Search results for "valve"

Effects of Rastering Velocity on Electrospun Polyeurthane Structure and Mechanical Properties

2010

Chameleonic appearance of caseous calcification of the mitral valve – still a problem for its appropriate management

2021

According to the research literature, the caseous calcification of the mitral annulus (CCMA) is a rare variant of the mitral annulus calcification (MAC) entity, described mostly in elderly women. The aim of this study was to present the case of a 53-year-old female patient with caseous calcification of the mitral valve annulus and posterior cusp, which was diagnosed as papillary fibroelastoma. An echo-dense and quasi-homogeneous tumoral mass, measuring 1.6/1.4 cm, at the level of the posterior mitral ring was detected by echocardiographic examination, as well as by cardiac magnetic resonance imaging (MRI). Histopathological analysis revealed fibrous connective tissue with myxoid areas, hyal…

Analysis of Offshore Knuckle Boom Crane - Part One: Modeling and Parameter Identification

2013

This paper presents an extensive model of a knuckle boom crane used for pipe handling on offshore drilling rigs. The mechanical system is modeled as a multi-body system and includes the structural flexibility and damping. The motion control system model includes the main components of the crane's electro-hydraulic actuation system. For this a novel black-box model for counterbalance valves is presented, which uses two different pressure ratios to compute the flow through the valve. Experimental data and parameter identification, based on both numerical optimization and manual tuning, are used to verify the crane model. The demonstrated modeling and parameter identification techniques target…

Leakage-detection in blade pitch control systems for wind turbines

2012

The main contribution of the work is a systematic study evaluating the performance of different filters for leakage detection in pitch control systems. The effectiveness of the proposed methods is examined in a Matlab/Simulink real-time environment. The test bed consists of the following elements: hydraulic power unit, servo valve, two leakage bypasses, hydraulic cylinder, payload and xPC-based control system. The filters are tested with the state-augmentation and the hypothesis testing approaches. To our knowledge, the comparison of these different approaches has not been done previously for this type of application. The paper concludes on the accuracy and sensitivity of the leakage detect…

Robust adaptive backstepping control design for a Nonlinear Hydraulic-Mechanical System

2009

The complex dynamics that characterize hydraulic systems make it difficult for the control design to achieve prescribed goals in an efficient manner. In this paper, we present the design and analysis of a robust nonlinear controller for a Nonlinear Hydraulic-Mechanical (NHM) System. The system consists of an electrohydraulic servo valve and two hydraulic cylinders. Specifically, by considering a part of the dynamics of the NHM system as a norm-bounded uncertainty, two adaptive controllers are developed based on the backstepping technique that ensure the tracking error signals asymptotically converge to zero despite the uncertainties in the system according to the Barbalat lemma. The resulti…

An open access database for the evaluation of heart sound algorithms

2016

In the past few decades, analysis of heart sound signals (i.e. the phonocardiogram or PCG), especially for automated heart sound segmentation and classification, has been widely studied and has been reported to have the potential value to detect pathology accurately in clinical applications. However, comparative analyses of algorithms in the literature have been hindered by the lack of high-quality, rigorously validated, and standardized open databases of heart sound recordings. This paper describes a public heart sound database, assembled for an international competition, the PhysioNet/Computing in Cardiology (CinC) Challenge 2016. The archive comprises nine different heart sound databases…

Design, fabrication, and analysis of a spin-valve based current sensor

2004

Abstract In this work, we suggest a novel current sensor design, based on spin valve technology, with a full Wheatstone bridge configuration. The principal characteristic is that the four magnetoresistance sensing elements, fully active, are deposited and patterned at the same time. This way, differences among them should be insignificant, so improving voltage offset and drift temperature parameters. The complete IC fabrication process involves only three lithography steps, making the process cheaper and faster. In order to get a balanced bridge, the measured current must be properly driven, by means of an auxiliary PCB. Some prototypes, with different input impedances, have been fabricated…

A Non-Invasive Thermal Drift Compensation Technique Applied to a Spin-Valve Magnetoresistive Current Sensor

2011

A compensation method for the sensitivity drift of a magnetoresistive (MR) Wheatstone bridge current sensor is proposed. The technique was carried out by placing a ruthenium temperature sensor and the MR sensor to be compensated inside a generalized impedance converter circuit (GIC). No internal modification of the sensor bridge arms is required so that the circuit is capable of compensating practical industrial sensors. The method is based on the temperature modulation of the current supplied to the bridge, which improves previous solutions based on constant current compensation. Experimental results are shown using a microfabricated spin-valve MR current sensor. The temperature compensati…

A DC behavioral electrical model for quasi-linear spin-valve devices including thermal effects for circuit simulation

2011

An advanced model for quasi-linear spin-valve (SV) structures is presented for circuit simulation purposes. The model takes into account electrical and thermal effects in a coupled way in order to allow a coherent representation of the sensor physics for design purposes of electronics applications based on these sensor devices. The model was implemented in Verilog-A and used in a commercial circuit simulator. For testing the model, different SV structures have been specifically fabricated and measured. The characterization included DC measurements as well as steady-state and transient thermal analysis. From the experimental data, the parameters of the model have been extracted. The model re…

Extended friction model of a hydraulic actuated system

2012

The main contribution of this paper is an experimental validation and comparison of three different friction models for an electro-hydraulic servo system. The first is the well-kn own LuGre model which incorporates dynamic friction effects. The second model is based on a relatively recent publication by Yanada in 2008 [6], which incorporates liquid film thickness in the servo valve. The third model is a new contribution presented in this paper, where valve underlap and mass acceleration are combined with the LuGre model. The experimental results show that for hydraulic systems, the film thickness model is an improvement over the LuGre model, while the new model presented in this paper is an…