Modular self-reconfiguring robotic systems or self-reconfigurable modular robots are autonomous kinematic machines with variable morphology. Beyond conventional actuation, sensing and control typically found in fixed-morphology robots,
self-reconfiguring robots are also able to deliberately change their
own shape by rearranging the connectivity of their parts, in order to
adapt to new circumstances, perform new tasks, or recover from damage.
For example, a robot made of such components could assume a worm-like shape to move through a narrow pipe, reassemble into something with spider-like legs to cross uneven terrain, then form a third arbitrary object (like a ball or wheel that can spin itself) to move quickly over a fairly flat terrain; it can also be used for making "fixed" objects, such as walls, shelters, or buildings.
In some cases this involves each module having 2 or more connectors for connecting several together. They can contain electronics, sensors, computer processors, memory and power supplies; they can also contain actuators that are used for manipulating their location in the environment and in relation with each other. A feature found in some cases is the ability of the modules to automatically connect and disconnect themselves to and from each other, and to form into many objects or perform many tasks moving or manipulating the environment.
By saying "self-reconfiguring" or "self-reconfigurable" it means that the mechanism or device is capable of utilizing its own system of control such as with actuators or stochastic means to change its overall structural shape. Having the quality of being "modular" in "self-reconfiguring modular robotics" is to say that the same module or set of modules can be added to or removed from the system, as opposed to being generically "modularized" in the broader sense. The underlying intent is to have an indefinite number of identical modules, or a finite and relatively small set of identical modules, in a mesh or matrix structure of self-reconfigurable modules.
Self-reconfiguration is different from the concept of self-replication, which is not a quality that a self-reconfigurable module or collection of modules needs to possess. A matrix of modules does not need to be able to increase the quantity of modules in its matrix to be considered self-reconfigurable. It is sufficient for self-reconfigurable modules to be produced at a conventional factory, where dedicated machines stamp or mold components that are then assembled into a module, and added to an existing matrix in order to supplement it to increase the quantity or to replace worn out modules.
A matrix made up of many modules can separate to form multiple matrices with fewer modules, or they can combine, or recombine, to form a larger matrix. Some advantages of separating into multiple matrices include the ability to tackle multiple and simpler tasks at locations that are remote from each other simultaneously, transferring through barriers with openings that are too small for a single larger matrix to fit through but not too small for smaller matrix fragments or individual modules, and energy saving purposes by only utilizing enough modules to accomplish a given task. Some advantages of combining multiple matrices into a single matrix is ability to form larger structures such as an elongated bridge, more complex structures such as a robot with many arms or an arm with more degrees of freedom, and increasing strength. Increasing strength, in this sense, can be in the form of increasing the rigidity of a fixed or static structure, increasing the net or collective amount of force for raising, lowering, pushing, or pulling another object, or another part of the matrix, or any combination of these features.
There are two basic methods of segment articulation that self-reconfigurable mechanisms can utilize to reshape their structures: chain reconfiguration and lattice reconfiguration.
For example, a robot made of such components could assume a worm-like shape to move through a narrow pipe, reassemble into something with spider-like legs to cross uneven terrain, then form a third arbitrary object (like a ball or wheel that can spin itself) to move quickly over a fairly flat terrain; it can also be used for making "fixed" objects, such as walls, shelters, or buildings.
In some cases this involves each module having 2 or more connectors for connecting several together. They can contain electronics, sensors, computer processors, memory and power supplies; they can also contain actuators that are used for manipulating their location in the environment and in relation with each other. A feature found in some cases is the ability of the modules to automatically connect and disconnect themselves to and from each other, and to form into many objects or perform many tasks moving or manipulating the environment.
By saying "self-reconfiguring" or "self-reconfigurable" it means that the mechanism or device is capable of utilizing its own system of control such as with actuators or stochastic means to change its overall structural shape. Having the quality of being "modular" in "self-reconfiguring modular robotics" is to say that the same module or set of modules can be added to or removed from the system, as opposed to being generically "modularized" in the broader sense. The underlying intent is to have an indefinite number of identical modules, or a finite and relatively small set of identical modules, in a mesh or matrix structure of self-reconfigurable modules.
