Auton Robot (2006) 21:165–183DOI 10.1007/s10514-006-8546-1

Design of the ATRON lattice-based self-reconfigurable robotEsben Hallundbæk Østergaard · Kristian Kassow ·Richard Beck · Henrik Hautop Lund

Accepted: 13 March 2006 / Published online: 25 August 2006C© Springer Science + Business Media, LLC 2006

Abstract Self-reconfigurable robots are robots that canchange their shape in order to better suit their given taskin their immediate environment. Related work on aroundfifteen such robots is presented, compared and discussed.Based on this survey, design considerations leading to a noveldesign for a self-reconfigurable robot, called “ATRON”,is described. The ATRON robot is a lattice-based self-reconfigurable robot with modules composed of two hemi-spheres joined by a single revolute joint. Mechanical designand resulting system properties are described and discussed,based on FEM analyses as well as real-world experiments. Itis concluded that the ATRON design is both competent andnovel. Even though the ATRON modules are minimalistic, inthe sense that they have only one actuated degree of freedom,the collective of modules is capable of self-reconfiguring inthree dimensions. Also, a question is raised on how to com-pare and evaluate designs for self-reconfigurable robots, witha focus on lattice-based systems.

Keywords Robotics . Self-reconfigurable . Morphology .

Mechanics . Design

1. Introduction

Self-reconfigurable robots are robots that can change theirshape in order to better suit their given task in their imme-diate environment. Research on self-reconfigurable robotsrelates well to the current trend in modern artificial intelli-

E. H. Østergaard (�) · K. Kassow · R. Beck · H. H. LundThe Maersk McKinney Moller Institute for ProductionTechnology, University of Southern Denmark,Campusvej 55, DK-5230 Odense M, Denmark

gence, where increasing attention is given to the relationshipbetween form and function, body and brain.

At present time, this technology is not used in any applica-tion, partly because there are other cheaper and better testedmethods, partly because there still is a lot of research workto be done on building and controlling self-reconfigurablerobotic systems. However, in the long term as productiongets cheaper and control gets better, there is a wide rangeof potential future application areas, such as nano-robotics,space-robotics, disaster-area robotics, assisting the disabled,toys, automatic construction and flexible production lines.In 2004 NASA launced “SuperBot” (Shen et al., 2006), anambitious project to develop self-reconfigurable robots fornavigation and life-protection on Mars.

During the last fifteen years, around fifteen research pro-totype self-reconfigurable robots have been built as roboticmodules that can physically connect to each other. Based ona survey of these systems, a novel design for a lattice-basedself-reconfigurable robot was created, called “ATRON”. Thisarticle describes considerations leading to the ATRON de-sign, and some details of the actual ATRON hardware.

2. Related work

Much work has so far been published in self-reconfigurablerobotic systems, both on constructing such systems, and oncontrolling them. This article focuses on the hardware andmorphology aspects of the self-reconfigurable robotic sys-tems, not on the control aspects.

Since Fukuda’s ground-breaking work on the CEBOT(Fukuda et al., 1989a, b, 1990; Fukuda and Nakagawa,1990) system, there has been a steadily increasing interestin research on self-reconfigurable robots. Published workexists on around fifteen physical prototypes, both 2D and 3D

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systems. All the systems use a population of either one or twokinds of modules. In the design of all the 3D systems, dealingwith gravity is of course a major concern. For most of the 2Dsystems, gravity only plays a role in friction with the ground,but in “RIKEN Vertical” (Hosokawa et al., 1998) and in“Chobie” (Inou et al., 2003) the system self-reconfigures inthe vertical plane, and thus has to deal with gravity-relatedissues such as bending and configuration stability.

In order to make self-reconfiguration less complicated,most of the existing 3D systems exploit a lattice struc-ture for easier alignment of the connectors during self-reconfiguration. All previously reported lattice-based 3Dsystems, including the Telecube (Vassilvitskii et al., 2002),M-TRAN (Murata et al., 2000), 3D-Unit (Murata et al.,1998), and Molecule (Kotay et al., 1998) exploit a sim-ple cubic lattice. Each of the existing systems has a uniquemechanical module design, all with unique implications onrobot motion capabilities, structural stability, speed of re-configuration etc. An important and difficult aspect of themechanical design of each of the systems is the design ofthe connector. Different approaches to the connector designhave been tried. A pin/hole (Yoshida et al., 2000), perma-nent magnets (Hosokawa et al., 1998; Murata et al., 2000),permanent shifting magnets (Vassilvitskii et al., 2002), elec-tro magnets and mechanical hooks (Kotay et al., 1998) areamong the approaches found in related literature.

A few systems border what we consider self-reconfigurable robots. The RBR system (Sawada et al., 2004)by Hayashi et al. is a modular robotic system for operationon the international space station. It consists of three six-DOF (degrees of freedom) arms connected to a central hub,and can self-reconfigure by joining the arms. The goal ofthe RBR system differs somewhat from the purpose of otherself-reconfigurable robotic research. Another system of rele-vance is the Tetrobot system by Hamilin, Lee and Sanderson(Lee and Sanderson, 2001, 2002). This system is not self-reconfigurable, but a modular robot that consists of nodesconnected by linear actuators.

2.1. Morphology taxonomy

For self-reconfigurable robotic systems, there seems to be atight coupling between the morphology of the module andthe capabilities of the robot as a whole. However, there is nogeneral method for achieving the individual modules’ mor-phology from the requirements of the whole robot. There-fore, it is interesting to study existing module morphologiesexamining their benefits and disadvantages.

Several different metaphors have been used when think-ing about self-reconfigurable robots. One division seemsto be between Discrete and Continuous robotic systems.At Xerox PARC, research systems are divided into ChainTypes and Lattice Types. Whereas M. Vona and D. Russ

talk about molecules in a Crystal, where blob bots andswarms might be regarded as Fluid. In the following, wewill distinguish between lattice-type systems and chain-typesystems.

2.1.0.1 Lattice-type systems exploit lattice regularity whenaligning connectors during self-reconfiguration. This allowsfor faster/easier self-reconfiguration. However, assumingthat all modules conform to the lattice can be problematicfor systems with very many modules.

2.1.0.2 Chain-type systems does not exploit a lattice whenaligning connectors for self-reconfiguration, and thus arerequired to have some other method for connector alignment.Joints and connectors have to be able to support chains ofseveral modules.

Notice that these two types do not contradict, and severalsystems do indeed claim to be both at the same time, such asM-TRAN and SuperBot.

