Roberto HOROWITZ - Profile on Academia.edu (original) (raw)

Papers by Roberto HOROWITZ

Journal of Dynamic Systems Measurement and Control-transactions of The Asme, Nov 1, 2005

This paper discusses the controller design of a PZTactuated suspension dual-stage servo system in... more This paper discusses the controller design of a PZTactuated suspension dual-stage servo system in hard disk drives. The proposed control structure includes an active vibration damping control loop and a trackfollowing control loop. The vibration damping control loop, which runs at a faster rate than the trackfollowing control loop, utilizes a PZT element on a PZT-actuated suspension as a vibration sensor to damp the resonance modes of the voice coil motor (VCM) and the PZT actuator. The vibration-damping controller is designed using Kalman filter based state feedback control techniques. A simple dual-stage track-following controller is designed, based on the damped actuator model, using the sensitivity function decoupling design method. Simulation and experimental results are presented to demonstrate the benefits of this control scheme in expanding servo control bandwidth and suppressing airflow excited structural vibrations.

Volume 3: Modeling and Validation; Multi-Agent and Networked Systems; Path Planning and Motion Control; Tracking Control Systems; Unmanned Aerial Vehicles (UAVs) and Application; Unmanned Ground and Aerial Vehicles; Vibration in Mechanical Systems; Vibrations and Control of Systems; Vibrations: M..., 2018

A data driven control design approach in the frequency domain is used to design track following f... more A data driven control design approach in the frequency domain is used to design track following feedback controllers for dual-stage hard disk drives using multiple data measurements. The advantage of the data driven approach over model based approach is that, in the former approach the controllers are directly designed from frequency responses of the plant, hence avoiding any model mismatch. The feedback controller is considered to have a Sensitivity Decoupling Structure. The data driven approach utilizes H∞ and H2 norms as the control objectives. The H∞ norm is used to shape the closed loop transfer functions and ensure closed loop stability. The H2 norm is used to constrain and/or minimize the variance of the relevant signals in time domain. The control objectives are posed as a locally convex optimization problem. Two design strategies for the dual-stage hard disk drive are presented.

Proceedings of the 2004 American Control Conference, 2004

Instrumenting a disk drive suspension with vibration sensing strain gages can enhance vibration s... more Instrumenting a disk drive suspension with vibration sensing strain gages can enhance vibration suppression in hard disk drives, provided that the gages are properly located and are sufficiently sensitive. The cost function of an optimal LQG controller with Kalman filter is proposed as an objective function for determining the optimal location and orientation of displacement sensors on a flexible structure, such as the placement of strain gages on a disk drive suspension. Analytical bounds are derived for the Kalman filter Riccati equation in a modal system with large sensor noise. These bounds produce analytical approximations that reduce the computational complexity of the LQG optimization approach with cheap control. Results are applied to a prototype disk drive suspension to identify sensor positions and sensor requirements. Methods of installing strain gages on steel at precise locations are briefly discussed.

IFAC Proceedings Volumes, 2011

Missing position-error-signal sampling data in hard disk drives (HDDs) results in their servo sys... more Missing position-error-signal sampling data in hard disk drives (HDDs) results in their servo systems having irregular sampling rates. Due to the natural periodicity of HDDs, which is related to the disk rotation, HDD servo systems with missing samples can be modeled as linear periodically timevarying (LPTV) systems. Based on previous H ∞ control synthesis results for general LPTV systems developed by some of the authors, an optimal H ∞ track-following control algorithm for HDD servo systems with missing samples is proposed. A simulation and implementation study, which has been carried out on a set of hard disk drives, demonstrates that the proposed control synthesis algorithm is able to handle missing samples and can be used to achieve the robust performance of a desired error rejection function for disturbance attenuation. Implementation results on multiple real hard disk drives validate the predicted robust performance.

