Mariano Lizarraga

An improved quaternion-based Kalman filter for real-time tracking of rigid body orientation

This paper presents an improved Kalman filter for real-time tracking of human body motions. An earlier version of the filter was presented at IROS 2001. Since then, the filter has been substantially improved. Real-time tracking of rigid body orientation is accomplished using the MARG (magnetic, angular rate, and gravity) sensors. A MARG sensor measures the three-dimensional local magnetic field, three-dimensional angular rate, and three-dimensional acceleration. A Kalman filter is designed to process measurements provided by the MARG sensors, and to produce real-time orientation represented in quaternions. There are many design decisions as related to choice of state vectors, output equations, process model, etc. The filter design presented in this paper utilizes the Gauss-Newton method for parameter optimization in conjunction with Kalman filtering. The use of the Gauss-Newton method, particularly the reduced-order implementation introduced in the paper, significantly simplifies the Kalman filter design, and reduces computational requirements.

Cooperative control of small UAVs for naval applications

This paper addresses the development of a cooperative control algorithm used to launch and recover a fleet of small UAV from a ship. The key features of the algorithm include trajectory generation for multiple UAV that accounts for their aerodynamic characteristics and guarantees deconfliction, particularly on final approach, and path following control for multiple UAV to track these trajectories. The proposed control approach is sufficiently flexible to allow for multiple formation configurations and sequential landing patterns. The paper includes simulation results and ends with conclusions and recommendations for future work.

Spatially deconflicted path generation for multiple UAVs in a bounded airspace

This paper presents a preliminary framework for generating spatially deconflicted paths for multiple UAVs using Bezier curves. The critical issue addressed is that of guaranteeing that all the paths lie inside a pre-defined airspace volume. Its is shown that Bezier curves reperesent a natural tool for meeting this requirement. The paper reviews the essential properties of the Bezier curves that are used to guarantee spatial deconfliction between the UAV paths as well as airspace volume contsraints. The generated curves are not only non-overlapping but separated by a minimum distance chosen prior to flight. It is then shown that the path generation problem can be formulated as a constrained optimization problem over a finite optimization set and solved using standard MATLAB optimization tools. Simulation results are presented along with its discussion. The paper includes an analysis of numerical solutions obtained as well as discussion of future work.

New Generation of Rapid Flight Test Prototyping System for small Unmanned Air Vehicles

This paper describes the development and application of a rapid prototyping system for flight testing of novel autonomous flight algorithms for unmanned air vehicles (UAVs) at the Naval Postgraduate School. The system provides a small team with the ability to rapidly prototype new theoretical concepts and flight-test their performance in realistic mission scenarios. The original development was done using MATRIXX Xmath/SystemBuild environment almost a decade ago. Currently, the system has been converted to the Mathworks MATLAB/Simulink development environment. This paper describes the hardware and software tools developed for the system and briefly discusses the variety of projects including vision-based target tracking, 3D path following, SUAV control over the network and high-resolution imagery on the fly.

Comparison of low-cost GPS/INS sensors for Autonomous Vehicle applications

Autonomous Vehicle applications (Unmanned Ground Vehicles, Micro-Air Vehicles, UAVpsilas, and Marine Surface Vehicles) all require accurate position and attitude to be effective. Commercial units range in both cost and accuracy, as well as power, size, and weight. With the advent of low-cost blended GPS/INS solutions, several new options are available to accomplish the positioning task. In this work, we experimentally compare three commercially available, off-the-shelf units insitu, in terms of both position, and attitude. The compared units are a Microbotics MIDG-II, a Tokimec VSAS-2GM, along with a KVH Fiber Optic Gyro. The position truth measure is from a Trimble Ag122 DGPS receiver, and the attitude truth is from the KVH in yaw. Care is taken to make sure that all measurements are taken simultaneously, and that the sensors are all mounted rigidly to the vehicle chassis. A series of measurement trials are performed, including light driving on coastal roads and highway speeds, static bench testing, and flight data taken in a light aircraft both flying up the coast as well as aggressively maneuvering. Allan Variance analysis performed on all of the sensors, and their noise characteristics are compared directly. A table is included with the final consistent models for these sensors, and a methodology for creating such models for any additional sensors as they are made available. The Microbotics MIDG-II demonstrates performance that is superior to the Tokimec VSAS-2GM, both in terms of raw positioning data, as well as attitude data. While both perform quite well during flight, the MIDG is much better during driving tests. This is due to the MIDG internal tightly-coupled architecture, which is able to better fuse the GPS information with the noisy inertial sensor measurements.