Self-reconfiguration is different from the concept of self-replication, which is not a quality that a self-reconfigurable module or collection of modules needs to possess. A matrix of modules does not need to be able to increase the quantity of modules in its matrix to be considered self-reconfigurable. It is sufficient for self-reconfigurable modules to be produced at a conventional factory, where dedicated machines stamp or mold components that are then assembled into a module, and added to an existing matrix in order to supplement it to increase the quantity or to replace worn out modules.
A matrix made up of many modules can separate to form multiple matrices with fewer modules, or they can combine, or recombine, to form a larger matrix. Some advantages of separating into multiple matrices include the ability to tackle multiple and simpler tasks at locations that are remote from each other simultaneously, transferring through barriers with openings that are too small for a single larger matrix to fit through but not too small for smaller matrix fragments or individual modules, and energy saving purposes by only utilizing enough modules to accomplish a given task. Some advantages of combining multiple matrices into a single matrix is ability to form larger structures such as an elongated bridge, more complex structures such as a robot with many arms or an arm with more degrees of freedom, and increasing strength. Increasing strength, in this sense, can be in the form of increasing the rigidity of a fixed or static structure, increasing the net or collective amount of force for raising, lowering, pushing, or pulling another object, or another part of the matrix, or any combination of these features.
There are two basic methods of segment articulation that self-reconfigurable mechanisms can utilize to reshape their structures: chain reconfiguration and lattice reconfiguration.
Structure and control
Modular
robots are usually composed of multiple building blocks of a relatively
small repertoire, with uniform docking interfaces that allow transfer
of mechanical forces and moments, electrical power and communication
throughout the robot.
The modular building blocks usually consist of some primary
structural actuated unit, and potentially additional specialized units
such as grippers, feet, wheels, cameras, payload and energy storage and
generation.
A taxonomy of architectures
Modular
self-reconfiguring robotic systems can be generally classified into
several architectural groups by the geometric arrangement of their unit
(lattice vs. chain). Several systems exhibit hybrid properties, and
modular robots have also been classified into the two categories of
Mobile Configuration Change (MCC) and Whole Body Locomotion (WBL).
Lattice
architecture: 12 modules of the homogeneous lattice system Micro Unit
assembled together shown with corresponding grid and docking points
network
- Lattice architecture have their units connecting their docking interfaces at points into virtual cells of some regular grid. This network of docking points can be compared to atoms in a crystal and the grid to the lattice of that crystal. Therefore, the kinematical features of lattice robots can be characterized by their corresponding crystallographic displacement groups (chiral space groups). Usually few units are sufficient to accomplish a reconfiguration step. Lattice architectures allows a simpler mechanical design and a simpler computational representation and reconfiguration planning that can be more easily scaled to complex systems.
- Chain architecture do not use a virtual network of docking points for their units. The units are able to reach any point in the space and are therefore more versatile, but a chain of many units may be necessary to reach a point making it usually more difficult to accomplish a reconfiguration step. Such systems are also more computationally difficult to represent and analyze.
- Hybrid architecture takes advantages of both previous architectures. Control and mechanism are designed for lattice reconfiguration but also allow to reach any point in the space.
Modular robotic systems can also be classified according to the way by which units are reconfigured (moved) into place.
- Deterministic reconfiguration relies on units moving or being directly manipulated into their target location during reconfiguration. The exact location of each unit is known at all times. Reconfiguration times can be guaranteed, but sophisticated feedback control is necessary to assure precise manipulation. Macro-scale systems are usually deterministic.
- Stochastic reconfiguration relies on units moving around using statistical processes (like Brownian motion). The exact location of each unit only known when it is connected to the main structure, but it may take unknown paths to move between locations. Reconfiguration times can be guaranteed only statistically. Stochastic architectures are more favorable at micro scales.
Modular robotic systems are also generally classified depending on the design of the modules.
- Homogeneous modular robot systems have many modules of the same design forming a structure suitable to perform the required task. An advantage over other systems is that they are simple to scale in size (and possibly function), by adding more units. A commonly described disadvantage is limits to functionality - these systems often require more modules to achieve a given function, than heterogeneous systems.
