We present an algorithmic framework for a multi-robot modular assembly system. Motivated by the prospects of in-space assembly, we focus on the NASA Automated Reconfigurable Mission Adaptive Digital Assembly Systems (AR-MADAS) framework, in which multiple types of robots work together in a team to build large structures. Unlike with other multi-robot construction systems, the geometry of structures that ARMADAS robots can build is not limited to the class of histogram shapes. To address the intractability of path planning for a robot system with the exponentially growing number of dimensions, we present a decoupled planning approach, where the assembly and path planning is performed iteratively by one robot team at a time. We present a number of data structures which help us avoid collisions and deadlocks in the resulting robot schedule.

In-space assembly is a key capability to enable construction of large-scale structures required for sustained human presence in space. Robotic assembly is critical to reduce required crew time and risk, while modularity ensures that solutions are versatile and adaptive to complex mission concepts. NASA's Automated Reconfigurable Mission Adaptive Digital Assembly Systems (ARMADAS) project demonstrated that robots with relatively low cost, size, and degrees-of-freedom (DoFs) can be used for large-scale modular lattice structure assembly. This is possible by using the structural modules for robotic systems metrology and error mitigation. Robots with reduced complexity may lead to advantages in initial and maintenance cost, offering an alternative to large, complex, and expensive robots. In this paper, we describe the Structure Omni-directional Foldable Explorer (SOF-E), a robot with significantly lower mass and DoF compared to the previous ARMADAS robot architecture. Although SOF-E is a five DoF robot with only two or three control states per actuator, it is capable of transporting and placing structural modules by collaborating with other instances of itself. We discuss the mechanical design and architecture of SOF-E, including analysis of energy usage during each operation. Experiments demonstrate that during locomotion and module transport tasks, SOF-E requires significantly lower energy than the previous cargo transport robot architecture, the Scaling Omni-directional Lattice Locomoting Explorer (SOLL-E). The cost of transport metric is used to compare the energy efficiency of the operation.

Coordinated multi-agent robotic construction provides a means to build infrastructure in extreme environments and improve efficiency in high performance applications. Planning methods are key to understanding and achieving the scope of such applications, and are typically tailored to specific models of construction material and a consideration of passivity or activity thereof. Here, we focus on the NASA Automated Reconfigurable Mission Adaptive Digital Assembly Systems (ARMADAS) model, which includes passive lightweight structural modules and small robots that traverse the structure. We present an algorithm for calculating a build plan for robots under the constraints of this type of system. We then evaluate the quality of this plan experimentally. Many of the techniques we use can be applied to any robotic assembly system whose robots perform locomotion over the structure that they are building.

In-space assembly is crucial to creating large-scale space structures and enabling long term space missions. Natural limitations in the size of transportation vehicles and ISRU production facilities necessitate an additive strategy with the size of the typical structural unit being essentially fixed and inversely proportional to the final assembly size. In prior robotic and space assembly examples, reversible mechanical integration of structural modules is typically achieved with actuated alignment and fastening mechanisms onboard every structural module. Additive assembly or manufacturing planning approaches often feature a “build front” that receives new materials or parts and progresses gradually across the target geometry. The system we describe here places much of the alignment and fastener actuation systems onboard a mobile robot that can operate at a build front while companion robots (Scaling Omni-directional Lattice Locomoting Explorer, SOLL-E) provide part or material transportation. The design and evaluation of this Mobile Meta-Material Interior Co-Integrator (MMIC-I), an inchworm-style locomoting robotic assembler, is described here with an emphasis on ease of assembly and a low number of unique parts for a simple design. It is designed to assist in alignment of cuboctahedron structural unit cells with captive fasteners, defining the build front in operation. Adjacent structural unit cells are locked together with specified axial and rotational actuation of the fasteners. Hardware prototypes show that the robot is able to successfully locomote to any indexed location within a lattice structure and bolt together each set of fasteners on any interface.

