A robot wanders around an unfamiliar environment, performing actions and observing their perceptual consequences. The robot's task is to construct a model of its environment that will allow it to predict the outcome of its actions and to determine what action sequences take it to particular goal states. In any reasonably complex situation, a robot that aims to manipulate its environment toward some desired end requires an internal representation of the environment because the robot can directly perceive only a small fraction of the global environmental state at any time; some portion of the rest must be stored internally if the robot is to act effectively. Rivest and Schapire (72, 74, 87) have studied this problem and have designed a symbolic algorithm to strategically explore and infer the structure of finite-state environments. At the heart of this algorithm is a clever representation of the environment called an update graph. This dissertation presents a connectionist implementation of the update graph using a highly specialized network architecture and a technique for using the connectionist update graph to guide the robot from an arbitrary starting state to a goal state. This technique requires a critic that associates the update graph's current state with the expected time to reach the goal state. At each time step, the robot selects the action that minimizes the output of the critic. The basic control acquisition technique is demonstrated on several environments, and it is generalized to handle a navigation task involving a more realistic environment characterized by a high-dimensional continuous state-space with real-valued actions and sensations in which a simulated cylindrical robot with a sensor belt operates in a planar environment. The task is short-range homing in the presence of obstacles. Unlike many approaches to robot navigation, our approach assumes no prior map of the environment. Instead, the robot has to use its limited sensory information to construct a model of its environment. A connectionist architecture is presented for building such a model. It incorporates a large amount of a priori knowledge in the form of hard-wired networks, architectural constraints, and initial weights. This navigation example demonstrates the use of a large modular architecture on a difficult task.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-8403 |
| Date | 01 January 1992 |
| Creators | Bachrach, Jonathan Richard |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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