- Heterogeneous modular robot systems have different modules, each of which do specialized functions, forming a structure suitable to perform a task. An advantage is compactness, and the versatility to design and add units to perform any task. A commonly described disadvantage is an increase in complexity of design, manufacturing, and simulation methods.
Other modular robotic systems exist which are not
self-reconfigurable, and thus do not formally belong to this family of
robots though they may have similar appearance. For example, self-assembling
systems may be composed of multiple modules but cannot dynamically
control their target shape. Similarly, tensegrity robotics may be
composed of multiple interchangeable modules but cannot
self-reconfigure.
Motivation and inspiration
There are two key motivations for designing modular self-reconfiguring robotic systems.
- Functional advantage: Self reconfiguring robotic systems are potentially more robust and more adaptive than conventional systems. The reconfiguration ability allows a robot or a group of robots to disassemble and reassemble machines to form new morphologies that are better suitable for new tasks, such as changing from a legged robot to a snake robot (snakebot) and then to a rolling robot. Since robot parts are interchangeable (within a robot and between different robots), machines can also replace faulty parts autonomously, leading to self-repair.
Autonomous modular robotics in space
- Economic advantage: Self reconfiguring robotic systems can potentially lower overall robot cost by making a range of complex machines out of a single (or relatively few) types of mass-produced modules.
Both these advantages have not yet been fully realized. A modular
robot is likely to be inferior in performance to any single custom robot
tailored for a specific task. However, the advantage of modular
robotics is only apparent when considering multiple tasks that would
normally require a set of different robots.
The added degrees of freedom make modular robots more versatile
in their potential capabilities, but also incur a performance tradeoff
and increased mechanical and computational complexities.
The quest for self-reconfiguring robotic structures is to some
extent inspired by envisioned applications such as long-term space
missions, that require long-term self-sustaining robotic ecology that
can handle unforeseen situations and may require self repair. A second
source of inspiration are biological systems that are self-constructed
out of a relatively small repertoire of lower-level building blocks
(cells or amino acids, depending on scale of interest). This
architecture underlies biological systems' ability to physically adapt,
grow, heal, and even self replicate – capabilities that would be
desirable in many engineered systems.
Manufacturer operating in the self-reconfiguring modular robot
industry include ABB Ltd., Kawasaki Heavy Industries, Ltd., Yaskawa
Electric Corporation, Fanuc Corporation, Kuka AG, Mitsubishi Electric
Corporation, Denso Corporation, Nachi-Fujikoshi Corp., Comau S.P.A.,
Universal Robots A/S, and CMA Robotics S.P.A.
Application areas
Given
these advantages, where would a modular self-reconfigurable system be
used? While the system has the promise of being capable of doing a wide
variety of things, finding the "killer application" has been somewhat elusive. Here are several examples:
Space exploration
One application that highlights the advantages of self-reconfigurable systems is long-term space missions.
These require long-term self-sustaining robotic ecology that can handle
unforeseen situations and may require self repair. Self-reconfigurable
systems have the ability to handle tasks that are not known a priori,
especially compared to fixed configuration systems. In addition, space
missions are highly volume- and mass-constrained. Sending a robot system
that can reconfigure to achieve many tasks may be more effective than
sending many robots that each can do one task.
Telepario
Another
example of an application has been coined "telepario" by CMU professors
Todd Mowry and Seth Goldstein. What the researchers propose to make are
moving, physical,
three-dimensional replicas of people or objects, so lifelike that human
senses would accept them as real. This would eliminate the need for
cumbersome virtual reality gear and overcome the viewing angle
limitations of modern 3D approaches. The replicas would mimic the shape
and appearance of a person or object being imaged in real time, and as
the originals moved, so would their replicas. One aspect of this
application is that the main development thrust is geometric
representation rather than applying forces to the environment as in a
typical robotic manipulation task. This project is widely known as
claytronics or Programmable matter (noting that programmable matter is a much more general term, encompassing functional programmable materials, as well).
Bucket of stuff
A
third long term vision for these systems has been called "bucket of
stuff". In this vision, consumers of the future have a container of
self-reconfigurable modules say in their garage, basement, or attic.
