Benjamin Jenett

BILL-E: Robotic Platform for Locomotion and Manipulation of Lightweight Space Structures

We describe a robotic platform for traversing and manipulating a modular 3D lattice structure. The robot is designed to operate within a specifically structured environment, which enables low numbers of degrees of freedom (DOF) compared to robots performing comparable tasks in an unstructured environment. This allows for simple controls, as well as low mass and cost. This approach, designing the robot relative to the local environment in which it operates, results in a type of robot we call a “relative robot.” We describe a bipedal robot that can locomote across a periodic lattice structure, as well as being able to handle, manipulate, and transport building block parts that compose the lattice structure. Based on a general inchworm design, the robot has added functionality for travelling over and operating on a host structure.

Relative Robots: Scaling Automated Assembly of Discrete Cellular Lattices

We propose metrics for evaluating the performance of robotically assembled discrete cellular lattice structures (referred to as digital materials) by defining a set of tools used to evaluate how the assembly system impacts the achievable performance objective of relative stiffness. We show that mass-specific stiffness can be described by the dependencies E∗(γ,D(n, f ,RA)), where E∗ is specific modulus, γ is lattice topology, and the allowable acceptance of the joint interface, D, is defined by an error budget analysis that incorporates the scale of the structure, and/or number of discrete components assembled, n, the type of robotic assembler, RA, and the static error contributions due to tolerance stack-up in the specified assembler structural loop, and the dynamic error limitations of the assembler operating at specified assembly rates, f . We refer to three primary physical robotic construction system topologies defined by the relationship between their configuration workspace, and the global configuration space: global robotic assembler (GR), mobile robotic assembler (MR), and relative robotic assemblers (RR), each exhibiting varying sensitivity to static, and dynamic error accumulation. Results of this analysis inform an iterative machine design process where final desired material performance is used to define robotic assembly system design parameters. INTRODUCTION Digital materials exhibit coded functionality by programmatically defining the type, and location of homogeneous or heterogeneous discrete building blocks such that their mechanical properties combine to perform as an explicitly defined continuum material. One example of a highly stiff, and ultra-light material is a high connectivity, non-stochastic, periodic, lattice structure composed of axially loaded truss elements [1]. Differentiating from 3D printing, discretization of the cellular lattice into reusable building-block elements enables fabrication, and reconfiguration, of explicitly defined heterogeneous meta-materials. The regular, periodic nature of the discrete cellular lattice can be exploited to simplify automated assembly by robotic processes. In this paper we lay out a methodology to identify the overall performance of robotic assembly of discrete cellular lattice with metrics based on machine class, scale of assembled material, and assembly rate. The critical dependency of robotic assembly is the ability for the interface between joined discrete cells (voxels) to accommodate error inherent to the assembly process while maintaining robust force/energy transfer across the node. Performance of discrete construction of three dimensional periodic lattice structures is based on the behavior of cellular solids with properties governed by their constituent material, and lattice topology [2]. Analogous to naturally occurring cellular materials such as bone, and sponge, these engineered periodic lattices act as continuum meta-materials [3], which can achieve ultralight stiffness to weight ratios by following relative density linear scaling relationships from the base material to the lattice [4, 5]. In discrete lattice construction, the parasitic mass contribution of the interface affects overall system mass-specific stiffness. Given a base material with youngs modulus Es, and density ρs, ideal stretch dominated behavior with specific modulus 1 Copyright c

Robotically assembled aerospace structures: Digital material assembly using a gantry-type assembler

This paper evaluates the development of automated assembly techniques for discrete lattice structures using a multi-axis gantry type CNC machine. These lattices are made of discrete components and are referred to as “digital materials.” We present the development of a specialized end effector that works in conjunction with the CNC machine to assemble these lattices. With this configuration we are able to place voxels at a rate of 1.5 per minute. The scalability of digital material structures due to the incremental modular assembly is one of its key traits and an important metric of interest. We investigate the build times of a 5×5 beam structure on the scale of 1 meter (325 parts), 10 meters (3,250 parts), and 30 meters (9,750 parts). Utilizing the current configuration with a single end effector, performing serial assembly with a globally fixed feed station at the edge of the build volume, the build time increases according to a scaling law of n4, where n is the build scale. Build times can be reduced significantly by integrating feed systems into the gantry itself, resulting in a scaling law of n3. A completely serial assembly process will encounter time limitations as build scale increases. Automated assembly for digital materials can assemble high performance structures from discrete parts, and techniques such as built in feed systems, parallelization, and optimization of the fastening process will yield much higher throughput.

