ab-domen. Since this one is a very variable amount, and agreater linear displacement does not increase the totalvolume that the whole system needs in an operatingroom, large dimensions has been chosen. In the real-


Fig. 6. Two passive wrist configurations that produce a spherical movement on the camera.

Fig. 7. Two passive wrist configurations that produce an conical movement on the camera.

ization of the prototype, a linear monocarrier with adisplacement of 700 mm has been arranged.

Figure 10 shows the cartesian workspace of the cam-era related to the resulting workspace of the robot arm.It can be noticed that the workspace of the camera canbe located in a wide range of positions inside the robotworkspace, thus allowing the system to be placed ac-cording to the necessities of every case.

5. Kinematic validation

Each laparoscopic procedure demands a particulardisposition of the surgical instruments regarding the

surgical field (the patient). This internal disposition de-termines the external layout (surgical team and equip-ment arrangement required to carry out the operation).It should be noticed that a robot carrying a surgical in-strument must achieve two goals: to move the camerato the desired point and not to interfere with the sur-gical team. Both objectives are closely related to thesurgical procedure, so it has to be studied in order toobtain: first, a viable position for the robot; and sec-ond, a validation of the system compatibility with eachprocedure. A certain position of the robot is feasibleonly if it allows accessing the surgical field, and thephysical structure of the robot does not interfere with


Fig. 8. Several positioning mechanisms considered.

Fig. 9. Camera workspace out of the abdomen.

the movement of the surgeon and his assistant, and doesnot impede the monitor visualization. In every kind ofintervention, several alternatives can be chosen, and itwill be discussed later.

The validation of the system compatibility with eachprocedure can be done carrying out simulated opera-tions in an experimental operating room. In this way,

the construction of a prototype is required. Neverthe-less, when a new design consideration is taken into ac-count, another prototype must be constructed. Thus,the development stage may be improved by means ofa simulation tool which permits checking design com-patibility with the task and robot environment.

Among the several mathematical and simulation


Fig. 10. The ERM robot workspace and the outer laparoscopic camera workspace.

tools used in robotics, the configuration space has beenchosen to develop a validation procedure for surgicalmanipulators.

5.1. Configuration space

A robot configurationq is defined as a vector whosecomponents contain information about the current stateof the robot. The vector providing this informationis given, firstly, with two components: the positionpand the orientationθ. Then, the configuration can bedefined as follows:

q = (p, θ) = (x, y, z, α, β, γ)

It can be also defined, once the kinematic structure ofthe manipulator is set, as:

q = (q1, q2, q3, . . . , qn)

wheren represents a degree of freedom of the robot.The configuration spaceC of the robotR consists of

all the configurationsq that the robot can reach withinits workspace. T (q) is the subset ofC which per-mits to perform a given task, andB(q) is the subsetof C formed by the configurations occupied by obsta-cles [13].

Thus, the compatibility of a robot task with its envi-ronment is proved if the configurations set required tocomplete the task does not share any element with theconfigurations set defined by the obstacles. So that, acompatibility test is designed to define the configura-tions set of the taskT (q) and the obstacles setB(q),and to check that the intersection of both is the emptyset.

5.1.1. Obstacles in the configuration spaceThe first step to verify the compatibility based on the

configuration space is to obtain the above mentionedsetsT (q) andB(q).

The process to create the task configurations,T (q),consists in defining the set of points and orientationsthe end effector should adopt in the workspace to reachevery goal (usually in cartesian coordinates). Thesepoints are translated to the joint space of the robotthrough its inverse kinematic model. Then, it is ob-tained a set of points of the configuration space consti-tutingT (q).

However, definingB(q) is more difficult since notonly the end effector must be studied, but also the robotintermediate segments: if the inverse kinematic modelis used to transform the obstacles around the robotfrom cartesian space to configuration space, only the


collisions of the end effector are studied, and the robotintermediate structure is ignored. Thus, a collision testhas been developed,providing useful information aboutthe compatibility of the whole manipulator structurewith its surrounding obstacles.

