Research ArticleIn Silico Investigation of a Surgical Interface for Remote Controlof Modular Miniature Robots in Minimally Invasive Surgery

Apollon Zygomalas,1 Konstantinos Giokas,2 and Dimitrios Koutsouris2

1 Life Science Informatics-Medical Informatics, Department of Surgery, University of Patras, Rio, 26500 Patras, Greece2 Biomedical Engineering Laboratory, School of Electrical and Computer Engineering, National Technical University of Athens,15780 Zografou, Athens, Greece

Correspondence should be addressed to Apollon Zygomalas; azygomalas@upatras.gr

Received 30 May 2014; Accepted 3 August 2014; Published 9 September 2014

Academic Editor: Peng Hui Wang

Copyright © 2014 Apollon Zygomalas et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Aim. Modular mini-robots can be used in novel minimally invasive surgery techniques like natural orifice transluminal endoscopicsurgery (NOTES) and laparoendoscopic single site (LESS) surgery. The control of these miniature assistants is complicated. Theaim of this study is the in silico investigation of a remote controlling interface for modular miniature robots which can be usedin minimally invasive surgery. Methods. The conceptual controlling system was developed, programmed, and simulated usingprofessional robotics simulation software. Three different modes of control were programmed. The remote controlling surgicalinterface was virtually designed as a high scale representation of the respectivemodularmini-robot, therefore amodular controllingsystem itself. Results. With the proposedmodular controlling system the user could easily identify the conformation of themodularmini-robot and adequately modify it as needed. The arrangement of each module was always known. The in silico investigationgave useful information regarding the controllingmode, the adequate speed of rearrangements, and the number ofmodules neededfor efficient working tasks. Conclusions. The proposed conceptual model may promote the research and development of moresophisticated modular controlling systems. Modular surgical interfaces may improve the handling and the dexterity of modularminiature robots during minimally invasive procedures.

1. Introduction

Minimally invasive surgery is nowadays a consolidated alter-native to the traditional open surgery for a number ofoperations. Minimally invasive surgical techniques includelaparoscopy, single site surgery, and natural orifice translu-minal endoscopic surgery. Laparoscopy has proved to be lesstraumatic for the patient, with minimal operative blood loss,less postoperative pain, accelerated recovery, and excellentcosmesis. A new promising minimally invasive approach isthe laparoendoscopic single site (LESS) surgery, also knownby a variety of other names (e.g., single incision laparoscopicsurgery (SILS) and reduced port surgery (RPS)). LESS hasbecomepopular among surgeons as an alternative to standardlaparoscopic surgery for a variety of operations [1]. Theevolution of minimally invasive surgery to the natural orificetransluminal endoscopic surgery (NOTES) began in 2004

when Kalloo et al. published his study on the transgastricsurgery [2]. NOTES is very fascinating in terms of surgicaltechnique but its evolvement seems to be strictly connectedto technology [3].

Informatics and robotics offer novel tools to the modernsurgeon.The development of in vivo miniature robots for usein surgery is nowadays a reality with potential advantagesand possible application in minimally invasive surgery inthe future [4, 5]. A revolutionary idea is the developmentof modular miniature robots. Modular miniature robotsare composed of small subunits (modules) which couldbe assembled and construct a functional mini-robot [6].Controlling modular mini-robots is rather complicated. Itis essential therefore to develop appropriate software andhardware technology that will provide the surgeon with allnecessary information and give him an easy and precisecontrol of his miniature assistants. Using robotic simulation

Hindawi Publishing CorporationMinimally Invasive SurgeryVolume 2014, Article ID 307641, 5 pageshttp://dx.doi.org/10.1155/2014/307641

2 Minimally Invasive Surgery

Modular remote controlling system

96mm

Mini-robot Y

X Z

40mm 40

mm

Figure 1:Themodular remote controlling system (MCS) is identicalto the modular miniature robot but in large scale, thus four timeslarger.

software, we can virtually develop mini-robots and investi-gate their capabilities in silico.

The aim of this study is the experimental in silicoinvestigation of a conceptual model of a surgical remotecontrol interface for modular miniature robots that can beused in minimally invasive surgery.

2. Materials and Methods

The development of our conceptual model is based onthe idea that the user-surgeon could handle a modularremote controller similar, but in large scale, to the intra-abdominal modular mini-robot that he wants to control.He then could move the controller’s modules as he tries tofind a suitable configuration for his miniature assistant. Wetherefore designed a simple modular snake-like miniaturerobot consisting of four subunits and its respective modularremote controller and simulated them (Figure 1).

