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ABSTRACT: This paper introduces a preview control design method to reduce the settling time of dual-stage actuators (DSAs). A DSA system is comprised of two actuators connected in series, a primary (coarse) actuator, and a secondary (fine) actuator. The objective of the proposed design is to account for the redundancy of actuators and use the information of future reference levels in order to compute a pair of inputs to be applied before the output transition time. Experimental results show that the proposed design method significantly reduces the output transition time when compared to conventional forms of DSA control design.
IEEE/ASME Transactions on Mechatronics 09/2011; · 2.87 Impact Factor
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ABSTRACT: Preview Control design is proposed in order to reduce the settling time of Dual-Stage Actuators (DSA's). It is shown that a significantly better performance is achieved by exploring the extra degree of freedom provided by the secondary actuator before the output transition instant. Given the information of the immediate future reference point, the proposed strategy allows the slow actuator to move ahead of time while the fast actuator maintains the total output at the desired reference. Experimental results demonstrate the effectiveness of the proposed methodology when compared to a conventional form of DSA control design.
Decision and Control (CDC), 2010 49th IEEE Conference on; 01/2011
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ABSTRACT: In this paper we study statistical properties of the error covariance matrix of a Kalman filter, when it is subject to random measurement losses. We introduce a sequence of tighter upper bounds for the asymptotic expected error covariance (EEC). This sequence starts with a given upper bound in the literature and converges to the actual asymptotic EEC. Although we have not yet shown the monotonic convergence of this whole sequence, monotonic convergent subsequences are identified. The feature of these subsequences is that a tighter upper bound is guaranteed if more computation is allowed. An iterative algorithm is provided for computing each of these upper bounds. A byproduct of this paper is a more compact proof for a known necessary condition on the measurement arrival probability for the asymptotic EEC to be finite. A similar analysis leads to a necessary condition on the measurement arrival probability for the error covariance to have a finite asymptotic variance.
Decision and Control (CDC), 2010 49th IEEE Conference on; 01/2011
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9th IEEE International Conference on Control and Automation, ICCA 2011, Santiago, Chile, December 19-21, 2011; 01/2011
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Automatica. 01/2011; 47:2647-2657.
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ABSTRACT: This paper presents a unified approach to track seeking and following control of a hard disk drive (HDD) dual-stage actuator (DSA) system. Based on doubly coprime factorization (DCF) method, the DSA controller and the closed-loop dynamics are expressed explicitly in terms of two design parameters. This greatly simplifies the optimization of design parameters in meeting desired specifications. We then address how to use the design parameters to deal with specific problems in the DSA, i.e., control allocation for disturbance rejection and trajectory planning for track seeking. Simulated results are also presented to verify the effectiveness of the proposed DSA controller. Compared to previous works, the proposed approach can fulfill track seeking and following tasks by a single controller without switching. Moreover, the unified controller can achieve desirable performances for both tasks which are equivalent to that by two separate conventional controllers.
Control and Automation (ICCA), 2010 8th IEEE International Conference on; 07/2010
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ABSTRACT: This paper first reveals that the tracking and disturbance rejection problems can be decoupled into two independent optimization problems under the 2-DOF control framework. This result is then used for the design of a 2-DOF controller for a dual-stage actuator (DSA) system to provide desired performance of disturbance rejection and step tracking. The 2-DOF controller is designed based on the doubly coprime factorization approach, with which the closed-loop transfer function is expressed explicitly in terms of design parameters. This greatly simplifies the optimization of design parameters in meeting desired specifications. We further study how to use the design parameters to deal with specific problems in the DSA, i.e., control allocation and trajectory planning. For step tracking beyond the secondary actuator range, a nonlinear controller is also used for the primary actuator to complete the task. Experimental results demonstrate the practical implementation of the DSA control system and verify its effectiveness for step tracking and disturbance rejection and its robust performance under load changes.
IEEE/ASME Transactions on Mechatronics 07/2010; · 2.87 Impact Factor
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ABSTRACT: This paper investigates a factorization approach to sensitivity loop shaping for disturbance rejection in hard disk drives (HDDs). The advantage of the factorization approach is that the system sensitivity function can be expressed explicitly in terms of a unique design parameter. This greatly simplifies the control design process to make the system sensitivity function match a chosen target sensitivity function with guaranteed stability. By decomposing the controller structure, the design parameter is revealed to behave as a plug-in disturbance filter, the design of which is then presented to suppress the dominant disturbances at some specific frequencies. It is also shown that based on the nominal control system the proposed disturbance filter can reduce the sensitivity gains at specific frequencies without worsening the neighbouring sensitivity gains. Simulation together with implementation results demonstrate that the proposed method can effectively suppress the disturbances around the servo bandwidth and accordingly offers a superior tracking accuracy in comparison with other existing filters.