5.2. Kinematic validation of the wlr robot

The proposed robot is a manipulator with three de-grees of freedom. Therefore, its configuration space isgiven by means of:

q = (q1, q2, q3)

In order to establish theT (q) subset that a robot hasto adopt in a surgical procedure, the task workspacefor each case has been defined. This has been madeby taking into account the anatomical region of inter-est, the entry point of the instrument and the positionof the robot. A specification of every task has beenmade based on spherical coordinates with respect tothe camera reference system. Then, the resulting set ofpositions of the end effector -in spherical coordinates-has been translated into a set of cartesian positions ofthe robot wrist. Finally, these points are translated intothe joint space through the inverse kinematic model ofthe robot.

5.2.1. Obstacles in the operating theatreIn order to define theB(q) subset, the same strategy

that in the case ofT (q) can not be adopted, becauseall the possible incompatibilities are not covered. Acollision test has been developed to verify the config-urations of the robot which are incompatible with theconsidered obstacles. The study has been restricted topossible collisions with the surgeon and/or his assistant.Both have been modelled as cylinders with a diameterof 500 mm, and located in several positions accordingto the procedure that is being analysed. Thus, a set ofboundary configurations of the robot is obtained, andcan be represented in the configuration space togetherwith the taskT (q). In this representation, the compat-ibility of the robot with the considered procedure canbe verified by visual inspection.

5.2.2. Problem statementThe collision test can not be developed without a

previous definition of the robot position relative to thesurgical field. The purpose is not eliminating the as-sistant, but releasing him of manoeuvring the camera.This fact maintains the possibility of placing the assis-tant in his usual position. In this way, the incorporation

of a robot does not involve a dramatic change in themode the surgical team works.

Almost every surgical procedure can be performedthrough minimally invasive techniques. Nevertheless,in abdominal surgery only in six of them laparoscopyhas been accepted as the “gold standard”:

– Cholecystectomy– Nissen funduplicature– Inguino-femoral hernia– Adrenalectomy– Splenectomy– Diagnostic laparoscopy for the acute abdomen

Some of these procedures share the same staff distri-bution around the operating theatre and can be grouped.Thus, in each set of procedures, several positions forthe robot can be proposed (Fig. 11). The selected lo-cations are marked with a thick line. The criteria todiscard a place or another was to keep the robot as farfrom humans are possible, to minimize the possibilityof interferences, while keeping the assistant in the usualposition adopted in every procedure. The only one ex-ception was taken in the cholecystectomy, where therobot is located in place of the assistant, while this oneis moved to the other side of the patient (the assistant’snew position is not shown in the figure). The reason forthis is the experience during the experiments with a pre-vious system based on an industrial manipulator [14],where the surgical staff preferred such an arrangement.To compare the performances of both systems (the oldone and the new one), this layout has been maintained.

Every procedure demands a particular disposition ofthe entry point, zone of interest and robot position.In order to place these points of interest relative tothe surgical field, a reference system has been definedin the horizontal plane which the entry point of thecamera belongs to. As it has been described before,the manipulator should be able to reach any point ofa 550 mm-size square centred in the insertion point.This square is the base of the aforementioned referencesystem, whose origin is fixed on the bottom left corner(Fig. 12).

The surgeon and the assistant, modelled as cylinderswith a diameter of 500 mm,are the obstacles consideredfor the collision test. They are placed according to theoperating theatre disposition showed in Fig. 11. Thevalues for all the positions and the workspace size are,of course, approximated.


Fig. 11. Positions that a laparoscopic robot could take around the operating table.

5.2.3. ResultsSince the results obtained for each surgical procedure

are similar, only one case is detailed: right inguino-femoral hernia repair.

In this procedure, the surgeon is located at the pa-tient side opposite to the affected inguinal region, andthe assistant at the opposite side of the surgeon. Themonitor and the instruments are placed at the bottomof the patient (Fig. 13).

