  We present a method for efficient learning of control policies for multiple
related robotic motor skills. Our approach consists of two stages, joint
training and specialization training. During the joint training stage, a neural
network policy is trained with minimal information to disambiguate the motor
skills. This forces the policy to learn a common representation of the
different tasks. Then, during the specialization training stage we selectively
split the weights of the policy based on a per-weight metric that measures the
disagreement among the multiple tasks. By splitting part of the control policy,
it can be further trained to specialize to each task. To update the control
policy during learning, we use Trust Region Policy Optimization with
Generalized Advantage Function (TRPOGAE). We propose a modification to the
gradient update stage of TRPO to better accommodate multi-task learning
scenarios. We evaluate our approach on three continuous motor skill learning
problems in simulation: 1) a locomotion task where three single legged robots
with considerable difference in shape and size are trained to hop forward, 2) a
manipulation task where three robot manipulators with different sizes and joint
types are trained to reach different locations in 3D space, and 3) locomotion
of a two-legged robot, whose range of motion of one leg is constrained in
different ways. We compare our training method to three baselines. The first
baseline uses only joint training for the policy, the second trains independent
policies for each task, and the last randomly selects weights to split. We show
that our approach learns more efficiently than each of the baseline methods.