IEEE Transactions on Magnetics 06/2010; · 1.36 Impact Factor
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ABSTRACT: Both direct and indirect methods exist for identifying continuous-time linear systems. A direct method estimates continuous-time input and output signals from their samples and then use them to obtain a continuous-time model, whereas an indirect method estimates a discrete-time model first. Both methods rely on fast sampling to ensure good accuracy. In this paper, we propose a more direct method where a continuous-time linear model is directly fitted to the available samples. This method produces an exact model asymptotically, modulo some possible aliasing ambiguity, even when the sampling rate is relatively slow. We also state conditions under which the aliasing ambiguity can be resolved, and we provide experiments showing that the proposed method is a valid option when a slow sampling frequency must be used but a large number of samples is available.
IEEE Transactions on Signal Processing 06/2010; · 2.63 Impact Factor
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ABSTRACT: Using the subband technique, an LTI system can be implemented by the composition of an analysis filterbank, followed by a transfer matrix (subband model) and a synthesis filterbank. The advantage of this approach is that it offers a good tradeoff between latency and computational complexity. In this paper we propose an optimization method for approximating an LTI system using the subband technique. The proposed method includes optimal allocation of parameters from different FIR entries of the subband model, while keeping constant the total number of parameters, for a better utilization of the available coefficients. The optimization is done in a weighted least-squares sense considering either linear or logarithmic amplitude scale. Simulation results demonstrate the advantages of the proposed method when compared with classical implementation approaches using pole-zero transfer functions or segmented FFT algorithms.
IEEE Transactions on Signal Processing 04/2010; · 2.63 Impact Factor
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ABSTRACT: Although there has been a lot of research on analysis and synthesis of quantized feedback control systems, most results are developed for the case of a single quantizer (either measurement quantization or control signal quantization). In this technical note, we investigate the case of feedback control systems subject to both input and output quantization. This is motivated by the fact that it is common in remotely controlled systems that measurement and control signals are shared over a single digital network. More specifically, we consider a single-input single-output linear system with memoryless logarithmic quantizers. We firstly show that the output feedback quadratic stabilization problem in this setting can be addressed with no conservatism by means of a sector bound approach. Secondly, we provide a sufficient condition for quadratic stabilization via the solution of a scaled H<sub>??</sub> control problem. Finally, we analyze a problem of bandwidth allocation in the communication channel for finite-level input and output quantizers.
IEEE Transactions on Automatic Control 04/2010; · 2.11 Impact Factor
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ABSTRACT: Sensor quantization is a key factor that deteriorates the tracking performance of positioning systems with low-resolution optical encoders. This paper presents a method to improve the performance of such systems by merging an accelerometer of low cost. First, to reject the external disturbance, friction force and system perturbations, we design a disturbance observer (DOB) based on acceleration signals. Second, a reset kinematic state estimator (RKSE) is designed using acceleration signals to make the state estimate immune to both system perturbations and input disturbances. Third, a state feedback controller is designed based on the internal model principle (IMP) for accurate sinusoidal reference tracking. Simulations and experimental results are used to demonstrate the effectiveness of the proposed control method for tracking position reference commands and its robustness to system uncertainties.
IEEE Transactions on Control Systems Technology 02/2010; · 1.77 Impact Factor
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ABSTRACT: This paper presents the design and control of a rotary dual-stage actuator (DSA) system, which consists of a voice coil motor (VCM) and a piezoelectric (PZT) microactuator. The performance of the mechanical design is analyzed using a finite element method (FEM) software, whose simulation results are validated experimentally. A nonlinear tracking control is applied to the developed DSA platform for reduced settling time and improved disturbance rejection. Experimental results demonstrate that the applied control design reduces the settling time by up to 50% when compared to a conventional design. Moreover, it is shown that the DSA system can achieve an improvement of 80% regarding disturbance rejection when compared to a single-stage actuator.