Only three entry points are made, one of them forthe laparoscopic camera insertion. The work area islocated at the lower abdomen. The required internalworkspace is a cone with elliptical base. Its dimensionsmainly depend on anthropometric characteristics of thepatient, but a base of 150× 100 mm and a maximumpenetration of 180 mm can be reasonable values. A45◦ inclination of the cone axis from the vertical, anda 225◦ rotation around the vertical axis are considered.Figure 14 shows the camera workspace in this proce-dure, in cartesian coordinates.

The robot position is (−300,0) respect to the ref-erence system mentioned above. The surgeon andthe assistant positions are respectively (1150,850) and(0,550) with regard to the robot.

Figure 15 shows the results obtained forright el-bow configuration. The configurations set that therobot adopts during the intervention and the circles thatmodel the surgeon and the assistant can be observed inFig. 15a. Also, the robot configuration limit prior to acollision, is displayed (in this case with the assistant).Fig. 15b represents the problem in the configurationspace. The prismatic degree of freedom is representedby the vertical axis. Here the constraints take the shapeof two planes limiting a forbidden region. Each planerepresents the maximum angular value in a rotationaljoint in such a way that there is no collision neither withthe surgeon nor with the assistant.

In left elbowconfiguration, a collision with the as-sistant appears. This is represented in Fig. 16, wherenumerous positions of the robot are superposed to thespace reserved for the assistant. In the configuration


Fig. 12. Reference system to establish the robot position with respect to the surgical field.

Fig. 13. Right inguino-femoral hernia repair. The area of interest is shadowed.

space, this collision is translated in several points lo-cated beyond the limit of the first rotational joint.

As it has been seen, the process of kinematic vali-dation gives useful information in order to position therobot in the appropriate place. The study, that has beenextended to all the above mentioned surgical proce-dures, demonstrates that the system is able to work ineveryone. Moreover, it has allowed to select the bestconfiguration (right or left elbow) for each procedure.

6. The ERM system

Once the validation process was completed, andsince it presented a positive result for the considered

set of laparoscopic operations with the proposed kine-matic design, the WLR prototype has been finally con-structed as a part of the whole ERM system. This sys-tem has been designed to assist in laparoscopic surgeryby moving the camera both locally (by the use of verbalcommands) and remotely. It is a very simple system,intended to provide a low-cost exploitation and easymanagement. Teleoperation features have been addedto make available telecollaboration schemes, such astelementoring (an expert teaches a novice), teleproctor-ing (a remote person supervises a procedure) or tele-diagnosis (a remote physician identifies a disease). Toobtain the capability of moving the camera from a re-mote workstation, a telerobotic architecture has beendesigned. This architecture is based in the one pro-


Fig. 14. Required workspace in right inguino-femoral hernia repair.

posed in [5], and detailed in [7]. It allows local au-tonomy in the controlled robot, and since the trajectorygeneration and feedback control loop are local, the re-mote system teleoperation is stable under remote su-pervisory commands. The goal is to control the robotthrough standard TCP/IP networks. This way, a widerrange of applications is possible, since a larger numberof possible remote sites is available.

Some of the main characteristics of this system are itshardware and software modularity (for a configurationadapted to the application) and its wireless operation,what allows it to be moved manually and at any time, aswell as to operate in practically any standard operatingroom, since it does not have to be plug to the powersupply network. The system also includes wirelessvoice/data communication media.

Special efforts have been made to simplify the localsurgeon (or auxiliary staff) user interface, in such a waythat its set-up is automatically made just by turningthe system on. The fulcrum position in the patient ac-cording to his coordinates system is automatically andcontinuously obtained, to ensure a proper and precisemovement of the surgical tool and to maintain the de-sired orientation and penetration, even in the presenceof disturbances.

The ERM system has three main modules: the Wire-less Laparoscopic Robot, the Teleoperation Module andthe Extended Capabilities Module. Each one of thoseunits provides one or some functionalities and they can,

in principle, be used separately or jointly. The WirelessLaparoscopic Robot moves the camera in response tothe surgeon commands; the Teleoperation Module al-lows a remote surgeon to collaborate in, or supervise,the operation; and the Extended Capabilities Moduleprovides the connection of the system to the exterior,both with other manufactures’ equipments and withexternal databases.

