Akira Sano

Optimally regularized inverse of singular value decomposition and application to signal extrapolation

Abstract The singular value decomposition (SVD) is an excellent tool to attain reliable and stable least squares parameters estimation in ill-conditioned cases, by discarding small singular values adequately. However, large singular values and small singular values do not always separate neatly. In the present paper, we introduce multiple regularization parameters to modify the Moore-Penrose pseudo-inverse matrix for the purpose of stabilization of ill-posed least squares problems. Optimal values of the regularization parameters can be determined so as to minimize an estimated mean squares error (EMSE) criterion calculated by using only accessible signal data. Thus, the proposed scheme can successfully give threshold conditions whether smaller singular values should be adopted or discarded. The relationship with the optimal truncation of the singular values is also investigated analytically. Effectiveness of the proposed method is discussed in applications to optimal extrapolation of band-limited signals.

Model-based adaptive friction compensation for accurate position control

An adaptive friction compensator for position control is proposed using the generalized Maxwell-slip (GMS) friction model, with a new, linearly-parameterized Stribeck function. It employs a polynomial equation that is linear-in-the-parameter to approximate the nonlinear Stribeck effect in the GMS model, and simplifies the design of the adaptive friction compensator. The proposed compensator has a switching structure to accomodate for the hybrid nature of the GMS model, and contains a robustifying term to account for unmodelled dynamics. The stability of the proposed adaptive algorithm is analyzed and its stability conditions are clarified. The validity and effectiveness of the proposed, linearly-parameterized friction compensator is verified by simulations for the positional control of an inertia system under the influence of dynamic friction.

Blind Hammerstein Identification for MR Damper Modeling

This paper proposes a new blind approach to identification of Hammerstein systems, where a static nonlinearity precedes a linear dynamic system. By exploiting inputs piece-wise constant property, the denominator of the linear system is identified first together with the order and time delay. Then a modified subspace direct equalization method estimates the unmeasurable intermediate signal, based on which the nonlinearity and linear system are obtained separately. Effectiveness of the proposed approach is demonstrated through a real-time experiment for modeling of magneto-rheological (MR) dampers.

Channel identification and interference compensation for OFDM system in long multipath environment

Guard interval (GI) is usually applied to reduce the influence caused by multipath interferences in orthogonal frequency division multiplexing (OFDM) systems. However, the long multipath interferences will deteriorate the orthogonality of the sub-carriers if they have longer delay time than GI. It is illustrated that not only inter-symbol interference (ISI) but also inter-carrier interference (ICI) is caused by the collapse of orthogonality in the received signal. As a result, both the channel identification and equalization become difficult, and the communication performance cannot be guaranteed. In this work, a new channel identification algorithm is proposed to estimate the frequency response function from the spectral periodograms which are compensated by the replica of leakage error. Since most of the computation is performed in the frequency domain through fast Fourier transform, the algorithm has such low computational complexity that it can be implemented easily in applications.

Adaptive two degree-of-freedom vibration control for flexible plate with piezoelectric patches

The paper is concerned with a two degree-of-freedom vibration control of flexible plate with multiple piezoelectric patch pairs. The control system consists of a robust feedback controller and adaptive feedforward controller to deal with uncertainties in modeling and implementation. Two kinds of adaptive algorithm are presented to update the weight parameters of the adaptive feedforward controller. One is based on a simple robust adaptation, and the other is a virtual error approach with assured stability unlike ordinary filtered-x algorithms. The validity of the proposed approach is examined in simulations in which the adaptive algorithms are applied to vibration control of a clamped flexible rectangular plate.

Adaptive semi-active vibration isolation considering uncertainties of MR damper and suspension structure

The paper is concerned with a fully adaptive semiactive control scheme which can deal with uncertainties in both models of MR damper and suspension mechanism. The proposed approach consists of two adaptive control algorithms: One is an adaptive inverse control for compensating the nonlinear hysteresis dynamics of the MR damper, which can be realized by identifying a forward model of MR damper and then calculating the input voltage to MR damper to generate a reference damping force. It can also be realized directly by updating an inverse model of MR damper without identification of the forward model, which can directly work as an adaptive inverse controller. The other is an adaptive reference control which gives the desired damping force to match the seat dynamics to a specified reference dynamics even in the presence of uncertainties in the suspension structure. The stability of the total system including the two adaptation algorithms is discussed and its stability condition is explored. Validity of the proposed algorithm is also examined in simulation studies.

Adaptive semi-active control of suspension system with MR damper

Abstract The paper is concerned with a fully adaptive semi active control which can deal with uncertainties in both models of MR damper and suspension mechanism. The proposed approach consists of two adaptive control: One is an adaptive inverse control for compensating the nonlinear hysteresis dynamics of the MR damper, which can be realized by identifying a forward model of MR damper and then calculating the input voltage to MR damper to generate a reference damping force. It can also be realized directly by updating the inverse model of MR damper without identification of forward model, which works as an adaptive inverse controller. The other is an adaptive reference control which gives the desired damping force to match the seat dynamics to a specified reference dynamics even in the presence of uncertainties in the suspension system. Validity of the proposed algorithm is discussed in simulation studies.

Stability-assured robust adaptive control of semi-active suspension systems

The paper is concerned with a stable robust adaptive scheme for semiactive control of suspension system installed with MR damper, which can deal with uncertainties in both models of MR damper and suspension mechanism. The proposed scheme consists of two main adaptive controllers: One is an adaptive inverse control for compensating the nonlinear hysteresis dynamics of the MR damper, which can be realized by identifying a forward model of MR damper or by directly adjusting an inverse model of MR damper. The other is an adaptive reference control which gives the desired damping force to match the seat dynamics to a specified reference dynamics, which can also be designed by taking into account the passivity of the MR damper. The stability of the total system including the two adaptive controllers is discussed and its stability condition is explored. Validity of the proposed algorithm is also examined in simulation studies.

Direct and Indirect Stable Adaptive Control for Suspension Systems with MR Damper

Abstract The paper is concerned with stable adaptive schemes for semi-active control of suspension systems, which can deal with uncertainties in a nonlinear model of MR damper. To compensate for unknown nonlinear hysteresis dynamics of the MR damper, an adaptive inverse controller is implemented by indirect and direct methods. In the indirect method, on-line identification of a forward model of MR damper is executed. The direct method updates the inverse controller directly. Then a linear control scheme is designed and applied to the nonlinearly compensated system to give the desired damping force by taking into account the passivity of the MR damper. The effectiveness of the proposed adaptive semiactive control scheme is validated and the stability of the obtained total adaptive system is analyzed.

Identification and Error Analysis in Frequency Domain

The identification algorithm and error analysis are considered in frequency domain by using discrete Fourier transform and spectral analysis. A simple algorithm to estimate the signal spectra is proposed and the property of the estimation is analyzed. The feature of the proposed algorithms is that they can be implemented very easily and the information of model structure is not necessary