Design and Analysis of Computer Disk Drive Suspension Vibration Compensation Control

ASME 2008 Dynamic Systems and Control Conference, Parts A and B, 2008

This paper describes the integration of thin film ZnO strain sensors onto hard disk drive suspens... more This paper describes the integration of thin film ZnO strain sensors onto hard disk drive suspensions for improved vibration suppression for tracking control. Sensor location was designed using an efficient optimization methodology based on linear quadratic gaussian (LQG) control. Sensors were fabricated directly onto steel wafers that were subsequently made into instrumented suspensions. Prototype instrumented suspensions were installed into commercial hard drives and tested. For the first time, a sensing signal was successfully obtained while the suspension was flying on a disk as in normal drive operation. Preliminary models were identified from experimental transfer functions. Nominal H 2 control simulations demonstrated improved vibration suppression as a result of both the better resolution and higher sensing rate provided by the sensors.

ASME 2009 Dynamic Systems and Control Conference, Volume 2, 2009

This paper discusses the design and implementation of two track-following controllers for dual-st... more This paper discusses the design and implementation of two track-following controllers for dual-stage hard disk drive servo systems. The first controller is designed by combining an outer loop sensitivity-decoupling (SD) controller with an inner loop disturbance observer (DOB). The second is designed by combining mixed H2/H∞ synthesis techniques with an add-on integral action. The designed controllers were implemented and evaluated on a disk drive with a PZT-actuated suspension-based dual-stage servo system. Position error signal (PES) for the servo system was obtained by measuring the slider displacement with an LDV and injecting a simulated track runout.

This paper discusses the design and implementation of H2 guaranteed cost control for dual-stage h... more This paper discusses the design and implementation of H2 guaranteed cost control for dual-stage hard disk drive track-following servo systems. The proposed approach is based on H2 guaranteed cost analysis, in which an upper bound on the worst-case H2 performance of a discrete-time system with gain-bounded unstructured uncertainty is determined via several Riccati equations. Subsequently, the output feedback H2 guaranteed cost control synthesis algorithm is presented by exploiting Riccati equation structure to reduce the number and complexity of the semi-definite programs (SDPs) that need to be solved. The presented control synthesis methodology is then applied to a hard disk drive with a PZT-actuated suspension. Experimental results on the actual disk drive validate our control design.

2006 American Control Conference, 2006

This paper presents a robust H2 synthesis technique for designing a track-following servo system ... more This paper presents a robust H2 synthesis technique for designing a track-following servo system for a hard disk drive (HDD) product line. The goal is to design a single robust controller that minimizes the worst case H2 performance of an entire disk drive product line, assuming that dynamic variations in the product line (i.e. variations from one unit to another) are accurately characterized by affine variations in several of the actuator's model parameters, such as variations in the resonance frequency or damping ratio of a resonance mode. The advantages and disadvantages of the proposed method are discussed and an illustrative realistic example is presented. Track-following control of the magnetic read/write head in hard disk drives (HDDs) is of great importance in meeting recent and future requirements of extremely high track density. For a given system consisting of several components such as a suspension, sensors, and actuators, the track-following servo system control should attain the smallest possible track-misregistration, which is generally measured by the variance of the position error signal (PES), in the presence of measurement noise, track runout, windage, and external shock. In addition to optimality, robustness is essential in track-following control. In addition to the many disturbances that affect the control system, a controller has to be designed so that it maintains an acceptable track-following performance when installed in hundreds of thousands of HDD units of a given product line, where each unit may have slightly different dynamics. This paper proposes a robust and optimal control design methodology for a general servo system, which will be refereed to as a dual-stage multi-sensing (DSMS) system. The DSMS system has two actuators and several sensor measurements, and is expected to be necessary for achieving highly precise track-following in future HDDs. For this multivariable control system, it is not easy to systematically design a controller that provides both optimality and robustness by using classical control theory. Therefore, we will apply a recently developed robust H 2 synthesis theory [6] to the proposed DSMS system. In order to enhance performance, it is advantageous to exploit the freedom of using different sampling/hold rates in the DSMS system. In HDDs, the attainable sampling rate of the PES is generally limited by the disk spinning speed and the number of servo sectors in the disk, while

