Troy S. Prince

Evolutionary path planning for autonomous air vehicles using multi-resolution path representation

We introduce an evolutionary flight path planning algorithm capable of mapping paths for free-flying vehicles functioning under several aerodynamic constraints. An air-to-ground targeting scenario was selected to demonstrate the algorithm. The task of the path planner was to generate inputs flying a munition to a point where it could fire a projectile to eliminate a ground target. Vehicle flight constraints, path destination, and final orientation were optimized through fitness evaluation and iterative improvement of generations of candidate flight paths. Evolutionary operators comprised of one crossover operation and six mutation operators. Several cases for air-to-ground vehicle targeting have been successfully executed by the evolutionary flight path planning algorithm under challenging initial conditions. The results demonstrate that evolutionary optimization can achieve flight objectives for air vehicles without violating limits of the aircraft.

Deployable Flow Effectors for Phantom Yaw Control of Missiles at High Alpha

A high alpha phantom yaw control system for enhanced missile maneuverability and stabilization control has been developed. Open and closed-loop experiments on a fin-less 3:1 tangent ogive missile model were conducted to quantify the control effectiveness of the high alpha phantom yaw control system. The flow control system utilizes co-located actuators and sensors modules, force balance data, and a closed-loop controller. The co-located actuators and sensors modules incorporate eight deployable flow effectors and eight corresponding dynamic pressure sensors located circumferentially near the tip of the missile nose cone. Deployable flow effectors are active micro-vortex generators that control and manipulate pressure distribution along the forebody to produce significant side forces and yawing moments for missile control. Significant side forces caused by crossflow separation and natural baseline asymmetries were observed between 40° and 60° alpha. Deployable flow effectors were efficacious between 40° to 55° alpha in generating large side forces that cancelled the baseline flow asymmetry and producing yawing moments on either side of the slender body. Results demonstrate that flow effectors can be used to achieve a wide spectrum of control forces and to modulate the side forces around the missile forebody for desired effect. Dynamic test results showed that the closed-loop controller was successfully able to control the yawing moment on the missile during sweeps from 0° to 60° alpha at various sweep rates. Closed-loop experiments demonstrated the control system’s ability to maintain a desired side force corresponding to zero, left and right yaw. Nomenclature α (alpha) angle of attack, deg Red freestream Reynolds number based on model diameter, ρUod/μ U0 freestream velocity μ absolute viscosity d missile model diameter β angle of sideslip, deg θ DFE radial location on nose cone, deg Cn yawing-moment coefficient, MZ/qSrefd CY Side-force coefficient, FY/qSref MZ yawing moment FY side force Sref cross-sectional area of cylindrical portion of missile model, πd/4 PID Proportional Integral Derivative Kp proportional gain of the PID control law Ki integral gain of the PID control law Kd derivative gain of the PID control law

CONTROL OF AIRCRAFT STALL VIA EMBEDDED PRESSURE SENSORS AND DEPLOYABLE FLOW EFFECTORS

Experimental investigation of a transparent stall control system utilizing dynamic pressure sensors, deployable flow effectors, and a closed-loop feedback controller is presented. Findings on the distinctive nature of pressure fluctuations during pre-stall conditions served as the actuating signal for the controller to trigger the flow effectors. The deployable flow effectors act as micro-vortex generators that enhance the mixing of high momentum fluid flow outside the boundary layer with low momentum fluid flow within the boundary layer to prevent flow separation and thereby delay dynamic stall. Both open- and closed-loop flow control experiments were conducted on a 30°-sweep NACA 0020 airfoil at a Reynolds number of 0.6 x 10 6 for angles of attack ranging from 0° to 23°. Results from open-loop experiments show a 54% increase in the pressure coefficient (-Cp) prior to airfoil stall and a delay of stall angle of attack from 19° to 21°. Closed-loop experiments demonstrated the ability of the controller to successfully detect pre-stall conditions based on the information from dynamic pressure sensors. Detection and control of flow separation over flight control surfaces using the presented active flow control technique offer significant improvement to the performance of air vehicles.

