Modular Self-Reconfigurable Robotic Systems: A Survey on Hardware Architectures
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paper_title: Modular robot systems towards the execution of cooperative tasks in large facilities

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Large facilities present with wide range of tasks and modular robots present as a flexible robot solution. Some of the tasks to be performed in large facilities can vary from, achieving locomotion with different modular robot (M-Robot) configurations or the execution of cooperative tasks such as moving objects or manipulating objects with multiple modular robot configurations (M-Robot colony) and existing robot deployments. The coordination mechanisms enable the M-Robots to perform cooperative tasks as efficiently as specialised or standard robots. The approach is based on the combination of two communication types i.e., Inter Robot and Intra Robot communications. Through this communication architecture, tight and loose cooperation strategies are implemented to synchronise modules within an M-Robot configuration and to coordinate M-Robots belonging to the colony. These cooperation strategies are based on a closed-loop discrete time method, a remote clock reading method and a negotiation protocol. The coordination mechanisms and cooperation strategies are implemented into a real modular robotic system, SMART. The need for using such a mechanism in hazardous section of large scientific facilities is presented along with constraints and tasks. Locomotion execution of the mobile M-Robots colony in a bar-pushing task is used as an example for cooperative task execution of the coordination mechanisms and results are presented. We present the results of cooperative task execution using heterogeneous modular robotic system (MRS).It is performed using tight and loosely coupled inter and intra robot configurations.The approach is based on the use of an inventory of three types of basic modules of the modular robot system.The heterogeneity in MRS is an advantageous property for the diverse tasks in large facilities.
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paper_title: Modular and reconfigurable mobile robotics

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With increasing demand on reliable robotic platforms that can alleviate the burden of daily painstaking tasks, researchers have focused their effort towards developing robotic platforms that possess a high level of autonomy and versatility in function. These robots, capable of operating either individually or in a group, also possess the structural modular morphology that enables them to adapt to the unstructured nature of a real environment. Over the past two decades, significant work has been published in this field, particularly in the aspects of autonomy, mobility and docking. This paper reviews the primary methods in the literature related to the fields of modular and reconfigurable mobile robotics. By bringing together aspects of modularity, including docking and autonomy, and synthesizing the most relevant findings, there is optimism that a more complete understanding of this field will serve as a starting ground for innovation and integration of such technology in the urban environment.
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paper_title: Get back in shape! [SMA self-reconfigurable microrobots]

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Self-reconfigurable robotic systems composed of multiple modules have been investigated intensively with respect to their versatility, flexibility, and fault-tolerance. Although some microscale self-assembly systems have been reported, they are passively assembled to predetermined shape by surface tension in an irreversible manner and cannot form arbitrary shapes. To develop a modular microrobot that can actively reconfigure itself, we adopt an actuating mechanism driven by a shape memory alloy (SMA). One of the advantages of an SMA actuator is that it keeps a higher power-weight ratio on microscales than electromagnetic motors.
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paper_title: Scalable modular self-reconfigurable robots using external actuation

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This paper presents a method for scaling down the size and scaling up the number of modules of self- re configurable systems by focusing on the actuation mechanism. Rather than developing smaller actuators, the main actuator is removed entirely. Energy instead comes from the environment to provide motion in prescribed synchronous ways. Prescribed synchronous motions allow much faster assembly times than random Brownian motion which has been used before. An instantiation of this idea is presented using a motion platform to induce motions based on the inertial properties of the modules and the timed actuation of small latching mechanisms.
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paper_title: A physical implementation of the self-reconfiguring crystalline robot

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We discuss a physical implementation of the crystalline robot system. Crystalline robots consist of modules that can aggregate together to form distributed robot systems. Crystalline modules are actuated by expanding and contracting each unit. This actuation mechanism permits automated shape metamorphosis. We describe the crystalline module concept and a physical implementation of a robot system with ten units. We describe experiments with this robot.
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paper_title: A Modular Self-Reconfigurable Bipartite Robotic System: Implementation and Motion Planning

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In this manuscript, we discuss i>I-Cubes, a class of modular robotic system that is capable of reconfiguring itself in 3-D to adapt to its environment. This is a bipartite system, i.e., a collection of (i) active elements for actuation, and (ii) passive elements acting as connectors. Active elements (i>links) are 3-DOF manipulators that are capable of attaching/detaching from/to the passive elements (i>cubes), which can be positioned and oriented using links. Self-reconfiguration capability enables the system to perform locomotion tasks over difficult terrains the shape and size can be changed according to the task. This paper describes the design of the system, and 3-D reconfiguration properties. Specifics of the hardware implementation, results of the experiments with the current prototypes, our approach to motion planning and problems related to 3-D motion planning are given.
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paper_title: PetRo: Development of a modular pet robot

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Modular robots present many advantages that open opportunities for novel applications and greater variability in operational parameters. We present PetRo (which stands for Pet Robot) as a modular throwable, self-assembling and reconfigurable pet robot. Some of the design challenges and solutions selected are explained as well as the two main applications for which the robot architecture is being developed: namely as a companion pet and for search and rescue operations. Although both applications are being considered, this paper places emphasis on the first and the potential for human robot interactive communication is highlighted.
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paper_title: M-blocks: Momentum-driven, magnetic modular robots

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In this paper, we describe a novel self-assembling, self-reconfiguring cubic robot that uses pivoting motions to change its intended geometry. Each individual module can pivot to move linearly on a substrate of stationary modules. The modules can use the same operation to perform convex and concave transitions to change planes. Each module can also move independently to traverse planar unstructured environments. The modules achieve these movements by quickly transferring angular momentum accumulated in a self-contained flywheel to the body of the robot. The system provides a simplified realization of the modular actions required by the sliding cube model using pivoting. We describe the principles, the unit-module hardware, and extensive experiments with a system of eight modules.
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paper_title: Self-reconfiguring robots

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At the Dartmouth Robotics Laboratory, we have a vision of the future: a modular robot that can assume a snake shape to traverse a tunnel, reconfigure upon exiting as a six-legged robot to traverse rough terrain, and change shape and gait to climb stairs and enter a building. The key to such versatility is self-reconfiguration-a new way of thinking about robots that offers a rich class of questions about robot design, control, and use. To help realize our vision, we designed the Molecule, a small and simple robotic module, capable of self-reconfiguration in three dimensions.
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paper_title: Kinematics of a metamorphic robotic system

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A metamorphic robotic system is a collection of mechatronic modules, each of which has the ability to connect, disconnect, and climb over adjacent modules. A change in the macroscopic morphology results from the locomotion of each module over its neighbors. That is, a metamorphic system can dynamically self-reconfigure. Metamorphic systems can therefore be viewed as a large swarm of physically connected robotic modules which collectively act as a single entity. What separates metamorphic systems from other reconfigurable robots is that they possess all of the following properties: (1) self-reconfigurability without outside help; (2) a large number of homogeneous modules; and (3) physical constraints ensure contact between modules. In this paper, the kinematic constraints governing a particular metamorphic robot are addressed. >
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paper_title: 3D M-Blocks: Self-reconfiguring robots capable of locomotion via pivoting in three dimensions

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This paper presents the mechanical design of a modular robot called the 3D M-Block, a 50mm cubic module capable of both independent and lattice-based locomotion. The first M-Blocks described in [1] could pivot about one axis of rotation only. In contrast, the 3D M-blocks can exert on demand both forward and backward torques about three orthogonal axes, for a total of six directions. The 3D M-Blocks transform these torques into pivoting motions which allow the new 3D M-Blocks to move more freely than their predecessors. Individual modules can employ pivoting motions to independently roll across a wide variety of surfaces as well as to join and move relative to other M-Blocks as part of a larger collective structure. The 3D M-Block maintains the same form factor and magnetic bonding system as the one-dimensional M-Blocks [1], but a new fabrication process supports more efficient and precise production. The 3D M-blocks provide a robust and capable modular self-reconfigurable robotic platform able to support swarm robot applications through individual module capabilities and self-reconfiguring robot applications using connected lattices of modules.
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paper_title: Mechatronic design of a modular self-reconfiguring robotic system

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Design and implementation of I-Cubes, a modular self-reconfigurable robotic system, is discussed. I-Cubes is a bipartite collection of individual modules that can be independently controlled. The group consists of active elements, called links, which are 3-DOF manipulators capable of attaching to/detaching from the passive elements (cubes) acting as connectors. The cubes can be oriented and positioned by the links. Using actuation and attachment properties of the link and the cubes, the system can self-reconfigure to adapt to its environment. Tasks such as moving over obstacles, climbing stairs can be performed by changing the relative position and connection of the modules. The links are actuated using servomotors and worm gear mechanisms. Mechanical encoders and rotary switches provide position feedback for semi-autonomous control of the system. The cubes are equipped with a novel mechanism that provides inter-module attachment. Design and hardware implementation of the system as well as experimental results are presented.
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paper_title: Micro Self-Reconfigurable Robotic System using Shape Memory Alloy

