Real-time tracking of human body motion is an important technology in synthetic environments, robotics, and other human-computer interaction applications. This paper presents an extended Kalman filter designed for real-time estimation of the orientation of human limb segments. The filter processes data from small inertial/magnetic sensor modules containing triaxial angular rate sensors, accelerometers, and magnetometers. The filter represents rotation using quaternions rather than Euler angles or axis/angle pairs. Preprocessing of the acceleration and magnetometer measurements using the Quest algorithm produces a computed quaternion input for the filter. This preprocessing reduces the dimension of the state vector and makes the measurement equations linear. Real-time implementation and testing results of the quaternion-based Kalman filter are presented. Experimental results validate the filter design, and show the feasibility of using inertial/magnetic sensor modules for real-time human body motion tracking

/pdf/design-implementation-and-experimental-results-of-a-1rdc3xrkch.pdf

Design, Implementation, and Experimental Results of a Quaternion-Based Kalman Filter for Human Body Motion Tracking

A human body motion tracking system based on use of the MARG (Magnetic, Angular Rate, and Gravity) sensors has been under development at the Naval Postgraduate School and Miami University. The design of a quaternion-based Kalman filter for processing the MARG sensor data was described in [1]. This paper presents the real-time implementation and testing results of the quaternion-based Kalman filter. Experimental results validate the Kalman filter design, and show the feasibility of the MARG sensors for real-time human body motion tracking.

/pdf/implementation-and-experimental-results-of-a-quaternion-20j231gm54.pdf

Implementation and Experimental Results of a Quaternion-Based Kalman Filter for Human Body Motion Tracking

Adaptive tuning of a Kalman filter via fuzzy logic for an intelligent AUV navigation system

In this paper we describe the experimental implementation of an online algorithm for cooperative localization of submerged autonomous underwater vehicles (AUVs) supported by an autonomous surface craft. Maintaining accurate localization of an AUV is difficult because electronic signals, such as GPS, are highly attenuated by water. The usual solution to the problem is to utilize expensive navigation sensors to slow the rate of dead-reckoning divergence. We investigate an alternative approach that utilizes the position information of a surface vehicle to bound the error and uncertainty of the on-board position estimates of a low-cost AUV. This approach uses the Woods Hole Oceanographic Institution (WHOI) acoustic modem to exchange vehicle location estimates while simultaneously estimating inter-vehicle range. A study of the system observability is presented so as to motivate both the choice of filtering approach and surface vehicle path planning. The first contribution of this paper is to the presentation of an experiment in which an extended Kalman filter (EKF) implementation of the concept ran online on-board an OceanServer Iver2 AUV while supported by an autonomous surface vehicle moving adaptively. The second contribution of this paper is to provide a quantitative performance comparison of three estimators: particle filtering (PF), non-linear least-squares optimization (NLS), and the EKF for a mission using three autonomous surface craft (two operating in the AUV role). Our results indicate that the PF and NLS estimators outperform the EKF, with NLS providing the best performance.

Cooperative AUV Navigation using a Single Maneuvering Surface Craft

Kinematic global positioning system (GPS) positioning and underwater acoustic ranging can combine to locate an autonomous underwater vehicle (AUV) with an accuracy of /spl plusmn/30cm (2-/spl sigma/) in the global International Terrestrial Reference Frame 2000 (ITRF2000). An array of three precision transponders, separated by approximately 700 m, was established on the seafloor in 300-m-deep waters off San Diego. Each transponder's horizontal position was determined with an accuracy of /spl plusmn/8 cm (2-/spl sigma/) by measuring two-way travel times with microsecond resolution between transponders and a shipboard transducer, positioned to /spl plusmn/10 cm (2-/spl sigma/) in ITRF2000 coordinates with GPS, as the ship circled each seafloor unit. Travel times measured from AUV to ship and from AUV to transponders to ship were differenced and combined with AUV depth from a pressure gauge to estimate ITRF2000 positions of the AUV to /spl plusmn/1 m (2-/spl sigma/). Simulations show that /spl plusmn/30 cm (2-/spl sigma/) absolute positioning of the AUV can be realized by replacing the time-difference approach with directly measured two-way travel times between AUV and seafloor transponders. Submeter absolute positioning of underwater vehicles in water depths up to several thousand meters is practical. The limiting factor is knowledge of near-surface sound speed which degrades the precision to which transponders can be located in the ITRF2000 frame.

Absolute positioning of an autonomous underwater vehicle using GPS and acoustic measurements

This paper presents the design and development of an enhanced inertial navigation system that is to be integrated into the Morpheus autonomous underwater vehicle at Florida Atlantic University. The inertial measurement unit is based on the off-the-shelf Honeywell HG1700-AG25 3-axis ring-laser gyros and three-axis accelerometers and is aided with ground speed measurements obtained using an RDI Doppler-velocity-log sonar. An extended Kalman filter has been developed, which fuses together asynchronously the inertial and Doppler data, as well as the differential Global Positioning System positional fixes whenever they are available. A complementary filter was implemented to provide a much smoother and stable attitude estimate. Thus far, preliminary study has been made on characterizing the inertial navigation system-based navigation system performance, and the corresponding results and analyzes are provided.

