34 research outputs found
Evolved embodied phase coordination enables robust quadruped robot locomotion
Overcoming robotics challenges in the real world requires resilient control
systems capable of handling a multitude of environments and unforeseen events.
Evolutionary optimization using simulations is a promising way to automatically
design such control systems, however, if the disparity between simulation and
the real world becomes too large, the optimization process may result in
dysfunctional real-world behaviors. In this paper, we address this challenge by
considering embodied phase coordination in the evolutionary optimization of a
quadruped robot controller based on central pattern generators. With this
method, leg phases, and indirectly also inter-leg coordination, are influenced
by sensor feedback.By comparing two very similar control systems we gain
insight into how the sensory feedback approach affects the evolved parameters
of the control system, and how the performances differs in simulation, in
transferal to the real world, and to different real-world environments. We show
that evolution enables the design of a control system with embodied phase
coordination which is more complex than previously seen approaches, and that
this system is capable of controlling a real-world multi-jointed quadruped
robot.The approach reduces the performance discrepancy between simulation and
the real world, and displays robustness towards new environments.Comment: 9 page
Guiding Neuroevolution with Structural Objectives
The structure and performance of neural networks are intimately connected,
and by use of evolutionary algorithms, neural network structures optimally
adapted to a given task can be explored. Guiding such neuroevolution with
additional objectives related to network structure has been shown to improve
performance in some cases, especially when modular neural networks are
beneficial. However, apart from objectives aiming to make networks more
modular, such structural objectives have not been widely explored. We propose
two new structural objectives and test their ability to guide evolving neural
networks on two problems which can benefit from decomposition into subtasks.
The first structural objective guides evolution to align neural networks with a
user-recommended decomposition pattern. Intuitively, this should be a powerful
guiding target for problems where human users can easily identify a structure.
The second structural objective guides evolution towards a population with a
high diversity in decomposition patterns. This results in exploration of many
different ways to decompose a problem, allowing evolution to find good
decompositions faster. Tests on our target problems reveal that both methods
perform well on a problem with a very clear and decomposable structure.
However, on a problem where the optimal decomposition is less obvious, the
structural diversity objective is found to outcompete other structural
objectives -- and this technique can even increase performance on problems
without any decomposable structure at all
Co-optimising Robot Morphology and Controller in a Simulated Open-Ended Environment
Designing robots by hand can be costly and time consuming, especially if the
robots have to be created with novel materials, or be robust to internal or
external changes. In order to create robots automatically, without the need for
human intervention, it is necessary to optimise both the behaviour and the body
design of the robot. However, when co-optimising the morphology and controller
of a locomoting agent the morphology tends to converge prematurely, reaching a
local optimum. Approaches such as explicit protection of morphological
innovation have been used to reduce this problem, but it might also be possible
to increase exploration of morphologies using a more indirect approach. We
explore how changing the environment, where the agent locomotes, affects the
convergence of morphologies. The agents' morphologies and controllers are
co-optimised, while the environments the agents locomote in are evolved
open-endedly with the Paired Open-Ended Trailblazer (POET). We compare the
diversity, fitness and robustness of agents evolving in environments generated
by POET to agents evolved in handcrafted curricula of environments. Our agents
each contain of a population of individuals being evolved with a genetic
algorithm. This population is called the agent-population. We show that
agent-populations evolving in open-endedly evolving environments exhibit larger
morphological diversity than agent-populations evolving in hand crafted
curricula of environments. POET proved capable of creating a curriculum of
environments which encouraged both diversity and quality in the populations.
This suggests that POET may be capable of reducing premature convergence in
co-optimisation of morphology and controllers.Comment: 17 pages, 8 figure
Open-ended search for environments and adapted agents using MAP-Elites
Creatures in the real world constantly encounter new and diverse challenges
they have never seen before. They will often need to adapt to some of these
tasks and solve them in order to survive. This almost endless world of novel
challenges is not as common in virtual environments, where artificially
evolving agents often have a limited set of tasks to solve. An exception to
this is the field of open-endedness where the goal is to create unbounded
exploration of interesting artefacts. We want to move one step closer to
creating simulated environments similar to the diverse real world, where agents
can both find solvable tasks, and adapt to them. Through the use of MAP-Elites
we create a structured repertoire, a map, of terrains and virtual creatures
that locomote through them. By using novelty as a dimension in the grid, the
map can continuously develop to encourage exploration of new environments. The
agents must adapt to the environments found, but can also search for
environments within each cell of the grid to find the one that best fits their
set of skills. Our approach combines the structure of MAP-Elites, which can
allow the virtual creatures to use adjacent cells as stepping stones to solve
increasingly difficult environments, with open-ended innovation. This leads to
a search that is unbounded, but still has a clear structure. We find that while
handcrafted bounded dimensions for the map lead to quicker exploration of a
large set of environments, both the bounded and unbounded approach manage to
solve a diverse set of terrains
Evolution of linkages for prototyping of linkage based robots
Prototyping robotic systems is a time consuming process. Computer aided
design, however, might speed up the process significantly. Quality-diversity
evolutionary approaches optimise for novelty as well as performance, and can be
used to generate a repertoire of diverse designs. This design repertoire could
be used as a tool to guide a designer and kick-start the rapid prototyping
process. This paper explores this idea in the context of mechanical linkage
based robots. These robots can be a good test-bed for rapid prototyping, as
they can be modified quickly for swift iterations in design. We compare three
evolutionary algorithms for optimising 2D mechanical linkages: 1) a standard
evolutionary algorithm, 2) the multi-objective algorithm NSGA-II, and 3) the
quality-diversity algorithm MAP-Elites. Some of the found linkages are then
realized on a physical hexapod robot through a prototyping process, and tested
on two different floors. We find that all the tested approaches, except the
standard evolutionary algorithm, are capable of finding mechanical linkages
that creates a path similar to a specified desired path. However, the
quality-diversity approaches that had the length of the linkage as a behaviour
descriptor were the most useful when prototyping. This was due to the
quality-diversity approaches having a larger variety of similar designs to
choose from, and because the search could be constrained by the behaviour
descriptors to make linkages that were viable for construction on our hexapod
platform
Behavioural Plasticity Can Help Evolving Agents in Dynamic Environments but at the Cost of Volatility
Neural networks have been widely used in agent learning architectures; however, learnings for one task might nullify learnings for another. Behavioural plasticity enables humans and animals alike to respond to environmental changes without degrading learned knowledge; this can be achieved by regulating behaviour with neuromodulation—a biological process found in the brain. We demonstrate that by modulating activity-propagating signals, neurally trained agents evolving to solve tasks in dynamic environments that are prone to change can expect a significantly higher fitness than non-modulatory agents and also achieve their goals more often. Further, we show that while behavioural plasticity can help agents to achieve goals in these variable environments, this ability to overcome environmental changes with greater success comes at the cost of highly volatile evolution