2.2. Module motion capabilities

One important area to be further investigated is how themodule design affects the motion capabilities of the system.It seems that cleverly designed modules can severely reducethe complexity involved in reconfiguring. As an example,consider the Fracta system (2D) and the M-TRAN system(3D). In the Fracta system, any surface module can move toany of its neighbour positions as a single actuator command.In the M-TRAN system, moving to an adjacent position canrequire anything from five actuator commands and up, andmight also be impossible.

A theory that handles the relationship between moduledesign and system capabilities would be very useful whendesigning these systems. Efforts in this direction have beensparse, even though a few papers have addressed these prob-lems. In Kotay and Rus (1999) concave and convex tran-sitions are defined and identified as an important property,and it is shown that the Dartmouth Molecules are able toperform these transitions. In Yim et al. (2001b), Yim et al.define a class of self-reconfigurable robots, called the “Pro-teo Class” (similar to the definition of “Metamorphic Robot”by Pamecha et al. (1997)), and discuss motion capabilitiesof such a system.

Building self-reconfigurable robots is a complex trade-offbetween many mechanical, electrical and control consider-ations. Still, work in this area is in an exploratory phase,where systems are built and then later understood. Each ofthe surveyed systems represents a point in the design spaceof self-reconfigurable robots. As more and more points areexplored, hopefully a greater picture will emerge, and a the-ory for designing self-reconfigurable robots can be formed.For now, we can only make educated guesses.

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2.3. Motivation and applications

In the surveyed literature, the arguments for self-reconfigurable robots have been that they have the potentialto be

Robust They have self-repair capabilities arising from theirinherent redundancy.

Flexible Flexibility in performing various tasks due to self-reconfiguration.

Cheap Mass production can reduce the price of the indi-vidual modules to a degree where they can compete withfixed-configuration robots.

A number of application areas has been mentioned, suchas obstacle avoidance in highly unstructured environments,growing structures such as bridges, envelopment of objects,inspection in constrained environments (Pamecha et al.,1997), planetary exploration, growing satellite antennas,self-healing solar panel arrays and life-support on Mars.

2.4. Previously reported systems

Tables 1–3 compares the systems from the studied literatureon a number of parameters. Table 1 presents a comparisonon some geometrical properties. Table 2 summarizes someelectrical characteristics, and Table 3 summarizes some ofthe systems’ physical properties.

Each of the surveyed systems is the product of anumber of compromises between mechanical, electricaland control considerations. Also, the budget and personnelcompetences/skills are different for the different projects.We cannot say that any system is better or worse than theothers. What we can do, is that we can try to learn from theexperience that the building of these systems has generated.Since the connector mechanism is such an important partof any self-reconfigurable robotic system, the differentapproaches will be described briefly.

2.5. Connector mechanisms

As argued in Khoshnevis et al. (2001) one of the ma-jor issues in design of a self-reconfigurable robotic sys-tem, is the design of the attachment mechanism. In thesurveyed papers, attachment mechanisms using magnets,and attachment mechanisms using mechanical latches werethe most dominant. In all the presented systems, exceptFracta, the attachment mechanisms consume no power whileattached.

2.5.1. Shape memory alloy and pin/hole mechanism

The Polybot G2 and CONRO use similar attachment mech-anisms. The mechanism for Polybot G2 is shown in Fig. 1.

Fig. 1 Polybot G2 attachment mechanism

Citation from the Polybot web site (about Polybot G2):“Four grooved pins enter four holes and are grabbed bya latching mechanism that is released by a shape mem-ory alloy actuator. Each face has a 4 times redundantcustom made hermaphroditic electric connector to enablepower and communications to be passed from module tomodule”.

This mechanism has the advantage that attaching and stay-ing attached is a passive process. Actuation is only requiredwhen modules need to detach.

The MEL Micro unit also uses Shape Memory Alloy(SMA) and a pin/hole mechanism. In the Micro unit, SMAis used in the female piece to mechanically lock the malepiece by driving two pins through small holes in the malepiece.

2.5.2. Electro magnets

The first two prototypes of the Robotic Molecule usedelectro magnets for connection. In the third prototype,electro magnets were discarded because of high powerconsumption, and a gripper-type connector was usedinstead.

A combination of permanent magnets and electro mag-nets is used in the Fracta robot, as shown in the left sideof Fig. 2 (Murata et al., 1994). Fracta is unique among thereviewed systems, since the electro magnets from the attach-ment mechanism are also used for motion, as shown in theright side of Fig. 2. A Fracta module contains no movingparts.

2.5.3. Permanent magnets

Version I and II of the M-TRAN modules use a combinationof permanent magnets, shape memory alloy, and springs, asshown in Fig. 3 (Murata et al., 2000).

The Telecube uses a “Switching Permanent MagnetLatch” as attachment mechanism. Attachment/detachment

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Table 1 Geometrical characteristics of various self-reconfigurable robotic systems. The systems are sorted firstly from 2D toward 3D andsecondly rougly by their mechanical complexity. The ATRON system is included for comparison

System DimActuat.DOF

Connectors(Actuated)

Lattice MorphologySchematic

MEL, Fracta (Murata et al., 1994) 2D 0 6 (3) Hexagonal

U. Ryukyus, Gear-Type Unit (Tokashiki et al., 2003) 2D 1 6(0) Hexagonal

JHU, Metamorphic (Chirikjian, 1994) 2D 3 6 (3) Hexagonal

Dartmouth, Crystalline (Rus and Vona, 2001) 2D 1 4 (2) Square

MEL, Micro-unit (Yoshida et al., 2000) 2D 2 4 (2) Square

TIT, Chobie (Inou et al., 2003) 2D (Vert.) 2 4 (2) Square

RIKEN, Vertical (Hosokawa et al., 1998) 2D (Vert.) 2 1 (1) Square

USC/ISI, Conro (Castano et al., 2000) 3D 2 4 (1) None

Xerox PARC, Polybot (Yim et al., 2001a) 3D 1 2 (2) Cubic

MEL, M-TRAN (Murata et al., 2002) 3D 2 6 (3) Cubic

USC/ISI, SuperBot (Shen et al., 2006) 3D 3 6 (6) Cubic

Xerox PARC, Telecube (Vassilvitskii et al., 2002) 3D 1 6(6) Cubic

MEL, 3D-Unit (Murata et al., 1998) 3D 6 6 (6) Cubic

TIT, Pneumatic (Inou et al., 2002) 3D 4 4 (4) Cubic

Dartmouth, Molecule (Kotay et al., 1998) 3D 4 10 (10) Cubic

CMU, I-Cubes (Unsal and Khosla, 2000) 3D 3 2 (2) Cubic

Maersk Institute, ATRON (Jørgensen et al., 2004) 3D 1 8 (4) Surface-Centred Cubic

♀: Male connector; : Female connector; �: Unisex or hermaphroditic connector.

