5,126 research outputs found
Inclination Measurement of Human Movement Using a 3-D Accelerometer With Autocalibration
In the medical field, accelerometers are often used for measuring inclination of body segments and activity of daily living (ADL) because they are small and require little power. A drawback of using accelerometers is the poor quality of inclination estimate for movements with large accelerations. This paper describes the design and performance of a Kalman filter to estimate inclination from the signals of a triaxial accelerometer. This design is based on assumptions concerning the frequency content of the acceleration of the movement that is measured, the knowledge that the magnitude of the gravity is 1 g and taking into account a fluctuating sensor offset. It is shown that for measuring trunk and pelvis inclination during the functional three-dimensional activity of stacking crates, the inclination error that is made is approximately 2/spl deg/ root-mean square. This is nearly twice as accurate as compared to current methods based on low-pass filtering of accelerometer signals
Accurate Telescope Mount Positioning with MEMS Accelerometers
This paper describes the advantages and challenges of applying
microelectromechanical accelerometer systems (MEMS accelerometers) in order to
attain precise, accurate and stateless positioning of telescope mounts. This
provides a completely independent method from other forms of electronic,
optical, mechanical or magnetic feedback or real-time astrometry. Our goal is
to reach the sub-arcminute range which is well smaller than the field-of-view
of conventional imaging telescope systems. Here we present how this
sub-arcminute accuracy can be achieved with very cheap MEMS sensors and we also
detail how our procedures can be extended in order to attain even finer
measurements. In addition, our paper discusses how can a complete system design
be implemented in order to be a part of a telescope control system.Comment: Accepted for publication in PASP, 12 page
Compensation of Magnetic Disturbances Improves Inertial and Magnetic Sensing of Human Body Segment Orientation
This paper describes a complementary Kalman filter design to estimate orientation of human body segments by fusing gyroscope, accelerometer, and magnetometer signals from miniature sensors. Ferromagnetic materials or other magnetic fields near the sensor module disturb the local earth magnetic field and, therefore, the orientation estimation, which impedes many (ambulatory) applications. In the filter, the gyroscope bias error, orientation error, and magnetic disturbance error are estimated. The filter was tested under quasi-static and dynamic conditions with ferromagnetic materials close to the sensor module. The quasi-static experiments implied static positions and rotations around the three axes. In the dynamic experiments, three-dimensional rotations were performed near a metal tool case. The orientation estimated by the filter was compared with the orientation obtained with an optical reference system Vicon. Results show accurate and drift-free orientation estimates. The compensation results in a significant difference (p<0.01) between the orientation estimates with compensation of magnetic disturbances in comparison to no compensation or only gyroscopes. The average static error was 1.4/spl deg/ (standard deviation 0.4) in the magnetically disturbed experiments. The dynamic error was 2.6/spl deg/ root means square
Suspension Testing of 3 Heavy Vehicles - Methodology and Preliminary Frequency Analysis
Three air-sprung heavy vehicles (HVs) were instrumented and tested on typical suburban and highway road sections at typical operational speeds. The vehicles used were a tri-axle semi-trailer towed with a prime mover, an interstate coach with 3 axles and a school bus with 2 axles. The air springs (air bags) of the axle/axle group of interest were configured such that they could be connected using either standard longitudinal air lines or an innovative suspension system comprising larger-than-standard longitudinal air lines. Data for dynamic forces on axles, wheels and chassis were gathered for the purposes of: analysis of the relative performance of the HVs for the two sizes of air lines; informing the QUT/Main Roads project Heavy vehicle suspensions – testing and analysis; and providing a reference source for future projects. This reports sets down the methodology and preliminary results of the testing carried out. Accordingly, Fast-Fourier plots are provided to show indicative frequency spectra for HV axles, wheel forces and air springs during typical use. The results are documented in Appendices 3 to 5. There appears to be little or no correlation between dynamic forces in the air springs and the wheel forces in the HVs tested. Axle-hop at frequencies between 10-15 Hz predominated for unsprung masses in the HV suspensions tested. Air-spring forces are present in the sub-1.0 Hz to approximately 2 Hz frequency range. With the qualification that only one set of data from each test speed is presented herein, in general, the peaks in the frequency spectra of the body-bounce forces and wheel forces were reduced for the tests with the larger longitudinal air lines. More research needs to be done on the load sharing mechanisms between axles on air-sprung HVs. In particular, how and whether improved load sharing can be effected and whether better load sharing between axles will reduce dynamic wheel and chassis forces. This last point, in particular, in relation to the varied dynamic measures used by the HV testing community to compare different suspension types
