TEXPLORE: Temporal Difference Reinforcement Learning for Robots and Time-Constrained Domains. (2012)
Robots have the potential to solve many problems in society, because of their ability to work in dangerous places doing necessary jobs that no one wants or is able to do. One barrier to their widespread deployment is that they are mainly limited to tasks where it is possible to hand-program behaviors for every situation that may be encountered. For robots to meet their potential, they need methods that enable them to learn and adapt to novel situations that they were not programmed for. Reinforcement learning (RL) is a paradigm for learning sequential decision making processes that could solve the problems of learning and adaptation on robots. This thesis identifies four key challenges that must be addressed for an RL algorithm to be practical for robotic control tasks. These RL for Robotics Challenges are: 1) it must learn in very few samples; 2) it must learn in domains with continuous state features; 3) it must handle sensor and/or actuator delays; and 4) it should continually take actions in real-time. This thesis focuses on addressing all four of these challenges. In particular, this thesis is focused on time-constrained domains where the first challenge is critically important. In these domains, the agent's lifetime is not long enough for it to explore the domain thoroughly, and it must learn in very few samples.

Although existing RL algorithms successfully address one or more of the RL for Robotics Challenges, no prior algorithm addresses all four of them. To fill this gap, this thesis introduces TEXPLORE, the first algorithm to address all four challenges. TEXPLORE is a model-based RL method that learns a random forest model of the domain which generalizes dynamics to unseen states. Each tree in the random forest model represents a hypothesis of the domain's true dynamics, and the agent uses these hypotheses to explores states that are promising for the final policy, while ignoring states that do not appear promising. With sample-based planning and a novel parallel architecture, TEXPLORE can select actions continually in real-time whenever necessary.

We empirically evaluate each component of TEXPLORE in comparison with other state-of-the-art approaches. In addition, we present modifications of TEXPLORE's exploration mechanism for different types of domains. The key result of this thesis is a demonstration of TEXPLORE learning to control the velocity of an autonomous vehicle on-line, in real-time, while running on-board the robot. After controlling the vehicle for only two minutes, TEXPLORE is able to learn to move the pedals of the vehicle to drive at the desired velocities. The work presented in this thesis represents an important step towards applying RL to robotics and enabling robots to perform more tasks in society. By enabling robots to learn in few actions while acting on-line in real-time on robots with continuous state and actuator delays, TEXPLORE significantly broadens the applicability of RL to robots.

Code available at: http://www.ros.org/wiki/rl-texplore-ros-pkg
Dissertation PDF linked under PDF below.
Slides with Video linked under slides below. Note the videos may not work in Ubuntu.
Videos available separately on youtube.
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PhD Thesis, The University of Texas at Austin. Code available at: http://www.ros.org/wiki/rl-texplore-ros-pkg.
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Todd Hester Postdoctoral Alumni todd [at] cs utexas edu