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Table 2 Electricalcharacteristics of someself-reconfigurable roboticsystems. The ATRON system isincluded for comparison

System CPU Power Communication Sensors

Fracta Z80 nob optical noneCrystalline Atmel AT89C2051 yes optical joint positionMicro-Unit Basic Stamp 2c no electrical noneChobie nonec no none forceCONRO Basic Stamp 2 yesa optical docking aidPolyPod Motorola

MC68HC11yesa optical&electrical joint position,

docking aid, forcePolyBot Motorola PowerPC

555yes optical&electrical joint position,

docking aid,orientation, force

M-TRAN 3×PIC, 1×TNPM yes electrical joint position,orientation

TeleCube no optical docking aid3D-Unit nonec no none joint position and

angleMolecule nonec no none noneI-Cubes PIC 16C63A/73Bc yes electrical joint positionATRON Atmel MEGA128L yes optical joint position,

orientation andproximity

aTest configurations showed thatthe use of external batteries wasrequired.bPower is supplied through thesurface that the modules areplaced on.cControlled by remote host.

Table 3 PhysicalCharacteristics of someself-reconfigurable systems. TheATRON system is included forcomparison

System Weight (g) Dimensions (cm) Connector type Unisex

Fracta 1200 ø12.5 Electro Magnets NoGear-Type Unit ø6 Perm. Magnets NoMetamorphic Mech. Hooks NoCrystalline 375 5 × 5 × 18

(contracted)Mech. Lock No

Micro-Unit 80 4 × 4 × 8 Mech. Hooks NoChobie 500 8 × 8 × 7.5 Mech. Grooves NoVertical Perm. Mag. and

Mech. ArmsNo

CONRO 115 10.8 × 5.4 × 4.5 Mech. Pin/Hole, SMA NoPolyPod NoPolybot 200 5 × 5 × 5 Mech. Pin/Hole, SMA YesM-TRAN 400 6 × 6 × 12 (versions I&II)

SMA+PermMagnets, (versionIII) Mech. Hooks

No

TeleCube 6 × 6 × 6 (contracted) Switching Perm.Magn

Yes

3D-Unit 7000 26.5 from tip to tip Mech. Grasp YesMolecule Mech. Hooks NoI-Cubes 200 6 × 6 × 6 Mech. Lock NoATRON 850 ø11 Mech. Hooks No

is done by “routing the flux lines of permanent magnets sothat the device either extends the magnetic flux or hides themagnetic flux internally1.”

1 From http://www.parc.xerox.com/spl/projects/modrobots/lattice/telecube/index.html

2.5.4. Mechanical locking

The current trend in self-reconfigurable robotic systemsseems to be to use mechanical locking for connections.Older systems, such as the I-CUBES shown in Fig. 4(Unsal et al., 1999), use a connector where a male part

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Fig. 2 Left: Fractas attachmentmechanism. Right: Motion ofFracta modules

Fig. 3 M-TRAN I and II attachment mechanism, a combination ofpermanent magnets, non-linear springs and a shape-memory-alloy coil

is inserted into a hole and rotated, and the pin locks themale part in place. The pin is actuated and can be pulledin to enable release of the male part. Due to the motion ca-pabilities caused by the mechanical design, the DartmouthMolecule design does not allow big connection surfaces,like the I-CUBES. In stead, the Molecule has point contactbetween modules, and a mechanical attachment mechanismfor dealing with this constraint is described in Kotay andRus (2000).

Currently, connecting hook mechanisms, such as theone used in the ATRON system, seem to gain popular-ity. The newest generation of the M-TRAN system alsouses a similar kind of hooks, and the SuperBot projecteven promises a unisex connector of this kind, even

Fig. 4 The I-Cubes attachment mechanism

though there have been no publications on this connectoryet.

2.6. Summary and discussion on related work

The fifteen or so systems that have been documented so far,have different mechanical and electrical characteristics andeach is interesting to study to find a relation between moduledesign and system motion capabilities.

An important issue in the field of self-reconfigurablerobots is scalability. However, for surveyed systems it isnot particularly clear how the system will scale as the num-ber of modules increases. How can the “weak” actuators ofeach module be used to create a ‘strong” global force? In thecase of Crystalline and Telecube it is pretty straightforward,but in the case of I-Cubes and many of the other lattice-based systems, it is hard to see how this would be possible.Also mechanical stability is a problem. For example, evenfor short chains, a horizontal chain of Telecubes will bendquite a lot due to gravity, so that the end module will not bewithin lattice tolerances.

Another important issue is the use of sensory information,although only very little work has so far been published onthe use of sensors during self-reconfiguration. The reasonfor this is probably that most of the systems still have morebasic problems to deal with than the awareness of the sur-rounding environment. In Støy et al. (2002) sensors are usedfor controlling the walking gait of the CONRO robot, but inthis work the robot does not self-reconfigure. In Inou et al.

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(2003) a force sensor is used to trigger a pre-programmedsequence of actions that stabilizes the structure by self-reconfiguration.

From the surveyed papers we gathered that:

– Based on the number of reports on succesful self-reconfiguration for lattice- versus non-lattice-based sys-tems, self-reconfiguration for non-lattice-based systemsseems to be much harder.

– Systems which only have actuation parallel to the direc-tion of connection can never rotate any modules, and thuscannot ever change their orientation.

– There seems to be a conflict between simplicity of moduledesign and simplicity of system motion capabilities.

– Reports on using sensors for controlling self-reconfiguration are still sparse.

Studying the mechanics of the existing 3D systems re-vealed that

– Mechanical simplicity is essential when designing, con-structing and maintaining a self-reconfigurable system.

– The connectors are often a weak point of the respectivedesigns. Many of the surveyed systems have problemswith the stiffness of the structure when many modules areconnected in a chain.

– Stiff actuators with good torque are attractive, as we needto hold and lift modules against gravity while keepingpositions within some tolerance in the lattice structure.

3. Basic ATRON module design

We desire stiff and strong joints as well as stiff and stableconnectors. By seperating the mechanics of the connectorsfrom that of the joints, more space is available around eachof the mechanisms for stabilizing structure.