Design and fabrication of a piezoelectric instrumented suspension for hard disk drives

SPIE Proceedings, 2006

A Quasi-Newton Algorithm for LQG Controller Design With Variance Constraints

ASME 2008 Dynamic Systems and Control Conference, Parts A and B, 2008

In this paper, we present a new algorithm for solving the LQG control problem with variance const... more In this paper, we present a new algorithm for solving the LQG control problem with variance constraints which utilizes derivative information about the relevant ℋ2 costs to achieve quasi-Newton convergence. Using a lifting procedure, this algorithm is then generalized to work with linear periodically time-varying systems. This algorithm is then applied to the design of controllers for hard disk drives in order to assess the limits of performance of a particular setup. It is demonstrated that just by utilizing multirate sampling and actuation characteristics (i.e. without changing the hardware), the performance of this particular setup can improved by more than 39%.

Proceedings of the 2011 American Control Conference, 2011

This paper discusses the optimal H ∞ control synthesis via discrete Riccati equations for hard di... more This paper discusses the optimal H ∞ control synthesis via discrete Riccati equations for hard disk drives (HDDs) with an irregular sampling rate. A HDD servo system with an irregular sampling rate, caused by missing position error signal sampling data, is modeled as a linear periodically timevarying (LPTV) system. An optimal H ∞ track-following control algorithm for HDD servo systems with irregular sampling rates is proposed, which is based on the previous H ∞ synthesis results for LPTV systems developed by some of the authors. A simulation and implementation study demonstrates that the proposed control synthesis technique is able to handle the irregular sampling rate and can be used to conveniently design a loop-shaping track-following servo that achieves the robust performance of a desired error rejection function for disturbance attenuation. Implementation results on an actual hard disk drive validate the simulation results.

IFAC Proceedings Volumes, 2008

State of the art high speed color printers require sheets being accurately positioned as they arr... more State of the art high speed color printers require sheets being accurately positioned as they arrive to the image transfer station (ITS). This goal has been achieved by constructing a steerable nips mechanism, which is located upstream from the ITS. This mechanism consists of two rollers which not only rotate to advance the paper along the track, but also steer the paper in the yaw direction. A recently developed nonlinear control strategy for the position of the sheet is briefly reviewed. The core of this paper focuses on the addition of a nonlinear observer used to estimate the longitudinal, lateral, and angular positions of a sheet, by detecting its motion along two of its perpendicular sides. The success of the approach presented is corroborated through simulations, in which the estimates from the extended Luenberger observer designed are used on a nonlinear feedback control strategy.

2008 American Control Conference, 2008

Dual-stage servo systems have been proposed as a method for attaining increased bit densities fro... more Dual-stage servo systems have been proposed as a method for attaining increased bit densities from computer hard disk drives. To aid in controller operation, the second-stage microactuator used in a dual-stage system should operate at low voltages, feature relative position sensing, and have dynamics that interact well with the dynamics of the original drive servo. This paper describes a high-aspect ratio electrostatic microactuator modified to improve dynamic interactions, relative position sensor performance, and device yield. A multi-rate, multivariable control design technique was used to evaluate the closedloop performance of a disk drive system with a microactuator and relative position sensing. Closed-loop simulations reveal that the proposed configuration can reduce off-track position error. Addressing both hardware design and control design, this paper demonstrates the success of an integrated mechatronic approach to hard disk drive servo control.