When the need arises, the consumer calls forth the robots to achieve a
task such as "clean the gutters" or "change the oil in the car" and the
robot assumes the shape needed and does the task.
History and state of the art
The
roots of the concept of modular self-reconfigurable robots can be
traced back to the "quick change" end effector and automatic tool
changers in computer numerical controlled machining centers in the
1970s. Here, special modules each with a common connection mechanism
could be automatically swapped out on the end of a robotic arm. However,
taking the basic concept of the common connection mechanism and
applying it to the whole robot was introduced by Toshio Fukuda with the
CEBOT (short for cellular robot) in the late 1980s.
The early 1990s saw further development from Greg Chirikjian,
Mark Yim, Joseph Michael, and Satoshi Murata. Chirikjian, Michael, and
Murata developed lattice reconfiguration systems and Yim developed a
chain based system. While these researchers started with from a
mechanical engineering emphasis, designing and building modules then
developing code to program them, the work of Daniela Rus and Wei-min
Shen developed hardware but had a greater impact on the programming
aspects. They started a trend towards provable or verifiable distributed
algorithms for the control of large numbers of modules.
One of the more interesting hardware platforms recently has been
the MTRAN II and III systems developed by Satoshi Murata et al. This
system is a hybrid chain and lattice system. It has the advantage of
being able to achieve tasks more easily like chain systems, yet
reconfigure like a lattice system.
More recently new efforts in stochastic self-assembly have been pursued by Hod Lipson and Eric Klavins. A large effort at Carnegie Mellon University headed by Seth Goldstein and Todd Mowry has started looking at issues in developing millions of modules.
Many tasks have been shown to be achievable, especially with
chain reconfiguration modules. This demonstrates the versatility of
these systems however, the other two advantages, robustness and low cost
have not been demonstrated. In general the prototype systems developed
in the labs have been fragile and expensive as would be expected during
any initial development.
There is a growing number of research groups actively involved in
modular robotics research. To date, about 30 systems have been designed
and constructed, some of which are shown below.
| System | Class, DOF | Author | Year |
|---|---|---|---|
| CEBOT | Mobile | Fukuda et al. (Tsukuba) | 1988 |
| Polypod | chain, 2, 3D | Yim (Stanford) | 1993 |
| Metamorphic | lattice, 6, 2D | Chirikjian (Caltech) | 1993 |
| Fracta | lattice, 3 2D | Murata (MEL) | 1994 |
| Fractal Robots | lattice, 3D | Michael(UK) | 1995 |
| Tetrobot | chain, 1 3D | Hamline et al. (RPI) | 1996 |
| 3D Fracta | lattice, 6 3D | Murata et al. (MEL) | 1998 |
| Molecule | lattice, 4 3D | Kotay & Rus (Dartmouth) | 1998 |
| CONRO | chain, 2 3D | Will & Shen (USC/ISI) | 1998 |
| PolyBot | chain, 1 3D | Yim et al. (PARC) | 1998 |
| TeleCube | lattice, 6 3D | Suh et al., (PARC) | 1998 |
| Vertical | lattice, 2D | Hosakawa et al., (Riken) | 1998 |
| Crystalline | lattice, 4 2D | Vona & Rus, (Dartmouth) | 1999 |
| I-Cube | lattice, 3D | Unsal, (CMU) | 1999 |
| Micro Unit | lattice, 2 2D | Murata et al.(AIST) | 1999 |
| M-TRAN I | hybrid, 2 3D | Murata et al.(AIST) | 1999 |
