Browsing by Subject "Sliding mode control"
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Item Optimally-robust nonlinear control of a class of robotic underwater vehicles(2006) Josserand, Timothy Matthew; Fernandez, Benito R.The subject of this dissertation is the optimally-robust nonlinear control of a class of robotic underwater vehicles (RUVs). The RUV class is characterized by high fineness ratios (length-to-diameter), axial symmetry, and passive roll stability. These vehicles are optimized for robotic applications needing power efficiency for long-range autonomous operations and motion stability for sensor performance improvement. A familiar example is the REMUS vehicle. The particular robot class is further identified by an inconsistent actuator arrangement where the number of inputs is fewer than the number of degrees of freedom, by the loss of controllability at low surge speeds due to the use of fin-based control actuation, and by an inherent heading instability. Therefore, this important type of RUV comprises an interesting and challenging class of systems to study from a control theoretic perspective. The optimally-robust nonlinear control method combines sliding mode control with stochastic state and model uncertainty estimation. First a regular form sliding mode control law is developed for the heading and depth control of the RUV class. The Particle Filter algorithm is then modified and applied to the particular case of estimating not only the RUV state for control feedback but also the functional uncertainty associated with partially modeled shallow water wave disturbances. The functional uncertainty estimate is used to dynamically adjust the sliding mode controller performance term gain according to the estimate of the wave phase and the RUV’s orientation with respect to the predominate wave direction. As a result, the RUV experiences increased performance over constant gain and Kalman Filter methods in terms of heading stability which increases effectiveness and decreased actuator power consumption which increases the RUV mission time. The proposed technique is general enough to be applied to other systems. An experimental RUV was designed and constructed to compare the performance of the regular form sliding mode controller with the conventional PID-type controller. It is demonstrated that the more complicated formulas of the regular form sliding mode controller can still be implemented real-time in an embedded system and that the controller’s performance with regard to modeling uncertainty justifies the added complexity.Item Sliding mode control of the reaction wheel pendulum(2014-12) Luo, Zhitong; Fernandez, Benito R.The Reaction Wheel Pendulum (RWP) is an interesting nonlinear system. A prototypical control problem for the RWP is to stabilize it around the upright position starting from the bottom, which is generally divided into at least 2 phases: (1) Swing-up phase: where the pendulum is swung up and moves toward the upright position. (2) Stabilization phase: here, the pendulum is controlled to be balanced around the upright position. Previous studies mainly focused on an energy method in swing-up phase and a linearization method in stabilization phase. However, several limitations exist. The energy method in swing-up mode usually takes a long time to approach the upright position. Moreover, its trajectory is not controlled which prevents further extensions. The linearization method in the stabilization phase, can only work for a very small range of angles around the equilibrium point, limiting its applicability. In this thesis, we took the 2nd order state space model and solved it for a constant torque input generating the family of phase-plane trajectories (see Appendix A). Therefore, we are able to plan the motion of the reaction wheel pendulum in the phase plane and a sliding mode controller may be implemented around these trajectories. The control strategy presented here is divided into three phases. (1) In the swing up phase a switching torque controller is designed to oscillate the pendulum until the system’s energy is enough to drive the system to the upright position. Our approach is more generic than previous approaches; (2) In the catching phase a sliding surface is designed in the phase plane based on the zero torque trajectories, and a 2nd order sliding mode controller is implemented to drive the pendulum moving along the sliding surface, which improves the robustness compared to the previous method in which the controller switches to stabilization mode when it reaches a pre-defined region. (3) In the stabilization phase a 2nd order sliding mode integral controller is used to solve the balancing problem, which has the potential to stabilize the pendulum in a larger angular region when compared to the previous linearization methods. At last we combine the 3 phases together in a combined strategy. Both simulation results and experimental results are shown. The control unit is National Instruments CompactRIO 9014 with NI 9505 module for module driving and NI 9411 module for encoding. The Reaction Wheel Pendulum is built by Quanser Consulting Inc. and placed in UT’s Advanced Mechatronics Lab.