1,720,964 research outputs found
Disturbance rejection in Hard Disk Drives with multi-rate estimated state feedback
No full textMulti-rate control has been proposed as a solution to improve the performance of Hard Disk Drives (HDDs) head servo positioning. Some authors report unexpected decrease in performance when using this approach. This paper presents an analytical method to obtain the closed-loop sensitivity function of a multi-rate control system, with estimated state feedback. By using this tool, it is shown why disturbance rejection in multi-rate control may be worse than in single-rate. The paper reports both simulation and experimental results, confirming the possible decrease in performance, when using a standard design for the multi-rate control, even when a first-order hold is used. The paper also presents a novel design procedure for the multi-rate estimator, which takes into account the spectral distribution of disturbances and yields to a better performance, compared to both single-rate and standard multi-rate control
Voltage Driven Hard Disk Drive with Voice Coil Model-based Control
No full textIn this paper we describe a new voltage driven head servo-positioning system for hard disk drives (HDDs) called Voice Coil Model-based Control (VCMC). Previous works [1],[2] have shown that the usual current amplifier used in driving the voice coil motor can be replaced by a simpler system, consisting a power voltage amplifier driven by an adaptive, multi-rate, zero-pole pre-filter that cancels out the VCM electrical pole. This fully digital solution can be implemented by using a switching power stage in place of the standard linear high power operational amplifier, with savings in both silicon area and power dissipation. The latter is further reduced with the voltage driver, since there is no need for the shunt resistor, placed in series to the VCM as a current sensor. The major drawback exhibited by a voltage driven HDDs is that the dynamics of the system to be controlled depend on the variations of the VCM coil resistance. Moreover, previous realizations, based on a multi-rate zero-pole pre-filter, did not account for the saturation of the driving power amplifier, causing a performance worsening for seeks with average size span. The drawback related to the dependence on the variations of motor resistance has been partially solved in [2], where the pre-filter is tuned at start-up, using the estimated VCM coil resistance given by an Extended Kalman Filter (EKF). This solution, however, presents a high computational complexity and cannot account for resistance variations when the HDD is in idle mode or during track following operations. During these phases, in fact, signal-to-noise ratio results not to be high enough to guarantee EKF convergence. The solutions proposed in this paper address all these issues. The VCMC is based on a new multi-rate 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. The performance obtained, when it is fully tuned, is the same as a current driven HDD during all operational phases. As for the pre-filter tuning, during seek operations, an adaptive algorithm based on a simplified least-square identification procedure, maintains the same performance level of the EKF with a lower computational complexity. Finally, several methods for estimating the value of VCM coil resistance during idle mode and track following operations will be compared. They are all based on the analysis of the information given by position error signal and VCM input. Experimental results, including those related to resistance estimation, will be presented in the final paper, showing that HDD servo-positioning performance obtained with the VCMC matches that obtained with a standard current loop, in both seek and track following operations
Hard Disk Drive with Voltage Driven Voice Coil Motor
No full textThe paper presents a novel approach for driving a Voice Coil Motor (VCM) in a Hard Disk Drive (HDD), based on an adaptive voltage driver. The adaptation of the driver compensates for the variations of VCM resistance and is performed either during seek operations and track following. As a result, the performance of the proposed driver matches closely that of a standard current driver
Track-Following Control with Active Vibration Compensation of a PZT Actuated Suspension Dual-Stage Servo System
No full textRealization 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
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