1,720,963 research outputs found
Voltage Driven Hard Disk Drive with Voice Coil Model-based Control
No full textIn this paper, we describe a new solution for driving the voice coil motor (VCM) in hard disk drives (HDDs), in which the usual current driver for the voice coil motor has been replaced by a voltage driver. When used in conjunction with PWM power stages, this solution becomes fully digital and has proven advantages in terms of cost, power dissipation and silicon area. To achieve the same performance of the current driver, the voltage driver requires a pre-filter placed at its input, to cancel out the electrical pole of the VCM. In the paper, we describe the voice coil model-based control (VCMC), a solution for implementing the pre-filter, which replicates the behavior of a current loop by using a model of the voice coil motor and its driver, including the saturation of the power stage. It is worth noticing that VCM resistance may change by 30% during HDD operations, increasing when the disk is performing repetitive seeks or decreasing when the disk cools down during track following. Such variation may lead to an unsatisfactory performance of the VCMC, so an adaptation mechanism, capable of tracking variations of VCM coil resistance, must be set up. This paper presents a pair of on-line estimation procedure, used to get the value of the VCM coil resistance during seek and track following, respectively. The first one is based on a standard LMS approach, aimed at identifying a simplified model of the plant with the least computational effort. The second exploits the presence of repetitive disturbances (RROs) to detect variations of plant gain and, in turn, of VCM resistance. It will be shown that both procedures are quite accurate in estimating variations of VCM resistance and their output can be used to perform on-line tuning of the VCMC. Experimental results show that the servo performance with the adaptive VCMC is not affected by resistance variation and equivalent to that of the standard current driver
Hard Disk Drive With Voltage-Driven Voice Coil Motor and Model-Based Control
No full textIn this paper, we describe the voice coil model-based control (VCMC), a new solution for driving the voice coil motor (VCM) in hard disk drives (HDDs), in which the usual current driver for the VCM has been replaced by a voltage driver. The VCMC replicates the behavior of a current loop by using a model of the VCM and its driver, including the saturation of the power stage. Since VCM resistance may change by 30% during HDD operations, the model used by VCMC must be adapted accordingly, in order to achieve the same performance as the standard current driver. This paper presents a pair of online estimation procedures used to get the value of the VCM coil resistance during seek and track following, respectively. It will be shown that both procedures are quite accurate in estimating variations of VCM resistance and their output can be used to perform online tuning of the VCMC. Experimental results show that the servo performance with the adaptive VCMC is not affected by resistance variation and it is equivalent to that of the standard current driver
Method for controlling a DC motor and relative open-loop voltage mode controller
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Method for estimating the resistance of a DC motor for positioning read/write heads of a hard disk
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Optimization of a Rack & Pinion Pneumatic Actuator by Applying Design-to-Value Integrated with Multiple Simulation Techniques
No full textIn this paper are presented the benefits of introducing a new original multidisciplinary methodology that integrates in a global homogeneous process the benefits of the state of the art of product development techniques, mechanical finite element analysis and collaborative teamwork strategies. For exposing this interdisciplinary and Holistic Product Development approach, a case study is presented, focusing on a re-design project of a pneumatic rack and pinion actuator for valve actuation, first time designed in 1984. During the project, developed focusing on teamwork activities, the benefits of an extensive use of simulation techniques have been exploited, for implementing the best design change proposals emerged thanks to the application of a Design-to-Value (DtV) process. Final objectives are to optimize the product weight and efficiency of the actuator, while maintaining high safety, reliability, and performances, and at the same time to simplify the design, with a reduction of components construction complexity. In a First step of the application of the methodology, the procedures and tools foreseen by the DtV process for fostering improvement ideas generation are applied. In a second phase, design techniques based on FEA ("Design by Analysis") are going to integrate the classical verifications of "Design by Formulas", used in the occasion of the first actuator design, obtaining a much higher level of accuracy confirmed by experimental validation phase. This new value-oriented design strategy, implemented with a sort of "secret ingredient" given by collaborative teamwork, allowed to obtain tangible benefits and introduce a totally renewed more efficient actuator
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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