A new meta-module for efficient reconfiguration of hinged-units modular robots

We present a robust and compact meta-module for edge-hinged modular robot units such as M-TRAN, SuperBot, SMORES, UBot, PolyBot and CKBot, as well as for central-point-hinged ones such as Molecubes and Roombots. Thanks to the rotational degrees of freedom of these units, the novel meta-module is able to expand and contract, as to double/halve its length in each dimension. Moreover, for a large class of edge-hinged robots the proposed meta-module also performs the scrunch/relax and transfer operations required by any tunneling-based reconfiguration strategy, such as those designed for Crystalline and Telecube robots. These results make it possible to apply efficient geometric reconfiguration algorithms to this type of robots. We prove the size of this new meta-module to be optimal. Its robustness and performance substantially improve over previous results.Peer ReviewedPostprint (author's final draft

Reconfiguration of 3D Crystalline Robots Using O(log n) Parallel Moves

We consider the theoretical model of Crystalline robots, which have been introduced and prototyped by the robotics community. These robots consist of independently manipulable unit-square atoms that can extend/contract arms on each side and attach/detach from neighbors. These operations suffice to reconfigure between any two given (connected) shapes. The worst-case number of sequential moves required to transform one connected configuration to another is known to be Theta(n). However, in principle, atoms can all move simultaneously. We develop a parallel algorithm for reconfiguration that runs in only O(log n) parallel steps, although the total number of operations increases slightly to Theta(nlogn). The result is the first (theoretically) almost-instantaneous universally reconfigurable robot built from simple units.Comment: 21 pages, 10 figure

Collision avoidance for persistent monitoring in multi-robot systems with intersecting trajectories

Persistent robot tasks such as monitoring and cleaning are concerned with controlling mobile robots to act in a changing environment in a way that guarantees that the uncertainty in the system (due to change and to the actions of the robot) remains bounded for all time. Prior work in persistent robot tasks considered only robot systems with collision-free paths that move following speed controllers. In this paper we describe a solution to multi-robot persistent monitoring, where robots have intersecting trajectories. We develop collision and deadlock avoidance algorithms that are based on stopping policies, and quantify the impact of the stopping times on the overall stability of the speed controllers.United States. Office of Naval Research. Multidisciplinary University Research Initiative (Award N00014-09-1-1051)National Science Foundation (U.S.). Graduate Research Fellowship Program (Award 0645960)Boeing Compan

An Analysis of the Million Module March algorithm applied to the ATRON robotic platform

The Million Module March algorithm is a locomotion planning algorithm for self-reconfiguring robotic systems. It was first introduced by Robert Fitch and Zack Butler. It has already been proven to successfully plan movement for a kinematic abstraction whose traits are very different from the kinematic traits of the ATRON system. In this work we further examine this algorithm, and an adaptation of it to the ATRON robotic system. We examine a two dimensional proof of the reachability of connected configurations of sliding squares, and expand the proof to the three dimensional SlidingCube model of a self-reconfiguring robot. Using this proof, we explore in greater detail the theoretical basis of the Million Module March algorithm. We then modify the simulator used in the original Million Module March works to simulate the ATRON platform, and run a series of experiments. Ultimately, it is determined that the algorithm does not consistently perform as desired on the ATRON platform. We demonstrate that this performance is due to the inability of ATRON\u27s kinematics to guarantee reachability of connected configurations, and that therefore no similar algorithm of sublinear complexity can be guaranteed to perform as desired

Self Assembly of Modular Robots with Finite Number of Modules Using Graph Grammar

We wish to design decentralized algorithms for self-assembly of robotic modules that have 100% yield even if the number of available building blocks is limited, and specically when the number of available building blocks is identical to the number of blocks required by the structure. In contrast to self-assembly at the nano and micro scales where abundant building blocks are available, modular robotic systems need to self-assemble from a limited number of modules. In particular, when self-assembly is used for reconguration, it is desirable that the new conformation includes all of the available modules. We propose a suite of algorithms that (1) generate a reversible graph grammar, i.e., generates rules for a desired structure that allow the structure not only to assemble, but also to disassemble, and (2) have a set of structures that are growing in parallel converge to a single structure using broadcast communication. We show that by omitting a reversal rule for the last attached module, self-assembly eventually completes, and that communication can drastically speed up this process. We verify our results by running simulations on Matlab and Player/Stage 2D simulato