Flight Validation of Metrics Driven L1 Adaptive Control

The paper addresses initial steps involved in the development and flight implementation of new metrics driven L1 adaptive flight control system. The work concentrates on (i) definition of appropriate control driven metrics that account for the control surface failures; (ii) tailoring recently developed L1 adaptive controller to the design of adaptive flight control systems that explicitly address these metrics in the presence of control surface failures and dynamic changes under adverse flight conditions; (iii) development of a flight control system for implementation of the resulting algorithms onboard of small UAV; and (iv) conducting a comprehensive flight test program that demonstrates performance of the developed adaptive control algorithms in the presence of failures. As the initial milestone the paper concentrates on the adaptive flight system setup and initial efforts addressing the ability of a commercial off-the-shelf autopilot with and without adaptive augmentation to recover from control surface failures.

L + 2 , an improved line of sight guidance law for UAVs

This paper describes a new guidance law that extends the pursuit guidance law previously developed by Park et. al. Several improvements are presented that allow operation in the real world. A stability analysis accounts for the dynamic response of the bank angle commands which leads to the definition of regions of instability. Another extension accounts for situations where the pursuit aim point is not defined by the previous work. A third extension changes the pursuit distance-to-go from a constant to a constant time-to-go so that the linearized transient response is independent of ground speed. Yet another extension defines a “homing” mode in which the UAV flies to a goal point without a defined path, commonly used as a “return-to-base,” either as a safety measure or as an end-of-mission order. Since there is no constraint that the goal point be stationary, we demonstrate that the new law can be used to follow a moving target whose location is known, such as a mobile ground control station. Simulations with a 6 degree-of-freedom aircraft model demonstrate these features.

Low Cost Rapidly Reconfigurable UAV Autopilot for Research and Development of Guidance, Navigation and Control Algorithms

This paper presents the development and preliminary results of a rapidly reconfigurable autopilot for small Unmanned Aerial Vehicles. The autopilot presented differs from current commercial and open source autopilots mainly as it has been designed to: (i ) be easily reprogrammable via Simulink (models are directly transferred to the autopilot through the Real-Time Workshop’s code-generation capability); (ii ) decouple the traditional tasks of attitude estimation/navigation and flight control by using two Digital Signal Controllers (one for each task) interconnected via a Serial Peripheral Interface; and, (iii ) being able to interact directly with Simulink as a Hardware-in-the-Loop simulator. This work details each of the main components of the autopilot and its ground control station software. Preliminary results for sensor calibration, Hardware-in-the-loop, ground and flight tests are presented.Copyright

Simulink Based Hardware-in-the-Loop Simulator for Rapid Prototyping of UAV Control Algorithms

This paper describes a recently developed architecture for a Hardware-in-the-Loop simulator for Unmanned Aerial Vehicles. The principal idea is to use the advanced modeling capabilities of Simulink rather than hard-coded software as the flight dynamics simulating engine. By harnessing Simulink’s ability to precisely model virtually any dynamical system or phenomena this newly developed simulator facilitates the development, validation and verification steps of flight control algorithms. Although the presented architecture is used in conjunction with a particular commercial autopilot, the same approach can be easily implemented on a flight platform with a different autopilot. The paper shows the implementation of the flight modeling simulation component in Simulink supported with an interfacing software to a commercial autopilot. This offers the academic community numerous advantages for hardware-in-the-loop simulation of flight dynamics and control tasks. The developed setup has been rigorously tested under a wide variety of conditions. Results from hardware-in-the-loop and real flight tests are presented and compared to validate its adequacy and assess its usefulness as a rapid prototyping tool.

SLUGS UAV: A flexible and versatile hardware/software platform for guidance navigation and control research

This paper presents the Santa Cruz Low-Cost UAV GNC Subsystem (SLUGS) developed at the University of California Santa Cruz. It is a versatile and flexible autopilot capable of controlling a small unmanned system. It is tightly integrated with MATLAB/Simulink, and allows for a simple and easy transition from pure simulation to HIL simulation to flight code. The hardwares main processing units are two low-cost dsPIC33F DSCs, one handling sensor input and the other managing the navigation and control loops. The sensor DSC implements a complementary attitude and position filter. An interprocessor communication protocol delivers fused attitude and position estimates to the control DSC. The control DSC implements low-level platform stabilization using PID loops, and higher level waypoint following based on a line-of-sight guidance law. Data is logged and available for replay post flight on both the ground station software, and also within MATLAB/Simulink. The hardware was installed on a low-cost single engine electric RC aircraft, and has been demonstrated to be capable of sustained autonomous flight. Several estimation topologies have been tested and developed using the system. The SLUGS is general, and can be adapted to multiple autonomous platforms such as helicopters, quadrotors, twin engine aircraft, ground, and marine surface vehicles.