For the development and simulation of the controller andthe respective mini-robot, we used the Webots version 6.0.0(Cyberbotics, Switzerland) [7]. All modules were designedusing simple 3D basic geometry objects. One cube and twocylinders construct the body of each module. The dimensionof a mini-robot module is 24mm × 10mm × 10mm. Themodular remote controlling system (MCS) subunits havethe same structure as those of the mini-robot but withdimensions of 96mm × 40mm × 40mm, thus four timeslarger. This size should be rather handy for a surgeon.

We designed two different types ofmodules: a connectionmodule and a camera module (Figure 2). All modules aresymmetrical in 𝑍 axis and are equipped with four activerotational servomotors which provide the assembled mini-robot with motion. Two servomotors are positioned on thefront side and two on the rear side. In this way, one motorgives a 180∘ arc motion on axis 𝑌, so as to have a motionof 90∘ left and 90∘ right and the other motor gives a 360∘motion on axis𝑍 (or𝑋) for a complete rotation of themodulewhen connected (Figure 2). Electromagnetic symmetricalconnectors with controlled connection/disconnection arepositioned on the front and rear sides of each subunit. Thecamera subunit of the mini-robot is equipped with two colorcameras and two white light-emitting diodes (LEDs). Thecamera module of the controlling system does not have

Y

X

Z

LEDsCamera

Connector

Connection module Camera module

Figure 2: A connection module and a camera module. A servomo-tor gives motion on an arc of 180∘ on axis 𝑌, (90∘ left and 90∘ right).A second motor gives a 360∘ motion on 𝑍 (or𝑋) axis.

functioning cameras. Finally, each subunit is provided withan emitter and a receiver to achieve a wireless bidirectionalmodule ID-based communication between the MCS and themini-robot.

One red and one blue LED are mounted on each MCSsubunit. These LEDs provide the user with visible informa-tion regarding the connection state.The blue LED is activatedwhen the front connector is inside the magnetic field ofthe paired connector of another module and red LED isactivated when the rear connector is inside the field. Detailedelectromechanic robotic components were not designed.Thiswas out of the aims of this study.

Three different controlling modes of the modular mini-robot were programmed. (A) The first is an absolute master-slave mapping mode where the configuration of the MCSis transmitted in real time to the modular mini-robot. Forexample, when the second module of the MCS is rotating,simultaneously the second module of the mini-robot per-forms an identical motion. (B) The second is a postactionmode (delayed master-slave mapping) in which the surgeoncan move the modules of the MCS to achieve a preferredconformation and then transmit the new arrangement tothe modular mini-robot when he desires (e.g., by pressingan appropriate button). (C) In the third mode, the usercan select a preprogrammed simple motion or configurationfrom a list of actions. The MCS and the miniature robotexecute simultaneously the command. Snake-like sinusoidalmotions were programmed to achieve robot locomotion.Motion scaling was incorporated for accurate manipulationduring the surgical procedure.

The C programming language with special libraries wasused for the development of the simulation’s programmablecontrollers using the built-in editor and compiler of Webots.All connection modules use a programmatically identicalcontroller that positions the servomotors using a module ID-based control table. Camera modules use another controllerwhich in addition implements the control of the videocamera.

A number of physics parameters were defined using thephysics nodes ofWebots.Mass distribution, gravity force, andfriction parameters were set, allowing the physics simulationengine to compute realistic forces.

Intra-abdominal structures like the intestine, the liver,and the gallbladder were designed using simple 3D objects

Minimally Invasive Surgery 3

Y

X

Z

Liver GallbladderCystic artery

Cystic duct

Left/right camera views

Mini-robotIntestinal loops

Figure 3: The intra-abdominal environment was simulated bysimple 3D structures representing the intestine, the liver, and thegallbladder. On the lower left corner of the figure, the mini-robot’sonboard camera views are shown.The gallbladder is suspended by agrasper like mini-robot (refer to [15]).

(Figure 3).The intraperitoneal environment was simulated inorder to investigate vision and motion of the modular mini-robot in relationship to the controlling capabilities of theMCS.

Remote control was investigated regarding configuration,kinematics, coordination, localization, and user interaction.

