Robotic Specialization in Autonomous Robotic Structural Assembly

Abstract

Robotic in-space assembly of large space structures is a long-term NASA goal to reduce launch costs and enable larger-scale missions. Recently, researchers have proposed using discrete lattice building blocks and co-designed robots to build high-performance, scalable primary structures for various on-orbit and surface applications. These robots would locomote on the lattice and work in teams to build and reconfigure building-blocks into a functional structures. However, the most reliable and efficient robotic system architecture, characterized by the number of different robotic `species’ and the allocation of functionality between species, is an open question. To address this problem, we decompose the robotic building-block assembly task into functional primitives and, in simulation, study the performance of the variety of possible resulting architectures. For a set consisting of five process types (move self, move the block, move friend, align bock, fasten block), we describe a method of feature space exploration and ranking based on energy and reliability cost functions. The solution space is enumerated, filtered for unique solutions, and evaluated against energy and reliability cost functions for various simulated build sizes. We find that a 2 species system, dividing the five mentioned process types between one unit cell transport robot and one fastening robot, results in the lowest energy cost system, at some cost to reliability. This system enables fastening functionality to occupy the building front while reducing the need for that functional mass to travel back and forth from a feed station. Because the details of a robot design affect the weighting and final allocation of functionality, a sensitivity analysis was conducted to evaluate the effect of changing mass allocations on architecture performance. Future systems with additional functionalities such as repair, inspection, and others may use this process to analyze and determine alternative robot architectures.

Controlled Indexing

• autonomous aerial vehicles,
• fasteners,
• robotic assembly,
• sensitivity analysis

Introduction

Low-density lattices are appealing as the primary structures for a wide variety of applications such as spacecraft [1], aircraft, and ground infrastructure. Recent work has shown that such structures can be constructed from efficiently manufactured building blocks by relatively simple mobile robots [2]. Especially for space applications, this structure and robot system has the potential for reconfigurability, scalability, and efficiency that could reduce launch energy, enhance mission adaptability, and provide long-term system life-cycle benefits. In order to design such systems, we wish to describe a method for dividing functional primitives of a building block assembly system into individual robot types and assess ingvarious architectures and their effect on the energy cost and reliability of the system. In this paper, we define the functional primitives and assess all possible enumerations to determine an optimal configuration. To achieve this, we develop an energy cost function based on the rearrangement cost of the robot mass and a reliability cost function based on the degrees of freedom of the robot. A brief overview of in-space assembly and building-block-based assembly is presented, followed by the study methodology and results. A discussion of the findings and lessons learned are presented.

Conclusion

Large-scale, robust robotic assembly of space structures is a paradigm-shifting capability that has the potential to decrease launch mass, increase mission flexibility, and enable larger-scale space missions and infrastructure. Discrete lattice building blocks and relative mobile robots offer an efficient and robust strategy towards this goal. This work laid theoretical groundwork for understanding the most efficient and robust system architecture for a relative robot and discrete lattice assembly system. Using representative energy and reliability cost functions, we simulated one dimensional builds to evaluate several system architectures that split robotic capabilities between one or more robot types. Results showed that a 2species robot assembly system will result in the lowest energy cost to build a structure, specifically one that divides the tasks of material movement and material joining. This system enables fastening functionality to occupy the build front while reducing the need for that functional mass to travel back and forth from a feed station. The most reliable architecture was the ’train’ architecture, but at the cost of significantly higher overall system mass. The next most reliable architectures were the 2 species architectures. Sensitivity analysis was conducted to show the effect of changing mass assumptions and allocations on system performance. This can guide system developers as more detailed mass allocations associated with specific robot designs become available. This work provides groundwork to be expanded into a 3D case, which will incorporate path planning elements and more detailed simulations.

Acknowledgments

The authors thank the NASA STMD Game-Changing Development (GCD) Program for supporting the AutomatedReconfigurable Mission Adaptive Digital Assembly Systems(ARMADAS) Project. We also thank Megan Ochalek, Ben-net Caraher, Raymond Jow, Rina Zhang, and Miriam Lennigfor critical discussions.

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FULL Paper PDF file:

Robotic Specialization in Autonomous RoboticStructural Assembly

Bibliography

author,

B. Bernus, G. Trinh, C. Gregg, O. Formoso and K. Cheung,

Year

2020

Title

Robotic Specialization in Autonomous Robotic Structural Assembly,

Publish in

2020 IEEE Aerospace Conference, Big Sky, MT, USA, 2020, pp. 1-10,

Doi

10.1109/AERO47225.2020.9172620.

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