3.1. Basic actuator design

The basic design that we pursue is an approximately spher-ical module, where actuation is realized as rotation aroundan axis diagonally through the sphere, with the sphere di-vided into two equally sized parts, as illustrated in Fig. 5.This design allows for a very stable construction around theactuated joint since a relatively large area (compared to thesize of the module) is available for mechanics.

3.2. Basic connector design

Designing the connectors is a compromise; in order to havefast and strong connectors with possibilities for power-sharing and inter-module communication, it would seem

to be an advantage to have a large surface of contact be-tween two connected modules. A large contact surface isbetter at dealing with the torque through the connector,as well as providing area for wired communication andpower transfer. But on the other hand, connectors with largecontact surfaces impose some requirements on the actua-tion of the system in order to dock and un-dock withoutcolliding.

The spherical basic module design makes it hard to havebig flat surfaces connecting to each other. With spheri-cal modules, connectors need to establish what is essen-tially point-to-point contacts between modules, which isnot desirable due to the reasons mentioned above. How-ever, the alternative being more complex modules withmore actuators, or modules with limited motion capabili-ties, we chose to try to deal with the problem of point-likeconnectors.

3.3. Basic system design

The basic design shown in Fig. 5 allows us to explore a spaceof actual designs by specifying the distribution of connectionpoints on the surface of the sphere, and by specifying theposition of the rotation joint in the sphere. Relying on a latticefor actuation and connection can make self-reconfigurationmuch easier, and many of the existing systems exploit somelattice structure for this reason.

In solid-state physics, a number of lattices consisting ofregular spheres has been explored and documented. For ourpurpose, the bonds between the lattice nodes correspond tothe connections between modules, and the relative positionsof the bonds correspond to the relative placement of con-nectors on the module. The combination of one of theselattice types and the geometrical placement of the actuatorin the module, spans a space of possible module designs.As opposed to the Proteo-class of self-reconfigurable robotsdescribed in Yim et al. (2001b), we can call this kind ofdesign for an “ATRON-class” design. ATRON-class mod-ules are essentially spheres with connectors on the surfaceand a rotation plane cut through the sphere. As opposed toProteo-class modules, ATRON-class modules cannot moveby themselves, but need the help from neighbouring mod-ules to move. This drawback imposes further requirementson cooperation between modules. However, ATRON-classmodules can have much simpler mechanical designs, mak-ing it more feasible to build a working system. ComparingProteo-class and ATRON-class system designs, it seems thatProteo-class is focused on making the control easy at the ex-pense of the mechanics, whereas the ATRON-class approachis the other way around. Focus is on (relative) mechanicalsimplicity, and the challenge is to have easy control at thesame time.

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Fig. 5 Left: The Basic Design Idea. Two half spheres joint together by an infinite revolute joint. This design is, in a sense, minimal in that eachmodule has only one joint. Right: The final design, with connectors in top hemisphere extended

Fig. 6 Various lattice structuresconsidered during the designphase for the ATRON system.The number of contact points isthe (maximum) number ofconnectors on the correspondingself-reconfigurable robotmodule. The two-colouringproperty (bottom row) isimportant if connectors aregendered. If the structure is suchthat we can solve thetwo-colouring problem for thecorresponding graph, we canavoid same-gender connectionsby making two populations ofmodules, one with all male andone with all female connectors

3.4. Lattice structures

Figure 6 summarizes some of the structures that we have beenconsidering. Well-known and well-studied lattices includeSimple Cubic, Body-Centred Cubic, Face-Centred Cubic,Hexagonal Close-pack and Cubic Close-pack lattices. Eachof these lattices can be characterized by the distribution ofcontact points on the surface of the sphere. These contactpoints correspond to the placements of the connector mech-anisms we consider in the self-reconfiguring robotic model.

The simple cubic lattice structure has been exploited ina number of lattice-based self-reconfigurable robots, suchas the M-TRAN, the Dartmouth Molecule, the MEL 3D-Unit and the Telecube. The simple cubic lattice satisfies thetwo-colouring property, which makes it possible to have twoseparate populations of modules, one with all female con-nectors and one with all male connectors. This property isexploited in the M-TRAN, the Dartmouth Molecule and theI-Cubes. One advantage of this approach is that when us-ing gendered connectors, basic motion in the system neveraligns two connectors of the same gender for connection.One drawback of this approach is that in the cases of Dart-

mouth Molecule and the I-Cubes, the approach effectivelyproduces two populations of modules, one with all male andone with all female connectors. Control complexities arisefrom the interdependencies of these two populations, due tothe required presence of members from both populations inevery part of robot.

3.5. Placing an ATRON in the lattice structure

By experimenting with the various lattice structures usingmock-up models made from wood and styrofoam, shown inFig. 7, we decided to focus on a structure related to the face-centred cubic lattice structure, labeled “Rhenium Oxide” inFig. 6. In face-centred cubic lattices, units are placed in aregular cubic lattice structure, as well as on the faces ofthe square surfaces in the lattice, as shown in Fig. 9. Thelattice we chose for the ATRON modules corresponds to theOxygen atoms of the ReO3 crystal lattice, shown in Fig. 9. Ifwe compare to a cubic lattice, the ATRONs are placed on thecentre of the surfaces of each cube. Figure 10 illustrates howthe ATRONs pack in two and three dimensions. We place theATRONs so that the revolution joint lies on the surface of the

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Fig. 7 Mock-up models usedfor experimenting with the basicmodule design

Fig. 8 Placement of the connector points relative to the revolution jointfor the ATRON system. The revolution joint is placed at equator, withthe rotation axis going through the poles. The connectors are placed at45◦ latitude and with even longitudinal distribution of 90◦

cube in the cubic lattice, with a rotation axis perpendicularto the surface.

The lattice structure shown in Fig. 10 requires attach-ment points at eight locations on the ATRON surface. Eachhalf-sphere should have four attachment points at 45◦ lati-tude, and with longitudinal distribution of 90◦, as shown inFig. 8.

3.6. Properties and consequences to motion capabilitiesfrom the ATRON basic design

The chosen design has implications on the properties of anATRON robot. As long as modules’ positions conform withthe lattice, we can place a Cartesian coordinate system suchthat for each ATRON the rotation axis is parallel to either thex-, y- or z-axis. This gives us three “flavours” of ATRONsbased on the orientation of their rotation axis, describedbelow as x, y and z. A module with the rotation axis parallelto the x-axis is called an x-ATRON.

– Each flavour forms a regular cubic lattice structure.– A y-ATRON connected to an x-ATRON will be converted

into a z-ATRON by a 90◦ rotation around the rotation axisof the x-ATRON.