6th IFAC Symposium on Mechatronic Systems, 2013, 2013

This paper examines the limits of performance in systems with periodic irregular sampling rate wh... more This paper examines the limits of performance in systems with periodic irregular sampling rate when the actuation is not necessarily synchronized with the sampling. For such a system, three sampling and actuation schemes are considered: when the sampling and control rate are both regular, when they are both irregular, and when the sampling rate is irregular while the control rate is regular. To ascertain the limits of performance of this type of systems under each sampling and actuation scheme, the system is modeled as a linear periodically time-varying (LPTV) system; optimal LQG control design with a variance constraint is applied to find the smallest achievable mean variance of the performance signal subject to a constraint on the mean control effort variance. In addition, to deal with the computational delay of the controller, an innovative discretization method is proposed which does not introduce any extra states into the state space model. The proposed method is exploited to determine the performance of a hard disk drive (HDD) in track-following mode. A simulation study demonstrates that in the presence of 30% irregularity in sampling time, using the irregular sampling and regular control action scheme for the HDD achieves an RMS 3σ value of the position error signal (PES) that is 40% smaller than the corresponding value achieved by using a controller provided by our industry partner, in which both the sampling and control rates are irregular.

Volume 1: Active Control of Aerospace Structure; Motion Control; Aerospace Control; Assistive Robotic Systems; Bio-Inspired Systems; Biomedical/Bioengineering Applications; Building Energy Systems; Condition Based Monitoring; Control Design for Drilling Automation; Control of Ground Vehicles, Man..., 2014

In this paper we employ a modified filtered-x least mean squares (MFX-LMS) method to synthesis an... more In this paper we employ a modified filtered-x least mean squares (MFX-LMS) method to synthesis an adaptive repetitive controller for rejecting periodic disturbances at selective frequencies. We show how a MFX-LMS algorithm can be utilized when the reference signal is deterministic and periodic. A new adaptive step size is proposed with the motivation to improve the convergence rate of the MFX-LMS algorithm and fade the steady state excess error caused by the variation of estimated parameters in a stochastic environment. A novel secondary path modeling scheme is proposed to compensate for the modeling mismatches online. We further discuss the application of this adaptive controller in hard disk drives that use Bit Patterned Media Recording. Finally we present the results of comprehensive realistic numerical simulations and experimental implementations of the algorithms on a hard disk drive servo mechanism that is subjected to periodic disturbances known as repeatable runout.

2014 Conference on Information Storage and Processing Systems, 2014

An adaptive feedforward controller design for tracking repeatable runout (RRO) in bit patterned m... more An adaptive feedforward controller design for tracking repeatable runout (RRO) in bit patterned media recording (BMPR) is proposed for single stage hard disk drives (HDD). The technique is based on modified filtered-x least mean squares (MFX-LMS) algorithm with deterministic periodic input, and a novel variable step size that boosts both the convergence rate and the steady state error. Comprehensive simulations and comparisons are provided to show the effectiveness of the proposed method.

2013 10th IEEE International Conference on Control and Automation (ICCA), 2013

This paper deals with the problem of irregular sampling rate in the discrete time track following... more This paper deals with the problem of irregular sampling rate in the discrete time track following control of read/write head in hard disk drives (HDD). Irregular sampling is gradually becoming an issue not to be ignored in modern HDDs. Current technological trend in the industry suggests an increasing need for assembling disks prewritten with servo patterns into the drive. As a result, misalignment between center of servo tracks and center of rotation is an unavoidable consequence. In this paper, a non-sequential probabilistic algorithm based on scenario is utilized to handle uncertainties with sampling rate in HDD. Effectiveness of the designed controller is underscored by simulation results.

Journal of Dynamic Systems, Measurement, and Control, 2006

In this paper we discuss the controller design of a PZT-actuated suspension dual-stage servo syst... more In this paper we discuss the controller design of a PZT-actuated suspension dual-stage servo system in hard disk drives. The proposed control structure includes an active vibration damping control loop and a track-following control loop. The vibration damping control loop, which runs at a faster rate than the track-following control loop, utilizes a PZT element on a PZT-actuated suspension as a vibration sensor to damp the resonance modes of the voice coil motor (VCM) and the PZT actuator. The vibration damping controller is designed using Kalman filter based state feedback control techniques. A simple dual-stage track-following controller is designed, based on the damped actuator model, using the sensitivity function decoupling design method. Simulation and experimental results are presented to demonstrate the benefits of this control scheme in expanding servo control bandwidth and suppressing airflow excited structural vibrations.

