1,586 research outputs found
A Novel Method for Sensorless Speed Detection of Brushed DC Motors
Many motor applications require accurate speed measurement. For brushed dc motors, speed can be measured with conventional observers or sensorless observers. Sensorless observers have the advantage of not requiring any external devices to be attached to the motor. Instead, voltage and/or current are measured and used to estimate the speed. The sensorless observers are usually divided into two groups: those based on the dynamic model, and those based on the ripple component. This paper proposes a method that measures the current of brushed dc motors and analyses the position of its spectral components. From these spectral components, the method estimates the motor speed. Three tests, performed each with the speeds ranging from 2000 to 3000 rpm either at constant-speed, at slowly changing speeds, or at rapidly changing speeds, showed that the average error was below 1 rpm and that the deviation error was below 1.5 rpm. The proposed method: (i) is a novel method that is not based on either the dynamic model or on the ripple component; (ii) requires only the measurement of the current for the speed estimation; (iii) can be used for brushed dc (direct current) motors with a large number of coils; and (iv) achieves a low error in the speed estimation
The Influence of Tractor-Seat Height above the Ground on Lateral Vibrations
Farmers experience whole-body vibrations when they drive tractors. Among the
various factors that influence the vibrations to which the driver is exposed are terrain
roughness, tractor speed, tire type and pressure, rear axle width, and tractor seat height
above the ground. In this paper the influence of tractor seat height above the ground on the
lateral vibrations to which the tractor driver is exposed is studied by means of a
geometrical and an experimental analysis. Both analyses show that: (i) lateral vibrations
experienced by a tractor driver increase linearly with tractor-seat height above the ground;
(ii) lateral vibrations to which the tractor driver is exposed can equal or exceed vertical
vibrations; (iii) in medium-size tractors, a feasible 30 cm reduction in the height of the
tractor seat, which represents only 15% of its current height, will reduce the lateral
vibrations by around 20%; and (iv) vertical vibrations are scarcely influenced by
tractor-seat height above the ground. The results suggest that manufacturers could increase
the comfort of tractors by lowering tractor-seat height above the ground, which will reduce
lateral vibrations
A Kalman Filter Implementation for Precision Improvement in Low-Cost GPS Positioning of Tractors
Low-cost GPS receivers provide geodetic positioning information using the
NMEA protocol, usually with eight digits for latitude and nine digits for longitude. When
these geodetic coordinates are converted into Cartesian coordinates, the positions fit in a
quantization grid of some decimeters in size, the dimensions of which vary depending on
the point of the terrestrial surface. The aim of this study is to reduce the quantization errors
of some low-cost GPS receivers by using a Kalman filter. Kinematic tractor model
equations were employed to particularize the filter, which was tuned by applying Monte
Carlo techniques to eighteen straight trajectories, to select the covariance matrices that
produced the lowest Root Mean Square Error in these trajectories. Filter performance was
tested by using straight tractor paths, which were either simulated or real trajectories
acquired by a GPS receiver. The results show that the filter can reduce the quantization
error in distance by around 43%. Moreover, it reduces the standard deviation of the heading
by 75%. Data suggest that the proposed filter can satisfactorily preprocess the low-cost GPS
receiver data when used in an assistance guidance GPS system for tractors. It could also be
useful to smooth tractor GPS trajectories that are sharpened when the tractor moves over
rough terrain
Temporal patterns in coral reef, seagrass and mangrove communities from Chengue bay CARICOMP site (Colombia): 1993-2008
Few monitoring programs have simultaneously assessed the dynamics of linked marine ecosystems (coral reefs, seagrass beds and mangroves) to document their temporal and spatial variability. Based on CARICOMP protocol we evaluated permanent stations in coral reefs, seagrass beds and mangroves from 1993 to 2008 in Chengue Bay at the Tayrona Natural Park, Colombian Caribbean. Overall, the studied ecosystems showed a remarkable stability pattern over the monitoring period. While there were annual variations in coral reefs (coral cover) and mangroves (litterfall) caused by hurricane Lenny in 1999, particular trends in seagrass (leaf area index and leaf productivity) appear to reflect the natural variability in this ecosystem. We suggest that monitoring sites at the three marine ecosystems had in general a healthy development in the last 16 years. Our results are critical to locally improve the management strategies (Tayrona Natural Park) and to understand the long-term dynamics of closely associated marine ecosystems in the Caribbean. Copyright © 2011 Elsevier B.V. All rights reserved
Characterization of Beginner Crossfit athletes in the city of Bucaramanga – Colombia / Caracterização de atletas iniciais de Crossfit na cidade de Bucaramanga - Colômbia
