Page 155 - Biomimetics : Biologically Inspired Technologies

Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c004 Final Proof page 141 21.9.2005 9:37am

Evolutionary Robotics and Open-Ended Design Automation 141

Turtle
forward(1) Bar
Actuator
joint(1), push, joint(1)
push, joint(1), forward(1)
forward(1), pop,
clockwise(2)
pop, clockwise(2)
joint(1), push, joint(1), forward(1),
pop, clockwaise(2)

(a) (b)

(c)

(d)
Direct Generative
1000 1000
0 −1000 0
Fitness change −2000 Fitness change −2000
−1000
−3000
−3000
−4000 −4000
−5000 −5000
1 10 100 1000 10000 1 10 100 1000 10000
Mutation Size Mutation Size
Figure 4.6 Evolving bodies and brains using generative encodings: (a) Schematic illustration of a construction
sequence and (b) the resulting robot with actuated joints. (c) Three examples of robots produced by evolving
L-systems that produce construction sequences, and (d) their physical instantiations. (e) A comparison of effects of
mutation in the direct encoding versus the generative encoding shows that the generative encoding has trans-
formed the space in a way that makes mutation more effective. (From Hornby, G. S., Lipson, H., Pollack, J. B.
(2003) Generative encodings for the automated design of modular physical robots, IEEE Transactions on Robotics
and Automation, 19(4). With permission.)

oscillates, using integer values from 0 to 5, and the relative phase-offset of the oscillation cycle is
taken from the turtle’s state. The commands ‘‘increase-offset’’ and ‘‘decrease-offset’’ change the
offset value n the turtle’s state by +25% of a total cycle. Command sequences enclosed by ‘‘{}’’
are repeated a number of times specified by the brackets’ argument.