Journal of Dynamic Systems Measurement and Control-transactions of The Asme, Nov 1, 2005

This paper discusses the controller design of a PZTactuated suspension dual-stage servo system in... more This paper discusses the controller design of a PZTactuated suspension dual-stage servo system in hard disk drives. The proposed control structure includes an active vibration damping control loop and a trackfollowing control loop. The vibration damping control loop, which runs at a faster rate than the trackfollowing control loop, utilizes a PZT element on a PZT-actuated suspension as a vibration sensor to damp the resonance modes of the voice coil motor (VCM) and the PZT actuator. The vibration-damping controller is designed using Kalman filter based state feedback control techniques. A simple dual-stage track-following controller is designed, based on the damped actuator model, using the sensitivity function decoupling design method. Simulation and experimental results are presented to demonstrate the benefits of this control scheme in expanding servo control bandwidth and suppressing airflow excited structural vibrations.

Volume 3: Modeling and Validation; Multi-Agent and Networked Systems; Path Planning and Motion Control; Tracking Control Systems; Unmanned Aerial Vehicles (UAVs) and Application; Unmanned Ground and Aerial Vehicles; Vibration in Mechanical Systems; Vibrations and Control of Systems; Vibrations: M..., 2018

A data driven control design approach in the frequency domain is used to design track following f... more A data driven control design approach in the frequency domain is used to design track following feedback controllers for dual-stage hard disk drives using multiple data measurements. The advantage of the data driven approach over model based approach is that, in the former approach the controllers are directly designed from frequency responses of the plant, hence avoiding any model mismatch. The feedback controller is considered to have a Sensitivity Decoupling Structure. The data driven approach utilizes H∞ and H2 norms as the control objectives. The H∞ norm is used to shape the closed loop transfer functions and ensure closed loop stability. The H2 norm is used to constrain and/or minimize the variance of the relevant signals in time domain. The control objectives are posed as a locally convex optimization problem. Two design strategies for the dual-stage hard disk drive are presented.

Proceedings of the 2004 American Control Conference, 2004

Instrumenting a disk drive suspension with vibration sensing strain gages can enhance vibration s... more Instrumenting a disk drive suspension with vibration sensing strain gages can enhance vibration suppression in hard disk drives, provided that the gages are properly located and are sufficiently sensitive. The cost function of an optimal LQG controller with Kalman filter is proposed as an objective function for determining the optimal location and orientation of displacement sensors on a flexible structure, such as the placement of strain gages on a disk drive suspension. Analytical bounds are derived for the Kalman filter Riccati equation in a modal system with large sensor noise. These bounds produce analytical approximations that reduce the computational complexity of the LQG optimization approach with cheap control. Results are applied to a prototype disk drive suspension to identify sensor positions and sensor requirements. Methods of installing strain gages on steel at precise locations are briefly discussed.

IFAC Proceedings Volumes, 2011

Missing position-error-signal sampling data in hard disk drives (HDDs) results in their servo sys... more Missing position-error-signal sampling data in hard disk drives (HDDs) results in their servo systems having irregular sampling rates. Due to the natural periodicity of HDDs, which is related to the disk rotation, HDD servo systems with missing samples can be modeled as linear periodically timevarying (LPTV) systems. Based on previous H ∞ control synthesis results for general LPTV systems developed by some of the authors, an optimal H ∞ track-following control algorithm for HDD servo systems with missing samples is proposed. A simulation and implementation study, which has been carried out on a set of hard disk drives, demonstrates that the proposed control synthesis algorithm is able to handle missing samples and can be used to achieve the robust performance of a desired error rejection function for disturbance attenuation. Implementation results on multiple real hard disk drives validate the predicted robust performance.