Introduction: In the last decade, the practice of CrossFit has become a training alternative that involves high intensity functional movements, which is why it has been increasing its practice exponentially, to this is added the commercial and marketing component in Colombia to through television programs. However, due to the complexity and demand in its performance, it has resulted in a discipline where certain indications and precautions must be followed, which raises concerns in health and training professionals, related to those people who start their practice. Objective: The purpose of the study was to characterize the most frequent injuries in beginning CrossFit athletes. Methodology: This cross-sectional study had a sample of 43 athletes, from gyms dedicated to training in this discipline, including the only two BOX centers Certified by the CrossFit company in the city of Bucaramanga. The information gathering technique was a closed interview. This study was approved by the ethics committee of Unidades Tecnológicas de Santander. Results:The mean age was 29 years, 54% female. 41% of the population reported 1 to 2 years of experience, followed by 3 to 4 years with 25.5%. The body mass index (BMI) was 24.97 ± 2.6 Kg / m2. 53.5% of the athletes trained an average of 4 to 5 times per week. 65% reported a day off in the training week, the majority (95%) reported supervision and advice from a professional. The regions of the body with the highest reported number of injuries are: shoulder (26%), knee (16.2%) and spine in the lumbar area (14.5%). The most recurrent type of injury was tendonitis (55%) and muscle tear (15%). Conclusion: The professionals who supervise the beginner athlete (1-3 years) should focus the adequate execution of the movements that involve the regions identified in the study, in the realization of the Work of the Day (WOD). Therefore, these injuries are the product of the high repetitions (volume) and loads (intensity) that involve these joints, characteristic of the discipline
Tumour growth: An approach to calibrate parameters of a multiphase porous media model based on in vitro observations of Neuroblastoma spheroid growth in a hydrogel microenvironment
To unravel processes that lead to the growth of solid tumours, it is necessary to link knowledge of cancer biology with the physical properties of the tumour and its interaction with the surrounding microenvironment. Our understanding of the underlying mechanisms is however still imprecise. We therefore developed computational physics-based models, which incorporate the interaction of the tumour with its surroundings based on the theory of porous media. However, the experimental validation of such models represents a challenge to its clinical use as a prognostic tool. This study combines a physics-based model with in vitro experiments based on microfluidic devices used to mimic a three-dimensional tumour microenvironment. By conducting a global sensitivity analysis, we identify the most influential input parameters and infer their posterior distribution based on Bayesian calibration. The resulting probability density is in agreement with the scattering of the experimental data and thus validates the proposed workflow. This study demonstrates the huge challenges associated with determining precise parameters with usually only limited data for such complex processes and models, but also demonstrates in general how to indirectly characterise the mechanical properties of neuroblastoma spheroids that cannot feasibly be measured experimentally
An SVM-Based classifier for estimating the state of various rotating components in agro-industrial machinery with a vibration signal acquired from a single point on the machine chassis
The goal of this article is to assess the feasibility of estimating the state of various rotating components in agro-industrial machinery by employing just one vibration signal acquired from a single point on the machine chassis. To do so, a Support Vector Machine (SVM)-based system is employed. Experimental tests evaluated this system by acquiring vibration data from a single point of an agricultural harvester, while varying several of its working conditions. The whole process included two major steps. Initially, the vibration data were preprocessed through twelve feature extraction algorithms, after which the Exhaustive Search method selected the most suitable features. Secondly, the SVM-based system accuracy was evaluated by using Leave-One-Out cross-validation, with the selected features as the input data. The results of this study provide evidence that (i) accurate estimation of the status of various rotating components in agro-industrial machinery is possible by processing the vibration signal acquired from a single point on the machine structure; (ii) the vibration signal can be acquired with a uniaxial accelerometer, the orientation of which does not significantly affect the classification accuracy; and, (iii) when using an SVM classifier, an 85% mean cross-validation accuracy can be reached, which only requires a maximum of seven features as its input, and no significant improvements are noted between the use of either nonlinear or linear kernels
Steering a Tractor by Means of an EMG-Based Human-Machine Interface
An electromiographic (EMG)-based human-machine interface (HMI) is a communication pathway between a human and a machine that operates by means of the acquisition and processing of EMG signals. This article explores the use of EMG-based HMIs in the steering of farm tractors. An EPOC, a low-cost human-computer interface (HCI) from the Emotiv Company, was employed. This device, by means of 14 saline sensors, measures and processes EMG and electroencephalographic (EEG) signals from the scalp of the driver. In our tests, the HMI took into account only the detection of four trained muscular events on the driver’s scalp: eyes looking to the right and jaw opened, eyes looking to the right and jaw closed, eyes looking to the left and jaw opened, and eyes looking to the left and jaw closed. The EMG-based HMI guidance was compared with manual guidance and with autonomous GPS guidance. A driver tested these three guidance systems along three different trajectories: a straight line, a step, and a circumference. The accuracy of the EMG-based HMI guidance was lower than the accuracy obtained by manual guidance, which was lower in turn than the accuracy obtained by the autonomous GPS guidance; the computed standard deviations of error to the desired trajectory in the straight line were 16 cm, 9 cm, and 4 cm, respectively. Since the standard deviation between the manual guidance and the EMG-based HMI guidance differed only 7 cm, and this difference is not relevant in agricultural steering, it can be concluded that it is possible to steer a tractor by an EMG-based HMI with almost the same accuracy as with manual steering
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan
This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good
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