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1. Recognition and Reconfiguration of Lattice-Based Cellular Structures by Simple Robots

   https://doi.org/10.1109/ICRA40945.2020.9196700  

   Niehs, Eike; Schmidt, Arne; Scheffer, Christian; Biediger, Daniel E.; Yannuzzi, Michael; Jenett, Benjamin; Abdel-Rahman, Amira; Cheung, Kenneth C.; Becker, Aaron T.; Fekete, Sandor P. (May 2020, 2020 IEEE International Conference on Robotics and Automation (ICRA))

   null (Ed.)

   We consider recognition and reconfiguration of lattice-based cellular structures by very simple robots with only basic functionality. The underlying motivation is the construction and modification of space facilities of enormous dimensions, where the combination of new materials with extremely simple robots promises structures of previously unthinkable size and flexibility; this is also closely related to the newly emerging field of programmable matter. Aiming for large-scale scalability, both in terms of the number of the cellular components of a structure, as well as the number of robots that are being deployed for construction requires simple yet robust robots and mechanisms, while also dealing with various basic constraints, such as connectivity of a structure during reconfiguration. To this end, we propose an approach that combines ultra-light, cellular building materials with extremely simple robots. We develop basic algorithmic methods that are able to detect and reconfigure arbitrary cellular structures, based on robots that have only constant-sized memory. As a proof of concept, we demonstrate the feasibility of this approach for specific cellular materials and robots that have been developed at NASA. 

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2. Hierarchical Shape Construction and Complexity for Slidable Polyominos under Uniform External Forces

   https://doi.org/10.1137/1.9781611975994.160  

   Balanza-Martinez, Jose; Caballero, David; Cantu, Angel; Flores, Mauricio; Gomez, Timothy; Luchsinger, Austin; Reyes, Rene; Schweller, Robert; Wylie, Tim (January 2020, ACM-SIAM Symposium on Discrete Algorithms)

   Advances in technology have given us the ability to create and manipulate robots for numerous applications at the molecular scale. At this size, fabrication tool limitations motivate the use of simple robots. The individual control of these simple objects can be infeasible. We investigate a model of robot motion planning, based on global external signals, known as the tilt model. Given a board and initial placement of polyominoes, the board may be tilted in any of the 4 cardinal directions, causing all slidable polyominoes to move maximally in the specified direction until blocked.We propose a new hierarchy of shapes and design a single configuration that is strongly universal for any w×h bounded shape within this hierarchy (it can be reconfigured to construct any w×h bounded shape in the hierarchy). This class of shapes constitutes the most general set of buildable shapes in the literature, with most previous work consisting of just the first-level of our hierarchy. We accompany this result with a O(n4logn)-time algorithm for deciding if a given hole-free shape is a member of the hierarchy. For our second result, we resolve a long-standing open problem within the field: We show that deciding if a given position may be covered by a tile for a given initial board configuration is PSPACE-complete, even when all movable pieces are 1×1 tiles with no glues. We achieve this result by a reduction from Non-deterministic Constraint Logic for a one-player unbounded game. 

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3. Reconfiguration of a 2D Structure Using Spatio-Temporal Planning and Load Transferring

   https://doi.org/10.1109/ICRA57147.2024.10611057  

   Garcia, Javier; Yannuzzi, Michael; Kramer, Peter; Rieck, Christian; Fekete, Sándor P; Becker, Aaron T (May 2024, IEEE)

   We present progress on the problem of reconfiguring a 2D arrangement of building material by a cooperative group of robots. These robots must avoid collisions, deadlocks, and are subjected to the constraint of maintaining connectivity of the structure. We develop two reconfiguration methods, one based on spatio-temporal planning, and one based on target swapping, to increase building efficiency. The first method can significantly reduce planning times compared to other multi-robot planners. The second method helps to reduce the amount of time robots spend waiting for paths to be cleared, and the overall distance traveled by the robots. 

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4. Connected Reconfiguration of Polyominoes Amid Obstacles using RRT

   https://doi.org/10.1109/IROS47612.2022.9981184  

   Garcia, Javier; Yannuzzi, Michael; Kramer, Peter; Rieck, Christian; Becker, Aaron T. (October 2022, 2022 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS))

   This paper investigates using a sampling-based approach, the RRT*, to reconfigure a 2D set of connected tiles in complex environments, where multiple obstacles might be present. Since the target application is automated building of discrete, cellular structures using mobile robots, there are constraints that determine what tiles can be picked up and where they can be dropped off during reconfiguration. We compare our approach to two algorithms as global and local planners, and show that we are able to find more efficient build sequences using a reasonable amount of samples, in environments with varying degrees of obstacle space. 

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5. Topology Design and Optimization of Modular Soft Robots Capable of Homogenous and Heterogenous Reconfiguration

   https://doi.org/10.1115/1.4062265  

   Freeman, Caitlin; Conzola, Justin; Vikas, Vishesh (June 2023, Journal of Computational and Nonlinear Dynamics)

   Abstract The deformability of soft material robots provides them with the ability to transform between complex shapes and forms. This unique ability facilitates Modular Soft Robots (MSoRos) to assemble and reconfigure into different configurations, e.g., planar and spherical. These topologies display widely different locomotion modes that are desirable to navigate different environments, e.g., crawling or rolling for these cases. This research presents topology design and optimization methodology of MSoRos capable of both homogeneous and heterogeneous reconfiguration in spherical and planar configurations. Homogeneous reconfiguration refers to the scenario when all the modules are identical, while the heterogeneous contains nonidentical modules. The sequential design approach uses a polyhedron (Archimedean or Platonic) as the base solid to define module characteristics. As the design processes involve nonlinear projections, the base polyhedron also dictates the type of reconfiguration—heterogeneous (Archimedean) or homogeneous (Platonic). Thereafter, it applies the polyhedron vertex alignment principle to ensure geometric alignment of the modules during reconfiguration. Planar and spherical distortion metrics are defined to quantify distortions due to reconfiguration. Subsequently, the optimal topology is obtained by minimizing a cost function that is a weighted sum of the two distortion metrics. The result is a set of MSoRos capable of distinct 1D and 2D planar configurations (both heterogeneous and homogeneous) and multiple 3D spherical configurations of varying radii (both heterogeneous and homogeneous). The methodology is validated on a MSoRo system based on the combination of a cuboctahedron (Archimedean solid) and a cube and an octahedron (Platonic solids). 

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