Design and Analysis of Computer Disk Drive Suspension Vibration Compensation Control

ASME 2008 Dynamic Systems and Control Conference, Parts A and B, 2008

This paper describes the integration of thin film ZnO strain sensors onto hard disk drive suspens... more This paper describes the integration of thin film ZnO strain sensors onto hard disk drive suspensions for improved vibration suppression for tracking control. Sensor location was designed using an efficient optimization methodology based on linear quadratic gaussian (LQG) control. Sensors were fabricated directly onto steel wafers that were subsequently made into instrumented suspensions. Prototype instrumented suspensions were installed into commercial hard drives and tested. For the first time, a sensing signal was successfully obtained while the suspension was flying on a disk as in normal drive operation. Preliminary models were identified from experimental transfer functions. Nominal H 2 control simulations demonstrated improved vibration suppression as a result of both the better resolution and higher sensing rate provided by the sensors.

ASME 2009 Dynamic Systems and Control Conference, Volume 2, 2009

This paper discusses the design and implementation of two track-following controllers for dual-st... more This paper discusses the design and implementation of two track-following controllers for dual-stage hard disk drive servo systems. The first controller is designed by combining an outer loop sensitivity-decoupling (SD) controller with an inner loop disturbance observer (DOB). The second is designed by combining mixed H2/H∞ synthesis techniques with an add-on integral action. The designed controllers were implemented and evaluated on a disk drive with a PZT-actuated suspension-based dual-stage servo system. Position error signal (PES) for the servo system was obtained by measuring the slider displacement with an LDV and injecting a simulated track runout.

This paper discusses the design and implementation of H2 guaranteed cost control for dual-stage h... more This paper discusses the design and implementation of H2 guaranteed cost control for dual-stage hard disk drive track-following servo systems. The proposed approach is based on H2 guaranteed cost analysis, in which an upper bound on the worst-case H2 performance of a discrete-time system with gain-bounded unstructured uncertainty is determined via several Riccati equations. Subsequently, the output feedback H2 guaranteed cost control synthesis algorithm is presented by exploiting Riccati equation structure to reduce the number and complexity of the semi-definite programs (SDPs) that need to be solved. The presented control synthesis methodology is then applied to a hard disk drive with a PZT-actuated suspension. Experimental results on the actual disk drive validate our control design.

2006 American Control Conference, 2006

This paper presents a robust H2 synthesis technique for designing a track-following servo system ... more This paper presents a robust H2 synthesis technique for designing a track-following servo system for a hard disk drive (HDD) product line. The goal is to design a single robust controller that minimizes the worst case H2 performance of an entire disk drive product line, assuming that dynamic variations in the product line (i.e. variations from one unit to another) are accurately characterized by affine variations in several of the actuator's model parameters, such as variations in the resonance frequency or damping ratio of a resonance mode. The advantages and disadvantages of the proposed method are discussed and an illustrative realistic example is presented. Track-following control of the magnetic read/write head in hard disk drives (HDDs) is of great importance in meeting recent and future requirements of extremely high track density. For a given system consisting of several components such as a suspension, sensors, and actuators, the track-following servo system control should attain the smallest possible track-misregistration, which is generally measured by the variance of the position error signal (PES), in the presence of measurement noise, track runout, windage, and external shock. In addition to optimality, robustness is essential in track-following control. In addition to the many disturbances that affect the control system, a controller has to be designed so that it maintains an acceptable track-following performance when installed in hundreds of thousands of HDD units of a given product line, where each unit may have slightly different dynamics. This paper proposes a robust and optimal control design methodology for a general servo system, which will be refereed to as a dual-stage multi-sensing (DSMS) system. The DSMS system has two actuators and several sensor measurements, and is expected to be necessary for achieving highly precise track-following in future HDDs. For this multivariable control system, it is not easy to systematically design a controller that provides both optimality and robustness by using classical control theory. Therefore, we will apply a recently developed robust H 2 synthesis theory [6] to the proposed DSMS system. In order to enhance performance, it is advantageous to exploit the freedom of using different sampling/hold rates in the DSMS system. In HDDs, the attainable sampling rate of the PES is generally limited by the disk spinning speed and the number of servo sectors in the disk, while

