1,720,957 research outputs found
Realization of an adaptive voltage driver for Voltage Coil Motors
No full textIn this paper we describe a head servo-positioning system for hard disk drives (HDDs), in which the usual current command for the voice coil motor has been replaced by a simpler voltage command. This solution has proven advantages in terms of cost, since the voltage driver does not require any resistive shunt for current measurement and phase-shaping passive networks for the current controller. Also, it requires a lower pin count and can be easily implemented with a PWM power stage. The voltage driver consists of a voltage-controlled power stage, with a pre-filter placed at its input, plus a back e.m.f. feed-forward compensator. The role of the pre-filter is to provide a transfer function between input signal and VCM current as close as possible to that of a standard current loop, so providing a one-to-one replacement to standard current drivers. To achieve this, it can be shown that the filter must cancel out the low-frequency pole of the VCM, located in a position which depends on the electrical impedance of the VCM itself. This, however, may change by ±30% during HDD operations, due to self-heating and consequent variation of the VCM resistance. Such variation may lead to an unsatisfactory performance of the voltage driver, so an adaptation mechanism, capable of tracking variations of VCM coil resistance, must be set up. This paper presents an on-line estimation procedure, based on an extended Kalman filter (EKF), capable of estimating the VCM coil resistance with a high degree of accuracy. EKF, however, usually brings a high computational load, making it unsuitable for real-time, low-cost embedded applications. The paper presents two reduced-order model of the VCM, for which the EKF can be implemented with 30 and 50% less computational effort, respectively, while maintaining a good estimate of the VCM coil resistance. The paper reports experimental results of VCM resistance estimation, obtained with the proposed algorithm, running in 30 S on a 25 MHz, fixed-point DSP. Also, the on-line estimation is used to adapt the pre-filter. Experimental results show that the servo performance with adaptive voltage driver is not affected by resistance variation and equivalent to that of the standard current driver
Realization of a Hard Disk Drive Head Servo-Positioning System with a Voltage-driven Voice-Coil Motor
No full textIn this paper we describe a head servo-positioning system for hard disk drives (HDDs), in which the usual current command for the voice coil motor has been replaced by a simpler voltage command. Current command of the voice coil motor (VCM) has been preferred so far, due to its good performance in terms of robustness. with this solution, in fact, the characteristics of the system to be controlled by the servo-controller are rather independent from all possible variations of electrical impedance of the VCM and power supply voltage. However, this solution has some drawbacks. In fact, in order to realize the current command, a current loop uses a shunt resistor as a current sensor and a linear high power operational amplifier with some phase-shaping network as a current driver. Both shunt resistor and linear amplifier are major sources of power dissipation. Moreover, linear amplifiers need a large area on the silicon chip, increasing the cost of the power device. On the other hand, a fully digital current loop would require a costly A/D converter, and this is one of the reasons why the current controller is still implemented in analog way, thus impeding the implementation of smart control strategies at this level. All the above considerations have led to the realization of a servo system with a voltage-driven VCM. We developed a solution in which current measurement is no longer needed in order to guarantee the correct behavior of the servo controller. The solution is based on a digital, multi-rate pre-filter, driving a voltage amplifier. The filter is designed in such a way that the transfer function between input signal and VCM current is close to that of a standard current loop, so providing a one-to-one replacement to standard current drivers. With the proposed solution, no measurement on the VCM current or voltage is required. It can be shown that with a proper tuning of the pre-filter, the proposed solution exhibits a good robustness against variations of VCM parameters. Since the proposed solution is fully digital, digitally driven switching power stages can be used. Experimental results, including those related to robustness issues, show that the HDD servo-positioning performance obtained with the new voltage-driven system matches that obtained with a standard current loop, in both seek and track following operations. Finally, in order to adapt the pre-filter to operating conditions, an on-line parameter estimation procedure, capable of determining VCM windings resistance, is presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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