3. Results

Themodular controlling system allowed the user to immedi-ately determine the conformation of themodularmini-robot.Real-time mode allowed for a standard use of the mini-robotexecuting pair commands as needed. This was the simplestway to control the miniature robot when it was stationary,thus while operating on tissues, for example. It seems tobe impossible to provoke locomotion of the mini-robotusing the real-time mode, as this procedure needs a quickand precise coordination of all the subunits. Fast changesof the conformation using rotational movements with over0.25 rad/sec resulted in unpredictable positioning of the robotmainly due tomoment of forces (Table 1).The actuation speedis user-dependent. An actuation speed limiter resolved theproblem but restricted the user performance. It was easierto operate in real-time mode when the rear subunit of thesystem was fixed, thus a configuration similar to an externalmagnetic anchoring system (MAGS) [8]. It was difficult tocontrolmore than four subunits in real-timemode.The largernumber of subunits complicated the behavior of the mini-robot because of additional forces like moment forces andfriction which the user has to consider mentally in real-time.

The postaction mode helped to find different conforma-tions without synchronous modification of the micro-robot.The user was able to find the most suitable configuration forhis activity. However, in many occasions, using this modesignificantly changed the arrangement and orientation ofthe intra-abdominal robot in an unpredictable way. Thisfact is caused by the torque which was developed duringhigh speed (>0.25 rad/sec) rotational motions of the modulesand subsequently due to collisions with some surroundingstructures. For that reason, the postaction mode speed wasset to 0.1 rads/sec. This mode proved useful when it was usedto predict a stable configuration for operation.The postactionmode is by default ineffective for locomotion. It seems that

there is no limit in the number of subunits that can be handledby this controllingmode, although the higher the number, theharder the control and the prediction of its result.

The preprogrammed action mode proved to be the onlyone to provide an acceptable locomotion of the mini-robotand a quick rearrangement of its subunits. During theexecution of commands under this mode, the MCS wasaccessible to the operator. However, the operator could onlystart and stop a preprogrammed action and not modify it.There seems to be no limit in the number of subunits that canbe handled using this mode. Regarding robot locomotion,the more the subunits used, the better the results were.High rotational speed (>0.25 rad/sec) of the servomotorsgave acceptable locomotion of the robot. Nevertheless, ifa preprogrammed conformation without locomotion wasdesirable, then the high rotational speed of the servomotorsresulted in some occasions to unpredictable positioning ofthe robot mainly due to torque. A speed limit of 0.1 rad/secwas set for all the preprogrammed actions except for thesinusoidal locomotion.

The configuration of the modular mini-robot was alwaysidentified only by observing the MCS conformation. How-ever, its positioning and orientation were not predictable allthe time. This principally occurred due to collisions withthe surrounding structures or slippage (i.e., on intestine)(Figure 4). Another reason for the unpredictable positioningwas the development of considerable torque during highspeed rotational motions (>0.25 rad/sec). The mini-robotexecuted all the commands sent by the MCS but its modulesmotion depended on their interaction with the surroundingstructures which in some occasions blocked amotion or evenforced a disconnection of a module.

The LEDs of the MCS provided visual informationregarding the connection state of the miniature modules.This proved to be useful while constructing the modularmini-robot. It was also helpful when accidental or voluntarydisconnection occurred. All the commands sent by theMCS were logged in order to let the user read informationregarding his actions.

4. Discussion

Surgery is historically connected with scars and pain. Thisaspect can be eliminated by minimally invasive surgeryand especially with LESS and NOTES. However, software,hardware, novel surgical tools, and approaches should beevolved. Miniature robots can be equipped with surgicaltools and sensors in order to provide information from theabdominal cavity and the possibility of remotely controlledsurgical operations [9]. Miniature robots could be handledeven by nonspecialized personnel and remote-controlled bysurgeons miles away from the patient [10].

The use of modular mini-robots for minimally invasivesurgery poses difficulties to surgeons related to the coordi-native controlling of the robotic subunits. A single moduleby itself cannot operate, but modules arranged together canachieve complex tasks and controlling such a system could berather difficult. The surgical robots are commonly controlled

4 Minimally Invasive Surgery

Modular remote controlling system

Mini-robot

Y

X Z

(a)

Modular remote controlling system

Mini-robot

(b)

Figure 4: (a) Identical conformation betweenMCS andmini-robot with slightly different (acceptable) positioning of the second. (b) Identicalconformation but very different orientation and positioning.

Table 1: Modular remote controlling system operating modes.