Development of Mission Adaptive Digital Composite Aerostructure Technologies (MADCAT)

This paper reviews the development of the Mission Adaptive Digital Composite Aerostructures Technologies (MADCAT) v0 demonstrator aircraft, utilizing a novel aerostructure concept that combines advanced composite materials manufacturing and fabrication technologies with a discrete construction approach to achieve high stiffness-todensity ratio ultra-light aerostructures that provide versatility and adaptability. This revolutionary aerostructure concept has the potential to change how future air vehicles are designed, built, and flown, with dramatic reductions in weight and manufacturing complexity – the number of types of structural components needed to build air vehicles – while enabling new mission objectives. We utilize the innovative digital composite materials and discrete construction technologies to demonstrate the feasibility of the proposed aerostructure concept, by building and testing a scaled prototype UAV, MADCAT v0. This paper presents an overview of the design and development of the MADCAT v0 flight demonstrator.

Design of multifunctional hierarchical space structures

We describe a system for the design of space structures with tunable structural properties based on the discrete assembly of modular lattice elements. These lattice elements can be constructed into larger beam-like elements, which can then be assembled into large scale truss structures. These discrete lattice elements are reversibly assembled with mechanical fasteners, which allows them to be arbitrarily reconfigured into various application-specific designs. In order to assess the validity of this approach, we design two space structures with similar geometry but widely different structural requirements: an aerobrake, driven by strength requirements, and a precision segmented reflector, driven by stiffness and accuracy requirements. We will show agreement between simplified numerical models based on hierarchical assembly and analytical solutions. We will also present an assessment of the error budget resulting from the assembly of discrete structures. Lastly, we will address launch vehicle packing efficiency issues for transporting these structures to lower earth orbit.

Digital cellular solid pressure vessels: A novel approach for human habitation in space

It is widely assumed that human exploration beyond Earths orbit will require vehicles capable of providing long-duration habitats that simulate an Earthlike environment — consistent artificial gravity, breathable atmosphere, and sufficient living space-while requiring the minimum possible launch mass. This paper examines how the qualities of digital cellular solids — high-performance, repairability, reconfigurability, tunable mechanical response — allow the accomplishment of long-duration habitat objectives at a fraction of the mass required for traditional structural technologies. To illustrate the impact digital cellular solids could make as a replacement to conventional habitat subsystems, we compare recent proposed deep space habitat structural systems with a digital cellular solids pressure vessel design that consists of a carbon fiber reinforced polymer (CFRP) digital cellular solid cylindrical framework that is lined with an ultra-high molecular weight polyethylene (UHMWPE) skin. We use the analytical treatment of a linear specific modulus scaling cellular solid to find the minimum mass pressure vessel for a structure and find that, for equivalent habitable volume and appropriate safety factors, the use of digital cellular solids provides clear methods for producing structures that are not only repairable and reconfig-urable, but also higher performance than their conventionally-manufactured counterparts.

SpRoUTS (Space Robot Universal Truss System): Reversible Robotic Assembly of Deployable Truss Structures of Reconfigurable Length

Automatic deployment of structures has been a focus of much academic and industrial work on infrastructure applications and robotics in general. This paper presents a robotic truss assembler designed for space applications - the Space Robot Universal Truss System (SpRoUTS) - that reversibly assembles a truss from a feedstock of hinged andflat-packed components, by folding the sides of each component up and locking onto the assembled structure. We describe the design and implementation of the robot and show that the assembled truss compares favorably with prior truss deployment systems.