ON THE DESIGN, IMPLEMENTATION AND FLIGHT TESTING OF INTEGRATED GUIDANCE AND CONTROL SYSTEMS FOR UNMANNED AIR VEHICLES


ISAAC KAMINER
DEPARTMENT OF AERONAUTICS AND ASTRONAUTICS
NAVAL POSTGRADUATE SCHOOL

In a great number of envisioned mission scenarios Unmanned Air Vehicles (UAVs) will be required to follow inertial reference trajectories accurately in 3-D space. To achieve this goal, the following systems must be designed and implemented on-board UAV's: i) navigation, to provide estimates of linear and angular positions and velocities of the vehicle, ii) guidance, to process navigation/inertial reference trajectory data and output set-points for the vehicle's (body) velocity and attitude, and iii) control, to generate the actuator signals that are required to drive the actual velocity and attitude of the vehicle to the values commanded by the guidance scheme.

The advent of GPS (Global Positioning System) has afforded UAV systems engineers a powerful new means of obtaining accurate navigation data that is required for precise tracking of given inertial trajectories. However, traditional guidance and control schemes used to steer the vehicle along such trajectories may prove inadequate in the case where frequent heading changes are required or in the presence of shifting wind. Traditionally, such systems are designed separately, using well established design methods for control and simple strategies such as line of sight (LOS) for guidance. During the design phase, the control system is usually designed with a sufficiently large bandwidth to track the commands that are expected from the guidance system. However, since the two systems are effectively coupled, stability and adequate performance of the combined system about nominal trajectories are not guaranteed. In practice, this problem can be resolved by judicious choice of guidance law parameters (such as so-called visibility distance in LOS strategy), based on extensive computer simulations. Even when stability is obtained, however, the resulting strategy leads to finite trajectory tracking errors, the magnitude of which depends on the type of trajectory to be tracked (radius of curvature, vehicle's desired speed, etc).

In this talk, I will discuss a new methodology for the design of guidance and control systems for UAVs, whereby the two systems are designed simultaneously. This methodology has two main advantages over traditional ones: i) the resulting trajectory tracking system achieves zero steady state tracking error for a class of so-called trimming trajectories, and ii) the design methodology explicitly addresses the problem of stability and performance of the combined guidance and control systems. The talk will cover the theoretical aspects of the methodology. This will be followed by a discussion of the application of the methodology to the design, implementation and flight testing of an integrated guidance and control system for a UAV Frog operated by the UAV Lab at the Naval Postgraduate School.