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Schlagwörter:
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Zusammenfassung:
While operational space control is of essential importance
for robotics and well-understood from an analytical
point of view, it can be prohibitively hard to achieve accurate
control in face of modeling errors, which are inevitable in
complex robots, e.g., humanoid robots. In such cases, learning
control methods can offer an interesting alternative to analytical
control algorithms. However, the resulting supervised learning
problem is ill-defined as it requires to learn an inverse mapping
of a usually redundant system, which is well known to suffer
from the property of non-convexity of the solution space, i.e.,
the learning system could generate motor commands that try
to steer the robot into physically impossible configurations. The
important insight that many operational space control algorithms
can be reformulated as optimal control problems, however, allows
addressing this inverse learning problem in the framework of
reinforcement learning. However, few of the known optimization
or reinforcement learning algorithms can be used in online
learning control for robots, as they are either prohibitively
slow, do not scale to interesting domains of complex robots,
or require trying out policies generated by random search,
which are infeasible for a physical system. Using a generalization
of the EM-based reinforcement learning framework suggested
by Dayan amp; Hinton, we reduce the problem of learning with
immediate rewards to a reward-weighted regression problem
with an adaptive, integrated reward transformation for faster
convergence. The resulting algorithm is efficient, learns smoothly
without dangerous jumps in solution space, and works well in
applications of complex high degree-of-freedom robots.
