Abstract
Collective motions emerging from the interaction of autonomous mobile individuals play a key role in many phenomena, from the growth of bacterial colonies to the coordination of robotic swarms. For these collective behaviors to take hold, the individuals must be able to emit, sense, and react to signals. When dealing with simple organisms and robots, these signals are necessarily very elementary; e.g., a cell might signal its presence by releasing chemicals and a robot by shining light. An additional challenge arises because the motion of the individuals is often noisy; e.g., the orientation of cells can be altered by Brownian motion and that of robots by an uneven terrain. Therefore, the emphasis is on achieving complex and tunable behaviors from simple autonomous agents communicating with each other in robust ways. Here, we show that the delay between sensing and reacting to a signal can determine the individual and collective long-term behavior of autonomous agents whose motion is intrinsically noisy. We experimentally demonstrate that the collective behavior of a group of phototactic robots capable of emitting a radially decaying light field can be tuned from segregation to aggregation and clustering by controlling the delay with which they change their propulsion speed in response to the light intensity they measure. We track this transition to the underlying dynamics of this system, in particular, to the ratio between the robots’ sensorial delay time and the characteristic time of the robots’ random reorientation. Supported by numerics, we discuss how the same mechanism can be applied to control active agents, e.g., airborne drones, moving in a three-dimensional space. Given the simplicity of this mechanism, the engineering of sensorial delay provides a potentially powerful tool to engineer and dynamically tune the behavior of large ensembles of autonomous mobile agents; furthermore, this mechanism might already be at work within living organisms such as chemotactic cells.
3 More- Received 7 September 2015
DOI:https://doi.org/10.1103/PhysRevX.6.011008
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Published by the American Physical Society
Physics Subject Headings (PhySH)
Focus
Sensing Delays Control Robot Swarming
Published 29 January 2016
A robot group clusters together or disperses based on each robot’s reaction time for sensing light, a finding useful for search-and-rescue missions.
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Popular Summary
The behavior and interaction of autonomous individuals capable of sensing and reacting to their environment play a critical role in many natural phenomena (e.g., bacteria colonies, school of fish, human crowds) and artificial systems (e.g., robotic swarms). It is often crucially important to understand how simple environmental cues can be interpreted to produce complex and tunable behaviors. Here, we experimentally and theoretically explore how the sensorial delay between when an agent senses a signal and the time when it reacts to the signal can be exploited in order to engineer the individual and collective long-term behavior of autonomous agents.
We consider phototactic robots that respond to the intensity of a 100-W infrared (850-nm) light source. The robots move in a two-dimensional plane, and their speed is dictated by the light intensity; higher intensity light results in a slower speed. The direction of movement of the robots is random, and the robots are unaware of the positions of other robots. We experimentally, theoretically, and numerically investigate adding a variable delay to describe the time period between which a signal is sensed and the time when the robot reacts. For positive delays, we find that robots cluster together. For negative delays (i.e., a prediction of a future state), the robots tend to avoid one another and instead explore the full spatial environment. We also explore how our findings can be extended to three dimensions.
We expect that our results can be applied to explain the behavior of ensembles of organisms.