713 research outputs found
Design of a Fuzzy Logic Controller for Skid Steer Mobile Robot
The control problem of four-wheeled skid steering mobile robots is quite challenging
mainly because the skid steering system is an underactuated system and its
mathematical model is highly uncertain. Skid steering configurations employ a
differential-drive technique in which the wheels rotation is limited to around one axis
and the lack of a steering wheel causes the navigation to be determined by the change
of speed in either side of the robot for turning. Equal speed in both sides causes a
straight-line motion. However, the implementation of the dead reckoning technique
on skid-steer mobile robots will limit the precision of current robot’s position
because skid-steer configuration intentionally relies on wheel slippage for normal
operation and this possesses some difficulties when implementing motion control
using the odometric system.
The thesis describes the design of a fuzzy logic controller to compensate the dead
reckoning limitation and implementation on a skid-steer mobile robot. The fuzzy
controller has two inputs (angle error and distance), two outputs (translational and
rotational speed) and 14 rules. These inputs are computed from the dead-reckoning method that is totally reliant on the odometry readings and data are fuzzified to be
the inputs of the fuzzy controller. The outputs are the analogue voltages to the left
and right motors, which drive the mobile robot. For simplicity, membership
functions consisting of triangular and trapezoid shapes have been adopted. The
membership functions of the fuzzy sets are chosen by trial-and-error based on
experimentation. The heuristic rules control the orientation of the robot according to
the information about the distances from the desired positions. The crisp output
values from the fuzzy logic controller are decoded and fed into a decision module
where the ratios of both sides motor voltage are determined for every smooth change
in speed of the motors.
To facilitate the implementation of control system, real-time execution is done in an
indoor environment. Data acquisition is done in a LABVIEW and a MATLAB
control algorithm is called in LABVIEW. A real mobile robot, PUTRABOT2 was
used to conduct the experiment. Performance evaluation is observed from the
accumulated error in orientation and its trajectory obtained after mapping the
information gathered from the real world via odometry sensors. Few features such as
the rise time, settling time and peak time of the output responses are analyzed.
Comparisons are made between fuzzy logic and PD controllers. Comparative results
among these two controllers indicate the superiority of the fuzzy approach with the
ability to minimize the position and orientation errors. Moreover, the trajectory
accuracy is very high and more reliable in the presence of unreliable odometry
readings
Synthesis of Switching Protocols from Temporal Logic Specifications
We propose formal means for synthesizing switching protocols that determine the sequence in which the modes of a switched system are activated to satisfy certain high-level specifications in linear temporal logic. The synthesized protocols are robust against exogenous disturbances on the continuous dynamics. Two types of finite transition systems, namely under- and over-approximations, that abstract the behavior of the underlying continuous dynamics are defined. In particular, we show that the discrete synthesis problem for an under-approximation can be formulated as a model checking problem, whereas that for an over-approximation can be transformed into a two-player game. Both of these formulations are amenable to efficient, off-the-shelf software tools. By construction, existence of a discrete switching strategy for the discrete synthesis problem guarantees the existence of a continuous switching protocol for the continuous synthesis problem, which can be implemented at the continuous level to ensure the correctness of the nonlinear switched system. Moreover, the proposed framework can be straightforwardly extended to accommodate specifications that require reacting to possibly adversarial external events. Finally, these results are illustrated using three examples from different application domains
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