– Two ATRONs of the same flavour cannot be connected toeach other.

– Each x-ATRON can be connected to up to four y- and fourz- ATRONs (two of each on each half).

Fig. 9 A Rhenium Oxide ReO3 crystal unit cell. The Oxygen atoms(large) in ReO3 are arranged in a face-centred cubic lattice structure.The structure of the ATRON modules resembles the structure of theOxygen atoms in a ReO3 crystal. Connections between ATRON mod-ules resemble the bonds between the ReO3 Oxygen atoms

– No sequence of transitions can switch positions of the twohalves of one ATRON.

– When two ATRON halves are connected through two spe-cific connectors, there is only one possible relative orien-tation and position between the two.

These properties hold for all permutations of x, y and z,as long as all modules are in the lattice.

3.6.1. Gender parity

Each ATRON-half has two male and two female connectors,placed so that opposite connectors have the same gender.It is possible to place all ATRONs in the lattice so that noconnector-gender clashes occur. One such placement is tomake all x-ATRONs have their male connectors in the y-direction, all y-ATRONs have their male connectors in thez-direction and all z-ATRONs have their male connectors inthe x-direction. This means that x-ATRONs have female con-nectors in the z-direction. Due to symmetry and the fact thatz-ATRONs have male connectors in the z-direction, and areconnected to x-ATRONs in the z-direction, z-ATRON maleconnectors are connected to x-ATRON female connectors.

We can define gender parity for one half-ATRON as zeroif the half is placed as described above, and one if it is not.If all ATRON-halves have gender parity of zero, then nogender clashes occur. As soon as one ATRON-half makes a

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Fig. 10 Bottom: Arrangement of the ATRON modules in three-dimensional space. Top: The two-dimensional equivalent, just for clar-ification. (a) Consider the ATRON with an octahedron wrapped aroundit. Let the octahedron be built from two pyramids with half the height oftheir base length. These two pyramids correspond to the two half cells

of the ATRON module. Let the ATRON touch the octahedron surfacein eight points, corresponding to the eight surfaces of the octahedron.(b) and (c) show how these octahedrals can be packed to form a cubicstructure (shown in (d) and (e)). The rotation plane of each ATRON isgiven by the cube surface it intersects

Fig. 11 The very first prototype constructed from LEGO

90◦ rotation, the gender parity of that half is flipped. Genderparity for any modules connected to that module is alsoflipped. So any self-reconfiguration sequence that preservesgender parity must have an even number of moves for eachhemisphere. Thus, whenever an ATRON-half makes a move,one more move is required to restore gender parity of thesystem.

3.6.2. Self-reconfiguration

The most important question is whether self-reconfigurationis possible with the chosen design. By experimenting withvarious LEGO and styrofoam mock-up prototypes, it wasfound that self-reconfiguration is indeed possible with thechosen design. The experiments were simply to perform se-quences of moves on the mock-up model that would go froma number of starting-configurations to a number of goal-configurations. These experiments revealed that the rotationjoint is required to have enough torque, and the connectorsenough stiffness, to rotate a horizontal chain of two con-nected modules against gravity.

3.7. Sensor and communication capabilities

The intended control method for the ATRON system is basedon mimicking mechanisms found in multi-cellular biologi-cal systems. Since most of the processes that control liv-ing cells are situated processes, meaning that they act andreact in their local environment, the ATRON system is re-quired to be able to react locally. For this reason, the ideaof having a global bus for communication was rejected. Amessage received from a global bus channel does not di-rectly give any information about who sent it. If we designthe system so that modules only communicate with theirneighbours, a module can be sure that whenever it receives amessage, that message is from one of its neighbours. Further-more, if we make independent communication hardware foreach of the module’s connectors, we can directly know fromwhich neighbour a message came. And since the ATRONlattice is such that there is only one possible relative orien-tation and position between two connected ATRON halves,we can know the position and orientation of the sendingpart.

For these reasons, each ATRON is equipped withneighbour-to-neighbour communication in each of the eightconnector sites. This makes it possible to figure out theglobal configuration using only communication among themodules, and makes it possible to experiment with variousabstractions of developmental biology models. After con-sidering magnetic (tape recorder magnets) and direct electri-cal connection for implementing the neighbour-to-neighbourcommunication, the choice fell on infra-red communication,since it is well-known technology, and since the same physi-cal components can be used to implement proximity sensors.The proximity sensors of the ATRON modules have a rangeof a few centimeters, and can be used to detect externalfeatures such as floors, walls and obstacles, as well as in-ternal features, such as other nearby modules. Additionally,each module has an accelerometer for measuring direction

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of gravity and providing the ability to detect movement thatis not self-initiated, such as being picked up or tipping over.

3.8. Basic ATRON design summary

Based on the above described considerations, the basic de-sign of the ATRON system became a lattice-based self-reconfigurable modular robot, where each approximatelyspherical module is constructed as two approximate hemi-spheres joined by an infinite revolute joint. Each hemispherehas two female connectors and two active male connectors,placed at 45◦ latitude and with even longitudinal distributionof 90◦. On a hemisphere, opposing connectors have samegender, so that when moving around the hemisphere everysecond connector is male, and every second is female. Eachconnector has an IR-proximity sensor and IR neighbour-to-neighbour communication, and the module has a tilt-sensor.

The ATRON module design is the result of a desire todevelop the simplest possible module. By making a verysimple module, we hope that we in future versions can reducethe sizes (and price) significantly, so that we can investigateissues such as intelligent dust and nano robotics.

The following sections will present more details on theactual implementation.

4. Realization of the ATRON modules

This section will in details describe several aspects of themechanical design, resulting in the design shown in Fig. 12.The ATRON module, shown in Fig. 14, is built mainly fromstrong aluminum and steel bars for the passive connectors.

4.1. Rotational joint mechanical design

The rotating joint is subjected to forces and torques in alldirections. Two basic designs for the rotating joint were con-sidered. The two designs (A and B illustrated in Fig. 13) bothuse ball bearings to reduce friction, stiction, and wear. In bothdesigns, D should be maximized to minimize load on bear-ings and angular play. Design A can use cheaper standard

bearings, and can be built so no play is possible betweenthe two hemispheres, if the two bearings are pretensionedrelative to each other. However, design A concentrates stressin and around the centre axle. Design B, though more ex-pensive because of the more exotic thin section ball bearingused, frees up valuable space in the centre of the module,and allows us to construct a planetary gear using the spaceinside the bearing. For these reasons design B was chosen,implemented using a thin section, four point of contact, ballbearing.

