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Controlling swimming and crawling in a fish robot using a central pattern generator
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Controlling swimming and crawling in a fish robot using a central pattern generator
Alessandro Crespi1  , Daisy Lachat1 , Ariane Pasquier1 and Auke Jan Ijspeert1
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School of Computer and Communication Science, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 14, 1015 Lausanne, Switzerland |
Received: 30 October 2006 Accepted: 3 December 2007 Published online: 22 December 2007
Abstract
Online trajectory generation for robots with multiple degrees of freedom is still a difficult and unsolved problem, in particular
for non-steady state locomotion, that is, when the robot has to move in a complex environment with continuous variations of
the speed, direction, and type of locomotor behavior. In this article we address the problem of controlling the non-steady
state swimming and crawling of a novel fish robot. For this, we have designed a control architecture based on a central pattern
generator (CPG) implemented as a system of coupled nonlinear oscillators. The CPG, like its biological counterpart, can produce
coordinated patterns of rhythmic activity while being modulated by simple control parameters.
To test our controller, we designed BoxyBot, a simple fish robot with three actuated fins capable of swimming in water and
crawling on firm ground. Using the CPG model, the robot is capable of performing and switching between a variety of different
locomotor behaviors such as swimming forwards, swimming backwards, turning, rolling, moving upwards/downwards, and crawling.
These behaviors are triggered and modulated by sensory input provided by light, water, and touch sensors. Results are presented
demonstrating the agility of the robot and interesting properties of a CPG-based control approach such as stability of the
rhythmic patterns due to limit cycle behavior, and the production of smooth trajectories despite abrupt changes of control
parameters.
The robot is currently used in a temporary 20-month long exhibition at the EPFL. We present the hardware setup that was designed
for the exhibition, and the type of interactions with the control system that allow visitors to influence the behavior of
the robot. The exhibition is useful to test the robustness of the robot for long term use, and to demonstrate the suitability
of the CPG-based approach for interactive control with a human in the loop.
This article is an extended version of an article presented at BioRob2006 the first IEEE/RAS-EMBS International Conference
on Biomedical Robotics and Biomechatronics.
Keywords Fish robot - Central pattern generator - Swimming - Crawling
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