Design and fabrication of a piezoelectric instrumented suspension for hard disk drives

SPIE Proceedings, 2006

A Quasi-Newton Algorithm for LQG Controller Design With Variance Constraints

ASME 2008 Dynamic Systems and Control Conference, Parts A and B, 2008

In this paper, we present a new algorithm for solving the LQG control problem with variance const... more In this paper, we present a new algorithm for solving the LQG control problem with variance constraints which utilizes derivative information about the relevant ℋ2 costs to achieve quasi-Newton convergence. Using a lifting procedure, this algorithm is then generalized to work with linear periodically time-varying systems. This algorithm is then applied to the design of controllers for hard disk drives in order to assess the limits of performance of a particular setup. It is demonstrated that just by utilizing multirate sampling and actuation characteristics (i.e. without changing the hardware), the performance of this particular setup can improved by more than 39%.

Proceedings of the 2011 American Control Conference, 2011

This paper discusses the optimal H ∞ control synthesis via discrete Riccati equations for hard di... more This paper discusses the optimal H ∞ control synthesis via discrete Riccati equations for hard disk drives (HDDs) with an irregular sampling rate. A HDD servo system with an irregular sampling rate, caused by missing position error signal sampling data, is modeled as a linear periodically timevarying (LPTV) system. An optimal H ∞ track-following control algorithm for HDD servo systems with irregular sampling rates is proposed, which is based on the previous H ∞ synthesis results for LPTV systems developed by some of the authors. A simulation and implementation study demonstrates that the proposed control synthesis technique is able to handle the irregular sampling rate and can be used to conveniently design a loop-shaping track-following servo that achieves the robust performance of a desired error rejection function for disturbance attenuation. Implementation results on an actual hard disk drive validate the simulation results.

IFAC Proceedings Volumes, 2008

State of the art high speed color printers require sheets being accurately positioned as they arr... more State of the art high speed color printers require sheets being accurately positioned as they arrive to the image transfer station (ITS). This goal has been achieved by constructing a steerable nips mechanism, which is located upstream from the ITS. This mechanism consists of two rollers which not only rotate to advance the paper along the track, but also steer the paper in the yaw direction. A recently developed nonlinear control strategy for the position of the sheet is briefly reviewed. The core of this paper focuses on the addition of a nonlinear observer used to estimate the longitudinal, lateral, and angular positions of a sheet, by detecting its motion along two of its perpendicular sides. The success of the approach presented is corroborated through simulations, in which the estimates from the extended Luenberger observer designed are used on a nonlinear feedback control strategy.

2008 American Control Conference, 2008

Dual-stage servo systems have been proposed as a method for attaining increased bit densities fro... more Dual-stage servo systems have been proposed as a method for attaining increased bit densities from computer hard disk drives. To aid in controller operation, the second-stage microactuator used in a dual-stage system should operate at low voltages, feature relative position sensing, and have dynamics that interact well with the dynamics of the original drive servo. This paper describes a high-aspect ratio electrostatic microactuator modified to improve dynamic interactions, relative position sensor performance, and device yield. A multi-rate, multivariable control design technique was used to evaluate the closedloop performance of a disk drive system with a microactuator and relative position sensing. Closed-loop simulations reveal that the proposed configuration can reduce off-track position error. Addressing both hardware design and control design, this paper demonstrates the success of an integrated mechatronic approach to hard disk drive servo control.