Systematic strategies for 3-dimensional modular robots

Modular robots have been studied an classified from different perspectives, generally focusing on the mechatronics. But the geometric attributes and constraints are the ones that determine the self-reconfiguration strategies. In two dimensions, robots can be geometrically classified by the grid in which their units are arranged and the free cells required to move a unit to an edge-adjacent or vertex-adjacent cell. Since a similar analysis does not exist in three dimensions, we present here a systematic study of the geometric aspects of three-dimensional modular robots. We find relations among the different designs but there are no general models, except from the pivoting cube one, that lead to deterministic reconfiguration plans. In general the motion capabilities of a single module are very limited and its motion constraints are not simple. A widely used method for reducing the complexity and improving the speed of reconfiguration plans is the use of meta-modules. We present a robust and compact meta-module of M-TRAN and other similar robots that is able to perform the expand/contract operations of the Telecube units, for which efficient reconfiguration is possible. Our meta-modules also perform the scrunch/relax and transfer operations of Telecube meta-modules required by the known reconfiguration algorithms. These reduction proofs make it possible to apply efficient geometric reconfiguration algorithms to this type of robots

Optimal self assembly of modular manipulators with active and passive modules

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Includes bibliographical references (p. 89-92).In this thesis, we describe algorithms to build self-assembling robot systems composed of active modular robots and passive bars. The robotic module is the Shady3D robot and the passive component is a rigid bar with embedded IR LEDs. We propose algorithms that demonstrate the cooperative aggregation of modular robotic manipulators with greater capability and workspace out of these two types of elements. The distributed algorithms are based on locally optimal matching. We demonstrate how to build an active structure by the cooperative aggregation and disassembly of modular robotic manipulators. A target structure is modeled as a dynamic graph. We prove that the same optimality - quadratic competitive ratio - as for the static graph can be achieved for the algorithms. We demonstrate how this algorithm can be used to build truss-like structures. We present results from physical experiments in which two 3DOF Shady3D robots and one rigid bar coordinate to self-assemble into a 6DOF manipulator. We then demonstrate cooperative algorithms for forward and inverse kinematics, grasping, and mobility with this arm.by Seung-kook Yun.S.M

Generating informative paths for persistent sensing in unknown environments

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 127-130).In this thesis, we present an adaptive control law for a team of robots to shape their paths to locally optimal configurations for sensing an unknown dynamical environment. As the robots travels through their paths, they identify the areas where the environment is dynamic and shape their paths to sense these areas. A Lyapunov-like stability proof is used to show that, under the proposed adaptive control law, the paths converge to locally optimal configurations according to a Voronoi-based coverage task, i.e. informative paths. The problem is first treated for a single robot and then extended to multiple robots. Additionally, the controllers for both the single-robot and the multi-robot case are extended to treat the problem of generating informative paths for persistent sensing tasks. Persistent sensing tasks are concerned with controlling the trajectories of mobile robots to act in a growing field in the environment in a way that guarantees that the field remains bounded for all time. The extended informative path controllers are proven to shape the paths into informative paths that are useful for performing persistent sensing tasks. Lastly, prior work in persistent sensing tasks only considered robotic systems with collision-free paths. In this thesis we also describe a solution to multi-robot persistent sensing, where robots have intersecting trajectories. We develop collision and deadlock avoidance algorithms and quantify the impact of avoiding collision on the overall stability of the persistent sensing task. Simulated and experimental results support the proposed approach.by Daniel Eduardo Soltero.S.M

Modular robots for making and climbing 3-D trusses

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 139-143).A truss climbing robot has been extensively investigated because of its wide range of promising applications such as construction and inspection of truss structures. It is designed to have degrees of freedom to move in three-dimensional truss structures. Although many degrees of freedom allow the robot to reach various position and orientation, it causes complexity of design and control. In this thesis, the concept of modular robots is suggested as a solution to reconcile a trade-off between the functionality and the simplicity of a truss climbing robot. A single module has fewer degrees of freedom than required to achieve full 3-D motion, but it can move freely in a 2-D plane. For full 3-D motion, multiple modules connect to and cooperate with each other. Thus, modular truss climbing robots can have both properties: functionality and simplicity. A modular truss climbing robot, called Shady3D, is presented as the hardware implementation of this concept. This robot has three motive degrees of freedom, and can form a six-degree-of-freedom structure by connecting to another identical module using a passive bar as a medium. Algorithms to move the robot in a 3-D truss structure have been developed and tested in hardware experiments.(cont.) The cooperation capability of two modules is also demonstrated. As a next step beyond truss climbing robots, the concept of a self-assembling truss robot with active and passive modules is presented. In this system, multiple Shady3D robots are employed as active modules and they become an active truss structure using passive bars. The procedure of self-assembling such a truss is demonstrated in computer simulations, which show a potential application in robotic truss assembly.by Yeoreum Yoon.S.M