Robohub.org
 

Robotic consensus

by
22 April 2016



share this:
Illustration: Christine Daniloff/MIT

Illustration: Christine Daniloff/MIT

Planning algorithms for teams of robots fall into two categories: centralized algorithms, in which a single computer makes decisions for the whole team, and decentralized algorithms, in which each robot makes its own decisions based on local observations.

With centralized algorithms, if the central computer goes offline, the whole system falls apart. Decentralized algorithms handle erratic communication better, but they’re harder to design, because each robot is essentially guessing what the others will do. Most research on decentralized algorithms has focused on making collective decision-making more reliable and has deferred the problem of avoiding obstacles in the robots’ environment.

At the International Conference on Robotics and Automation in May, MIT researchers will present a new, decentralized planning algorithm for teams of robots that factors in not only stationary obstacles, but moving obstacles, as well. The algorithm also requires significantly less communications bandwidth than existing decentralized algorithms, but preserves strong mathematical guarantees that the robots will avoid collisions.

In simulations involving squadrons of minihelicopters, the decentralized algorithm came up with the same flight plans that a centralized version did. The drones generally preserved an approximation of their preferred formation, a square at a fixed altitude — although to accommodate obstacles the square rotated and the distances between drones contracted. Occasionally, however, the drones would fly single file or assume a formation in which pairs of them flew at different altitudes.

“It’s a really exciting result because it combines so many challenging goals,” says Daniela Rus, the Andrew and Erna Viterbi Professor in MIT’s Department of Electrical Engineering and Computer Science and director of the Computer Science and Artificial Intelligence Laboratory, whose group developed the new algorithm. “Your group of robots has a local goal, which is to stay in formation, and a global goal, which is where they want to go or the trajectory along which you want them to move. And you allow them to operate in a world with static obstacles but also unexpected dynamic obstacles, and you have a guarantee that they are going to retain their local and global objectives. They will have to make some deviations, but those deviations are minimal.”

Rus is joined on the paper by first author Javier Alonso-Mora, a postdoc in Rus’ group; Mac Schwager, an assistant professor of aeronautics and astronautics at Stanford University who worked with Rus as an MIT PhD student in mechanical engineering; and Eduardo Montijano, a professor at Centro Universitario de la Defensa in Zaragoza, Spain.

Trading regions

In a typical decentralized group planning algorithm, each robot might broadcast its observations of the environment to its teammates, and all the robots would then execute the same planning algorithm, presumably on the basis of the same information.

But Rus, Alonso-Mora, and their colleagues found a way to reduce both the computational and communication burdens imposed by consensual planning. The essential idea is that each robot, on the basis of its own observations, maps out an obstacle-free region in its immediate environment and passes that map only to its nearest neighbors. When a robot receives a map from a neighbor, it calculates the intersection of that map with its own and passes that on.

This keeps down both the size of the robots’ communications — describing the intersection of 100 maps requires no more data than describing the intersection of two — and their number, because each robot communicates only with its neighbors. Nonetheless, each robot ends up with a map that reflects all of the obstacles detected by all the team members.

Four dimensions

The maps have not three dimensions, however, but four — the fourth being time. This is how the algorithm accounts for moving obstacles. The four-dimensional map describes how a three-dimensional map would have to change to accommodate the obstacle’s change of location, over a span of a few seconds. But it does so in a mathematically compact manner.

The algorithm does assume that moving obstacles have constant velocity, which will not always be the case in the real world. But each robot updates its map several times a second, a short enough span of time that the velocity of an accelerating object is unlikely to change dramatically.

On the basis of its latest map, each robot calculates the trajectory that will maximize both its local goal — staying in formation — and its global goal.

The researchers are also testing a version of their algorithm on wheeled robots whose goal is to collectively carry an object across a room where human beings are also moving around, as a simulation of an environment in which humans and robots work together.



tags: , ,


MIT News





Related posts :



New imaging method makes tiny robots visible in the body

Microrobots have the potential to revolutionize medicine. Researchers at the Max Planck ETH Centre for Learning Systems have now developed an imaging technique that for the first time recognises cell-​sized microrobots individually and at high resolution in a living organism.
20 May 2022, by

A draft open standard for an Ethical Black Box

Within the RoboTIPS project, we have developed and tested several model of Ethical Black Boxes, including one for an e-puck robot, and another for the MIRO robot.
19 May 2022, by

Unable to attend #ICRA2022 for accessibility issues? Or just curious to see robots?

There are many things that can make it difficult to attend an in person conference in the United States and so the ICRA Organizing Committee, the IEEE Robotics and Automation Society and OhmniLabs would like to help you attend ICRA virtually.
17 May 2022, by
ep.

350

podcast

Duckietown Competition Spotlight, with Dr Liam Paull

Dr. Liam Paull, cofounder of the Duckietown competition talks about the only robotics competition where Rubber Duckies are the passengers on an autonomous driving track.
17 May 2022, by

Designing societally beneficial Reinforcement Learning (RL) systems

In this post, we aim to illustrate the different modalities harms can take when augmented with the temporal axis of RL. To combat these novel societal risks, we also propose a new kind of documentation for dynamic Machine Learning systems which aims to assess and monitor these risks both before and after deployment.
15 May 2022, by

Innovative ‘smart socks’ could help millions living with dementia

‘Smart socks’ that track rising distress in the wearer could improve the wellbeing of millions of people with dementia, non-verbal autism and other conditions that affect communication.
13 May 2022, by





©2021 - ROBOTS Association


 












©2021 - ROBOTS Association