Decision and Control, 2009 held jointly with the 2009 28th Chinese Control Conference. CDC/CCC 2009. Proceedings of the 48th IEEE Conference on; 01/2010
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ABSTRACT: Sensor quantization is one of the key factors that deteriorate the tracking performance of positioning systems with low-resolution optical encoders. This paper presents a reset kinematic state estimator (RKSE) by merging an accelerometer to improve the performance of such systems. The RKSE is immune to both system perturbations and input disturbances and offers more accurate state estimation than the standard state estimator (SSE) without reset. The estimated state is fed back for sinusoidal position tracking control. Experimental results demonstrate the improved tracking accuracy and the robustness with the use of RKSE.
Decision and Control, 2009 held jointly with the 2009 28th Chinese Control Conference. CDC/CCC 2009. Proceedings of the 48th IEEE Conference on; 01/2010
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ABSTRACT: This paper investigates a factorization approach to sensitivity loop shaping for disturbance rejection in hard disk drives (HDDs). The advantage of the factorization approach is that the system sensitivity function can be expressed explicitly in terms of a unique design parameter. This greatly simplifies the control design process to make the system sensitivity function match a chosen target sensitivity function with guaranteed stability. By decomposing the stabilizing controller structure, we further present how to select the design parameter (also regarded as disturbance filter) to suppress the dominant disturbances at some specific frequencies. Simulation analysis and experimental results demonstrate that the proposed method can remarkably suppress the disturbances around the servo bandwidth and thus offers an improved tracking accuracy.
Control and Automation, 2009. ICCA 2009. IEEE International Conference on; 01/2010
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Proceedings of the 49th IEEE Conference on Decision and Control, CDC 2010, December 15-17, 2010, Atlanta, Georgia, USA; 01/2010
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ABSTRACT: The time-interleaved architecture permits the implementation of high-frequency analog-to-digital converters (ADCs) by multiplexing the output of several time-shifted low-frequency ADCs. An issue in the design of a time-interleaved ADC is the compensation of timing mismatch, which is the difference between the ideal and real sampling instants. In this paper, we propose a compensation method that, as opposite to existing approaches, does not assume that the input signal is band limited but assumes instead that it has a stationary known power spectrum. The compensation is then designed in a statistically optimal sense. This largely reduces the compensation order required to achieve a given reconstruction accuracy. Also, under the band-limited assumption, the proposed method achieves perfect reconstruction if no constraints are imposed on the order of the compensation. Simulation results show that a rough estimate of the input spectrum can be used without much performance loss, showing that an accurate knowledge of the input spectrum is not necessarily required.
Circuits and Systems I: Regular Papers, IEEE Transactions on 12/2009; · 1.97 Impact Factor
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ABSTRACT: In this letter we consider serially concatenated continuous phase modulation (SCCPM) schemes with symbolwise interleaving and an additional intra-symbol interleaving. We use extrinsic information transfer (EXIT) chart to optimize the outer code and intra-symbol interleaver. We show that, for various continuous phase modulation (CPM) parameters, the outer code with memory 2 may not always be the best choice. For CPM with modulation index h = 1/2, considerable improvements can be achieved by moderately increasing the outer code memory.
IEEE Communications Letters 11/2009; · 0.98 Impact Factor
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ABSTRACT: This paper presents a new two-degree-of-freedom (2DOF) control design method for a dual-stage actuator (DSA) positioning system consisting of a linear motor (LM) and a piezo actuator (PA). The 2DOF controller is proposed to achieve disturbance rejection and short-span tracking in the PA range and is designed using the doubly coprime factorization (DCF) approach, with which the closed-loop transfer function is expressed explicitly in terms of design parameters. This greatly simplifies the optimization of design parameters in meeting desired specifications. We further study how to use the design parameters to deal with specific problems in the DSA, i.e., control allocation and trajectory planning. Experimental results demonstrate the practical implementation of the DSA control system and verify its effectiveness for step tracking and disturbance rejection.
American Control Conference, 2009. ACC '09.; 07/2009
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ABSTRACT: This technical note studies quantized output feedback control of discrete-time linear systems using a finite-level quantizer. The main objective is to find a quantization strategy which is easily implementable and achieves asymptotic stabilization. Based on a known logarithmic quantization scheme, we introduce a simple dynamic scaling method for the quantizer. A suboptimal approach for the optimization of the number of quantization levels and the design of a corresponding quantized dynamic output feedback controller is given. The robustness of the dynamic quantization scheme with respect to input disturbances is also examined.
IEEE Transactions on Automatic Control 06/2009; · 2.11 Impact Factor