The three different modules of the system plus thelocal surgeon interface are described below.

6.1. The laparoscopic robot

This is the main element of the system. It has beendesigned as a three active degrees of freedom manip-ulator in a PRR configuration. The prismatic degreeof freedom is implemented via a monocarrier platformthat gives the linear displacement through a endlessscrew powered by an electrical motor. The RR seg-ment is constituted by two rectangular elements withsquare section moved by electrical motors. In the firstrotational joint, the motor actuation is applied directlyon the axis. The movement is driven to the second jointby a transmission chain.

As stated above, the orientation problem has beensolved by a passive wrist which consists of two jointsperpendicular to each other (Fig. 17). The first axis isparallel to the actuated joint (a rotation around Z axis),while the second one is located in a horizontal plane


Fig. 15. a) Robot positions (right elbow) during a right inguino-femoral hernia repair procedure. The circles represent the surgeon and theassistant. b) Positions in the configuration workspace.

(a rotation around X axis). The Fig. 18 shows the ageneral view of the robot.

The controller is integrated in the robot base and, byits side, there are two batteries providing the power sup-ply to the set. The surgeon has a wireless microphoneto send his commands to a local interface sub-module,usually a speech recognition system integrated as wellin the robot base. However, a joystick, a pedal or an-other means can be used to substitute or to complementthe voice interface.

The robot has been designed to occupy a small vol-ume and not to need clamping to the operating table.Those facts, together with the battery supply and thewireless microphone, make the system to be a wire-less system, thus facilitating the integration into theoperating theatre.

6.2. Teleoperation module

This module allows telecollaboration between twosurgeons, so that an expert may guide or supervise the


Fig. 16. a) Robot positions (left elbow) during a right inguino-femoral hernia repair procedure. The circles represent the surgeon and the assistant.b) Positions in the configuration workspace.

operation performed by the surgeon present at the oper-ating theatre. To facilitate this work scheme, the remotesurgeon receives the laparoscopic image, on which hecan make marks and comments. That information issent to the operating room, where it is showed overlaidon the laparoscopic image on the video monitor. Theremote surgeon can as well take the control of the robotfor the camera to show a region of interest. Besides,a video conference channel allows communication be-tween both surgeons.

The implementation of this module consists of twoparts: a component within the operating room anda remote workstation. The first element communi-cates with the rest of the operating room equipment viaa wireless communication network, and with the re-mote workstation via another communication network,which may be a conventional one. That is, one of itspurposes is to act as a bridge between the operatingroom network and the exterior. Another purpose ofthis component is to overlay the marks in the laparo-


Fig. 17. End effector of the WLR robot.

Fig. 18. The WLR robot.

scopic image if the Extended Capabilities Module isnot present.

The remote workstation consists of a standard PC,thus permitting a wide range of possible points forremote operation of the system. As input interface,the surgeon may use a standard mouse, but some othermedia, such as a master manipulator or aSpaceballcanbe used as well.

6.3. Extended capabilities module

The main component of this module is the Presenta-tion Server. This element communicates with the localinterface, which the local surgeon can use to demandinformation, such as previous patient’s explorations ordocumentation on the procedure in progress. Addi-tionally, if the operating room has surgical equipmentsprepared for centralized operation, such as those ofStorzTM or StrykerTM, the surgeon can also controlthem via the local interface. In this case, and until astandard on communication of that kind of equipmentsis not adopted, it is necessary to incorporate an adapta-tion module.

6.4. Local surgeon interface

Like most of the robotic surgical assistants, speechrecognition has been chosen to provide the commandinput. It allows a simple way of controlling the robot,avoiding to use hands or feet for this purpose. In addi-tion, this method improves sterilization since it avoidsphysical contact.