4.2. Communication and power-sharing betweenhemispheres

Self-reconfiguration is realized by a module connecting to itsneighbour, rotating a multiple of 90◦, letting the neighbourmodule connect to a third module, and releasing the ini-tial connection. Often, several such sequences are requiredto reach a desired target configuration, hence reconfigura-tion involves a lot of rotations. In order to avoid problemswith wires through the centre getting twisted, a slip-ringwas designed that allows for infinite revolution of the twohemispheres. Since it is desirable to limit the number ofwires passing through the slip-ring for economical and prac-tical reasons, it was decided to put a microprocessor in eachhemisphere, permitting us to have only power and serialcommunication wires through the slip ring. The slip ringdesign is shown in Fig. 15, with five concentric tracks thatcarry 10 volts, regulated 5 volts, ground, and two RS485signals.

This design of the centre allows for an infinite num-ber of revolutions around equator while still transferringpower and data between the two hemispheres. In addition,the slip ring is being used as reflective material for opti-cal encoders giving information on the absolute rotation ofthe two hemispheres as well as the current rotation speedand direction. This permits the control program to detectrotational motion between the two hemishperes that is notself-initated, thus offering a possibility to correct for externaldisturbances.

Fig. 12 The ATRON module,11 cm in diameter. Left: CADmodel of the ATRON modulewith plastic cover. Right: Photoof a fully functional ATRONmodule

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Fig. 13 Two designsconsidered for the rotating joint

Fig. 14 The ATRON modulemechanics. Left: Exploded viewof the CAD model. Right: Photoof the final design, includingelectronics, excluding the plasticcover

4.3. Defining the shape

Although the initial design was two hemispheres as illus-trated in Fig. 5, geometrical considerations based on Voronoiregions, hinted at in Fig. 10, lead to module shapes that are

two four-sided pyramids, with a number of carvings to allowrotation within an organism. Figure 16 illustrates how thesecarvings allow a module to be moved in an otherwise fullypacked lattice.

Fig. 15 Picture showing thecentre slip-ring design, and alsothe final stage of the planetarygear. Carbon shoes (northernhemisphere, left) are draggingalong concentric tracks on thegold-plated slip ring (southernhemishpere, right) allowing fortransfer of power and databetween the hemispheres. Thethree outmost tracks providegray-coded positioninformation that issupplemented by a finer-grainedencoder on the motor. Whenassembled, the two hemispheresare held together by the ballbearing, visible on the southernhemisphere picture. The bearingis press-fitted on the southernhemisphere and bonded to thenorth

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Fig. 16 In order to prevent collisions during basic motions, certainlimitations are imposed on the module shape. Imagine a fully packed(infinite) lattice of ATRONs. This illustration shows eight modules sit-ting in a plane in such a lattice. The four modules surrounded by adashed circle are connected to each other, and connected to a fifth mod-ule in the plane behind the illustrated plane. The rotation axle of the

fifth module is shown as a dot in the centre of the illustration. Had allmodules been spherical, the four central modules would collide withfour remaining modules, when rotated around the rotation axle. Basedon this observation, a shape was found that permits motion in a fullypacked structure

4.4. Connector mechanical design

Having settled on the shape defined by the above-mentionedcarvings, connection between neighbours has to be point-to-point connections in contrast to e.g. the M-TRAN,CONRO, and I-cubes (Unsal and Khosla, 2000) whohave surface-to-surface connections. A surface-to-surfaceconnection method has the advantage of distributing thestress from holding neighbouring modules on a largearea.

The connector is subjected to forces and torques in alldirections. Therefore, two modules should be connected inthree points or more. In order to minimize load and strainresulting from torques, the distance between the connectionpoints should be maximized. It was decided to go for anapproach using rotating arms, because linear guidance sys-tems generally are more expensive, less accurate and take upmore space than revolute joints. The length of the arms isdetermined from the distance between the arm-rotation axisand the female connector. Therefore, the connection pointswere also placed in order to minimize this distance. Fig-ure 17 shows the position of the connection points, usingthis strategy. Figure 18 illustrates how three hooks emergefrom the surface of the active connector and grab the passiveconnector.

The passive connector is built from two bars of stainlesssteel rigidly integrated in the hemisphere. The three hooksare driven by a DC motor via a lead screw. The mechanismdriving the arms is not backdrivable in the extented armposition, hence no power is required to maintain connection.In order to simplify the mechanical design, the arms rotateon parallel axes. This allows us to combine the two lower

Fig. 17 Connection points for a male and female connector. The hookspivot around joints on the frame of the male part and attach to matchingpositions on the female part

arms in one arm, and to use a fairly simple mechanism forsynchronizing movement of lower and upper arm.

4.5. Mechanical design of the frame

The frame is designed with the intent of allowing very tighttolerances on relative position of bearing seat, axles for con-nector arms and female connector axles, while keeping pro-duction costs reasonable. On the first two prototypes of the

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Fig. 18 CAD drawings of twoATRON modules connecting.By connecting using threepoints, a strong and stiffconnection is obtained. Left:Connection initiated. Right:Connection completed

module the entire frame was produced on a 2D CNC millingmachine, since this was much cheaper than moulding theparts. Because of time-constraints it was decided not to de-velop a frame design suitable for moulding, the frames forthe 100 modules that have been built are, therefore, also en-tirely CNC machined. A frame designed for moulding couldreduce the weight of the modules and lower production costs.The frame is seen on Figs. 14 and 19.

5. Experiments

One of the main concerns of not having flat connection sur-faces in the ATRON system was the mechanical strengthand stiffness of the connectors. In a situation such as the oneshown in Fig. 20, sloppy connectors would lead to significantdeformation.