| Pneumatic | lattice, 2D | Inou et al., (TiTech) | 2002 |
| Uni Rover | mobile, 2 2D | Hirose et al., (TiTech) | 2002 |
| M-TRAN II | hybrid, 2 3D | Murata et al., (AIST) | 2002 |
| Atron | lattice, 1 3D | Stoy et al., (U.S Denmark) | 2003 |
| S-bot | mobile, 3 2D | Mondada et al., (EPFL) | 2003 |
| Stochastic | lattice, 0 3D | White, Kopanski, Lipson (Cornell) | 2004 |
| Superbot | hybrid, 3 3D | Shen et al., (USC/ISI) | 2004 |
| Y1 Modules | chain, 1 3D | Gonzalez-Gomez et al., (UAM) | 2004 |
| M-TRAN III | hybrid, 2 3D | Kurokawa et al., (AIST) | 2005 |
| AMOEBA-I | Mobile, 7 3D | Liu JG et al., (SIA) | 2005 |
| Catom | lattice, 0 2D | Goldstein et al., (CMU) | 2005 |
| Stochastic-3D | lattice, 0 3D | White, Zykov, Lipson (Cornell) | 2005 |
| Molecubes | hybrid, 1 3D | Zykov, Mytilinaios, Lipson (Cornell) | 2005 |
| Prog. parts | lattice, 0 2D | Klavins, (U. Washington) | 2005 |
| Microtub [6] | chain, 2 2D | Brunete, Hernando, Gambao (UPM) | 2005 |
| Miche | lattice, 0 3D | Rus et al., (MIT) | 2006 |
| GZ-I Modules | chain, 1 3D | Zhang & Gonzalez-Gomez (U. Hamburg, UAM) | 2006 |
| The Distributed Flight Array | lattice, 6 3D | Oung & D'Andrea (ETH Zurich) | 2008 |
| Evolve | chain, 2 3D | Chang Fanxi, Francis (NUS) | 2008 |
| EM-Cube | Lattice, 2 2D | An, (Dran Computer Science Lab) | 2008 |
| Roombots | Hybrid, 3 3D | Sproewitz, Moeckel, Ijspeert, Biorobotics Laboratory, (EPFL) | 2009 |
| Programmable Matter by Folding | Sheet, 3D | Wood, Rus, Demaine et al., (Harvard & MIT) | 2010 |
| Sambot | Hybrid, 3D | HaiYuan Li, HongXing Wei, TianMiao Wang et al., (Beihang University) | 2010 |
| Moteins | Hybrid, 1 3D | Center for Bits and Atoms, (MIT) | 2011 |
| ModRED | Chain, 4 3D | C-MANTIC Lab, (UNO/UNL) | 2011 |
| Programmable Smart Sheet | Sheet, 3D | An & Rus, (MIT) | 2011 |
| SMORES | Hybrid, 4, 3D | Davey, Kwok, Yim (UNSW, UPenn) | 2012 |
| Symbrion | Hybrid, 3D | EU Projects Symbrion and Replicator | 2013 |
| ReBiS - Re-configurable Bipedal Snake | Chain, 1, 3D | Rohan, Ajinkya, Sachin, S. Chiddarwar, K. Bhurchandi (VNIT, Nagpur) | 2014 |
| Soft Mod. Rob. Cubes | Lattice, 3D | Vergara, Sheng, Mendoza-Garcia, Zagal (UChile) | 2017 |
Some current systems
Polybot G3 Modular self-reconfigurable robot
- PolyBot G3 (2002)
A chain self-reconfiguration system. Each module is about 50 mm on a
side, and has 1 rotational DOF. It is part of the PolyBot modular robot
family that has demonstrated many modes of locomotion including walking:
biped, 14 legged, slinky-like, snake-like: concertina in a gopher hole,
inchworm gaits, rectilinear undulation and sidewinding gaits, rolling
like a tread at up to 1.4 m/s, riding a tricycle, climbing: stairs,
poles pipes, ramps etc. More information can be found at the polybot
webpage at PARC.
Metamorphosis by a self-reconfigurable robot, M-TRAN III
- M-TRAN III (2005)
A hybrid type self-reconfigurable system. Each module is two cube
size (65 mm side), and has 2 rotational DOF and 6 flat surfaces for
connection. It is the 3rd M-TRAN prototypes. Compared with the former
(M-TRAN II), speed and reliability of connection is largely improved. As
a chain type system, locomotion by CPG (Central Pattern Generator)
controller in various shapes has been demonstrated by M-TRAN II. As a
lattice type system, it can change its configuration, e.g., between a 4
legged walker to a caterpillar like robot. See the M-TRAN webpage at
AIST.