This paper presents the design and development of a transport and placement robot that demonstrates autonomous assembly of structural building blocks. The robots are intended to serve as a critical component of automated structural assembly and maintenance systems. The Scaling Omni-directional Lattice Locomoting Explorer (SOLL-E) uses a 5-DoF bipedal inchworm locomotion architecture with locking foot and cargo grippers. The locomotion system employs large magnet gap diameter BLDC motors with moderate timing belt gearing for primary joints, and DC planetary gearmotors for turning. Foot and cargo grippers are identical, with servo-actuated locking mechanisms. Three modular controller boards are used to control these actuators in real-time, with command and telemetry data transferred between the server and each controller board via WiFi. Functionality and performance were evaluated in a ground demonstration.

In this video, 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. We present algorithmic methods that are able to detect and reconfigure arbitrary polyominoes, based on finite-state robots, while also preserving connectivity of a structure during reconfiguration. Specific results include methods for determining a bounding box, scaling a given arrangement, and adapting more general algorithms for transforming polyominoes.

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.

We propose a flexible, reconfigurable robot which achieves rectilinear locomotion by coupling structural deformation and directional friction promoting a locomotion strategy ideal for traversing narrow channels. The robot uses two linear actuators to generate structural waves, which propagate through the robot lifting and changing the direction of motion of the contact points (feet) between the robot and ground. The reconfigurations of the robot allow different structural waveforms to alter the robot's gait. The paper describes the modular lattice structure used to build the robot; the finite element modeling approach used to understand the structural deformation induced by the linear actuators as well as the experimental validation of the prototype robot.

The Milli-Motein (Millimeter-Scale Motorized Protein) is ca chain of programmable matter with a 1 cm pitch. It can fold itself into digitized approximations of arbitrary three-dimensional shapes. The small size of the Milli-Motein segments is enabled by the use of our new electropermanent wobble stepper motors, described in this paper, and by a highly integrated electronic and mechanical design. The chain is an interlocked series of connected motor rotors and stators, wrapped with a continuous flex circuit to provide communications, control, and power transmission capabilities. The Milli-Motein uses off-the-shelf electronic components and fasteners, and custom parts fabricated by conventional and electric discharge machining, assembled with screws, glue, and solder using tweezers under a microscope. We perform shape reconfiguration experiments using a four-segment Milli-Motein. It can switch from a straight line to a prescribed shape in 5 seconds, consuming 2.6 W power during reconfiguration. It can hold its shape indefinitely without power. During reconfiguration, a segment can lift the weight of one but not two segments as a horizontal cantilever.

Understanding how linear strings fold into 2-D and 3-D shapes has been a long sought goal in many fields of both academia and industry. This paper presents a technique to design self-assembling and self-reconfigurable systems that are composed of strings of very simple robotic modules. We show that physical strings that are composed of a small set of discrete polygonal or polyhedral modules can be used to programmatically generate any continuous area or volumetric shape. These modules can have one or two degrees of freedom (DOFs) and simple actuators with only two or three states. We describe a subdivision algorithm to produce universal polygonal and polyhedral string folding schemas, and we prove the existence of a continuous motion to reach any such folding. This technique is validated with dynamics simulations as well as experiments with chains of modules that pack on a regular cubic lattice. We call robotic programmable universally foldable strings “moteins” as motorized proteins.

In poorly constrained extra-vascular environments such as hollow viscera, current catheter navigation techniques are restricted to simple paths and therefore limit a doctor's ability to position the catheter. This paper presents a new catheter positioning system that enables faster and more accurate catheter placement, with fewer scans. The proposed robotic catheter navigation system can execute curved paths and maintain any number of three-dimensional turns using tension stiffening guide-wires composed of a set of disposable friction-locking beads. An external, reusable control system is used to automate the movement of the catheter. This control system uses a custom-designed graphical kinematic analysis program that predicts contact forces, changes in conformation due to external forces, tip deflection and failure modes of the catheter as it advances.