Modeling and Control of Robot-Structure Coupling During In-Space Structure Assembly

This paper considers the problem of robot-structure coupling dynamics during in-space robotic assembly of large flexible structures. A two-legged walking robot is used as a construction agent, whose primary goal is to stably walking on the flexible structure while carrying a substructure component to a designated location. The reaction forces inserted by the structure to the walking robot are treated as bounded disturbance inputs, and a trajectory tracking robotic controller is proposed that combines the standard full state feedback motion controller and an adaptive controller to account for the disturbance inputs. In this study, a reduced-order Euler-Bernoulli beam structure model is adapted, and a finite number of co-located sensors and actuators are distributed along the span of the beam structure. The robot-structure coupling forces are treated as a bounded external forcing function to the structure, and hence an output covariance constraint problem can be formulated, in terms of linear matrix inequality, for optimal structure control by utilizing the direct output feedback controllers. The numerical simulations show the effectiveness of the proposed robot-structure modeling and control methodology

Combining a hierarchical task network planner with a constraint satisfaction solver for assembly operations involving routing problems in a multi-robot context

This work addresses the combination of a symbolic hierarchical task network planner and a constraint satisfaction solver for the vehicle routing problem in a multi-robot context for structure assembly operations. Each planner has its own problem domain and search space, and the article describes how both planners interact in a loop sharing information in order to improve the cost of the solutions. The vehicle routing problem solver gives an initial assignment of parts to robots, making the distribution based on the distance among parts and robots, trying also to maximize the parallelism of the future assembly operations evaluating during the process the dependencies among the parts assigned to each robot. Then, the hierarchical task network planner computes a scheduling for the given assignment and estimates the cost in terms of time spent on the structure assembly. This cost value is then given back to the vehicle routing problem solver as feedback to compute a better assignment, closing the loop and repeating again the whole process. This interaction scheme has been tested with different constraint satisfaction solvers for the vehicle routing problem. The article presents simulation results in a scenario with a team of aerial robots assembling a structure, comparing the results obtained with different configurations of the vehicle routing problem solver and showing the suitability of using this approach.Unión Europea ARCAS FP7-ICT-287617Unión Europea H2020-ICT-644271Unión europea H2020-ICT-73166

Structural assembly in space

A cost algorithm for predicting assembly costs for large space structures is given. Assembly scenarios are summarized which describe the erection, deployment, and fabrication tasks for five large space structures. The major activities that impact total costs for structure assembly from launch through deployment and assembly to scientific instrument installation and checkout are described. Individual cost elements such as assembly fixtures, handrails, or remote minipulators are also presented

Autonomous structure assembly using potential field functions

The work in this paper aims to introduce a new technique for artificial potential field methods based on a superquadric representation of the obstacle shapes, and a quaternion representation of the object orientation. The superquadric functions facilitate the representation of the actual shape of the obstacles to provide additional free space for the motion of the maneuvering objects, consequently reducing maneuvering effort for these objects. The quaternion representation overcomes the singularities produced when using Euler angles and is more convenient for real time implementation. Potential field methods provide a robust means of generating distributed controls for mobile robots (terrestrial or space) to enable automated assembly tasks. The problem of local minimum formation when dealing with objects having straight edges is also addressed in this paper through changing the superquadric function shape simultaneously in accordance with the relative position and orientation of the objects. The proposed potential function enables maneuvering objects to decide which motion, both in translation and rotation, leads to the quickest descent of the artificial potential most effectively. These coupled translation/rotation manoeuvres show significant benefits over de-coupled translation maneuvers

The \u3cem\u3eChlamydomonas\u3c/em\u3e Genome Reveals the Evolution of Key Animal and Plant Functions

Chlamydomonas reinhardtii is a unicellular green alga whose lineage diverged from land plants over 1 billion years ago. It is a model system for studying chloroplast-based photosynthesis, as well as the structure, assembly, and function of eukaryotic flagella (cilia), which were inherited from the common ancestor of plants and animals, but lost in land plants. We sequenced the ∼120-megabase nuclear genome of Chlamydomonas and performed comparative phylogenomic analyses, identifying genes encoding uncharacterized proteins that are likely associated with the function and biogenesis of chloroplasts or eukaryotic flagella. Analyses of the Chlamydomonas genome advance our understanding of the ancestral eukaryotic cell, reveal previously unknown genes associated with photosynthetic and flagellar functions, and establish links between ciliopathy and the composition and function of flagella

A self-organisation model for mobile robots in large structure assembly using multi-agent systems

Mobile, self-organising robots are seen to be a possible solution to over-come the current limitations of fixed, dedicated automation systems particularly in the area of large structure assembly. Two of the key challenges for traditional ded-icated automation systems in large structure assembly are considered to be the trans-portation of products and the adaptation of manufacturing processes to changes in requirements. In order to make dynamic, self-organising systems a reality, several challenges in the process dynamics and logistical control need to be solved. In this paper, we propose a Multi-Agent System (MAS) approach to self-organise mobile robots in large structure assembly. The model is based on fixed-priority pre-emptive scheduling and uses a blackboard agent as a central information source and to facil-itate more common goal directed distributed negotiation and decision making be-tween agents representing the different needs of products and available mobile re-sources (robots)

Architecture of viral genome-delivery molecular machines.

From the abyss of the ocean to the human gut, bacterial viruses (or bacteriophages) have colonized all ecosystems of the planet earth and evolved in sync with their bacterial hosts. Over 95% of bacteriophages have a tail that varies greatly in length and complexity. The tail complex interrupts the icosahedral capsid symmetry and provides both an entry for viral genome-packaging during replication and an exit for genome-ejection during infection. Here, we review recent progress in deciphering the structure, assembly and conformational dynamics of viral genome-delivery tail machines. We focus on the bacteriophages P22 and T7, two well-studied members of the Podoviridae family that use short, non-contractile tails to infect Gram-negative bacteria. The structure of specialized tail fibers and their putative role in host anchoring, cell-surface penetration and genome-ejection is discussed

Wheat glutenin polymers 1. structure, assembly and properties

The importance of wheat glutenin polymers in determining the processing quality of wheat is generally accepted. Similarly, genetic and molecular studies have provided detailed information on the sequences of the glutenin subunits and identified associations between individual subunits and either good or poor quality for breadmaking. However, our knowledge of the polymers themselves, including their molecular masses, structures and pathways of synthesis and assembly, remains incomplete and is largely based on studies carried out between 20 and 50 years ago. The current paper therefore reviews this knowledge and identifies priorities for future research which is required to facilitate the use of modern molecular tools to develop improved types of wheat for future requirement

Shape computations without compositions

Parametric CAD supports design explorations through generative methods which compose and transform geometric elements. This paper argues that elementary shape computations do not always correspond to valid compositional shape structures. In many design cases generative rules correspond to compositional structures, but for relatively simple shapes and rules it is not always possible to assign a corresponding compositional structure of parts which account for all operations of the computation. This problem is brought into strong relief when design processes generate multiple compositions according to purpose, such as product structure, assembly, manufacture, etc. Is it possible to specify shape computations which generate just these compositions of parts or are there additional emergent shapes and features? In parallel, combining two compositions would require the associated combined computations to yield a valid composition. Simple examples are presented which throw light on the issues in integrating different product descriptions (i.e. compositions) within parametric CAD