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This paper presents micro self-reconfigurable modular robotic systems using shape memory alloy (SMA). The system is designed so that various shapes can be autonomously formed by a group of identical mechanical units. The unit realizes rotational motion by using an actuator mechanism composed of two SMA torsion coil springs. We have realized micro-size prototype units and examined their fundamental functions by experiments. An extended 3D system and its self-reconfiguration algorithm are also discussed.
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paper_title: Em-cube: cube-shaped, self-reconfigurable robots sliding on structure surfaces

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Many previous works simulate cube-shaped modular robots to explain their systems and algorithms. This paper explores a cube-shaped, self-reconfigurable system composed of EM-Cube robot modules. The paper describes the system's design, implementation, movement algorithms, and experimentation. It reports on the hardware and software, and presents the algorithms of linear walking, convex and concave transition, and locomotion. Finally, it discusses EM-Cube locomotion experiments.
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paper_title: A 3-D self-reconfigurable structure

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A three-dimensional, self-reconfigurable structure is proposed. The structure is a fully distributed system composed of many identical 3-D units. Each unit has functions of changing local connection, information processing, and communication among neighborhood units. Groups of units cooperate to change their connection so that the shape of the whole solid structure transforms into an arbitrary shape. Also, the structure can repair itself by rejecting faulty units, replacing them with spare units. This kind of self-maintainability is essential to structure's longevity in hazardous or remote environments such as space or deep sea where human operators cannot approach. We have designed and built a prototype unit to examine the feasibility of the 3-D self-reconfigurable concept. The design of the unit, method of reconfiguration, hardware implementation, and results of preliminary experiments are shown. In the last part of the paper, distributed software for self-reconfiguration is discussed.
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paper_title: Useful metrics for modular robot motion planning

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In this paper the problem of dynamic self-reconfiguration of a class of modular robotic systems referred to as metamorphic systems is examined. A metamorphic robotic system is a collection of mechatronic modules, each of which has the ability to connect, disconnect, and climb over adjacent modules. We examine the near-optimal reconfiguration of a metamorphic robot from an arbitrary initial configuration to a desired final configuration. Concepts of distance between metamorphic robot configurations are defined, and shown to satisfy the formal properties of a metric. These metrics, called configuration metrics, are then applied to the automatic self-reconfiguration of metamorphic systems in the case when one module is allowed to move at a time. There is no simple method for computing the optimal sequence of moves required to reconfigure. As a result, heuristics which can give a near optimal solution must be used. We use the technique of simulated annealing to drive the reconfiguration process with configuration metrics as cost functions. The relative performance of simulated annealing with different cost functions is compared and the usefulness of the metrics developed in this paper is demonstrated.
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paper_title: Modular ATRON: modules for a self-reconfigurable robot

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This paper describes the mechanical and electrical design of a new lattice based self-reconfigurable robot, called the ATRON. The ATRON system consists of several fully self-contained robot modules, each having their own processing power, power supply, sensors and actuators. The ATRON modules are roughly spheres with equatorial rotation. Each module can be connected to up to eight neighbors through four male and four female connectors. In this paper, we describe the realization of the design, both the mechanics and the electronics. Details on power sharing and power consumption is given. Finally, this paper includes a brief outline of our future work on the ATRON system.
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paper_title: Reliable External Actuation for Extending Reachable Robotic Modular Self-Reconfiguration

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External actuation in self-reconfigurable modular robots promises to allow modules to shrink down in size. Synchronous external motions promise to allow fast convergence and assembly times. XBot is a modular system that uses synchronous external actuation, but has a limited range of reachable configurations stemming from a single motion primitive of a module rotating about another. This paper proposes to extend the motion primitives by using moves with two modules swinging in a dynamic chain. The feasibility of these motion primitives is proven experimentally. A parameterization of the external actuation motion profiles is explored to define a space of physically valid motion profiles. The larger the space, the more robust the motion primitives will be to inexact initial conditions and to imprecision in the external actuation mechanisms. Additionally, this paper proves a configuration of XBot meta-modules can reach any configuration using just these motion primitives.
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paper_title: A 3-D self-reconfigurable structure and experiments

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A three-dimensional self-reconfigurable structure made of identical units is proposed. Each unit has six arms on the surface of its base cube which can connect to neighboring units mechanically. By the connection, cubic lattice structure is formed. A unit can carry its neighbor unit from one node of the lattice to another by rotating its arm by 90 degrees. Repeating this movement, the structure can reconfigure itself to realize various 3D structures. General process of reconfiguration were proposed for this system. Four units were made and basic motions of self-reconfiguration were verified.
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paper_title: Robust and reversible self-reconfiguration

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Modular, self-reconfigurable robots are robots that can change their own shape by physically rearranging the modules from which they are built. Self-reconfiguration can be controlled by e.g. an off-line planner, but numerous implementation issues hamper the actual self-reconfiguration process: the continuous evolution of the communication topology increases the risk of communications failure, generating code that correctly controls the self-reconfiguration process is non-trivial, and hand-tuning the self-reconfiguration process is tedious and error-prone. To address these issues, we have developed a distributed scripting language that controls self-reconfiguration of the ATRON robot using a robust communication scheme that relies on local broadcast of shared state. This language can be used as the target of a planner, offers direct support for parallelization of independent operations while maintaining correct sequentiality of dependent operations, and compiles to a robust and efficient implementation. Moreover, a novel feature of this language is its reversibility: once a self-reconfiguration sequence is described the reverse sequence is automatically available to the programmer, significantly reducing the amount of work needed to deploy self-reconfiguration in larger scenarios. We demonstrate our approach with long-running (reversible) self-reconfiguration experiments using the ATRON robot and a reversible self-reconfiguration experiment using simulated MTRAN modules.
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paper_title: Programmable parts: a demonstration of the grammatical approach to self-organization

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In this paper, we introduce a robotic implementation of the theory of graph grammars (Klavins et al., 2005), which we use to model and direct self-organization in a formal, predictable and provably-correct fashion. The robots, which we call programmable parts, float passively on an air table and bind to each other upon random collisions. Once attached, they execute local rules that determine how their internal states change and whether they should remain bound. We demonstrate through experiments how they can self-organize into a global structure by executing a common graph grammar in a completely distributed fashion. The system also presents a challenge to the grammatical method (and to distributed systems approaches in general) due to the stochastic nature of its dynamics. We conclude by discussing these challenges and our initial approach to addressing them.
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paper_title: Miche: Modular Shape Formation by Self-Dissasembly

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We describe the design, implementation, and experimentation with a collection of robots that, starting from an amorphous arrangement, can be assembled into arbitrary shapes and then commanded to self-disassemble in an organized manner. Each of the 28 modules in the system is implemented as a 1.8-inch autonomous cube-shaped robot able to connect to and communicate with its immediate neighbors. Two cooperating microprocessors control each module's magnetic connection mechanisms and infrared communication interfaces. When assembled into a structure, the modules form a system that can be virtually sculpted using a computer interface. We report on the hardware design and experiments from hundreds of trials.
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paper_title: Robot pebbles: One centimeter modules for programmable matter through self-disassembly

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This paper describes the design, fabrication, and experimental results of a programmable matter system capable of 2D shape formation through subtraction. The system is composed of autonomous 1cm modules which use custom-designed electropermanent magnets to bond, communicate, and share power with their neighbors. Given an initial block composed of many of these modules latched together in a regular crystalline structure, our system is able to form shapes by detaching the unnecessary modules. Many experiments show that the modules in our system are able to distribute data at 9600bps to their neighbors with a 98.5% success rate after four retries, and the connectors are able to support over 85 times the weight of a single module.
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paper_title: Self-organizing collective robots with morphogenesis in a vertical plane

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This paper presents a novel concept of self-organizing collective robots with morphogenesis in a vertical plane. It is potentially applicable to autonomous mobile robots. For physical reconfiguration of a swarm of robots against gravity, new types of mechanisms and control strategies are proposed and demonstrated. Prototype robots have been fabricated in order to confirm the basic feasibility of the mechanisms. Each robot is composed of a body and a pair of arms. The body can be regarded as a cube with edge length of 90 mm, and is equipped with permanent magnets for bonding with another robot. The arms change the bonding configuration by rotating and sliding motions. As for the control strategies, we proposed the algorithms which can locally generate specific global formations of robots, with minimum interactions between neighboring robots. The overall scheme is similar to cellular automata. The control algorithms proposed have been tested by simulations.
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paper_title: Self-assembling machine

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The design of a machine which is composed of homogeneous mechanical units is described. We show the design of both hardware and control software of the unit. Each unit can connect with other units and change the connection by itself. In spite of its simple mechanism, a set of these units realizes various mechanical functions. We developed the control software of the unit which realizes "self-assembly," one of the basic functions of this machine. A set of these units can form a given shape of the whole system by themselves. The units exchange information about local geometric relation by communication, and cooperate to form the whole shape through a diffusion-like process. There is no upper level controller to supervise these units, and the software of each unit is completely the same. Three actual units have been built to test the basic movements, and the function of self-assembly has been verified by computer simulation. >
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paper_title: Three dimensional stochastic reconfiguration of modular robots