A high-temperature shape memory alloy sensor for combustion monitoring and control

Innovations in the use of thin film SMA materials have enabled the development of a harsh environment pressure sensor useful for combustion monitoring and control. Development of such active combustion control has been driven by rising fuel costs and environmental pressures. Active combustion control, whether in diesel, spark ignited or turbine engines requires feedback to the engine control system in order to adjust the quantity, timing, and placement of fuel charges. To be fully effective, sensors must be integrated into each engine in a manner that will allow continuous combustion monitoring (turbine engines) or monitoring of each discrete combustion event (diesel and SI engines). To date, the sensors available for detection of combustion events and processes have suffered from one or more of three problems: 1) Low sensitivity: The sensors are unable to provide and adequate signal-to-noise ratio in the high temperature and electrically noisy environment of the engine compartment. Attempts to overcome this difficulty have focused on heat removal and/or temperature compensation or more challenging high temperature electronics. 2) Low reliability: Sensors and/or sensor packages have been unable to withstand the engine environment for extended periods of time. Issues have included gross degradation and more subtle issues such as migration of dopants in semiconductor sensor materials. 3) High cost: The materials that have been used, the package concepts employed, and the required support electronics have all contributed to the high cost of the few sensor systems available. Prices have remained high due to the limited demand associated with the poor reliability and the high price itself. Ternary titanium nickel alloys, with platinum group metal substitution for the nickel, are deposited as thin films on MEMS-based diaphragms and patterned to form strain gages of a standard metal film configuration. The strain induced phase transformation of the SMA is used as a natural signal enhancement. These sensors are maintained at a temperature just in excess of the austenite finish temperature (Af). When the diaphragm is deformed by an applied pressure, the film undergoes the reversible martensite phase transformation. The fraction of the austenite transformed to martensite is a fraction of the applied pressure. The large difference in the resistivity of the two phases results in a very sensitive strain gage, and hence a pressure sensor with a very high gage factor. The combination of the thin film and the fact that the transformation is strain induced (rather than thermally induced) results in a sensor with very high response rate. In fact, the response rate of the sensor has been shown to be strictly a function of the mechanical response of the diaphragm. Unlike other sensor systems, the temperature of the SMA sensor is controlled above the temperature of the local environment. By controlling above the temperature of the environment, the sensor is largely immune to temperature fluctuations that can affect the response of other sensors. This technology has been demonstrated for a variety of target temperature regimes and a variety of pressure regimes. Sensor design and testing to date has ranged from 180C to >500C; and design pressures of 50 to 3500 psi, with higher pressures achievable. Characterization has included analysis of the response rate, the temperature sensitivity, reliability, and the effect of gross alloy changes. Sensor performance has also been evaluated in a diesel engine test cell. Ongoing work includes the sensitivity to minor composition changes, sensitivity to film thickness, and extended reliability and engine testing.

An insect-inspired targeting/evasion reflex for autonomous air vehicles

This paper investigates a biologically inspired target seeking reflex for the endgame phase of autonomous munition flight. The reflex is based upon an artificial neural network model of the American Cockroachs escape reflex, and combines exteroceptive and proprioceptive inputs to produce output commands to a Linear Quadratic Regulator (LQR) autopilot that guides the munition to an optimal path destination and orientation for target strike. Simulation and flight test results are presented that demonstrate the reflexs capability for instantaneous target strike on evasive targets, even in the presence of false or disruptive sensor data.

Computationally efficient predictive adaptive control for robot control in dynamic environments and task domains

This paper presents the tuning and implementation of a computationally efficient adaptive predictive control algorithm for robotic utility. The controller addresses the need for practical, computationally efficient, robust real-time adaptive control for multivariable robotic systems. It exploits a special matrix representation to obtain substantial reductions in the computational expense relative to standard methods. We report the design, modeling, and implementation of the controller on a simple pick-and-place manipulator and on an industrial robot loading heavy shells within the magazine of a naval vessel. The proposed controller demonstrates the ability to adapt to varying actuator performance and rapidly changing sea states. Future work involves the implementation and testing of the controller during actual naval operations. We believe this work may serve as a foundation to address control issues for robots working in uncertain dynamic environments and provide a basis for design and control of shipboard robotic devices.

An insect-inspired endgame targeting reflex for autonomous munitions

A target-seeking system for autonomous munitions in the endgame stage of flight is developed based upon a neural network model of the cockroach escape reflex. Despite significant differences in objectives, certain aspects of the cockroach escape response are consistent with desired characteristics of a target seeking system. An evolutionary target-seeking algorithm was generated to gather data to train the neural net target-seeking system. Targeting data was generated through intensive offline computing, which the target-seeking reflex was trained to reproduce on-line instantly. A linear quadratic regulator (LQR) autopilot executes reflexive guidance commands. With the trained target-seeking system installed on a candidate air to-ground munition, simulations show that the reflex may react to strike targets very quickly. Context dependency was demonstrated through the actions of the reflex striking targets moving on rapidly changing, evading, and unpredictable trajectories, as well as through false and disruptive sensor data.