Hierarchical Rule-Base Reduction Fuzzy Control for Constant Velocity
Path Tracking of a Differential Steer Vehicle
Abstract
A new form of waypoint navigation controller for a skid-steer vehicle is
presented, which consisted of a multiple input-single output nonlinear
fuzzy angular velocity controller. The mem- bership functions of the
fuzzy controller employed a trape- zoidal structure with a completely
symmetric rule-base. No- tably, Hierarchical Rule-Base Reduction (HRBR)
was incorpo- rated into the controller to select only the rules most
influen- tial on state errors. This was done by selecting inputs/outputs
and generating a hierarchy of inputs using a Fuzzy Relations Control
Strategy (FRCS). Similar to some traditional fuzzy con- trollers, the
system provided coverage for the global operat- ing environment.
However, a rule for every possible combi- nation of variables and states
was no longer necessary. Con- sequently, HRBR fuzzy controllers
effectively increase both the number of inputs and their associated
fidelity without the rule-base dramatically increasing. To contextualize
the performance of the controller, a background on vehicle dy- namic
modeling methodologies and an in-depth explanation of the related
simulation model are provided. An examina- tion of the proposed
controller is then completed employing test courses. The test courses
examine the effects of steer- ing disturbance, phase lag, and overshoot
as expressed in Root Mean Square Error (RMSE), Max Error (ME), and
Course Completion Time (CCT). Finally, simulation and experimental
results for the controller’s performance were compared with a
state-of-the-art waypoint navigation vehicle controller, ge- ometric
pure pursuit. The fuzzy was found to outperform the pure pursuit
experimentally by 52.1 percent in RMSE, 26.8 percent in ME, and 1.07
percent in CCT, on average, validat- ing the viability of the
controller.