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Here we introduce one simulated and two physical three-dimensional stochastic modular robot systems, all capable of self-assembly and self-reconfiguration. We assume that individual units can only draw power when attached to the growing structure, and have no means of actuation. Instead they are subject to random motion induced by the surrounding medium when unattached. We present a simulation environment with a flexible scripting language that allows for parallel and serial selfassembly and self-reconfiguration processes. We explore factors that govern the rate of assembly and reconfiguration, and show that self-reconfiguration can be exploited to accelerate the assembly of a particular shape, as compared with static self-assembly. We then demonstrate the ability of two different physical three-dimensional stochastic modular robot systems to self-reconfigure in a fluid. The second physical implementation is only composed of technologies that could be scaled down to achieve stochastic self-assembly and self-reconfiguration at the microscale.
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paper_title: Telecubes: mechanical design of a module for self-reconfigurable robotics

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A Telecube is a cubic module that has six prismatic degrees of freedom whose sides can expand more than twice its original length and has the ability to magnetically (de)attach to other modules. Many of these modules can be connected together to form a modular self-reconfigurable robot. The paper presents the intended functions, discusses the physical requirements of the modules and describes two key mechanical components: a compact telescoping linear actuator and a switching permanent magnet device.
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paper_title: Millibot Trains for Enhanced Mobility

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The objective of this work is to enhance the mobility of small mobile robots by enabling them to link into a train configuration capable of crossing relatively large obstacles. In particular, we are building on Millibots, semiautonomous, tracked mobile sensing/communication platforms at the 5-cm scale previously developed at Carnegie Mellon University. The Millibot Train concept provides couplers that allow the Millibot modules to engage/disengage under computer control and joint actuators that allow lifting of one module by another and control of the whole train shape in two dimensions. A manually configurable train prototype demonstrated the ability to climb standard stairs and vertical steps nearly half the train length. A fully functional module with powered joints has been developed and several have been built and tested. Construction of a set of six modules is well underway and will allow testing of the complete train in the near future. This paper focuses on the development, design, and construction of the electromechanical hardware for the Millibot Train.
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paper_title: Hormone-based control for self-reconfigurable robots

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Self-reconfigurable or metamorphic robots can change their individual and collective shape and size to meet operational demands. Since these robots are constructed from a set of autonomous and connectable modules (or agents), controlling them is a challenging task. The difficulties stem from the facts that all locomotion, perception, and decision making must be distributed among a network of modules, that this network has a dynamic topology, that each individual module has only limited resources, and that the coordination between modules is highly complex and diverse. To meet these challenges, this paper presents a distributed control mechanism inspired by the concept of hormones in biological systems. We view hormones as special messages that can trigger different actions in different modules, and we exploit such properties to coordinate motions and perform reconfiguration in the context of limited communications and dynamic network topologies. The paper develops a primitive theory of hormone-based control, reports the experimental results of applying such a control mechanism to our CONRO metamorphic robots, and discusses the generality of the approach for a larger class of distributed autonomous systems.
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paper_title: Method of Autonomous Approach, Docking and Detaching Between Cells for Dynamically Recontigurable Robotic System CEBOT

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The concept of the new dynamically reconfigurable robotic system (DRRS) are its realization as the cell-structured distributed robotic system CEBOT are discussed in this paper. CEBOT can reconfigurate itself to optimal structure depending on purpose and environment. These robotic systems are very advantageous for space robotics, since the available resources are limited in space. This robotic system is possible owing to the use of separable self-controlled units called "cells" ; thus the robotic system is called a cell-structured robot #(CEBOT). CEBOT has unique features such as a dynamically reconfigurable structure, on-line task adaptability, fault tolerance, etc. With simple elementary cells clustered into large structures or modules, complicated tasks can be executed (this concept is found in biological organisms). We propose this concept, control and sensor system structure, and automatic approach control. The efticiency of CEBOT is shown by the results of automatic approaching, connecting and separating experiments.
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paper_title: M3Express: A low-cost independently-mobile reconfigurable modular robot

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This paper presents M3Express (Modular-Mobile-Multirobot), a new design for a low-cost modular robot. The robot is self-mobile, with three independently driven wheels that also serve as connectors. The new connectors can be automatically operated, and are based on stationary magnets coupled to mechanically actuated ferromagnetic yoke pieces. Extensive use is made of plastic castings, laser cut plastic sheets, and low-cost motors and electronic components. Modules interface with a host PC via Bluetooth® radio. An off-board camera, along with a set of modules and a control PC form a convenient, low-cost system for rapidly developing and testing control algorithms for modular reconfigurable robots. Experimental results demonstrate mechanical docking, connector strength, and accuracy of dead reckoning locomotion.
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paper_title: Study on three-dimensional active cord mechanism: development of ACM-R2

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Describes the development of ACM-R2, which is new version of the active cord mechanism with 3D mobility. This ACM-R2 has installed a driving mechanism called "M-drive". This mechanism enables the ACM-R2 to acquire a high output/mass ratio and torque limiting joints, which works as a normal joint and deforms under excessive torque. It has also installed a new type of torque sensor, the "float differential torque sensor" on each joint. Additionally the ACM-R2 has also a self-contained structure with control computer and battery in the joint units. These specific driving mechanisms and the self-contained structure enable ACM-R2 to demonstrate new propulsion methods and motions combining the ability of a manipulator and a locomotor.
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paper_title: Hormone-inspired adaptive communication and distributed control for conro self-reconfigurable robots

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Presents a biologically inspired approach to two basic problems in modular self-reconfigurable robots: adaptive communication in self-reconfigurable and dynamic networks, and distributed collaboration between the physically coupled modules to accomplish global effects such as locomotion and reconfiguration. Inspired by the biological concept of hormone, the paper develops the adaptive communication (AC) protocol that enables modules continuously to discover changes in their local topology, and the adaptive distributed control (ADC) protocol that allows modules to use hormone-like messages in collaborating their actions to accomplish locomotion and self-reconfiguration. These protocols are implemented and evaluated, and experiments in the CONRO self-reconfigurable robot and in a Newtonian simulation environment have shown that the protocols are robust and scaleable when configurations change dynamically and unexpectedly, and they can support online reconfiguration, module-level behavior shifting, and locomotion. The paper also discusses the implication of the hormone-inspired approach for distributed multiple robots and self-reconfigurable systems in general.
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paper_title: Docking among independent and autonomous CONRO self-reconfigurable robots

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Docking between independent groups of self-reconfigurable robotic modules enables the merger of two or more independent self-reconfigurable robots. This ability allows independent reconfigurable robots in the same environment to join together to complete a task that would otherwise not be possible with the individual robots prior to merging. The challenges for this task include: (1) coordinate and align two independent self-reconfigurable robots using the docking guidance system available only at the connectors of the docking modules; (2) overcome the inevitable errors in the alignment by a novel and coordinated movements from both docking ends; (3) ensure the secure connection at the end of docking; (4) switch configuration and let modules to discover the changes and new connections so that the two docked robots will move as a single coherent robot. We have developed methods for overcome these challenging problems and accomplished for the first time an actual docking between two independent CONRO robots each with multiple modules.
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paper_title: Cooperation through self-assembly in multi-robot systems

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This paper illustrates the methods and results of two sets of experiments in which a group of mobile robots, called s-bots, are required to physically connect to each other—i.e., to selfassemble—to cope with environmental conditions that prevent them to carry out their task individually. The first set of experiments is a pioneering study on the utility of self-assembling robots to address relatively complex scenarios, such as cooperative object trasport. The results of our work suggest that the s-bots possess hardware characteristics which facilitate the design of control mechanisms for autonomous self-assembly. The second set of experiments is an attempt to integrate within the behavioural repertoire of an s-bot decision making mechanisms to allow the robot to autonomously decide whether or not environmental contingencies require self-assembly. The results show that it is possible to synthesise, by using evolutionary computation techniques, artificial neural networks that integrate both the mechanisms for sensory-motor coordination and for decision making required by the robots in the context of self-assembly.
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paper_title: Cooperative Hole Avoidance in a Swarm-bot

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In this paper, we study coordinated motion in a swarm robotic system, called a swarm-bot. A swarm-bot is a self-assembling and self-organising artifact, composed of a swarm of s-bots, mobile robots with the ability to connect to and disconnect from each other. The swarm-bot concept is particularly suited for tasks that require all-terrain navigation abilities, such as space exploration or rescue in collapsed buildings. As a rst step toward the development of more complex control strategies, we investigate the case in which a swarm-bot has to explore an arena while avoiding to fall into holes. In such a scenario, individual s-bots have sensory-motor limitations that prevent them to navigate ecien tly and that can be overcome exploiting the physical connections and the cooperation among the s-bots. In order to synthesise the s-bots’ controller, we rely on articial evolution, which we show to be a powerful tool for the production of simple and eectiv e solutions to the hole avoidance task.
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paper_title: Ultrasonic based autonomous docking on plane for mobile robot