6th IFAC Symposium on Mechatronic Systems, 2013, 2013

This paper examines the limits of performance in systems with periodic irregular sampling rate wh... more This paper examines the limits of performance in systems with periodic irregular sampling rate when the actuation is not necessarily synchronized with the sampling. For such a system, three sampling and actuation schemes are considered: when the sampling and control rate are both regular, when they are both irregular, and when the sampling rate is irregular while the control rate is regular. To ascertain the limits of performance of this type of systems under each sampling and actuation scheme, the system is modeled as a linear periodically time-varying (LPTV) system; optimal LQG control design with a variance constraint is applied to find the smallest achievable mean variance of the performance signal subject to a constraint on the mean control effort variance. In addition, to deal with the computational delay of the controller, an innovative discretization method is proposed which does not introduce any extra states into the state space model. The proposed method is exploited to determine the performance of a hard disk drive (HDD) in track-following mode. A simulation study demonstrates that in the presence of 30% irregularity in sampling time, using the irregular sampling and regular control action scheme for the HDD achieves an RMS 3σ value of the position error signal (PES) that is 40% smaller than the corresponding value achieved by using a controller provided by our industry partner, in which both the sampling and control rates are irregular.

Volume 1: Active Control of Aerospace Structure; Motion Control; Aerospace Control; Assistive Robotic Systems; Bio-Inspired Systems; Biomedical/Bioengineering Applications; Building Energy Systems; Condition Based Monitoring; Control Design for Drilling Automation; Control of Ground Vehicles, Man..., 2014

In this paper we employ a modified filtered-x least mean squares (MFX-LMS) method to synthesis an... more In this paper we employ a modified filtered-x least mean squares (MFX-LMS) method to synthesis an adaptive repetitive controller for rejecting periodic disturbances at selective frequencies. We show how a MFX-LMS algorithm can be utilized when the reference signal is deterministic and periodic. A new adaptive step size is proposed with the motivation to improve the convergence rate of the MFX-LMS algorithm and fade the steady state excess error caused by the variation of estimated parameters in a stochastic environment. A novel secondary path modeling scheme is proposed to compensate for the modeling mismatches online. We further discuss the application of this adaptive controller in hard disk drives that use Bit Patterned Media Recording. Finally we present the results of comprehensive realistic numerical simulations and experimental implementations of the algorithms on a hard disk drive servo mechanism that is subjected to periodic disturbances known as repeatable runout.

2014 Conference on Information Storage and Processing Systems, 2014

An adaptive feedforward controller design for tracking repeatable runout (RRO) in bit patterned m... more An adaptive feedforward controller design for tracking repeatable runout (RRO) in bit patterned media recording (BMPR) is proposed for single stage hard disk drives (HDD). The technique is based on modified filtered-x least mean squares (MFX-LMS) algorithm with deterministic periodic input, and a novel variable step size that boosts both the convergence rate and the steady state error. Comprehensive simulations and comparisons are provided to show the effectiveness of the proposed method.

2013 10th IEEE International Conference on Control and Automation (ICCA), 2013

This paper deals with the problem of irregular sampling rate in the discrete time track following... more This paper deals with the problem of irregular sampling rate in the discrete time track following control of read/write head in hard disk drives (HDD). Irregular sampling is gradually becoming an issue not to be ignored in modern HDDs. Current technological trend in the industry suggests an increasing need for assembling disks prewritten with servo patterns into the drive. As a result, misalignment between center of servo tracks and center of rotation is an unavoidable consequence. In this paper, a non-sequential probabilistic algorithm based on scenario is utilized to handle uncertainties with sampling rate in HDD. Effectiveness of the designed controller is underscored by simulation results.

Journal of Dynamic Systems, Measurement, and Control, 2006

In this paper we discuss the controller design of a PZT-actuated suspension dual-stage servo syst... more In this paper we discuss the controller design of a PZT-actuated suspension dual-stage servo system in hard disk drives. The proposed control structure includes an active vibration damping control loop and a track-following control loop. The vibration damping control loop, which runs at a faster rate than the track-following control loop, utilizes a PZT element on a PZT-actuated suspension as a vibration sensor to damp the resonance modes of the voice coil motor (VCM) and the PZT actuator. The vibration damping controller is designed using Kalman filter based state feedback control techniques. A simple dual-stage track-following controller is designed, based on the damped actuator model, using the sensitivity function decoupling design method. Simulation and experimental results are presented to demonstrate the benefits of this control scheme in expanding servo control bandwidth and suppressing airflow excited structural vibrations.