- AMOEBA-I (2005)
AMOEBA-I, a three-module reconfigurable mobile robot was developed in
Shenyang Institute of Automation (SIA), Chinese Academy of Sciences
(CAS) by Liu J G et al. AMOEBA-I
has nine kinds of non-isomorphic configurations and high mobility under
unstructured environments.Four generations of its platform have been
developed and a series of researches have been carried out on their
reconfiguration mechanism, non-isomorphic configurations, tipover
stability, and reconfiguration planning. Experiments have demonstrated
that such kind structure permits good mobility and high flexibility to
uneven terrain. Being hyper-redundant, modularized and reconfigurable,
AMOEBA-I has many possible applications such as Urban Search and Rescue
(USAR) and space exploration.
Stochastic-3D (2005)
High spatial resolution for arbitrary three-dimensional shape
formation with modular robots can be accomplished using lattice system
with large quantities of very small, prospectively microscopic modules.
At small scales, and with large quantities of modules, deterministic
control over reconfiguration of individual modules will become
unfeasible, while stochastic mechanisms will naturally prevail.
Microscopic size of modules will make the use of electromagnetic
actuation and interconnection prohibitive, as well, as the use of
on-board power storage.
Three large scale prototypes were built in attempt to demonstrate
dynamically programmable three-dimensional stochastic reconfiguration
in a neutral-buoyancy environment. The first prototype used
electromagnets for module reconfiguration and interconnection. The
modules were 100 mm cubes and weighed 0.81 kg. The second prototype used
stochastic fluidic reconfiguration and interconnection mechanism. Its
130 mm cubic modules weighed 1.78 kg each and made reconfiguration
experiments excessively slow. The current third implementation inherits
the fluidic reconfiguration principle. The lattice grid size is 80 mm,
and the reconfiguration experiments are under way.
Molecubes in motion
Molecubes (2005)
This hybrid self-reconfiguring system was built by the Cornell
Computational Synthesis Lab to physically demonstrate artificial
kinematic self-reproduction. Each module is a 0.65 kg cube with 100 mm
long edges and one rotational degree of freedom. The axis of rotation is
aligned with the cube's longest diagonal. Physical self-reproduction of
a three- and a four-module robots was demonstrated. It was also shown
that, disregarding the gravity constraints, an infinite number of
self-reproducing chain meta-structures can be built from Molecubes.
The Programmable Parts (2005)
The programmable parts are stirred randomly on an air-hockey
table by randomly actuated air jets. When they collide and stick, they
can communicate and decide whether to stay stuck, or if and when to
detach. Local interaction rules can be devised and optimized to guide
the robots to make any desired global shape. More information can be
found at the programmable parts web page.
SuperBot (2006)
The SuperBot modules fall into the hybrid architecture. The
modules have three degrees of freedom each. The design is based on two
previous systems: Conro (by the same research group) and MTRAN
(by Murata et al.). Each module can connect to another module through
one of its six dock connectors. They can communicate and share power
through their dock connectors. Several locomotion gaits have been
developed for different arrangements of modules. For high-level
communication the modules use hormone-based control, a distributed,
scalable protocol that does not require the modules to have unique ID's.
Miche (2006)
The Miche system is a modular lattice system capable of arbitrary
shape formation. Each module is an autonomous robot module capable of
connecting to and communicating with its immediate neighbors. When
assembled into a structure, the modules form a system that can be
virtually sculpted using a computer interface and a distributed process.
The group of modules collectively decide who is on the final shape and
who is not using algorithms that minimize the information transmission
and storage. Finally, the modules not in the structure let go and fall
off under the control of an external force, in this case gravity.
More details at Miche (Rus et al.).
A 10-module configuration of the Distributed Flight Array in flight.
The Distributed Flight Array (2009)
The Distributed Flight Array is a modular robot consisting of
hexagonal-shaped single-rotor units that can take on just about any
shape or form. Although each unit is capable of generating enough thrust
to lift itself off the ground, on its own it is incapable of flight
much like a helicopter cannot fly without its tail rotor. However, when
joined together, these units evolve into a sophisticated multi-rotor
system capable of coordinated flight and much more.