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Autonomous docking between independent robotic modules is critical for self-reconfigurable robots. This ability allows independent reconfigurable robots in the same environment to join together to complete a task that would otherwise not be possible with the individual robots prior to merging. This paper presents an easy and inexpensive implementation of such a system using only one ultrasonic transmitter and one receiver on each of two docking modules of JL-1. The characteristic of ultrasonic signal, being sensitive to distance and angle between transmitter and receiver, is applied to align two robots in this paper. Experiments have indicated that alternating active rotation and ultrasonic based guidance method can align two robots in one line, and ready for docking. The theory proposed in paper is general and can be applied to other inter-docking process on plane.
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paper_title: Autonomous Self-Assembly in Swarm-Bots

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In this paper, we discuss the self-assembling capabilities of the swarm-bot, a distributed robotics concept that lies at the intersection between collective and self-reconfigurable robotics. A swarm-bot is comprised of autonomous mobile robots called s-bots. S-bots can either act independently or self-assemble into a swarm-bot by using their grippers. We report on experiments in which we study the process that leads a group of s-bots to self-assemble. In particular, we present results of experiments in which we vary the number of s-bots (up to 16 physical robots), their starting configurations, and the properties of the terrain on which self-assembly takes place. In view of the very successful experimental results, swarm-bot qualifies as the current state of the art in autonomous self-assembly
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paper_title: JL-2: A Mobile Multi-robot System with Docking and Manipulating Capabilities

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This paper presents a new version of the JL series reconfigurable multi-robot system called JL-2. By virtue of the docking manipulator composed of a parallel mechanism and a cam gripper, every mobile robot in the JL-2 system is able to not only perform tasks in parallel, e.g. moving and grasping, but also dock with each other even if there are large misalignments between two robots. A motorized spherical joint is formed between two docked robots to enhance the locomotion capability of JL-2. To fulfill the demands of reconfiguration, a distributed control system and sonar based docking guidance system are designed for the JL-2 prototype. Based on the above design, the JL-2 prototype has been built and successfully demonstrated to confirm the validity and functionality of the proposed capabilities.
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paper_title: Swarm-Bot: A New Distributed Robotic Concept

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The swarm intelligence paradigm has proven to have very interesting properties such as robustness, flexibility and ability to solve complex problems exploiting parallelism and self-organization. Several robotics implementations of this paradigm confirm that these properties can be exploited for the control of a population of physically independent mobile robots. ::: ::: The work presented here introduces a new robotic concept called swarm-bot in which the collective interaction exploited by the swarm intelligence mechanism goes beyond the control layer and is extended to the physical level. This implies the addition of new mechanical functionalities on the single robot, together with new electronics and software to manage it. These new functionalities, even if not directly related to mobility and navigation, allow to address complex mobile robotics problems, such as extreme all-terrain exploration. ::: ::: The work shows also how this new concept is investigated using a simulation tool (swarmbot3d) specifically developed for quickly designing and evaluating new control algorithms. Experimental work shows how the simulated detailed representation of one s-bot has been calibrated to match the behaviour of the real robot.
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paper_title: Performance benefits of self-assembly in a swarm-bot

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Mobile robots are said to be capable of self- assembly when they can autonomously form physical connections with each other. Despite the recent proliferation of self- assembling systems, little work has been done on using self- assembly to add functional value to a robotic system, and even less on quantifying the contribution of self-assembly to system performance. In this study we demonstrate and quantify the performance benefits of i) acting as a physically larger self-assembled entity, ii) using self-assembly adaptively and iii) making the robots morphologically aware (the self-assembled robots leverage their new connected morphology in a task specific way). In our experiments, two real robots must navigate to a target over a-priori unknown terrain. In some cases the terrain can only be overcome by a self-assembled connected entity. In other cases, the robots can reach the target faster by navigating individually.
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paper_title: New locomotion gaits

paper_content:

This paper investigates new modes of robot land locomotion, in particular statically stable non-wheeled, non-tracked locomotion. These locomotion gaits are accomplished by a reconfigurable modular robot called Polypod using a control scheme combining a small number of primitive control modes for each module. The design of Polypod is first reviewed, then two and three-dimensional locomotion gaits are described along with two "exotic" gaits. These gaits have been implemented on Polypod or simulated on a graphic workstation. >
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paper_title: Design of transmote: A modular self-reconfigurable robot with versatile transformation capabilities

paper_content:

This paper presents the design and implementation of a new modular self-reconfigurable robot, called Transmote. The proposed robot has several novel features that make it suitable for search and rescue operations in complex environments. A single module can move independently by coordinating three joints. Multiple modules can connect with each other to form versatile assembled robotic structures with more powerful locomotion capabilities. The assembled structures can also transform between each other or fully disassemble into individual modules again. The modules, which communicate with each other through ZigBee compliant protocols, can build emergency communication and monitoring networks when spread to the areas without communication infrastructures. Preliminary experimental results demonstrate locomotion, mechanical docking, and transformation of several example configurations.
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paper_title: Swarm-bot: An experiment in swarm robotics

paper_content:

This paper provides an overview of the SWARM-BOTS project, a robotics project sponsored by the Future and Emerging Technologies program of the European Commission (IST-2000-31010). We describe the s-bot, a small autonomous robot with self-assembling capabilities that we designed and built within the project. Then we illustrate the cooperative object transport scenario that we chose to use as a test-bed for our robots. Last, we report on results of experiments in which a group of s-bots perform a variety of tasks within the scenario which may require self-assembling, physical cooperation and coordination.
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paper_title: Object transport by modular robots that self-assemble

paper_content:

We present a first attempt to accomplish a simple object manipulation task using the self-reconfigurable robotic system swarm-bot. The number of modular entities involved, their global shape or size and their internal structure are not pre-determined, but result from a self-organized process in which the modules autonomously grasp each other and/or an object. The modules are autonomous in perception, control, action, and power. We present quantitative results, obtained with six physical modules, that confirm the utility of self-assembling robots in a concrete task
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paper_title: Development of active cord mechanism ACM-R3 with agile 3D mobility

paper_content:

This paper describes the development of ACM-R3, which is a new version of the active cord mechanism with three-dimensional mobility. This ACM-R3 is equipped with large passive wheels which wrap its overall body, and has frictional characteristic as snake-like skin. It is also equipped with radio controlled servomotors with some gears added to them, and held tightly by shell flames so that it can move steadily and with high power. Each unit of ACM-R3 consists of a very simple structure, batteries, and electronic circuits to control itself. Consequently, ACM-R3 consists of as many units as we want to use, and is suitable for the platform of snake-like robotics researchers. ACM-R3 can demonstrate new propulsion methods and motions, combining the ability of a manipulator and a propulsion unit.
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paper_title: PolyBot: A Modular Reconfigurable Robot

paper_content:

Modular, self-reconfigurable robots show the promise of great versatility, robustness and low cost. This paper presents examples and issues in realizing those promises. PolyBot is a modular, self-reconfigurable system that is being used to explore the hardware reality of a robot with a large number of interchangeable modules. Three generations of PolyBot have been built over the last three years which include ever increasing levels of functionality and integration. PolyBot has shown versatility, by demonstrating locomotion over a variety of terrain and manipulating a variety of objects. PolyBot is the first robot to demonstrate sequentially two topologically distinct locomotion modes by self-reconfiguration. PolyBot has raised issues regarding software scalability and hardware dependency and as the design evolves the issues of low cost and robustness are being addressed while exploring the potential of modular, selfreconfigurable robots.
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paper_title: AMOEBA-I: A Shape-Shifting Modular Robot for Urban Search and Rescue

paper_content:

This work intends to enhance the mobility and flexibility of a tracked mobile robot through changing its shape in unstructured environments. A shape-shifting mobile robot, AMOEBA-I, has been developed. With three tracked modules, AMOEBA-I has nine locomotion configurations and three of them are symmetrical configurations. The key advantage of this design over other mobile robots is its adaptability and flexibility because of its various configurations. It can change its configuration fluently and automatically to adapt to different environments or missions. A modularized structure of the control system is proposed and designed for AMOEBA-I to improve the fault tolerance and substitutability of the system. The strategies of cooperative control, including cooperative shape shifting, cooperative turning and cooperative obstacle negotiation, have been proposed to improve the capability of shape shifting, locomotion and obstacle negotiation for AMOEBA-I. A series of experiments have been carried out, and demon...
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paper_title: Development of a genderless and fail-safe connection system for autonomous modular robots

paper_content:

One of the most challenging tasks on developing hardware of modular robots is to design a reliable and flexible connection system. This paper presents the design and implementation of a GENderless and FAil-safe (GENFA) connection system for autonomous modular robots that possesses self-assembly, self-reconfiguration and self-healing capabilities. By using the GENFA connector, a group of autonomous modular robots can assemble into a single robotic organism. With robust mechanical and electrical connection, a single robotic organism can disassemble into a set of disconnected units. In this paper, the detailed design of a connection system is presented. Then, mechanical strength and misalignment tolerance are studied theoretically. Some experimental tests are conducted with miniature mobile robots, and some experimental results show that the GENFA connection system is power efficient, fail-safe, and has limited misalignment tolerance.
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paper_title: Design and implementation of UBot: A modular Self-Reconfigurable Robot

paper_content:

The design and implementation of a novel modular Self-Reconfigurable Robot (SRR) called UBot is reviewed in this paper. Firstly, the philosophy of hardware design is presented. The module is designed with criteria such as cubic-shape, homogeneity, and strong connections to fulfill the requirements of complex three-dimensional reconfiguration and locomotion. Each robotic module has two degrees of freedom and four connecting surfaces with hook-type connecting mechanism. A group of modules can transform between different configurations by changing their local connections, achieve complicated modes of motion and accomplish a large variety of tasks. Secondly, a 3D dynamics simulator for UBot SRR is developed, where robot locomotion and transfiguration simulation could be done. A worm-like robot evolution is performed with results of a variety of high-performance locomotion patterns. Finally, Experiments are performed about autonomous docking, multi-mode locomotion and self-reconfiguration. The validity of docking method, CPG-network control and reconfiguration planning method is verified through locomotion and transformation tests of configurations such as snake-type, quadruped walking-type, omni-directional cross-type and loop-type.
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paper_title: Roombots—Towards decentralized reconfiguration with self-reconfiguring modular robotic metamodules

paper_content:

This paper presents our work towards a decentralized reconfiguration strategy for self-reconfiguring modular robots, assembling furniture-like structures from Roombots (RB) metamodules. We explore how reconfiguration by locomotion from a configuration A to a configuration B can be controlled in a distributed fashion. This is done using Roombots metamodules—two Roombots modules connected serially—that use broadcast signals, lookup tables of their movement space, assumptions about their neighborhood, and connections to a structured surface to collectively build desired structures without the need of a centralized planner.
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paper_title: M-TRAN: self-reconfigurable modular robotic system

paper_content:

In this paper, a novel robotic system called modular transformer (M-TRAN) is proposed. M-TRAN is a distributed, self-reconfigurable system composed of homogeneous robotic modules. The system can change its configuration by changing each module's position and connection. Each module is equipped with an onboard microprocessor, actuators, intermodule communication/power transmission devices and intermodule connection mechanisms. The special design of M-TRAN module realizes both reliable and quick self-reconfiguration and versatile robotic motion. For instance, M-TRAN is able to metamorphose into robotic configurations such as a legged machine and hereby generate coordinated walking motion without any human intervention. An actual system with ten modules was built and basic operations of self-reconfiguration and motion generation were examined through experiments. A series of software programs has also been developed to drive M-TRAN hardware, including a simulator of M-TRAN kinematics, a user interface to design appropriate configurations and motion sequences for given tasks, and an automatic motion planner for a regular cluster of M-TRAN modules. These software programs are integrated into the M-TRAN system supervised by a host computer. Several demonstrations have proven its capability as a self-reconfigurable robot.
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paper_title: Multimode locomotion via SuperBot robots

paper_content:

This paper presents a modular and reconfigurable robot for multiple locomotion modes based on reconfigurable modules. Each mode consists of characteristics for the environment type, speed, turning-ability, energy-efficiency, and recover ability from failures. The paper demonstrates this solution by the Superbot robot that combines advantages from MTRAN, CONRO and others. Experimental results, both in real robots and in simulation, have shown the validity of the approach and demonstrated the movements of forward, backward, turn, sidewinder, maneuver, and travel on batteries up to 500 meters on a flat terrain. In physics-based simulation, Superbot can perform as snake, caterpillar, insect, spider, rolling track, H-walker, etc., and move 1.0 meter/second on flat terrain with less than 6 W/module, and climb slopes of no less 40 degrees
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paper_title: ORTHO-BOT : A Modular Reconfigurable Space Robot Concept

paper_content:

A new set of challenging tasks are envisaged for future robotic planetary space missions. In contrast to conventional exploration rovers, industrial robotic roles are required for object manipulation and transportation in e.g. habitat construction. This prompts research into more robust failsafe robot designs, having greater mission redundancy for cost-effectiveness, with adjustable structures for multi-tasking. A Modular Reconfigurable design is investigated to meet these requirements using linear actuation over revolute since this alternative approach to modular robotics can form truss type structures providing inherently stable structures appropriate to the given task type. For ease of reconfiguration a connectivity solution is sought that may be simple enough to allow self-reconfiguration thus enabling extremely remote autonomous operation. In effort to meet this challenge the ORTHO-BOT developmental concept is introduced in this paper. Based on the core module developed thus far, a walking design has been successfully demonstrated in simulation to fulfil the key requirement of locomotion. Though the focus for this research is aimed at space-based roles conceptual solutions developed should also find useful application in terrestrial remote or hazardous environments.
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paper_title: Design of iMobot, an intelligent reconfigurable mobile robot with novel locomotion

paper_content:

The design and novel features of a reconfigurable modular robot, called iMobot, with four controllable degrees of freedom is presented in this paper. iMobot, which is designed for search and rescue operations as well as other applications such as research and teaching, has versatile locomotion, including a unique feature of driving as though with wheels and lifting itself into a camera platform. Future work is envisioned for using these modules in clusters to achieve advanced mobility. The accompanying video demonstrates the various locomotion of the modular robot.
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paper_title: Tetrobot: a modular system for hyper-redundant parallel robotics

paper_content:

A modular system for the design, implementation, and control of a class of highly redundant parallel robotic mechanisms is described. The Tetrobot system features a novel concentric multilink spherical (CMS) joint which allows an arbitrary number of links to share a common center of rotation. The CMS joint facilitates the construction of a wide variety of variable geometry truss mechanisms using an integrated control and computational framework. A distributed control algorithm is based on an iterative virtual force based solution which propagates the goal positions of target nodes to determine systematic adjustments of actuators. Capabilities of the Tetrobot system have been demonstrated by the construction of several configurations of up to 18 nodes, 48 links, and 15 actuators. Implementations of a double Stewart platform and a six-legged walker, constructed from the same set of parts, are described in this paper.
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paper_title: M-TRAN II: metamorphosis from a four-legged walker to a caterpillar

paper_content:

We have been developing a self-reconfigurable modular robotic system (M-TRAN) which can make various 3-D configurations and motions. In the second prototype (M-TRAN II), various improvements are integrated in order to realize complicated reconfigurations and versatile whole body motions. Those are a reliable connection/detachment mechanism, on-board multi-computers, high speed inter-module communication system, low power consumption, precise motor control, etc. Programing environments are also integrated to design self-reconfiguration processes, to verify motions in dynamics simulation, and to realize distributed control on the hardware. Hardware design, developed software and experiments are presented in this paper.
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paper_title: Self-Soldering Connectors for Modular Robots

paper_content:

The connection mechanism between neighboring modules is the most critical subsystem of each module in a modular robot. Here, we describe a strong, lightweight, and solid-state connection method based on heating a low melting point alloy to form reversible soldered connections. No external manipulation is required for forming or breaking connections between adjacent connectors, making this method suitable for reconfigurable systems such as self-reconfiguring modular robots. Energy is only consumed when switching connectivity, and the ability to transfer power and signal through the connector is inherent to the method. Soldering connectors have no moving parts, are orders of magnitude lighter than other connectors, and are readily mass manufacturable. The mechanical strength of the connector is measured as 173 N, which is enough to support many robot modules, and hundreds of connection cycles are performed before failure.
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paper_title: Evolved and Designed Self-Reproducing Modular Robotics

paper_content:

Long-term physical survivability of most robotic systems today is achieved through durable hardware. In contrast, most biological systems are not made of robust materials; long-term sustainability and evolutionary adaptation in nature are provided through processes of self-repair and, ultimately, self-reproduction. Here we demonstrate a large space of possible robots capable of autonomous self-reproduction. These robots are composed of actuated modules equipped with electromagnets to selectively control the morphology of the robotic assembly. We show a variety of 2-D and 3-D machines from 3 to 2n modules, and two physical implementations that each achieves two generations of reproduction. We show both automatically generated and manually designed morphologies
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paper_title: Emulating self-reconfigurable robots - design of the SMORES system

paper_content:

Self-reconfigurable robots are capable of changing their shape to suit a task. The design of one system called SMORES (Self-assembling MOdular Robot for Extreme Shape-shifting) is introduced. This system is capable of rearranging its modules in all three classes of reconfiguration; lattice style, chain style and mobile reconfiguration. This system is capable of emulating many of the other existing systems and promises to be a step towards a universal modular robot.
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paper_title: A motion planning method for a self-reconfigurable modular robot

paper_content:

This paper addresses motion planning of a homogeneous modular robotic system. The modules have self-reconfiguration capability so that a group of the modules can construct a robotic structure. Motion planning for self-reconfiguration is a kind of computationally difficult problem because of many combinatorial possibilities of modular configuration and the restricted degrees of freedom of the module; only two rotation axes per module. We will show a motion planning method for a class of multimodule structures. It is based on global planning and local motion scheme selection that is effective to solve the complicated planning problem.
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paper_title: SUPERBOT: A Deployable, Multi-Functional, and Modular Self-Reconfigurable Robotic System

paper_content:

Self-reconfigurable robots are modular robots that can autonomously change their shape and size to meet specific operational demands. Recently, there has been a great interest in using self-reconfigurable robots in applications such as reconnaissance, rescue missions, and space applications. Designing and controlling self-reconfigurable robots is a difficult task. Hence, the research has primarily been focused on developing systems that can function in a controlled environment. This paper presents a novel self-reconfigurable robotic system called SuperBot, which addresses the challenges of building and controlling deployable self-reconfigurable robots. Six prototype modules have been built and preliminary experimental results demonstrate that SuperBot is a flexible and powerful system that can be used in challenging real-world applications.
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paper_title: Roombots-mechanical design of self-reconfiguring modular robots for adaptive furniture

paper_content:

We aim at merging technologies from information technology, roomware, and robotics in order to design adaptive and intelligent furniture. This paper presents design principles for our modular robots, called Roombots, as future building blocks for furniture that moves and self-reconfigures. The reconfiguration is done using dynamic connection and disconnection of modules and rotations of the degrees of freedom. We are furthermore interested in applying Roombots towards adaptive behaviour, such as online learning of locomotion patterns. To create coordinated and efficient gait patterns, we use a Central Pattern Generator (CPG) approach, which can easily be optimized by any gradient-free optimization algorithm. To provide a hardware framework we present the mechanical design of the Roombots modules and an active connection mechanism based on physical latches. Further we discuss the application of our Roombots modules as pieces of a homogenic or heterogenic mix of building blocks for static structures.
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paper_title: The UBot modules for self-reconfigurable robot

paper_content:

The design philosophy of UBot module is proposed in this paper. A novel modular self-reconfigurable robot called UBot is presented. The UBot module is compact, strength, flexible and capable of performing efficient locomotion, self-reconfiguration and manipulation tasks. This robot consists of several standard modules. Each module is cubic structure based on universal joint, and has four connecting surfaces that can connect to or disconnect from adjacent modules. A hook-type connecting mechanism is designed, which could connect to or disconnect from adjacent modules quickly and reliably. This mechanism is self-locking after connected, and energy-saving. Wireless communication technology was employed in the module, which can avoid cable-winding and improve flexibility of locomotion and self-reconfiguration. One simple orientation detecting system is designed, which can detect four possible orientations by metal contact points. A group of UBot modules can adapt their configuration and function to changing environment without external help by changing their connections and positions. To achieve small oversize and mass, compact mechanical structures and electrical systems are adopted in module designing. At last, the experiment of connecting mechanism and locomotion of UBot has been implemented.
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paper_title: Towards robotic self-reassembly after explosion

paper_content:

This paper introduces a new challenge problem: designing robotic systems to recover after disassembly from high-energy events and a first implemented solution of a simplified problem. It uses vision-based localization for self- reassembly. The control architecture for the various states of the robot, from fully-assembled to the modes for sequential docking, are explained and inter-module communication details for the robotic system are described.
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paper_title: TETROBOT: a modular approach to parallel robotics

paper_content:

The TETROBOT is an actuated robotic structure which may be reassembled into many different configurations while still being controlled by the same hardware and software architecture. The TETROBOT system addresses the needs of application domains, such as space, undersea, mining, and construction, where adaptation to unstructured and changing environments and custom design for rapid implementation are required.
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paper_title: A Modular Self-Reconfigurable Robot with Enhanced Locomotion Performances: Design, Modeling, Simulations, and Experiments

paper_content:

This paper presents the design and implementation of a modular self-reconfigurable robot with enhanced locomotion capabilities. It is a small hexahedron robot which is 160 mm × 140 mm × 60 mm in size and 405 g in weight. The robot is driven by three omnidirectional wheels, with up and down symmetrical structure. The robot can perform rectilinear and rotational locomotion, and turn clockwise and counterclockwise without limitation. A new docking mechanism that combines the advantages of falcula and pin-hole has been designed for attaching and detaching different modules. The communication and image data transmission are based on a wireless network. The kinematics and dynamics of the single module has been analyzed, and the enhanced locomotion capabilities of the prototype robot are verified through experiments. The maximum linear velocity is 25.1cm/s, which is much faster than other modular self-reconfigurable robots. The mobility of two connected modules is analyzed in the ADAMS simulator. The locomotion of the docking modules is more flexible. Simulations on the wheel and crawling locomotion are conducted, the trajectories of the robot are shown, and the movement efficiency is analyzed. The docking mechanisms are tested through docking experiments, and the effectiveness has been verified. When the transmission time interval between the adjacent packets is more than 4 ms, the wireless network will not lose any packet at the maximum effective distance of 37 m in indoor environments.
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paper_title: Soldercubes: a self-soldering self-reconfiguring modular robot system

paper_content:

Soldercubes are a self-reconfiguring modular robot (MR) system whose modules are light weight, low cost, and designed with manufacturability for large batch production in mind. The frequently cited promises of modular robotics--versatility, robustness, and low cost--assume the availability of large numbers of modules. However, modules in most MR prototypes are large, mechanically complex, expensive, and difficult to manufacture. Soldercubes partially overcome this contradiction through optimizing some components for volume manufacturing processes. With the integration of a soldering connector which weighs only 2 g and has no moving parts, Soldercubes are among the cheapest, lightest and smallest among comparable self-reconfiguring MR systems. This paper describes the Soldercube module design in detail, reports on experiments in a lattice configuration, explores non-lattice applications of the system, and discusses the effects of utilising volume manufacturing processes in module production. All Soldercubes design files are released as open source hardware.
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paper_title: Distributed Self-Reconfiguration of M-TRAN III Modular Robotic System

paper_content:

A new prototype of a self-reconfigurable modular robot, M-TRAN III, has been developed, with an improved fast and rigid connection mechanism. Using a distributed controller, various control modes are possible: single-master, globally synchronous control or parallel asynchronous control. Self-reconfiguration experiments using up to 24 modules were undertaken by centralized or decentralized control. Experiments using decentralized control examined a modular structure moved in a given direction as a flow produced by local self-reconfigurations. In all experiments, system homogeneity and scalability were maintained: modules used identical software except for their ID numbers. Identical self-reconfiguration was realized when different modules were used in initial configurations.
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paper_title: Programming reconfigurable modular robots

paper_content:

Highly reconfigurable modular robots face unique control and programming challenges due to the large scale of the robotic systems, high level of reconfigurability of the systems, and high number of controllable degrees of freedom in the system. Modular robot systems such as iMobot must face these challenges in novel ways. This paper presents a unified software framework which facilitates the programming, coordination, and cooperation among multiple modular reconfigurable robots. The framework consists of Ch, a C/C++ scripting environment; Mobile-C, a C/C++ mobile agent framework; and CiMobot, an object-oriented C++ class capable of controlling multiple robot modules simultaneously. Three experiments with iMobots were performed using the new software framework. First, an iMobot is controlled autonomously using the software framework. Next, an iMobot is controlled in a master/slave scenario using the same code-base. Finally, the robot is controlled by a mobile agent using the software framework. The robotic system functions correctly and similarly for each of the experimental scenarios.
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paper_title: A Multi-Sensory Autonomous Docking Approach for a Self-Reconfigurable Robot without Mechanical Guidance

paper_content:

The most important feature of a Self-Reconfigurable Robot (SRR) is that it is reconfigurable and self-repairing. At the centre of these capabilities is autonomous docking. One difficulty for docking is the alignment between two robots. Current strategies overcome this by integrating a mechanical guiding device within the connecting mechanism. This increases the robustness of docking but compromises the flexibility of reconfiguration. In this paper, we present a new autonomous docking strategy that can overcome the drawbacks of current approaches. The new strategy uses a novel hook-type connecting mechanism and multi-sensory guidance. The hook-type connecting mechanism is strong and rigid for reliable physical connection between the modules. The multi-sensory docking strategy, which includes visual-sensor-guided rough positioning, Hall-sensor-guided fine positioning, and the locking between moving and target modules, guarantees robust docking without sacrificing reconfigurability. The proposed strategy is ...
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paper_title: Morpho: A self-deformable modular robot inspired by cellular structure

paper_content:

We present a modular robot design inspired by the creation of complex structures and functions in biology via deformation. Our design is based on the Tensegrity model of cellular structure, where active filaments within the cell contract and expand to control individual cell shape, and sheets of such cells undergo large-scale shape change through the cooperative action of connected cells. Such deformations play a role in many processes, e.g. early embryo shape change and lamprey locomotion. Modular robotic systems that replicate the basic deformable multicellular structure have the potential to quickly generate large-scale shape change and create dynamic shapes to achieve different global functions. Based on this principle, our design includes four different modular components: (1) active links, (2) passive links, (3) surface membranes, and (4) interfacing cubes. In hardware implementation, we show several self-deformable structures that can be generated from these components, including a self-deformable surface, expandable cube, terrain-adaptive bridge [C.-H. Yu et al., 2007]. We present experiments to demonstrate that such robotic structures are able to perform real time deformation to adapt to different environments. In simulation, we show that these components can be configured into a variety of bio-inspired robots, such as an amoeba-like robot and a tissue-inspired material. We argue that self-deformation is well-suited for dynamic and sensing-adaptive shape change in modular robotics.
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paper_title: A robotically reconfigurable truss

paper_content:

This paper addresses the design of passive robotically-reconfigurable truss structures and progress towards a robot capable of manipulating such structures. The elements are designed to be inserted and removed singly in “random access,” thus eliminating some assembly order constraints and enabling a physical realization of the construction process. The proposed robot is a “hinge” robot that can demonstrate manipulating said elements. The robot is also designed to be able to traverse arbitrary scale truss structures. With the addition of reconfiguration algorithms discussed by Lobo in [1], we suggest that such reconfigurable structures and robots could open the door to a machine metabolic process where structures are decomposed and recomposed autonomously to meet varying needs to a variety of applications from infrastructure recovery to space exploration.
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paper_title: Factory floor: A robotically reconfigurable construction platform

paper_content:

Passive robotically-reconfigurable truss structures offer considerable utility as they can quickly adjust to changing functional requirements and resources at a level of sophistication that no human builder could match. Furthermore, robot built structures can be constructed in environments such as surface of Mars or in micro-gravity, which would otherwise be too time consuming or dangerous for humans. In this paper we discuss some of the mechanical design challenges of developing a passive robotically-reconfigurable truss system, and present the concept of the factory floor, which can construct truss-like structures without climbing on them. In the proposed system, each level is constructed on a ground plane using a truss and node configuration and is elevated to make room for the next level. This process is repeated to create 3D truss structures or reversed to decompose the structure for the next task.
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paper_title: Shape-shifting materials for programmable structures

paper_content:

In this paper we discuss how the jamming phenomenon of granular materials might be exploited to achieve programmable matter – a robotic material that permits user specified shape changes. Opportunities for applying this research to the field of architecture are discussed. Experimental results are presented, which reveal the performance of a wide variety of materials under jamming conditions.
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paper_title: Mechanical design of odin, an extendable heterogeneous deformable modular robot

paper_content:

Highly sophisticated animals consist of a set of heterogenous modules decided by nature so that they can survive in a complex environment. In this paper we present a new modular robot inspired by biology called Odin. The Odin robot is based on a deformable lattice and consists of an extendable set of heterogeneous modules. We present the design and implementation of a cubic closed-packed (CCP) joint module, a telescoping link, and a flexible connection mechanism. The developed robot is highly versatile and opens up for a wide range of new research in modular robotics.
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paper_title: A modular robot that exploits a spontaneous connectivity control mechanism

paper_content:

This paper discusses a fully decentralized algorithm able to control the morphology of a two-dimensional modular robot called "Slimebot", consisting of many identical modules, according to the environment encountered. One of the significant features of our approach is that we explicitly exploit "emergent phenomena" stemming from the interplay between control and mechanical systems in order to control the morphology in real time. To this end, we particularly focus on a "functional material" and a "mutual entrainment", the former of which is used as a spontaneous connectivity control mechanism between the modules, and the latter of which plays as the core of the control mechanism for the generation of locomotion. Simulation results indicate that the proposed algorithm can induce locomotion, which allows us to successfully control the morphology of the modular robot in real time according to the situation without losing the coherence of the entire system.
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paper_title: Programmable matter

paper_content:

In the past 50 years, computers have shrunk from room-size mainframes to lightweight handhelds. This fantastic miniaturization is primarily the result of high-volume nanoscale manufacturing. While this technology has predominantly been applied to logic and memory, it's now being used to create advanced microelectromechanical systems using both top-down and bottom-up processes. One possible outcome of continued progress in high-volume nanoscale assembly is the ability to inexpensively produce millimeter-scale units that integrate computing, sensing, actuation, and locomotion mechanisms. A collection of such units can be viewed as a form of programmable matter.
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paper_title: Development of a transformable mobile robot composed of homogeneous gear-type units

paper_content:

Recently, there has been significant research interest in homogeneous modular robots that can transform (i.e. reconfigure their overall shape). However, many of the proposed transformation mechanisms are too expensive and complex to be practical. The transformation process is also normally slow, and therefore the mechanisms are not suitable for situations where frequent, quick reconfiguration is required. To solve these problems, we have studied a transformable mobile robot composed of multiple homogeneous gear-type units. Each unit has only one actuator and cannot move independently. But when engaged in a swarm configuration, units are able to move rapidly by rotating around one another. The most important problem encountered when developing our multi-module robot was determining how units should join together. We designed a passive attachment mechanism that employs a single, six-pole magnet carried by each unit. Motion principles for the swarm were confirmed in simulation, and based on these results we constructed a series of hardware prototypes. In our teleoperation experiments we verified that a powered unit can easily transfer from one stationary unit to another, and that the swarm can move quickly in any direction while transforming.
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paper_title: Claytronics: An Instance of Programmable Matter

paper_content:

Programmable matter refers to a technology that will allow one to control and manipulate three-dimensional physical artifacts (similar to how we already control and manipulate two-dimensional images with computer graphics). In other words, programmable matter will allow us to take a (big) step beyond virtual reality, to synthetic reality, an environment in which all the objects in a user’s environment (including the ones inserted by the computer) are physically realized. Note that the idea is not to transport objects nor is it to recreate an objects chemical composition, but rather to create a physical artifact that will mimic the shape, movement, visual appearance, sound, and tactile qualities of the original object. The enabling hardware technology behind synthetic reality is Claytronics, a form of programmable matter that can organize itself into the shape of an object and render its outer surface to match the visual appearance of that object. Claytronics is made up of individual components, called catoms—for Claytronic atoms—that can move in three dimensions (in relation to other catoms), adhere to other catoms to maintain a 3D shape, and compute state information (with possible assistance from other catoms in the ensemble). In our preliminary designs, each catom is a self-contained unit with a CPU, an energy store, a network device, a video output device, one or more sensors, a means of locomotion, and a mechanism for adhering to other catoms. Creating a physical replica of an arbitrary moving 3D object that can be updated in real time involves many challenges. The research involved in addressing these scientific challenges is likely to have broad impact beyond synthetic reality. Particularly relevant to the ASPLOS community, for example, is how to build and program a robust distributed system containing millions of computers that must cooperate extensively in a harsh environment where their configuration and goals are constantly changing? It is already possible to reproduce static 3D objects [5, 2]. To create a dynamic 3D object, however, we will build upon ideas from such diverse areas as modular and reconfigurable robotics [6, 3] and amorphous computing [1]. A Claytronics system forms a shape through the interaction of the individual catoms. For example, suppose we wish to synthesize a physical “copy” of a person. The catoms would first determine their relative location and orientation. Using that information they would then form a network in a distributed fashion and organize themselves into a hierarchical structure, both to improve locality and to facilitate the planning and coordination tasks. The goal (mimicking a human form) would then be specified abstractly, perhaps as a series of “snapshots” or as a collection of virtual deforming “forces”, and then broadcast to the catoms. Compilation of the specification would then provide each catom with a local plan for achieving the desired global shape. At this point, the catoms would start to move around each other using forces generated on-board, either magnetically or electrostatically, and adhere to each other using, for example, a nanofiber-adhesive mechanism [4]. Finally, the catoms on the surface would display an image; rendering the color and texture characteristics of the source object. If the source object begins to move, a concise description of the movements would be broadcast allowing the catoms to update their positions by moving around each other. The end result is that the system appears to be a single coordinated system. One key motivation for our work is that technology has reached a point where we can realistically build a programmable matter system which is guided by design principles which will allow it to ultimately scale to millions of sub-millimeter catoms. In fact, we expect our prototype for 2D Claytronics to be operational before ASPLOS’04. Our goal is that the system be usable now and scalable for the future. Thus, the guiding design principle, behind both the hardware and the software, is scalability. Hardware mechanisms need to scale towards micronsized catoms and million-catom ensembles. For example, the catom hardware minimizes static power consumption (e.g., no static power is used for adhesion) and avoids moving parts (e.g., the locomotion mechanism currently uses magnetic forces). Software mechanisms need to be scale invariant. For example, our localization and orientation algorithms are completely distributed, parallel, and, are indifferent to catom size. Claytronics will be a test-bed for solving some of the most challenging problems we face today: how to build complex, massively distributed dynamic systems. It is also a step towards truly integrating computers into our lives—by having them integrated into the very artifacts around us and allowing them to interact with the world.
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paper_title: Stress-driven MEMS assembly + electrostatic forces = 1mm diameter robot

paper_content:

As the size of the modules in a self-reconfiguring modular robotic system shrinks and the number of modules increases, the flexibility of the system as a whole increases. In this paper, we describe the manufacturing methods and mechanisms for a 1 millimeter diameter module which can be manufactured en masse. The module is the first step towards realizing the basic unit of claytronics, a modular robotic system designed to scale to millions of units.
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paper_title: A Development of a Modular Robot That Enables Adaptive Reconfiguration

paper_content:

This paper discusses experimental verifications of a two-dimensional modular robot called "Slimebot", consisting of many identical modules. The Slimebot exhibits adaptive reconfiguration by exploiting a fully decentralized algorithm able to control its morphology according to the environment encountered. One of the significant features of our approach is that we explicitly exploit "emergent phenomena" stemming from the interplay between control and mechanical systems in order to control the morphology in real time. To this end, we particularly focus on a "functional material" and a "mutual entrainment" among nonlinear oscillators, the former of which is used as a spontaneous connectivity control mechanism between the modules, and the latter of which acts as the core of the control mechanism for the generation of locomotion. Experimental results indicate that the proposed algorithm can induce locomotion, which allows us to successfully control the morphology of the modular robot in real time according to the situation without losing the coherence of the entire system.
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paper_title: Planar Microassembly by Parallel Actuation of MEMS Microrobots

paper_content:

We present designs, theory, and results of fabrication and testing for a novel parallel microrobotic assembly scheme using stress-engineered MEMS microrobots. The robots are 240-280 mum times 60 mum times 7-20 mum in size and can be controlled to dock compliantly together, forming planar structures several times this size. The devices are classified into species based on the design of their steering arm actuators, and the species are further classified as independent if they can be maneuvered independently using a single global control signal. In this paper, we show that microrobot species are independent if the two transition voltages of their steering arms, i.e., the voltages at which the arms are raised or lowered, form a unique pair. We present control algorithms that can be applied to groups of independent microrobot species to direct their motion from arbitrary nondead-lock configurations to desired planar microassemblies. We present designs and fabrication for four independent microrobot species, each with a unique transition voltage. The fabricated microrobots are used to demonstrate directed assembly of five types of planar structures from two classes of initial conditions. We demonstrate an average docking accuracy of 5 mum and use self-aligning compliant interaction between the microrobots to further align and stabilize the intermediate assemblies. The final assemblies match their target shapes on average 96%, by area.
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paper_title: The robot is the tether: active, adaptive power routing modular robots with unary inter-robot connectors

paper_content:

This paper describes a novel approach to powering a radical type of microrobot. Our long-term aim is to enable the construction of ensembles of millions of coordinated near-spherical, submillimeter microrobots. Both the large number of potential simultaneous neighbors of each robot (12) and the difficulty of fine actuation at such small scales preclude the use of complex connectors previously developed in many modular robotics efforts. Instead, we propose to leverage multirobot cooperation to simplify the mechanics of modular robot docking. In our approach, the robots actively cooperate to route virtual power busses (both supply and ground) to all the robots in the ensemble using only unary (single conductor) electrical connectors between robots. A unary connector allows for larger tolerances in engagement angle, simplifies robot manufacture, speeds reconfiguration, and maximizes the proportion of the connector surface area useful for carrying current. The algorithms we present permit a robot ensemble to efficiently harvest and distribute power from sources discovered in the environment and/or carried by the ensemble. We evaluate these algorithms in a variety of simulated deployment conditions and report on the impact of hardware defects, limited on-board power storage, and the ensemble-environment interface.
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paper_title: An untethered, electrostatic, globally controllable MEMS micro-robot

paper_content:

We present an untethered, electrostatic, MEMS micro-robot, with dimensions of 60 /spl mu/m by 250 /spl mu/m by 10 /spl mu/m. The device consists of a curved, cantilevered steering arm, mounted on an untethered scratch drive actuator (USDA). These two components are fabricated monolithically from the same sheet of conductive polysilicon, and receive a common power and control signal through a capacitive coupling with an underlying electrical grid. All locations on the grid receive the same power and control signal, so that the devices can be operated without knowledge of their position on the substrate. Individual control of the component actuators provides two distinct motion gaits (forward motion and turning), which together allow full coverage of a planar workspace. These MEMS micro-robots demonstrate turning error of less than 3.7/spl deg//mm during forward motion, turn with radii as small as 176 /spl mu/m, and achieve speeds of over 200 /spl mu/m/sec with an average step size as small as 12 nm. They have been shown to operate open-loop for distances exceeding 35 cm without failure, and can be controlled through teleoperation to navigate complex paths. The devices were fabricated through a multiuser surface micromachining process, and were postprocessed to add a patterned layer of tensile chromium, which curls the steering arms upward. After sacrificial release, the devices were transferred with a vacuum microprobe to the electrical grid for testing. This grid consists of a silicon substrate coated with 13-/spl mu/m microfabricated electrodes, arranged in an interdigitated fashion with 2-/spl mu/m spaces. The electrodes are insulated by a layer of electron-beam-evaporated zirconium dioxide, so that devices placed on top of the electrodes will experience an electrostatic force in response to an applied voltage. Control waveforms are broadcast to the device through the capacitive power coupling, and are decoded by the electromechanical response of the device body. Hysteresis in the system allows on-board storage of n=2 bits of state information in response to these electrical signals. The presence of on-board state information within the device itself allows each of the two device subsystems (USDA and steering arm) to be individually addressed and controlled. We describe this communication and control strategy and show necessary and sufficient conditions for voltage-selective actuation of all 2/sup n/ system states, both for our devices (n=2), and for the more general case (where n is larger.).
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paper_title: A Middleware Based Control Architecture for Modular Robot Systems

paper_content:

Robot technology has been widely used in industrial production and daily life. Unfortunately, due to the uncertainty of the environment and the diversity of functions, the complexity of the robot software is growing dramatically, in which a lot of repetitive works are done. To solve this problem, the modularization of robots and robot middleware has been proposed. From the perspective of modularization, interoperability, scalability and ease-of-use, this paper proposes a loose-coupled, service-oriented modular robot middleware (MoRoM) architecture. In this architecture, we define the standard interface to encapsulate services each functional component provides, realize system automatic configuration (plug and play), and provide a message notification mechanism as well as program frameworks. To verify the proposed middleware, we implement it using ACE-TAO, which is a real-time CORBA implementation, and test it in a modular robot system. The test shows that this architecture is suitable for improving reusability, interoperability and scalability of robot software.
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paper_title: Programming modular robots with the TOTA middleware

paper_content:

Modular robots represent a perfect application scenario for multiagent coordination. The autonomous modules composing the robot must coordinate their respective activities to enforce a specific global shape or a coherent motion gait. Here we show how the TOTA ("Tuples On The Air") middleware can be effectively exploited to support agents' coordination in this context. The key idea in TOTA is to rely on spatially distributed tuples, spread across the robot, to guide the agents' activities in moving and reshaping the robot. Three simulated examples are presented to support our claims.
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Title: Modular Self-Reconfigurable Robotic Systems: A Survey on Hardware Architectures

Section 1: Introduction
Description 1: Provide an overview of modular self-reconfigurable robots (MSRR), their advantages, and the motivation for research in this field.

Section 2: Modular Robots, Hardware Architectures
Description 2: Discuss the evolution of MSRR hardware architectures, various classification paradigms, and the major categories and subcategories of MSRR based on physical characteristics, abilities, and structural formations.

Section 3: Lattice Structured Systems
Description 3: Describe MSRR designs that follow a lattice structure, providing examples, design characteristics, and key technical details of representative systems.

Section 4: Chain Structured Systems
Description 4: Discuss MSRR designs following a chain structure, detailing their features, capabilities, and examples of significant prototypes.

Section 5: Hybrid Structured Systems
Description 5: Explore MSRR designs that incorporate both lattice and chain structures, elaborating on their design benefits, examples, and technical aspects.

Section 6: Truss Structured Systems
Description 6: Examine MSRR designs based on truss structures, detailing specific design aspects, examples, and the applications these systems are suited for.

Section 7: Free-Form Structured Systems
Description 7: Describe MSRR designs that allow free-form structural formations, including key design principles, examples, and the unique capabilities these systems provide.

Section 8: Conclusion
Description 8: Summarize the research presented, noting the creative and interdisciplinary nature of MSRR development, and outline the areas for future research and potential advancements in MSRR technologies.

Section 9: Conflicts of Interest
Description 9: State the authors' declaration regarding any conflicts of interest related to the research presented in the paper.