Operating mode Actuation speed Ideal number ofmodules Pros Cons

Absolute master-slavemapping User-dependent 4 Natural operation User dependent action

speed controlDelayed master-slavemapping Set to 0.1 rad/sec 4–6 Predictable conformation Unpredictable positioning

and orientation

Preprogrammed Set according to the desiredaction 4–6 Locomotion No user interaction

from outside the patient’s body under indirect video assistedvision with the use of a joystick-like surgical interface [4, 11,12]. Snake-like modular mini-robots can be in some casescompared to flexible endoscopes. Having this in mind, weshould consider the study of Allemann et al. who provedthat the use of robotized endoscopes with joystick interfaceis insufficient to enhance immediate intuitiveness of flexibleendoscopy for NOTES [13]. Because of the complexity oflocomotion and the precision of the task that modular mini-robots should perform, novel remote controlling systemsshould be developed in order to make the surgeon, and notthe engineer, operate. The surgeon who will use modularminiature robots should feel safe and relaxed; therefore, aremote controlling system should be simple and accurate.

Wortman et al. presented a miniature robot prototype inwhich surgical interface is a kinematically matched master-slave configuration scaledmodel of the robot’s arms [14].Thismaster system allows the surgeon to control the robot bydirectly mapping each joint. The scale of master-slave is 1.8 : 1in length. Our conceptual model has the same basic idea ofpairing master-slave configuration but is proposed for totallyintracorporeal modular miniature robots (internal robots)[15]. The system of Wortman et al. provides the user withdirect control over each joint of themini-robot, allowing for abetter sense of control. However, because none of the joints isprovidedwithmotors, themaster arm cannot be held in placewhen the robot arm is locked.Themastermust be returned toan orientation similar to the robot before it can be unlocked.Our conceptual model of controller is equipped with motorsand by default its configuration is always the same as that ofthe intra-abdominal miniature robot.

Our experimental investigation gave some useful infor-mation regarding the type of control, the working speedof the servomotors, and the number of modules that amodular robot can have in order to be efficiently controlled(Table 1). Although the real-time control of the mini-robot isthe most natural to be utilized during a surgical operation,it is difficult to control more than four subunits and itis impossible to induce locomotion of the whole roboticsystem.On the other hand, the usefulness of postactionmoderesulted in doubt. This situation was created because of theunpredictable interaction of the robotic subunits with thesurrounding structures during rearrangement. Furthermore,if the rotational speed of the servomotors was high duringthe rearrangements, then the torque was considerable. Thisfact should be taken into consideration in such a miniaturescale. However, using this type of control, it was easier to findan appropriate conformation for a stable operational robot.Thepreprogrammedmodewas the only one that provided therobot with locomotion. However, when activated, the robotconformation changes as the preprogrammed commandsneed, and this sometimes may have unpredictable resultsregarding the interactions with the surrounding structuresand the modules moment forces as mentioned above.

The positioning of the subunits on the modular mini-robot was always known and in the case of the real world thesurgeon could virtually “touch” his mini-robot through histwin big brother remote controller. Slow and steady motionof the modules is desirable in order to minimize torque andachieve desirable conformation, positioning, and orientation.However, a more detailed study by a team of roboticsspecialists and the use of more sophisticated simulation

Minimally Invasive Surgery 5

libraries that take into account all the characteristics of therobot and the environment in which it operates are required.It is essential to construct and study in vivo such a mini-robot and its surgical interface. Effective cooperation betweensurgeons, robotics specialists, and informatics specialists isfundamental for a successful use of miniature robots inminimally invasive surgery.

Although this was a simple and basic simulation, it maybe useful for a future construction of remote controllingsurgical interfaces that can be used in order to controlmodularminiature robots duringminimally invasive surgicalprocedures. Another idea is to modify this conceptual modelas a “hand glove”which a surgeon canwear and control with ithis miniature assistants (everymodule could be a phalange ora part of the upper limb, e.g., the front camera module pairedto a finger, the second module paired to the hand, the thirdmodule paired to the forearm, and the fourth module pairedto the arm). The present work represents only a conceptualin silico experimental study with no intention to solvemechanical, electrical, and robotic engineering problems ingeneral.

5. Conclusions

The design of the proposed conceptual model may facilitatethe development of more sophisticated and complex mod-ular controlling systems. Modular surgical interfaces mayimprove the handling and the dexterity of modular miniaturerobots during minimally invasive procedures.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

Acknowledgments

This work represents a part of the study conducted as aMaster of ScienceThesis in Medical Informatics-Life ScienceInformatics during 2008 and 2010 at the University of Patras,Greece. Thanks are due to Professor Hatziligeroudis andProfessor Papatheodorou (Department of Computer Engi-neering and Informatics, University of Patras) for their helpon computer programming and thesis correction.Thanks aredue to Dr. Drosou (Biologist) for her indications on tissuebehavior and snakes locomotion.

References

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