An off-the-shelf speech recognition hardware mod-ule (from Sensory Inc.) has been used, and it is trainedto recognize a small set of intuitive commands like“Move Up”, “Move Left”, “Move Out”, . . . These com-mands must be trained with the surgeon voice. The se-lected module has the capability to play oral messagesto confirm to the operator that the instruction has beenrecognized and that it is to be executed. The moduleis programmable in C-like language, so it is also incharge of the local interface control, carried out in avery compact and simple way without the need of a PCcomputer.


Fig. 19. An overview of the modular concept of the ERM system.

7. Experiments

The project is currently undergoing the certificationstage by the Spanish Health Authorities. An additionaladvantage of the modular configuration of the systemis the possibility of facing this certification separately,so each module follows its own procedure. Thus, theWireless Laparoscopic Robot, the first module, is com-pleting the last preliminary steps before experimentson humans.

The certification procedure is not completely unifiedin the European Union. Every category involves differ-ent requisites for the placing on the market of a product.The Wireless Laparoscopic Robot fits into one of thecategories demanding less requirements, thanks to sev-eral aspects of its design, like the passive wrist, the bat-tery supply or the lack of a computer and an operatingsystem. This simplicity, in the design as well as in thecertification procedure, diminishes the cost associatedto the placing on the market of the system.

As a part of a previous stage, before the clinical trialson humans, several experiments on animals have beencarried out. These were performed in local mode, thatis, without using the other two modules of the system.One of the tested aspects was the set-up time, measuredfrom the moment the robot is entered into the operatingroom to the instant it can be commanded by the surgeon.

Once the robot is located in the desired point, only abutton must be pushed to start working. This actionlaunches the initialisation, as well as the local interface,which is based on speech recognition. If the traininghas been previously completed, the set-up time is lessthan two minutes. On the contrary, if it is performed inthe operating room, the set-up time reaches six minutes.

The surgeon can decide to withdraw the robot, forany reason (e.g., because of a conversion of the pro-cedure from laparoscopy to laparotomy). Then the re-quired time (withdrawal time) is approximately half aminute: the only required actions are disengaging thelaparoscope from the end-effector (without any tool),releasing the wheel brakes and then drawing back therobot.

Up to date, several procedures on experimentationanimals have been carried out including cholecystec-tomies, Nissen funduplicatures and anastomosis (notincluded in the set of procedures, but similar in dis-position and zone of interest to those of the cholecys-tectomy). The main purpose of the performed exper-iments is to compare the efficiency between the robotand a human assistant. Nevertheless, obtaining deci-sive results is difficult since common indices of be-haviour for the robot and a human assistant cannot bedefined. In particular, the high precision when locat-ing the end of the laparoscopic inside the abdomen is a


remarkable feature of the robot. This magnitude is im-possible to acquire when a human assistant operates thecamera. In the other hand, some facts, as the surgeonsfatigue or their comfort, cannot be estimated becauseof its subjective nature. However, during these trialsthe involved surgeons expressed their satisfaction aboutthe system performances. Despite they received notraining about the speech recognition interface, morethan 90% out of the commands were successfully rec-ognized. During these trials the correspondence be-tween the information obtained through the proposedvalidation procedure and the actual performance of theWireless Laparoscopic Robot was confirmed. No inter-ference between the surgical staff and the manipulatorwas reported, while the movement of the laparoscopiccamera fulfilled the expectations.

8. Conclusions

This paper is focused on design and validation ofsurgical robots. A set of requirements and constrainshas been presented. According to it, a robotic assistanthas been proposed. The WLR robot has been designedas a three actives degrees of freedom manipulator with apassive wrist which consists of two joints perpendicularto each other.

The proposed system has been validated through asimulation tool based on the configuration space. Thus,the results have demonstrated that the WLR robot isappropriate to develop the tasks it has been designedfor. In addition, the simulation has permitted choosingthe most suitable robot configuration (right elbow, leftelbow) for each considered procedure. In the end, sev-eral experiments with alive animals has been performedin an experimental operating theatre, which confirmsthe previous validation process and verify the good re-sponse of the WLR robot.

Acknowledgments

The work described in this paper was supported bythe Spanish Government through the research projectFIS 00/0050-02.

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on laparoscopic robot design and validation

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