5.1. FEM analysis

In order to identify the modulus of elasticity and the yieldstrength of the ATRON material, a FEM analysis on a singleATRON module was performed. It should be noted that theATRON material is anisotropic, however, this analysis onlyinvestigates the properties in one direction. If the connectors(and the module as a whole) had been symmetric aroundthe 45◦ planes through the module, then the material wouldbe orthotropic. Figure 19 shows a module subjected to theload, which, according to the FEM analysis, is the maximumload before some areas of the module are stressed beyondyield strength for aluminum 7075 (frame and connector) andstainless steel (axles). According to the FEM analysis onone module, the maximum tensile force between two op-posing connectors, without experiencing stress beyond yieldstrength anywhere in the module, is 800 N. At this point theelongation of the module is 0,23 mm. From this, the modulusof elasticity can be calculated as:

E = σproportional

ε≈ Fyield/A

(l2 − l1)/ l1= 800 N ∗ 110 mm

(110 mm)2 ∗ 0.23 mm

= 32N

mm2

assuming σyield ≈ σproportional

The yield stress of the module is calculated as:

σyield = 800 N

(110 mm)2= 0.067 MPa

Figure 19 shows a module subjected to a horizontalload of 120 N, a greater load will result in plastic de-formation of the module, resulting in shear stress in themodule. From this the shear modulus of elasticity can becalculated:

G = τaverage/γ ≈ F/A

d/h= 120 N/(110 mm)2

0.68 mm/110 mm� 1.6

N

mm2

where d is the horizontal deflection, h is the height of thedeflected area, and γ is the angle of the deflection.

5.2. Real world validation

In order to validate the FEM analysis, a simple test wasmade comparing the deformation of real ATRON modulesto deformation in the FEM model. The test set-up and resultsare given in Fig. 20.

The test showed a vertical displacement of the fifth mod-ule of 3 mm, while the FEM analysis gave an expecteddeflection of 1.4 mm. However, the FEM analysis does nottake into account the play in the bearing. According to themanufacturer of the bearing the angular play in the bear-ing is 0.0009 radians. Tilt will occur in the bearings of allthree modules with horizontal rotation, but only the tilt inthe two inner modules will affect the measurements. By sim-ple geometric calculations, this tilt will cause a deflectionof the outmost module of about 0.4 mm. Therefore, a to-tal deflection of about 1.4 mm + 0.4 mm = 1.8 mm shouldbe expected. When the real test shows 3 mm deflection, itis probably due to play between axles and frame. The testshows that the FEM analysis is quite accurate despite thementioned simplifications.

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Fig. 19 FEM analysis of amodule. A load of 120 N arehorizontally applied at the topconnector (arrows), while themodule is being fixated at thebottom connector (otherarrows). The plot shows that the120 N gives a staticdisplacement of up to 0.68 mm

Fig. 20 Mechanicaldeformation test for fiveATRON modules connected in ahorizontal chain using fourconnectors. Top: FEM analysisdisplacement plot. Displacementis exaggerated for visualization.The colour shows thedisplacement of each elementcaused by gravitational pull.Deformation of the outmostmodule is about 1.4 mm.Bottom: Real-worlddeformation test. The horizontalline was put onto the pictureafter it was taken. Measurementsshow a displacement of theoutmost module of about 3 mm

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5.3. Discovered material properties

The mass density ρ of the ATRON material is calculated as:

ρ = M/V = 0.85 kg ∗ 3

(0.11 m ∗ √2)3

� 720 kg/m3

Figure 21 shows the most common properties for somematerials, and the properties of the ATRON material.

In many applications the important parameter is the ratioof yield stress to mass density, and iron is approximately 312times better than the ATRON material in this respect. Thematerial that the ATRONs are mostly made of, Aluminium7075, is even 1000 times better. This is because most ofthe material in the ATRON module does not increase itsstrength, but is used as structural support for different partsthat have to do with the ability to self-reconfigure. Also, theweight of these parts only increases the strength in a fewcases. However, the ATRON module is one of the first self-reconfigurable materials and there are great possibilities forimprovements.

5.4. Reconfiguration experiments

As this article focuses on the design of the ATRON modules,the specific control approaches used to control them will notbe covered here. A number of papers has been publishedon controlling an ATRON robot. In Østergaard and Lund(2003) artificial co-evolution was explored for generatingcluster-walk behaviour for cluster of modules. In Østergaardand Lund (2004) and Brandt and Østergaard (2004) a rule-based approach is described to create controllers invariant tothe cluster sizes. In Christensen et al. (2004) a meta-modulecontrol approach is described. Figure 22 shows a few of theexperiments we have performed on the real modules.

In general, the realization of the basic module designlives up to expectations. The mechanical stiffness of thesystem permits relatively large structures, and the abilityfor a module to move through an otherwise fully packedstructure is a very useful feature. This gives better motioncapabilities in tight spaces.

Figure 23 illustrates a possible application, in which agroup of ATRON modules negotiates two obstacles. The self-reconfiguration capability permits the robots to traverse verydifficult terrain, enabling it to move itself inside a collapsedbuilding and provide structural support, while looking outfor people.

6. Discussion and conclusion

Designing and building self-reconfigurable robots involvescomplex trade-offs between many mechanical, electrical

and control considerations. Still, work in this area is in anexploratory phase, where systems are built and then laterunderstood. The ATRON system, as well as each of thesurveyed systems, represents a point in the design spaceof self-reconfigurable robots. As more of this space isexplored, hopefully a greater picture will emerge that canlead to a theory for designing self-reconfigurable robots.

In a number of the surveyed papers, it is argued that self-reconfigurable robots have the potential to be robust, flexibleand cheap. A number of application areas has been men-tioned, such as obstacle avoidance in highly unstructured en-vironments, growing structures such as bridges, envelopmentof objects, inspection in constrained environments (Pamechaet al., 1997), planetary exploration, growing satellite anten-nas and self-healing solar panel arrays.

Reports on self-reconfigurable robots performing evenremotely useful tasks are still lacking. However, the fieldis still young, and it seems that a lot of people believe inthe potential of the approach, such as NASA launching theSuperBot project. Probably, further research in this area willgenerate significant spin-off.

Based on the considerations described in this article, thebasic design of the ATRON system became a lattice-basedself-reconfigurable modular robot, where each approxi-mately spherical module is constructed as two approximatehemispheres joined by an infinite revolute joint. Eachhemisphere has two female connectors and two maleconnectors, placed at 45◦ latitude and with an even longi-tudinal distribution of 90◦. On each hemisphere, opposingconnectors have the same gender, so that when movingaround the hemisphere every second connector is male, andevery second is female. Each connector has an IR-proximitysensor and IR neighbour-to-neighbour communication. TheATRON design successfully deals with the hard problemsrelated to gravity, in that the structural stiffness and motorstrength are sufficient to re-configure in all three dimensions.

The ATRON design seems to be a capable one indeed, bothin terms of mechanical properties, and in terms of motioncapabilities. However, this is a subjective opinion. Futurework might produce metrics and criteria that permit us toevaluate and compare specific module designs, even thoughthere is a large number of factors to take into consideration.Hopefully, this article can contribute to the forming of suchtheory.