Measuring and Correcting Wind-Induced Pointing Errors of the Green Bank Telescope Using an Optical Quadrant Detector
Wind-induced pointing errors are a serious concern for large-aperture
high-frequency radio telescopes. In this paper, we describe the implementation
of an optical quadrant detector instrument that can detect and provide a
correction signal for wind-induced pointing errors on the 100m diameter Green
Bank Telescope (GBT). The instrument was calibrated using a combination of
astronomical measurements and metrology. We find that the main wind-induced
pointing errors on time scales of minutes are caused by the feedarm being blown
along the direction of the wind vector. We also find that wind-induced
structural excitation is virtually non-existent. We have implemented offline
software to apply pointing corrections to the data from imaging instruments
such as the MUSTANG 3.3 mm bolometer array, which can recover ~70% of
sensitivity lost due to wind-induced pointing errors. We have also performed
preliminary tests that show great promise for correcting these pointing errors
in real-time using the telescope's subreflector servo system in combination
with the quadrant detector signal.Comment: 17 pages, 11 figures; accepted for publication in PAS
Measurement of Three-Dimensional Welding Torch Orientation for Manual Arc Welding Process
Methods and systems are provided herein for measuring 3D apparatus (e.g., manual tool or tool accessory) orientation. Example implementations use an auto-nulling algorithm that incorporates a quaternion-based unscented Kalman filter. Example implementations use a miniature inertial measurement unit endowed with a tri-axis gyro and a tri-axis accelerometer. The auto-nulling algorithm serves as an in-line calibration procedure to compensate for the gyro drift, which has been verified to significantly improve the estimation accuracy in three-dimensions, especially in the heading estimation
Statistical Sensor Fusion of a 9-DoF MEMS IMU for Indoor Navigation
Sensor fusion of a MEMS IMU with a magnetometer is a popular system design,
because such 9-DoF (degrees of freedom) systems are capable of achieving
drift-free 3D orientation tracking. However, these systems are often vulnerable
to ambient magnetic distortions and lack useful position information; in the
absence of external position aiding (e.g. satellite/ultra-wideband positioning
systems) the dead-reckoned position accuracy from a 9-DoF MEMS IMU deteriorates
rapidly due to unmodelled errors. Positioning information is valuable in many
satellite-denied geomatics applications (e.g. indoor navigation, location-based
services, etc.). This paper proposes an improved 9-DoF IMU indoor pose tracking
method using batch optimization. By adopting a robust in-situ user
self-calibration approach to model the systematic errors of the accelerometer,
gyroscope, and magnetometer simultaneously in a tightly-coupled post-processed
least-squares framework, the accuracy of the estimated trajectory from a 9-DoF
MEMS IMU can be improved. Through a combination of relative magnetic
measurement updates and a robust weight function, the method is able to
tolerate a high level of magnetic distortions. The proposed auto-calibration
method was tested in-use under various heterogeneous magnetic field conditions
to mimic a person walking with the sensor in their pocket, a person checking
their phone, and a person walking with a smartwatch. In these experiments, the
presented algorithm improved the in-situ dead-reckoning orientation accuracy by
79.8 - 89.5% and the dead-reckoned positioning accuracy by 72.9 - 92.8%, thus
reducing the relative positioning error from metre-level to decimetre-level
after ten seconds of integration, without making assumptions about the user's
dynamics
Solar array flight experiment/dynamic augmentation experiment
This report presents the objectives, design, testing, and data analyses of the Solar Array Flight Experiment/Dynamic Augmentation Experiment (SAFE/DAE) that was tested aboard Shuttle in September 1984. The SAFE was a lightweight, flat-fold array that employed a thin polyimide film (Kapton) as a substrate for the solar cells. Extension/retraction, dynamics, electrical and thermal tests, were performed. Of particular interest is the dynamic behavior of such a large lightweight structure in space. Three techniques for measuring and analyzing this behavior were employed. The methodology for performing these tests, gathering data, and data analyses are presented. The report shows that the SAFE solar array technology is ready for application and that new methods are available to assess the dynamics of large structures in space
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