Control of a Wheeled Mobile Robot with Centered Orientable Wheels and an Offset Alpha Sensor for Radiation Surveying Applications

Ramanathan, Vikram
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This thesis considers the modeling, control and path planning of wheeled mobile robots with four Centered Orientable Conventional (COC) wheels, intended to assist with alpha radiation surveys. When compared to non-conventional wheels, COC wheels perform better over rough terrain, are not subject to vertical chatter and offer better braking capability. However, COC wheels are pseudoomnidirectional and subject to nonholonomic constraints. Several established modeling and control techniques define and control the Instantaneous Center of Rotation (ICR); however, this method involves singular configurations that are not trivial to eliminate. This work proposes a method that uses a novel ICR-based kinematic model to avoid these singularities, and an ICR-based nonlinear controller for one “master” wheel. The other “slave” wheels simply track the resulting kinematic relationships between the “master” wheel and the ICR. Thus, the nonlinear control problem is reduced from 12th to 3rd-order, becoming much more tractable. Simulations with a feedback linearization controller verify the approach.