Enhancement of the inertial navigation system for the Morpheus autonomous underwater vehicles

Under sampling of the coastal oceans remains a persistent problem for standard oceano-graphic measurement practice wherein an instrument package is tethered to a research vessel. The overhead costs associated with operating a large research vessel impose a strict minimum on the cost of data collected. Owing to the overheads, significant improvements in sampling technology on the tethered platform can only produce modest gains in the cost effectiveness. In contrast, untethered vehicles if operated simultaneously have the potential to increase cost effectiveness significantly by distributing the overhead costs over several sampling platforms. Furthermore, synoptic and pseudosynoptic data can be collected with multiple autonomous underwater vehicles (AUVs), thereby providing the type of information critical to dynamic process modeling unattainable with non-synoptic data. While the goal of simultaneous multiple-vehicle operation has been espoused over the last few years, AUV technology and practice have until...

Strategies for simultaneous multiple autonomous underwater vehicle operation and control

The Advanced Marine Systems Lab at Florida Atlantic University has developed a new ultramodular plastic mini autonomous underwater vehicle (AUV), called the Morpheus, for littoral military and coastal oceanographic sampling, survey, and mapping. The name Morpheus was chosen because the Greek god Morpheus could change shape or "morph." The higher degree of modularity of the Morpheus AUV allows it to "morph" or change its size and components for different applications. This vehicle is composed of modular injection-molded plastic pressure vessels and a cabling system that allow the modules to be rearranged without rewiring bulkheads. The plastic pressure vessels are inexpensive, inherently mass-producible, extremely corrosion-resistant, and have low magnetic signatures. The pressure vessels are small but are sized to fit most standard electronic board standards. The mini AUV can be anywhere from 4 to 10 ft in length, depending on its mission. The vehicle architecture is an adaptation of the Ocean Explorer AUV system and uses an ANSI 709.1 (LonTalk) distributed control network for connecting all sensors and actuator subsystems as smart nodes. The modularity in containers, control, and power makes this vehicle rapidly reconfigurable and easy to repair or upgrade. This paper will present details of the motivation, design, and construction of the new mini AUV. The Morpheus was deployed during the summer of 2000 in field exercises for very shallow and shallow water mine counter measures. Some results from these tests will be presented.

The Morpheus ultramodular autonomous underwater vehicle

This paper presents preliminary experimental results on small-sized autonomous underwater vehicle navigation in shallow water environments. The vehicle was chosen to be our second-generation Ocean Voyager II which has been integrated with on-board GPS/INS sensors. These first-cut results reveal practical problems when using raw GPS fixes to perform high-precision real-time navigation. Among these, the most damaging factor is the observed correlated noise (which has a long time constant and large magnitude) embedded in the GPS data. With such disturbance, one cannot distinguish between instantaneous signal and noise over a short time scale (especially with sporadic fixes), and consequently the position estimator will be greatly biased. However, with regular incoming fixes, one can process the error between dead-reckoned and GPS signal in order to minimize the influence of the correlated noise under the assumption that any drift due to sensor bias or currents is relatively time-invariant. This processing thus enables one to estimate the drift and drift rate over time reliably for post-processed vehicle localization. In addition to the results in this paper, a differential GPS and Doppler-velocity-log sensor are currently implemented on our Ocean Explorer which is expected to provide much improved navigational performance. The chosen differential GPS sensor has so far demonstrated successful tracking at 2 feet below water surface, thus reinforcing a potential solution for clandestine operations.

New experimental results on GPS/INS navigation for Ocean Voyager II AUV

: The general objective is to investigate the basic and applied problems associated with the efficacious reconnaissance of littoral waters in support of mine warfare and oceanographic tasks. Specifically with this proposal, we wish to quantify the shallow-water performance of the sensor systems and platforms in relation to harsh environmental conditions and high sea states. In particular for platforms we wish to address the performance issues with respect to navigation, communication, control and conditional mission planning during which the underwater acoustic propagation properties are severely affected by the bubble formation and mixing properties induced by storm fronts. We wish to address design and implementation problems associated with our current docking design and performance in stormy conditions.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA625462&Location=U2&doc=GetTRDoc.pdf

P.E. An

Papers

Enhancement of the inertial navigation system for the Morpheus autonomous underwater vehicles

Strategies for simultaneous multiple autonomous underwater vehicle operation and control

The Morpheus ultramodular autonomous underwater vehicle

New experimental results on GPS/INS navigation for Ocean Voyager II AUV

Sampling and Survey with AUVs in Adverse Weather Conditions