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Indoor Navigation for Unmanned Aerial Vehicles

Low-cost range sensors solve mapping and localization problems confronting UAVs.

This research proposed the use of inexpensive, lightweight range sensors for indoor unmanned aerial vehicle (UAV) navigation. Two potential range sensors were tested for suitability and error characteristics. The SHARP infrared range sensors provide a narrow beam and a higher resolution distance measurement, at the expense of de creased range (approximately 150–180 cm maximum). The MaxBotix® EX1™ ultrasonic range sensors had a longer range (up to 6.45 m) and a wider beam.

The Simulated Room Sweep provided this room mapping plot (a) before and(b) after correcting for vehicle drift. The vehicle is rotated through a heading change of 360° while measuring range to the front, back, left, and right.
In addition, the sonar has unique measurement properties due to the physics of the metrology technique used for ranging. The sonar sends out a sound pulse that expands on a spherical front. When this wavefront encounters an object, it is reflected back toward the sensor. When the first return is detected, a time-of-flight calculation is used to determine range. As a result, the perpendicular distance to a wall will always have the shortest return. Hence, if one of the sonar can detect a wall at all, it will always return the perpendicular distance to that wall.

Similar effects were observed when the sensors were aimed at the corner of a room. Thus, the sonar range sensors return the same distance regardless of moderate changes in angle to the target. This makes them useful for altitude ranging, as the vehicle roll and pitch do not greatly affect the distance measurement to the ground. The sonar are less useful for scanning a room to make a 2D plot of the room, although by using a histogram analysis, room dimensions were determined from experimental sonar data. In addition, simulations were performed using sonar and the histogram analysis to determine room dimensions in real time. The addition of a yaw-rate gyro was simulated, which, along with wall-following behavior to correct for drift, could allow a heading estimate to be maintained during the flight as well. With a heading estimate and the combination of sonar and IR sensors for ranging, a small, passively stable aerial platform could be used for basic mapping and localization.

Once the range sensors were analyzed, and their measurement and error characteristics were determined, simulations were completed to develop and refine mapping and localization techniques using the low-cost range sensors. Finally, a two-phase flight test program was initiated to further develop navigation, guidance, and control algorithms. During the first phase of the flight test, altitude control and longitudinal control were demonstrated. During the second phase of the flight test program, heading control and lateral control were developed. The completion of the flight test program demonstrated the capability to navigate unknown indoor environments using only simple, ultra-low-cost range sensors mounted to a passively stable coaxial rotorcraft vehicle.

This work was done by D. Michael Sobers, Jr., Girish Chodhary, and Eric N. Johnson of Georgia Institute of Technology. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp  under the Physical Sciences category. GIT-0001

Topics:
Aircraft Flight tests Physical Sciences Unmanned aerial vehicles Vehicles
This Brief includes a Technical Support Package (TSP).
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Indoor Navigation for Unmanned Aerial Vehicles

(reference GIT-0001) is currently available for download from the TSP library.

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    Defense Tech Briefs Magazine

    This article first appeared in the February, 2010 issue of Defense Tech Briefs Magazine (Vol. 4 No. 1).

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    Overview

    The document presents research on indoor navigation for unmanned aerial vehicles (UAVs), focusing on the development and testing of a control system and navigation algorithm that allows UAVs to autonomously explore and map unknown indoor environments. The study emphasizes the use of low-cost range sensors, such as sonar and infrared (IR) sensors, to facilitate navigation and obstacle avoidance in complex indoor settings.

    The research is structured around two phases of flight testing. In the first phase, an initial avionics system was employed, which included multiple sonar sensors for longitudinal and lateral ranging, an altitude sonar, and IR sensors for heading estimation. The data from these sensors were processed on the ground, allowing for manual control of the UAV during initial tests. The results highlighted the need for independent operation of sonar sensors to avoid interference, leading to a recommended sampling strategy that improved the update rate for altitude measurements.

    The second phase involved more advanced testing, where the UAV was flown in a controlled environment, specifically the IARC arena, to navigate a maze autonomously. The flight tests began with manual takeoff, followed by the activation of an altitude control loop, which was tuned for optimal performance. Once altitude control was established, the yaw, longitudinal, and lateral control loops were adjusted to ensure satisfactory navigation capabilities. The UAV was able to maintain a desired distance from walls and execute turns within the maze, demonstrating effective guidance logic.

    Throughout the testing, the UAV operated with a combination of sensors, including a camera for imagery collection, although optical flow methods for velocity measurement were not utilized. The flight tests lasted approximately seven minutes, during which all systems operated simultaneously, showcasing the integration of various technologies.

    The findings from this research indicate that UAVs can successfully navigate and map indoor environments using low-cost sensors and robust control algorithms. The study contributes to the field of autonomous navigation, providing insights into sensor integration, control loop tuning, and guidance strategies necessary for effective indoor exploration. Overall, the research highlights the potential for UAVs to operate in complex environments, paving the way for future applications in search and rescue, surveillance, and facility management.

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