There are a few problems with the ATRON design. Weclaim that the design allows for simple mechanics, sincethere is only one actuated degree of freedom. However, sincethe hard part is the connectors, this argument is somewhatoutweighed by the complexity of the conntors.

Also, it is still unclear what the advantages are forlattice-type systems. In “Keeping the Analog Genie in the[Discrete] Bottle” (Walker et al., 1999), Walker et al. arguethat using “Digital Robotics” (lattice-based) could increase

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Fig. 21 ATRON materialproperties compared to variousother materials. Comparison isonly valid for very largeATRON structures

Fig. 22 Left: Picture of 24 ATRON modules performing self-reconfiguration. Right: Three groups of seven ATRON modules. Fromleft to right, the configurations are snake, cluster-walk and car. Rubber

bands on the outmost hemisphere on each wheel of the car providetraction. See Fig. 12 for a better view of the rubber band

Fig. 23 Seven ATRON modules traversing an obstacle course, con-sisting of a step and a tunnel. When the car-like structure encoutersthe step, a cluster-walking behaviour is initated. After the step, thecluster is transformed into a snake-like structure, to travel through the

tunnel (under the styrofoam). After passing through, the ATRONs self-reconfigure into a car-like structure again, to travel more efficientlyover the floor

potential for fault detection and modularity. However, chain-type robots might have a greater potential for scalability. Inour understanding, a lattice makes it easier to perform self-reconfiguration, in that joints can be placed in predefinedpositions when connecting.

However, lattice-based systems might have problems withscalability. It seems very hard to maintain the lattice witha system of very many modules. Also, another scalabilityissue is how to create a “strong” global force using rela-tively “weak” actuators of each module. Probably, in thelong term, future module designs should have capailitiesto self-align and connect without relying on a lattice forpositioning, meaning good joint control, some form of sen-sor feedback, and connectors with good tolerances.

Most of the surveyed systems utilize a lattice structurefor self-reconfiguration. We noticed that exploitation of alattice system for self-reconfiguration does not necessarilyrestrict the system to work only in the lattice. If the actua-tors of the robot can place the joints at intermediate posi-tions, a lattice-based system can also work as a chain-typesystem.

7. Summary

Self-reconfiguring robotic system design offers major theo-retical challenges in many areas, including mechanical engi-neering, electrical engineering, robot control theory, multi-robot control and software engineering. When designing amodule, all of the above aspects have to be considered. Idealdesigns are cheap and easy to build, have simple electronicsand are easy to control. Presumably, no solution is optimalin all aspects, so we are looking for a solution that satisfiesthese properties in some balance.

The ATRON module design is the result of a desire todevelop the simplest possible module. By making a verysimple module, we hope that we in future versions can reducethe sizes significantly, so that we can investigate issues suchas intelligent dust and nano robotics.

The current ATRON design is both a competent andnovel design for a self-reconfigurable robot. Even thoughthe ATRON modules in a sense are minimal, in that theyhave only one actuated degree of freedom, the collective ofmodules is capable of self-reconfiguring in three dimensions.

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Acknowledgments This work was partly funded by EU’s Informa-tion Society Technologies Programme, IST-2001-33060, HYDRA, Fu-ture and Emerging Technologies. David Brandt, Lars Dalgaard, MortenWinkler Jørgensen, Danny Kyrping, Leonid Paramonov, Charlotte Ry-berg and other members of the AdapTronics Group have contributed tothe work on the ATRON hardware.

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Esben Hallundbæk Østergaard, Ph.D.,holds a Masters Degree in Computer Sciencefrom University of Aarhus, and a Ph.D.degree in Computer Systems Engineeringfrom University of Southern Denmark. Hehas been working as a research scientistat University of Southern California at theUSC Robotics Research Laboratories, andas a visiting researcher at the distributedsystems group at the Advanced Institute of

Science and Technology (AIST) in Tsukuba, Japan. He is currentlyworking as a Post Doc at the Maersk McKinney Moller Institute forProduction Technology at the University of Southern Denmark, andas an embedded software developer for Universal Robots ApS. Dr.Østergaard is former world champion in Robot Soccer, and has writtenmore than 15 scientific papers. His research interests span from robotsoccer through self-reconfigurable robots to industrial automation,in general, the fuzzy boundary dividing computer science from thephysical world.

Kristian Kassow, Cand. Polyt., received amasters degree in Mechanical Engineeringfrom Technical University of Denmark in2003. He worked as a research assistant on theHydra Project 2003–2004, before starting atGrundfos Sensor Division in 2004, also doingMechanical design of electromechanicalcomponents. In 2005 Kristian co-foundedUniversal Robots ApS together with Dr.Østergaard and a third colleagues from the

Maersk Institute. Kristian Kassow is Director for Universal RobotsApS.

Richard Beck, Cand. Polyt. Mr. Beck holdsa Masters Degree in Computer SystemsEngineering from University of SouthernDenmark. He is currently working as aResearch Assistant at the Maersk McKinneyMoller Institute for Production Technology atthe University of Southern Denmark. His re-search interests are mainly self-reconfigurablerobots and robotic systems in general.Currently he is working on the development

of intelligent building block for use in feature playgrounds.

Henrik Hautop Lund, full profes-sor. Is head of the AdapTronics Group(www.adaptronics.dk) at the Maersk In-stitute, University of Southern Denmark.His AdapTronics Group has won worldchampionships (RoboCup Humanoids FreeStyle World Championship 2002, and FIRAKheperaSot World Championship 2002) andhas been awarded several best paper awardsfor applying modern artificial intelligence to

robotics. His research focuses on the role of morphology in intelligentautonomous systems, and his group is performing research in thefield of modern artificial intelligence. Previously, he founded theLEGO Lab at the CIT/University of Aarhus in 1997, and worked asresearch associate from 1992 to 1995 at the Institute of Psychology,The National Research Council, Rome , Italy , doing research in thefields of artificial life, neural networks, and evolutionary computation.Further, he worked as research associate during 1996 and 1997 inthe Department of Artificial Intelligence at University of Edinburgh,UK, doing research on biologically inspired robotics and evolutionaryrobotics. He has led numerous large research projects and projectsinvolving collaboration between academic institutions and privatecompanies. He founded the RoboCluster, a cluster of competenciesin robotics comprising more than 100 interested parties (mainlyindustrial partners) in the region of Southern Denmark. He is memberof the Danish National Research Council appointed by the ministerof research, technology and innovation. His robot development workhas been presented to HM Queen of Denmark, HM Emperor of Japan,prime ministers, etc. He has published more than 100 scientific articles.

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