Roombots (2009)
Roombots have a hybrid architecture. Each module has three degree
of freedom, two of them using the diametrical axis within a regular
cube, and a third (center) axis of rotation connecting the two spherical
parts. All three axes are continuously rotatory. The outer Roombots DOF
is using the same axis-orientation as Molecubes, the third, central
Roombots axis enables the module to rotate its two outer DOF against
each other. This novel feature enables a single Roombots module to
locomote on flat terrain, but also to climb a wall, or to cross a
concave, perpendicular edge. Convex edges require the assembly of at
least two modules into a Roombots "Metamodule". Each module has ten
available connector slots, currently two of them are equipped with an
active connection mechanism based on mechanical latches.
Roombots are designed for two tasks: to eventually shape objects of
daily life, e.g. furniture, and to locomote, e.g. as a quadruped or a
tripod robot made from multiple modules.
Sambot (2010)
Being inspired form social insects, multicellular organism and
mophogenetic robots. The aim of the Sambot is to develop swarm robotics
and conduct research on the swarm intelligence, self-assembly and
co-evolution of the body and brain for autonomous morphogeneous.
Differing from swarm robot, self-reconfigurable robot and morphgenetic
robot, the research focuses on self-assembly swarm modular robots that
interact and dock as an autonomous mobile module with others to achieve
swarm intelligence and furtherly discuss the autonomous construction in
space station and exploratory tools and artificial complex structures.
Each Sambot robot can run as an autonomous individual in wheel and
besides, using combination of the sensors and docking mechanism, the
robot can interact and dock with the environments and other robots. By
the advantage of motion and connection, Sambot swarms can aggregate into
a symbiotic or whole organism and generate locomotion as the bionic
articular robots. In this case, some self-assembling, self-organizing,
self-reconfiguring, and self-repairing function and research are
available in design and application view. Inside the modular robot whose
size is 80(W)X80(L)X102(H) mm, MCU (ARM and AVR), communication
(Zigbee), sensors, power, IMU, positioning modules are embedded.
More information can be found at Self-assembly Swarm Modular Robots
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Motein
- Moteins (2011)
It is mathematically proven that physical strings or chains of simple
shapes can be folded into any continuous area or volumetric shape.
Moteins employ such shape-universal folding strategies, with as few as
one (for 2D shapes) or two (for 3D shapes) degrees of freedom and simple
actuators with as few as two (for 2D shapes) or three (for 3D shapes)
states per unit.
- Symbrion (2013)
Symbrion
(Symbiotic Evolutionary Robot Organisms) was a project funded by the
European Commission between 2008 - 2013 to develop a framework in which a
homogeneous swarm of miniature interdependent robots can co-assemble
into a larger robotic organism to gain problem-solving momentum. One of
the key aspects of Symbrion is inspired by the biological world: an
artificial genome that allows storing and evolution of suboptimal
configurations in order to increased the speed of adaptation. A large
part of the developments within Symbrion is open-source and
open-hardware.
Quantitative accomplishment
- The robot with most active modules has 56 units (polybot centipede, PARC)
- The smallest actuated modular unit has a size of 12 mm
- The largest actuated modular unit (by volume) has the size of 8 m^3 (GHFC)giant helium filled catoms, CMU
- The strongest actuation modules are able to lift 5 identical horizontally cantilevered units.(PolyBot g1v5, PARC)
- The fastest modular robot can move at 23 unit-sizes/second.(CKbot, dynamic rolling, ISER'06)
- The largest simulated system contained many hundreds of thousands of units.
Challenges, solutions, and opportunities
Since
the early demonstrations of early modular self-reconfiguring systems,
the size, robustness and performance has been continuously improving. In
parallel, planning and control algorithms have been progressing to
handle thousands of units. There are, however, several key steps that
are necessary for these systems to realize their promise of adaptability, robustness and low cost.
These steps can be broken down into challenges in the hardware design,
in planning and control algorithms and in application. These challenges
are often intertwined.
Hardware design challenges
The
extent to which the promise of self-reconfiguring robotic systems can
be realized depends critically on the numbers of modules in the system.
