Ryan T. Ratliff

Distributed Formation Flight Control Using Constraint Forces

A new approach for formation flight control of multiple aircraft is presented. Constraint forces are used to derive the dynamics of a constrained, multibody system. A stable, distributed control algorithm is designed based on the information flow graph for a group of aircraft. The aircraft will achieve a particular formation while ensuring an arbitrarily small bounded navigation tracking error with parameter uncertainties of the entire group. It is assumed that uncertainty exists in the drag coefficient of each aircraft. An adaptation algorithm is developed to compensate forthe uncertainty andestimate the drag coefficient. The advantageof the proposeddistributed control algorithm is that it allows the addition/removal of other aircraft into/from the formation seamlessly with simple modifications of thecontrolinput.Furthermore,thealgorithmprovidesinherentscalability.Simulationswereconductedtoverifythe proposed approach.

Distributed Formation control of multiple aircraft using constraint forces

A new approach for formation flight control of multiple aircraft is presented. Constraint forces are used to derive the dynamics of a constrained, multi-body system. A stable, distributed control algorithm is designed based on the information flow graph for a group of aircraft. The aircraft will achieve a particular formation while ensuring accurate navigation of the entire group. It is assumed that uncertainty exists in the drag coefficient of each aircraft. An adaptation algorithm is developed to compensate for the uncertainty and estimate the drag coefficient. The advantage of the proposed distributed control algorithm is that it allows the addition/removal of other aircraft into/from the formation seamlessly with simple modifications of the control input. Furthermore, the algorithm provides inherent scalability. Simulations were conducted to verify the proposed approach.

Commutational ramp load control for disk drive actuators

The research investigates the feasibility of a ramp load/unload (L/UL) controller using a conventional, non-L/UL disk drive actuator. Therefore, disk drives with lower cost and higher torque actuators can realize the linear shock resistance benefits of ramp loading. A disk drive designed with a conventional actuator is outfitted with a ramp and optimized for L/UL operation. While on the ramp, there exists a set in the state space where the actuator dynamics are uncontrollable. A state trajectory is generated that, when tracked, moves the actuator through the uncontrollable set and equilibrium points for a successful load onto the disk at the desired load velocity. A continuous, state-feedback controller with varying gains is designed for tracking. A unique disk drive is manufactured with ramp load capability and experiments are performed to verify the design and modeling results.

Advances in Agile Maneuvering for High Performance Munitions

A new paradigm is presented for agile maneuvering of air vehicle weapon systems. Maneuvers are facilitated using only aerodynamic moments to rapidly reorient the airframe resulting in extremely high angles of attack. This form of agility is technically challenging as it requires maneuvering through uncontrollable, unstable regions of the flight envelope. The airframe will experience periods of severe degradation or complete loss of aerodynamic control effectiveness. Accomplishing this maneuver increases the range and effectiveness of the weapon through higher terminal velocities and potentially reduces or eliminates the additional monetary and performance costs associated with traditional reaction jets or thrust vectoring. A detailed dynamic analysis is presented along with related challenges.

Departure resilient control for autonomous air vehicles

A new approach for developing guidance and control laws for aircraft that have departed controlled flight is presented. The method leverages and produces flight trajectories similar to what pilots would perform. The method induces a periodic orbit and then escapes from the periodic orbit into normal flight. The problem is approached from the inertial reference frame in order to better define the behavior of periodic orbit dynamics. A control law that effectively maps the aircraft inertial dynamics to bifurcations facilitates the production of periodic orbit behavior. In addition to circular orbits, the control law proves to expand the set to elliptical orbits and presents a framework for alternative orbit geometries.

Fault tolerant robust flight control using surface actuator hinge moments

A robust, flight control law is investigated to provide fault tolerance for air vehicles experiencing inertial state measurement sensor degradation. The method is particularly useful on low cost, precision weapons pursuing dynamic targets. Observation techniques are facilitated by representing the surface actuator aerodynamic induced hinge moment by a function that is Lipschitz within the actuator sweep angle. A stable output feedback flight control law, requiring only actuator angular position and current measurements, is designed to handle the hinge moment effects and track a predetermined angle-of-attack reference trajectory. Benefits include improved effectiveness, improved reliability without additional hardware, and a cost and weight savings. Simulations are conducted on a tactical missile interceptor to evaluate the controller at various operating conditions in the flight envelope.

Adaptive Control of a Missile Fuel Control Valve

Adaptive control methods are investigated for a missile fuel control valve actuator system. The actuator possesses uncertain, nonlinear dynamics which include various torque bias components. A full state feedback design is proposed subject to a finite difference approximation of actuator velocity. Radial basis functions and feedforward neural networks are employed to estimate the uncertainty. The controller provides bounded tracking and guarantees a uniform ultimate boundedness of all the signals in the corresponding closed-loop system. An output feedback solution is also developed using an adaptive observer where the nonlinearity is represented as a polynomial with uncertain coefficients. The closed loop, output feedback system provides asymptotic tracking performance with bounded coefficient estimation. Simulations are conducted to evaluate and compare both designs.

Uncontrollable Singularities in Nonlinear Systems

The problem of tracking through singular sub-manifolds is extended to include regions of uncontrollability. A special, pragmatic class of nonlinear systems with uncontrollable, singular points is analyzed. The unique behavior of these systems is compared to systems with controllable, input singularities such as the well-known ball and beam system that has enjoyed considerable attention throughout the literature. Analysis reveals the deficiency of existing control solutions to properly handle an input singularity that is also uncontrollable. A sufficient condition for successfully maneuvering through an uncontrollable, singular submanifold is derived providing a basis for reference trajectory design. An illustrative example of practical applicability is presented for a disk drive, commutational ramp load actuator

Design and seek control of a disc drive actuator with nonlinear magnetic bias

The research investigates the design and performance capabilities of a voice-coil motor actuator (VCMA) for a disc drive with a nonlinear magnetic bias. A VCMA is designed to meet specific seek performance requirements. A nonlinear magnetic bias is independently designed to compensate for non-operational shock. A model-based adaptive controller was developed to meet the seek performance requirements and simultaneously handle effects of the nonlinear bias. The performance criteria was based on minimizing the time required for a seek maneuver without controller saturation. The proposed adaptive controller was compared to an often used linear state-feedback controller with the magnetic bias present. Simulations were conducted to verify the results.

Commutational Output Feedback Control for Disk Drive Ramp Loading

The feasibility of a ramp load controller using a conventional disk drive actuator is investigated. The controller eliminates the necessity of increased material requirements common in ramp load disk drives. Therefore, disk drives with lower cost, higher performance actuators can realize the linear shock protection benefits of ramp loading. A disk drive designed with a conventional actuator is outfitted with a ramp and optimized for ramp load operation. While on the ramp, there exists a set in the state space where the actuator dynamics are uncontrollable. An input commutation is required within the uncontrollable region to sustain the direction of actuator motion. Additionally, the motor torque factor, magnetic restoration bias, and friction torque are nonlinear and can be represented by functions that are Lipschitz within the actuator ramp angle. A state trajectory is generated that, when tracked, moves the actuator through the uncontrollable set for a successful load onto the disk at the desired load velocity. Because position and velocity information are not available during a load maneuver, an output feedback controller is necessary. A stable, output feedback tracking controller is designed to track the trajectory and handle the nonlinear effects. A unique disk drive is manufactured and experiments are performed to verify the complete ramp loading design strategy.