E. Komendera, N. Correll (2014): Precise Assembly of 3D Truss Structures Using EKF-based Error Prediction and Correction. In: International Symposium on Experimental Robotics (ISER), Marrakech, Morocco, 2014.

We describe a method to construct precise truss structures from non-precise commodity parts. Trusses with precision in the order of micrometers, such as the truss of a space telescope, can be accomplished with precisely machined truss connection systems. This approach is expensive, heavy, and prone to failure, e.g., when a single element is lost. In the past, we have proposed a novel concept in which non-precise commodity parts can be aligned using precise jigging robots and then welded in place. Even when using highly precise sensors and actuators, this approach can still lead to errors due to thermal expansion and structural deformation. In this paper, we describe and experimentally evaluate an EKF-based SLAM approach that allows a team of intelligent precision jigging robots (IPJR) to maintain a common estimate of the structure’s pose, improve this estimate during loop closures in the construction process, and uses this estimate to correct for errors during construction. We also show that attaching a new node to the assembly site with the lowest uncertainty signi cantly increases accuracy.

M. A. McEvoy, E. Komendera, N. Correll (2014): Assembly Path Planning for Stable Robotic Construction. In: IEEE International Conference on Technologies for Practical Robot Applications (TePRA), pp. 1-6, Boston, MA, 2014.

We propose an algorithm for assembly path planning that takes stability of the structure during construction into account. Finite Element Analysis (FEA) is used to evaluate the intermediate stages of the assembly for stability. The algorithm presented here assembles a structure by greedily taking the most stable option at each step in the assembly process, and has complexity \mathcal{O}(n!), albeit most structures are effectively assembled with complexity \mathcal{O}(n^2). We demonstrate the workings of the proposed hybrid discrete/FEA search algorithm in simulation on a series of truss structures. In particular, we show that the algorithm is able to identify correct orderings that led to stable assembly, and discuss structures for which a greedy approach will fail.

E. Komendera, J. Dorsey, W. Doggett, N. Correll (2014): Truss Assembly and Welding by Intelligent Precision Jigging Robots. In: IEEE International Conference on Technologies for Practical Robot Applications (TePRA), Boston, MA, 2014.
This paper describes an Intelligent Precision Jigging Robot (IPJR) prototype that enables the precise alignment and welding of titanium space telescope optical benches. The IPJR, equipped with m accuracy sensors and actuators, worked in tandem with a lower precision remote controlled manipulator. The combined system assembled and welded a 2 m truss from stock titanium components. The calibration of the IPJR, and the difference between the predicted and the truss dimensions as-built, identified additional sources of error that should be addressed in the next generation of IPJRs in 2D and 3D.
E. Komendera, D. Reishus,  J. Dorsey, W. Doggett, N. Correll (2014): Precise Truss Assembly using Commodity Parts and Low Precision Welding. In: Intelligent Service Robotics , 7 (2), pp. 93-102, 2014.

Hardware and software design and system integration for an intelligent precision jigging robot (IPJR), which allows high precision assembly using commodity parts and low-precision bonding, is described. Preliminary 2D experiments that are motivated by the problem of assembling space telescope optical benches and very large manipulators on orbit using inexpensive, stock hardware and low-precision welding are also described. An IPJR is a robot that acts as the precise “jigging”, holding parts of a local structure assembly site in place, while an external low precision assembly agent cuts and welds members. The prototype presented in this paper allows an assembly agent (for this prototype, a human using only low precision tools), to assemble a 2D truss made of wooden dowels to a precision on the order of millimeters over a span on the order of meters. The analysis of the assembly error and the results of building a square structure and a ring structure are discussed. Options for future work, to extend the IPJR paradigm to building in 3D structures at micron precision are also summarized.

J. Dorsey, W. Doggett, E. Komendera, N. Correll, R. Hafley, B. King (2012): An Efficient and Versatile Means for Assembling and Manufacturing Systems in Space. AIAA SPACE 2012 Conference & Exposition, 2012.

Within NASA Space Science, Exploration and the Office of Chief Technologist, there are Grand Challenges and advanced future exploration, science and commercial mission applications that could benefit significantly from large-span and large-area structural systems. Of particular and persistent interest to the Space Science community is the desire for large (in the 10- 50 meter range for main aperture diameter) space telescopes that would revolutionize space astronomy. Achieving these systems will likely require on-orbit assembly, but previous approaches for assembling large-scale telescope truss structures and systems in space have been perceived as very costly because they require high precision and custom components. These components rely on a large number of mechanical connections and supporting infrastructure that are unique to each application. In this paper, a new assembly paradigm that mitigates these concerns is proposed and described. A new assembly approach to implement the paradigm is developed incorporating: Intelligent Precision Jigging Robots, Electron-Beam welding, robotic handling/manipulation, operations assembly sequence and path planning, and low precision weldable structural elements. Key advantages of the new assembly paradigm, as well as concept descriptions and ongoing research and technology development efforts for each of the major elements are summarized.

V. Rai, A. van Rossum, N. Correll (2011): Self-Assembly of Modular Robots from finite number of modules using Graph Grammars. In: In Proceedings of the International Conference on Intelligent Robots and Systems, pp. 4783-4789, IEEE/RSJ San Francisco, CA, 2011.
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 specifically 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 reconfiguration, 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.



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