To date, only systems with up to about 50 units have been demonstrated,
with this number stagnating over almost a decade. There are a number of
fundamental limiting factors that govern this number:
- Limits on strength, precision, and field robustness (both mechanical and electrical) of bonding/docking interfaces between modules
- Limits on motor power, motion precision and energetic efficiency of units, (i.e. specific power, specific torque)
- Hardware/software design. Hardware that is designed to make the software problem easier. Self-reconfiguring systems have more tightly coupled hardware and software than any other existing system.
Planning and control challenges
Though
algorithms have been developed for handling thousands of units in ideal
conditions, challenges to scalability remain both in low-level control
and high-level planning to overcome realistic constraints:
- Algorithms for parallel-motion for large scale manipulation and locomotion
- Algorithms for robustly handling a variety of failure modes, from misalignments, dead-units (not responding, not releasing) to units that behave erratically.
- Algorithms that determine the optimal configuration for a given task
- Algorithms for optimal (time, energy) reconfiguration plan
- Efficient and scalable (asynchronous) communication among multiple units
Application challenges
Though
the advantages of Modular self-reconfiguring robotic systems is largely
recognized, it has been difficult to identify specific application
domains where benefits can be demonstrated in the short term. Some
suggested applications are
- Space exploration and Space colonization applications, e.g. Lunar colonization
- Construction of large architectural systems
- Deep sea exploration/mining
- Search and rescue in unstructured environments
- Rapid construction of arbitrary tools under space/weight constraints
- Disaster relief shelters for displaced peoples
- Shelters for impoverished areas which require little on-the-ground expertise to assemble
Grand Challenges
Several robotic fields have identified Grand Challenges that act as a catalyst for development and serve as a short-term goal in absence of immediate killer apps.
The Grand Challenge is not in itself a research agenda or milestone,
but a means to stimulate and evaluate coordinated progress across
multiple technical frontiers. Several Grand Challenges have been
proposed for the modular self-reconfiguring robotics field:
- Demonstration of a system with >1000 units. Physical demonstration of such a system will inevitably require rethinking key hardware and algorithmic issues, as well as handling noise and error.
- Robosphere. A self-sustaining robotic ecology, isolated for a long period of time (1 year) that needs to sustain operation and accomplish unforeseen tasks without any human presence.
- Self replication A system with many units capable of self replication by collecting scattered building blocks will require solving many of the hardware and algorithmic challenges.
- Ultimate Construction A system capable of making objects out of the components of, say, a wall.
- Biofilter analogy If the system is ever made small enough to
be injected into a mammal, one task may be to monitor molecules in the
blood stream and allow some to pass and others not to, somewhat like the
blood–brain barrier. As a challenge, an analogy may be made where system must be able to:
- be inserted into a hole one module's diameter.
- travel some specified distance in a channel that is say roughly 40 x 40 module diameters in area.
- form a barrier fully conforming to the channel (whose shape is non-regular, and unknown beforehand).
- allow some objects to pass and others not to (not based on size).
- Since sensing is not the emphasis of this work, the actual detection of the passable objects should be made trivial.
Inductive transducers
A
unique potential solution that can be exploited is the use of inductors
as transducers. This could be useful for dealing with docking and
bonding problems. At the same time it could also be beneficial for its
capabilities of docking detection (alignment and finding distance),
power transmission, and (data signal) communication. A proof-of-concept
video can be seen
here.
The rather limited exploration down this avenue is probably a
consequence of the historical lack of need in any applications for such
an approach.
Google Groups
Self-Reconfiguring and Modular Technology is a group for discussion of the perception and understanding of the developing field.robotics.
Modular Robotics Google Group
is an open public forum dedicated to announcements of events in the
field of Modular Robotics. This medium is used to disseminate calls to
workshops, special issues and other academic activities of interest to
modular robotics researchers. The founders of this Google group intend
it to facilitate the exchange of information and ideas within the
community of modular robotics researchers around the world and thus
promote acceleration of advancements in modular robotics. Anybody who is
interested in objectives and progress of Modular Robotics can join this
Google group and learn about the new developments in this field.
Websites dedicated specifically to exploring this technology
- "Flexibility Envelope". Self Reconfiguring Modular Robotics And The Future Created.
- "Self Reconfigurable Modular Technology". Collection of Web Sites, Web Pages, Video Clips, Articles, and Documents.
