Evaluating performance of multivariable vibration isolators : a frequency domain identification approach applied to an industrial AVIS:A frequency domain identification approach applied to an industrial AVIS

Vibration isolation is essential for industrial high-precision systems in suppressing the influence of external disturbances. The aim of this paper is to develop an identification method to estimate the transmissibility matrix for such systems. The transmissibility matrix is a key performance indicator in vibration isolation, but its identification is severely limited by the heavy weight and size of many industrial systems. Two non-parametric system identification methods based on periodic and spectral analysis are compared. It is shown that spectral analysis can benefit from random floor excitations at low frequencies and periodic shaker excitations at high frequencies. Using this method, a transmissibility matrix between 1 and 100 Hz is successfully measured on an industrial active vibration isolation system (AVIS), demonstrating that the proposed method is suitable for identification of these heavy-weight systems.</p

Evaluating performance of multivariable vibration isolators : a frequency domain identification approach applied to an industrial AVIS:A frequency domain identification approach applied to an industrial AVIS

Vibration isolation is essential for industrial high-precision systems in suppressing the influence of external disturbances. The aim of this paper is to develop an identification method to estimate the transmissibility matrix for such systems. The transmissibility matrix is a key performance indicator in vibration isolation, but its identification is severely limited by the heavy weight and size of many industrial systems. Two non-parametric system identification methods based on periodic and spectral analysis are compared. It is shown that spectral analysis can benefit from random floor excitations at low frequencies and periodic shaker excitations at high frequencies. Using this method, a transmissibility matrix between 1 and 100 Hz is successfully measured on an industrial active vibration isolation system (AVIS), demonstrating that the proposed method is suitable for identification of these heavy-weight systems.</p

Prognostically useful gene-expression profiles in acute myeloid leukemia

BACKGROUND: In patients with acute myeloid leukemia (AML) a combination of methods must be used to classify the disease, make therapeutic decisions, and determine the prognosis. However, this combined approach provides correct therapeutic and prognostic information in only 50 percent of cases. METHODS: We determined the gene-expression profiles in samples of peripheral blood or bone marrow from 285 patients with AML using Affymetrix U133A GeneChips containing approximately 13,000 unique genes or expression-signature tags. Data analyses were carried out with Omniviz, significance analysis of microarrays, and prediction analysis of microarrays software. Statistical analyses were performed to determine the prognostic significance of cases of AML with specific molecular signatures. RESULTS: Unsupervised cluster analyses identified 16 groups of patients with AML on the basis of molecular signatures. We identified the genes that defined these clusters and determined the minimal numbers of genes needed to identify prognostically important clusters with a high degree of accuracy. The clustering was driven by the presence of chromosomal lesions (e.g., t(8;21), t(15;17), and inv(16)), particular genetic mutations (CEBPA), and abnormal oncogene expression (EVI1). We identified several novel clusters, some consisting of specimens with normal karyotypes. A unique cluster with a distinctive gene-expression signature included cases of AML with a poor treatment outcome. CONCLUSIONS: Gene-expression profiling allows a comprehensive classification of AML that includes previously identified genetically defined subgroups and a novel cluster with an adverse prognosis

The internal and external face of Dutch environmental policy: A case of fading environmental leadership?

With regard to European Union (EU) environmental directives, member states seem to show a discrepancy between external ambitions as expressed in the European arena, and realisation of these ambitions at home. Depending on the level of their internal and external ambitions, states may ideal-typically take four positions: laggards, symbolic leaders, pioneers or pushers. Furthermore, the actions of member states can be characterised with the help of different types of leadership: structural, cognitive, entrepreneurial and exemplary. Taking the case of the Netherlands, we hypothesise that there is an external face, operationalised with reference to the Dutch role in the formation process of four major environmental directives (air quality, nature conservation, agricultural pollution by nitrate and water quality), and an internal face, observed through the practices of domestic implementation of those directives. Looking at environmental policy processes over time, the gap between external and internal faces actually widened as practical implementation evolved. We conclude that the overall development of the Netherlands as an environmental leader was influenced not only by changes in the wider political and societal environment, but also by an increasing awareness of the discrepancy between the country’s external and internal faces. In the more recent cases, especially water quality, the focus of leadership shifted from substantive to governance ambitions. Despite a waning implementation record, the Netherlands still shows forms of entrepreneurial and, particularly, cognitive leadership

Filtered-error recursive least squares optimization for disturbance feedforward control in active vibration isolation

This paper addresses the filtered-error recursive least squares (FeRLS) algorithm for disturbance feedforward control in active vibration isolation systems. The controller structure consists of a generalized finite-impulse response (FIR) filter to include a set of pre-determined poles and self-tuning zeros. In addition, residual noise shaping is included to add frequency weighting and improve robustness. Compared to existing filtered-error least mean squares (FeLMS) algorithms, two major improvements are distinguished. First, faster convergence is obtained without the necessity of pre-whitening and an orthonormal basis. Second, the parameters are estimated without steady-state variance. These improvements are demonstrated using simulation studies, which show the potential of the algorithm in active vibration isolators

Evaluating performance of multivariable vibration isolators : a frequency domain identification approach applied to an industrial AVIS: A frequency domain identification approach applied to an industrial AVIS

Vibration isolation is essential for industrial high-precision systems in suppressing the influence of external disturbances. The aim of this paper is to develop an identification method to estimate the transmissibility matrix for such systems. The transmissibility matrix is a key performance indicator in vibration isolation, but its identification is severely limited by the heavy weight and size of many industrial systems. Two non-parametric system identification methods based on periodic and spectral analysis are compared. It is shown that spectral analysis can benefit from random floor excitations at low frequencies and periodic shaker excitations at high frequencies. Using this method, a transmissibility matrix between 1 and 100 Hz is successfully measured on an industrial active vibration isolation system (AVIS), demonstrating that the proposed method is suitable for identification of these heavy-weight systems

Self-tuning disturbance feedforward control with drift prevention for air mount systems

A MIMO disturbance feedforward control strategy is presented to isolate an industrial active vibration isolation system with air mounts from broadband floor vibrations. The feedforward controller compensates for the static damping and stiffness of the air mount suspension, leading to significant improvement of the vibration isolation performance. At low frequencies the controller gain is limited using higher-order weak integrators to prevent drift and actuator saturation. To minimize performance limitations due to model uncertainties, the MIMO feedforward controller is implemented as an IIR filter with fixed poles and self-tuning zeros, having the ability to fine-tune the parameters online using a combination of filtered-ϵ least mean squares (FϵLMS) optimization and residual noise shaping. An experimental validation on a full-scale vibration isolation system with air mounts shows performance improvements up to 30 dB for frequencies between 30 and 80 Hz

Two-sensor control in active vibration isolation using hard mounts

To isolate precision machines from floor vibrations, active vibration isolators are often applied. In this paper, a two-sensor control strategy, based on acceleration feedback and force feedback, is proposed for an active vibration isolator using a single-axis active hard mount. The hard mount provides a stiff support while an active control system is used to get the desired isolation performance. In our previous work, we showed that a sensor fusion control strategy for active hard mounts can be used to realize three performance objectives simultaneously: providing isolation from floor vibrations, achieving a low sensitivity for direct disturbance forces, and adding damping to internal modes of the supported precision machine. In the present work, an enhanced control strategy is presented, referred to as two-sensor control. We will show that two-sensor control outperforms sensor fusion, because it has more possibilities for loop-shaping and has better stability properties. The two-sensor control strategy is successfully validated on an experimental setu